ELECTROPHORETIC DEPOSITION OF HEXAGONAL BORON NITRIDE FILMS AND COATINGS AND THEIR APPLICATIONS

Abstract

Embodiments relate to methods for preparing a hexagonal boron nitride (hBN) suspension and forming films, coatings, or membranes via electrophoretic deposition.

Description

FIELD OF THE INVENTION

Embodiments relate to methods for preparing hexagonal boron nitride (hBN) films, coatings, and/or membranes by electrophoretic deposition. In some embodiments, the method can involve preparing hexagonal boron nitride films, coatings, and/or membranes on electrically conductive surfaces via electrophoretic deposition with an hBN suspension made up of negatively charged hBN sheets in an organic solvent.

BACKGROUND OF THE INVENTION

Interest in solution processable two-dimensional (2D) materials has increased dramatically in recent years because they are attractive building blocks for next-generation catalyst systems, anticorrosion coatings, solid lubricants, molecular sensing devices, electrochemical energy storage devices, and large-area thin-film electronics. The most prominent 2D materials are graphene, transition metal dichalcogenides (TMDs), and hexagonal boron nitride (hBN), which are semimetallic, semiconducting, and insulating, respectively. Graphene has a single atomic layer structure and is impermeable to molecules, making it an excellent material for anticorrosion and antioxidation coatings. In comparison, hBN, which shows the same impermeability to molecules just like graphene, is a better coating material when compared to graphene and possess superior thermal stability and chemical inertness. hBN is a layered material comprising of planar hexagonal networks of covalently bonded B and N atoms as in the case of graphite. The main difference from graphite is that the covalent bonds between the B and N atoms are polar and partially ionic due to the electronegativity difference between these atoms. 2D hBN has emerged as a novel 2D material because of its unique optical properties in the deep-UV region, mechanical robustness, thermal stability, chemical inertness, and excellent lubricating properties. hBN is a wide band-gap insulator with polar bonds, excellent thermal, optical, electrochemical, and dielectric properties. These unique properties have promoted its use in various applications, including nanoelectronics, photonics, single photon emission, anticorrosion coatings, and membranes. In addition, hBN has a relatively low density of 2.2 g/cm³, which makes it an excellent candidate material for lighter weight aerospace materials and coatings. However, there are few scalable low temperature processes for making high quality large area hBN films and coatings with high compactness and controllable thicknesses. At present, mechanical exfoliation of bulk hBN crystals is the most commonly used formation method, which produces good quality crystals, but this method cannot produce continuous films and is labor intensive and is not feasible for industrial production. Although chemical vapor deposition (CVD) has been used to grow 2D hBN films, current CVD processes for hBN require temperatures of up-to 1000° C. on copper or nickel foils. In addition, it is not possible to transfer large continuous 2D hBN films onto other different substrates with irregular shapes, for example. Solution processed large are hBN films have been deposited on different surfaces and used for anticorrosion coatings and electronic and electrochemical devices by different printing and coating techniques. However, the hBN coatings prepared in the prior art are made from dispersions containing surface stabilizing additives, resulting in hBN films and coatings that are poorly compacted and exhibit poor adhesion on metal surfaces, and therefore, the hBN coatings are not suitable for being used as anticorrosion coatings and have poor performances in electrochemical and electronic devices. Therefore, a method capable of producing large area hBN films with a reduced deposition temperature, with high compactness and good adhesion on metal surfaces and controllable film thickness from the nanometer level upwards is highly desired.

Recent work has demonstrated success in performing the reductive intercalation of hBN by molten alkali metal to form an alkali metal (AM) intercalated hBN (AM(hBN)_X) system. In this AM(hBN)_X) system, the hBN sheets encapsulate a layer or bilayer of alkali metal atoms within the hBN galleries. Electronic structure/density functional theory calculations indicate that alkali metal atoms intercalate into hBN through interaction with defects/vacancies which also appear to ‘pillar’ the hBN sheets to facilitate further alkali metal infiltration into the hBN galleries. The intercalated state appears to support a 2D electron gas resident on the alkali metal layer with some charge transfer to the hBN layers. The intercalation of hBN with alkali atoms activates the hBN and is associated with a subsequent exfoliation into 2D hBN in dry aprotic organic solvents to form fully exfoliated negatively charged 2D hBN sheets. It has been demonstrated that the exfoliated 2D hBN suspensions in THE under inert conditions are stable for several months.

The construction of uniform large area films and coatings of 2D hBN from hBN dispersions still represents a formidable challenge that must be overcome to realize potential of this material in different applications. Therefore, there is a real need for utilizing these exfoliated 2D hBN suspensions in organic aprotic solvents to prepare large area, uniform and clean hBN films, coatings, and/or membranes with a quality and variable thicknesses suitable for envisioned applications. Moreover, how to provide an hBN film, coating, or membrane, with a large adhesive force on the substrate surface, good corrosion resistance, simple preparation method, mild process conditions, environmental friendliness, and suitability for metal corrosion prevention, electrical insulating coatings, solid lubricants, and dielectric material in electrochemical and electronic device fabrication becomes a technical problem to be solved at present. These exfoliated hBN sheets in aprotic organic solvents are an excellent candidate for use as hBN suspensions to produce hBN films or coatings deposited by the disclosed electrophoretic deposition method.

SUMMARY OF THE INVENTION

Embodiments relate to methods for preparing hexagonal boron nitride (hBN) films, coatings, and/or membranes by electrophoretic deposition. The preparation method can involve preparing an exfoliated hBN suspension containing negatively charged exfoliated hBN sheets in an aprotic organic solvent, and depositing hBN films, coatings, and/or membranes from the hBN suspension using electrophoretic deposition. Pictures and characterization of different hBN coated substrates including, gold, copper, steel nail, transparent indium tin oxide (ITO) coated glass, carbon fiber, and nickel foam, deposited by the disclosed method are provided within the figures of this disclosure.

The preparation method of the hBN suspension provided by this disclosure is simple, mild in process conditions, environment-friendly, pollution-free, and suitable for industrial production. Meanwhile, the hBN films, coatings, and/or membranes prepared from the hBN suspension by electrophoretic deposition provided by the disclosed process have good compactness and high adhesive force on the conductive surface and is/are suitable for use as anticorrosion coatings. Embodiments disclosed herein also relate to depositing hBN lubricating coatings and electrical insulating hBN coatings on electrical conductors, hBN dielectric layers in capacitors, batteries, and electronic devices, and the preparation of multilayer heterostructures comprising a layer of hBN film or coating and other 2D material layers such as graphene films or coatings for use in electronic and electrochemical devices.

An exemplary embodiment can relate to a method for preparing a hexagonal boron nitride (hBN) suspension. The method can involve performing steps of: mixing and dissolving a metal in a solvent to form a mixture, wherein the solvent includes (A) a polar aprotic organic solvent, (A′) a mixture of polar aprotic organic solvents, or (B) ammonia; and dispersing hBN powder containing one or more hBN sheet or exfoliated hBN powder containing one or more hBN sheet in the mixture, wherein the metal provides a counterion to negatively charge the one or more hBN sheet. In addition, or in the alternative, the method can involve performing steps of: combining hBN powder containing one or more hBN sheet or exfoliated hBN powder containing one or more hBN sheet with a metal to form a mixture, wherein the metal provides a counterion to negatively charge the one or more hBN sheet; applying heat to the mixture to generate a metal-intercalated hBN material; and exposing the metal-intercalated hBN material to a solvent, the solvent including (A) a polar aprotic organic solvent, (A′) a mixture of polar aprotic organic solvents, or (B) ammonia. In addition, or in the alternative, the method can involve performing steps of: combining hBN powder containing one or more hBN sheet or exfoliated hBN powder containing one or more hBN sheet and a polyelectrolyte to form a mixture; dispersing the mixture in an organic polar aprotic a solvent, the solvent including (A) a polar aprotic organic solvent, (A′) a mixture of polar aprotic organic solvents, or (B) ammonia, wherein the polyelectrolyte adsorbs onto the hBN and to impart a negative charge to the one or more hBN sheet.

In some embodiments, the metal can be one or more alkali metals, one or more alkaline earth metals, one or more alkali metal electrides, one or more alkaline earth metal electrides, or a combination thereof.

In some embodiments, the metal can be Li, K, Na, R, Cs, Fr, Be, Mg, Ca, Ba, Sr, and/or Ra.

In some embodiments, the counterion can be Li⁺, K⁺, Na, Rb⁺, Cs⁺, Fr⁺, Be²⁺, Mg²⁺, Ca²⁺, Ba²⁺, Sr²⁺, and/or Ra²⁺.

In some embodiments, the polyelectrolyte can be a nucleic acid, a protein, a teichoic acid, a polypeptides, and/or a polysaccharide.

In some embodiments, the solvent can be tetrahydrofuran (THF), acetone, acetonitrile, dimethoxyethane (DME), sulfolane, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-methylpyrrolidone (NMP), N-methylformamide, acetone, acetonitrile, dichloromethane, dimethylformamide (DMF), dimethylpropyleneurea, and/or ethyl acetate, hexamethylphosphoric triamide.

In some embodiments, mixing and dispersing can occur for a duration within a range from 0 hours to 96 hours. Mixing and dispersing can occur while the mixture is subjected to a temperature within a range from −22° C. to 220° C.

In some embodiments, concentration of the exfoliated hBN in the hBN suspension can be within a range from 0.01 g/L to 10 g/L.

In some embodiments, the method can involve separating the hBN suspension from the mixture via centrifugation.

An exemplary embodiment can relate to a method of depositing hexagonal boron nitride (hBN) on a substrate. The method can involve placing an anode electrode in an environment containing an exfoliated hBN suspension, the exfoliated hBN suspension including one or more negatively charged hBN sheets, the anode comprising the substrate. The method can involve placing a cathode electrode in the environment. The method can involve applying a voltage difference across the anode electrode and the cathode electrode. The method can involve forming, via electrophoretic deposition, a hBN film, coating, and/or membrane on at least a portion of the substrate.

In some embodiments, the hBN film, coating, and/or membrane can be formed directly on a surface of the substrate. In some embodiments, the hBN film, coating, and/or membrane can be formed on a layer of material formed on the substrate.

In some embodiments, the material can include any one or combination of graphene, MoS₂, or WS₂.

In some embodiments, the hBN film, coating, and/or membrane can be used as an anticorrosion coating, an antioxidation coating, a lubricant coating, an insulating coating, a thermally or electrically conductive coating, a heat dissipation coating, and/or a dielectric coating for the substrate.

Further features, aspects, objects, advantages, and possible applications of the present invention will become apparent from a study of the exemplary embodiments and examples described below, in combination with the Figures, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, aspects, features, advantages and possible applications of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings, in which:

FIG. 1 is a simplified schematic diagram of exemplary steps to achieve electrophoretic deposition of hBN on electrically conductive surface.

FIG. 2 is a scheme showing an exemplary preparation of the hBN suspension by using the reductive dispersion of potassium intercalated hBN in tetrahydrofuran (THF) to produce fully exfoliated negatively charged hBN sheets in THF.

FIG. 3 shows the pictures of potassium intercalated hBN suspensions in THE at different times, the deep blue color changes to sky blue, until it remained a light bluish-grey color after 3 days of stirring when the hBN suspension is ready for use in electrophoretic deposition or for further processing.

FIG. 4 presents the absorption spectra of the hBN suspension, where the hBN suspension is characterized by a band in the UV range at 256 nm and 324 nm with no tailing into higher wavelength region.

FIG. 5 shows an exemplary schematic of the hBN electrophoretic deposition set up, photograph of the positive electrode following electrophoretic deposition, and an optical micrograph showing a grid section over which Raman measurements were taken to characterize the deposited hBN.

FIG. 6 is Raman characterization of an exemplary hBN coating deposited on a positive electrode. The Raman spectrum collected using a green laser with λ=533 nm shows characteristic peak at 1367 cm⁺¹ that is due to the E_2g phonon mode confirming presence of uncharged deposited hBN nanosheets. The intensity map of the hBN peak at ˜ 1367 cm⁻¹ shows the nanosheets are only deposited on to the metallic gold coated part of the electrode (e.g., only in the region of the electric field). The Si peak is only present on the part of the electrode without the gold coating.

FIG. 7 shows pictures of exemplary hBN coatings on different substrates including gold coated Si/SiO₂, a steel nail, a copper foil, ITO coated glass, and a steel blade.

FIG. 8 shows a scanning electron microscopy (SEM) image of an exemplary electrophoretically deposited hBN coating on a gold coated Si/SiO₂ substrate using an exemplary hBN suspension containing small flakes (300 nm lateral size).

FIG. 9 shows a scanning electron microscopy (SEM) image of an exemplary electrophoretically deposited hBN coating on a gold coated Si/SiO₂ substrate using an exemplary hBN suspension containing large flakes (up to 20 μm lateral size).

FIG. 10 shows a scanning electron microscopy (SEM) image of an exemplary electrophoretically deposited hBN coating on a gold coated Si/SiO₂ substrate using an exemplary hBN suspension containing a mixture of small and large hBN (300 nm up to 20 μm).

FIG. 11 presents a SEM image of a cross section of an exemplary electrophoretically deposited hBN coating on copper of approximately 1.5 μm.

FIG. 12 presents a SEM image of a cross section of an exemplary hBN coating on a gold coated Si/SiO₂ substrate of approximately 3.4 μm.

FIG. 13 presents a SEM image of an exemplary hBN coating on a nickel foam showing that irregular substrates can also be coated using electrophoretic deposition.

FIG. 14 is a picture of a steel nail with a section covered by an exemplary electrophoretically deposited hBN coating after exposure to a concentrated salt solution to accelerate corrosion. Corrosion is noticed on the uncoated section after 4 hours, while the hBN coated sections remain protected from corrosion. For comparison, stainless steel nails were studied under the same conditions and they were not corroded as expected.

FIG. 15 is a picture of a copper foil with a section covered by an exemplary electrophoretically deposited hBN coating after heat treatment in air at 400° C. The uncoated section is completely oxidized into dark cuprous oxide while the hBN coated sections shows less oxidation.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of an embodiment presently contemplated for carrying out the present invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles and features of the present invention. The scope of the present invention should be determined with reference to the claims.

Embodiments further relate to methods for preparing a hexagonal boron nitride (hBN) film, coating and/or membrane. The hBN film, coating, and/or membrane can be formed by deposition. For instance, embodiments of the hBN suspension can be used to generate a hBN flakes, each flake comprising one or more exfoliated hBN sheets. The hBN sheet can be an hBN nanosheet. The hBN flakes can be deposited on a substrate to form a film, coating, and/or membrane on the substrate. The deposition can be via electrophoretic deposition.

The method can involve preparing an exfoliated hBN suspension. The hBN suspension can include one or more exfoliated hBN sheets, wherein any one or combination of hBN sheets can be a nanosheet. Any one or combination of the exfoliated hBN sheets can be negatively charged. The method of negatively charging the sheets will be explained in more detail later. The negative charge can facilitate deposition of the sheets on the sheets onto the substrate via electrophoretic deposition.

Preparation Method I

The method can involve dispersing an hBN powder or previously exfoliated hBN powders in a solution containing an alkali or alkaline earth metal or an alkali metal electride such as alkali metal naphthalene salt (electride) dissolved in a polar aprotic organic solvent (A) or a mixture (A′) of polar aprotic organic solvents, or ammonia.

Exemplary metals can be Li, K, Na, R, Cs, Fr, Be, Mg, Ca, Ba, Sr, Ra. These can be used to provide for or generate counterions, such as Li⁺, K⁺, Na, Rb⁺, Cs⁺, Fr⁺, Be²⁺, Mg²⁺, Ca²⁺, Ba²⁺, Sr²⁺, Ra²⁺ for example.

Preparation Method II

The method can involve heating a mixture of hBN powder or previously exfoliated hBN powder with a metal (e.g., one or more alkali metals, one or more alkaline earth metals), or a combination thereof) to form an intercalated hBN system. Exemplary metals can be Li, K, Na, R, Cs, Fr, Be, Mg, Ca, Ba, Sr, Ra. This can be done These can be used to provide for or generate intercalated counterions, such as Li⁺, K⁺, Na, Rb⁺, Cs⁺, Fr⁺, Be²⁺, Mg²⁺, Ca²⁺, Ba²⁺, Sr²⁺, Ra²⁺ for example.

The method can involve placing the mixture in a container and heating the mixture. This can be done to generate an alkali metal-intercalated hBN material.

The method can subsequently involve exposing the alkali metal-intercalated hBN material to a polar organic aprotic solvent to form a hBN suspension containing negatively charged exfoliated hBN sheets in the solvent. The solvent can be a polar aprotic organic solvent. The solvent can be (A) a polar aprotic organic solvent, (A′) a mixture of polar aprotic organic solvents, (B) ammonia, etc.

Preparation Method III

A polyelectrolyte (a nucleic acid, a protein, a teichoic acid, a polypeptides, a polysaccharide, etc.) together with an hBN powder or preferably with a previously exfoliated hBN powder can be dispersed in a solvent. The solvent can be a polar aprotic organic solvent. The solvent can be (A) a polar aprotic organic solvent, (A′) a mixture of polar aprotic organic solvents, (B) ammonia, etc.

In Either Preparation I or Preparation II or Preparation III

The mixing can be via mechanical stirring, magnetic stirring, ultrasonic dispersing, etc. The mixing and dispersing can occur for a duration that is within a range of 0 h-96 h. The mixing and dispersing can be done within a temperature range of −22 to 220° C. The temperature can be held constant or varied during the mixing and dispersing.

The concentration of the exfoliated hBN in the hBN suspension can be within a range of 0.01 to 10 g/L. A concentration range of 0.05 to 2 g/L may be preferred for some applications.

The negative charge for the sheets can be supplied by reducing the hBN with one or more alkali metals. With the addition of polyelectrolyte, one or more hBN sheets can carry a charge due to a polyelectrolyte adsorbed on its surface.

The aprotic organic solvent can be any one or combination of tetrahydrofuran (THF), acetone, acetonitrile, dimethoxyethane (DME), sulfolane, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-methylpyrrolidone (NMP), N-methylformamide, acetone, acetonitrile, dichloromethane, dimethylformamide (DMF), dimethylpropyleneurea, ethyl acetate, hexamethylphosphoric triamide, etc.

The hBN suspension in the mixture can be separated out via centrifugation (e.g., ultracentrifugation) to obtain well exfoliated thin hBN flakes.

Deposition

The one or more hBN flakes can be deposited onto at least a portion of a substrate. This can be via electrophoretic deposition (e.g., electrocoating, cathodic electrodeposition, anodic electrodeposition, and electrophoretic coating, electrophoretic painting, etc.). The deposition can generate an embodiment of the hBN suspension as a film, a coating, and/or a membrane on the substrate. As the deposition is contemplated to be electrophoretic deposition, the surface of the substrate to which the hBN suspension is deposited can be electrically conductive. For instance, the substrate can be metal, metal alloy, Si (with a conductive surface deposited thereon), SiO₂ (with a conductive surface deposited thereon) gold, copper, steel nail, aluminum, transparent indium tin oxide (ITO) coated glass, carbon fiber, nickel foam, etc.

It should be noted that the deposition can be directly on the substrate or directly on the conductive portion of the substrate. For instance, the hBN suspension can be formed on the substrate or conductive portion thereof without layer transfer. It is understood, however, that a layer transfer can be used, an intervening layer can be used, etc. Thus, in some embodiments, an intervening layer can be deposited on the substrate and the hBN suspension can be deposited on the intervening layer.

An exemplary deposition process can involve preparing an exfoliated hBN suspension in a manner described herein. As noted herein, the mixture used to form the exfoliated hBN suspension can contain metals to provide for or generate counterions. The combination of electronically negatively charged hBN sheets and the metal counterions from reducing the metal can result in a stable and electrically conductive solution which can enable the electrophoretic deposition to occur. The hBN suspension can be placed into a container. Two electrodes (an anode electrode and a cathode electrode), each connected to a voltage source, can be placed into the hBN suspension. The anode electrode, being the positive electrode, comprises the substrate to which the exfoliated hBN sheets are deposited. For instance, at least a portion of the anode electrode can be made from Si (with a conductive surface deposited thereon), SiO₂ (with a conductive surface deposited thereon) gold, copper, steel nail, transparent indium tin oxide (ITO) coated glass, carbon fiber, nickel foam, etc. A voltage difference can be applied across the electrodes. This voltage difference can deposit (via electrophoretic mechanisms) exfoliated hBN sheets onto the anode electrode, and in particular the substrate portion of the anode electrode. The deposition can be performed for a predetermined amount of time, for a predetermined number of times, etc. to generate a film, coating, and/or membrane of desired thickness on the substrate. In addition, or in the alternative, the thickness can be controlled by adjusting hBN concentration in the hBN suspension, adjusting deposition voltage, etc. The thickness can be within a range from 0.3 nm to 100 microns. After deposition, the exfoliated hBN sheet coated substrate can be rinsed, dried (e.g., dried under vacuum), and annealed (e.g., subjected to heat).

Heterostructure Films, Coatings, and/or Membranes

The deposition can occur in layers. For instance, the deposition can be performed to generate a first layer of hBN on the substrate. The deposition can be performed again to generate a second layer of hBN on the substrate. The second layer can be on top of the first layer or on a different portion of the substrate. The second layer can have the same or different hBN thickness, hBN concentration, etc. In some embodiments, the first layer can be hBN and the second layer can be a different material (e.g., graphene, MoS₂, WS₂, etc.). In some embodiments, the first layer can be graphene, MoS₂, WS₂, etc. and the second layer can be hBN. The substrate can have deposition on a first area and deposition on a second area that is different from the first area. Any of the first or second areas can be homogonous structure, a heterostructure, etc. There can be any number of layers and there can be any number of combinations or permutations of heterostructure.

The hBN (either homogonous or heterostructure) film, coating, and/or membrane can be used in a wide range of applications. For instance, the film, coating, and/or membrane can be used as an anticorrosion coating, an antioxidation coating, a lubricant coating, an insulating coating, a thermally or electrically conductive coating, a heat dissipation coating, a dielectric coating, etc.

As can be appreciated from the above, embodiments can relate to methods for preparing hexagonal boron nitride (hBN) films, coatings and membranes by electrophoretic deposition. More specifically, embodiments relate to a method for preparing hexagonal boron nitride films or coatings on electrically conductive surfaces using electrophoretic deposition.

The preparation method can include steps of: preparing an exfoliated hBN suspension containing negatively charged exfoliated hBN sheets in an aprotic organic solvent, and depositing hBN films, coatings and membranes from the hBN suspension using electrophoretic deposition. Pictures and characterization of different hBN coated substrates including, gold, copper, steel nail, transparent indium tin oxide (ITO) coated glass, carbon fiber, and nickel foam, deposited by the disclosed method are shown in the figures. The preparation method of the hBN suspension provided by embodiments disclosed herein is simple, mild in process conditions, environment-friendly, pollution-free, and suitable for industrial production. Meanwhile, the hBN films, coatings and membranes prepared from the hBN suspension by electrophoretic deposition exhibit good compactness and high adhesive force on the conductive surface and is suitable for being used as anticorrosion coatings.

Embodiments further provide for deposition of hBN lubricating coatings, electrical insulating hBN coatings on electrical conductors, hBN dielectric layers in capacitors, batteries, and electronic devices, and the preparation of multilayer heterostructures comprising a layer of hBN film or coating and other 2D material layers such as graphene films or coatings for use in electronic and electrochemical devices.

Compared with the prior art, embodiments disclosed herein have the following beneficial effects:

• • (1) Through the interaction among the components in the hBN suspension, the exfoliated negatively charged hBN sheets, the alkali metal counterions, the aprotic organic solvent; the prepared hBN suspension has good uniformity, electrical conductivity, and stability, the Zeta potential of the hBN suspension is highly negative, making electrophoretic deposition of high quality hBN film, coating or membrane possible.
  • (2) The compactness of the prepared hBN film, coating or membrane is good, the adhesion and the compactness on the substrate surface are high, the thickness of the hBN film or coating can be varied from 0.3 nm to 20 microns, the penetration of oxygen, water molecules and other small molecules can be effectively prevented. After the sample plated with the hBN film or coating is heated in air, the hBN coating on the surface layer of the metal sample is complete and is difficult to scrape and has no obvious corrosion or oxidation phenomenon, so that the prepared hBN coating has good corrosion and oxidation resistance and is suitable for being used as a metal corrosion/oxidation-resistant coating. Embodiments are additionally directed to a multilayer article comprising an electrically conducting substrate, an intervening layer such as graphene, and a layer of 2D hBN.
  • (3) It is also possible to fabricate multilayer heterostructure films or coatings containing an electrophoretically deposited hBN film or and other 2D material layers such as graphene film or coatings. Possible heterostructures examples are, hBN/graphene, hBN/graphene/hBN, graphene/hBN, or graphene/hBN/graphene.

EXAMPLES

Example 1: K-Intercalated hBN Material with a Structure Indicated in FIG. 2 (Right) and a Preparation Method Thereof

The preparation method of the K-intercalated hBN material comprises the following steps inside an inert glovebox environment:

• • To form a K-intercalated hBN material, 4 g of hBN powder, and 1.63 g freshly cleaned potassium (stoichiometry K(hBN)₄) were placed together in a glass vial inside an argon filled glove box and heated for 5 hours at 200° C. on a heating plate under occasional stirring.
  • Afterwards, the vial is allowed to cool down to room temperature and the K-intercalated hBN material with the structure represented in FIG. 1 (right) is collected. The resulting K-intercalated hBN material is further processed to form an hBN suspension in the following example.

Example 2: An hBN Suspension as Represented in the Scheme in FIG. 9 (Left) and a Preparation Method Thereof

The preparation method of the hBN suspension comprises the following steps inside an inert glovebox environment:

• • Under inert atmosphere, 3 g of K-intercalated hBN powder was dispersed in 500 ml of dry THF (6 g/L) and this mixture (a deep blue suspension indicated in the picture in FIG. 3 (right) was tightly capped and mixed for 3 days with a magnetic stirrer (500 revolutions per minute (r.p.m.)). As the mixing continued, the deep blue color changed to sky blue, until it remained a light bluish-grey color after 3 days of stirring as indicated in pictures FIG. 3 in the middle and on the left. After stirring, the suspension was left to stand overnight to allow undissolved hBN aggregates to form and settle at the bottom. The well dispersed suspension containing exfoliated negatively charged hBN in THF was extracted with a pipette and retained for use as hBN suspension for further processing and for electrophoretic deposition. The other part of the well dispersed white hBN suspension in THF was centrifuged in 15 ml glass centrifuge tubes at 1,000 r.p.m. for 20 min to remain with an hBN suspension containing predominantly monolayer negatively charged hBN sheets suspended in THF with K⁺ counterions. The solutions were found to be stable under an inert atmosphere. Their absorption spectrum is characterized by a band in the UV range at 256 nm and 324 nm with no tailing into higher wavelength region as indicated in the absorption spectra in FIG. 4. This 256 nm and 324 nm band is associated with the presence of charged (reduced) hBN flakes in solution because of its disappearance upon air oxidation. Upon exposure to air, its intensity dramatically decreases within less than 1 hour as indicated in the absorption spectra in FIG. 4.

Example 3: Preparing hBN Film, Coating, or Membrane on an Electrically Conductive Substrate by Electrophoretic Deposition

The method for preparing hBN film, coating, or membrane on an electrically conductive substrate by electrophoretic deposition comprises the following steps inside an inert glovebox environment:

• • A gold coated oxidized silicon substrate (anode) was immersed into the hBN suspension containing exfoliated negatively charged hBN sheets in a glass beaker as indicated in the schematic in FIG. 5 (top right).
  • Another gold coated substrate (cathode) was immersed into the hBN suspension on the opposite side of gold coated oxidized silicon substrate (anode) to be coated as indicated in the schematic in FIG. 5 (top right).
  • A 9 V bias potential was then applied across the gold coated oxidized silicon substrate (anode) to be coated and the gold coated substrate (cathode) using a 9 V li-ion battery for 18 hours.
  • The substrate used on the positive electrode is shown in the picture in FIG. 5 (top left). Following electrophoretic deposition, an optical micrograph taken on an area of the positive electrode encompassing the uncoated SiO₂ and the gold coated area shows that an hBN coating was only deposited on the conductive gold coated area (FIG. 5 (bottom)). Raman spectra were taken on this area as well. Raman spectra taken from the positive electrode presented in FIG. 6 (top) using a green laser with λ=532 nm exhibit a characteristic peak at 1367 cm⁻¹ that is due to the E_2g phonon mode and is analogous to the G peak in graphene, confirming the presence of uncharged deposited hBN nanosheets. Furthermore, an intensity map of the hBN peak at ˜1367 cm⁻¹ presented in FIG. 6 (bottom left) shows the nanosheets only deposit on to the metallic gold coated part of the electrode (e.g., only in the region of the electric field). Identical measurements from the negative electrode showed no hBN features. This experiment confirms that the dispersed nanosheets are negatively charged. It also highlights that once this charge is lost, the sheets do not re-dissolve but, instead, remain adhered strongly to the electrode.
  • Similar hBN coatings were coated on different substrates including gold coated Si/SiO₂, steel nail, copper foil, steel blade as indicated in the pictures in FIG. 7.
  • FIGS. 8-10 display the scanning electron microscopy (SEM) images of hBN coatings made by electrophoretic deposition on gold coated Si/SiO₂ substrate. The hBN nanosheets lie flat on the substrate and the top layers are transparent to electron beams to see the bottom layers. Different flake sizes can be deposited on substrates by electrophoretic deposition, small (300 nm), large (up to 10 microns) and mixed (from 300 nm up to 10 μm) as represented in the SEM images in FIG. 8, FIG. 9 and FIG. 10, respectively. The thickness of the hBN coating on the conductive substrate can be controlled by time of electrophoretic deposition, concentration of hBN flakes in the hBN suspension, and the voltage applied. FIG. 11 presents a SEM image of a cross section of an hBN coating on copper of approximately 1.5 μm made by electrophoretic deposition. Coatings up to 3.4 μm can be deposited as indicated in the SEM image of a cross section of an hBN coating on a gold coated Si/SiO₂ substrate in FIG. 12 (right).
  • Similar coatings were also deposited on irregular substrates like nickel foam as indicated in the SEM image in FIG. 13.

Example 4: An hBN Anticorrosion Coating on Steel Made by Electrophoretic Deposition

The preparation method of the hBN coating on steel by electrophoretic deposition. The performance of the hBN anticorrosion coating provided by the above examples and are tested on the steel nails as follows:

• • The steel nail with a section containing an hBN anticorrosion coating made by electrophoretic deposition and uncoated section as indicated in the picture in FIG. 14 (insert on top right) was placed in a petri dish containing a concentrated sodium chloride (salt) solution to accelerate the corrosion while observing whether the surface of the steel nail is corroded, and the corrosion condition as indicated in FIG. 14. For comparison bare stainless-steel nails were tested under similar conditions.
  • After 4 hours, the bare surface of the steel nail started getting corroded as indicated by the characteristic brown rust appearance (FIG. 14). Only parts of the steel nail with the hBN coating were not corroded after 4 hours showing good corrosion resistance as indicated in the picture in FIG. 14. The stainless-steel nails were not corroded as expected.

Example 5: An hBN Antioxidation Coating on Copper Made by Electrophoretic Deposition

The preparation method of the hBN coating on copper by electrophoretic deposition. The performance of the hBN antioxidation coating provided by the above examples and are tested on the copper foils as follows:

• • The copper foil with a section coated with an hBN antioxidation coating made by electrophoretic deposition and a bare section was heated in a tube furnace at 400° C. under air flow for 1 hour to accelerate the oxidation and observing whether any surface of the copper foil is oxidized and the oxidation condition.
  • The bare copper surface visually showed extensive coverage of dark colored cuprous oxide (Cu₂O), while very little coverage of the dark Cu₂O was visually observed on the hBN coated copper sections as indicated in the picture in FIG. 15. This result was corroborated by Raman spectroscopy measurements. Intensive Raman signals of Cu₂O vibrational modes were observed from the unprotected Cu sections after heat treatment at 400° C., while very small quantities of cupric oxide (Cu₂O) were observed on the hBN coated section of the copper foil.

Comparative Example 1

This comparative example provides a hBN suspension and a method for preparing the same, differing from Example 2 only in that the hBN suspension does not contain an alkali metal or alkali metal electrides, and was prepared by ultrasonication in air. The other conditions are the same as Example 2.

The preparation method of the hBN suspension comprises the following steps: 2 g of hBN powder was dispersed in 500 ml of dry THF (6 g/L) and this mixture was ultrasonicated using a tip sonicator. After ultrasonication, the suspension was left to stand overnight to allow undispersed hBN aggregates to form and settle at the bottom. The well dispersed suspension containing hBN nanosheets in THF was extracted with a pipette and retained for use as hBN suspension for use in electrophoretic deposition.

The hBN suspension prepared in this example was not stable as it started aggregating after a few minutes.

Comparative Example 2

This comparative example provides a method to deposit an hBN film or coating on an electrically conductive substrate by electrophoretic deposition, differing from Example 3 only in that the hBN suspension prepared in comparative Example 1 was used and the plating was undertaken in air.

The method for preparing hBN film, coating, or membrane on an electrically conductive substrate by electrophoretic deposition comprises the following steps in air: A gold coated oxidized silicon substrate (anode) was immersed into the hBN suspension containing the hBN nanosheets in a glass beaker as indicated in the schematic in FIG. 5 (top right).

Another gold coated substrate (cathode) was immersed into the hBN suspension on the opposite side of gold coated oxidized silicon substrate (anode) to be coated as indicated in the schematic in FIG. 5 (top right).

A 9 V bias potential was then applied across the gold coated oxidized silicon substrate (anode) to be coated and the gold coated substrate (cathode) using a 9 V alkaline battery for 18 hours.

Identical optical imaging, Raman measurements, and SEM imaging from the negative electrode showed no hBN features. This experiment confirms that the dissolved nanosheets should be negatively charged for the electrophoretic deposition to take place.

It should be understood that modifications to the embodiments disclosed herein is made to meet a particular set of design criteria. Therefore, while certain exemplary embodiments of the material and methods of making and using the same have been discussed and illustrated herein, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points.

REFERENCES

The following references are each relied upon and incorporated herein in their entirety.

• 1. Kahn, E. et al. Functional hetero-interfaces in atomically thin materials. Mater. Today (2020) doi: 10.1016/j.mattod.2020.02.021.
• 2. Lei, Y. et al. Graphene and Beyond: Recent Advances in Two-Dimensional Materials Synthesis, Properties, and Devices. (2022) doi: 10.1021/acsnanoscienceau.2c00017.
• 3. Liu, Z. et al. Ultrathin higherature oxidation-resistant coatings of hexagonal boron nitride. Nat. Commun. 4, 1-8 (2013).
• 4. Golberg, D. et al. Boron nitride nanotubes and nanosheets. ACS Nano 4, 2979-2993 (2010).
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• 6. Jo, I. et al. Thermal conductivity and phonon transport in suspended few-layer hexagonal boron nitride. Nano Lett. 13, 550-554 (2013).
• 7. Alam, M. T., Bresnehan, M. S., Robinson, J. A. & Haque, M. A. Thermal conductivity of ultra-thin chemical vapor deposited hexagonal boron nitride films. Appl. Phys. Lett. 104, 1-6 (2014).
• 8. Zheng, J. C. et al. High thermal conductivity of hexagonal boron nitride laminates. 2D Mater. 3, (2016).
• 9. Watanabe, K., Taniguchi, T. & Kanda, H. Direct-bandgap properties and evidence for ultraviolet lasing of hexagonal boron nitride single crystal. Nat. Mater. 3, 404-409 (2004).
• 10. Siria, A. et al. Giant osmotic energy conversion measured in a single transmembrane boron nitride nanotube. Nature 494, 455-458 (2013).
• 11. Dean, C. R. et al. Boron nitride substrates for high-quality graphene electronics. Nat. Nanotechnol. 5, 722-726 (2010).
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• 13. Zhang, J., Tu, R. & Goto, T. Preparation of Ni-precipitated hBN powder by rotary chemical vapor deposition and its consolidation by spark plasma sintering. J. Alloys Compd. 502, 371-375 (2010).
• 14. Gorbachev, R. V. et al. Hunting for monolayer boron nitride: Optical and raman signatures. Small 7, 465-468 (2011).
• 15. Ma, K. Y. et al. Epitaxial single-crystal hexagonal boron nitride multilayers on Ni (111). Nature 606, 88-93 (2022).
• 16. Jiang, H. et al. Boron Nitride Nanosheet Dispersion at High Concentrations. ACS Appl. Mater. Interfaces 13, 44751-44759 (2021).
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Claims

1. A method for preparing a hexagonal boron nitride (hBN) suspension, the method comprising: performing steps of: mixing and dissolving a metal in a solvent to form a mixture, wherein the solvent includes (A) a polar aprotic organic solvent, (A′) a mixture of polar aprotic organic solvents, or (B) ammonia; anddispersing hBN powder containing one or more hBN sheet or exfoliated hBN powder containing one or more hBN sheet in the mixture, wherein the metal provides a counterion to negatively charge the one or more hBN sheet;or;performing steps of: combining hBN powder containing one or more hBN sheet or exfoliated hBN powder containing one or more hBN sheet with a metal to form a mixture, wherein the metal provides a counterion to negatively charge the one or more hBN sheet;applying heat to the mixture to generate a metal-intercalated hBN material; andexposing the metal-intercalated hBN material to a solvent, the solvent including (A) a polar aprotic organic solvent, (A′) a mixture of polar aprotic organic solvents, or (B) ammonia;or;performing steps of: combining hBN powder containing one or more hBN sheet or exfoliated hBN powder containing one or more hBN sheet and a polyelectrolyte to form a mixture;dispersing the mixture in an organic polar aprotic a solvent, the solvent including (A) a polar aprotic organic solvent, (A′) a mixture of polar aprotic organic solvents, or (B) ammonia, wherein the polyelectrolyte adsorbs onto the hBN and to impart a negative charge to the one or more hBN sheet.

2. The method of claim 1, wherein: the metal is one or more alkali metals, one or more alkaline earth metals, one or more alkali metal electrides, one or more alkaline earth metal electrides, or a combination thereof.

3. The method of claim 1, wherein: the metal is Li, K, Na, R, Cs, Fr, Be, Mg, Ca, Ba, Sr, and/or Ra.

4. The method of claim 1, wherein: the counterion is Li+, K+, Na, Rb+, Cs+, Fr+, Be2+, Mg2+, Ca2+, Ba2+, Sr2+, and/or Ra2+.

5. The method of claim 1, wherein: the polyelectrolyte is a nucleic acid, a protein, a teichoic acid, a polypeptides, and/or a polysaccharide.

6. The method of claim 1, wherein: the solvent is tetrahydrofuran (THF), acetone, acetonitrile, dimethoxyethane (DME), sulfolane, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-methylpyrrolidone (NMP), N-methylformamide, acetone, acetonitrile, dichloromethane, dimethylformamide (DMF), dimethylpropyleneurea, and/or ethyl acetate, hexamethylphosphoric triamide.

7. The method of claim 1, wherein: mixing and dispersing occur for a duration within a range from 0 hours to 96 hours;mixing and dispersing occur while the mixture is subjected to a temperature within a range from −22° C. to 220° C.

8. The method of claim 1, wherein: concentration of the exfoliated hBN in the hBN suspension is within a range from 0.01 g/L to 10 g/L.

9. The method of claim 1, further comprising: separating the hBN suspension from the mixture via centrifugation.

10. A method of depositing hexagonal boron nitride (hBN) on a substrate, the method comprising: placing an anode electrode in an environment containing an exfoliated hBN suspension, the exfoliated hBN suspension including one or more negatively charged hBN sheets, the anode comprising the substrate;placing a cathode electrode in the environment;applying a voltage difference across the anode electrode and the cathode electrode;forming, via electrophoretic deposition, a hBN film, coating, and/or membrane on at least a portion of the substrate.

11. The method of claim 10, wherein: the hBN film, coating, and/or membrane is formed directly on a surface of the substrate; and/orthe hBN film, coating, and/or membrane is formed on a layer of material formed on the substrate.

12. The method of claim 11, wherein: the material includes any one or combination of graphene, MoS2, or WS2.

13. The method of claim 10, wherein: the hBN film, coating, and/or membrane is used as an anticorrosion coating, an antioxidation coating, a lubricant coating, an insulating coating, a thermally or electrically conductive coating, a heat dissipation coating, and/or a dielectric coating for the substrate.