Supercooled liquid metal droplets with protective shells

Abstract

A droplet includes a core including an alloy comprising a majority of a first metallic element and a minority of a second element, wherein the core is in a liquid state below a solidus temperature of the alloy. A shell is arranged to enclose the core and includes an outer surface comprising a majority of the second element and a minority of the first metallic element, wherein the shell is in a solid state below the solidus temperature of the alloy. The alloy can include a solder material that can be used to form a solder joint below the solidus temperature of the alloy.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Nonprovisional Patent Application No. 17 / 383,150, filed July 22, 2021, entitled “UNDERCOOLED LIQUID METALLICDROPLETS HAVING A PROTECTIVE SHELL,” which claims the benefit and priority of U.S. Provisional Patent Application No. 63 / 056,448, filed July 24, 2020, also entitled “UNDERCOOLED LIQUID METALLICDROPLETS HAVING A PROTECTIVE SHELL.” The entire disclosure of each of the aforementioned applications is incorporated herein by reference. Background Technology

[0003] Currently, there are various electronic devices that incorporate cryogenic materials, which are unsuitable for welded connections due to the high processing temperatures required for soldering. New cryogenic welding materials and processes are needed for electronic devices with cryogenic materials. Summary of the Invention

[0004] Some embodiments of this disclosure relate to a supercooled liquid metal droplet surrounded by a protective shell that holds the core in a liquid state below its solidus temperature. The protective shell may be relatively free of nucleation sites and may impose a thermodynamic barrier preventing the core from transforming into a solid below its solidus temperature. The shell may comprise one or more layers arranged according to the reduction potential of each element. The shell may be coated with a fluid that protects the exterior of the protective shell from oxidation and degradation. In some embodiments, the liquid metal droplet can be used to weld materials at temperatures below the droplet's solidus temperature.

[0005] In some embodiments, the droplet includes a core comprising a majority of a first metallic element and a small portion of a second element, wherein the core is in a liquid state below the solidus temperature of the first metallic element. A shell is arranged to encapsulate the core and includes an outer surface comprising a majority of the second element and a small portion of the first metallic element, wherein the shell is in a solid state below the solidus temperature of the first metallic element. In various embodiments, the second element is a metal. In some embodiments, the second element is a quasi-metallic element. In various embodiments, the shell includes a concentration gradient of the second element, transitioning from a first concentration at the inner surface of the shell to a second concentration at the outer surface, wherein the first concentration is less than the second concentration.

[0006] In some embodiments, the droplet further includes a fluid disposed on its outer surface. In various embodiments, the outer shell contains a third element at a concentration lower than that of the first and second elements. In some embodiments, the shell includes a concentration gradient of at least the first and second elements to prevent the core from solidifying. In various embodiments, the first and second elements at the outer surface are oxides of the first and second elements. In some embodiments, the first metal element has a lower E0 than the second element. o In various implementation schemes, the second element has a higher E value than the first metallic element. o .

[0007] In some embodiments, the droplet comprises a core containing at least one metallic element in a liquid phase, and a shell in a solid phase arranged to completely encapsulate the core. The shell includes a concentration gradient of at least one metallic element that varies along its thickness, wherein the shell prevents the metallic element from transforming into a solid phase at temperatures below the solidus temperature of the at least one metallic element. In various embodiments, the shell has at least two layered regions, each of the at least two layered regions being defined by a unique element having a dominant concentration in each layered region.

[0008] In some embodiments, at least one metal element is a first metal element, and the core includes a second metal element at a concentration lower than that of the first metal element. In various embodiments, the first metal element forms a major percentage in the inner region of the shell, and the second metal element forms a major percentage in the outer region of the shell. In some embodiments, the concentration of the first metal element decreases from the inner region of the shell to the outer region of the shell, and the concentration of the second metal element increases from the inner region of the shell to the outer region of the shell.

[0009] In some embodiments, changes in the concentrations of the first and second metal elements produce a thermodynamic shift in the activation energy of the core transitioning from the liquid phase to the solid phase. In various embodiments, the inner region of the shell comprises oxides and low oxides of the first metal element, and the outer region of the shell comprises oxides and low oxides of the second metal element. In some embodiments, the second metal element has a lower E0 than the first metal element. o .

[0010] In some embodiments, the droplet comprises a supercooled liquid core containing a first element, a second element, and a third element, wherein the concentration of the first element is higher than that of the second and third elements. A solid shell surrounds the liquid core and contains a concentration gradient of the first, second, and third elements. In various embodiments, the first, second, and third elements are arranged in layers to form the shell.

[0011] In some embodiments, the method of forming a droplet includes forming a liquid core of the droplet from an alloy comprising a first element, a second element, and a third element, and forming a solid shell around the liquid core. The solid shell includes an innermost layer and an outermost layer, the innermost layer having a predominant concentration of one of the first, second, and third elements, and the outermost layer having a different predominant concentration of one of the first, second, and third elements. The method also includes cooling the liquid core and the solid shell below the solidus temperature of the alloy while keeping the core in a liquid state.

[0012] In some embodiments, the solid shell comprises three layers, wherein the innermost layer has a dominant concentration of a first element, the middle layer has a dominant concentration of a second element, and the outermost layer has a dominant concentration of a third element. In various embodiments, the shell is formed in an oxidizing environment. In some embodiments, the oxidizing environment is controlled by altering the oxygen partial pressure within it. In various embodiments, the innermost layer has a higher Ep than the middle layer. o And the middle layer has a larger E than the outermost layer. o In some implementations, the thickness of one or more of the three layers of the solid shell is determined by the duration of exposure to an oxidizing environment.

[0013] In some implementations, the shell is formed in a reducing environment. In various implementations, the innermost layer has a lower E0 than the intermediate layers. o Furthermore, the middle layer has a lower E value than the outermost layer. o In some embodiments, the thickness of one or more of the three layers of the solid shell is determined by the duration of exposure to a reducing environment. In various embodiments, the method further includes exposing the solid shell to one or more chelating agents to remove at least a portion of the outermost layer. In various embodiments, one or more chelating agents may be used to polish the outer surface of the shell, which can improve activation, droplet deposition, and droplet flow—properties that can improve the performance of droplets in solder paste materials (e.g., combinations of droplets and flux). In some embodiments, one or more chelating agents include at least one of carboxylates, amides, alkoxides, amines, thiols, or phosphates. In various embodiments, the method further includes an etching process for polishing the inner layers of the solid shell.

[0014] This invention achieves many advantages over conventional techniques. For example, embodiments of the invention provide the ability to weld materials at temperatures below the solidus temperature of the core element. Attached Figure Description

[0015] Figure 1 A simplified partial cross-sectional view of a droplet having a supercooled liquid metal core enclosed in a solid metal shell, according to an embodiment of the present disclosure, is depicted.

[0016] Figure 2AA partial cross-sectional view is shown of an example of a droplet having two shells formed in an oxidizing environment, according to an embodiment of the present disclosure;

[0017] Figure 2B The diagram shows the relative values ​​of each element and its oxides (e.g., Sn and Bi) to... Figure 2A An exemplary concentration gradient curve showing the relative concentration of the droplet's cross-section;

[0018] Figure 2C A partial cross-sectional view is shown of an example of a droplet having a three-layered shell formed in an oxidizing environment, according to an embodiment of the present disclosure;

[0019] Figure 2D The diagram shows the relative values ​​of each element and its oxides (e.g., Bi, Sn, and In) to... Figure 2C An exemplary concentration gradient curve showing the relative concentration of the droplet's cross-section;

[0020] Figure 3 The steps associated with a method for forming a supercooled droplet according to an embodiment of the present disclosure are shown, the supercooled droplet comprising a liquid metal core encapsulated by a solid shell comprising at least two layers;

[0021] Figure 4 The steps associated with a method for forming a supercooled droplet according to an embodiment of the present disclosure are shown, the supercooled droplet comprising a liquid metal core encapsulated by a solid shell, the solid shell comprising an outer surface having a different composition from the liquid metal core;

[0022] Figure 5A A partial cross-sectional view is shown of an example of a droplet having a two-layer shell formed in a reducing environment, according to an embodiment of the present disclosure;

[0023] Figure 5B The diagram shows the relative values ​​of each element and its oxides (e.g., Sn and Bi) to... Figure 5A An exemplary concentration gradient curve showing the relative concentration of the droplet's cross-section;

[0024] Figure 5C A partial cross-sectional view is shown of an example of a droplet having a three-layered shell formed in a reducing environment, according to an embodiment of the present disclosure;

[0025] Figure 5D The diagram shows the relative values ​​of each element and its oxides (e.g., Bi, Sn, and In) to... Figure 5C An exemplary concentration gradient curve showing the relative concentration of the droplet's cross-section;

[0026] Figure 6AA Darken-Gurry diagram of an embodiment according to this disclosure, covered and compared with a redox indicator analog, is shown.

[0027] Figure 6B It is based on the introduction of E° and vapor pressure according to the embodiments of this disclosure. Figure 6A The image;

[0028] Figure 7A This is a schematic diagram of surface-tunable suppression of the curing of core-shell metal particles according to an embodiment of this disclosure;

[0029] Figure 7B This is a high-angle annular dark-field scanning transmission electron microscope image of the shell according to an embodiment of the present disclosure;

[0030] Figure 8 The stability of supercooled Field metal particles according to an embodiment of the present disclosure is shown;

[0031] Figure 9A HAADF STEM images of metal particles with oxide thickness of protruding shells according to embodiments of the present disclosure, processed by a Sobel filter, are shown.

[0032] Figure 9B It shows Figure 9A Analysis of the oxide thickness of the shell of the metal particles shown;

[0033] Figure 9C It shows Figure 9A SEM image of the metal particles shown;

[0034] Figure 9D A graph illustrating the variation of the number of supercooling cycles relative to the heating cycle is shown according to an embodiment of this disclosure;

[0035] Figure 9E A graph illustrating the change in surface area to volume ratio relative to supercooling is shown according to an embodiment of the present disclosure;

[0036] Figure 10 A graph showing the relationship between the variation of ΔΤδ and the yield variation of various alloys according to embodiments of the present disclosure;

[0037] Figure 11A A table showing the different properties of organic ligands studied according to embodiments of this disclosure;

[0038] Figure 11B A table showing the changes in the properties of the oxide shell according to embodiments of this disclosure;

[0039] Figure 12A The correlation between component variations and supercooling according to embodiments of this disclosure is illustrated;

[0040] Figure 12B The correlation between enthalpy change and supercooling is shown according to embodiments of this disclosure;

[0041] Figure 13 A table showing the evaluation of various alloys and the results thereof according to embodiments of this disclosure;

[0042] Figure 14A The DSC traces of supercooled SAC305 particles according to an embodiment of the present disclosure are shown.

[0043] Figure 14B The theoretical quantity of surface work according to the embodiments of this disclosure is shown in relation to the particle radius;

[0044] Figure 15 The particle size distribution of the synthesized original particles according to the embodiments of the present disclosure is shown;

[0045] Figure 16 A table showing constants for elements used in some embodiments according to embodiments of this disclosure;

[0046] Figure 17 Tables showing the undercooling levels and yields of various alloys before and after reflux, according to some embodiments of this disclosure, are provided; and

[0047] Figure 18 This is an extended view of a hypothetical surface oxide architecture for Field metal according to an embodiment of this disclosure. Detailed Implementation

[0048] The technology disclosed herein generally relates to supercooled liquid metal droplets encapsulated in a solid shell. More specifically, the technology disclosed herein relates to metal droplets that are in a stable liquid state below their solidus temperature and are encapsulated in a shell having one or more solid metal and / or organic layers. In some embodiments, the shell may be designed to suppress (e.g., prevent) the phase transition of the droplet from liquid to solid, as explained in more detail below. Various inventive embodiments are described herein, including methods, processes, systems, configurations, etc.

[0049] For example, in some embodiments, droplets are formed encapsulated by shells having two or more layers, each layer comprising a concentration gradient and defined by a principal element. In another example, droplets are formed encapsulated by shells whose outer composition is primarily an element different from the principal element of the core. In some embodiments, droplets may be formed in an oxidizing atmosphere to promote the formation of a particular outer layer or layer arrangement, while in other embodiments, droplets may be formed in a reducing atmosphere to promote the formation of different particular outer layers or layer arrangements.

[0050] To better understand the characteristics and aspects of supercooled liquid metal droplets encapsulated in a solid metal shell according to this disclosure, further context of this disclosure is provided in the following sections by discussing several specific configurations of supercooled metal droplets according to embodiments of this disclosure. These embodiments are merely examples, and other embodiments may have other configurations using different elements, fluid materials, gases, layer structures, etc.

[0051] Figure 1 A simplified partial cross-sectional view of a droplet 100 having a supercooled liquid metal core 105 enclosed by a solid metal shell 110, according to an embodiment of this disclosure, is depicted. In some embodiments, when the droplet 100 is exposed to a temperature below the solidus temperature of the liquid metal core, the shell 110 can prevent the supercooled liquid metal core 105 from solidifying by providing an inner surface without nucleation sites and / or by generating "thermodynamic tension," which increases the energy threshold for a liquid-to-solid phase transition, as explained in more detail below. Figure 1 As depicted, shell 110 comprises two layers 115 and 120, each of which may have a different composition, as described in more detail below. In some embodiments, shell 110 may be made of one, two, three, or more layers, wherein each layer may be defined by a different element in a predominant concentration. In other embodiments, shell 110 may be terminated with ligand 125 or other liquids, as described in more detail below.

[0052] More specifically, as defined herein, layers (e.g., 115, 125) are regions of shell 110 with a dominant concentration of a particular element. The approximate boundaries of each layer (e.g., innermost start and outermost end) are defined at locations where the particular element is no longer dominant, and another element has a dominant concentration. Thus, each layer may also be referred to as an enrichment region, wherein each enrichment region may be defined by the dominance of a particular element, and wherein each enrichment region may have a concentration gradient of two or more elements. In some embodiments, the concentration gradients may be designed to generate thermodynamic tension that inhibits phase transitions in the core, as described in more detail below.

[0053] In some implementations with multiple layers, each layer can be configured according to the reduction potential E of the principal element within that layer. o Arranged relative to the reduction potential of the main elements in other layers. More specifically, in some embodiments, having a minimum E o Elements that (for example, those with the greatest tendency to form oxides in oxidizing environments) can form the outermost layer of the shell and have the highest E oElements with the lowest tendency to form oxides (e.g., those with the lowest tendency to form oxides) may form the innermost layer of the shell. Conversely, when formed under reducing conditions, the reverse shell arrangement may be formed. In other embodiments, the arrangement of each layer may depend on other factors, such as the tendency of each element to react with the gas or fluid in which droplets form. In some embodiments, the shell 110 may terminate at least partially in a fluid, which may be a ligand or other composition that improves the stability of the shell, as described in more detail below.

[0054] Two shells in an oxidizing environment

[0055] Figure 2A A partial cross-sectional view is shown as an example of a droplet having a two-layered shell formed in an oxidizing environment, according to an embodiment of the present disclosure. Figure 2A As shown, the liquid metal core 205 of droplet 200 is mainly composed of elemental bismuth (Bi) and residual elemental tin (Sn). Figure 2A In the depicted embodiments, core 205 comprises 58 wt% Bi and 42 wt% Sn; however, in other embodiments, these elements may have any other suitable ratio. For example, in one embodiment, core 205 comprises 95 wt% Bi and 5 wt% Sn. In some embodiments, the liquid metal core 205 is a single metallic element, while in other embodiments, it may be an alloy of multiple metallic elements or a combination of metallic, semi-metallic, quasi-metallic, and / or non-metallic elements, as described in further detail below. Figure 2A As further shown, the core 205 includes a shell 210 with two layers, wherein layer 1 (215) is the innermost layer and layer 2 (220) is the outermost layer. Figure 2A In the example shown, layer 1 (225) is mainly composed of bismuth oxide (Bi). a O b The layers consist of , where a and b are any rational numbers, and layer 2 (220) is primarily composed of tin oxide (Sn). c O d The composition consists of (where c and d are any rational numbers). In some embodiments, each layer 215, 220 may have a concentration gradient of multiple metal oxides and may be defined by a dominant metal oxide (e.g., layer 1 (215) is mainly bismuth oxide and layer 2 (220) is mainly tin oxide), as described in more detail below.

[0056] The inner surface 225 of layer 1 (215) may have a relatively smooth surface free of nucleation sites, thereby preventing the nucleation and growth (i.e., phase transition) of the liquid metal core 205 into a solid state at temperatures below the solidus temperature of the core material (e.g., below 138 °C for eutectic 58Bi42Sn). In some embodiments, a concentration gradient within shell 210 may generate thermodynamic tension that creates an increased energy barrier for the liquid-to-solid phase transition, thereby increasing the stability of the liquid metal core 205 in the liquid state, even further below its solidus temperature.

[0057] Figure 2B The diagram shows the relative values ​​of each element and its oxides (e.g., Sn and Bi) to... Figure 2A The diagram shows an exemplary concentration gradient curve representing the relative concentration of a cross-section of droplet 200. These concentration gradients are merely illustrative, and other embodiments may have different elements and / or different concentration gradients. Figure 2B As shown in the concentration curve 245, starting from the left part of the curve within the liquid core 205, the concentration of element Sn is relatively constant around 42%, and the concentration of element Bi is also relatively constant around 58%.

[0058] First proceed to level 1 (215) (i.e., towards...). Figure 2B Concentration curves (right side of Figure 245), elements Sn and Bi as oxides (e.g., Bi). a O b and Sn c O d Bis(II) and tin(II) are present, and the concentrations of the two elements (e.g., their oxides) change rapidly, with bismuth oxide increasing to about 90% and tin oxide decreasing to about 10% in the middle portion of layer 1 (215). Towards the right side of layer 1 (215), the concentration of bismuth oxide decreases while the concentration of tin oxide increases, such that at the interface between layer 1 (215) and layer 2 (220), the concentrations of tin oxide and bismuth oxide are equal. Therefore, within layer 1, the concentration of Bi is greater than that of Sn, and thus layer 1 (215) can be identified as having a majority of Bi and a small portion of Sn.

[0059] Moving now into layer 2 (220), the bismuth oxide composition continues to decrease to approximately 10%, while the tin oxide concentration reaches a maximum of approximately 90%. Therefore, at the outer surface 235 of the shell 210, tin oxide has a higher concentration than bismuth oxide. In some embodiments, the environment during the formation of the shell 210 can be a so-called "oxidizing environment," which includes one or more forms of oxygen that promote the formation of oxides (e.g., tin oxide and bismuth oxide). In some embodiments, the outer surface 235 may be covered in a fluid 230 that stabilizes the outer surface from oxidation and / or degradation, as described in more detail below.

[0060] The concentration gradient within shell 210 generates thermodynamic tension that inhibits the phase transition from liquid to solid in the liquid core 205. More specifically, the concentration gradient can generate relatively large surface dipoles, resulting in relatively large Laplace pressure jump conditions, meaning the core is under relatively high pressure to maintain these conditions. For solidification, a critical nucleating agent size is required, which implies diffusion away from this tension, further increasing the free energy of the entire droplet 200. However, the free energy of droplet 200 should decrease for this to become a spontaneous process. This situation creates an increased barrier to solidification. As evidence of this condition, high-melting-point alloys, upon cooling, form glassy (e.g., amorphous) structures, contrary to the crystalline structures preferred by metals under normal conditions. This change to amorphous structures suggests that the liquid-to-solid transition may occur in suppressed hypereutectic or hypoeutectic compositions.

[0061] exist Figure 2A and Figure 2B In the example shown, the liquid metal core 205 is primarily composed of element Bi, and the shell 210 comprises two layers, wherein the outer surface is primarily composed of a metal oxide (e.g., Sn) different from that of the metal core. c O d More specifically, core 205 is mainly composed of Bi, and the outer surface of the droplet is mainly composed of Sn.

[0062] In some embodiments, the core 205 may include a relatively small percentage of other elements, which may include, for example, elements that dominate the outer surface. As described herein, a minority percentage may be less than a relative majority percentage. In other embodiments, the outer surface may include a relatively small percentage (e.g., less than 50%, less than 10%, less than 1%) of other elements, which may include, for example, elements that dominate the core.

[0063] In some embodiments, the shell 210 may have a layer in which the principal element of the outer surface of the shell differs from the principal element of the core. For example, in one embodiment, the principal element of the liquid metal core is tin, while the principal element of the shell is indium. That is, the core may be primarily tin with a small amount of indium, while the outer surface of the shell may be primarily indium (e.g., indium oxide) with a small amount of tin (e.g., tin oxide).

[0064] As used herein, the terms oxide (e.g., tin oxide) and chemical notation (e.g., Sn) are used interchangeably. c O d ) represents all possible tin oxides, where c and d are rational numbers. Furthermore, a particular oxide (e.g., rational numbers c and d) can vary throughout a particular droplet, where one form of tin oxide may be present in layer 1 (215) and another form may be present in layer 2 (220).

[0065] In some embodiments, fluid 230 may provide a physical barrier to the physical and chemical adsorption of shell 210. In one embodiment, the fluid is a ligand or other solution, such as, but not limited to: amino solutions, thiolated solutions, carboxylic acids, any organic acid, any inorganic acid, phosphotungstic acid, hexafluorophosphate, trichloroacetic acid, tribromoacetic acid, chloroacetic acid, zwitterionic substances (e.g., glutamic acid, serine, etc.), dicarboxylic acids (e.g., glutaric acid, malonic acid, fumaric acid, oxalic acid, pimelic acid, etc.), acid anhydrides, aldehydes, or other functional groups that are converted in situ to reactive substances (e.g., dicarboxylic acids, acetals, ketals, hemiacetals, etc.). Those skilled in the art who benefit from this disclosure will understand that the fluids listed above are not exhaustive, and other organic and non-organic fluids may be used and are within the scope of this disclosure. In another embodiment, after formation, the outer surface of shell 210 may be contacted with a gas (such as nitrogen) to prevent oxidation and / or degradation of shell 210. In yet another embodiment, the outer surface of shell 210 may terminate in a relatively inert metal, such as gold, silver, nickel, or platinum. In one implementation, the outer surface may be stable and free of fluids, gases, or terminals.

[0066] In some embodiments, the process can be carried out in an oxidizing environment during the formation of shell 210. In one embodiment, one or more forms of oxygen (e.g., O, O₂) can be used. 2 O 3 (e.g.,) is injected in gaseous form into the solution forming droplets 200 to promote rapid oxide formation and shell 210 growth. In some embodiments, this change may be referred to as altering the oxygen partial pressure. Furthermore, an oxidizing environment can promote the formation sequence of the shell and the sequence of shell layers, i.e., the element with the highest potential for oxide formation dominates the shell and forms the outer surface of the shell. The duration of exposure to an oxidizing environment and / or the oxygen concentration can alter the thickness of one or more layers of the shell. Similarly, changing the environment to a reducing atmosphere (where oxidation is prevented by removing oxygen and other oxidizing gases) can alter the sequence of shell layers. A reducing atmosphere can be formed via reducing gases (such as hydrogen, carbon monoxide) and gases that will be oxidized by any oxygen present (such as hydrogen sulfide).

[0067] Three-layered shell in an oxidizing environment

[0068] Figure 2C A partial cross-sectional view is shown as an example of a droplet having a three-layered shell formed in an oxidizing environment, according to an embodiment of the present disclosure. Figure 2C As shown, the liquid metal core 255 of droplet 250 is mainly composed of element bismuth (Bi) with smaller amounts of elements indium (In) and tin (Sn). Figure 2CIn the depicted embodiments, core 255 comprises 57 wt% Bi, 25 wt% In, and 17 wt% Sn; however, in other embodiments, these elements may have any other suitable ratio. In some embodiments, the liquid metal core 255 is a single metallic element, while in other embodiments, it may be an alloy of multiple metallic elements or a combination of metallic, semi-metallic, quasi-metallic, and / or non-metallic elements, as described in further detail below. Figure 2C As further shown, the core 255 includes a shell 260 with three layers, wherein layer 1 (265) is the innermost layer, layer 2 (270) is the middle layer, and layer 3 (275) is the outermost layer. Figure 2C In the example shown, layer 1 (265) is mainly composed of bismuth oxide (Bi). a O b Layer 2 (270) is composed of tin oxide (Sn), where a and b are any rational numbers. c O d (where c and d are any rational numbers) and layer 3 (275) is mainly composed of indium oxide (In). e O f , where e and f are any rational numbers. In some embodiments, each layer 265, 270, 275 may have a concentration gradient of multiple metal oxides and may be defined by a primary metal oxide (e.g., layer 1 (265) is primarily bismuth oxide, layer 2 (270) is primarily tin oxide, and layer 3 (275) is primarily indium oxide), as described in more detail below.

[0069] The inner surface 285 of layer 1 (265) may have a relatively smooth surface free of nucleation sites, thereby preventing the nucleation and growth (i.e., phase transition) of the liquid metal core 255 into a solid state at temperatures below the solidus temperature of the core material (e.g., below 62°C for 57Bi26In17Sn). In some embodiments, a concentration gradient within shell 260 may generate thermodynamic tension that creates an increased energy barrier for the liquid-to-solid phase transition, thereby increasing the stability of the liquid metal core 255 in the liquid state, even further below its solidus temperature.

[0070] Figure 2D The diagram shows the relative values ​​of each element and its oxides (e.g., Bi, Sn, and In) to... Figure 2C The diagram shows an exemplary concentration gradient curve representing the relative concentration of the cross-section of droplet 250. These concentration gradients are merely illustrative, and other embodiments may have different elements and / or different concentration gradients. Figure 2DAs shown in the concentration curve 290, starting from the left part of the curve within the liquid core 285, the concentration of element Bi is relatively constant around 57%, the concentration of element In is relatively constant around 26%, and the concentration of element Sn is also relatively constant around 17%.

[0071] First, proceed to level 1 (265) (i.e., towards...). Figure 2D Concentration curves (right side of Figure 290), elements Bi, Sn, and In as oxides (e.g., Bi). a O b Sn c O d and In e O f Bismuth oxide is present, and the concentration of each element (e.g., its oxide) varies, with bismuth oxide increasing to become dominant, while tin oxide increases at a slower rate and indium oxide decreases. Towards the right side of layer 1 (265), the concentration of bismuth oxide is greater than that of tin oxide and indium oxide, so layer 1 (265) can be identified as having a majority of Bi.

[0072] Moving now into layer 2 (270), the bismuth oxide composition decreases while the tin oxide concentration increases to dominate layer 2. Therefore, layer 2 (270) can be identified as having a predominance of tin. Moving now into layer 3 (275), the tin oxide and bismuth oxide compositions decrease while indium continues to increase and dominate layer 3. Therefore, layer 3 (275) can be identified as having a predominance of indium. Thus, at the outer surface 293 of shell 260, indium oxide has a higher concentration than bismuth oxide or tin oxide. In some embodiments, during the formation of shell 210, the environment can be a so-called “oxidizing environment,” which includes one or more forms of oxygen that promote the formation of oxides (e.g., indium oxide, tin oxide, and bismuth oxide). In some embodiments, the outer surface 293 may be covered in a fluid 280 that stabilizes the outer surface from oxidation and / or degradation, as described in more detail below.

[0073] The concentration gradient within shell 260 generates thermodynamic tension, which inhibits the phase transition from liquid to solid in the liquid core 255. Figure 2C and Figure 2D In the example shown, the liquid metal core 255 is primarily composed of element Bi, and the shell 260 comprises three layers, wherein the outer surface 293 is primarily composed of a metal oxide (e.g., In) different from that of the metal core. e O f More specifically, core 255 is primarily composed of Bi, and the outer surface of the droplet is primarily composed of In.

[0074] In some embodiments, the core 255 may include a relatively small percentage of other elements, which may include, for example, elements that dominate the outer surface. As described herein, a minority percentage may be less than a relative majority percentage. In other embodiments, the outer surface may include a relatively small percentage (e.g., less than 50%, less than 10%, less than 1%) of other elements, which may include, for example, elements that dominate the core.

[0075] In some embodiments, the shell 260 may have an outer layer in which the principal element of the outer surface of the shell differs from the principal element of the core. For example, in one embodiment, the principal element of the liquid metal core is bismuth, while the principal element of the shell is indium. That is, in some embodiments, the core may be primarily bismuth with a small amount of indium, and the outer surface of the shell may be primarily indium (e.g., indium oxide) with a small amount of bismuth (e.g., bismuth oxide).

[0076] In some embodiments, fluid 230 may provide a physical barrier to the physical and chemical adsorption of shell 260, as described in further detail above. In still other embodiments, the outer surface 293 of shell 260 may terminate in a relatively inert metal, such as gold, silver, nickel, or platinum. In one embodiment, the outer surface may be stable and free of fluid, gas, or termination.

[0077] In some embodiments, the process can be carried out in an oxidizing environment during the formation of shell 210. In one embodiment, one or more forms of oxygen (e.g., O, O₂) can be used. 2 O 3 (e.g., gas) is injected into the solution forming droplets 250 to promote rapid oxide formation and shell 260 growth. Furthermore, an oxidizing environment can promote the formation sequence of the shell and the sequence of shell layers, i.e., the element with the highest potential for oxide formation dominates the shell and forms the outer surface of the shell. Therefore, changing the environment to a reducing atmosphere (where oxidation is prevented by removing oxygen and other oxidizing gases) can alter the sequence of shell layers. A reducing atmosphere can be formed via reducing gases (such as hydrogen, carbon monoxide) and gases that will be oxidized by any oxygen present (such as hydrogen sulfide). Similarly, changing the duration of exposure to reducing gases in the environment and / or the concentration of reducing gases in the environment can alter the thickness of one or more layers of the shell. In another embodiment, the environment can be dynamically changed between reducing and oxidizing environments during shell growth to promote the formation of specific shell layers in a specific sequence.

[0078] Figures 2A to 2D The relative concentrations of Sn, In, Bi, and related oxides shown are for illustrative purposes only. Those skilled in the art who benefit from this disclosure will understand that other embodiments may have different relative concentrations and / or different elements.

[0079] Manufacturing process

[0080] Figure 3 The steps associated with a method 300 for forming a supercooled droplet according to an embodiment of the present disclosure are shown, the supercooled droplet comprising a liquid metal core encapsulated by a solid shell comprising at least two layers. Figure 3 As described above, in step 305, a molten solution comprising most of element A and a small portion of element B is prepared. In some embodiments, the molten solution can be formed by heating element A and adding element B. In other embodiments, elements A and B may already be mixed but exist as a solid, which can be simply heated to form a molten solution.

[0081] In step 310, the molten solution from step 305 is immersed in a fluid. In some embodiments, the fluid comprises a conjugate acid-base pair, wherein the acid component is configured to polish the shell in situ, and the base is configured to stabilize the shell against physical and / or chemical adsorption. More specifically, in one embodiment, the acid component smooths the inner surface of the shell to minimize nucleation sites that could cause the liquid metal core to solidify upon cooling below the solidus temperature. In other embodiments, other types of fluids may be used. In further embodiments, one or more gases, such as, but not limited to, oxygen, may be added to the fluid to promote oxide formation, or a reducing gas may be added to delay oxide formation. Exemplary gases are described in more detail herein and may be used to promote a specific formation sequence of one or more layers of the shell.

[0082] In step 315, the molten solution may be separated into droplets upon immersion in a fluid and / or gas. In some embodiments, a mechanical shearing device (such as a high-speed blade immersed in a fluid) may be used to separate the molten solution. During shearing, each droplet is surrounded by a fluid and / or a gas that can be introduced into the fluid. The fluid and / or gas may be selected and / or modified during the shearing process to design the shell properties and / or the sequence of shell layers as the droplets form. That is, shell formation may occur in a chemically dynamic (e.g., varying gas flow rate, gas composition, gas partial pressure, temperature, fluid composition) and mechanically dynamic (e.g., varying shear rate, shear stress, etc.) environment that can be optimized to form a specific shell composition.

[0083] In step 320, a shell may be formed around each droplet. In some embodiments, the shell may comprise more than one layer, each of which may be defined by a different element of predominant concentration. During shell formation, elements dispersed in the bulk can be stabilized on the surface of the core due to their potential for oxidation and / or their stronger affinity for the fluid. Movement and diffusion of elements within the core bring them to the surface, and reaction and stabilization at the surface retain them there to construct the shell, as discussed in more detail below.

[0084] In one embodiment, one or more elements in the fluid and the element may be selected to have a higher affinity for reacting than the element must form an oxide. That is, the fluid and the element may be designed to react preferentially. Therefore, the element with the highest affinity for the fluid will form the outermost layer, the element with the second highest affinity will form the middle layer, and the element with the second highest affinity will form the innermost layer. In one example, an amino fluid may be selected to preferentially react with transition metals. In another example, a sulfur-based fluid may be selected to preferentially react with gold, and a carboxylic acid-based fluid may be selected to preferentially react with indium, while a phosphate may be selected to preferentially react with gallium.

[0085] In various embodiments, the solid shell may be exposed to one or more chelating agents to remove at least a portion of the outermost layer. In some embodiments, the one or more chelating agents include at least one of carboxylates, amides, alkoxides, amines, thiols, or phosphates; however, other suitable chelating agents may be used.

[0086] In another embodiment, one or more elements may be selected to have a higher tendency to form oxides than the element's tendency to react with the fluid. Therefore, each layer may be selected based on the reduction potential E of the dominant element within that layer. o Arranged relative to the reduction potential of the main elements in other layers. More specifically, cohesive energy density and partial miscibility can be used to "select" lower E o The element is then pushed onto the surface of the core during processing to form a shell. This lower E o The element can be completely removed from the core bulk, substantially removed from the core bulk, or partially removed from the core bulk, depending on the desired final concentration of the element in the core and in the shell. This can be controlled by selecting fluid characteristics, oxidant concentration, partial pressure, and / or processing parameters such as temperature, time, etc.

[0087] In another embodiment, the competition between the reduction potential of one or more elements and their reaction potential with the fluid can be used to form a shell, thereby designing a multilayer shell with a specific arrangement of shell layers and layer composition. More specifically, the highest reaction potential can cause element A to react with the fluid, the second highest reaction potential can cause element B to react with oxygen to form an oxide, the second highest reaction potential can cause element C to react with the fluid, and so on. Therefore, by selecting appropriate elements, fluids, and / or gases, any organization and composition of the layers within the shell can be designed.

[0088] In some embodiments, a specific amount of an element (e.g., element B) may be included in a molten solution (e.g., where the molten solution comprises elements A and B), which preferentially forms part of the shell such that little or no element B remains in the liquid core of each droplet, thereby the core being essentially 100% element A. In some embodiments, the elements may be miscible (e.g., dissolve in each other), while in other embodiments, one or more of the elements may be immiscible and form an interstitial material that does not dissolve with alkali metals. In embodiments with immiscible elements, removing all or almost all of the immiscible elements from the core (i.e., removing them from the core to form the shell) can increase the amount of supercooling in the embodiments, where the specific element may precipitate from the solution in the core, thereby causing nucleation and subsequent solidification of the core. To remove element B from the core to form the shell, the fluid and / or gas may be selected to have a high potential for reacting with element B and a low potential for reacting with element A, such that the shell is preferentially formed by element B. In another embodiment, time and temperature may be adjusted during shell formation so that most or all of element B can diffuse into the shell. In another embodiment, a portion or substantially all of element B may be leached from the bulk.

[0089] In some embodiments, miscibility and reduction potential are utilized to construct an alloy that, under these dynamic processing conditions, will allow the element with the highest oxidation / reduction potential to accumulate on the outer surface of the shell. In cases where this component is not highly soluble relative to other alloy components (e.g., In in Sn relative to Ge, or Bi in In relative to Ge), the tendency to accumulate on the surface can be increased. In some embodiments, modified Darken-Gurry diagrams and / or Hume-Rothery rules can be used to predict solubility in the bulk and correct these solubility parameters by the probability of their allocation to the surface to predict the final alloy composition.

[0090] In another embodiment, the specific compound formed can be controlled by controlling the time and temperature during shell formation. For example, when forming tin oxide, relatively short time and / or low temperature preferentially form 2+ tin oxide, and relatively long time and / or high temperature preferentially form 4+ tin oxide.

[0091] In step 325, each droplet, including its shell, is cooled below the solidus temperature of the core material. That is, after shell formation, the core composition has a specific solidus temperature, and due to the lack of nucleation sites on the inner surface of the shell and / or the concentration gradient of the shell, the liquid metal core can be cooled below its solidus temperature without causing the core to transform into a solid state. In some embodiments, the droplets are coated in a fluid that prevents shell degradation. In various embodiments, the droplet diameter is about 1 micrometer; however, in other embodiments, the droplet diameter is between 0.5 micrometers and 10 micrometers, and in yet another embodiment, the droplet diameter is between 0.25 micrometers and 100 micrometers.

[0092] It should be understood that method 300 is exemplary, and variations and modifications are possible. Steps described as sequential can be executed in parallel, the order of steps can be changed, and steps can be modified, combined, added, or omitted.

[0093] Figure 4 The steps associated with a method 400 for forming a supercooled droplet according to an embodiment of the present disclosure are shown, the supercooled droplet comprising a liquid metal core encapsulated by a solid shell, the solid shell including an outer surface having a different composition from the liquid metal core. Figure 4 As described above, in step 405, a molten solution comprising most of element A and a small portion of element B is prepared. In some embodiments, the molten solution can be formed by heating element A and adding element B. In other embodiments, elements A and B may already be mixed but exist as a solid, which can be simply heated to form a molten solution.

[0094] In step 410, the molten solution from step 505 is immersed in a fluid. In some embodiments, the fluid comprises a conjugate acid-base pair, wherein the acid component is configured to polish the shell in situ, and the base is configured to stabilize the shell against physical and chemical adsorption. More specifically, in one embodiment, the acid component smooths the inner surface of the shell to minimize nucleation sites that could cause the liquid metal core to solidify upon cooling below the solidus temperature. In other embodiments, other types of fluids may be used. In yet another embodiment, one or more gases, such as, but not limited to, oxygen, may be added to the fluid.

[0095] In step 415, the molten solution may be separated into droplets upon immersion in a fluid and / or gas. In some embodiments, a mechanical shearing device, such as a high-speed blade immersed in a fluid, may be used to separate the molten solution. During shearing, each droplet is surrounded by a fluid and / or gas. The fluid and / or gas may be selected to design the characteristics of the shell and / or droplets, as explained in more detail below.

[0096] In step 420, a shell can be formed around each droplet. In some embodiments, the shell may comprise more than one layer, wherein each layer may be defined by a different element of predominant concentration. In some embodiments, the liquid metal core comprises a majority element A and a small portion of element B, while the outer surface of the shell comprises a majority element B and a small portion of element A. As described above in step 320, various methods can be used to selectively design the composition and arrangement of each layer.

[0097] In step 425, each droplet, including its shell, is cooled below the solidus temperature of the core material. That is, after shell formation, the core composition has a specific solidus temperature, and due to the lack of nucleation sites on the inner surface of the shell and / or the concentration gradient of the shell, the liquid metal core can be cooled below its solidus temperature without causing the core to transform into a solid state. In some embodiments, the droplets are coated in a fluid that prevents shell degradation. In various embodiments, the droplet diameter is about 1 micrometer; however, in other embodiments, the droplet diameter is between 0.5 and 10 micrometers, and in yet another embodiment, the droplet diameter is between 0.25 and 100 micrometers.

[0098] In one embodiment, a solder alloy called SAC305, comprising tin, silver, and copper, is doped with germanium, such that the core of the droplet is essentially SAC305 and the outer shell is primarily germanium. In another embodiment, an alloy of bismuth and tin is doped with germanium, and the outer shell is primarily germanium.

[0099] In another implementation, after the droplets have formed, they can be subjected to temperature to increase the amount of supercooling they can withstand, as described in more detail below.

[0100] It should be understood that method 400 is exemplary, and variations and modifications are possible. Steps described as sequential can be executed in parallel, the order of steps can be changed, and steps can be modified, combined, added, or omitted.

[0101] Two shells in a reduced environment

[0102] Figure 5A A partial cross-sectional view is shown of an example of a droplet having a two-layer shell formed in a reducing environment, according to an embodiment of the present disclosure. Figure 5A The droplet 500 is similar to Figure 2A In the droplet 200, the core contains the same constituent elements at a similar concentration; however, droplet 500 is formed in a reducing environment, so instead of bismuth oxide forming on the outer surface like droplet 200, droplet 500 forms tin oxide on the outer surface.

[0103] like Figure 5AAs shown, the liquid metal core 505 of droplet 200 is mainly composed of elemental bismuth (Bi) and residual elemental tin (Sn). Figure 5A In the depicted embodiments, core 505 comprises 58 wt% Bi and 42 wt% Sn; however, in other embodiments, these elements may have any other suitable ratio. For example, in one embodiment, core 505 comprises 95 wt% Bi and 5 wt% Sn. In some embodiments, the liquid metal core 505 is a single metallic element, while in other embodiments, it may be an alloy of multiple metallic elements or a combination of metallic, semi-metallic, quasi-metallic, and / or non-metallic elements, as described in further detail below. Figure 5A As further shown, the core 505 includes a shell 510 with two layers, wherein layer 1 (515) is the innermost layer and layer 2 (520) is the outermost layer. Figure 5A In the example shown, layer 1 (525) is mainly composed of tin oxide (Sn). c O d (where c and d are any rational numbers) and layer 2 (220) is mainly composed of bismuth oxide (Bi). a O b , where a and b are any rational numbers. In some embodiments, each layer 515, 520 may have a concentration gradient of multiple metal oxides and may be defined by a dominant metal oxide (e.g., layer 1 (515) is primarily tin oxide and layer 2 (520) is primarily bismuth oxide), as described in more detail below.

[0104] The inner surface 525 of layer 1 (515) may have a relatively smooth surface free of nucleation sites, thereby preventing the nucleation and growth (i.e., phase transition) of the liquid metal core 505 into a solid state at temperatures below the solidus temperature of the core material (e.g., below 138 °C for eutectic 58Bi42Sn). In some embodiments, a concentration gradient within shell 510 may generate thermodynamic tension that creates an increased energy barrier for the liquid-to-solid phase transition, thereby increasing the stability of the liquid metal core 505 in the liquid state, even further below its solidus temperature.

[0105] Figure 5B The diagram shows the relative values ​​of each element and its oxides (e.g., Sn and Bi) to... Figure 5A The diagram shows an exemplary concentration gradient curve representing the relative concentration of a cross-section of droplet 500. These concentration gradients are merely illustrative, and other embodiments may have different elements and / or different concentration gradients. Figure 5B As shown in the concentration curve 545, starting from the left part of the curve within the liquid core 505, the concentration of element Sn is relatively constant around 42%, and the concentration of element Bi is also relatively constant around 58%.

[0106] First, proceed to level 1 (515) (i.e., towards...). Figure 5B (The concentration curve is shown on the right side of Figure 545), with elements Sn and Bi as oxides (e.g., Sn). a O b and Bi c O d The presence of tin oxide and the rapid variation in the concentrations of the two elements (e.g., their oxides) are such that in the middle portion of layer 1 (515), tin oxide increases to about 90%, while bismuth oxide decreases to about 10%. Therefore, within layer 1 (515), the concentration of Sn is greater than that of Bi, and thus layer 1 can be identified as having a majority of Sn and a small portion of Bi.

[0107] Moving now into layer 2 (520), the tin oxide composition continues to decrease to approximately 10%, while the bismuth oxide concentration reaches a maximum of approximately 90%. Therefore, at the outer surface 535 of the shell 510, bismuth oxide has a higher concentration than tin oxide. In some embodiments, the environment during the formation of the shell 510 can be a so-called “reducing environment” that promotes the formation of bismuth oxide on the outer surface 535, and may include one or more forms of reducing gases, such as hydrogen, carbon monoxide, and gases that will be oxidized by any oxygen present, such as hydrogen sulfide. In some embodiments, the outer surface 535 may be covered in a fluid 530 that stabilizes the outer surface from oxidation and / or degradation, as described in more detail herein.

[0108] The concentration gradient within shell 510 can generate thermodynamic tension that inhibits the phase transition from liquid to solid in the liquid core 505. In some embodiments, the core 505 may include a relatively small percentage of other elements, which may include, for example, elements that dominate the outer surface. As described herein, a minority percentage may be less than a relatively majority percentage. In other embodiments, the outer surface may include a relatively small percentage (e.g., less than 50%, less than 10%, less than 1%) of other elements, which may include, for example, elements that dominate the core.

[0109] In some embodiments, fluid 530 may provide a physical barrier to the physical and chemical adsorption of shell 510. In still other embodiments, the outer surface of shell 510 may terminate in a relatively inert metal, such as gold, silver, nickel, or platinum. In one embodiment, the outer surface may be stable and without fluid, gas, or termination.

[0110] Three-layered shell in an oxidizing environment

[0111] Figure 5C A partial cross-sectional view is shown of an example of a droplet having a three-layered shell formed in a reducing environment, according to an embodiment of the present disclosure. Figure 5C The droplet 550 in the middle is similar to Figure 2CIn the droplet 250, the core contains the same constituent elements at a similar concentration; however, droplet 550 is formed in a reducing environment, so instead of indium oxide forming on the outer surface like droplet 250, droplet 550 forms bismuth oxide on the outer surface.

[0112] like Figure 5C As shown, the liquid metal core 555 of droplet 550 is mainly composed of element bismuth (Bi) with smaller amounts of elements indium (In) and tin (Sn). Figure 5C In the depicted embodiments, core 555 comprises 57 wt% Bi, 26 wt% In, and 17 wt% Sn; however, in other embodiments, these elements may have any other suitable ratio. In some embodiments, the liquid metal core 555 is a single metallic element, while in other embodiments, it may be an alloy of multiple metallic elements or a combination of metallic, semi-metallic, quasi-metallic, and / or non-metallic elements, as described in further detail below. Figure 5C As further shown, the core 555 includes a shell 560 with three layers, wherein layer 1 (565) is the innermost layer, layer 2 (570) is the middle layer, and layer 3 (575) is the outermost layer. Figure 5C In the example shown, layer 1 (565) is mainly composed of indium oxide (In). a O b Layer 2 (570) is composed of tin oxide (Sn), where a and b are any rational numbers. c O d (where c and d are any rational numbers) and layer 3 (575) is mainly composed of bismuth oxide (Bi e O f , where e and f are any rational numbers. In some embodiments, each layer 565, 570, 575 may have a concentration gradient of multiple metal oxides and may be defined by a primary metal oxide (e.g., layer 1 (565) is primarily indium oxide, layer 2 (570) is primarily tin oxide, and layer 3 (575) is primarily bismuth oxide), as described in more detail below.

[0113] The inner surface 585 of layer 1 (565) may have a relatively smooth surface free of nucleation sites, thereby preventing the nucleation and growth (i.e., phase transition) of the liquid metal core 555 into a solid state at temperatures below the solidus temperature of the core material (e.g., below 62°C for 57Bi26In17Sn). In some embodiments, a concentration gradient within shell 560 may generate thermodynamic tension that creates an increased energy barrier for the liquid-to-solid phase transition, thereby increasing the stability of the liquid metal core 555 in the liquid state, even further below its solidus temperature.

[0114] Figure 5DThe diagram shows the relative values ​​of each element and its oxides (e.g., Bi, Sn, and In) to... Figure 5C The diagram shows an exemplary concentration gradient curve representing the relative concentration of the cross-section of droplet 550. These concentration gradients are merely illustrative, and other embodiments may have different elements and / or different concentration gradients. Figure 5D As shown in the concentration curve 590, starting from the left side of the curve within the liquid core 55, the concentration of element Bi is relatively constant around 57%, the concentration of element In is relatively constant around 26%, and the concentration of element Sn is also relatively constant around 17%.

[0115] First, proceed to level 1 (565) (i.e., towards...). Figure 5D Concentration curves (right side of Figure 590), elements Bi, Sn, and In as oxides (e.g., In). a O b Sn c O d and Bi e O f The presence of each element (e.g., its oxide) is varied, with indium oxide increasing to become dominant, while tin oxide increases at a slower rate and bismuth oxide decreases. To the right of layer 1 (565), the concentration of indium oxide is greater than that of tin oxide and indium oxide, so layer 1 (565) can be identified as having a majority of In.

[0116] Moving now into layer 2 (570), the composition of indium oxide decreases while the concentration of tin oxide increases to dominate layer 2. Therefore, layer 2 (570) can be identified as having a predominance of tin. Moving now into layer 3 (575), the compositions of tin oxide and indium oxide decrease while bismuth continues to increase and dominate layer 3. Therefore, layer 3 (575) can be identified as having a predominance of bismuth. Thus, at the outer surface 593 of shell 560, bismuth oxide has a higher concentration than either indium oxide or tin oxide. In some embodiments, the environment during the formation of shell 510 can be a so-called “reducing environment” that promotes the formation of bismuth oxide on the outer surface 593 and may include one or more forms of reducing gases, such as hydrogen, carbon monoxide, and gases that will be oxidized by any oxygen present, such as hydrogen sulfide. In some embodiments, the outer surface 593 may be covered in a fluid 580 that stabilizes the outer surface from oxidation and / or degradation, as described in more detail herein.

[0117] A concentration gradient within shell 560 can generate thermodynamic tension that inhibits the phase transition from liquid to solid in the core 555. In some embodiments, the core 555 may include a relatively small percentage of other elements, which may include, for example, elements that dominate the outer surface. As described herein, a minority percentage may be less than a relatively majority percentage. In other embodiments, the outer surface may include a relatively small percentage (e.g., less than 50%, less than 10%, less than 1%) of other elements, which may include, for example, elements that dominate the core.

[0118] In some embodiments, fluid 580 may provide a physical barrier to the physical and chemical adsorption of shell 560, as described in further detail above. In still other embodiments, the outer surface 593 of shell 560 may terminate in a relatively inert metal, such as gold, silver, nickel, or platinum. In one embodiment, the outer surface may be stable and free of fluid, gas, or termination.

[0119] Figures 5A to 5D The relative concentrations of Sn, In, Bi, and related oxides shown are for illustrative purposes only. Those skilled in the art who benefit from this disclosure will understand that other embodiments may have different relative concentrations and / or different elements.

[0120] Suppressing phase transition through surface asymmetry

[0121] Surface species formation and autonomous differentiation in metals can be influenced by miscibility, reactivity, and environment. In non-reactive environments, surface species formation can be affected by flux, cohesive energy density, and surface energy minimization. Under oxidizing (e.g., environmental) conditions, reduction potential, curvature, and surface plasticity play a role and influence surface microstructure and stoichiometry. This species formation can alter the energy morphology of materials through surface work asymmetry. This complex surface architecture provides an active platform based on surface structure asymmetry and its inductive effect on solubility, which can be used to suppress liquid-solid transitions. Induced interfacial sequencing makes Cahn-Hilliard type diffusion unfavorable, thus inhibiting homogeneous nucleation. In situ formation of surface passivating oxides with decreasing size traps molten metal in a "containerless" state (because the oxides are a continuum from the bulk), while establishing a physical barrier to heterogeneous nucleating agents. Designing the distribution of components on metal particles and their surfaces can influence the degree of supercooling and provide a general approach to suppressing supercooling.

[0122] Homogeneous material mixing can be understood from discipline-specific rules. In metals (where entropy is dominant), solid solutions can be understood using the Hume-Rothery rule, which is typically found in two-dimensional Darken-Gurry diagrams. Figure 6ASolid solutions are captured in metals. In metals, the structural use of these materials drives interest in solid solutions, however, a molten liquid phase is typically required for processing. Although this need is exacerbated by advancements in flexible, wearable, and bioelectronics at lower temperatures, as most substrates are incompatible with temperatures above 100°C. Liquid-solid (LS) phase transitions can be considered to enable new applications for metals, particularly in hybrid / mixed material systems. However, this transition depends on underlying kinetics and thermodynamics. Kinetically, diffusion can be important for nucleation and growth, thus rapid quenching is often used to form metastable states, such as glass or supercooled liquids.

[0123] Thermodynamically, nucleating agents (exogenous or homogeneous) lower the activation barrier, thereby promoting the LS phase transition. The LS transition can be thermodynamically suppressed in cases of high nucleation barriers or unfavorable Cahn-Hilliard diffusion. Inhomogeneous (exogenous) nucleation can be eliminated via containerless methods or via surface barriers (such as passivating oxides). High entropy favors the liquid phase and significantly reduces the likelihood of homogeneous nucleation. High entropy can be achieved through the dispersion of the distribution of microstates occupied by the components of the alloy. High surface area-to-volume ratios, such as in nanoparticles, can lead to limited homogeneous nucleation. Appropriate size selection, combined with species formation on surface microstructures and passivating oxides, can induce a dispersion of the density of energy states (microstates) that the alloy components can occupy. This dispersion of energy states can lead to perturbations of the bulk energy morphology (similar to nanoparticles) and can therefore be used to tune diffusion and equilibrium states. Oxidation processes can be an indispensable component in understanding the miscibility and LS phase transition of metal powders prepared in an environment.

[0124] Redefining the Darken-Gurry diagram in oxidizing environments may involve using the standard reduction potential (E). 0 ) and cohesive energy density (CED) instead of valence. Consider examples of Bi, In, Sn for explanatory purposes only, and replace the Darken-Gurry diagram ( Figure 6A ) superimposed and combined with redox indicator analogs ( Figure 6B (Comparison) Figure 6B In this model, the introduction of E° and vapor pressure (instead of CED) allows for the prediction of surface species formation. For the improved Darken-Gurry diagram, the so-called preferred interaction parameter (PIP) is defined by regions in the 3D diagram, where overlapping regions imply solubility. 0Component dominance at the surface. In one example, in Field metal (BiInSn), a shell primarily composed of In₂O₃ should form, but significant doping with low-oxide Sn means that the interfacial Bi should separate beneath the oxide shell. However, this separated Bi occupies a trapping state because dissolving it in the bulk is energy-intensive when it pushes the mixture away from the eutectic. Introducing immiscible but significantly lower E... 0 Elements (such as Te) result in a TeO2 shell and may have a minor perturbation to the eutectic composition, but have an induced surface species formation effect. Figure 6A This species formation leads to increased thermodynamic stress, and is therefore more likely to inhibit the LS phase transition.

[0125] Conversely, high E 0 The introduction of components (such as Au) Figure 6B ) restrict it to the ontology, where E 0 Large differences in the surface energy can lead to the formation of intermetallic compounds, thereby promoting uniform nucleation and resulting in undesirable undercooling. Surface-driven thermodynamic tuning of the LS transformation can be achieved by: i) establishing a smooth, passivated oxide shell on the surface of the molten metal; ii) designing this oxide shell by appropriately selecting the alloy composition, processing temperature (to control thickness), and surface ligands; and iii) achieving this microstructure when the metal is overheated and under mechanical stress, then rapidly cooled to near the alloy's melting point, followed by ambient cooling. Appropriate selection of processing conditions and management of relaxation energy morphology can lead to suppressed solidification. Similarly, the activation energy can be lowered, resulting in divergent (asymmetric) tunable solidification based on the distribution of surface microstates.

[0126] Figure 7A This is a schematic diagram of the surface tunable suppression of the solidification of core-shell metal particles 700. Figure 7B The oxide thickness of shell 710 was analyzed using a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) with a Sobel filter. Since surface properties may not be dynamic, the resulting metastable state should be stable over a prolonged period of time and resilient to variable processing conditions if the oxide layer is not disrupted. Figure 8 The stability of the supercooled Field metal particles prepared by this method (under conditions of approximately 2 years of storage and 50 thermal cycles) is shown. Figure 8 Differential scanning calorimetry (DSC) traces of Field metal particles under different conditions are shown. Background Technology

[0128] Supercooled liquids become metastable due to the suppressed liquid-solid transition. The free energy change during the LS phase transition can be defined as:

[0129]

[0130] Where ΔHf is the enthalpy of fusion, Tm is the melting temperature, ΔT is the temperature difference between the melting point and the solidification point (ΔT / Tm is the degree of supercooling), Cp is the heat capacity, Γi is the interfacial excess, and μi is the chemical potential of surface component i. The first half of the equation (classical form) captures the bulk enthalpy-entropy balance as the driving force of the phase transition. The second half of the equation (corrected for surface anisotropy) captures the surface work, similar to the Gibbs-Duhem equation, although taking into account that the passivated oxides in the metallic alloy constitute components of compositional anisotropy and flux differentiation / specimenization (due to redox, cohesive energy density, and atomic radius). Therefore, the contribution of this self-sorted interfacial layer to the total energy of the material can be captured as the sum of the contributions of each component in the thin (approximately 0.7 nm–4 nm) oxide layer to the change in chemical potential Δμ across the entire surface. Until recently, the entropy confinement of the surface (too thin relative to the bulk) generally meant that the surface could be ignored. However, in terms of energy, interfacial metastability can determine the energy morphology of the material by inducing significant stretching that can be overcome during the phase transition. However, as the material approaches the phase transition point, this Δμ changes with temperature. Under certain conditions, the composition of the oxide layer undergoes an irreversible change with temperature, resulting in asymmetry near the phase transition point (e.g., the total energy depends on the direction of the LS transition). The significant increase in total surface work (e.g., through a sharp concentration gradient) leads to a decrease in the Gibbs free energy (ΔG). LS The change is positive, therefore the energy barrier associated with the tuning of the LS transition is positive.

[0131] In a droplet, the Laplace pressure jump condition (ΔP = 2γ / r; where γ = surface tension and r = radius) can induce mechanical equilibrium, but also induces an asymmetry in the chemical potential below the oxide interface. By definition, the surface tension term (γ) is the product of the interfacial excess (Γ) and the chemical potential difference (Δμ).

[0132]

[0133] However, liquid metals and associated oxides are therefore non-volatile, Γ i<<0. Considering the approximately 1nm-4nm composite oxides on the liquid metal, the steep concentration gradient makes the surface term significantly contribute to the pressure jump conditions and the associated thermodynamic potential of the bulk liquid metal. This interfacial excess and the complexity of the underlying Δμ mean that these surfaces can be used to design the bulk PV work under appropriate choices of processing conditions and alloy composition. By tuning the surface architecture of the molten metal droplet, the solid-liquid phase transition can be suppressed by: i) using self-organized surface oxides as “containers” to eliminate heterogeneous nucleation, and ii) using the chemical potential gradient generated by the resulting composite oxide structure to suppress homogeneous nucleation by generating an interface-driven asymmetric energy tension. This tension should be overcome for critical nucleus growth. Like entropy, this surface-driven tension increases the total free energy, thus further suppressing solidification (see Equation 1). Considering that the composition and size of the surface oxides evolve with time, stimulus, temperature, and diffusivity, the surface term evolves based on processing conditions and alloy composition (e.g., component reactivity). Under potentially high-volume processing conditions, the surface term contributes significantly to ΔG. LS The effects can therefore be captured as

[0134] This shows that as the complexity of the surface and interface increases, the ability to suppress uniform nucleation also increases (e.g., higher activation energy, ΔE). a Metastable interfaces can disrupt phase transition dynamics and can form the basis of the energy-morphology-reversal phase transition theory (LIPT). A similar total energy-morphology reversal is used here to synthesize and stabilize metastable supercooled liquid metal droplets.

[0135] result

[0136] Supercooled core-shell metal particles were synthesized using the SLICE (liquid shearing into composite particles) method. For most of this work, Field metal (32.5% Bi, 16.5% Sn, and 51% In, Tm ≈ 335 K) and eutectic bismuth-tin (58% Bi, 42% Sn, Tm ≈ 411 K) were used as base alloys; however, this method can be applied to other alloys. A molten ingot was sheared in the presence of a conjugate acid-base pair to form supercooled core-shell particles with a diameter of approximately 1 μm. In-situ polishing (acid) and stabilization (base) of thin oxide shells (approximately 4 nm) using the acid-base pair were then performed. Figure 8 A, Figure 8 B). Figure 9A HAADF STEM images of metal particles with oxide thickness protruding from shell 910, processed with a Sobel filter, are shown. Figure 9B It shows Figure 9AAnalysis of the oxide thickness of the shell 910 of the metal particles shown. DSC analysis of the synthesized particles was used to assess supercooling, yield, and purity. Other microscopic and spectroscopic methods (e.g., Figure 9C The particles were characterized using SEM (Sequencing Electron Microscopy). For Field metal, the yield of supercooled particles was >98%, while the degree of supercooling for freshly prepared particles was ΔT / Tm ≈ 0.34. Figure 8 ).

[0137] To evaluate the stability of the synthesized supercooled particles, accelerated and environmental aging experiments were conducted on the supercooled Field metal particles. The sample (15 g) was stored in ethyl acetate under environmental conditions (benchtop) for >2 years, resulting in a total loss of 43% of the supercooled particles within 8 months and reaching 57% within 2 years. Figure 9D A graph showing the change in the number of supercooling cycles relative to the number of heating cycles is shown. Figure 9E A graph showing the change in surface area to volume ratio relative to supercooling is presented. ΔT / Tm changed from 0.34 to 0.14 over two years, but the yield was not lost. The change in ΔT / Tm is likely due to the continued growth of the oxide shell and / or the loss of protective ligands. This data implies that supercooled metal particles are stable to accidental environmental disturbances over long periods. To further support this, a second sample was subjected to accelerated aging by weekly thermal cycling (200 K to 373 K) over 70 cycles. For the accelerated-aged sample, a significant change in ΔT / Tm was observed ( Figure 9E The freezing points of these supercooled particles gradually increase, but approach the asymptote at approximately 273 K, exhibiting an exponentially decreasing trend (maximum value ΔΔ(ΔT / Tm) = 0.15). Figure 9E Thermally driven growth within the oxide shell, loss of surface ligands, and related changes in surface morphology due to repeated expansion and contraction contribute to the decrease in ΔT / Tm. When the particles were heated to 473 K (where total supercooling loss was observed), a gradual increase in particle size was observed from an initial size of approximately 1 μm. This change also directly affects ΔT / Tm. Powder X-ray diffraction confirmed the change in overall crystallinity with temperature. The amorphous supercooled material transformed into a fully crystalline state upon heating to 473 K, indicating solidification. This was further confirmed by coupled TGA-IR-MS, where loss of surface ligands was observed from 475 K to 573 K, followed by a gradual increase in mass with enhanced oxidation and sintering.

[0138] Preservation of the organic layer is a crucial factor in maintaining the stability of these core-shell metal particles. Organic ligands act as physical barriers (limited physical and chemisorption) to the thin-surface oxide shell. Changes in surface morphology were observed after repeated heating cycles, while the control sample (held in ambient conditions) remained spherical and smooth. Surface defects can be precursors to further oxide growth, which reduces the interfacial chemical potential gradient per unit volume (Δμ tension) and ultimately decreases ΔT / Tm. Slow oxygen diffusion at lower temperatures confirms this trend in freezing point variation. An asymptote of ΔT / Tm appears when the oxide reaches a critical thickness. Figure 9D This results in significantly slower oxygen diffusion. According to this study, the particle surface can play a role in supercooling. Maintaining a smooth, ligand-stable surface is an important factor in stabilizing supercooling; however, other factors can also play a significant role. Figure 10 A graph showing the relationship between the change in ΔT and the yield change of various alloys is provided; however, this graph is for illustrative purposes only, and any of the alloys described or other alloys may be used to prepare core-shell metal particles.

[0139] Interface-driven undercooling of various alloys

[0140] According to Equation 1, interface-driven chemical potential changes can alter the kinetics of the LS phase transition. To characterize the role of the surface beyond the observed stabilization, the chemical properties of the main surface components were investigated. First, organic ligands with different properties, acetic acid analogues, and other (four in total) moieties were studied to better bind with the passivation oxide (Figure 11). To understand the effect of the surface oxide, various low and high standard reduction potentials (E0) were used. 0 The component is introduced into the BiSn base alloy.

[0141] Influence of oxide shell and interface properties

[0142] Figure 12A The relationship between component changes and supercooling is shown, and Figure 12B This illustrates the relationship between enthalpy change and supercooling. More details for each alloy are shown in [the diagram / document / etc.]. Figure 17Table 1700. This data is described in more detail in the publication entitled “Stabilization of Undercooled Metals via Passivating Oxide Layers”, Angew. Chem. Int. Ed. 2021, 60, 5928-5935, and in the related supporting information of Andrew Martin et al. entitled “Stabilization of Undercooled Metals via Passivating Oxide Layers” published in Angewandte Chemie, the entire contents of which are incorporated herein by reference for all purposes. Figure 13 The table shows the variations in undercooling and yield of BiSn-based alloys with different additives, forming a eutectic phase, or simply adding a small amount (imp.).

[0143] Field metal (eutectic BiInSn alloy) formation is mainly on the surface of indium oxide (minimum E 0 The oxide shell exhibited significant supercooling (ΔT / Tm = 0.34). To evaluate the effect of the oxide shell on supercooling, particles were prepared from eutectic BiSn (yield = 89%, ΔT / Tm = 0.36). Figure 12A and Figure 13 Compared to ternary BiInSn, binary BiSn gives a slightly higher ΔT / Tm, although the yield of supercooled particles is slightly lower. The effects of additives on the BiSn base alloy were evaluated (by forming 3, 4, or 5-component eutectic alloys or adding small “impurities”). First, to determine that the yield variation is not a result of changes in compositional entropy (based solely on the number of components constituting the alloy), other indium-free ternary alloys were evaluated. When In (in Field metal) is replaced by Pb (E... 0 = -0.13V, Ross alloy, BiSnPB), obtained quantitative yield (100%), although the degree of supercooling was slightly reduced (T / Tm = 0.30, Figure 12B Increase the compositional entropy of BiSnPbCd (Wood alloy, Cd E). 0 =-0.4V) leads to a yield (95%) and supercooling (T / Tm=0.21, Figure 13 The decline of both. Reintroduction of In(E) 0 Preparing BiSnPbCdIn alloys at -0.34V resulted in a recovery of quantitative yield (100%), but with supercooling losses (T / Tm = 0.13). The compilation of these data indicates that an increase in compositional entropy is not always associated with an increase in metastability. Figure 13 Although the resulting alloys typically lead to higher yields, ΔT / Tm remains constant or decreases with increasing composition. (Compared to Sn(E))0 Compared to (the main component in the oxide shell of BiSn particles), most of the additive components that form these alloys have a lower E0.14. 0 Therefore, it is possible that lower E 0 The addition of components plays a role in reconstructing the surface architecture and altering the undercooled behavior. To better understand this, gallium-containing (E) components are used... 0 The homologue (BiSnGa) with a voltage of -0.51V was quantitatively supercooled (yield = 73.4%, ΔT / Tm = 0.29). Figure 13 Due to the strong Ga-Sn interaction, the addition of Ga alters the surface and bulk behavior, resulting in a significant shift in thermal behavior (captured by a substantial broadening of the solidification and melting peaks in the thermal spectrum).

[0144] To determine the effect of the major components on the oxide shell (from E... 0 From this perspective, and by determining the chemical potential gradient accordingly, it will have a higher potential than Sn(E). 0 =-0.14V) higher or lower E 0 A small amount (e.g., ≤1%) of “impurities” is introduced into the eutectic BiSn. Figure 13 Results based on DSC traces from each sample of the undercooled alloy are summarized. Typically, higher E... 0 The addition of impurities does not alter the main components of the oxide shell, although it introduces perturbations in the low oxide density at the surface and in the bulk cohesive energy density. The latter, more favorablely, will lead to a decrease in metastability due to a high tendency to form critical nucleating agents. Ge(E) 0 Adding 0.1V (1%) resulted in a similar ΔT / Tm, but with a slightly lower yield. Increasing the amount of Ge (approximately 15%) led to a decrease in ΔT / Tm. For lower E... 0 Impurities, possibly oxide shells, are dominated by additives. Adding a small amount of Sb(E) 0 = -0.51V, 1%) and Te(E) 0 = -0.90V, 1%) resulted in ΔT / Tm = 0.31 (63% yield) and ΔT / Tm = 0.35 (81% yield), respectively. Both additives led to the expected reduction in supercooling and yield in the system because they are both surface modifiers.

[0145] Besides variations in surface oxides and cohesive energy density, nucleation agent formation can depend on flux. Flux in viscous media or solids can be proportional to atomic radius. Adding larger atoms such as Ho(E)... 0 =-2.33V) and Au(E) 0=1.83V) leads to relatively significant changes in both ΔT / Tm (0.26 and 0.33) and yield (82.3% and 65.11%, respectively). Based on these data, ΔT / Tm decreases with changes in the oxide shell structure or cohesive energy density. Specific preparation methods can lead to statistical enrichment of small components in a few particles, thus altering the yield and degree of supercooling. Darken-Gurry and TC-YM plots show that solid solubility can be limited even when the Pauling electronegativity difference is >0.4, and even when atomic sizes are comparable.

[0146] Understanding Compositional Entropy

[0147] To evaluate the cause of the inconsistency between yield and undercooling, the correlation between the number of components ΔT and ΔT / Tm for all prepared BiSn homologues was assessed. It was observed that increasing the number of components forming the eutectic alloy generally led to a decrease in both Tm and ΔT / Tm; however, other additives could have different effects. Adding relatively large amounts of impurities (see...) Figure 13 The addition of Ge leads to a similar decrease. Therefore, an increase in the number and amount of components in the alloy can interfere with the ability to suppress solidification, possibly due to the formation of intermetallic compounds upon cooling. An increase in favorable interactions is correlated with the enthalpy of the system. Thus, despite the increase in compositional entropy, the increase in cohesive energy density reduces the entropic advantage of suppressing solidification. For example, the addition of Ga confirms this behavior. Although Ga will theoretically dominate oxides, its strong interaction with Sn contributes to bulk relaxation. To confirm this inference, the correlation between ΔHf and the transformation point was evaluated. All three parameters (Tm, ΔT, and ΔT / Tm) decrease with increasing enthalpy of melting, although at different rates. Therefore, alloys with stronger bulk interactions may be challenging to supercool.

[0148] Figure 14A The DSC traces of the supercooled SAC305 particles are shown. Figure 14B This shows the relationship between the theoretical amount of surface work and particle radius. When related to the solubility parameter, it resembles the Darken-Gurry plot, with medium size and E... 0 Poor impurity elements tend to give the highest ΔT / Tm. To test this hypothesis, the 3-component alloy (SAC305 solder) was undercooled, and this resulted in ΔT / Tm = 0.3 (95.2% yield). Figure 14B Compared to any BiSn-based alloy, SAC305 exhibits a significantly higher ΔHf, and therefore requires a much greater amount of surface work to achieve a comparable degree of supercooling.

[0149] Predictive analysis and simplification of supercooling behavior

[0150] In some implementations, based on accumulated data on various alloys, maximum undercooling can be achieved in 2-3 composition alloys with moderate ΔHf. The correlation between the average minimum undercooling and ΔHf for each additive indicates a critical point in approximately 3 composition alloys. An overall surface plot is generated when ΔHf and the number of compositions in the alloy are compared with ΔT / Tm. The trend in this plot shows that, in some implementations, a maximum value is found in a window of 2-3 composition alloys with moderate ΔHf. This implies that enthalpy-entropy balance may be important in achieving high levels of undercooling through tuning surface work. Based on Equation 1, if the enthalpy and entropy contributions in the system are balanced, these two terms are eliminated, resulting in a simplified description of the associated free energy:

[0151]

[0152] Equation 3 shows that when ΔHf≈0, ΔG depends on the surface work. Therefore, the surface composition in the liquid metal core-shell particles indicates an LS phase transition. This simplified equation also shows that alloys with high ΔHf (such as SAC305) may require more work to achieve the same supercooling as BiSn. The theoretical amount of surface work that can be enhanced based on curvature (increased Laplace pressure jump) means that, as expected, the degree of supercooling should increase with decreasing particle diameter. The supercooling behavior of the synthesized particles can be predicted by using SLICE to tunable the particle size distribution.

[0153] This work demonstrates a novel approach to suppressing the LS phase transition by tuning the interfacial surface tension of the metal core-shell particles.

[0154] i. Supercooled particles can be stabilized using an organic core-shell structure. Organic ligands limit chemical and physical adsorption on smooth, passivated oxides, thereby improving stability. Under ambient conditions, most particles remain supercooled after storage for >2 years.

[0155] ii. Proper selection of alloy components enhances the enthalpy-compositional entropy balance, which can be important in maximizing surface work and thus supercooling. Balancing the miscibility and distribution between the surface and bulk enables tunable supercooling and stability.

[0156] iv. Solubility is redefined by introducing a preferred interaction parameter (PIP), which captures regulated miscibility due to surface reactions. In addition to predicting solubility, this parameter also predicts surface species formation, and thus the correlated divergence of interfacial tension. Therefore, favorable liquid miscibility, along with the accompanying separation of less miscible components to the surface, foreshadows improved supercooling (metastability).

[0157] Experimental methods

[0158] Bismuth-tin alloying: Tin ingots are melted and then transferred to a crucible. The mass of tin in the crucible is recorded as 42% of the total alloy weight, and 58% by weight bismuth pellets are calculated based on the mass of tin to obtain the eutectic composition. Other metals of varying composition percentages are deposited into the molten tin pool and mixed until completely dissolved. Then, bismuth pellets are added to the mixture and mixed until completely dissolved.

[0159] BiSn-based alloy particle synthesis: Various supercooled metal particles with bismuth-tin base alloys were synthesized as follows. 1 g of trichloroacetic acid was mixed into 200 ml of diethylene glycol in a beaker. Approximately 5 g of metal pellets were added to the solution, and the mixture was heated to 433 K with stirring on a hot plate. A high-speed rotating blade was used for the shearing process, with a variable heating band wrapped around the apparatus, and the apparatus was sealed with an aramid felt to limit heat dissipation during the shearing process. The diethylene glycol solution was transferred to the apparatus and sheared at approximately 27,000 rpm for 4 minutes, during which the shearing blade was raised to create an angle of approximately 10° on one side. Once complete, the solution was extracted and washed with ethanol and ethyl acetate while cooling under ambient conditions. The solution was filtered using a Buchner filter with a Whatman GF / F paper filter. The filtered particles were washed, collected, and stored in ethyl acetate.

[0160] SAC 305 particle synthesis: 0.5 ml paraffin oil, 0.2 g trichloroacetic acid, 0.2 g poly(acrylic acid), and 0.5 g SAC305 alloy were placed in a 5 ml beaker heated in an oil bath. The solution was heated to 533 K and maintained at this temperature to keep the metal in liquid form. The particles were sheared using a rotating blade at approximately 27,000 rpm for 6 minutes. The particles were then extracted and quenched in an ethanol bath, followed by cooling to room temperature. Once at room temperature, the particles were decanted and washed with ethyl acetate to remove trace amounts of oil.

[0161] Differential Scanning Calorimetry (DSC) Analysis: To measure the level of supercooling, a DSC (model Q2000, TA Instruments) equipped with a liquid nitrogen cooling unit was used. Particles stored in an ethyl acetate solution were transferred to an aluminum disk, and the ethyl acetate contents were evaporated under ambient conditions. The sample was then hermetically sealed with an aluminum cap. The sample was heated from a standby temperature of 313 K to 573 K (varying depending on the alloy) at a heating rate of 10 K / min, and then cooled to 203 K at the same rate. Several alloys were cycled through the heating and cooling cycles to observe reflux and recycling behavior. Data analysis was performed using TA TRIOS software.

[0162] Scanning electron microscopy (SEM) characterization: Metal particles stored in ethyl acetate solution were transferred onto a silicon wafer using a pipette and then characterized using a scanning electron microscope (FEI Quanta 250FEI-SEM). Samples were mounted on a standard SEM mount (Ted Pella Inc.) with copper tape adhered to them. The SEM was operated under high vacuum at a voltage of 10kV–15kV, achieving a spot size of 3 at a working distance of 10mm. Micrographs were taken at various magnifications using an Everhart-Thorley secondary electron detector and a backscatter detector.

[0163] High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) characterization: Synthesized metal particles were drop-cast onto a copper TEM grid (Ted Pella Inc.) and mounted on a double-tilted TEM sample holder. Images were acquired using a FEI Titan Themis 300 with aberration correction for a probe-corrected TEM operating at 200 kV. EDS analysis was performed on the same instrument using a Super-X EDX detector. Oxide shell thickness approximation was performed using the "Find Edges" function in the J. Sobel filter, which allows for the calculation of pixel contrast intensity along the drawn lines, where higher intensity corresponds to brighter colors (white) and decreased intensity corresponds to oxide layers (black).

[0164] Thermogravimetric analysis (TGA)-infrared (IR)-mass spectrometry (MS) analysis: A coupled TGA-IR-MS instrument (Netzsch STA449F1) was used to analyze mass changes and escaping gases released during particle heat treatment. Samples were deposited and dried in an alumina crucible with a matched reference crucible. Simulated dry air (80% oxygen, 20% nitrogen) was used as the purge gas. The sample was then loaded and run through a heating ramp step at 10 °C / min. The acquired data were analyzed using Proteus and Opus software.

[0165] Free energy and symmetry

[0166] The Gibbs free energy (G) is a thermodynamic potential that can be used as a tool to determine whether an event occurring at a given constant temperature and pressure is favorable. A thermodynamic system undergoes a favorable transition if a change in G (ΔG) from one state to another results in a lower energy state (i.e., ΔG < 0). The main component of the Gibbs free energy equation involves the balance between enthalpy (H) and entropy (S), and its reading is as follows: G = H - TS. Enthalpy is a state function that accommodates the internal energy and PV work of the system (H = U + PV), where U is the internal energy of the system, which can be further extended to U = TdS - PdV + δw′ (δw′ is the non-pv or non-mechanical work done on the system). If the G term is extended to the more common derivative form, it ends with the familiar ΔG = ΔH - TΔS + δw′. In some calculations, δw′ is neglected by assuming no non-pv work is done on the system. The equation then becomes a competition between whether the process is enthalpy-dominant (increasing order) or entropy-dominant (increasing symmetry), which can be described, for example, by solidification (low temperature, atomic ordering, exothermic, enthalpy-dominant) or melting (high temperature, atomic disorder, endothermic, entropy-dominant) processes, respectively.

[0167] Landau's phase transition theory expresses the thermodynamic potential as a function of an order parameter (θ), providing a novel perspective on phase transition events. In Landau's theory, an ordered event will result in θ approaching 0, where the nearest-neighbor interaction is ordered along one direction and therefore U is dominant (the same principle as enthalpy-dominated events or solidification, although in this case the order is addressed magnetic order M). At the opposite end, disorder or high entropy will result in θ approaching 1. Extending from Landau, Ising's theory exchanges the constant J (directly dealing with the parameter of the nearest-neighbor interaction), the coordination number (q), and the Boltzmann constant (K). B The form provides better quantification parameters for the balance between symmetry levels. In Ising theory, ordered symmetry balance is... Or Jq = K B The critical point is reached at time T. This can be considered as a balance between enthalpy and entropy, which is then transferred back to the Gibbs free energy.

[0168] The correlation between thermodynamic potentials, as assumed by Gibbs, Landau, and Ising, provides tools for controlling phase transitions, particularly liquid-solid phase transitions that are important for supercooling.

[0169] nucleation

[0170] Supercooling is a process that occurs within the liquid-solid transition window, also known as solidification or nucleation. Solidification is an event that begins with nucleation due to the minimization of the system's energy, when the free energy difference between the liquid and solid states is negative (ΔG). lsWhen <0), this is advantageous. Different free energy terms can be used to explain this phenomenon; however, the Gibbs free energy (ΔG) assumes constant temperature and pressure and can be used to explain this event. There are various nucleation initiation mechanisms, which can be classified into two main categories: homogeneous and heterogeneous. Homogeneous nucleation can be described by the following equation:

[0171]

[0172] Here, ΔG corresponds to the free energy of the particle / droplet. ΔG is governed by volume and interface terms based on radius (r), volume free energy (Δg), and interfacial energy (γ). Due to the proportions of these volume and interface terms, there exists a division between interface-dominated (low r) and volume-dominated (high r) regions. At a certain radius, the transition point between these two regions is denoted by the nuclear critical size (r). * The maximum value of ) indicates the activation energy required to reach this critical size. * =16πγ 3 / 3Δg 2 The definition can be used to define the start of the curing process. Therefore, achieving a high activation energy can be used to achieve a high degree of supercooling.

[0173] The definition of homogeneous nucleation is primarily determined by inherent processes and characteristics. On the other hand, heterogeneous nucleation depends on external processes arising from nucleating seeds existing within the system boundaries. The formation of heterogeneous nucleating agents can be explained using the interfacial tension balance equation.

[0174] γ ls =γ sv +γ lv cosθ (5)

[0175] Where γ ls γ sv and γ lv These are the interfacial tensions of the liquid-solid, solid-vapor, and liquid-vapor interfaces, respectively, and θ is the wetting angle. Given this relationship, the heterogeneous nucleating agent reaches r * The volume is much smaller than that of a homogeneous nucleating agent and depends on the wetting angle. The rate of volume reduction can be expressed by: f(θ) = 1 / 4(2 - 3cosθ + cosθ) 3 θ) Explanation. Here, f(θ) is now the ratio between the critical inhomogeneous and homogeneous nucleation energies. Multiple non-uniform nucleation modes exist, and this relationship indicates that the critical energy for non-uniform nucleation is lower than that for uniform nucleation. Therefore, non-uniform nucleation can be eliminated by using containerless methods in various undercooling studies to remove any surface contact. Another approach is to achieve complete non-wetting. This is achieved by introducing a high activation energy barrier to prevent both nucleation modes from ultimately leading to extreme undercooling in the metallic system.

[0176] Supercooled thermodynamics

[0177] The free energy of a thermodynamic system at constant temperature and pressure can be defined by the Gibbs free energy, typically expressed as ΔG = ΔH - TΔS, where H and S are the enthalpy and entropy of the system, respectively. The system's free energy depends on the equilibrium of these two quantities, and phase transitions can be driven by either enthalpy or entropy. When ΔG < 0, the process is considered favorable; therefore, for the case of supercooling (liquid-solid transition), G... S –G L <0. The free energy term can be further derived into the specific heat term (C). p ),in And ΔH f =TΔS f This, in turn, gives the relationship shown in Equation 1 in the text.

[0178]

[0179] Where ΔH f It is the enthalpy of fusion, T m It is the melting temperature, and ΔT is the temperature difference between the melting point and the solidification point, ΔT / T m The term is used to determine the degree of supercooling in the system. Various studies have been conducted to evaluate C under different assumptions that would lead to an increase in ΔG. p The increase in . This change ultimately increases the degree of supercooling. Some models introduce the so-called maximum supercooling limit. Studies of liquid-solid transitions focus on enthalpy and entropy terms (based on PV), generally neglecting the presence of interface and surface terms, which were previously discussed in nucleation theory because they typically have a small or negligible effect on the overall system. However, given different processing conditions, surface terms can dominate the bulk, forcing high interfacial tensions toward the bulk.

[0180] Figure 15 The particle size distribution of the synthesized particles is shown, which in this embodiment is 0.1 micrometers to 1.5 micrometers; however, other embodiments may have different particle size ranges.

[0181] Undercooling of various BiSn-based alloys

[0182] Figure 16 A table showing constants for elements used in some implementations is provided. Figure 17 Table 1700 shows, according to some embodiments of this disclosure, the undercooling levels and yields of various alloys before and after reflux. (This information is obtained from T...) m Subtract T f ΔT is calculated. The yield is calculated by taking the ratio of the areas under the melt and freeze curves.

[0183]

[0184] ΔT and yield were calculated for both the original synthesized sample and the refluxed sample. The true yield was reported from the refluxed sample when the reflux process removed any solids lines present during the synthesis process.

[0185] Effects of organic ligands

[0186] When the inductive properties of the organic shells are completely opposite, a comparison of ΔT / Tm shows that the inferred surface chemical potential gradient varies under the positive or negative inductive surface portions. This could be due to an inductive effect or due to the nature of the ligand-oxide bond when the electron density of the binding site is perturbed. Introducing this inductive effect into the synthesis of SAC305 particles, the ΔT / Tm of these particles... m The concentration can be increased from 0.21 to 0.3, pushing the freezing point to <100°C. The stabilization of these particles is also confirmed by the presence of organic ligands, as these particles can withstand multiple thermal cycles without experiencing significant cold transitions.

[0187] Figure 17 A list of data illustrating the effects of different ligands on the synthesis of BiSn particles is presented. The influence of the organic ligands used to synthesize the core-shell particles was studied by using various acids, thereby altering the inductive effect due to variations in the electronegativity of the ligands. The most common experiments performed in this work were conducted using trichloroacetic acid, which is highly electron-withdrawing (i.e., highly electronegative). This behavior induces a negative inductive effect on the surfaces to which these ligands are attached, resulting in electron strain (negative dipole moment) at the interface. When acids with opposite electronegativity (e.g., phosphotungstic acid) are used, a positive inductive effect is applied, and thus electron compression occurs. Both negative and positive inductive effects can produce high degrees of supercooling (e.g., >0.34), but the yields differ.

[0188] The influence of the inductive effect was investigated using ligands with low electronegativity (tribromoacetic acid and chloroacetic acid). Both acids used resulted in lower degrees of supercooling and lower yields. These results further indicate that surface-induced effects from the organic shell itself play a role in driving the supercooling behavior of the core-shell particles.

[0189] Liquid metal surface oxides

[0190] This part of the disclosure describes the opportunity to passivate oxide particles in liquid metal. The complexity and order beneath the surface provide opportunities to prevent uniform nucleation and achieve enhanced undercooling. The plasticity beneath the liquid metal surface exhibits self-healing properties, thus minimizing E. oThe components dominate the surface unless they are stoichiometrically limited. This plasticity provides an opportunity to synthesize organometallic polymers that self-assemble in situ into high aspect ratio nanomaterials. Induced surface species formation means that, under appropriate oxidant stress, oxide thickness and composition can be tuned, leading to temperature-dependent compositional inversion and so-called chameleon metals.

[0191] Figure 18 This is an extended view of the hypothetical surface oxide architecture used for Field metals. In this case, it is assumed that the surface has no mass and volume (e.g., a Gibbs-Duhem plane, GDP). In other cases, the surface constitutes a continuum of the bulk, differing only in the number density of the components occupying such regions (Gibbs-Duhem interfaces, GDI). Thermodynamically, a surface can encompass the mass and energy dissipation boundary levels of any system. Therefore, defining a surface solely in terms of mass distribution may be insufficient. Considering energy distribution, GDP requires bimodality, as the transition from one phase to another would constitute two points in space where energy values ​​are feasible, and there are instantaneous energy jumps. This situation negates any appearance of equilibrium and is therefore potentially impossible. On the other hand, a GDI with a decreasing concentration gradient can describe material systems with low or high cohesive energy density (vapor pressure). In crystalline materials, it can be argued that the lattice plane is clearly defined, thus GDP is appropriate in this case. Considering a flat crystalline metallic system (pressure jump = 0, vapor pressure ≈ 0), and taking into account the nature of metallic bonds, an “electron sea” should occupy the surface. Considering the dual nature of electrons and the uncertainty principle, defining the trajectory of a surface negates the flux (velocity) of surface electrons, and vice versa. Assuming the existence of an energy gradient (GDI) near the surface of an equilibrium hybrid material, autonomous species formation is likely driven by curvature in the Lowengrub-Voigt model or thermal oxidative composition inversion.

[0192] In some implementations, the following governing rules drive speciation. For reactive components, preferential bond formation can lead to order and organization over relatively short distances (1 nm–2 nm), such as in hydrocarbon self-assembly monolayers. In more stochastic systems, such as the formation of passivating oxides on metallic alloys, redox-driven differentiation can occur over several nanometers. Thus, a material surface can be a complex construct due to its size (nm) energy distribution, composition, structure, and reactivity.

[0193] Liquid metal particles:

[0194] Most metals oxidize rapidly in air to form a thin layer of oxide. This thin layer of passivated oxide can be considered the surface of the particles, but since oxides are not metals, they are thermodynamically distinct components. In this respect, a surface is defined as a set of components that are not part of the object under consideration. Despite their differences, passivated oxides and energetically distinct interfacial metal layers constitute a surface.

[0195] Passivated oxides may differ from self-assembled monolayers (SAMs) on coin metals, where the organic and metallic components are distinct entities. Unlike monolayer systems with defined connection points, such as in Au-S bonds, passivated oxides are dynamic continuums emerging from the bulk and are a result of equilibrium systems. This relationship leads to tensor properties of surface tension, which are opposite to the scalar properties of SAMs. The governing rules governing this can depend on the environment (temperature, reactive substances, pressure, etc.), the reactivity of the alloy components, the cohesive energy density (the degree of similarity between alloy components), the diffusivity (and therefore atomic radii), and the thermodynamic state of the bulk. The high vapor pressures of the metal and oxides preclude the possibility of concentration gradients, which in turn impose an energy bimodality at the metal-oxide interface, indicating the presence of cross-plane energy jumps (GDPs). Thus, some gradient in composition or energy states may exist as the metal-oxide layer approaches from the oxide or metal side of the interface. Therefore, regardless of the definition used, the surface is a metastable region of the material, whose energy states can only be averaged across the divergence of energy states at each point on the surface. In an environment, the diffusion layer of species-modified surface materials (σ) reflects the energy gradient between the system and its surroundings, and this gradient can be dynamic and sensitive to small perturbations. An equilibrium state is established based on the standard reduction potentials of the components below, their flux tendencies, and their interactions with other alloy components. Figure 19 illustrates this behavior of BiInSn (Field metal). Therefore, understanding this surface depends on the observation length scale, time and its complexity, as well as other properties. Passivation oxides are typically larger than most SAMs (e.g., eutectic gallium indium oxide ≈ 2 nm, while decanethiol SAM ≈ 1 nm).

[0196] analogy

[0197] SAMs are a specific example of thin (nano) layers on metallic surfaces that significantly alter material properties, including work function, tribo / wetting properties, conductivity, and plasmonic activity. SAMs can form through thermodynamically driven self-assembly processes, resulting in highly ordered structures. Deposited thin layers of material offer significant opportunities in more fundamental regions, most notably structure-property relationships and interfacial phenomena. SAM systems can be modeled as two interfaces surrounding a bulk (typically a hydrocarbon), where each of the three components can be studied individually by tuning the basic building blocks (molecules). Due to the small size of the molecules and their dependence on molecular orientation, any minute change to the surface can alter the entire system. However, SAMs can be analyzed under well-controlled conditions. Applications of SAMs can be categorized into two types: some applications directly utilize the structure-property relationships of SAM molecules. For example, the monomolecular nature of SAMs leads to their use in molecular electronics and as candidates for tunable hydrophobic coatings. On the other hand, the highly tunable nature of SAMs makes them a large candidate platform for building / anchoring other components on metallic surfaces.

[0198] Studies on passivated oxide layers in liquid metal particles are very limited, partly due to challenges in characterization techniques. This difficulty stems primarily from the compositional complexity within the underlying metal-oxide interface over very small distances. However, when properly formed and / or designed, this passivated oxide layer offers various advantages to the material. In non-reactive droplets, the surfaces of micron- to nanometer-sized particles exhibit sharp energy and compositional gradients, which are primarily trapped by interfacial excess Γi and Laplace pressure jump conditions (ΔP = 2γ / r, where γ is the surface tension and r is the particle radius). By definition, this sharp gradient serves to establish an energy and mechanical balance between the particle and its surrounding environment. However, for metal droplets, exposure to environmental conditions leads to the rapid formation of a passivated oxide layer. In metal alloys, the difference in redox potential and diffusivity means that competitive oxidation at exposure time t = 0 leads to the lowest standard reduction potential (E0). 0 The surface of the oxides formed is dominated by the most abundant and diffuse components. However, over time, kinetically resolved self-sorting and species formation often occur, resulting in the appearance of monometallic oxides on the surface of the metal alloy. This sorting / structure is dominated by (but not limited to) E 0 Stoichiometry, atomic size, cohesive energy density, atomic flux, oxidant diffusion rate, temperature, and pressure all play a role. At a certain thickness, oxidation becomes infinitely slow and reaches equilibrium.

[0199] In an oxidizing environment, all elements within the alloy have an equal probability of oxidation at t = 0. This is only disturbed by their stoichiometry and tendency to occupy the surface. Kinetically, this becomes a competition for dominance of the outer surface of the oxide layer by the most "favorable" element. In EGaIn, this element is gallium. Over time, as the oxidant flux slowly decreases, the oxide reaches d_c^p, leading to the formation of a lower layer of low oxides derived from the less reactive components that are kinetically limited to complete oxidation. For eutectic, selective consumption of some alloy components in the alloy composition produces an energy-unfavorable hypoeutectic, which leads to the enrichment of unreacted components at the metal-oxide interface, reflected throughout the oxide shell. However, sharp compositional gradients present interfaces with large chemical potential gradients (Δμ), thus exhibiting metastable surfaces. Δμ coupled to ΔP exhibits stress divergence proportional to the particle size. Such gradients affect the properties of the particles.

[0200] Based on the asymmetric energy distribution on the surface oxide, bulk energy dissipation can be disrupted and relaxation induced by tuning surface stress. Given the high symmetry of molten metal (i.e., the lack of order as defined in Landau phase transition theory), the formation of passivating oxides and the underlying enrichment (e.g., eutectic composition) must introduce some pressure on free diffusion. Nucleating agent growth must overcome surface tension. Even after nucleating agent seed formation, a competition arises between growth (decrease in bulk energy) and contraction (increase in surface energy), with the process favoring the former as size increases. It can be said that the magnitude of the nucleation rate is sensitive to the value of the interfacial energy; even a small percentage change in σls (solid-liquid interfacial free energy) can alter the predicted rate by several orders of magnitude. Alternatively, a second non-dynamic solid-liquid interface, along with associated order and free energy transfer, exists beneath the passivating oxide layer, resulting in two solid-liquid interfacial free energy perturbations that must be overcome for successful nucleation growth: the nucleating agent interface and the oxide interface.

[0201] Unlike dynamic nucleator seed interfaces where the shrinkage of the nucleating agent is overcome with growth, the structure of passivated oxides is fixed and cannot be disturbed by growth. Therefore, by designing the surface oxides for miscibility with respect to the bulk (liquid) components, the growth of the nucleating agent can be significantly influenced, especially in small (<10 μm) particles. Thus, passivated oxides should result in significant suppression of the liquid-solid phase transition, thereby enhancing supercooling. Previously, supercooling was achieved, for example, by removing non-homogeneous nucleating agents using containerless methods. However, containerless methods do not remove homogeneous nucleating agents (a process arising from structural fluctuations in the liquid) and therefore do not utilize the interfacial tension of non-dynamic surface oxides.

[0202] Smaller particles are more likely to be supercooled. This size effect is due to the large surface area to volume ratio that limits uniform nucleation. Consider the Gibbs free energy (ΔG) as: ΔG = ΔH - TΔS + δw' (where ΔH and ΔS are the changes in enthalpy and entropy, respectively, T = temperature, and δw' = non-PV work). Under proper enthalpy-entropy compensation, surface work (δw') can dominate ΔG. While the above method heavily relies on tilting the bulk enthalpy-entropy balance to manipulate the phase transition, δw' and the surface contribution are generally assumed to be negligible due to entropy constraints. However, curved surfaces are metastable by definition and are therefore free energy stress sources that can alter the energy profile of the entire material. Thus, designing surface oxides can lead to these size dependencies (surface area to volume ratio) extending beyond the nanoscale to the microscale.

[0203] The surface work term is the amount of energy required to hold a surface per unit area, δw^'=γdA. By definition, surface tension is the product of interfacial excess and chemical potential difference. The complex compositional gradient demonstrated above produces a large curvature-dependent Δμ gradient. Therefore, in small particles with large surface areas, the amount of δw' can overcome the enthalpy-entropy balance and suppress the liquid-solid phase transition (ΔGLS>0), even when these perturbations are small. As demonstrated by the long-term stability of particles prepared in this way, the structural complexity of oxides can be sufficient under appropriate tuning.

[0204] Beyond its effect on free energy, the formation of a uniform, smooth passivated oxide layer creates a physical barrier against heterogeneous nucleating agents, thus enhancing stability in the supercooled state. This understanding enables the synthesis of stable supercooled liquid metal core-shell (ULMCS) particles, enabling thermally free soldering and a wide range of other environmental or cryogenic metal processing. Since the surface is a primary driver of metastability, the rupture of the oxide shell leads to transient flow, coalescence, and solidification. Recent developments have allowed for the supercooling of commercially available lead-free solder SAC 305, enabling cryogenic surface mounting and electronic packaging. This cryogenic sintering allows for the integration of conductive traces or circuits onto additional temperature-sensitive substrates, i.e., organic and polymeric materials. Understanding surface oxides raises the Blass paradox: surface species formation can induce reverse microstructures on liquid metals.

[0205] Although droplet 100 (see Figure 1 While described and shown as a particular composition and construction, embodiments of this disclosure are adaptable for use with a variety of compositions and constructions. Any element and combination thereof may be used for the core and shell. The shell may have any number of inorganic and / or organic layers.

[0206] In the foregoing description, embodiments of this disclosure have been described with reference to numerous specific details that may vary with implementation. Therefore, this specification and the accompanying drawings should be considered exemplary rather than restrictive. The scope of this disclosure, and the only and exclusive indicator that the applicant intends to define its scope, is the literal and equivalent scope of the set of claims issued in this application, and is a particular form of such claims, including any subsequent amendments. Specific details of particular embodiments may be combined in any suitable manner without departing from the spirit and scope of the embodiments of this disclosure.

[0207] Additionally, spatially relative terms such as “bottom” or “top” may be used to describe the relationship of an element and / or feature to another element and / or feature, as illustrated in the figures, for example. It will be understood that spatially relative terms are intended to cover different orientations of the device in use and / or operation other than those depicted in the figures. For example, if the device in the figures is flipped, an element described as the “bottom” surface may then be oriented “above” other elements or features. The device may be oriented in other ways (e.g., rotated 90 degrees or otherwise), and the spatially relative descriptors used herein are interpreted accordingly.

[0208] As used herein, the terms “and,” “or,” and “and / or” can include a variety of meanings, which are also expected to depend at least in part on the context in which such terms are used. Generally, when used to relate a list such as A, B, or C, “or” is intended to mean A, B, and C (used herein in an inclusive sense) and A, B, or C (used herein in an exclusive sense). Furthermore, as used herein, the term “one or more” can be used to describe any feature, structure, or characteristic of the singular, or can be used to describe some combination of features, structures, or characteristics. However, it should be noted that this is merely an exemplary example, and the subject matter protected by the claims is not limited to this example. Additionally, when used to relate a list such as A, B, or C, the term “at least one of…” can be interpreted as meaning any combination of A, B, and / or C, such as A, B, C, AB, AC, BC, AA, AAB, ABC, AABBCCC, etc.

[0209] Throughout this specification, references to “an example,” “example,” “some examples,” or “exemplary implementation” mean that a particular feature, structure, or characteristic described in conjunction with a feature and / or example may be included in at least one feature and / or example of the subject matter protected by the claims. Therefore, the appearance of the phrases “in an example,” “in some examples,” “in some implementations,” or other similar phrases throughout this specification does not necessarily refer to the same feature, example, and / or limitation. Furthermore, a particular feature, structure, or characteristic may be combined in one or more examples and / or features.

[0210] In some implementations, the operation or processing may involve the physical manipulation of physical quantities. Typically, although not essential, such quantities may also take the form of electrical or magnetic signals that can be stored, transmitted, combined, compared, or otherwise manipulated. Primarily for common usage, it has proven convenient to sometimes refer to such signals as bits, data, values, elements, symbols, characters, items, numbers, counts, etc. However, it should be understood that all such terms or similar terms will be associated with appropriate physical quantities and are merely convenient notations. Unless explicitly stated otherwise, as will be apparent from the discussion herein, it should be understood that throughout this specification, discussions using terms such as “processing,” “estimating,” “calculating,” “determining,” etc., refer to the actions or processes of a particular device (such as a dedicated computer, dedicated computing device, or similar dedicated electronic computing device). Therefore, in the context of this specification, a dedicated computer or similar dedicated electronic computing device is capable of manipulating or transforming signals that are generally represented as physical electronic or magnetic quantities within the memory, registers, or other information storage devices, transmission devices, or display devices of the dedicated computer or similar dedicated electronic computing device.

[0211] In the foregoing detailed description, numerous specific details have been set forth to provide a thorough understanding of the subject matter protected by the claims. However, those skilled in the art will understand that the subject matter protected by the claims can be practiced without these specific details. In other instances, methods and apparatuses that would be understood by those of ordinary skill in the art have not been described in detail so as not to obscure the subject matter protected by the claims. Therefore, it is contemplated that the subject matter protected by the claims is not limited to the specific examples disclosed, but rather that such protected subject matter may also encompass all aspects falling within the scope of the appended claims and their equivalents.

Claims

1. A droplet, the droplet comprising: a core comprising an alloy, the alloy comprising a majority of a first metallic element and a minority of a second element, wherein the core is in a liquid state below a solidus temperature of the alloy; and a shell completely encapsulating the core and comprising an outer surface comprising a majority of the second element and a minority of the first metallic element, wherein the shell is in a solid state below the solidus temperature of the alloy.

2. The droplet of claim 1, wherein the second element is a metal.

3. The droplet of claim 1, wherein the second element is a metalloid.

4. The droplet of claim 1, wherein the shell comprises an innermost layer having a majority concentration of the first metallic element and an outermost layer having a majority concentration of the second element.

5. The droplet of claim 4, wherein the innermost layer has a greater E o .

6. The droplet of claim 4, wherein the innermost layer has a lower E o .

7. The droplet of claim 4, wherein the innermost layer and the outermost layer comprise oxides of the first metallic element and the second element.

8. The droplet of claim 1, further comprising a ligand coating on the outer surface.

9. A method of forming a droplet, the method comprising: forming a liquid core of the droplet from an alloy comprising a first element, a second element, and a third element; forming a solid shell around the liquid core and completely encapsulating the liquid core, the solid shell comprising an innermost layer having a majority concentration of one of the first element, the second element, and the third element and an outermost layer having a majority concentration of a different one of the first element, the second element, and the third element; and cooling the liquid core and the solid shell to below a solidus temperature of the alloy while maintaining the liquid core in a liquid state.

10. The method of claim 9, wherein the solid shell comprises three layers, and wherein the innermost layer has a majority concentration of the first element, an intermediate layer has a majority concentration of the second element, and the outermost layer has a majority concentration of the third element.

11. The method of claim 10, wherein the solid shell is formed in an oxidizing environment.

12. The method of claim 11, wherein the oxidizing environment is controlled by varying an oxygen partial pressure in the oxidizing environment.

13. The method of claim 11, wherein the innermost layer has a greater E o , and wherein the intermediate layer has a greater E o than the outermost layer.

14. The method of claim 11, wherein a thickness of one or more of the three layers of the solid shell is determined by a time of exposure to the oxidizing environment.

15. The method of claim 10, wherein the solid shell is formed in a reducing environment.

16. The method of claim 15, wherein the innermost layer has a lower E o , and wherein the intermediate layer has a lower E o than the outermost layer.

17. The method of claim 15, wherein a thickness of one or more of the three layers of the solid shell is determined by a time of exposure to the reducing environment.

18. The method of claim 10, further comprising exposing the solid shell to one or more chelating agents to remove at least a portion of the outermost layer.

19. The method of claim 18, wherein the one or more chelating agents comprise at least one of a carboxylate, an amide, an alkoxide, an amine, a thiol, or a phosphate.

20. The method of claim 10, further comprising an etch process to polish an inner layer of the solid shell.

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