Method of producing nanomaterial suspension, method of nanomaterial deposition and nanomaterial device

Abstract

Disclosed herein is a method of nanomaterial deposition. The method comprises: providing a nanomaterial suspension, performing a surface treatment on a target surface of a substrate to form a charged surface on the substrate, immersing the charged surface in the nanomaterial suspension to electrostatically form a nanomaterial layer on the charged surface of the substrate. The nanomaterial suspension may be produced by: disposing a nanomaterial bulk crystal on a first electrode of an electrochemical cell; providing a voltage across the first electrode and the second electrode, to form an intercalated crystal from the nanomaterial bulk crystal; and exfoliating / sonicating the intercalated crystal in a suspension liquid to form the nanomaterial suspension. The nanomaterial suspension comprises nanomaterial exfoliations with a first electrical charge and the charged surface of the substrate has a second electrical charge, wherein the second electrical charge is an opposing charge to the first electrical charge.

Description

METHOD OF PRODUCING NANOMATERIAL SUSPENSION, METHOD OF NANOMATERIAL DEPOSITION AND NANOMATERIAL DEVICECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to the Singapore application no. 10202302385T filed August 24, 2023, the contents of which are hereby incorporated by reference in their entirety for all purposes.TECHNICAL FIELD

[0002] This application relates to material deposition, and more particularly to a method of nanomaterial deposition, a method of producing a nanomaterial suspension, and a nanomaterial device.BACKGROUND

[0003] Two-dimensional materials (2DMs) are gaining significant attention due to the inherent intriguing physical and chemical properties, and wide applications in electronics and optoelectronics. A key challenge for integrating 2DMs with current foundry techniques is developing a scalable, cost-effective production method, such as a production method compatible with Complementary Metal-Oxide-Semiconductor (CMOS) processes.

[0004] Conventional production methods, such as chemical vapor deposition (CVD), molecular beam epitaxy (MBE), magnetron sputtering, and atomic layer deposition (ALD), often require costly equipment, complex controls as well as post-growth transfer. Such limitations often increase the complexity of the device fabrication process, adversely impacting the reliability of the two-dimensional (2D) materials-based electronics and hindering large- scale fabrication.SUMMARY

[0005] According to an aspect, disclosed herein a method of producing a nanomaterial suspension, the method may comprise: disposing a nanomaterial bulk crystal on a first electrode of an electrochemical cell, wherein the electrochemical cell comprises the first electrode and a second electrode immersed in an electrolyte, wherein the second electrode comprises a conductive material, wherein the electrolyte comprises an ammonium compound, a polymer and a first solvent; providing a voltage across the first electrode and the second electrode, to form an intercalated crystal from the nanomaterial bulk crystal; and exfoliating the intercalated crystal in a suspension liquid to form the nanomaterial suspension, wherein the nanomaterial suspension comprises nanomaterial exfoliations with a first electrical charge in the suspension liquid, the first electrical charge being one of: a positive charge and a negative charge.

[0006] The method may further comprise: selectably applying one of a positive bias and a negative bias as the voltage across the first electrode and second electrode to form the intercalated crystal. The method may further comprise: selectably configuring the first electrode as one of a cathode and an anode; and the second electrode as another of the cathode and the anode, wherein responsive to applying the positive bias as the voltage across the first electrode and second electrode, the first electrical charge of the nanomaterial exfoliations may be a positive charge, wherein responsive to applying the negative bias as the voltage across the first electrode and second electrode, the first electrical charge of the nanomaterial exfoliations may be a negative charge.

[0007] The nanomaterial bulk crystal may comprise at least one bulk crystal selected from a group consisting of: graphite, graphene, molybdenum disulfide (M0S2), tungsten disulfide (WS2), tungsten diselenide (WSe2), black phosphorus (BP), and indium selenide (P Ses). The first solvent may be selected from a group consisting of: acetonitrile and dimethylformamide (DMF). The electrolyte may further comprise: a quaternary ammonium bromide, apolyvinylpyrrolidone (PVP) and a propylene carbonate, wherein the quaternary ammonium bromide may have a concentration range of 0.1 mg / mL to 10 mg / mL, wherein the polyvinylpyrrolidone (PVP) may have a concentration range of 0.1 g / L to 10 g / L, and wherein a volumetric ratio between the electrolyte liquid to the propylene carbonate may be in a range of 4: 1 to 1: 1. The suspension liquid may be a second solvent selected from a group consisting of: de-ionized water, isopropyl alcohol, ethanol, dimethylformamide (DMF) and N-methyl-2- pyrrolidone (NMP). The electrochemical cell may be a three-electrode electrochemical cell, further comprising a reference electrode. In some embodiments, the conductive material may be one of: platinum, stainless steel, nickel, titanium and carbon.

[0008] According to another aspect, a method of nanomaterial deposition may comprise: providing the nanomaterial suspension, the nanomaterial suspension comprising nanomaterial exfoliations with the first electrical charge; performing a surface treatment on a target surface of a substrate to form a charged surface on the substrate, wherein the charged surface may have a second electrical charge, wherein the second electrical charge may be an opposing charge to the first electrical charge; immersing the charged surface in the nanomaterial suspension to electrostatically form a nanomaterial layer on the charged surface of the substrate, wherein the nanomaterial suspension may be in an operating temperature range, the operating temperature range including a room temperature, wherein the nanomaterial layer may comprises nanomaterial exfoliations dispersed on the target surface.

[0009] The surface treatment may comprise: cleaning the target surface of the substrate using sonication; performing a plasma treatment on the target surface to form a plasma-treated surface; and immersing the plasma-treated surface of the substrate in a surface treatment solution to form the charged surface, wherein the surface treatment solution comprises a silane compound. In some embodiments, the charged surface may be a positively charged surface, and the silane compound may comprise a (3-aminopropyl)triethoxysilane (APTES) solution. Theplasma treatment comprises an oxygen plasma treatment. The (3-aminopropyl)triethoxysilane (APTES) solution may have a concentration in a range of 1 wt% to 5 wt% in ethanol. In other embodiments, the charged surface may be a negatively charged surface, and the silane compound may comprise at least one of: 3-Mercaptopropyltrimethoxysilane (MPTMS) and carboxyethylsilanetriol (CEST). A thickness of the nanomaterial layer formed may be responsive to a concentration of the nanomaterial exfoliations in the nanomaterial suspension. The operating temperature range may comprise a minimum temperature corresponding to a freezing point of the suspension liquid. The nanomaterial layer may comprise a substantially uniform thickness across the target surface.

[0010] The method may further comprise: performing the surface treatment on a second target surface of the substrate to form a second charged surface on the second target surface, the second target surface corresponding to the nanomaterial layer, wherein the second charged surface has the second electrical charge; immersing the second charged surface in the nanomatcrial suspension to electrostatically form a second nanomatcrial layer on the second charged surface of the substrate, wherein the nanomaterial layer and the second nanomaterial layer may form a 2D heterostructure.

[0011] According to another aspect, disclosed herein a nanomaterial device may comprise: a substrate defining a charged surface; a nanomaterial layer formed on the charged surface of the substrate, the nanomaterial layer formed from nanomaterial exfoliates, wherein the nanomaterial layer may comprise a substantially uniform thickness across the charged surface. The nanomaterial device may further comprise a second nanomaterial layer disposed on the nanomaterial layer to form a 2D heterostructure.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Various embodiments of the present disclosure are described below with reference to the following drawings:

[0013] FIG. 1 is a schematic diagram of an electrochemical system for producing a nanomaterial suspension in accordance with some embodiments of the present disclosure.

[0014] FIG. 2 is a process flow diagram of a method of producing a nanomaterial suspension in accordance with some embodiments of the present disclosure.

[0015] FIG. 3 is a schematic diagram of an electrochemical system in accordance with an exemplary embodiment of the present disclosure.

[0016] FIG. 4 is a schematic diagram illustrating the mechanism of an intercalant-assisted electrochemical exfoliation method in accordance with some embodiments of the present disclosure.

[0017] Fig. 5A is a graph illustrating the size distribution of the M0S2 nanosheets exfoliated using the method in accordance with one embodiment of the present disclosure. The inset image is the corresponding M0S2 nanosheets dispersed in isopropyl alcohol.

[0018] Fig. 5B is a graph illustrating the size distribution of the WS2 nanosheets exfoliated using the method in accordance with one embodiment of the present disclosure. The inset image is the corresponding WS2 nanosheets dispersed in isopropyl alcohol.

[0019] Fig. 5C is a graph illustrating the size distribution of the WSe2 nanosheets exfoliated using the method in accordance with one embodiment of the present disclosure. The inset image is the corresponding WSe2 nanosheets dispersed in isopropyl alcohol.

[0020] Fig. 6 is a graph showing the UV-Vis spectra of the M0S2, WSC2, and WS2 dispersion prepared using the method in accordance with some embodiments of the present disclosure.[0021 J Fig. 7A-7C are atomic resolution high-angle annular dark field STEM images of M0S2, WSc2:and WS2 nanosheets exfoliated using the method in accordance with some embodiments of the present disclosure.

[0022] FIG. 8 is a flow chart illustrating a method of surface treatment for a substrate surface in accordance with some embodiments of the present disclosure.

[0023] FIGs. 9A to 9C are schematic diagrams illustrating the surface charges of the substrate after the surface treatment in accordance with various embodiments of the present disclosure.

[0024] FIG. 10 is a flow chart illustrating a method of nanomaterial deposition method according to various embodiments of the present disclosure.

[0025] FIGs. 1 1 A to 1 1C are schematic diagrams illustrating the surface charge of the substrate during the thin film deposition in accordance with various embodiments of the present disclosure.

[0026] FIG. 12A is an optical image of a blank sapphire substrate.

[0027] Fig. 12B is an optical image of WS2 thin film deposited on a sapphire substrate using the method in accordance with one embodiment of the present disclosure.

[0028] Fig. 12C is an optical image of M0S2 thin film deposited on a sapphire substrate using the method in accordance with one embodiment of the present disclosure.

[0029] Fig. 12D is an optical image of WSe? thin film deposited on a sapphire substrate using the method in accordance with one embodiment of the present disclosure.

[0030] Fig. 13A is a graph showing the Raman spectra of 8 spots randomly selected from WS2 film of FIG. 12B deposited on a wafer using the method in accordance with one embodiment of the present disclosure.[0031J Fig. 13B is a graph showing the Raman spectra of 8 spots randomly selected from M0S2 films of FIG. 12C deposited on a wafer using the method in accordance with one embodiment of the present disclosure.

[0032] Fig. 13C is a graph showing the Raman spectra of 8 spots randomly selected from WSe2 films of FIG. 12D deposited on a wafer using the method in accordance with one embodiment of the present di closure.

[0033] Fig. 14A is an image of M0S2 field effect transistor (FET) devices on a 4-inch wafer fabricated using the method in accordance with one embodiment of the present disclosure.

[0034] Fig. 14B is an optical image of the M0S2 FET devices fabricated using the method in accordance with one embodiment of the present disclosure in a selected region.

[0035] Fig. 14C is a zoom-in optical image of a single M0S2 FET device fabricated using the method in accordance with one embodiment of the present disclosure.

[0036] Fig. 14D is a graph illustrating the drain current vs. gate voltage in an electrical measurement on the M0S2 FET devices fabricated using the method in accordance with one embodiment of the present disclosure.

[0037] Fig. 14E is a graph illustrating the drain current vs. drain voltage in an electrical measurement on the M0S2 FET devices fabricated using the method in accordance with one embodiment of the present disclosure.

[0038] Fig. 14F is a graph illustrating the field-effect mobility vs. gate voltage in an electrical measurement on the M0S2 FET devices fabricated using the method in accordance with one embodiment of the present disclosure.

[0039] Fig. 15 are images of M0S2 film deposited on a Ixlcm2wafer, 4-inch wafer, 6-inch wafer, and 8-inch wafer using the method in accordance with some embodiments of the present disclosure.DETAILED DESCRIPTION

[0040] The following detailed description is made with reference to the accompanying drawings, showing details and embodiments of the present disclosure for the purposes of illustration. Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments, even if not explicitly described in these other embodiments. Additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0041] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0042] Tn the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance as generally understood in the relevant technical field, e.g., within 10% of the specified value.

[0043] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0044] The term “nanomaterial” may generally be defined by a material that has at least one dimension in the nanometer scale (1-100 nanometers).

[0045] According to various embodiments of the disclosure, a simple and scalable method and system for forming nanomaterial layer(s) or 2-dimensional material(s) (2DM) thin film(s) on a substrate at room temperature is presented. Departing from conventional methods relating to bottom-up growth of 2D layered materials, such as CVD or PVD, which require an elevated operational temperature, the proposed method and system enables high-throughput production of uniform or substantially uniform 2DM thin film(s) at room temperature. In avoidance of doubt, the 2DM thin film may include one 2-dimensional material (2DM) layer or multiple 2- dimensional materials (2DMs) layers. The 2DM / 2DMs may collectively be referred to asnanomaterials. In various embodiments, the 2DM thin film may be formed from a nanomaterial suspension or nanomaterial solution. Advantageously, the 2DM as produced from the proposed method and system may be in the form of thin films and formed as heterostructures. In addition, the proposed method and system may be used for the fabrication of 2DM thin films suitable for electronics applications, or “with electronic-grade quality”. In addition, the proposed method and system may allow the production or fabrication of 2DM thin films allowing scaling of production up to an industrial level of 8 inches to 12 inches wafers.

[0046] In some embodiments, the 2DM thin film may be deposited via a self- assembling of 2D materials nanosheets in a nanomaterial solution. The growth of the 2DMs thin film may be attributed to the electrostatic forces between the 2D material nanosheets and a substrate. The substrate may be pre-treated to enable a spontaneous deposition and coalescence of the nanosheets, thus forming a continuous 2D material thin film network. The nanomaterial layer formed from the proposed method and system may include various structures, such as a monolayer structure, a bilaycr structure, a multiple-layer structure, etc.

[0047] The present disclosure may include aspects of i) producing or forming of a nanomaterial suspension; ii) preparation or surface treatment of a substrate surface; and iii) deposition of a nanomaterial layer or 2DM thin film, as will be described in later sections.

[0048] In various embodiments, the present disclosure includes a method of producing a nanomaterial suspension. The nanomaterial suspension may include nanomaterial exfoliations in a liquid suspension, such as monolayer 2DMs or multilayer 2DMs in a liquid suspension. The nanomaterial exfoliations may also be known as nanomaterial dispersions or 2DM dispersions. In some examples, the nanomaterial suspension may comprise 2DM nanosheets. The method of forming a nanomaterial suspension may include exfoliating or sonicating monolayer or multilayer 2DM nanosheets from bulk 2DMs crystals or bulk crystals via an electrochemical-assisted exfoliation method. The method may also comprise the production orformulation of stable 2DMs dispersions or 2DMs suspension from the exfoliated / sonicated 2DMs nanosheets, using a solvent, such as one or more organic solvent(s) and / or one or more inorganic solvent(s).

[0049] In some embodiments, the present disclosure also includes a method of forming a nanomaterial layer or a 2DMs thin film on a surface-treated substrate. The 2DM thin film may include a continuous multilayer structure and / or a continuous monolayer structure. The method of forming 2DM thin film may comprise using the nanomaterial suspension as disclosed previously. The substrates suitable for the method of forming the 2DM thin film may be selected from: Si / SiCh wafer, glass, sapphire, silicon carbide, platinum, gold, copper, nickel, or polyimide.

[0050] According to various embodiments, the substrate may be an electrically inactive, polymer, or metal film. The substrate may comprise any of an insulator and a semiconductor. Prior to forming the nanomaterial layer via deposition of one or more 2DM thin films, the method may also include a surface treatment of the substrate. The substrate may undergo a sequential surface treatment process which may include a surface cleaning step, a physical treatment step, and a chemical treatment step.

[0051] In some embodiments, the 2DM thin film(s) or nanomaterial layer(s) as formed according to the proposed method may comprise graphite, graphene, boron nitride, molybdenum disulfide (M0S2), tungsten disulfide (WS2), tungsten diselenide (WSe?), black phosphorus (BP), indium selenide (In2Se3) or any combination of thereof.

[0052] The proposed methods as disclosed herein include the advantage of a low- temperature and transfer-free nature process, over the existing 2D material deposition methods, such as regarding CVD, and PVD methods. In addition, the proposed methods are environmentally friendly, cost-effective, and versatile, enabling a wide range of applications usable to deposit va ious 2D nanomaterials on various substrates. With industrial-levelscalability, the proposed method enables economies of scale and potential cost savings in the production of 2D nanomaterials layer by an order of magnitude.

[0053] According to an aspect of the present disclosure, FIG. 1 illustrates a schematic diagram illustrating an electrochemical system or an electrochemical cell 100 for producing a nanomaterial suspension in accordance with various embodiments. The electrochemical cell 100 may comprise an electrolyte 1 10. The electrochemical cell 100 may include a first electrode or a working electrode 120, and a second electrode or a counter electrode 130, both of which are immersed or disposed in the electrolyte 110. In some embodiments, the electrochemical cell 100 may further include a third electrode or a reference electrode 140 also immersed in the electrolyte 110. A power source 105 may be coupled in an electrical connection between the first / working electrode 120 and the second / counter electrode 130. The power source 105 may apply a voltage across the first / working electrode 120 and the second / counter electrode 130.

[0054] According to various embodiments, the electrochemical cell 100 may be configured to produce a nanomatcrial suspension. The nanomatcrial suspension may act as a material source for the deposition of nanomaterial layers or 2D material thin films.

[0055] According to various embodiments of producing a nanomaterial suspension, a nanomaterial bulk crystal 210 may be mounted to the first / working electrode 120. In an example, the nanomaterial bulk crystal 210 may be fixed or coupled to the first / working electrode 120 directly by an alligator clip. The nanomaterial bulk crystal 210 may have a layered structure 210 as schematically shown in FIG. 1. According to various embodiments, the second / counter electrode 130 may include a conductive material. In some examples, the conductive material may include: platinum, stainless steel, titanium, nickel, and carbon. In some examples, the conductive material may be in the form of a platinum wire or a platinum foil. In other examples, the conductive material may be in the form of a platinum rod, a stainless steel rod and a carbon rod. In other embodiments, the second / counter electrode 130 may beformed as a platinum wire or a platinum foil. The electrolyte 110 may be a mixture of or a combination of: an ammonium compound, a polymer and a solvent. According to various embodiments, the ammonium compound may include ionic species 220 provided in the electrolyte 110. The power source 105 may be controlled to apply a voltage or potential difference across the first / working electrode 120 and the second / counter electrode 130. This forms a voltage or a potential difference across the nanomaterial bulk crystal and the platinum wire / foil. Responsive to the voltage applied across the nanomaterial bulk crystal and the platinum wire / foil, the ionic species 220 in the electrolyte 110 is driven by the voltage to be inserted or intercalated into the layered structure 210 of the nanomaterial bulk crystal and form an intercalated crystal 230.

[0056] Tn some embodiments, the nanomaterial bulk crystal may comprise one or more bulk crystal(s) selected from: graphite, graphene, boron nitride, molybdenum disulfide (M0S2), tungsten disulfide (WS2), tungsten diselenide (WSe2), black phosphorus (BP), and indium selenide ilmScd.

[0057] In various embodiments, the electrochemical cell 100 may be selectably configured or controlled to form either negatively charged nanomaterials or positively charged nanomaterials.

[0058] In an exemplary embodiment as shown in FIG. 1, the nanomaterial bulk crystal (first electrode 120) is configured as a cathode and the platinum wire / foil (second electrode 130) is configured as an anode. The voltage applied to the first electrode 120 and the second electrode 130 is in a negative bias. Responsive to the voltage, the intercalated crystal 230 as formed comprises negatively charged nanomaterials or negatively charged 2DM nanosheets.

[0059] In an alternative exemplary embodiment, the nanomaterial bulk crystal (first electrode 120) is configured as an anode and the platinum wire / foil (second electrode 130) is configured as a cathode. Accordingly, the voltage applied to the first electrode 120 and thesecond electrode 130 is in a positive bias. Responsive to the voltage, the intercalated crystal 230 as formed comprises positively charged nanomaterials or positively charged 2DM nano sheets.

[0060] In various embodiments, the intercalated crystal 230 may be exfoliated in a suspension liquid to form a nanomaterial suspension. Based on the charge of the intercalated crystal as formed, the nanomaterial suspension may include nanomaterial exfoliations with positive / negative charge(s) in the suspension liquid.

[0061] In various embodiments, the applied bias during the intercalation may determine the surface charge of the exfoliated nanosheets. In an example, for producing a nanomaterial suspension comprising transition metal dichalcogenides (TMDC) exfoliations (e.g. M0S2, WSe2, WS2etc), a TMDC crystal may be mounted to the cathode of the electrochemical cell, where a negative bias may be applied. Hence, after the exfoliation process, the resultant nanomaterial exfoliations or TMDCs nanosheets in the nanomaterial suspension may be negatively charged.

[0062] In another example, for producing a nanomaterial suspension of graphene exfoliations, a graphite crystal may be mounted to the anode of the electrochemical cell, where a positive bias may be applied. Hence, after the exfoliation process, the resultant graphene nanosheets in the nanomaterial suspension may be positively charged.

[0063] According to various embodiments, FIG. 2 shows a process flow of a method 500 of producing a nanomaterial suspension. The method 500 comprises the following steps: disposing a nanomaterial bulk crystal on a first electrode (working electrode 120) of an electrochemical cell (510). The electrochemical cell may comprise the first electrode and a second electrode (counter electrode 130) immersed in an electrolyte. The second electrode may comprise platinum. The electrolyte may comprise an ammonium compound, a polymer and a solvent.

[0064] According to various embodiments, the ammonium compound in the electrolyte may be quaternary ammonium bromide, quaternary ammonium tetrafluoroborate, quaternary ammonium chloride or quaternary ammonium sulfate. The polymer in the electrolyte may be polyvinyl pyrrolidone (PVP) or sodium cholate. The solvent in the electrolyte may be a mixture of dimethylformamide (DMF) and propylene carbonate.

[0065] According to various embodiments, the method 500 may further include: providing a voltage across the first electrode and the second electrode (520), to form an intercalated crystal from the nanomaterial bulk crystal. As described in the above section, the voltage may drive ionic species in the electrolyte to be inserted or intercalated into the layered structure of the nanomaterial bulk crystal to form the intercalated crystal.

[0066] According to various embodiments, the method 500 may further include: exfoliating the intercalated crystal in a suspension liquid to form the nanomaterial suspension (540). In some examples, the exfoliation of the intercalated crystal may include using sonication methods or sonicating the intercalated crystal. The nanomatcrial suspension may include nanomatcrial exfoliations with a first electrical charge in the suspension liquid. Responsive to the charge of the intercalated crystal as described in the earlier section, the first electrical charge may be either a positive charge or a negative charge.

[0067] In some embodiments, the method of producing the nanomaterial suspension 500 may further comprise: selectably applying a positive bias or a negative bias as the voltage across the first electrode (working electrode 120) and the second electrode (counter electrode 130) to form the intercalated crystal (530). That is, a positive bias or a negative bias may be selectably applied to the nanomaterial bulk crystal according to a desirable charge of the intercalated crystal required. With positive bias applied to the nanomaterial bulk crystal, the nanomaterial suspension may include nanomaterial exfoliations with positive charge(s) in the suspension liquid. Alternatively, with a negative bias applied to the nanomaterial bulk crystal, thenanomaterial suspension may include nanomaterial exfoliations with negative charge(s) in the suspension liquid.

[0068] In some embodiments, the intercalation reaction may be conducted with an electrochemical cell in a two-electrode configuration. This allows an economical electrochemical cell solution for the production of nanomaterial suspension. In other embodiments, the intercalation reaction may be conducted with an electrochemical cell in a three-electrode configuration. The third electrode or reference electrode enables better control and monitoring of the applied voltage in the intercalation process. In some embodiments, the first / working electrode 120 may be configured as a cathode and the second / counter electrode 130 may be configured as an anode.

[0069] According to various embodiments, an electrolyte concentration of the electrolyte and the voltage applied across the electrodes may be varied to adjust a reaction rate of the intercalation process. The voltage applied and the duration of the voltage applied may be determined based on the desirable amount of the intercalated crystal formed.

[0070] In some embodiments, the electrolyte may include quaternary ammonium bromide (0.1 mg / mL to 10 mg / mL) in a PVP (0.1 g / L to 10 g / L) solution in a mixture of DMF and propylene carbonate, with the DMF: propylene carbonate volumetric ratio of 4: 1 to 1 : 1. In some embodiments, the electrolyte may contain ammonium compound (0.1 mg / mL to 10 mg / mL) and PVP (0.1~0.5wt / %) in acetonitrile. In some embodiments, the applied voltage may be in a range of 4.5 V to 8.5 V and the duration of the applied voltage may be in a range of 0.5 hour to 5 hours. In other embodiments, the applied voltage may be in a range of 5 V to 10 V and the duration of the applied voltage may be in a range of 1 hour to 4 hours.

[0071] FIG. 3 is a schematic diagram illustrating an electrochemical cell for producing a nanomaterial suspension according to an exemplary embodiment of the present disclosure. The ionic species 220 in the electrolyte is tetraheptylammonium bromide and the solvent moleculeis propylene carbonate. With negative bias applied to the nanomaterial bulk crystal, the tetraheptylammonium bromide (ionic species 220) is inserted into the layered structure of the nanomaterial bulk crystal 210.

[0072] Upon formation, the intercalated crystal may be collected, rinsed, and exfoliated via sonication to produce the nanomaterial suspension. In some embodiments, the intercalated crystal may be collected by vacuum filtration and repeatedly rinsed with absolute ethanol, for example thrice. Subsequently, the intercalated crystal may be exfoliated or sonicated in DMF solution, for example, for 30 minutes in DMF solution. In some embodiments, the intercalated crystal may instead be sonicated in isopropyl alcohol (IPA) or ethanol to produce the nanomaterial suspension.

[0073] FIG. 4 is a schematic diagram illustrating the mechanism of the intercalant-assisted electrochemical exfoliation method in accordance with an exemplary embodiment of the present disclosure. The nanomaterial bulk crystal may be a M0S2 crystal. The nanomaterial bulk crystal may include multiple layers of atoms arranged in a two-dimensional plane. There are strong covalent bonds present within each layer of atoms, or in other words, within the layer. There may also be weaker van der Waals forces between the layers of atoms, or in other words, between the layers. After the intercalation, the ionic species (the ammonium compound) in the electrolyte may intercalate into the layered structure of the bulk crystal, further weakening the van der Waals forces between the layers. Upon exfoliation or sonication, the intercalated crystal formed from the nanomaterial bulk crystal may be fragmented into nanomaterial exfoliations such as monolayer and / or few-layer nanosheets dispersed in the suspension liquid to form a nanomaterial suspension.

[0074] In some embodiments, after sonication, the obtained nanomaterial suspension may be further centrifuged to selectively collect the nanomaterial suspension with a certain size or diameter. In one embodiment, the obtained nanomaterial suspension may be further centrifugedwith a rate of 1000 revolutions per minute (rpm) for a duration of 3 minutes, and the supernatant is collected as the nanomaterial suspension for the thin film deposition. The nanomaterial suspension may be formed with de-ionized water, ethanol, IPA, DMF, N-Methyl-2-pyrrolidone (NMP), or other solvents as the suspension liquid according to specific applications. The obtained nanomaterial exfoliations or nanosheets may be negatively charged if the applied voltage during intercalation is selected to be negative, and the obtained nanosheets may be positively charged if the applied voltage during intercalation is selected to be positive.

[0075] In some embodiments, the concentration of the nanomaterial exfoliations or nanosheets in the nanomaterial suspension may be in a range of about 0.01 mg / mL to about 0.4mg / mL. In some embodiments, the concentration of the nanosheets in the nanomaterial suspension may be at least about 0.01 mg / mL. In some embodiments, the concentration of the nanosheets in the nanomaterial suspension may be at most about 0.4 mg / mL. In some embodiments, the concentration of the nanosheets in the nanomaterial suspension may be in a range of about 0.01 mg / mL to about 0.02 mg / mL, about 0.01 mg / mL to about 0.05 mg / mL, about 0.01 mg / mL to about 0.1 mg / mL, about 0.01 mg / mL to about 0.15 mg / mL, about 0.01 mg / mL to about 0.2 mg / mL, about 0.01 mg / mL to about 0.25 mg / mL, about 0.01 mg / mL to about 0.3 mg / mL, about 0.01 mg / mL to about 0.35 mg / mL, about 0.01 mg / mL to about 0.4 mg / mL, about 0.02 mg / mL to about 0.05 mg / mL, about 0.02 mg / mL to about 0.1 mg / mL, about 0.02 mg / mL to about 0.15 mg / mL, about 0.02 mg / mL to about 0.2 mg / mL, about 0.02 mg / mL to about 0.25 mg / mL, about 0.02 mg / mL to about 0.3 mg / mL, about 0.02 mg / mL to about 0.35 mg / mL, about 0.02 mg / mL to about 0.4 mg / mL, about 0.05 mg / mL to about 0.1 mg / mL, about 0.05 mg / mL to about 0.15 mg / mL, about 0.05 mg / mL to about 0.2 mg / mL, about 0.05 mg / mL to about 0.25 mg / mL, about 0.05 mg / mL to about 0.3 mg / mL. In some embodiments, the concentration of the nanosheets in the nanomaterial suspension is about 0.01 mg / mL, about0.02 mg / mL, about 0.05 mg / mL, about 0.1 mg / mL, about 0.15 mg / mL, about 0.2 mg / mL, about 0.25 mg / mL, about 0.3 mg / mL, about 0.35 mg / mL, or about 0.4 mg / mL.

[0076] In some embodiments, the productivity of nano sheets from the nanomaterial bulk crystal may be in a range of about 50% to about 100%. In some embodiments, the productivity of nanosheets from the nanomaterial bulk crystal may be at least about 50%. In some embodiments, the productivity of nanosheets from the nanomaterial bulk crystal may be about 100%. In some embodiments, the productivity of nanosheets from the nanomaterial bulk crystal may be in a range of about 50% to about 55%, about 50% to about 60%, about 50% to about 65%, about 50% to about 70%, about 50% to about 75%, about 50% to about 80%, about 50% to about 85%, about 50% to about 90%, about 50% to about 95%, about 50% to about 100%, about 55% to about 60%, about 55% to about 65%, about 55% to about 70%, about 55% to about 75%, about 55% to about 80%, about 55% to about 85%, about 55% to about 90%, about 55% to about 95%, about 55% to about 100%, about 60% to about 65%, about 60% to about 70%, about 60% to about 75%, about 60% to about 80%, about 60% to about 85%, about 60% to about 90%, about 60% to about 95%, about 60% to about 100%, about 65% to about 70%, about 65% to about 75%, about 65% to about 80%, about 65% to about 85%, about 65% to about 90%, about 65% to about 95%, about 65% to about 100%, about 70% to about 75%, about 70% to about 80%, about 70% to about 85%, about 70% to about 90%, about 70% to about 95%, about 70% to about 100%, about 75% to about 80%, about 75% to about 85%, about 75% to about 90%, about 75% to about 95%, about 75% to about 100%, about 80% to about 85%, about 80% to about 90%, about 80% to about 95%, about 80% to about 100%>, about 85% to about 90%, about 85% to about 95%, about 85% to about 100%, about 90% to about 95%, about 90% to about 100%, or about 95% to about 100%. In some embodiments, the productivity of nanosheets from the nanomaterial bulk crystal is about 50%, about 55%, about60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 95%, or about 100%.

[0077] In some embodiments, the nanomaterial suspension may comprise nanosheets with an average length in a range of about 50 nm to about 3,600 nm. In some embodiments, the nanomaterial suspension may comprise a plurality of nanosheets with a length of at least about 50 nm. In some embodiments, the nanomaterial suspension may comprise a plurality of nanosheets with an average length of at most about 3,600 nm. In some embodiments, the nanomaterial suspension may comprise a plurality of nanosheets with an average length in a range of about 50 nm to about 100 nm, about 50 nm to about 200 nm, about 50 nm to about 300 nm, about 50 nm to about 400 nm, about 50 nm to about 500 nm, about 50 nm to about 750 nm, about 50 nm to about 1 ,000 nm, about 50 nm to about 1 ,250 nm, about 50 nm to about 1,500 nm, about 50 nm to about 1,600 nm, about 100 nm to about 200 nm, about 100 nm to about 300 nm, about 100 nm to about 400 nm, about 100 nm to about 500 nm, about 100 nm to about 750 nm, about 100 nm to about 1,000 nm, about 100 nm to about 1,250 nm, about 100 nm to about 1,500 nm, about 100 nm to about 1,600 nm, about 200 nm to about 300 nm, about 200 nm to about 400 nm, about 200 nm to about 500 nm, about 200 nm to about 750 nm, about 200 nm to about 1,000 nm, about 200 nm to about 1,250 nm, about 200 nm to about 1,500 nm, about 200 nm to about 1,600 nm, about 300 nm to about 400 nm, about 300 nm to about 500 nm, about 300 nm to about 750 nm, about 300 nm to about 1,000 nm, about 300 nm to about 1,250 nm, about 300 nm to about 1,500 nm, about 300 nm to about 1,600 nm, about 400 nm to about 500 nm, about 400 nm to about 750 nm, about 400 nm to about 1 ,000 nm, about 400 nm to about 1,250 nm, about 400 nm to about 1,500 nm, about 400 nm to about 1,600 nm, about 500 nm to about 750 nm, about 500 nm to about 1,000 nm, about 500 nm to about 1,250 nm, about 500 nm to about 1,500 nm, about 500 nm to about 1,600 nm, about 750 nm to about 1,000 nm, about750 nm to about 1,250 nm, about 750 nm to about 1,500 nm, about 750 nm to about 1,600 nm.about 1,000 nrn to about 1,250 nm, about 1,000 nm to about 1,500 nrn, about 1,000 nm to about 1,600 nm, about 1,250 nm to about 1,500 nm, about 1,250 nm to about 1,600 nm, or about 1,500 nm to about 1,600 nm. In some embodiments, the nanomaterial suspension may comprise nanosheets with an average length of about 50 nm, about 100 nm, about 200 nm, about 300 nm, about 400 nm, about 500 nm, about 750 nm, about 1,000 nm, about 1,250 nm, about 1,500 nm, about 1 ,600 nm, about 1 ,800 nm, about 2,000 nm, about 2,200 nm, about 2,500 nm, about 3,000 nm or about 3,600 nm.

[0078] In some embodiments, the nanomaterial suspension may comprise nanosheets with an average thickness of about 0.35 nm to about 10 nm. In some embodiments, the nanomaterial suspension may comprise nanosheets with an average thickness of at least about 0.35 nm. In some embodiments, the nanomaterial suspension may comprise nanosheets with an average thickness of at most about 10 nm. In some embodiments, the nanomaterial suspension may comprise nanosheets with an average thickness in a range of about 0.35 nm to about 0.5 nm, about 0.35 nm to about 1 nm, about 0.35 nm to about 2 nm, about 0.35 nm to about 3 nm, about 0.35 nm to about 4 nm, about 0.35 nm to about 5 nm, about 0.35 nm to about 6 nm, about 0.35 nm to about 7 nm, about 0.35 nm to about 8 nm, about 0.35 nm to about 9 nm, about 0.35 nm to about 10 nm, about 0.5 nm to about 1 nm, about 0.5 nm to about 2 nm, about 0.5 nm to about3 nm, about 0.5 nm to about 4 nm, about 0.5 nm to about 5 nm, about 0.5 nm to about 6 nm, about 0.5 nm to about 7 nm, about 0.5 nm to about 8 nm, about 0.5 nm to about 9 nm, about 0.5 nm to about 10 nm, about 1 nm to about 2 nm, about 1 nm to about 3 nm, about 1 nm to about4 nm, about 1 nm to about 5 nm, about 1 nm to about 6 nm, about 1 nm to about 7 nm, about 1 nm to about 8 nm, about 1 nm to about 9 nm, about 1 nm to about 10 nm, about 2 nm to about 3 nm, about 2 nm to about 4 nm, about 2 nm to about 5 nm, about 2 nm to about 6 nm, about 2 nm to about 7 nm, about 2 nm to about 8 nm, about 2 nm to about 9 nm, about 2 nm to about10 nm, about 3 nm to about 4 nm, about 3 nm to about 5 nm, about 3 nm to about 6 nm, about3 nm to about 7 nm, about 3 nrn to about 8 nm, about 3 nrn to about 9 nm, about 3 nm to about 10 nm, about 4 nm to about 5 nm, about 4 nm to about 6 nm, about 4 nm to about 7 nm, about4 nm to about 8 nm, about 4 nm to about 9 nm, about 4 nm to about 10 nm, about 5 nm to about6 nm, about 5 nm to about 7 nm, about 5 nm to about 8 nm, about 5 nm to about 9 nm, about 5 nm to about 10 nm, about 6 nm to about 7 nm, about 6 nm to about 8 nm, about 6 nm to about 9 nm, about 6 nm to about 10 nm, about 7 nm to about 8 nm, about 7 nm to about 9 nm, about7 nm to about 10 nm, about 8 nm to about 9 nm, about 8 nm to about 10 nm, or about 9 nm to about 10 nm. In some embodiments, the nanomaterial suspension contains a plurality of nanosheets with an average thickness of about 0.35 nm, about 0.5 nm, about 1 nm, about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, or about lO nm.

[0079] In some embodiments, the exfoliated nanosheets with sizes ranging from a few hundred nanometers to several micrometers may be dispersed in a variety of different solvents, including isopropyl alcohol, dimethylformamide, ethanol, dc-ionizcd water in a single form or a combination of with a certain ratio based on the applications.

[0080] The nanomaterial suspension as produced according to the proposed method may include a narrow range of sizes. Advantageously, the substantially uniform sizes of the nanomaterial exfoliations may aid in later processes in the forming of a nanomaterial layer on a substrate. FIGs. 5A to 5C are examples showing a distribution of sizes of the nanomaterial exfoliations produced from the proposed method. It is evident that the nanomaterial exfoliations or nanosheets formed may include a substantial uniform exfoliation size.

[0081] FIG. 5A illustrates a size distribution of the liquid-exfoliated nanosheets of M0S2 in accordance with one embodiment of the present disclosure. The inset image is the corresponding M0S2 nanosheets dispersed in isopropyl alcohol. FIG. 5B illustrates the size distribution of the liquid-exfoliated nanosheets of WS2 in accordance with one embodiment ofthe present disclosure. The inset image is the corresponding WS2 nanosheets dispersed in isopropyl alcohol. FIG. 5C illustrates the size distribution of the liquid-exfoliated nanosheets of WSe? in accordance with one embodiment of the present disclosure. The inset image is the corresponding WSe2 nanosheets dispersed in isopropyl alcohol.

[0082] In some embodiments, the liquid exfoliated 2DM exfoliations or nanosheets (e.g. M0S2, WS2, and WSe2) preserve the respective high semiconducting quality and single crystallinity of pristine crystal structure as evidenced by the UV-Vis spectroscopy of the M0S2, WSe2 and WS2 dispersion as FIG. 6 shows. FIGs. 7A to 7C further shows the atomic resolution high-angle annular dark field scanning transmission electron microscopy (STEM) image of the liquid exfoliated M0S2, WSe2 and WS2 nanosheets.

[0083] According to another aspect of the present disclosure, a method of surface treatment may be performed on a substrate prior to the deposition of nanomaterials / thin films on the substrate. The surface treatment may be performed to enable nanomaterial deposition in later steps. According to various embodiments, the surface treatment may form a charged surface on the substrate. The charged surface may be a positive charge surface or a negative charge surface.

[0084] FIG. 8 is a flow chart illustrating the method of surface treatment of the substrate surface in accordance with some embodiments of the present disclosure. The method 600 of surface treatment may include: cleaning a target surface of a substrate (610), for example, using sonication. The method 600 may further include: performing a plasma treatment on the target surface to form a plasma-treated surface (620). The method 600 may further include: immersing the plasma-treated surface of the substrate in a surface treatment solution comprising a silane compound, to form a charged surface (630). The silane compound may include one or more functional groups. According to some embodiments, the surface treatment solution may include one or more silane compounds. In an example, the surface treatment solution may be a (3-aminopropyl)triethoxysilane (APTES) solution. In some embodiments, the plasma treatment may be an oxygen plasma treatment (640).

[0085] In some embodiments, the method of surface treatment 600 may be performed on various substrates, such as silicon wafers, quartz, glass, polyimide film, metal film, SiC, et al. The wide variety of substrates suitable for the surface treatment 600 allows a broad spectrum of applications for nanomaterials deposition. Tn other words, such surface treatments advantageously enable uniform growth of 2DM layers on different substrates, ranging from rigid to flexible substrates (e.g. polyimide film), and semiconducting (Si substrate) to insulating substrates (e.g. SiO2 and quartz). The surface treatment may account for or have a high tolerance to the surface roughness of substrates. In other words, the surface treatment may be used on a “rough” surface to ready it for nanomaterial deposition.

[0086] In an exemplary embodiment, the target surface of the substrate may be cleaned by a variety of cleaning liquids, such as acetone, IPA, and de-ionized water, under sonication for 30 minutes, respectively. Subsequently, the substrate or at least the target surface may be treated by oxygen plasma with a power of 20 W for 2 min under an O2 flow rate of 50 seem. Thereafter, the substrate may be immersed in a surface treatment solution, such as a (3- aminopropyl)triethoxy silane (APTES) solution for 1-4 hours at 20-80 °C, to produce a positively charged surface on the substrate. In some embodiments, the APTES solution may have a concentration in a range of 1 wt% to 5 wt% in ethanol.

[0087] In accordance with alternative embodiments of the present disclosure, a negatively charged surface may be formed on the substrate, i.e. negatively charged functional groups may be introduced onto a substrate surface through the application of specific silane compounds. Similar to above, the surface treatment solution may include one or more silane compounds. Exemplary silane compounds may include, but are not limited to, 3- Mercaptopropyltrimethoxysilane (MPTMS) and carboxyethylsilanetriol (CEST). The silanecompounds may introduce thiol (-SH) or carboxyl (-COOH) moieties onto the substrate surface. The thiol (-SH) or carboxyl (-COOH) functional groups may acquire a negative charge, thereby imparting a net negative surface charge to the treated surface on the substrate. The selection of the specific silane compound may be determined based on the requirements of the application and the desired surface properties of the substrate.

[0088] FIGs. 9A-9C are schematic diagrams illustrating a charged surface 310 of the substrate 300 upon completion of the surface treatment 310 according to embodiments of the present disclosure. The charged surface 310 may include charges substantially uniformly distributed across the surface. In an embodiment as shown in FIG. 9A, the charged surface 310 of the substrate 300 has a positive surface charge 301 upon completion of the surface treatment 310. In another embodiment as shown in FIG. 9B, the charged surface 310 of the substrate 300 includes the positive surface charges 301 and hydrogen bonds 302 upon completion of the surface treatment 310. In yet another embodiment as shown in FIG. 9C, the charged surface 310 of the substrate 300 includes negative surface charges 303 upon completion of the surface treatment 310.

[0089] According to another aspect of the present disclosure, a method of nanomaterial deposition is disclosed according to various embodiments. In some embodiments, the method of nanomaterial deposition may be performed independently from the method of producing the nanomaterial suspension as well as the method of surface treatment of the substrate, as described in previous sections. Alternatively, the method of nanomaterial deposition may include the method of producing the nanomaterial suspension as well as the method of surface treatment of the substrate.

[0090] FIG. 10 is a flow chart illustrating a method 700 of nanomaterial deposition or 2DM thin film deposition, according to embodiments of the present disclosure. In some embodiments, the method 700 of nanomaterial deposition comprises: providing thenanomaterial suspension (710). Alternatively, the method 700 may include producing the nanomaterial suspension 710 according to previous sections. The nanomaterial suspension 710 may include nanomaterial exfoliations with a first electrical charge in a liquid suspension.

[0091] In addition, the method 700 may further include: providing a charged surface on a substrate. The charged surface may be obtained via performing a surface treatment on a substrate according to previous sections. The surface treatment may be performed on a target surface of a substrate to form a charged surface on the substrate (720), wherein the charged surface has a second electrical charge. For the purpose of nanomaterial deposition, the second electrical charge of the charged surface may be an opposing charge to the first electrical charge of the nanomaterial exfoliations. For example, the charged surface may be positively charged and the nanomaterial exfoliations may be negatively charged. Tn another example, the charged surface may be negatively charged and the nanomaterial exfoliations may be positively charged.

[0092] Further, the method 700 may further include: immersing the charged surface in the nanomatcrial suspension to electrostatically form a nanomatcrial layer on the charged surface of the substrate (730), wherein the nanomaterial layer comprises nanomaterial exfoliations dispersed on the target surface. In various embodiments, the nanomaterial suspension may be in an operating temperature range during nanomaterial deposition. The operating temperature range may include a room temperature, i.e. 25 degrees Celsius. In other words, the method 700 may be performed at room temperature. In other embodiments, the method 700 may be performed at a temperature lower than the room temperature.

[0093] FIGs. 1 1 A to 1 1C are schematic diagrams illustrating the nanomaterial layer 320 of the substrate obtained after nanomaterial deposition or thin film deposition, according to embodiments of the present disclosure. FIG. 11 A shows a nanomaterial layer 320 formed on a substrate 300 with positive surface charge 301. The substrate 300 with positive surface charge301 being previously immersed in a nanomaterial suspension, wherein the nanomaterialexfoliations or nanosheets in the nanomaterial suspension are negatively charged. FIG. 11 A shows a nanomaterial layer 320 formed on a substrate 300 with positive surface charge 301 and hydrogen bonds 302. The substrate 300 with positive surface charge 301 and hydrogen bonds 302 being previously immersed in a nanomaterial suspension, wherein the nanomaterial exfoliations or nanosheets in the nanomaterial suspension are negatively charged. FIG. 11C shows a nanomaterial layer 320 formed on a substrate 300 with negative surface charge 301. The substrate 300 with negative surface charge 301 being previously immersed into the nanomaterial suspension, wherein the nanosheets in the nanomaterial suspension are positively charged.

[0094] According to various embodiments, as the surface charge of the substrate 300 and the charge 301 of the nanomaterial exfoliations are opposing to each other, a nanomaterial layer or thin film may be formed on the substrate 300 due to electrostatic interaction. In some embodiments, the van der Waals force may also contribute to the formation of the thin film of nanomatcrial layer. In some embodiments, nanomatcrial layers may be sequentially or concurrently deposited on both opposing surfaces of the substrate.

[0095] In some embodiments, upon immersing the substrate 300 in the nanomaterial suspension for a predetermined time duration to form the nanomaterial layer 320, the substrate 300 may be removed from the nanomaterial suspension. Thereafter, the substrate 300 with nanomaterial layer 320 formed thereon may be rinsed with isopropyl alcohol, ethanol, or deionized water, followed by drying with nitrogen gas blow. The substrate 300 with a fully and uniformly covered nanomaterial thin film may be obtained. Notably, the resultant nanomaterial suspension (used nanomaterial suspension) after the thin film deposition may be recyclable for subsequent depositions, which may cut down the production costs.

[0096] In various embodiments, the nanomaterial layer 320 may include a thickness (t). Due to the uniformity of charges in the charged surface on the substrate 300, the nanomaterial layer320 may include a substantially uniform thickness (t) across the charged surface or the target surface. In various embodiments, a thickness (t) of the nanomaterial layer formed may be dependent on a thickness of the nanomaterial exfoliations. In other embodiments, a thickness (t) of the nanomaterial layer formed may be dependent on a charge density of the charged surface. In other embodiments, a thickness (t) of the nanomaterial layer formed may be responsive to a concentration of the nanomaterial exfoliations in the nanomaterial suspension.

[0097] According to various applications, multiple depositions may be performed on the same side of the substrate to produce multiple stacked nanomaterial layers. In some embodiments, a second surface treatment may be performed on the deposited nanomaterial layer to form a second charged surface on the deposited nanomaterial layer. The second charged surface may have the second electrical charge. By immersing the second charged surface in a nanomaterial suspension with the first electrical charge, a second nanomaterial layer may be electrostatically formed on the deposited nanomaterial layer. It may be understood that one or more nanomaterial layers may be sequentially deposited on the cxisting / prcvious nanomaterial layer thus forming a nanomaterial multilayer structure. In some embodiments, the nanomaterial multilayer may be 2D heterostructures comprising different nanomaterial layers.

[0098] In some embodiments, the operating temperature range may include a minimum temperature corresponding to a freezing point of the suspension liquid. Table 1 sets out the respective freezing points of the various suspension liquids: de-ionized water, ethanol, 1PA, DMF, and N-Methyl-2-pyrrolidone (NMP). One reason for the freezing point of the suspension liquid being the minimum operating temperature is due to the solidification of the suspension liquid, thus impeding the movement of the nanomaterial exfoliations in the suspension liquid.Table 1. Freezing points of the suspension liquid

[0099] In some embodiments, the material deposition process may be conducted at room temperature without the need for expensive equipment, resources, and sophisticated process control. This may be possible due to the exfoliations or exfoliated 2D nanosheets preserving pristine crystal quality and clean van der Waals interfaces, thus ensuring excellent physical and chemical properties of the final thin film. Therefore, the proposed method presents a different approach for the fabrication and production of 2DM layers as compared to conventional high- temperature growth through CVD, MBE, ALD, et al. Such a low-temperature deposition process shows great potential for myriads of applications in sensors, thin-film transistor liquid crystal displays, charge-couple devices, and monolithic 3D circuits.

[0100] Experiments

[0101] Tn some experiments, the nanomaterial layer or thin film deposited on the substrate using the proposed method in the present disclosure exhibits excellent uniformity and coverage. FIG. 12A shows an optical image of a blank 2-inch sapphire as a substrate. FIG. 12B shows an optical image of an exemplary WS2 thin film formed on a 2-inch sapphire substrate using the deposition method in the present disclosure. FIG. 12C shows an optical image of an exemplary M0S2 thin film formed on a 2-inch sapphire substrate using the deposition method in the present disclosure. FIG. 12D shows an optical image of an exemplary WSe thin film formed on a 2- inch sapphire substrate using the deposition method in the present disclosure. As shown in FIGs. 12B to 12D, the exemplar}' 2-inch M0S2 film, WS2 film, and WSe2 film deposited on the respective sapphire substrates exhibit excellent uniformity and coverage. In addition, FIGs. 13A to 13C show the respective Raman results collected at random spots across the entire wafer of the exemplary M0S2, WS2, and WSe2 film of FIGs. 12B to 12D. The random spots show identical Raman peaks, demonstrating the excellent uniformity of the nanomaterial layers produced.[00102J Using the proposed method in the present disclosure, the nanomaterial layer or thin film deposited on the substrate exhibits smooth and continuous surfaces. According to various experiments, entire wafer as produced using the proposed method is uniformly covered with M0S2 nanosheets or nanomaterial exfoliations. With 2D layered morphology, the ultrathin M0S2 nanosheets evenly and tightly overlap with each other to form a continuous thin film with reduced areal density of grain boundaries within the horizontal plane as evidenced by the scanning electron microscopy.

[0103] In addition, the M0S2 layers are tightly stacked together in the vertical direction. The method provides large-area plane-to-plane contact with nearly atomically flat 2D interfaces, ensuring efficient charge transport across the M0S2 stacks. FIGs. 14A to 14C show an exemplary 4-inch M0S2 field effect transistor (FET) fabricated using the proposed method. FIG. 14A is an image of M0S2 field effect transistor (FET) devices on a 4-inch wafer. FIG. 14B is an optical image of the M0S2 FET devices in a selected region. FIG. 14C shows zoom-in optical images of a single M0S2 FET device. FIGs. 14D to 14F show the corresponding electrical measurements of the FET device of FIG.14A. Fig. 14D is a graph illustrating the drain current vs. gate voltage in an electrical measurement on the M0S2 FET devices. Fig. 14E is a graph illustrating the drain current vs. drain voltage in an electrical measurement on the M0S2 FET devices. Fig. 14F is a graph illustrating the field-effect mobility vs. gate voltage in an electrical measurement on the M0S2 FET devices. The M0S2 transistor shows a good gate modulation with an on / off ratio near 105. The output current shows an ohmic conduction with a high current reaching 2.5 p A under 2.0 V drain voltage. The mobility calculated from the M0S2 FET is as high as 6.3 cm2 / (Vs) which is higher than a transistor made from polycrystalline Si (around 0.1 cm2 / (Vs)). The FET results indicate that the method provided herein is a powerful technique that could enable the production of electronic grade 2DMs film.[00104 J FIG. 15 shows a series of M0S2 nanomaterial layers or thin films deposited by using the method in accordance with some embodiments of the present disclosure. It may be appreciated that using the proposed method, a variety of sizes of M0S2 thin films ranging from 1x1 cm2up to 8 inches may be produced, demonstrating the excellent scalability of the proposed method. The various nanomaterial layers as shown in FIG. 15 demonstrates the scalability of the production of 2DM layers at room temperature. The deposited 2DM film shows high electronic-grade quality and wafer-scale uniformity, which may be used as ideal building blocks for various applications. In addition, the cost involved in the production is kept low with no expensive equipment, resources and sophisticated process control being involved in the preparation process, significantly reducing the production cost.

[0105] The present disclosure discloses a simple and scalable method for forming a wide range of nanomaterial layer(s) and heterostructures at room temperature. In some embodiments, with the deposition of multiple nanomaterial layers, a 2D heterostructure may be formed. In comparison to conventional methods such as CVD, MBE, and Magnetron, the method of the present disclosure allows for high throughput production of 2DMs thin film or nanomaterial layer up to 12 inches wafer sizes, while maintaining excellent electronic properties. The method of the present disclosure may be used for low-cost 2DMs and large-scale manufacturing and being compatibly integrated with current semiconductor Si techniques without the need for additional process control. The method of the present disclosure may achieve room-temperature growth and fabrication, allowing emerging applications in monolithic three-dimensional circuits and wearable electronics. The method of the present disclosure may also be employed as an environmentally friendly process by using an inert or benign solvent such as ethanol, IPA, or even de-ionized water.

[0106] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutuallyinconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that may also appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.

[0107] All examples described herein, whether of methods, materials, or products, are presented for the purpose of illustration and to aid understanding and are not intended to be limiting or exhaustive. Modifications may be made by one of ordinary skill in the art without departing from the scope of the invention as claimed.

Claims

CLAIMS1. A method of producing a nanomaterial suspension, the method comprising: disposing a nanomaterial bulk crystal on a first electrode of an electrochemical cell, wherein the electrochemical cell comprises the first electrode and a second electrode immersed in an electrolyte, wherein the second electrode comprises a conductive material, wherein the electrolyte comprises an ammonium compound, a polymer and a first solvent; providing a voltage across the first electrode and the second electrode, to form an intercalated crystal from the nanomaterial bulk crystal; and exfoliating the intercalated crystal in a suspension liquid to form the nanomaterial suspension, wherein the nanomaterial suspension comprises nanomaterial exfoliations with a first electrical charge in the suspension liquid, the first electrical charge being one of: a positive charge and a negative charge.

2. The method as recited in claim 1, further comprising: selectably applying one of a positive bias and a negative bias as the voltage across the first electrode and second electrode to form the intercalated crystal.

3. The method as recited in claim 2, further comprising: selectably configuring the first electrode as one of a cathode and an anode; and the second electrode as another of the cathode and the anode.

4. The method as recited in claim 2, wherein responsive to applying the positive bias as the voltage across the first electrode and second electrode, the first electrical charge of the nanomaterial exfoliations is a positive charge.5, The method as recited in claim 2, wherein responsive to applying the negative bias as the voltage across the first electrode and second electrode, the first electrical charge of the nanomaterial exfoliations is a negative charge.

6. The method as recited in claim 1, wherein the nanomaterial bulk crystal comprises at least one bulk crystal selected from a group consisting of: graphite, graphene, boron nitride, molybdenum disulfide (M0S2), tungsten disulfide (WS2), tungsten diselenide (WSej), black phosphorus (BP), and indium selenide (h Ses).7, The method as recited in claim 1, wherein the first solvent is selected from a group consisting of: acetonitrile and dimethylformamide (DMF).

8. The method as recited in claim 1 , wherein the electrolyte further comprises: a quaternary ammonium bromide, a polyvinylpyrrolidone (PVP) and a propylene carbonate.9, The method as recited in claim 8, wherein the quaternary ammonium bromide has a concentration range of 0.1 mg / mL to 10 mg / mL, wherein the polyvinylpyrrolidone (PVP) has a concentration range of 0.1 g / L to 10 g / L, and wherein a volumetric ratio between the electrolyte liquid to the propylene carbonate is in a range of 4: 1 to 1:1.

10. The method as recited in claim 1, wherein the suspension liquid is a second solvent selected from a group consisting of: de-ionized water, isopropyl alcohol, ethanol, dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP).

11. The method as recited in claim 1, wherein the electrochemical cell is a three-electrode electrochemical cell, further comprising a reference electrode.

12. The method as recited in claim 1, wherein the conductive material is one of: platinum, stainless steel, titanium, nickel, and carbon.

13. The method as recited in claim 1 , wherein the nanomaterial bulk crystal is selected from a group consisting of: a transition metal dichalcogenides (TMDC) bulk crystal and a graphene bulk crystal.

14. A method of nanomaterial deposition, the method comprising: providing the nanomaterial suspension as recited in any of the above claims, the nanomaterial suspension comprising nanomaterial exfoliations with the first electrical charge; performing a surface treatment on a target surface of a substrate to form a charged surface on the substrate, wherein the charged surface has a second electrical charge, wherein the second electrical charge is an opposing charge to the first electrical charge; immersing the charged surface in the nanomaterial suspension to electrostatically form a nanomaterial layer on the charged surface of the substrate,wherein the nanomaterial suspension is in an operating temperature range, the operating temperature range including a room temperature, wherein the nanomaterial layer comprises nanomaterial exfoliations dispersed on the target surface.

15. The method as recited in claim 14, wherein the surface treatment comprises: cleaning the target surface of the substrate using sonication; performing a plasma treatment on the target surface to form a plasma- treated surface; and immersing the plasma-treated surface of the substrate in a surface treatment solution to form the charged surface, wherein the surface treatment solution comprises a silane compound.

16. The method as recited in claim 15, wherein the plasma treatment comprises an oxygen plasma treatment.

17. The method as recited in claim 15, wherein the charged surface is a positively charged surface, and wherein the silane compound comprises a (3-aminopropyl)triethoxysilane (APTES) solution.

18. The method as recited in claim 17, wherein the (3-aminopropyl)triethoxysilane (APTES) solution has a concentration in a range of 1 wt% to 5 wt% in ethanol.

19. The method as recited in claim 15, wherein the charged surface is a negatively charged surface, and wherein the silane compound comprises at least one of: 3- Mercaptopropyltrimethoxysilane (MPTMS) and carboxyethylsilanetriol (CEST).

20. The method as recited in claim 14, wherein a thickness of the nanomaterial layer formed is responsive to a concentration of the nanomaterial exfoliations in the nanomaterial suspension.

21. The method as recited in claim 14, wherein the operating temperature range comprises a minimum temperature corresponding to a freezing point of the suspension liquid.

22. The method as recited in claim 14, wherein the nanomaterial layer comprises a substantially uniform thickness across the target surface.

23. The method as recited in claim 14, further comprising: performing the surface treatment on a second target surface of the substrate to form a second charged surface on the second target surface, the second target surface corresponding to the nanomaterial layer, wherein the second charged surface has the second electrical charge; immersing the second charged surface in the nanomaterial suspension to electrostatically form a second nanomaterial layer on the second charged surface of the substrate.

24. The method as recited in claim 23, wherein the nanomaterial layer and the second nanomaterial layer form a 2D heterostructure.

25. A nanomateriai device, comprising: a substrate defining a charged surface; a nanomateriai layer formed on the charged surface of the substrate, the nanomaterial layer formed from nanomateriai exfoliates, wherein the nanomateriai layer comprises a substantially uniform thickness across the charged surface.

26. The nanomateriai device as recited in claim 25, further comprising a second nanomateriai layer disposed on the nanomateriai layer to form a 2D heterostructure.

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