Magnetic nanowires having ternary zintl phase and method of making same

Abstract

Provided is a nanostructure of a ternary Zintl phase of a stoichiometric formula of X5Y2Z6. The ternary Zintl phase is in a crystalline state, and the nanostructure is selected from a nanowire and a film. In the formula X is selected from Eu, Ca, Sr, and Yb; Y is In or Ga; and Z is As or Sb.

Description

MAGNETIC NANO WIRES HAVING TERNARY ZINTL PHASE ANDMETHOD OF MAKING SAMECROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of US Provisional Patent Application No. 63 / 671,293, filed July 15, 2024 and Israeli Patent Application No. 310522, filed January 29, 2024, titled “MAGNETIC NANOWIRES HAVING TERNARY ZINTL PHASE AND METHOD OF MAKING SAME”, the contents of which are all incorporated herein by reference in their entirety.FIELD OF THE INVENTION

[0002] The present invention relates generally to nanostructures. More specifically, the present invention relates to magnetic nanostructures having a ternary Zintl phase.BACKGROUND OF THE INVENTION

[0003] Molecular beam epitaxy (MBE) is a process in which a thin single-crystal layer is deposited on a single-crystal substrate using atomic or molecular beams generated in Knudsen cells contained in an ultra-high vacuum chamber.

[0004] Growing nanowires in MBE is a challenging process in which many parameters of the individual and combined crystallographic and growth phase diagrams must match. Therefore, the variety of compounds that can be grown as nano wires is rather limited.

[0005] Previous studies have shown that semiconductor nanowires, such as InAs nanowires can be grown using the MBE process.

[0006] However, a combination of a semiconductor and a magnetic material in the form of nanowires have not been reported.SUMMARY OF THE INVENTION

[0007] Some aspects of the invention are related to a nanostructure, comprising: a ternary Zintl phase of a stoichiometric formula of X5Y2Z6 wherein the ternary Zintl phase is in a crystalline state; and wherein the nanostructure is selected from a nanowire and a film and wherein:X is selected from Eu, Ca, Sr, and Yb;Y is In or Ga; andZ is As or Sb.

[0008] In some embodiments,(i) X is selected from Eu, Ca, Sr, and Yb; Y is In; and Z is As; or(ii) X is selected from Eu, Sr, and Ba; Y is In; and Z is Sb.

[0009] In some embodiments, a crystal of the ternary Zintl phase may have one of, a Pbam space group, and a Pnma space group. In some embodiments, X is Ca; Y is Ga; and Z is As or Sb. In some embodiments, a crystal of the ternary Zintl phase may have a Pbam space group or a Pnma space group.

[0010] In some embodiments, the X5Y2Z6 ternary Zintl phase may have a crystal structure which includes subgroups of the orthorhombic crystal. In some embodiments, the Y and Z form an anionic lattice. In some embodiments, the nanostructure may be nanowire having a length of between 1 to 10 pm. In some embodiments, the nanostructure may be a nanowire having a diameter of between 10 to 200 nm.

[0011] In some embodiments, the nanowire may include a core-shell nanowire, the core-shell nanowire may include a shell consisting essentially of the ternary Zinc Blende phase. In some embodiments, the core comprising essentially of a crystalline material of Formula YZ, having a Zinc Blende crystal structure.

[0012] In some embodiments, the nanostructure is a film having a thickness of between 10 to 200 nm. In some embodiments, the nanostructure may be a film having a bilayer structure, wherein the bilayer structure includes: a substrate having a stochiometric formula of ZY and a Zinc Blende crystal structure; and a layer comprising the ternary Zintl phase of a stoichiometric formula of X5Y2Z6.

[0013] Some additional aspects of the invention may be directed to a nanowire, comprising: a core having a Zinc blende crystal structure; and a shell comprising a ternary Zintl phase of a stoichiometric formula of X5Y2Z6, wherein: a. the core is InAs, and X is selected from Eu, Ca, Sr, or Yb, Y is In, and Z is As;b. the core is InSb, and X is selected from Eu, Sr, Ca, Yb, or Ba, Y is In, and Z is Sb; c. the core is GaAs, and X is Ca, Y is Ga and Z is As; or d. the core is GaSb and X is Eu, Ca, or Yb, Y is Ga and Z is Sb.

[0014] In some embodiments, the nano wire may have a length of between 1 to 10 |im. In some embodiments, the nanowire may have a diameter of between 10 to 200 nm. In some embodiments, the thickness of the shell is at least 1 monolayer.

[0015] Some additional aspects of the invention may be directed to a film, comprising: a substrate having a stochiometric formula of ZY and a Zinc Blende crystal structure; and a layer covering at least a portion of the substrate including a ternary Zintl phase of a stoichiometric formula of X5Y2Z6, wherein: a. the substrate is InAs, and X is selected from Eu, Ca, Sr, or Yb, Y is In, and Z is As; b. the substrate is InSb, and X is selected from Eu, Sr, Ca, Yb, or Ba, Y is In, and Z is Sb; c. the substrate is GaAs, and X is Ca, Y is Ga and Z is As; or d. the substrate is GaSb and X is Eu, Ca, or Yb, Y is Ga and Z is Sb.

[0016] In some embodiments, the layer may have a thickness of between 10 to 200 nm.

[0017] Some additional aspects of the invention may be directed to a microchip. The microchip may include a substrate having a stochiometric formula of ZY and a Zinc Blende crystal structure; and a pattern grown on the substrate, and comprising a ternary Zintl phase of a stoichiometric formula of X5Y2Z6, wherein: a. the substrate is InAs, and X is selected from Eu, Ca, Sr, or Yb, Y is In, and Z is As; b. the substrate is InSb, and X is selected from Eu, Sr, Ca, Yb, or Ba, Y is In, and Z is Sb; c. the substrate is GaAs, and X is Ca, Y is Ga and Z is As; or d. the substrate is GaSb and X is Eu, Ca, or Yb, Y is Ga and Z is Sb.

[0018] Some aspects of the invention are directed to a device, comprising: a nanostructure and / or a nanowire according to any one of the embodiments disclosed herein, and two conductive layers sandwiching the nanostructure and / or the nanowire. In some embodiments, the nanowire is arranged at one of: a. the longitudinal direction of the nanostructure and / or the nanowire is substantially perpendicular to the surface of each conductive layer of the two conductive layers; or b. the longitudinal direction of the nanostructure and / or the nanowire is tilted at 35° with respect to the surface of each conductive layer of the two conductive layers.

[0019] In some embodiments, the device may further include a dielectric material encompassing the nanowire while filling a volume between the two conductive layers.

[0020] Some additional aspects of the invention are directed to a method of making a nanostructure / nanowire, comprising: a. providing a target nanostructure / nanowire having a stoichiometric formula YZ and a Zinc Blende crystal structure; and b. providing a flux of gas comprising of X and Y atoms at a flux ratio of between 0.5 / 100 to 1.5 / 100 at a temperature of between 300 to 600 °C; thereby, initiating a solid-state growth of a ternary Zintl compound having a stoichiometric formula of X5Y2Z6, wherein: a. X is selected from Eu, Ca, Sr, and Yb; b. Y is In or Ga; and c. Z is As or Sb.

[0021] In some embodiments, a duration of the provision of the flux is between 60 to 240 minutes. In some embodiments, the method further comprises: selecting a required thickness of the ternary Zintl compound to be grown; receiving a diameter of the target nanowire; and determining the duration of the provision of the flux based on the selected thickness of the target nanostructure.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention,however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

[0023] Fig. 1 A is an illustration and a flowchart of a method of making a nanowire according to some embodiments of the invention;

[0024] Fig. IB is an illustration of a system for making a nanowire according to some embodiments of the invention;

[0025] Figs. 2A, 2B, and 2C are illustrations of crystal structures of InAs, EudmAsr,. and CadmAsr, according to some embodiments of the invention;

[0026] Figs. 3A, 3B, and 3C are illustrations of a nanowire and cross-section in nanowires according to some embodiments of the invention;

[0027] Figs. 3D and 3E are illustrations of a cross-section view of films according to embodiments of the invention;

[0028] Fig. 4 is an illustration of a device according to some embodiments of the invention;

[0029] Fig. 5 shows TEM and SEM images of EudmAsr, crystal on InAsSb core, according to some embodiments of the invention;

[0030] Fig. 6 shows TEM-EDS lattice images of atomic positions according to some embodiments of the invention;

[0031] Fig. 7 shows several microscopy images (a) and (b) SEM of as-grown Eu5In2As6 nanowires sample, (c) TEM of a single nanowire, (d) and (e) top view SEM and side view TEM of Eudm Ase epilayer, according to some embodiments of the invention; and

[0032] Fig. 8 includes graphs of Magnetic Properties Measurement System (MPMS) measurement of as-grown EudmAse nanowires sample according to some embodiments of the invention.

[0033] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0034] One skilled in the art will realize the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting of the invention described herein. Scope of the invention is thus indicated by the appended claims, rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

[0035] In some embodiments, the term “process” and the term “method” are used interchangeably.

[0036] Some aspects of the invention are directed to a nanostructure having a ternary Zintl phase of a stoichiometric formula of X5Y2Z6. The nanostructure may be a nanowire or a film. Such nanostructures may have a magnetic property. In a nonlimiting example, intrinsically magnetic ordered crystals were grown in the form of nanostructures by depositing a magnetic shell / layer comprising Eu and As on a semiconducting Zinc Blende InAs core / substrate. The ternary Zinc Blende phase may be grown using topotactic (also known as topotaxial) growth. In some embodiments, indium may migrate from the core to the shell. In some embodiments, Eu migrates from the shell to the core. In some embodiments, indium may migrate from the core to the shell and Eu migrates from the shell to the core across the rather unchanged As structure (e.g., the As acts as a skeleton).

[0037] In some embodiments, the present invention provides a magnetic compound in the form of a nanowire or a film. In some embodiments, the present invention surprisingly provides a magnetic nano wire or a magnetic film formed using a solid- state method based on a topotactic process. In some embodiments, the topotactic growth process is bi-directional, where both the core / substrate and the shell / layer undergo a transition to a uniform structure. In some embodiment, this fabrication process is unique compared to other methodologies relating to topotactic processes where a third element dictates the structure.

[0038] In some embodiments, the term nanostructure comprises a nanowire, a film or the like. In some embodiments, the term nanostructure is interchangeable with theterm nanowire or film. In some embodiments, the terms film or nano wire are interchangeable with the term nanostructure.

[0039] Reference is now made to Fig. 1A which is an illustration and a flowchart of a method of making a nanostructure / nanowire according to some embodiments of the invention. In optional step 10, the method may include providing a target nanostructure having a stoichiometric formula YZ and a Zinc Blende crystal structure or a Wurtzite crystal structure (e.g., a Wurtzite with many stacking faults), wherein the target nanostructure is selected from a target nanowire and a target substrate. In some embodiments, providing the target nanostructure may include epitaxially growing a target nanowire or a target substrate having the stoichiometric formula YZ and a Zinc Blende crystal structure or a Wurtzite crystal structure (e.g., a Wurtzite with many stacking faults). For example, an InAs nanowire may be epitaxially grown in a molecular beam epitaxy (MBE) system. A nonlimiting example for such a system is provided in Fig. IB. In some embodiments, the target nanowire may be InSb, GaAs, GaSb, or any combination thereof.

[0040] A nonlimiting example for growing InAs nanowires may include using InAs single crystal wafers having either (001) or (111) crystallographic orientations, as substrates. The substrate may be glued with indium on a moly block. In some embodiments, the moly block is substantially devoid of water. In some embodiments, the moly block is devoid of water. In some embodiments, the moly block is pre-heated to approximately 200 °C for the removal of water.

[0041] The substrates may be inserted into a preparation chamber (e.g., chamber 105 of Fig. IB) connected to a growth chamber (e.g., chamber 110 of Fig. IB) where an oxide layer is first removed. In some embodiments, an oxide layer is removed at approximately 650 °C. In the following step, gold nanodroplets on the surface of the substrates are formed. In one embodiment, gold nanodroplets are formed on the surface of the substrates. In one embodiment, gold nanodroplets are formed on the surface of the substrates by evaporating a gold layer. In one embodiment, the gold layer is approximately 1 nm (e.g., between 2 to 5 layers). In one embodiment, the gold droplets catalyze the growth of InAs nano wires.

[0042] The substrates now covered by gold nanodroplets are inserted into the growth chamber. In some embodiments, As or Sb in a gas phase may be added into the growthchamber. In some embodiments, As or Sb in a gas phase may be added into the growth chamber at 200 to 350 °C, and any value therebetween, (e.g., 245 °C for As and higher than 285 °C for P). The added gas forms a pressure of between 1.5 to 3.5 10’8tor, and any value therebetween, for 40 to 80 (e.g., 60) minutes (min) within the chamber.

[0043] In some embodiments, following the provision of As or Sb gas, for 40 to 80 min, (or any value therebetween) the substrate is heated up to 400 to 650 °C for balling (shrinking of the surface of metal liquid) and Oswald ripening the gold into catalyst droplets. Oswald ripening refers to the dissolving of the small droplets (e.g., gold droplets) and the redeposition of the small droplets onto larger droplets. For example, InAs substrate having (001) crystallographic orientation may be heated to 600 °C at a heating rate of 20 to 30 °C / min. In another example, InAs substrate having (111) crystallographic orientation may be heated to 420 °C at a heating rate of 20 to 30 °C / min.

[0044] After the completion of the balling process, the temperature of the substrates is cooled down to the growth temperature. In one embodiment, after the completion of the balling process, the temperature of the substrates is cooled down to the growth temperature which for InAs is between 390 to 410 °C (e.g., 400 °C). For example, the substrates may be cooled down at a cooling rate of 10 to 5 °C / min. During the cooling down period (e.g., at the middle of the process) Indium (or Ga) is in a gas phase may be introduced into the chamber. For example, In may be introduced at a temperature of 735 °C and Ga may be introduced at a temperature of 1000 °C.

[0045] The nucleation and growth of the YZ Zinc Blende or a Wurtzite crystal structure (e.g., a Wurtzite with many stacking faults) nanostructures are monitored by electron diffraction (e.g., using reflection high-energy electron diffraction (RHEED), which detects the change from the substrate planar morphology to the Zinc blende crystal structure or a Wurtzite crystal structure of the nanowires.

[0046] In some embodiments, the size of the gold droplets determines the diameter of the nanowires. In some embodiments, the duration of the growth (e.g., one hour) determines the length (e.g., ~1 pm) of the nanowires, for example, 1 to 10 pm.

[0047] In a nonlimiting example, As at a pressure of 9.0-6.0 xlO-6Torr and In at a pressure of 1.2-7 x 10’7Torr may be added during the growth phase, at a flux ratio of typically about 100 As / In. The flux ratio determines the aspect ratio of the wire.

[0048] In some embodiments, step 10 may include providing a target nanostructure, such as, a film having the stoichiometric formula YZ and a Zinc Blende crystal structure or a Wurtzite crystal structure (e.g., a Wurtzite with many stacking faults). The film may be epitaxially grown as disclosed herein above or may be prepared by any known method. In such case, the film may be placed inside a chamber 110, as shown in Fig. IB herein below.

[0049] In step 20 the method may include applying to the target nanostructure (e.g., the nano wire or the substrate) a flux of gas comprising of X and Y atoms at a flux ratio of between 0.5 / 100 to 1.5 / 100 and at a temperature of between 300 to 600 °C, thereby initiating, a solid-state growth of a ternary Zintl compound. The ternary Zintl compound may have a stoichiometric formula of X5Y2Z6.

[0050] In some embodiments, X may be selected from Eu or Sr, Y is In, and Z is As. In some embodiments, X may be selected from Eu or Sr, Y is In, and Z is As or Sb. In some embodiments, X may be selected from Eu, Sr, Ba, Ca or Yb, Y is In, and Z is Sb. In some embodiments, X may be Eu or Ca, Y is Ga and Z is As or Sb.

[0051] In a nonlimiting example, X is Eu. In a nonlimiting example, X is Eu and a flux of Eu at a pressure of 2.0xl0-8Torr is added to the chamber at a temperature of 450 °C. Simultaneously, when the provision is stopped, Z pressure is kept. In one embodiment, simultaneously, when the provision is stopped, the As pressure is kept at 9.0xl0-6Torr. In one embodiment, a deposited shell of XZ coats the nanowire. In one embodiment, a deposited shell of XZ coats the InAs nanowire. The result, in some embodiments, is a deposited shell of XZ (e.g., EuAs, EU2AS3, etc.) coating the InAs nanowire.

[0052] In one embodiment, the coating is evaporated. In one embodiment, the EuAs coating is evaporated. The EuAs coating may be evaporated at a rate of ~25 nm per hour while the substrate temperature is in the range of 370 to 440 °C, for example, at 420 °C. Evaporation time may be between 1 to 4 hours.

[0053] At the end of this process, the X flux is terminated and the substrate carrying the nanowires is cooled down while Z is still streamed / flowed into the chamber until the temperature drops, at which the As provision is terminated. In one embodiment, at the end of this process, Eu flux is terminated and the substrate carrying the nanowiresis cooled down while As is still streamed / flowed into the chamber until the temperature drops below 300°C, at which the As provision is terminated.

[0054] In some embodiments, the disclosed process triggers diffusion of Y (e.g., In) from the YZ (e.g., InAs) core / substrate and X (e.g., Eu) from the deposited XZ shell or XZ film to form of X5Y2Z6 (e.g., EudmAsr,) crystal via a topotactic process. In this process X and Z atoms exchange positions while the Y atoms maintain their original framework in the YZ original single crystal. The Z atoms form hexagonal framework in the template (the original YZ Zinc blende / Wurtzite single crystal) and the target phase (the X5Y2Z6 phase). Therefore, the hexagonal Z framework may be considered as a skeleton for both the YZ and the X5Y2Z6 phases. Such growth, in which one element dictates the structure of a compound is known in the art as the topotactic exchange process.

[0055] In some embodiments, the solid-state conversion in the topotactic process may occur when additional Z (such as but not limited to As) is evaporated on the single crystal YZ (e.g. InAs) nanostructure / nanowire / substrate, in the presence of a strong electropositive element (for example, Europium). Although only Eu and As are provided during the topotactic process, Y atoms (e.g., In) participate in the diffusion / conversion process that results in the formation of the X5Y2Z6 phase. In the topotactic process, EudmAsr, overlaid with unit-cells of InAs such that the As lattice remains the same.

[0056] In some embodiments, the method may further include selecting a required thickness of the ternary Zintl compound to be grown. For example, when the nanostructure is a nanowire, the diameter of the YZ nanowire core may be between 10 to 200 nm, for example, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm, 180 nm, 200 nm or any value therebetween. In another example, the thickness of the shell, grown on the core, may be at least 1 crystallographic monolayer, for example, 5, 10, 50, 100, 150 or any value therebetween, or more crystallographic monolayers. As used herein, a crystallographic monolayer comprises a layer of single unit-cell. As used herein, a monolayer comprises a single layer of the ternary Zintl unit cells.

[0057] In yet another example, when the nanostructure is a film, the thickness of the substrate may be between 10 nm to 2 mm and the thickness of the X5Y2Z6 layer may be between 10 to 200 nm. In some embodiments, the X5Y2Z6 layer may include atleast 1 crystallographic monolayer, for example, 5, 10, 50, 100, 150 or any value therebetween, or more crystallographic monolayers.

[0058] In some embodiments, the method may include determining the duration of the provision of the flux based on the selected thickness and / or the diameter of the target nanowire. For example, the duration of the provision of the flux may be between 60 to 240 minutes.

[0059] Reference is now made to Fig. 1C which is an illustration of a nonlimiting example of a system for making a nanostructure (e.g., a nanowire or a film) according to some embodiments of the invention. A molecular beam epitaxy (MBE) system 100 (e.g., a Riber-32) may include a preparation chamber 105 at which a sample may undergo several preparation processes, such as but not limited to, oxidation layer removal, metal layer / droplets depositions and the like. The preparation chamber may be held under a controlled atmosphere, such as, vacuum and may be connected to a growth chamber 110 via valve 106.

[0060] Growth chamber 110 of system 100 may include an ultra-high-vacuum (UHV) system (not illustrated) and cryogenic panels 115 for ensuring UHV inside chamber 110 throughout the growth phase. UHV is defined as an atmosphere having a pressure smaller than l.OxlO-7Pa; l.OxlO-9mbar; or 7.5xlO-10Torr.

[0061] Growth chamber 110 of system 100 may house a sample / target holder and a heater 120 located substantially in the middle of chamber 110. Sample holder 120 may be configured to rotate (as indicated by arrows ‘x’ and ‘y’) around at least one axis ‘x’ and ‘y’, for example, using manipulator 128. Sample holder 120 may include a heating element (not illustrated) configured to heat a sample attached to holder 120. Sample holder 120 may be connected to beam-equivalent pressure (BEP) ionizing gauges 125 for measuring the fluxe from effusion cells 130 and 135.

[0062] Effusion cells 130 and 135 may include cells for evaporation or sublimation of solid material to create beams of atoms of individual elements / compounds in an ultrahigh vacuum (UHV). The beams generated in effusion cells 130 and 135 are directed toward the substrate 120 surface where the solidification occurs. In a nonlimiting example, effusion cells 130 and 135 may be used for the generation of the As flux, the In flux, and the Eu flux. In some embodiments, each one of effusion cells130 and 135 may include a shutter 138 for controlling the addition of the flux from the effusion cell.

[0063] System 100 may further include a reflection high-energy electron diffraction (RHEED) gun 140 and a fluorescence screen 150. RHEED gun 140 and fluorescence screen 150 may be included in a RHEED system for characterizing the surface of the sample in chamber 110.

[0064] Reference is now made to Figs. 2A, 2B, 2C which are illustrations of crystal structures (e.g., unit-cells) of InAs, EudmAsr,. and SrdroAse according to some embodiments of the invention. The InAs unit-cell 200 illustrated in Fig. 2A is representative of all YZ Zinc blende crystal structures according to some embodiments of the invention. The YZ Zinc blende crystal structure is the structure of the target nanostructure / nanowire / substrate which is the phase from which the X5Y2Z6 ternary Zintl phase is grown using the solid-state conversion topotactic process discussed herein. In some embodiments, the YZ crystal structure may be a Wurtzite crystal structure (e.g., a Wurtzite with many stacking faults).

[0065] In some embodiments, the X5Y2Z6 ternary Zintl phase may be fabricated by the method of Fig. IB, for example, using MBE system 100.

[0066] In some embodiments, X is selected from Eu, Ca, and Sr; Y is In; and Z is As or Sb. For example, the X5Y2Z6 ternary Zintl phase may be the EudmAsr, or SrdroAse crystal structure 210, illustrated in Fig. 2B or EudmSbe crystal structure 220 illustrated in Fig. 2C. In some embodiments, X is selected from Eu, Sr, Ca, Yb and Ba; Y is In; and Z is Sb. For example, the X5Y2Z6 ternary Zintl phase may be Snl P^ In some embodiments, at least one or all of the X5Y2Z6 ternary Zintl phases may have a Pbam space group.

[0067] In some embodiments, X is Ca; Y is Ga; and Z is As or Sb. For example, the X5Y2Z6 ternary Zintl phase may be CasGa2As6. In some embodiments, at least one or all of the X5Y2Z6 ternary Zintl phases may have a Pbam space group.

[0068] In some embodiments, X is Eu; Y is Ga, In or Al; and Z is As. For example, the X5Y2Z6 ternary Zintl phase may be EU5AI2AS6. In some embodiments, at least one or all of the X5Y2Z6 ternary Zintl phases may have a Pnma space group.

[0069] In some embodiments, the X5Y2Z6 ternary Zintl phase may have a crystal structure which includes subgroups of the orthorhombic crystal.

[0070] In some embodiments, the Y and Z atoms in the X5Y2Z6 ternary Zintl phase form an anionic lattice. In some embodiments, the Y and Z atoms in the X5Y2Z6 ternary Zintl phase form an anionic lattice. In some embodiments, X in the X5Y2Z6 ternary Zintl phase forms a cationic structure. In some embodiments, the Y and Z atoms in the X5Y2Z6 ternary Zintl phase form an anionic lattice while the X forms the cationic structure. In some embodiments, the Z atoms (e.g., In and Sb) may occupy positions of a hexagonal lattice, similar to the positions of these atoms in the target YZ Zinc blende crystal structure or a Wurtzite crystal, thereby, the Z atoms may be regarded as the skeleton for the bi-directional solid-state diffusion of the In and Eu atom.

[0071] Additional nonlimiting examples for various compounds having the formula X5Y2Z6 are given in table 1.

[0072] Table 1

[0073] According to some embodiments of the invention included herein is a method for fabricating a film comprising a compound having formula X5Y2Z6 on a YZ Zinc Blende substrate or on a Wurtzite crystal structure (e.g., a Wurtzite with many stacking faults). According to some embodiments of the invention, a method such as the method shown in Fig. 1A may be used for fabricating a thin film of a compound having the formula X5Y2Z6 on a YZ Zinc Blende substrate.

[0074] In some embodiments, the method may include epitaxially growing a substrate having a stoichiometric formula YZ and a Zinc Blende crystal structure. For example, an InAs substrate may be epitaxially grown in a molecular beam epitaxy (MBE) system. In some embodiments, the target substrate may be InSb, GaAs or GaSb.

[0075] In some embodiments, the method may include providing a flux of gas comprising of X and Y atoms at a flux ratio of between 0.1 / 100 to 10 / 100 and at a temperature of between 300 to 600 °C, thereby initiating, a solid-state growth of a ternary Zintl compound. The ternary Zintl compound may have a stoichiometric formula of X5Y2Z6.

[0076] In some embodiments, X is selected from Eu or Sr, Y is In, and Z is As. In some embodiments, X is selected from Eu or Sr, Y is In, and Z is As or Sb. In some embodiments, X is selected from Eu, Sr, Ba, Ca or Yb, Y is In, and Z is Sb. In some embodiments, X is Eu or Ca, Y is Ga and Z is As or Sb.

[0077] In a nonlimiting example, X is Eu and a flux of Eu at a pressure of 2.0xl0-8Torr is added to the chamber at a temperature of 450 °C. Simultaneously, When the provision is stopped, the As pressure is kept at 9.0xl0-6Torr. The result is a deposited shell of XZ (e.g., EuAs, EU2AS3, etc.) coating the InAs nanowire.

[0078] The EuAs coating is evaporated at a rate of ~25 nm per hour while the substrate temperature is in the range of 370 to 440 °C, for example, at 420 °C. Evaporation time may be between 1 to 4 hours.

[0079] At the end of the process, the X (such as Eu) flux is terminated and the substrate is cooled down while As is still streamed / flowed into the chamber until the temperature drops below 300°C, at which the As provision is terminated.

[0080] In some embodiments, the disclosed process triggers diffusion of Y (e.g., In) from the YZ (e.g., InAs) substrate and X (e.g., Eu) from the deposited XZ layer to form of X5Y2Z6 (e.g., EudmAse) crystal via a topotactic process. In this process X and Z atoms exchange positions while the Y atoms maintain their original framework in the YZ original single crystal. The Z atoms form a hexagonal framework in the template substrate (the original YZZinc blende / Wurzite single crystal) and the target phase (the X5Y2Z6 phase). Therefore, the hexagonal Z framework may be considered as a skeleton for both the YZ and the X5Y2Z6 phases. Such growth, in which one element dictates the structure of a compound is known in the art as the topotactic exchange process.

[0081] In some embodiments, the solid-state conversion in the topotactic process occurs when additional As is evaporated on the single crystal YZ (e.g. InAs) substrate, in the presence of a strong electropositive element, for example,Europium. Although only Eu and As are provided during the topotactic process, Y atoms (e.g., In) participate in the diffusion / con version process that results in the formation of the X5Y2Z6 phase layer. In the topotactic process, EudmAse overlaid with unit-cells of InAs such that the As lattice remains the same, as discussed herein above.

[0082] In some embodiments, the method may further include selecting a required thickness of the ternary Zintl layer to be grown. For example, the thickness of the X5Y2Z6 phase layer may be at least 1 crystallographic monolayer, for example, 5, 10, 50, 100, 150, or any value therebetween, or more crystallographic monolayers. As used herein, a crystallographic monolayer may include a layer of a single unit-cell. In some embodiments, the entire YZ substrate may be converted into a thin film the X5Y2Z6 phase using the topotactic process discussed herein.

[0083] In some embodiments, the method may include determining the duration of the provision of the flux based on the selected thickness of the X5Y2Z6 phase layer. For example, the duration of the provision of the fluxes may be between 60 to 240 minutes.

[0084] Reference is now made to Figs. 3A and 3B which are illustrations of a side view and a cross-section view of a nanowire according to embodiments of the invention. In some embodiments, nanowire 300 may include the ternary Zintl phase of the stoichiometric formula of X5Y2Z6, discussed herein above. In some embodiments, nanowire 300 may be fabricated by the method illustrated in Fig. 1A, for example, using MBE system 100.

[0085] In some embodiments, the entire nanowire 300 may be a single crystal of the X5Y2Z6 ternary Zintl. For example, nano wire 300 may include a single crystal of structure 210 (illustrated in Fig. 2B), a single crystal of structure 220 or a single crystal of structure 230 (illustrated in Fig. 2C).

[0086] In some embodiments, nanowire 300 may have a length of between 1 to 10 pm, for example, between 1 to 2 pm, 1 to 4 pm, 2 to 6 pm, 4 to 8 pm, 5 to 10 pm or any value or range therebetween.

[0087] In some embodiments, nanowire 300 may have a diameter of between 10 to 200 nm, for example, between 10 to 50 nm, 20 to 80 nm, 40 to 100 nm, 80 to 150 nm, 120 to 180, 100 to 200 nm, or any value or range therebetween.

[0088] In some embodiments, the nanowire may have a core-shell structure, the coreshell nanowire may include a core in contact with a shell, and wherein the shell comprises ternary Zintl phase, as illustrated and discussed in Fig. 3C.

[0089] Reference is now made to Fig. 3C which is an illustration of another nanowire according to some embodiments of the invention. In some embodiments, a nano wire 350 may have a core-shell structure comprising a core having the Zinc Blende crystal structure or a Wurtzite crystal structure (e.g., a Wurtzite with many stacking faults) and a shell comprising the ternary Zintl phase of the stoichiometric formula of X5Y2Z6. In some embodiments, the core is InAs, and X is selected from Eu or Sr, Y is In, and Z is As. In some embodiments, the core is InSb, and X is selected from Eu, Sr, Ca, Yb or Ba, Y is In, and Z is Sb. In some embodiments, the core is GaAs, and X is Ca, Y is Ga and Z is As. In some embodiments, the core is GaSb and X is Eu, Ca or Yb, Y is Ga and Z is Sb. In some embodiments, nanowire 350 may have a semiconducting core and a magnetic shell.

[0090] For example, nanowire 350 may have a core of a structure 200 comprising InAs and shell having crystal structure 220, illustrated in Figs. 2A-2C. In another example, nanowire 350 may have a core of structure 200, illustrated in Fig. 2A, comprising InSb and shell having crystal structure 230. In yet another example, nanowire 350 may have a core of structure 200 comprising GaAs and a shell having crystal structure 230.

[0091] In some embodiments, nanowire 350 may be fabricated by the method of Fig. 1A, for example, using MBE system 100.

[0092] In some embodiments, nanowire 350 may have a length of between 1 to 10 pm, for example, between 1 to 2 pm, 1 to 4 pm, 2 to 6 pm, 4 to 8 pm, 5 to 10 pm or any value or range therebetween.

[0093] In some embodiments, the thickness of the shell is at least 1 layer, for example, 2, 3, 4, 5, 10, 15, 20, 50, 100, 150, 200, 300 monolayers, and any value therebetween.

[0094] Reference is now made to Figs. 3D and 3E which are illustrations of a crosssection view of films according to embodiments of the invention. In some embodiments, film 400 may include a bilayer structure comprising: a substrate 410 having a stochiometric formula of ZY and a Zinc Blende crystal structure (e.g., having unit-cell 200 illustrated in Fig. 2A) or a Wurtzite crystal structure (and a layer 420having a ternary Zintl phase of the stoichiometric formula of X5Y2Z6 (e.g., having unit-cells 210, 220, and 230 illustrated in Figs. 2B-2D). In some embodiments, film 450 may include only layer 420 having a ternary Zintl phase of the stoichiometric formula of X5Y2Z6.

[0095] In some embodiments, the total thickness of films 420 and 450 may be between 10 to 200 nm, for example, between 10 to 50 nm, 20 to 80 nm, 40 to 100 nm, 80 to 150 nm, 120 to 180, 100 to 200 nm, or any value or range therebetween. In some embodiments, the thickness of layer 420 in thin film 400 may be at least 1 monolayer, for example, 2, 3, 4, 5, 10, 15, 20, 50, 100, 150, 200, 300 monolayers, and any value therebetween.

[0096] In some embodiments, substrate 410 or a portion thereof may be covered by layer 420. In some embodiments, substrate 410 may be partially or non-continuously covered by layer 420. Accordingly, layer 420 may include a pattern having a ternary Zintl phase of the stoichiometric formula of X5Y2Z6. In some embodiments, such a film may include a magnetic pattern of the ternary Zintl phase topologically grown on top of a semiconducting Zinc Blende crystal structure or a Wurtzite crystal structure of the stochiometric formula of ZY, thereby forming a microchip. The pattern may be formed by masking areas on substrate 410, using any known method, prior to the provision of the flux of gas comprising of X and Y atoms. In some embodiments, the pattern may be formed by masking areas on substrate 410, using any known method, prior to the provision of the flux of gas comprising of X and Y atoms at a flux ratio of between 0.5 / 100 to 1.5 / 100, accoridng to step 20 of the method of Fig. 1A.

[0097] Reference is now made to Fig. 4 which is an illustration of a device according to some embodiments of the invention. Device 500 may include one or more nanowires according to any one of the embodiments disclosed hereinabove, for example, nanowires, 300 or 350; and two conductive layers 510 sandwiching the one or more nanowires. In some embodiments, one or more nanowires 300 or 350 are arranged such that the longitudinal direction of each nanowire is substantially perpendicular to the surface of each conductive layer 510. Alternatively, one or more nanowires 300 or 350 are arranged such that the longitudinal direction of each nanowire is tilted at 10-55°, and any value therebetween, with respect to the surface of each conductive layer 510. Alternatively, one or more nanowires 300 or 350 arearranged such that the longitudinal direction of each nanowire is tilted at 35° with respect to the surface of each conductive layer 510. In some embodiments, when one or more nanowires are nanowires 350, device 500 may include nano wires comprising both a semiconducting core (e.g., InAs) and a magnetic shell (e.g., EudmAsr,).

[0098] In some embodiments, device 500 may further include a dielectric material 520 encompassing one or more nanowires while filling a volume between the two conductive layers. In some embodiments, the device is a conducting device. In some embodiments, the device is a semiconducting device.Examples

[0099] Eu5ln2As6 nanowire was grown on an InAs nanowire using the topotactic conversion process discussed herein above with respect to Fig. 1A using the system discussed with respect to Fig. IB. Nanowires comprising the EudmAsr, were investigated using several characterization methods.

[0100] Reference is now made to Fig. 5 which shows transmission electron microscopy (TEM) images (a) and high-angle annular dark-field imaging (HAADF) of the In and Eu in the crystal and energy-dispersive X- ray spectroscopy (EDS) of EudmAse crystals on InAs core according to some embodiments of the invention. As clearly shown in the TEM image and verified by the EDS, a full conversion of the InAs phase into the EudmAse crystal was demonstrated. Terminating the process prior to achieving full conversion may allow producing the core-shell nanowires 350 discussed with respect to Fig. 3C. Controlling parameters of the growth, such as, temperature and time, may allow controlling the thickness of the grown EudmAse shell.

[0101] Reference is now made to Fig. 7 which shows lattice images simulated from TEM-EDS images of the Eu5In2As6 (a) and the Eu5In2As6 lattice structure overlaid with a HAADF image (b) according to some embodiments of the invention. As shown in all the images, a good match was found for all atoms in the Eu5In2As6 crystal.

[0102] Additional examples may include Zintl compounds comprising both ionic and covalent bonding. In particular, the Zintl phases containing a magnetic atom such as Europium have intrigued the interest in their topological properties. In recent study the unique incorporation of Eu into InAs nanowires (NWs) during in situ MBE growthwas demonstrated. It was later demonstrated topotaxial mutual exchange of magneto topological Zintl NWs consisting of Eu3ln2As4 crystallites.

[0103] Some examples related to the present invention include newly demonstrated solid-state process comprising of evaporation of Eu and As over gold assisted pre-grown InAs NWs with a pure wurtzite structure. The research was extended to the MBE growth of NWs comprising of EudmAsr, Zintl crystallites. These can be formed by a similar unconventional new mutual cation exchange when the original nanowires have the zinc blende structure or a Wurtzite crystal structure. That is obtained by introducing a very small amount of Sb to the original InAs NWs, thus changing their structure from wurtzite to zinc blende. In this original exchange reaction which Eu and In disentangled mutually exchange via the arsenic sub lattice retaining the aspect ratio of the original InAsSb NWs yet forming an EudmAsr, Zintl, as shown in Fig 8 a to c.

[0104] Both types of Zintl NWs were grown on zinc blende InAs substrates with typical bulk growth taking place on the substrate in between the NWs. The formation of a 2D Eudm Ase layer was confirmed, which forms due to the substrate-predominant zinc blend structure. The research was extended to include the growth and characterization of 2D EudmAsr, Zintl layers which just like the NWs, to the best of the inventors’ knowledge, have never been demonstrated before, see the images Fig.8 d-e showing top view SEM and side view TEM of EudmAsr, epilayer.

[0105] The properties of the new Zintl nanostructures, including their composition, crystal structure and magnetic order, were thoroughly characterized. Local Superconducting Quantum Interference Device (SQUID) and MPMS as shown in Fig. 9. The Measurements exhibit some interesting magnetic properties while Density functional theory (DFT) calculation sheds light on their fascinating and promising electronic properties which will be part of this presentation.

[0106] Table 2 summarizes nanostructures fabricated accoridng to embodiments of the invention.

[0107] Table 2*ZB= Zinc Blande

[0108] Unless explicitly stated, the method embodiments described herein are not constrained to a particular order or sequence. Furthermore, all formulas described herein are intended as examples only and other or different formulas may be used. Additionally, some of the described method embodiments or elements thereof may occur or be performed at the same point in time.

[0109] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents may occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

[0110] Various embodiments have been presented. Each of these embodiments may of course include features from other embodiments presented, and embodiments not specifically described may include various features described herein.

Claims

CLAIMS1. A nanostructure, comprising: a ternary Zintl phase of a stoichiometric formula of X5Y2Z6 wherein the ternary Zintl phase is in a crystalline state; and wherein:X is selected from Eu, Ca, Sr, and Yb;Y is In or Ga; andZ is As or Sb.

2. The nanostructure of claim 1, wherein the nanostructure is a nanowire or a film.

3. The nanostructure of claim 1 or claim 2, wherein(i) X is selected from Eu, Ca, Sr, and Yb; Y is In; and Z is As; or(ii) X is selected from Eu, Sr, and Ba; Y is In; and Z is Sb.

4. The nanostructure of claim 1 or claim 2, wherein X is Ca; Y is Ga; and Z is As or Sb.

5. The nanostructure of claims 3 and 4, wherein said crystal of said ternary Zintl phase has a Pbam space group or a Pnma space group.

6. The nanostructure of any one of claims 1 to 5, wherein the X5Y2Z6 ternary Zintl phase has a crystal structure which includes a subgroup of a orthorhombic crystal.

7. The nanostructure of claim 6, wherein said Y and Z form an anionic lattice.

8. The nanostructure of any one of claims 1 to 7, wherein said nanostructure is a nanowire having a length of between 1 to 10 pm.

9. The nanowire of any one of claims 1 to 8, wherein said nanostructure is a nanowire having a diameter of between 10 to 200 nm.

10. The nanostructure of any one of claims 1 to 9, wherein said nanostructure is a nanowire comprising a core-shell structure.

11. The nanostructure of claim 10, wherein said core comprises of a crystalline material of Formula YZ, having a Zinc Blende crystal structure.

12. The nanostructure of any one of claims 1 to 11, wherein said nanostructure is a film having a thickness of between 10 to 200 nm.

13. The nanostructure of any one of claims 1 to 12, wherein said nanostructure is a film having a bilayer structure comprising:a substrate having a stochiometric formula of ZY and a Zinc Blende crystal structure; and a layer comprising the ternary Zintl phase of a stoichiometric formula of X5Y2Z6.

14. A nanowire, comprising: a core having a Zinc Blende crystal structure; and a shell comprising a ternary Zintl phase of a stoichiometric formula of X5Y2Z6, wherein: a. the core is InAs, and X is selected from Eu, Ca, Sr, or Yb, Y is In, and Z is As; b. the core is InSb, and X is selected from Eu, Sr, Ca, Yb, or Ba, Y is In, and Z is Sb; c. the core is GaAs, and X is Ca, Y is Ga and Z is As; or d. the core is GaSb and X is Eu, Ca, or Yb, Y is Ga and Z is Sb.

15. The nanowire of claim 14, having a length of between 1 to 10 pm.

16. The nanowire of any one of claims 14 and 15, having a diameter of between 10 to 200 nm.

17. The nanowire of any one of claims 14 to 16, wherein said shell comprises at least one crystallographic monolayer.

18. A film, comprising: a substrate having a stochiometric formula of ZY and a Zinc Blende crystal structure; and a layer covering at least a portion of the substrate, wherein the layer comprises a ternary Zintl phase of a stoichiometric formula of X5Y2Z6, and wherein: a. the substrate is InAs, and X is selected from Eu, Ca, Sr, or Yb, Y is In, and Z is As; b. the substrate is InSb, and X is selected from Eu, Sr, Ca, Yb, or Ba, Y is In, and Z is Sb; c. the substrate is GaAs, and X is Ca, Y is Ga and Z is As; or d. the substrate is GaSb and X is Eu, Ca, or Yb, Y is Ga and Z is Sb.

19. The film of claim 18, wherein the layer has a thickness of between 10 to 200 nm.

20. A microchip, comprising: a substrate having a stochiometric formula of ZY and a Zinc Blende crystal structure; and a pattern grown on the substrate, having a ternary Zintl phase of a stoichiometric formula of X5Y2Z6, wherein: a. the substrate is InAs, and X is selected from Eu, Ca, Sr, or Yb, Y is In, and Z is As; b. the substrate is InSb, and X is selected from Eu, Sr, Ca, Yb, or Ba, Y is In, and Z is Sb; c. the substrate is GaAs, and X is Ca, Y is Ga and Z is As; or d. the substrate is GaSb and X is Eu, Ca, or Yb, Y is Ga and Z is Sb.

21. A method of making a nanostructure comprising a ternary Zintl phase of a stoichiometric formula of X5Y2Z6 wherein the ternary Zintl phase is in a crystalline state, comprising: a. proving a target nanostructure having a stoichiometric formula YZ and a Zinc Blende crystal structure, wherein the target nanostructure comprises a target nanowire or a target substrate; and b. providing a flux of gas comprising of X and Y atoms at a flux ratio of between 0.5 / 100 to 1.5 / 100 and at a temperature of between 300 to 600 °C; thereby, making a nanostructure comprising a ternary Zintl phase of a stoichiometric formula of X5Y2Z6 wherein the ternary Zintl phase is in a crystalline state, wherein:A. X is selected from Eu, Ca, Sr, and Yb;B . Y is In or Ga; andC. Z is As or Sb.

22. The method of claim 21, wherein proving said target nanostructure comprises epitaxially growing said target nanostructure.

23. The method of claim 21 or claim 22, wherein a duration of the provision of the flux is between 60 to 240 minutes.

24. The method of any one of claims 21 to 23, further comprising: a. selecting a required thickness of the ternary Zintl compound to be grown; b. determining the duration of the provision of the flux based on the selected thickness and a size of the target nanostructure.

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