Preparation of metallenes

Abstract

A method for synthesizing metallenes is disclosed, which involves providing a MAX phase, intercalating a noble metal A' into the MAX phase to produce a MA'X phase, and etching off MX slabs from the MA'X phase to produce free-standing 2D single- atom-thick sheets of noble metals A'. The resulting metallenes have unique properties and potential applications in various fields, such as electronics, catalysis, photonics, sensing, and biomedicine.

Description

[0001] PREPARATION OF METALLENES

[0002] Field

[0003] The technology relates to the field of materials science, specifically the synthesis and production of free-standing 2D single-atom-thick materials of metallic elements (metallenes). These materials exhibit unique electronic properties and high surface- area-to-volume ratios, making them suitable for various applications in electronics, catalysis, photonics, sensing, and biomedicine.

[0004] Background

[0005] Noble metals, such as gold, silver, platinum, palladium, indium, and rhodium, possess superior properties for a variety of applications in electronics, catalysis, photonics, sensing, and biomedicine. These metals have been the subject of extensive research due to their unique plasmonic, electronic, and catalytic properties compared to their bulk counterparts. Anisotropic structures of noble metals, particularly free-standing 2D single-atom-thick structures known as metallenes (e.g., goldene for gold), have garnered significant interest as they offer not only extraordinary properties but also high surface-to-volume ratios. This makes the necessary volume of noble metals for applications and the costs much smaller than conventional noble metal materials.

[0006] Despite their beneficial properties and practical needs, noble metals are scarce on earth and expensive. Furthermore, few metallenes of noble metals have been experimentally realized, and no scalable synthetic methods have been developed for producing them. This lack of progress in producing metallenes hinders their potential use in various applications.

[0007] Another key challenge in producing metallenes is their structural stability. Due to the nature of 3D metallic bonding, noble metals are thermodynamically unstable in 2D structures. Identifying novel synthetic methods would be essential; especially, surfactants, which stabilize the 2D structures, would play a crucial role. To resolve the stability issue, interdisciplinary factors must be considered, such as physical properties of atomic bonding and chemical inertness of noble metal elements. Numerous types of vapor deposition have demonstrated epitaxial growth of metal films on lattice-matched substrates. During deposition, however, noble metals thus far unavoidably form three-dimensional or multilayer islands due to a strong thermodynamic tendency for coalescence. This results in, at best, nm-thick continuous noble metal layers. For the case of Au, unique synthetic routes of atomically-thin sheets have been developed, such as the synthesis of Au sheets with 1 -2 atomic-thick layers diffused into a layered double hydroxides template, free-standing single-atom- thick Au framed in bulk Au-Ag alloy by electron beam irradiation, and single-atom-thick gold quantum dots (QDs) stabilized on hexagonal boron nitride surfaces, among others.

[0008] However, these gold sheets are produced with physical confinements under impractical extreme conditions. Thus, truly free-standing single-atom-thick 2D metallene structures at a large scale remain unrealized for Au. Similarly, synthetic processes of free-standing metallenes of other noble metals with practical and scalable methods have not been developed. The lack of effective synthetic or other methods to produce stable metallenes is a major technical challenge that needs to be addressed.

[0009] Summary

[0010] According to a first aspect of the disclosure, a method for synthesizing metallenes is provided, which includes providing a MAX phase material, intercalating a noble metal A into the MAX phase to produce a MAX phase, and etching off MX slabs from the MAX phase to produce free-standing 2D single-atom-thick sheets of noble metals A. This method allows for the production of metallenes with unique properties and potential applications in various fields, such as electronics, catalysis, photonics, sensing, and biomedicine.

[0011] Optionally in some examples, the MAX phase is provided in the form of a film, a particle, or a bulk. This flexibility in the form of the MAX phase allows for the synthesis of metallenes with different sizes and shapes, catering to specific application requirements.

[0012] Optionally in some examples, intercalated A layer of noble metals may be two-, three- , four-, or five-atoms-thick. This variation enables the production of multilayer metallenes with various thicknesses, each with unique properties and potential applications.

[0013] Optionally in some examples, the film has a thickness of up to 100 nm or greater than 100 nm. This variation in film thickness enables the production of metallenes with different volume, area, and layer thickness, which can affect their properties and potential applications.

[0014] Optionally in some examples, the MAX phase comprises Mn+1Xn slabs, wherein M is a transition metal, X is selected from the group consisting of carbon, nitrogen, and boron, and n is an integer from 1 to 5. This variety in the composition of the MAX phase allows for the synthesis of metallenes with different properties and characteristics.

[0015] Optionally in some examples, the method further comprises removing remaining noble metals on the MA'X phase before etching off the MX slabs. This step ensures the purity of the resulting metallenes, which can improve their performance in various applications.

[0016] Optionally in some examples, the removal of remaining noble metals is performed using chemical-mechanical polishing. This technique provides a precise and efficient way to remove unwanted noble metals from the MA'X phase.

[0017] Optionally in some examples, the noble metal A is selected from the group consisting of gold, platinum, iridium, rhodium, palladium, and silver. This range of noble metals allows for the synthesis of various types of metallenes, each with unique properties and potential applications.

[0018] Optionally in some examples, the etching is performed using an etching mixture comprising Murakami's reagent and a surfactant. This etching mixture ensures the effective removal of MX slabs from the MA'X phase, resulting in high-quality metallenes.

[0019] Optionally in some examples, the Murakami's reagent comprises potassium ferricyanide, potassium hydroxide, and water, with a preferred range of 2 to 5 mg of potassium ferricyanide and potassium hydroxide in 10 mL of water. This specific composition of Murakami's reagent ensures effective etching of the MAX phase.

[0020] Optionally in some examples, the chemical employed in the reagent is one of copper potassium cyanide, silver potassium cyanide, potassium tetracyanonickelate, potassium tetracyanoplatinate, potassium dicyanoaurate, potassium tetracyanopalladate, or potassium permanganate.

[0021] Optionally in some examples, the surfactant is one of cetyltrimethylammonium bromide (CTAB), cetrimonium chloride (CTAC), myristyltrimethylammonium bromide, (16- Mercaptohexadecyl)trimethylammonium bromide, or cysteine, with a concentration in the range of 1 to 10 mmol / L. The use of surfactants as stabilizers in the etching process helps prevent coalescence of the 2D noble metal structures of metallenes, ensuring their stability and quality.

[0022] Optionally in some examples, the etching is performed in darkness and has a duration of 2 to 60 days. Performing the etching in darkness ensures the stability of the 2D noble metal structures of metallenes and prevents undesirable reactions or processes that may occur in the presence of light.

[0023] Optionally in some examples, the metallenes have a composition comprising noble metals selected from the group consisting of gold, platinum, iridium, rhodium, palladium, and silver. This variety in the composition of metallenes allows for the synthesis of different types of metallenes, each with unique properties and potential applications.

[0024] Optionally in some examples, the metallenes are goldene, produced from TisAuC2 MAX phases and / or Ti4AuCs MAX phases. Goldene, as a single-atom-thick gold sheet, exhibits unique electronic properties and high surface-area-to-volume ratios, making it ideal for various applications, such as catalysis, sensing, and electronics.

[0025] According to a second aspect of the disclosure, a metallene synthesized by the method described above is provided, wherein the metallene is one of goldene, platinumene (or so called platinene), iridiumene (or so called iridene), rhodiumene (or so called rhodene), palladiumene (or so called palladene), and silverene. These metallenes, with their unique properties and characteristics, have potential applications in various fields, such as electronics, catalysis, photonics, sensing, and biomedicine.

[0026] Brief Description of the Drawings

[0027] Examples are described in more detail below with reference to the appended drawings. Figure 1 is a schematic illustration of the synthetic process of a) free-standing 2D single-atom-thick sheets of noble metals (metallenes) and b) free-standing 2D single- atom-thick Au sheets (goldene).

[0028] Figure 2 shows X-ray photoelectron spectroscopy spectra of Au 4f emissions for goldene and a bulk reference Au.

[0029] Detailed Description

[0030] The detailed description set forth below provides information and examples of the disclosed technology with sufficient detail to enable those skilled in the art to practice the disclosure.

[0031] Figure 1 shows a schematic illustration of the synthetic process of (a) free-standing 2D single-atom-thick sheets of noble metals (metallenes) and (b) free-standing 2D single- atom-thick Au sheets (goldene). For the case of goldene, in part 1 , the deposition of TisSiC2 films is depicted. In part 2, the intercalation of Au into TisSiC2 to produce TisAuC2 is shown. In part 3, the selective etching of TisC2 slabs to produce goldene is depicted. The figure demonstrates the overall process of synthesizing metallenes, starting with the deposition of a MAX phase film, followed by the intercalation of a noble metal, and finally the production of the desired metallene.

[0032] Figure 2 presents X-ray photoelectron spectroscopy (XPS) spectra of Au 4f emissions for goldene and a bulk reference Au. The binding energy of Au 4f emissions from goldene is higher than that of the bulk Au as a reference by 0.9 eV due to its 2D structure. This figure highlights the unique electronic properties of the synthesized goldene compared to bulk gold, demonstrating the successful preparation of single- atom-thick sheets of noble metals with distinct properties. 1. Providing MAX Phase

[0033] The method for producing metallenes begins with the provision of a MAX phase material. The MAX phase is a layered material with a unique structure that consists of Mn+iXn slabs, where M represents a transition metal, X is an element such as carbon (C), nitrogen (N), or boron (B), and n is an integer from 1 to 5. The MAX phase may be provided in various forms, including a film, a particle, or a bulk. The MAX phase may comprise layers of A elements, which are interleaved with the Mn+iXnslabs in the MAX phase films. The A layers can determine the specific noble metals that can be intercalated into the MAX phase materials.

[0034] 1. 1. Selection of MAX Phase Materials

[0035] In some examples, the selection of the MAX phase materials is a step in the synthesis of metallenes. The MAX phase materials may comprise a variety of transition metals (M), such as scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), hafnium (Hf), tantalum (Ta), and tungsten (W). The X layer in the MAX phase may comprise carbon (C), nitrogen (N), or boron (B). The A layers may comprise elements such as aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), gallium (Ga), germanium (Ge), arsenic (As), cadmium (Cd), indium (In), tin (Sn), and lead (Pb). The selection of the MAX phase materials can influence the type of noble metal that can be intercalated into the MAX phase, thereby affecting the type of metallene that can be synthesized.

[0036] 1.2 Preparation of MAX Phase Films

[0037] In some examples, the MAX phase is provided in the form of a film.

[0038] 1.2.1. Film Thickness Considerations

[0039] The thickness of the MAX phase films can be controlled during the deposition process to achieve the desired thickness. The thickness of the MAX phase films can influence the intercalation of the noble metal into the MAX phase and the resulting thickness, layer thickness, area, and volume of the metallene sheets. 1.2.2. Deposition Techniques

[0040] In some examples, the deposition of the MAX phase films may be achieved through various techniques. Physical vapor deposition (PVD) techniques, such as sputtering or evaporation, may be used to deposit the MAX phase films. Chemical vapor deposition (CVD) techniques may also be used, which involve the reaction of gaseous precursors to form the MAX phase films on a substrate. Atomic layer deposition (ALD) techniques may be used, which involve the sequential reaction of gaseous precursors to form the MAX phase films layer by layer. The choice of deposition technique can influence the quality and properties of the MAX phase films, and hence the resulting metallene sheets.

[0041] 1.3. MAX Phase Particle and Bulk Forms

[0042] In some examples, the MAX phase may be provided in the form of particles or bulk. The MAX phase particles may be synthesized through various techniques, such as ball milling, sol-gel synthesis, or other suitable techniques. The MAX phase bulk may be synthesized through techniques such as hot pressing, spark plasma sintering solid state reaction, or other suitable techniques. The form of the MAX phase can influence the intercalation of the noble metal into the MAX phase and the resulting form of the metallene sheets.

[0043] 2. Intercalation of Noble Metals

[0044] The method for synthesizing metallenes involves the intercalation of a noble metal A into the provided MAX phase. This step is crucial as it leads to the formation of a MA'X phase, which is an intermediate structure in the synthesis of metallenes. The noble metal A may be selected from a group of noble metals or their alloys, including but not limited to gold (Au), platinum (Pt), iridium (Ir), rhodium (Rh), palladium (Pd), and silver (Ag). The intercalation process may involve several steps, including the cleaning and preparation of the MAX phase films, the application of the noble metal layer, and an annealing process.

[0045] 2. 1. Selection of Noble Metals

[0046] In some examples, the selection of the noble metal A for intercalation into the MAX phase is a step in the synthesis of metallenes. The noble metal A may be selected based on its chemical properties, its compatibility with the selected MAX phase, and the desired properties of the resulting metallene. The noble metal A' may comprise gold (Au), platinum (Pt), iridium (Ir), rhodium (Rh), palladium (Pd), silver (Ag), or their alloys comprising the multiple elements. The selection of the noble metal A can influence the properties of the resulting metallene, including its chemical stability, electronic properties, and potential applications.

[0047] 2.2. Intercalation Process

[0048] In some examples, the intercalation of the noble metal A into the MAX phase involves several steps. These steps may include the cleaning and preparation of the MAX phase films, the application of the noble metal layer, and an annealing process including interdiffusion. The intercalation process may be carefully controlled to ensure the successful formation of the MAX phase and the desired properties of the resulting metallene. In some examples, intercalated A layer of noble metals may be two-, three- , four-, or five-atoms-thick. This variation enables the production of multilayer metallenes with various thicknesses, each with unique properties and potential applications.

[0049] 2.2.1. Cleaning and Preparation of MAX Phase Films

[0050] In some examples, the MAX phase films are cleaned and prepared before the intercalation of the noble metal A. The cleaning process may involve the use of a cleaning solution, such as buffered hydrofluoric acid (HF), to remove surface residual oxides from the MAX phase films. The cleaning process may be followed by a rinsing step to remove any remaining cleaning solution. The preparation of the MAX phase films may involve the application of a noble metal layer to the cleaned MAX phase films. The noble metal layer may be applied at room temperature and may have a thickness that is twice or thicker than the thickness of the MAX phase films. Some noble metals may have thickness thinner than twice the thickness of the MAX phase films.

[0051] 2.2.2. Application of Noble Metal Layer

[0052] In some examples, the noble metal layer is applied to the cleaned MAX phase films. The noble metal layer may comprise the selected noble metal A, which may be gold (Au), platinum (Pt), indium (Ir), rhodium (Rh), palladium (Pd), silver (Ag), or their alloys comprising the multiple elements. The noble metal layer may be applied at room temperature, and may have a thickness that is twice or thicker than the thickness of the MAX phase films. Some noble metals may have thickness thinner than twice the thickness of the MAX phase films. The application of the noble metal layer may be achieved through various techniques, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), or other suitable techniques.

[0053] 2.2.3. Annealing Process

[0054] In some examples, the noble metal-covered MAX phase films are annealed to facilitate the intercalation of the noble metal A into the MAX phase. The annealing process may involve heating the noble metal-covered MAX phase films at a specific temperature for a specific duration. For instance, the annealing process may involve heating the Au- covered TisSiC2 phase films at a temperature of 670 °C for 12 hours. Suitable annealing temperature and duration may be applied for other combinations of noble metals and MAX phases. The annealing process may be performed in an inert gas atmosphere to avoid oxidation. During the annealing process, an exchange reaction may occur between the noble metal A and the A elements within the MAX phase films, leading to the formation of the MAX phase. The annealing process may be carefully controlled to ensure the successful intercalation of the noble metal A into the MAX phase and the formation of the MAX phase with the desired properties.

[0055] 3. Removal of Remaining Noble Metals

[0056] The preparation of metallenes involves the intercalation of a noble metal A into the MAX phase to form a MA'X phase. Following this intercalation process, there may be remaining noble metals on the surface of the MA'X phase. In some examples, these remaining noble metals are removed before proceeding to the next step of the preparation process, which involves the etching off of MX slabs from the MA'X phase to produce the desired metallenes. The removal of remaining noble metals can help to ensure the purity and quality of the resulting metallenes.

[0057] 3. 1. Chemical-Mechanical Polishing

[0058] In some examples, the removal of remaining noble metals from the MA'X phase is performed using a process known as chemical-mechanical polishing. This process involves the use of a polishing slurry, which may comprise various components that work together to remove the remaining noble metals from the surface of the MA'X phase. The chemical-mechanical polishing process can be carefully controlled to ensure the effective removal of remaining noble metals without causing damage to the MA'X phase or the resulting metallenes.

[0059] 3.1.1. Polishing Slurry Composition

[0060] In some examples, the polishing slurry used in the chemical-mechanical polishing process may comprise various components. These components may include fumed silica, iodine, potassium iodide, citric acid, trisodium citrate, and deionized water for the removal of remaining Au. The specific composition of the polishing slurry can be adjusted based on the specific requirements of the chemical-mechanical polishing process and the properties of the MA'X phase and the remaining noble metals. For instance, the polishing slurry may comprise 0.1 -3.5 g of fumed silica, 0.15-1.5 g of iodine, 0.15-15 g of potassium iodide, 10-20 g of citric acid, 2.5-5 g of trisodium citrate, and 150-250 mL of deionized water for the removal of remaining Au.

[0061] 3.1.2. Polishing Process

[0062] In some examples, the chemical-mechanical polishing process involves the application of the polishing slurry to the surface of the MA'X phase. The polishing slurry may be applied using a suitable applicator, and the MA'X phase may be polished using a suitable polishing tool. The polishing process may be performed under controlled conditions to ensure the effective removal of remaining noble metals from the surface of the MA'X phase. Following the polishing process, the MA'X phase may be rinsed to remove any remaining polishing slurry and the removed noble metals. The polished MA'X phase may then be dried and prepared for the next step of the synthesis process, which involves the etching off of MX slabs to produce the desired metallenes.

[0063] 4. Etching Process

[0064] The method for preparing metallenes involves an etching process, which is a crucial step in the production of free-standing 2D single-atom-thick sheets of noble metals A. This process involves the application of an etching mixture onto the MA'X phase, which reacts with the MX slabs within the MA'X phase to remove them. The etching process may be carefully controlled to ensure the successful production of the desired metallenes. 4. 1. Etching Mixture Preparation

[0065] The etching mixture may comprise various components, including Murakami's reagent and a surfactant. The etching mixture may also comprise a derivative chemical and a surfactant. The derivative chemical may be selected from the group consisting of: copper potassium cyanide, silver potassium cyanide, potassium tetracyanonickelate, potassium tetracyanoplatinate, potassium dicyanoaurate, potassium tetracyanopalladate, or potassium permanganate.

[0066] 4.1.1. Murakami's Reagent

[0067] In some examples, the Murakami's reagent is a key component of the etching mixture. The Murakami's reagent may comprise 1 part potassium ferricyanide and 1 part potassium hydroxide in water. The Murakami's reagent may comprise 2 to 5 mg of potassium ferricyanide and potassium hydroxide in 10 mL of water. The Murakami's reagent can effectively react with the MX slabs within the MA'X phase to remove them, thereby facilitating the production of the desired metallenes.

[0068] In some examples, the etching mixture comprising potassium ferricyanide may be replaced by derivative chemicals. The derivative chemical may be one of copper potassium cyanide, silver potassium cyanide, potassium tetracyanonickelate, potassium tetracyanoplatinate, potassium dicyanoaurate, potassium tetracyanopalladate, or potassium permanganate.

[0069] 4.1.2. Surfactants

[0070] In some examples, the etching mixture may comprise a surfactant. The surfactant may be one of cetyltrimethylammonium bromide (CTAB), cetrimonium chloride (CTAC), myristyltrimethylammonium bromide, (16-Mercaptohexadecyl)trimethylammonium bromide, or cysteine. The surfactant may have a concentration in the range of 1 to 10 mmol / L. The concentration may be lower than 1 mmol / L for some combinations of surfactants and noble metals. The surfactant can act as a stabilizer in the etching process, preventing the coalescence of the 2D noble metal structures of the metallenes. This can help to ensure the successful production of free-standing 2D single-atom-thick sheets of noble metals A. 4.2. Etching Procedure

[0071] In some examples, the etching procedure involves several steps. These steps may include the application of the etching mixture onto the MA'X phase, allowing the etching mixture to react with the MX slabs within the MA'X phase, monitoring the etching process to ensure the desired etching duration is achieved, removing the etching mixture after the desired duration, rinsing the metallene sheets with water or a suitable solvent to remove any remaining etchant, and drying the resulting metallene sheets.

[0072] 4.2.1. Application of Etching Mixture

[0073] In some examples, the etching procedure begins with the application of the etching mixture onto the MA'X phase. The etching mixture may be applied using a suitable applicator, and the MA'X phase may be exposed to the etching mixture for a specific duration. The application of the etching mixture can be carefully controlled to ensure the effective removal of the MX slabs from the MA'X phase.

[0074] 4.2.2. Etching Duration and Conditions

[0075] In some examples, the etching process may be performed under specific conditions and for a specific duration. The etching process may be performed in darkness, which can help to ensure the stability of the 2D noble metal structures of the metallenes and prevent undesirable reactions or processes that may occur in the presence of light. The etching process may have a duration of 1 to 60 days, which can be adjusted based on the specific requirements of the etching process and the properties of the MA'X phase and the MX slabs.

[0076] 4.2.3. Removal and Rinsing of Etching Mixture

[0077] In some examples, after the desired etching duration is achieved, the etching mixture is removed from the MA'X phase. The MA'X phase may then be rinsed with water or a suitable solvent to remove any remaining etchant. The rinsing process can help to ensure the purity and quality of the resulting metallene sheets. After the rinsing process, the resulting metallene sheets may be dried to obtain free-standing 2D single- atom-thick sheets of noble metals A. 5. Metallene Properties and Characterization

[0078] The method for synthesizing metallenes results in the production of free-standing 2D single-atom-thick sheets of noble metals A', also known as metallenes. These metallenes exhibit unique properties that distinguish them from their bulk metal counterparts. The properties of the metallenes can be characterized using various techniques to confirm their structure, composition, and other attributes.

[0079] 5. 1. Structural and Chemical Stability

[0080] In some examples, the metallenes synthesized using the disclosed method exhibit high structural and chemical stability. This stability is a crucial property that enables the metallenes to maintain their unique structure and composition under various conditions. The structural stability of the metallenes refers to their ability to retain their 2D single-atom-thick sheet structure without undergoing deformation or disintegration. The chemical stability of the metallenes refers to their resistance to chemical reactions that could alter their composition or structure. The structural and chemical stability of the metallenes can be confirmed through various characterization techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning force microscopy (SFM), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS).

[0081] 5.2. Electronic Properties

[0082] In some examples, the metallenes exhibit unique electronic properties that are distinct from those of their bulk metal counterparts. These unique electronic properties are a result of the 2D single-atom-thick sheet structure of the metallenes, which can influence the behavior of electrons within the material. The electronic properties of the metallenes can be characterized using various techniques, such as X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and electron energy loss spectroscopy (EELS). For instance, the binding energy of Au 4f emissions from goldene, a type of metallene composed of gold, is higher than that of the bulk Au as a reference by 0.9 eV due to its 2D structure.

[0083] 5.3. Surface-Area-to-Volume Ratios

[0084] In some examples, the metallenes exhibit high surface-area-to-volume ratios due to their 2D single-atom-thick sheet structure. This property is advantageous as it can enhance the performance of the metallenes in various applications. For instance, higher surface-area-to-volume ratios can enhance catalytic activity, making the metallenes ideal for catalysis applications. More surface area can also enhance sensitivity in sensing applications, allowing for detection of smaller concentrations of analytes. Improved surface-area-to-volume ratios can lead to higher efficiency in electronic devices, enabling faster and more precise electronic processes. The surface-area-to-volume ratios of the metallenes can be determined using various characterization techniques, such as Brunauer-Emmett-Teller (BET) analysis and atomic force microscopy (AFM).

[0085] 5.4. Scalability and Size Considerations

[0086] In some examples, the method for synthesizing metallenes is scalable and can be completed with an industrial standard size of 12 inches. This scalability is advantageous as it allows for the production of large quantities of metallenes, making the method suitable for industrial applications. The size of the metallenes can be controlled during the synthesis process to achieve the desired dimensions. The size of the metallenes can be characterized using various techniques, such as scanning electron microscopy (SEM) and atomic force microscopy (AFM). The scalability and size considerations of the method can influence the potential applications of the metallenes in various fields, such as electronics, catalysis, photonics, sensing, and biomedicine.

[0087] 6. Applications of Metallenes

[0088] The method for synthesizing metallenes, as described in the present disclosure, results in the production of free-standing 2D single-atom-thick sheets of noble metals A, also known as metallenes. These metallenes exhibit unique properties that make them suitable for various applications in different fields. The applications of metallenes may include electronics, catalysis, photonics, sensing, and biomedicine. The specific application of the metallenes may be determined based on their unique properties, such as their high surface-area-to-volume ratios, their unique electronic properties, and their high structural and chemical stability. 6. 1. Electronics

[0089] In some examples, the metallenes may be used in various electronic applications. The unique electronic properties of the metallenes, such as their high conductivity and their unique electronic band structure, make them ideal for use in electronic devices. The metallenes may be used in the fabrication of electronic components, such as transistors, diodes, and capacitors. The metallenes may also be used in the production of electronic circuits, where they can serve as conductive paths for the flow of electric current. The high surface-area-to-volume ratios of the metallenes can lead to higher efficiency in electronic devices, enabling faster and more precise electronic processes. The scalability of the method for synthesizing metallenes, which can be completed with an industrial standard size of 12 inches, makes it suitable for the mass production of electronic components and circuits.

[0090] 6.2. Catalysis

[0091] In some examples, the metallenes may be used in catalysis applications. The high surface-area-to-volume ratios of the metallenes can enhance their catalytic activity, making them ideal for use in various catalytic processes. The metallenes may serve as catalysts in chemical reactions, where they can increase the rate of the reactions without being consumed in the process. The metallenes may be used in the catalysis of various types of reactions, including oxidation reactions, reduction reactions, and other types of chemical transformations. The unique electronic properties of the metallenes, such as their ability to donate or accept electrons, can influence their catalytic activity and selectivity. The unique plasmonic properties of the metallenes can also influence their catalytic activity and selectivity.

[0092] 6.3. Photonics

[0093] In some examples, the metallenes may be used in photonics applications. The unique optical properties of the metallenes, such as their ability to interact with light at the nanoscale, make them ideal for use in photonic devices. The metallenes may be used in the fabrication of photonic components, such as waveguides, photodetectors, and light-emitting diodes (LEDs). The metallenes may also be used in the production of photonic circuits, where they can serve as pathways for the flow of light. The high surface-area-to-volume ratios of the metallenes can enhance their interaction with light, leading to improved performance in photonic devices. The unique electronic and plasmonic properties of the metallenes can also influence their optical and photonic properties.

[0094] 6.4. Sensing

[0095] In some examples, the metallenes may be used in sensing applications. The high surface-area-to-volume ratios of the metallenes can enhance their sensitivity, allowing for the detection of smaller concentrations of analytes. The metallenes may be used in the fabrication of sensors, where they can serve as sensing elements that respond to changes in their environment. The metallenes may be used in various types of sensors, including chemical sensors, biological sensors, and physical sensors. The unique electronic and plasmonic properties of the metallenes, such as their ability to change their electrical resistance in response to changes in their environment, can influence their sensing performance.

[0096] 6.5. Biomedicine

[0097] In some examples, the metallenes may be used in biomedical applications. The biocompatibility of the metallenes, combined with their unique physical and chemical properties, make them ideal for use in various biomedical applications. The metallenes may be used in the fabrication of biomedical devices, such as implants, prosthetics, and drug delivery systems. The metallenes may also be used in biomedical imaging, where they can serve as contrast agents that enhance the visibility of biological structures in imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT). The metallenes may be also used to treat diseases, such as cancers, where they can be activated due to their unique plasmonic properties. The high surface-area-to-volume ratios of the metallenes can enhance their interaction with biological systems, leading to improved performance in biomedical applications.

[0098] 6.6. Decorative

[0099] In some examples, the metallenes may be used to colour liquids by suspension or surface by coating with their unique photonic and plasmonic properties.

[0100] 7. Alternative Metallenes and MAX Phases

[0101] The disclosed method for synthesizing metallenes is not limited to the production of specific types of metallenes or the use of specific types of MAX phases. In some examples, the method may be adapted to synthesize alternative types of metallenes and to use alternative types of MAX phases. This adaptability of the method can expand its applicability and versatility, allowing for the production of a wide range of metallenes with diverse properties and potential applications.

[0102] 7. 1. Other Noble Metals

[0103] In some examples, the noble metal A' that is intercalated into the MAX phase to produce the MAX phase may comprise other noble metals and their alloys beyond those specifically mentioned in the previous sections. These other noble metals may include, but are not limited to, ruthenium (Ru), osmium (Os), and rhenium (Re). The selection of the noble metal A can be based on various factors, including the desired properties of the resulting metallene, the compatibility of the noble metal with the selected MAX phase, and the specific requirements of the intended application of the metallene. The use of other noble metals can expand the range of metallenes that can be synthesized using the disclosed method, thereby enhancing its versatility and applicability.

[0104] 7.2. Mixed Superstructure MAX Phases

[0105] In some examples, the MAX phase that is provided for the synthesis of metallenes may comprise mixed superstructure MAX phases. These mixed superstructure MAX phases may comprise Mn+iXn slabs, where M represents a transition metal, X is an element such as carbon (C), nitrogen (N), or boron (B), and n is an integer from 1 to 5. The mixed superstructure MAX phases may also comprise layers of A elements, which are interleaved with the Mn+iXn slabs in the MAX phase films. The A layers can determine the specific noble metal that can be intercalated into the MAX phase films. The use of mixed superstructure MAX phases can influence the properties of the resulting metallene, including its structure, composition, and electronic properties. The use of mixed superstructure MAX phases can also expand the range of MAX phases that can be used in the disclosed method, thereby enhancing its versatility and applicability.

[0106] Example 1 : A method for synthesizing metallenes, comprising providing a MAX phase, intercalating a noble metal A into the MAX phase to produce a MAX phase, and etching off MX slabs from the MA'X phase to produce free-standing 2D single-atom- thick sheets of noble metals A'.

[0107] Example 2: The method of example 1 , wherein the MAX phase is provided in a form of a film, a particle, or a bulk.

[0108] Example 3: The method of example 2, wherein the film has a thickness of up to 100 nm.

[0109] Example 4: The method of example 2, wherein the film has a thickness of greater than 100 nm.

[0110] Example 5: The method of any preceding example, wherein the MAX phase comprises Mn+iXn slabs, wherein M is a transition metal, X is selected from the group consisting of carbon, nitrogen, and boron, and n is an integer from 1 to 5.

[0111] Example 6: The method of any preceding example, further comprising removing remaining noble metals on the MA'X phase before etching off the MX slabs.

[0112] Example 7: The method of example 6, wherein the removal of remaining noble metals is performed using chemical-mechanical polishing.

[0113] Example 8: The method of any preceding example, wherein the noble metal A is selected from the group consisting of gold, platinum, iridium, rhodium, palladium, and silver.

[0114] Example 9: The method of any preceding example, wherein the etching is performed using an etching mixture comprising Murakami's reagent and a surfactant.

[0115] Example 10: The method of example 9, wherein the Murakami's reagent comprises potassium ferricyanide, potassium hydroxide, and water.

[0116] Example 11 : The method of example 10, wherein the Murakami's reagent comprises 2 to 5 mg of potassium ferricyanide and potassium hydroxide in 10 mL of water. Example 12: The method of example 10, wherein the alternative chemical to potassium ferricyanide in the etching mixture is one of copper potassium cyanide, silver potassium cyanide, potassium tetracyanonickelate, potassium tetracyanoplatinate, potassium dicyanoaurate, potassium tetracyanopalladate, or potassium permanganate.

[0117] Example 13: The method of example 10 or example 11 , wherein the surfactant is one of cetyltrimethylammonium bromide (CTAB), cetrimonium chloride TAC), myristyltrimethylammonium bromide, (16-Mercaptohexadecyl)trimethylammonium bromide, or cysteine.

[0118] Example 14: The method of example 13, wherein the surfactant has a concentration in the range of 1 to 10 mmol / L.

[0119] Example 15: The method of example 13, wherein the surfactant has a concentration lower than 1 mmol / L.

[0120] Example 16: The method of any of examples 9 to 15, wherein the etching is performed in darkness.

[0121] Example 17: The method of any of examples 9 to 16, wherein the etching has a duration of 1 to 60 days.

[0122] Example 18: The method of any preceding example, wherein the metallenes have a composition comprising noble metals selected from the group consisting of gold, platinum, iridium, rhodium, palladium, silver and their alloys comprising the multiple elements.

[0123] Example 19: The method of any preceding example, wherein the metallenes are goldene, produced from TisAuC2 and Ti4AuCs MAX phases.

[0124] Example 20: The method of any preceding example, wherein the multilayer metallenes are goldene with two-, three-, four-, or five-atoms-thick layers, produced from TisAu2C2 (or Ti4Au2Cs), TisAu3C2 (or Ti4Au3Cs), TisAu4C2 (or Ti4Au4Cs), and Ti3AusC2 (or Ti4Au5Cs) MAX phases.

[0125] Example 21 : A metallene synthesized by the method according to any preceding example, wherein the metallene is one of goldene, platinumene (or so called platinene), iridiumene (or so called iridene), rhodiumene (or so called rhodene), palladiumene (or so called palladene), silverene and their alloys comprising the multiple elements.

[0126] The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms "comprises," "comprising," "includes," and / or "including" when used herein specify the presence of stated features, integers, actions, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, actions, steps, operations, elements, components, and / or groups thereof.

[0127] It will be understood that, although the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the present disclosure.

[0128] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe a relationship of one element to another element as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

[0129] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0130] It is to be understood that the present disclosure is not limited to the aspects described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the present disclosure and appended claims. In the drawings and specification, there have been disclosed aspects for purposes of illustration only and not for purposes of limitation, the scope of the disclosure being set forth in the following claims.

Claims

Claims1. A method for synthesizing metallenes, comprising: providing a MAX phase; intercalating a noble metal A into the MAX phase to produce a MAX phase; and etching off MX slabs from the MAX phase to produce free-standing 2D single- atom-thick sheets of noble metals A.

2. The method according to claim 1 , wherein the MAX phase is provided in a form of a film, a particle, or a bulk.

3. The method according to any preceding claim, wherein the MAX phase comprises Mn+iXn slabs, wherein M is a transition metal, X is selected from the group consisting of carbon, nitrogen, and boron, and n is an integer from 1 to 5.

4. The method according to any preceding claim, further comprising removing remaining noble metals on the MAX phase before etching off the MX slabs.

5. The method according to claim 4, wherein the removal of remaining noble metals is performed using chemical-mechanical polishing.

6. The method according to any preceding claim, wherein the etching to exfoliate the metallenes is performed using an etching mixture comprising Murakami's reagent and a surfactant.

7. The method according to claim 6, wherein the Murakami's reagent comprises 2 to 5 mg of potassium ferricyanide and potassium hydroxide in 10 mL of water.

8. The method according to claim 6 or claim 7, wherein the surfactant is one of cetyltrimethylammonium bromide (CTAB), cetrimonium chloride (CTAC), myristyltrimethylammonium bromide, (16-Mercaptohexadecyl)trimethylammonium bromide, or cysteine.

9. The method according to claim 8, wherein the surfactant has a concentration in the range of 1 to 10 mmol / L.

10. The method according to any one of claims 1 to 5, wherein the etching to exfoliate the metallenes is performed using an etching mixture comprising a derivative chemical selected from the group consisting of: copper potassium cyanide, silver potassium cyanide, potassium tetracyanonickelate, potassium tetracyanoplatinate, potassium dicyanoaurate, potassium tetracyanopalladate, or potassium permanganate.11 . The method according to any preceding claim, wherein the etching is performed in darkness.

12. The method according to any preceding claim, wherein the etching has a duration of 1 to 60 days.

13. The method according to any preceding claim, wherein the multilayer metallenes have two-, three-, four-, or five-atom s-thick layers, produced from MA’X phases with two-, three-, four-, or five-atom s-thick A’ layers of noble metals.

14. The method according to any preceding claim, wherein the metallenes are goldene, produced from TisAuC2 MAX phases and / or Ti4AuCs MAX phases.

15. A metallene synthesized by the method according to any preceding claim, wherein the metallene is one of goldene, platinumene (or so called platinene), iridiumene (or so called iridene), rhodiumene (or so called rhodene), palladiumene (or so called palladene), silverene, and their alloys comprising the multiple elements.

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