JP2018534224A - Integrated monolithic film of highly oriented graphene halide - Google Patents

Abstract

Formula C6ZxOy, wherein Z is a halogen element selected from F, Cl, Br, I, or a combination thereof, x = 0.01-6.0, y = 0-5.0 and x + y ≦ 6 1.0), which is an integrated layer (10 nm to 500 μm) of highly oriented graphene halide. This integrated layer has a halogenated graphene crystal having an interplanar spacing d002 of 0.35 nm to 1.2 nm (more typically 0.4 to 1.0 nm) as measured by X-ray diffraction. The integrated layer includes a plurality of constituent halogenated graphene surfaces that are substantially parallel to each other along one direction, the plurality of constituent halogens having an average deviation angle of these halogenated graphene surfaces that is less than 10 degrees. It has a graphene surface.

Description

  The present invention relates generally to the field of graphene materials, and is particularly composed of a plurality of originally separated halogenated graphene sheets or molecules that are oriented and chemically coalesced and integrated together to form a monolith monolith. The present invention relates to a novel form of a halogenated graphene film.

  Carbon has five unique crystal structures including diamond, fullerene (0D nanographite material), carbon nanotube or carbon nanofiber (1D nanographite material), graphene (2D nanographite material) and graphite (3D graphite material) It is known. Carbon nanotube (CNT) refers to a tubular structure grown in single or multiple layers. Carbon nanotubes (CNT) and carbon nanofibers (CNF) have a diameter on the order of several nanometers to several hundred nanometers. These longitudinal hollow structures impart unique mechanical, electrical and chemical properties to the material. CNT or CNF is a one-dimensional nanocarbon or 1D nanographite material.

  Graphene surface of graphite microcrystals in natural graphite particles or artificial graphite particles can obtain individual graphene sheets of carbon atoms by exfoliation and extraction or isolation, provided that interplane van der Waals forces can be overcome Can do. Isolated graphene sheets of individual carbon atoms are commonly referred to as single layer graphene. A stack of a plurality of graphene surfaces bonded by van der Faels force in the thickness direction with a graphene surface interval of about 0.3354 nm is generally called multilayer graphene. Multi-layer graphene platelets have up to 300 graphene faces (<100 nm thickness), but more typically up to 30 graphene faces (<10 nm thickness), even more typically up to 20 It has a graphene surface (<7 nm thickness), most typically up to 10 graphene surfaces (commonly referred to in the scientific community as multi-layer graphene). Single layer graphene and multilayer graphene or graphene oxide sheets are collectively referred to as “nanographene platelets” (NGP). Graphene or graphene oxide sheets / platelets (collectively NGP) is a new type of carbon nanomaterial (2D nanocarbon) that is distinct from 0D fullerene, 1D CNT and 3D graphite.

  Our research group was a pioneer in the development of graphene materials and related manufacturing methods in 2002: (1) B. Z. Jang and W.W. C. Huang, “Nano-scaled Graphene Plates”, US Pat. No. 7,071,258 (07/04/2006), filed Oct. 21, 2002; Z. Jang et al., “Process for Producing Nano-scaled Graphene Plates”, US Patent Application No. 10 / 858,814 (06/03/2004); Z. Jang, A.M. Zhamu, and J.A. Guo, “Process for Producing Nano-scaled Platelets and Nanocomposites”, US patent application Ser. No. 11 / 509,424 (08/25/2006).

As shown in FIG. 5 (A) (process flow chart) and FIG. 5 (B) (schematic diagram), isolated or separated graphene or graphene oxide sheets (NGP) are typically incorporated into natural graphite particles. It is obtained by intercalating a strong acid and / or an oxidizing agent to obtain a graphite intercalation compound (GIC) or graphite oxide (GO). The presence of chemical species or functional groups in the interstitial space between the graphene surfaces serves to increase the graphene spacing (d ₀₀₂ , measured by X-ray diffraction), and in other cases in the c-axis direction The van der Waals forces that maintain the graphene surfaces along each other are greatly reduced. GIC or GO most often converts natural graphite powder (20 in FIG. 5 (A) and 100 in FIG. 5 (B)) to sulfuric acid, nitric acid (oxidant) and another oxidant (eg, potassium permanganate or Manufactured by dipping in a mixture of sodium perchlorate). The resulting GIC (22 or 102) is actually some kind of graphite oxide (GO) particle. The excess of acid is then removed by repeated washing and rinsing of the GIC or GO in water to provide a suspension or dispersion of graphite oxide containing individual visually recognizable graphite oxide particles dispersed in water. The body is obtained. After this rinsing step, there are two processing paths.

  Path 1 includes removing water from the suspension to obtain “expandable graphite” that is substantially a mass of dry GIC or dry graphite oxide particles. When expansive graphite is exposed to temperatures typically in the range of 800 to 1,050 ° C. for about 30 seconds to 2 minutes, the GIC undergoes a rapid volume expansion of 30 to 300 times, resulting in a “graphite worm” (24 or 104), which are aggregates of still interconnected graphite flakes that are each exfoliated but not largely separated. An SEM image of the graphite worm is shown in FIG.

  In path 1A, these graphite worms (exfoliated graphite or “interconnected / non-isolated graphite flake network”) are recompressed to typically 0.1 mm (100 μm) to 0.5 mm (500 μm). ) A flexible graphite sheet or foil (26 or 106) having a thickness in the range of. Alternatively, the graphite worm is simply destroyed for the purpose of producing so-called “expanded graphite flakes” (108) containing graphite flakes or platelets that are largely over 100 nm thick (and therefore not nanomaterials by definition). You can choose to use a low-strength air mill or shear.

  Exfoliated graphite worms, expanded graphite flakes, and masses of recompressed graphite worms (commonly referred to as flexible graphite sheets or flexible graphite foils) are all 1D nanocarbon materials (CNT or CNF) and 2D nanocarbon materials ( It is a 3D graphite material that is fundamentally different from and distinct from any graphene sheet or platelet, NGP). Flexible graphite (FG) foil can be used as a heat spreader material, but typically has a maximum in-plane thermal conductivity of less than 500 W / mK (more typically <300 W / mK) and 1, The in-plane electrical conductivity is 500 S / cm or less. These low conductivity values indicate that many defects, wrinkled or folded graphite flakes, interruptions or gaps between graphite flakes and non-parallel flakes (eg, many flakes from the desired orientation direction> FIG. 6 is a direct result of the SEM image of FIG. 6B tilted at an angle deviating by 30 °. Many flakes are tilted with respect to each other at a very large angle (eg, 20-40 degrees misorientation). The average deviation angle is greater than 10 °, more typically> 20 °, and often> 30 °.

  In path 1B, as disclosed in our US patent application Ser. No. 10 / 858,814, separate single and multilayer graphene sheets (collectively referred to as NGP, 33 or 112) To form, high strength mechanical shear is applied to exfoliated graphite (eg, a sonicator, high shear mixer, high strength air jet mill or high energy ball mill is used). Single layer graphene can be as thin as 0.34 nm, while multilayer graphene can have a thickness of up to 100 nm, but more typically less than 20 nm.

  Path 2 requires ultrasonic treatment of the graphite oxide suspension for the purpose of separating / isolating individual graphene oxide sheets from the graphite oxide particles. This is because the distance between graphene surfaces is increased from 0.3354 nm in natural graphite to 0.6-1.1 nm in highly oxidized graphite oxide, greatly increasing the van der Waals forces that maintain adjacent surfaces together. Is based on the perception that The ultrasonic power may be sufficient to further separate the sheet of graphene surfaces to form a separated, isolated or individual graphene oxide (GO) sheet. Next, these graphene oxide sheets are typically 0.001 wt% to 10 wt%, more typically 0.01 wt% to 5 wt%, most typically less than 2 wt% It can be chemically or thermally reduced to obtain “reduced graphene oxide” (RGO) having an oxygen content.

  For purposes of defining the claims of this application, graphene or NGP includes individual (isolated or separated) sheets / platelets of single-layer and multilayer pristine graphene, graphene oxide or reduced graphene oxide (RGO) . Pristine graphene has substantially 0% oxygen. RGO typically has an oxygen content of 0.001% to 5% by weight. Graphene oxide (including RGO) can have 0.001 wt% to 50 wt% oxygen.

  Isolated solid NGP (ie, separate separate sheets / platelets of pristine graphene, GO and RGO with typical length / width of 100 nm to 10 μm) can be macroscopically, for example, by using a papermaking process When sized films, membranes or paper sheets (34 or 114 in FIG. 5A or FIG. 5B) are typically filled with high thermal conductivity as an example of useful physical properties Does not show rate. This is mainly due to the idea that these sheets / platelets are typically poorly oriented and many types of defects are formed in the film / film / paper. In particular, paper-like structures or mats made from graphene, GO, or RGO platelets (eg, paper sheets made by vacuum assisted filtration methods) have many defects, wrinkles formed or folded graphene sheets , Showing interruptions or gaps between platelets and non-parallel platelets (eg, SEM image of FIG. 7B), thereby providing relatively poor thermal conductivity, low electrical conductivity, low breakdown strength and Low structural strength results. These paper-like structures or aggregates of individual NGP, GO or RGO platelets alone (no resin binder) also have a tendency to flake off, and conductive particles are released into the air, but with a binder resin present , The decrease in conductivity of the structure is greatly reduced.

Graphene thin films (<5 nm and most typically <2 nm) can be made by catalytic chemical vapor deposition CVD of a hydrocarbon gas (eg, C ₂ H ₄ ) on a Ni or Cu surface. By using Ni or Cu as a catalyst, carbon atoms obtained by decomposition of hydrocarbon gas molecules at 800 to 1,000 ° C. are deposited on the surface of the Ni or Cu foil to form a single layer or several layers of polycrystalline material. A sheet of graphene (in this case, 2-5 layers) is formed. These ultra-thin graphene films are optically transparent and electrically conductive and are intended for applications such as touch screens (used in place of indium tin oxide or ITO glass) or semiconductor devices (used in place of silicon Si) The Ni or Cu catalyzed CVD processes are not suitable for the deposition of more than 5-10 graphene surfaces (typically <5 nm, more typically <2 nm), beyond which the underlying Ni Or Cu catalyst can no longer obtain a catalytic effect. There is no experimental evidence to show that CVD graphene films with a thickness greater than 5 nm are possible. Furthermore, the CVD process is known to be very expensive.

  From the viewpoint of semiconductor physics, on the other hand, a multilayer graphene sheet becomes a metal or a conductor, and a single layer graphene sheet becomes a semimetal. Single-layer pristine graphene is classified as a semi-metal because there is no energy band gap because its valence band and conduction band are in contact with each other (in contrast, semiconductor Si has its electron configuration) Has an energy band gap of 1.1 eV between the conduction band and the valence band. The absence of a band gap limits the use of graphene in modern electronic devices. The band structure of single-layer graphene can be modified to widen the band gap by many methods, such as halogenation, oxidation, hydrogenation or non-covalent bonding of various molecules and species.

  On the other hand, highly oxidized graphene or graphene oxide (GO) is considered an insulating material and can possibly be used as a dielectric. However, this is a drawback because of the low thermal stability (with respect to heat exposure) of GO, its dielectric resistivity is reduced and heat treatment steps are often used during the manufacture of electronic devices. Furthermore, multi-layer pristine graphene (> 3 layers) and reduced graphene oxide (RGO) are conductors that cannot be substantially used as dielectric materials and insulating materials. An example of this is shown in FIG.

  Dielectric materials have received much attention due to their potential use in gate dielectrics, dynamic random access memories, artificial muscles and energy storage devices. A dielectric (ceramic) capacitor for energy storage has problems of low workability (for example, processing temperature is usually higher than 1,000 ° C.), high density and low dielectric breakdown strength. Conventional high dielectric perovskite ceramics such as barium titanate-containing composites cannot be used in situations where various shapes are required. Compared to inorganic ceramics, polymers are more suitable in higher electric fields. Furthermore, polymers have the advantages of light weight, low cost, ease of processing and self-healing over inorganic ceramics. However, the low operating temperature limits the further development of polymer dielectrics. Commercially available capacitors are only used in limited applications such as cell phones, video / audio systems and personal computers. For example, biaxially oriented polypropylene polymer capacitors can only operate at temperatures below 105 ° C. Thus, materials with high dielectric constants, especially materials that can be used in high temperature environments, can be large in device applications.

In view of these shortcomings of current dielectric materials, the inventors have investigated the possibility of using graphene-derived materials for dielectric applications. After thorough and extensive research, the inventors have surprisingly discovered that halogenated graphene materials with a thickness greater than 10 nm are good dielectric materials. Halogenated graphene is a group of graphene derivatives in which some carbon atoms are covalently bonded to halogen atoms. The carbon atom bonded to the halogen has sp ³ hybridization, and the other carbon atom has sp ² hybridization. This indicates that halogenated graphene (also called halogenated graphene) can be an insulating material in some cases. For this purpose, a thicker halogenated graphene film (> 10 nm, preferably> 100 nm, more preferably> 1 μm, more preferably> 10 μm) is desirable. However, ultra thin films of graphene fluoride (eg, << 10 nm) are manufactured by fluorination after contact CVD preparation of pristine graphene, but have a combination of desirable physical and chemical properties Thicker fluorinated graphene films are not available. While most current devices are required to have thicker dielectric components, it is known in the art that thicker dielectric materials (thicker than 5-10 nm) tend to have low breakdown strength. It has been.

US Pat. No. 7,071,258 US patent application Ser. No. 10 / 858,814 US patent application Ser. No. 11 / 509,424

  Therefore, the object of the present invention is the cost to produce a thicker film of graphene-derived material exhibiting high breakdown strength, high dielectric constant, sufficient mechanical strength, good thermal stability and good chemical stability. It is to provide a highly effective method.

The present invention provides a method for producing a highly oriented halogenated graphene sheet or an integrated layer of molecules, the film having a thickness of 10 nm to 500 μm. The method comprises the steps of: (a) preparing either a graphene oxide dispersion having a graphene oxide sheet dispersed in a fluid medium or a graphene oxide gel having graphene oxide molecules dissolved in the fluid medium, A graphene oxide sheet or graphene oxide molecule containing an amount of oxygen greater than 5% by weight; and (b) providing a layer of graphene oxide dispersion or graphene oxide gel on the surface of the support substrate under shear stress conditions and A step of depositing, wherein the feeding and depositing procedure is a thinning induced by shearing of a graphene oxide dispersion or gel to form a wet layer of graphene oxide on a support substrate, and a graphene oxide sheet or molecule including orientation and induced by shear, step _{a; (c) C 6 Z x} O y formula ( Z is a halogen element selected from F, Cl, Br, I or a combination thereof, and x = 0.01 to 6.0, y = 0 to 5.0, and x + y ≦ 6.0 (I) a halogenating agent is introduced into the wet layer of graphene oxide and a chemical reaction between the halogenating agent and the graphene oxide sheet or molecule Forming a wet layer of graphene halide, and removing the fluid medium from the wet layer of graphene halide, or (ii) removing the fluid medium from the wet layer of graphene oxide to dry the graphene oxide dry layer And introducing a halogenating agent into the dry layer of graphene oxide and causing a chemical reaction between the halogenating agent and the graphene oxide sheet or molecule And (d) removing the fluid medium from the wet layer of graphene halide and measuring 0.35 nm to 1.2 nm (preferably 0.40 to 1.0 nm, more preferably, as measured by X-ray diffraction). And forming an integrated layer of halogenated graphene having an interplanar spacing d _{002 (} typically 0.40 nm to 0.90 nm). In contrast to the original natural graphite, which is typically 0.3359 nm, an interplanar spacing in the range of 0.350 to 1.0 nm is a halogen element or halogen-containing chemical group (one In the case of part, it can be noted that in addition to this, some residual O or O-containing groups) exist on the graphene surface.

With regard to the timing sequence, it can be noted that the halogenating agent can be introduced before, during or after removal of the liquid medium from the wet layer of GO.
In one preferred embodiment, the integrated layer of oriented halogenated graphene, having y = 0 and x = from 0.01 to 6.0 (oxygen is completely removed) Formula _C 6 _Z x _{O y.} In another preferred embodiment, the monolayer of oriented halogenated graphene has the formula C ₆ Z _x O _y with y = 0.1 and x = 0.1-5.0 (having a low oxygen content) Have

  The halogenated graphene sheets in the dry integrated layer of graphene halide are substantially parallel to each other along one direction, and the average deviation angle of these sheets is less than 10 degrees. It should be noted that in papers based on conventional GO or RGO sheets, the graphene sheets or platelets are tilted with respect to each other at a very large angle (eg 20-40 degree misorientation). it can. The average deviation angle from the desired orientation angle is greater than 10 °, more typically> 20 °, and often> 30 °.

The inventors have discovered that the electrical and dielectric properties of GO films rapidly deteriorate when the temperature of aging or heat treatment exceeds 100 ° C. For example, if a GO film is exposed to 200 ° C. heat for several hours, the electrical resistivity may drop from 10 ⁻⁶ Ω-cm to 10 ⁺² Ω-cm, which is 8 orders of magnitude of resistivity. The GO becomes a dielectric material that is completely useless. In contrast, the highly oriented halogenated graphene integrated film C ₆ Z _x O _y according to the present invention can be thermally stable up to 1000-2,500 ° C. depending on the chemical composition. Higher maximum useful temperatures are obtained with higher x values or higher x / (y + x) ratios. When x = 1, the thermal stability temperature can be as high as 2,000-2,500 ° C.

  It has been found that the integrated film according to the present invention typically has a tensile strength of 60 MPa to 140 MPa and a tensile modulus of 3.0 to 12 GPa. Surprisingly, they have a high structural integrity.

In certain embodiments, with respect to timing, step (b) can occur during or after step (b). Therefore, the present invention is a step of preparing either (a) a graphene oxide dispersion having a graphene oxide sheet dispersed in a fluid medium or a graphene oxide gel having graphene oxide molecules dissolved in a fluid medium. The graphene oxide sheet or graphene oxide molecule contains an amount of oxygen exceeding 5% by weight; and (b) introducing a halogenating agent into the graphene oxide dispersion or gel, and the halogenating agent; A step of generating a chemical reaction with the graphene oxide sheet or molecule to form a dispersion of halogenated graphene sheet or a gel of halogenated graphene molecule, wherein the halogenated graphene sheet is C ₆ Z _x O _y of formula (wherein, Z is, F, Cl, Br, from I, or a combination thereof And (c) a supporting group under shear stress conditions, wherein x is from 0.01 to 6.0, y is from 0 to 5.0, and x + y is 6.0. Supplying and depositing a layer of the halogenated graphene dispersion or gel on the surface of the material, the supplying and depositing procedure for forming a wet layer of halogenated graphene on the support substrate Thinning induced by shearing of the halogenated graphene dispersion or gel and orientation induced by shearing of the halogenated graphene sheet or molecules; and (d) the flow from a wet layer of halogenated graphene by removing the medium, form an integral layer of the halogenated graphene having a plane spacing _{d 002} of 0.35nm~1.2nm when measured by X-ray diffraction Method comprising the steps of also provided.

  Further, the halogenated graphene sheets in the dry integrated layer of graphene halide are substantially parallel to each other along one direction, and the average deviation angle of these sheets is less than 10 degrees. After some degree of aging, the integrated layer is a plurality of constituent halogenated graphene surfaces that are substantially parallel to one another along one direction, and these layers are less than 10 degrees (more typically less than 5 degrees). It has a plurality of constituent halogenated graphene surfaces having an average deviation angle of the halogenated graphene surface.

  In various embodiments, the starting graphene oxide sheet contains single layer graphene oxide or several layers of graphene oxide sheets each having 2 to 10 graphene oxide surfaces. The fluid medium may be water, alcohol, a mixture of water and alcohol, or an organic solvent.

The fluorinating agent preferably contains a liquid, gaseous or plasma species containing a halogen element selected from F, Cl, Br, I or combinations thereof. In certain embodiments, the fluorinating agent contains a liquid, gaseous or plasma species that contains a halogen element selected from F, Cl, Br, I, or combinations thereof. In a particularly preferred embodiment, the fluorinating agent is hydrofluoric acid, hexafluorophosphoric acid or HPF ₆ , XeF ₂ , F ₂ gas, F ₂ / Ar plasma, CF ₄ plasma, SF ₆ plasma, HCl, HPCl ₆ , XeCl ₂ , Cl ₂ gas, Cl ₂ / Ar plasma, CCl ₄ plasma, SCl ₆ plasma, HBr, XeBr ₂ , Br ₂ gas, Br ₂ / Ar plasma, CBr ₄ plasma, SBr ₆ plasma, HI, XeI ₂ , I ₂ , I ₂ / Ar plasma, CI ₄ plasma, SI ₆ plasma or combinations thereof.

  The feeding and deposition steps can include printing, spraying, coating and / or casting procedures combined with shear stress procedures. The coating method can include slot die coating or comma coating procedures. More preferably, the feeding and deposition steps comprise a reverse roll transfer coating procedure.

  In one preferred variant of the reverse roll transfer coating process, the feeding and deposition steps comprise applying a layer of graphene oxide dispersion or graphene oxide gel onto the surface of a coating roller that rotates at a first linear velocity in a first direction. Providing a support film in which a coating roller is driven at a second linear velocity in a second direction opposite to the first direction, wherein the coating roller includes supplying a graphene oxide applicator layer And a wet layer of graphene oxide is formed on the support film. The support film can be driven by a reverse support roller that is disposed at a working distance from the application roller and rotates in a second direction opposite to the first direction.

  The speed ratio defined as (the second linear velocity) / (the first linear velocity) is preferably 1/5 to 5/1, more preferably more than 1/1 and less than 5/1. It is. When the outer surface of the coating roller moves at the same speed as the linear movement speed of the support film, the speed ratio is 1/1 or 1. As an example, when the outer surface of the coating roller moves at a speed three times the linear moving speed of the support film, the speed ratio is 3/1. In some embodiments, the speed ratio is greater than 1/1 and less than 5/1. Preferably, the speed ratio is greater than 1/1 and not greater than 3/1.

  In some embodiments, supplying the graphene oxide dispersion or graphene oxide gel onto the surface of the application roller comprises using a metering roller and / or a doctor blade to apply a graphene oxide of the desired thickness on the surface of the application roller. Forming an applicator layer. The method can include manipulating 2, 3 or 4 rollers.

  In a preferred embodiment, the support film is driven by a reversing support roller that is disposed at a working distance from the application roller and rotates in a second direction opposite to the first direction. The speed at the outer surface of the support roller determines the second linear velocity (of the support film). Preferably, the support film is supplied from a feed roller, and the dried layer of halogenated graphene supported by the support film is wound on a take-up roller, and the method is performed in a roll-to-roll manner.

  Preferably, the method according to the present invention comprises a graphene oxide wetting after step (b) in an aging chamber of 25 ° C. to 100 ° C. and a humidity level of 20% to 99% over an aging time of 1 hour to 7 days. The method further includes aging the layer, aging the wet graphene halide layer after step (c), or aging the monolithic halogenated graphene layer after step (d). The method can further include a compression step during or after step (d) to reduce the thickness of the integral layer.

In the method of the present invention, an integrated layer of oriented graphene halide is heat-treated for a desired length of time at a first heat treatment temperature of more than 100 ° C. but not more than 3,200 ° C. The method may further comprise the step (e) of producing a graphite film having a spacing d ₀₀₂ and a total oxygen / halogen content of less than 1 wt%. The method can further include a compression step during or after the heat treatment step to reduce the thickness of the graphite film.

  In the method according to the present invention, the graphene oxide sheet in the graphene oxide dispersion preferably occupies a weight fraction of 0.1% to 25% based on the total weight of the graphene oxide sheet and the liquid medium. More preferably, the graphene oxide sheet in the graphene oxide dispersion occupies a weight fraction of 0.5% to 15%. In some embodiments, the graphene oxide sheet occupies a weight ratio of 3% to 15% based on the total weight of the graphene oxide sheet and the liquid medium. In some embodiments, the graphene oxide dispersion or graphene oxide gel has greater than 3 wt% graphene oxide dispersed in a fluid medium to form a liquid crystal phase.

  The graphene oxide dispersion or graphene oxide gel of the present invention is a reaction vessel at a reaction temperature at a reaction temperature for a time sufficient to obtain the graphene oxide dispersion or the graphene oxide gel. The graphite material can be prepared by immersing in an oxidizing liquid, natural graphite, artificial graphite, intermediate phase carbon, intermediate phase pitch, mesocarbon microbeads, soft carbon, hard carbon, coke, carbon fiber , Carbon nanofibers, carbon nanotubes or combinations thereof.

  The graphene oxide dispersion or graphene oxide gel of the present invention can be obtained from a graphite material having the largest original graphite grain size, and the resulting halogenated graphene film is larger than this largest original grain size. It is a polycrystalline graphene structure having a large crystal grain size. This larger grain size is due to the thermal treatment of GO sheets, GO molecules, halogenated molecules or halogenated sheets, chemical linking and coalescence of graphene oxide / halogenated graphene sheets or graphene oxide / halogenated graphene molecules in an edge-to-edge manner. Or by the idea of inducing chemical bonds. It can be noted that such a connection between edges greatly increases the length or width of the graphene sheet or molecule. For example, when a halogenated graphene sheet having a length of 300 nm is combined with a halogenated graphene sheet having a length of 400 nm, a sheet having a length of about 700 nm can be obtained as a result. Such coalescence between edges of a plurality of halogenated graphene sheets makes it possible to produce a graphene film having a huge crystal grain size that could not be obtained by other methods.

  In one embodiment, the graphene oxide dispersion or graphene oxide gel is obtained from a graphite material having a plurality of graphite microcrystals that do not exhibit a preferred crystal orientation as measured by X-ray diffraction or electron diffraction, and results The obtained halogenated graphene film has a single-crystal or polycrystalline graphene structure having a preferred crystal orientation when measured by the X-ray diffraction method or the electron diffraction method.

  Any coating procedure capable of generating shear stress on a GO sheet or halogenated GO sheet can be performed with the method according to the invention, for example slot die coating, comma coating and reverse roll transfer coating can be performed. . The reverse roll procedure arranges GO sheets or GO molecules themselves along a particular direction (eg, X or length direction) or two particular directions (eg, X and Y directions or length and width directions). In particular, it is particularly effective for enabling a preferred orientation to be formed. Even more surprising, during the subsequent heat treatment of the GO layer, these preferred orientations are maintained and in many cases further improved. Most surprisingly, such a preferred orientation is very high insulation along the desired direction of the resulting halogenated graphene film (even in the case of thick films, for example from 10 nm to> 500 μm). It is important to finally obtain the breaking strength, dielectric constant, elastic modulus and tensile strength. During the coating or casting process, except for the method based on the reverse roll procedure according to the present invention, the thickness of the coated or cast film (layer) is not too thick (for example, more than 50 μm), and other methods are highly advanced The orientation of the GO or halogenated sheet cannot be realized. In general, conventional casting or comma coating processes result in a dry layer of graphene oxide having a thickness of 50 μm or less, more typically 20 μm or less, and most typically 10 μm or less when dried. The coated or cast film (wetting layer) needs to be thin enough. With extensive and thorough experimental studies, we expect the reverse roll procedure to be effective in this way to achieve and maintain a highly favorable orientation, even for very thick films. It came to recognize without.

An integrated layer of oriented halogenated graphene produced according to the present invention typically exceeds 4.0 (more typically more than 5.0 and many more) when measured at a layer thickness of 100 nm. In some cases greater than 10 or even greater than 15 dielectric constant, typically between 10 ⁸ Ω-cm and 10 ¹⁵ Ω-cm and / or greater than 5 MV / cm (more typically 10 MV) / Breakdown voltage, in some cases exceeding 12 MV / cm, and in other cases further exceeding 15 MV / cm).

  The present invention also provides a microelectronic device containing an integrated layer of halogenated graphene as a dielectric component.

This new class of materials (ie, highly oriented GO-derived halogenated graphene film GOGH) has the following characteristics that distinguish it from individual graphene / GO / RGO / GH sheets / platelet paper / film / film layers: Have:
(1) This GOGH film is an integrated halogenated graphene (GH) element that is a polycrystalline structure composed of a plurality of well-arranged and interconnected grains having a very large grain size. In HOGH, all graphene planes in all crystal grains are oriented substantially parallel to each other (that is, the crystallographic c-axis of all crystal grains is directed substantially in the same direction).

  (2) Using the reverse roll procedure, very high orientations of GH platelets can be achieved not only for thin films but also for thick films (> 10 nm). For the same thickness, the reverse roll procedure allows for higher orientation and higher crystal integrity.

  (3) GOGH is not a simple aggregate or laminate of multiple individual platelets of graphene / GO / RGO / GH (halogenated graphene), but identifiable or individual flakes obtained from the original GO sheet / Integrated graphene elements that do not contain platelets. These originally individual flakes or platelets are chemically bonded or linked together to form larger grains (grain size is larger than the original platelet / flake size).

  (4) This GOGH is not manufactured by bonding individual flakes or platelets to each other using a binder or adhesive. Instead, under selected aging or heat treatment conditions, well-aligned GO / GH sheets or GO / GH molecules chemically coalesce with each other primarily in an edge-to-edge fashion to form large 2D graphene grains However, it can optionally be combined with adjacent GO / GH sheets below or above to form a 3D network of graphene chains. Linking each other or forming a covalent bond results in a graphene element in which the GO / GH sheets are bonded and integrated without the use of externally applied linkers or binder molecules or polymers.

(5) This GOGH, which is a polycrystal having substantially the same crystallographic c-axis on all the graphene surfaces, is obtained from GO, and this GO originally has a plurality of graphite crystallites randomly oriented. It can be obtained by moderate or vigorous oxidation of natural graphite or artificial graphite particles, respectively. With an oxidation time long enough to be chemically oxidized to a GO dispersion (moderate to vigorous oxidation of graphite) or GO gel (fully separated GO molecules dissolved in water or another polar liquid) These starting or original graphite microcrystals have an initial length (L _{a in the} crystallographic a-axis direction), an initial width (L _{b in the} b-axis direction) and a thickness (c Axis L _c ). The resulting GOGH typically have a much greater length or width than L _a and L _b of the original graphite crystallites.

  (6) The method for producing this monolithic monolithic layer of highly oriented GH can be performed on a continuous roll-to-roll basis and is therefore scalable and cost-effective.

It is the schematic of the GO / GH layer transfer apparatus based on the reverse roll for manufacturing a highly oriented GO / GH film. FIG. 2 is a schematic view of a GO / GH layer transfer apparatus based on another reverse roll for producing a highly oriented GO / GH film. FIG. 6 is a schematic view of a GO / GH layer transfer apparatus based on yet another reverse roll for producing a highly oriented GO / GH film. FIG. 6 is a schematic view of a GO / GH layer transfer apparatus based on yet another reverse roll for producing a highly oriented GO / GH film. (A) shows various prior art methods for producing exfoliated graphite products (flexible graphite foil and flexible graphite composite material) and pyrolytic graphite (lower part), producing graphene oxide gel or GO dispersion. It is a flowchart shown with a method. (B) is a schematic diagram showing a method for producing conventional paper, mat, film and membrane of simply agglomerated graphite or NGP flakes / platelets. All methods begin with intercalation and / or oxidation treatment of graphite material (eg, natural graphite particles). (A) is an SEM image of a graphite worm sample after thermal exfoliation of graphite intercalation compound (GIC) or graphite oxide powder. (B) is an SEM image of a cross section of a flexible graphite foil, showing many graphite flakes with an orientation that is not parallel to the surface of the flexible graphite foil, and many defects, twisted or folded Flakes are also shown. (A) is an SEM image of a GO-derived film, in which a plurality of graphene surfaces (having an initial length / width of 30 nm to 300 nm in the original graphite particles) are oxidized, peeled off, reoriented, and seamlessly Combined into a continuous length graphene sheet or layer that can continue with a width or length of tens of centimeters (only 50 μm width of a 10 cm wide graphite film is shown in this SEM image) . (B) is a SEM image of a cross section of a conventional graphene paper / film made from individual graphene sheets / platelets using a papermaking process (eg, vacuum assisted filtration). This image shows that many individual graphene sheets are folded or interrupted (not integrated) and the orientation is not parallel to the film / paper surface and many defects or defects Has a complete part. (C) is a schematic diagram and an accompanying SEM image showing a method of forming HOGF composed of a plurality of graphene surfaces that are parallel to each other and chemically bonded in the thickness direction or the crystallographic c-axis direction. (D) is one of the possible chemical coupling mechanisms (only two GO molecules are shown as an example, and many GO molecules are chemically coupled to each other to form a graphene layer) it can). It is the dielectric breakdown strength of GO films, GO-derived graphene fluoride films (produced by reverse roll transfer coating method) and polyimide films plotted as a function of film thickness. GO-derived fluorinated graphene film and chlorinated graphene film (both reverse roll transfer procedures) plotted as a function of degree of fluorination (atomic ratio F / (F + O)) or degree of chlorination (atomic ratio Cl / (Cl + O)) And the dielectric breakdown strength produced by the casting procedure). GO derived fluorinated graphene film (made by reverse roll transfer procedure) and GO-made fluorination made by conventional paper making procedure (vacuum assisted filtration) plotted as a function of degree of fluorination with respect to atomic ratio F / (F + O) It is the dielectric breakdown strength of graphene paper. It is a dielectric constant of GO-derived fluorinated graphene film and brominated graphene film plotted as a function of the degree of fluorination (atomic ratio F / (F + O)) or the degree of bromination (atomic ratio Br / (Br + O)).

A method for producing a highly oriented halogenated graphene sheet or an integrated layer of molecular monolith (single material or single phase) is provided, wherein the film has a thickness of 10 nm to 500 μm. The halogenated graphene is a chemical formula of C ₆ Z _x O _y (wherein Z is a halogen element selected from F, Cl, Br, I, or a combination thereof, and x = 0.01 to 6.0) Y = 0-5.0 and x + y ≦ 6.0). The production of this integrated layer starts with graphene oxide (GO) in the form of a suspension (dispersion) or gel. In particular, the method prepares either (a) a graphene oxide (GO) dispersion having a graphene oxide sheet dispersed in a fluid medium or a graphene oxide gel having graphene oxide molecules dissolved in the fluid medium. Step, wherein the graphene oxide sheet or graphene oxide molecules exceeds 5% by weight (typically 5% to 46%, but preferably 10% to 46%, more preferably 20% to 46%) oxygen Start with a step containing the amount.

  This is followed by supplying and depositing a layer of graphene oxide dispersion or graphene oxide gel on the surface of the supporting substrate under shear stress conditions, wherein the supplying and depositing procedure oxidizes on the supporting substrate. Step (b) is carried out comprising thinning induced by shearing of the graphene oxide dispersion or gel to form a wet layer of graphene and orientation induced by shearing of the graphene oxide sheet or molecules. This step includes or is followed by spraying, printing, extruding the wet phase of GO onto a solid substrate surface (eg, PET film, Al foil, glass surface, etc.) that includes or is followed by a shear procedure. Including molding, casting and / or coating. The presence of shear stress is important to align the GO sheets or molecules along the desired direction.

Next, step (c) of the third step is performed to chemically replace the O or oxygen-containing functional group with a halogen element or halogen-containing group. In the present specification, halogen means F, Cl, Br, I or a combination thereof. Therefore, this step (c) introduces a halogenating agent into the wet layer of graphene oxide and causes a chemical reaction between the halogenating agent and the graphene oxide sheet or molecule to produce C ₆ Z _x O _y. Wherein Z is a halogen element selected from F, Cl, Br, I or a combination thereof, x = 0.01 to 6.0, y = 0 to 5.0 and x + y ≦ 6 . Is accompanied by forming a wet layer of halogenated graphene. The fluorinating agent can contain a liquid, gaseous or plasma species containing a halogen element selected from F, Cl, Br, I or combinations thereof. Halogenated graphene is a group of graphene derivatives in which some carbon atoms are covalently bonded to halogen atoms. The carbon atom bonded to the halogen has sp ³ hybridization, and the other carbon atom has sp ² hybridization. The physical and chemical properties of halogenated graphene (also described as halogenated graphene) are strongly dependent on the degree of halogenation.

Next, following step (c), the flowing medium is removed from the wet layer of graphene halide and the halogenation has an interplanar spacing d _{002 of} 0.35 nm to 1.2 nm as measured by X-ray diffraction. Step (d) of forming an integrated layer of graphene is performed. The removal of the liquid fluid can take place before, during or after the halogenation reaction.

To perform the halogenation reaction, for example, a hydrofluoric acid or hexafluorophosphoric acid (HPF ₆ ) liquid can be injected into the GO suspension or GO gel stream before, during or after the feed / deposition stage. it can. Alternatively, F ₂ gas, Cl ₂ gas, Br ₂ gas and / or I ₂ gas (vapor) is introduced into the chamber containing the wet GO layer to allow the halogen gas molecules to penetrate into the wet GO layer, Can react with GO inside and above. Alternatively, one can choose to remove the liquid medium from the wet layer of GO to form a dry layer of GO and then introduce a halogenating agent to react with GO. The dried layer of GO can preferably be treated with a halogen-containing gas or plasma.

In particular, the fluorinating agent is hydrofluoric acid, hexafluorophosphoric acid or HPF ₆ , XeF ₂ , F ₂ gas, F ₂ / Ar plasma, CF ₄ plasma, SF ₆ plasma, HCl, HPCl ₆ , XeCl ₂ , Cl ₂ gas, Cl ₂ / Ar plasma, CCl ₄ plasma, SCl ₆ plasma, HBr, XeBr ₂ , Br ₂ gas, Br ₂ / Ar plasma, CBr ₄ plasma, SBr ₆ plasma, HI, XeI ₂ , I ₂ , I ₂ / Ar plasma, CI ₄ plasma, SI ₆ plasma, or combinations thereof.

  A highly preferred delivery and deposition procedure is a reverse roll transfer coating that inherently induces high shear stress in the suspension or gel coated on the roller. As schematically illustrated in FIG. 1 as a preferred embodiment, a method for producing a monolithic monolithic layer of highly oriented graphene halide (HOGH) is a graphene oxide dispersion (GO dispersion) fed to a trough 208. ) Or the preparation of graphene oxide gel (GO gel). The rotational movement of the application roller 204 in the first direction allows the GO dispersion or gel continuous layer 210 to be fed onto the outer surface of the application roller 204. An optional doctor blade 212 is used to adjust the thickness (amount) of the graphene oxide (GO) applicator layer 214. This applicator layer is continuously fed onto the surface of the support film 216 moving in a second direction (e.g. driven by a reversing roller 206 rotating in a direction opposite to the first direction) A wetting layer 218 is formed. This wet layer of GO is then subjected to a liquid removal process (eg, in a heated environment and / or using a vacuum pump).

  In summary, the method begins with the preparation of either a graphene oxide dispersion having a graphene oxide sheet dispersed in a fluid medium or a graphene oxide gel having graphene oxide molecules dissolved in the fluid medium, and graphene oxide The sheet or graphene oxide molecule has an oxygen content greater than 5% by weight. The graphene oxide dispersion or graphene oxide gel is then dispensed and fed onto the surface of the application roller rotating in a first direction at a first linear velocity (linear velocity of the outer surface of the application roller) to provide a graphene oxide applicator A graphene oxide applicator layer is transferred onto the surface of the support film driven at a second linear velocity in a second direction opposite to the first direction and oxidized on the support film Form a wet layer of graphene.

  In a preferred embodiment, the support film is driven by a reverse support roller (eg, 206 in FIG. 1) located at a working distance from the application roller and rotating in a second direction opposite the first direction. The second linear velocity (of the support film) is determined by the speed at the outer surface of this support roller. Preferably, the support film is supplied from a feed roller, and the dried layer of graphene oxide supported by the support film is wound on a take-up roller, and the method is performed in a roll-to-roll manner.

  This method is further illustrated in FIGS. 2, 3 and 4. In a preferred embodiment, as shown in FIG. 2, a GO dispersion / gel trough 228 naturally forms between the application roller 224 and the metering roller 222 (also referred to as a doctor roller). The GO applicator layer 230 is formed on the outer surface of the application roller 224 by relative movement or rotation of the application roller 224 relative to the metering roller 222 at a desired speed. This GO applicator layer is then transferred to provide a GO wetting layer 232 on the surface of the support film 234 (driven by a support roller 226 that rotates in a direction opposite to the direction of rotation of the applicator roller 224). Form. Next, the wet layer can be halogenated and dried.

  In another preferred embodiment, a GO dispersion / gel trough 244 is naturally formed between the application roller 238 and the metering roller 236, as shown in FIG. Relative movement or rotation of the applicator roller 238 relative to the metering roller 236 at a desired speed forms a GO applicator layer 248 on the outer surface of the applicator roller 238. A doctor blade 242 can be used to scrape the GO gel / dispersion on the outer surface of the metering roller 236. This GO applicator layer 248 is then transferred to a GO wetting layer 250 on the surface of the support film 246 (driven by the support roller 240 rotating in a direction opposite to the direction of rotation of the applicator roller 238). Form. Next, the wet layer can be halogenated and dried.

  In yet another preferred embodiment, a GO dispersion / gel trough 256 naturally forms between the application roller 254 and the metering roller 252 as shown in FIG. The GO applicator layer 260 is formed on the outer surface of the application roller 254 by relative movement or rotation of the application roller 254 relative to the metering roller 252 at the desired speed. This GO applicator layer 260 is then transferred to form a GO wet layer 262 on the surface of the support film 258 that is driven to move in a direction opposite to the direction of tangential rotation of the applicator roller 254. The support film 258 can be supplied from a feeding roller (not shown) and can be taken up (wound up) on a take-up roller (not shown) which may be a driving roller. In this example, there are at least four rollers. Next, the wet layer can be halogenated and dried. In the case of liquid medium removal, there must be a heating zone after the GO wet layer is formed to at least partially remove the liquid medium (eg, water) from the wet layer to form a dry layer of GO. Can do.

  In certain embodiments, supplying the graphene oxide dispersion or graphene oxide gel onto the surface of the application roller comprises applying an applicator of the desired thickness of graphene oxide onto the surface of the application roller using a metering roller and / or a doctor blade. Forming a layer. In general, the method of the present invention comprises operating 2, 3 or 4 rollers. Preferably, the method of the present invention includes a reverse roll coating procedure.

  It can be noted that the speed ratio defined as (second linear velocity) / (first linear velocity) is 1/5 to 5/1. When the outer surface of the coating roller moves at the same speed as the linear movement speed of the support film, the speed ratio is 1/1 or 1. As an example, when the outer surface of the coating roller moves at a speed three times the linear moving speed of the support film, the speed ratio is 3/1. As a result, the transferred GO wet layer is approximately three times as thick as the GO applicator layer. Very unexpectedly, this allows the production of much thicker layers and still maintains a high GO orientation in the wet and dry layers. This is very important and desirable because advanced GO sheet orientation could not be achieved with thick films (eg> 50 μm thick) by using other coating techniques such as casting or comma coating and slot die coating It is a result. In some embodiments, the speed ratio is greater than 1/1 and less than 5/1. Preferably, the speed ratio is greater than 1/1 and not greater than 3/1. Slot die coatings or comma coatings can also apply shear forces to induce the necessary orientation of GO or GH sheets or molecules.

  Preferably, the method of the present invention is performed in an aging chamber at an aging temperature of 25 ° C to 200 ° C (preferably 25 ° C to 100 ° C, more preferably 25 ° C to 55 ° C) and a humidity level of 20% to 99% for 1 hour. Further comprising aging the wet or dry layer of graphene oxide for an aging time of ˜7 days to form an aged layer of graphene oxide. Microscopic observation reveals that the average length / width of the GO sheet is significantly increased (2 to 3 times) after aging, and the inventors surprisingly found that this aging procedure allows for an edge-to-edge approach. It was confirmed that chemical ligation or coalescence of a part of GO sheet or molecule was possible. As a result, the sheet orientation can be maintained, and the connection between the edges to the subsequent huge crystal grains or crystal regions can be promoted.

In certain embodiments, the method of the present invention provides a dry layer of graphene oxide over a desired length of time at a first heat treatment temperature of greater than 100 ° C. but not greater than 3,200 ° C. (preferably not greater than 2500 ° C.). Or further heat treating the dried and aged layer to form a film having an interplanar spacing d _{002 of} less than 0.4 nm and an oxygen and / or halogen content of less than 5% by weight. The method of the present invention can further include a compression step to reduce the thickness of the graphene film during or after this heat treatment step.

  In the method according to the present invention, the graphene oxide sheet in the graphene oxide dispersion preferably occupies a weight fraction of 0.1% to 25% based on the total weight of the graphene oxide sheet and the liquid medium combined. More preferably, the graphene oxide sheet in the graphene oxide dispersion occupies a weight fraction of 0.5% to 15%. In certain embodiments, the graphene oxide sheet comprises a weight ratio of 3% to 15% based on the total weight of the graphene oxide sheet and the liquid medium combined. In some embodiments, the graphene oxide dispersion or graphene oxide gel has greater than 3 wt% graphene oxide dispersed in a fluid medium to form a liquid crystal phase.

  Monolithic integrated halogenated graphene films include chemically bonded and coalesced graphene surfaces. These planar aromatic molecules or graphene surfaces (hexagonal carbon atoms with the desired amount of oxygen-containing groups and / or halogen-containing groups) are parallel to each other. The lateral dimensions (length or width) of these faces are enormous and are typically several times or even orders of magnitude greater than the largest microcrystalline dimension (or largest constituent graphene face dimension) of the starting graphite particles. The halogenated graphene film according to the present invention is a “giant graphene crystal” or “giant planar graphene particle” in which all constituent graphene surfaces are substantially parallel to each other. This is a unique and new class of materials that have never been found, developed or suggested to exist.

  The dry halogenated graphene (GH) layer has a high birefringence between the in-plane direction and the direction perpendicular to the plane. The layer of oriented graphene oxide and / or halogenated graphene itself is surprisingly a very unique and new class of materials with very strong cohesion (self-bonding, self-polymerization and self-crosslinking properties). These characteristics are not taught or suggested in the prior art. GO is obtained by immersing the powder or filament of starting graphite material in an oxidizing liquid medium (eg, a mixture of sulfuric acid, nitric acid and potassium permanganate) in a reaction vessel. The starting graphite material may be selected from natural graphite, artificial graphite, mesophase carbon, mesophase pitch, mesocarbon microbeads, soft carbon, hard carbon, coke, carbon fiber, carbon nanofiber, carbon nanotube or combinations thereof it can.

  When the starting graphite powder or filament is mixed in an oxidizing liquid medium, the resulting slurry is a heterogeneous suspension and appears dark and opaque. If the oxidation of the graphite proceeds for a sufficient length of time at the reaction temperature, the reaction mass can eventually become a light green and yellowish suspension, but it remains opaque. The degree of oxidation is sufficiently high (eg, having an oxygen content of 20% to 50% by weight, preferably 30% to 50%), and all the original graphene surfaces are completely oxidized and exfoliated, and each oxidized When the graphene surface (here, graphene oxide sheet or molecule) is separated to the extent that it is surrounded by the molecules of the liquid medium, a GO gel is obtained. This GO gel is an optically translucent, substantially homogeneous solution, as opposed to a heterogeneous suspension.

  This GO suspension or GO gel typically contains some excess of acid and advantageously undergoes some degree of acid dilution to increase the pH value (preferably> 4.0). be able to. The GO suspension (dispersion) preferably contains at least 1 wt% GO sheet dispersed in a liquid medium, more preferably at least 3 wt%, most preferably at least 5 wt%. It is advantageous to have a sufficient amount of GO sheets to form the liquid crystal phase. The inventors have surprisingly found that liquid crystal state GO sheets are most likely to be easily oriented under the influence of shear stress caused by commonly used casting or coating processes.

  The graphene oxide suspension oxidizes the graphite material (in the form of powder or fibers) over an amount of time sufficient to obtain a GO sheet dispersed in the remaining liquid at the reaction temperature in the reaction vessel. It can be prepared by dipping in to form a reactive slurry. Typically, this residual liquid is a mixture of an acid (eg, sulfuric acid) and an oxidizing agent (eg, potassium permanganate or hydrogen peroxide). This residual liquid is then washed and replaced with water and / or alcohol to form a GO dispersion in which individual GO sheets (single layer or multilayer GO) are dispersed in the fluid. This dispersion is a heterogeneous suspension of individual GO sheets suspended in a liquid medium, optically opaque, dark (relatively low degree of oxidation) or light green and yellowish color (oxidation) Looks high).

  Here, the GO sheet contains a sufficient amount of oxygen-containing functional groups, and the resulting dispersion (suspension or slurry) is subjected to mechanical shearing or sonication to produce water and / or alcohol or other When a discrete GO sheet or molecule is formed (not just a dispersion) dissolved in a polar solvent, a material state called a “GO gel” is reached in which all individual GO molecules are surrounded by molecules in the liquid medium. can do. The GO gel is translucent and appears to be a homogeneous solution that cannot visually discern recognizable individual GO or graphene sheets. Useful starting graphite materials include natural graphite, artificial graphite, mesophase carbon, mesophase pitch, mesocarbon microbeads, soft carbon, hard carbon, coke, carbon fiber, carbon nanofiber, carbon nanotube or combinations thereof It is done. When the oxidation reaction proceeds to the required degree and the individual GO sheets are completely separated (at this stage the graphene surface and edges are heavily modified with oxygen-containing groups), an optically clear or translucent solution is formed. This is a GO gel.

  Preferably, the GO sheets in such GO dispersions or GO molecules in such GO gels are present in an amount of 1% to 15% by weight, although there may be more or less. More preferably, the GO sheet is 2% to 10% by weight in the suspension. Most preferably, the amount of GO sheet is an amount sufficient to form a liquid crystal phase in the dispersing liquid. GO sheets typically have an oxygen content in the range of 5% to 50%, more typically 10% to 50%, and most typically 20% to 46% by weight. .

  The above features are further described below and described in detail. As shown in FIG. 5B, the graphite particles (for example, 100) are typically composed of a plurality of graphite microcrystals or crystal grains. Graphite microcrystals are composed of layers of hexagonal network layers of carbon atoms. The faces of these layers of hexagonally arranged carbon atoms are substantially flat and oriented or arranged to be substantially parallel and equidistant from each other in the individual crystallites. These layers of hexagonal carbon atoms, commonly referred to as graphene layers or bottoms, are weakly bonded to each other in their thickness direction (crystallographic c-axis direction) by weak van der Waals forces, and these graphene layers The groups are arranged in microcrystals. Graphite microcrystalline structures are usually characterized with respect to two axes or directions, the c-axis direction and the a-axis (or b-axis) direction. The c-axis is a direction perpendicular to the bottom surface. The a-axis or b-axis is a direction parallel to the bottom surface (perpendicular to the c-axis direction).

Highly ordered graphite particles have a crystallographic a-axis direction along the length of L _a, width and crystallographic c thickness along the axial direction L _c of L _b along the crystallographic b-axis direction It can consist of crystallites of considerable size. The constituent graphene surfaces of the microcrystals are highly aligned or oriented with respect to each other, and therefore these anisotropic structures produce many highly directional properties. For example, the thermal conductivity and electrical conductivity of microcrystals are high along the plane direction (a-axis or b-axis direction), but relatively low in the vertical direction (c-axis). As shown in the upper left part of FIG. 5 (B), the different microcrystals in the graphite particles are typically oriented in different directions, so the specific properties of the multicrystalline graphite particles are all The average value in the direction of the constituent microcrystals.

Because of the weak van der Waals forces that maintain parallel graphene layers, the natural graphene layer spacing can be significantly increased to significantly expand in the c-axis direction by treating natural graphite, An expanded graphite structure can be formed in which the layered nature of the carbon layer is substantially maintained. Methods for producing flexible graphite are well known in the art. In general, natural graphite flakes (for example, 100 in FIG. 5B) are intercalated in an acid solution to produce a graphite intercalation compound (GIC, 102). The GIC is washed, dried and then stripped by brief exposure to high temperatures. As a result, the flakes expand or peel up to 80 to 300 times the original dimension in the c-axis direction of graphite. Exfoliated graphite flakes are worm-like in appearance and are therefore commonly referred to as worms 104. From these highly expanded graphite flake worms, aggregates or integration of expanded graphite having a typical density of about 0.04 to 2.0 g / cm ³ in most applications, without the use of a binder Sheets such as webs, papers, strips, tapes, foils, mats, etc. (typically referred to as “flexible graphite” 106) can be formed.

  The upper left part of FIG. 5 (A) shows a flowchart showing a prior art method used for the production of a flexible graphite foil and a flexible graphite composite material impregnated with a resin. These methods typically involve intercalating a graphite particle 20 (eg, natural graphite or synthetic graphite) with an intercalant (typically a strong acid or acid mixture) to produce a graphite intercalation compound 22 (GIC). Start by getting. After washing in water to remove excess acid, GIC becomes “expandable graphite”. Next, the GIC or expandable graphite is exposed to a high temperature environment (eg, in a tubular furnace preset to a temperature in the range of 800 to 1,050 ° C.) for a short time (typically 15 seconds to 2 minutes). . By this heat treatment, graphite expands from 30 times to several hundred times even in the c-axis direction, and a worm-like structure 24 (graphite worm) can be obtained, which is peeled but not separated. Contains graphite flakes and has large pores intervening between these interconnected flakes. An example of a graphite worm is shown in FIG.

  In one prior art method, exfoliated graphite (or graphite worm mass) is recompressed using calendering or roll pressing techniques to produce flexible graphite foil (FIG. 5A 26 or FIG. B) 106) are obtained, which are typically 100-300 μm thick. An SEM image of the cross section of the flexible graphite foil is shown in FIG. 6B, which shows a number of graphite flakes having an orientation that is not parallel to the surface of the flexible graphite foil, including many defects and There is an incomplete part.

  Mainly due to the misorientation of these graphite flakes and the presence of defects, commercially available flexible graphite foil usually has an in-plane electrical conductivity of 1,000 to 3,000 S / cm and a through-plane direction ( The electrical conductivity in the thickness direction or the Z direction) is 15 to 30 S / cm, the in-plane thermal conductivity is 140 to 300 W / mK, and the thermal conductivity in the through-plane direction is about 10 to 30 W / mK. . These defects and misorientation can also contribute to low mechanical strength (eg, defects are potential stress concentration sites where cracking preferentially begins). These properties are insufficient for many temperature management applications, and the present invention is configured to address these issues.

  In another prior art method, exfoliated graphite worm 24 can be impregnated with resin, then compressed and cured to form flexible graphite composite 28, which is also typically of low strength. Furthermore, when impregnated with resin, the electrical and thermal conductivity of the graphite worm can be reduced by two orders of magnitude.

  Alternatively, exfoliated graphite is subjected to a high-strength mechanical shearing / separation process using a high-strength air jet mill, a high-strength ball mill, or an ultrasonic device so that all graphene platelets are thinner than 100 nm. Can be produced as a separated nanographene platelet 33 (NGP) which is thinner than 10 nm and is often single layer graphene (also indicated as 112 in FIG. 5B). NGP is composed of one graphene sheet or a plurality of graphene sheets each having a two-dimensional hexagonal structure of carbon atoms.

  Furthermore, using low strength shear, the graphite worm tends to separate into so-called expanded graphite flakes having a thickness of> 100 nm (108 in FIG. 5B). Using the paper or mat manufacturing method, Graphite paper or mat 106 can be formed from these flakes, which is a simple agglomeration or laminate of individual flakes having defects, interruptions and misorientations between the individual flakes. is there.

  For purposes of defining the shape and orientation of NGP, NGP is described as having a length (maximum dimension), width (second largest dimension), and thickness. This thickness is the smallest dimension and in this application is less than 100 nm, preferably less than 10 nm. If the platelet is approximately circular, the length and width are described as diameters. For NGP as defined herein, both length and width may be less than 1 μm, but may exceed 200 μm.

  Graphene film / paper from multiple NGP masses (including individual sheets / platelets of single and / or several layers of graphene or graphene oxide, 33 in FIG. 5A) using film or paper manufacturing methods (34 in FIG. 5A or 114 in FIG. 5B) can be manufactured. FIG. 7B shows an SEM image of a cross section of graphene paper / film made from individual graphene sheets using a papermaking process. This image shows the presence of a large number of individual graphene sheets that have been folded or interrupted (not integrated), and the majority of the platelet orientation is not parallel to the film / paper surface, and many defects or There is an incomplete part. NGP agglomerates have a thermal conductivity of over 1,000 W / mK only when the film or paper is cast and pressed strongly into a sheet having a thickness of less than 10 μm, even when closely packed. Indicates the rate. Heat spreaders in many electronic devices are usually required to be thicker than 10 μm but thinner than 35 μm).

  Another graphene-related product is graphene oxide gel 21 (FIG. 5A). This GO gel is obtained by immersing graphite material 20 in powder or fiber form in a strong oxidizing liquid in a reaction vessel to form a suspension or slurry that is initially optically opaque and dark in color. It is done. This optical opacity is due to the fact that individual graphite flakes at the beginning of the oxidation reaction and individual oxide graphene flakes at a later stage scatter and / or absorb visible wavelengths, resulting in an opaque, totally dark fluid mass. It reflects that it becomes. When the reaction between the graphite powder and the oxidant can proceed for a sufficient length of time at a sufficiently high reaction temperature and all of the resulting GO sheets are completely separated, the opaque suspension is brown. It typically turns into a translucent or transparent solution, which at this stage is a “graphene oxide gel” that contains no distinct individual graphite flakes or graphite oxide platelets (21 in FIG. 5A). It is a uniform fluid called. When fed and deposited using the reverse roll coating according to the present invention, molecular orientation of the GO gel occurs to form a layer of highly oriented GO 35 that can be heat treated into a graphite film 37.

  Again, this graphene oxide gel is typically optically transparent or translucent, without having discernable individual flakes / platelets of graphite, graphene or graphene oxide dispersed therein. Visually uniform. In the GO gel, the GO molecules “dissolve” uniformly in the acidic liquid medium. In contrast, suspensions of individual graphene sheets or graphene oxide sheets in fluids (eg, water, organic acids or solvents) appear dark, black or dark brown, even to the naked eye, or low magnification optics Individual graphene or graphene oxide sheets can be recognized or identified using a microscope (100 to 1,000 times).

  A graphene oxide suspension or GO gel is obtained from a graphite material (eg, natural graphite powder) having a plurality of graphite microcrystals that do not exhibit a preferred crystal orientation as measured by X-ray diffraction or electron diffraction. However, the resulting graphite film exhibits a very high preferred crystal orientation as measured by the same X-ray diffraction method or electron diffraction method. This involves chemical modification, transformation, rearrangement, reorientation, linking or crosslinking, coalescence and integration, and halogenation of the constituent graphene surfaces of the hexagonal carbon atoms that make up the particles of the original or starting graphite material. This is yet another proof of what happened.

Example 1: Production of individual oxidized nanographene platelets (NGP) or GO sheets Short graphite fibers with an average diameter of 12 μm and natural graphite particles are used separately as starting materials, which are concentrated sulfuric acid, nitric acid and permanganese A graphite intercalation compound (GIC) was prepared by immersion in a mixture of potassium acid (as chemical intercalation and oxidant). The starting material was first dried in a vacuum oven at 80 ° C. for 24 hours. Next, a mixture of concentrated sulfuric acid, fuming nitric acid and potassium permanganate (in a weight ratio of 4: 1: 0.05) is slowly added to the three-necked flask containing the fiber fragments under proper cooling and stirring. It was. After 5 to 16 hours of reaction, the acid-treated graphite fibers or natural graphite particles were filtered and washed thoroughly with deionized water until the pH level of the solution reached 6. After drying at 100 ° C. overnight, the obtained graphite intercalation compound (GIC) or graphite oxide fiber was redispersed in water and / or alcohol to form a slurry.

  In one sample, 500 grams of graphite oxide fiber was mixed with a 2,000 ml alcohol solution consisting of a 15:85 ratio of alcohol and distilled water to obtain a slurry mass. Next, ultrasonic irradiation with an output of 200 W was performed on the mixture slurry for various lengths of time. After 20 minutes of sonication, the GO fibers effectively peeled and separated into thin graphene oxide sheets having an oxygen content of about 23 wt% to 31 wt%.

  The reverse roll transfer procedure was then performed, and from the resulting suspension, a thin and thick film of GO (10 nm, 100 nm, 1-25 μm, 100 μm and 500 μm thickness) on a polyethylene terephthalate (PET) film. Was made. For comparison purposes, an equivalent thickness range GO layer was also produced by drop casting and comma coating techniques.

  In order to produce a halogenated graphene film, typically a few aging and halogenation treatments including a halogenation treatment at 25-250 ° C. for 1-24 hours after 1-8 hours at an aging temperature of 30-100 ° C. This was carried out on a single GO film. A typical form is shown in FIG.

Example 2 Production of Single-Layer Graphene Oxide Sheet from Mesocarbon Microbeads (MCMB) Mesocarbon microbeads (MCMB) were manufactured by China Steel Chemical Co. , Kaohsiung, Taiwan. This material has a density of about 2.24 g / cm ³ and a median particle size of about 16 μm. MCMB (10 grams) was intercalated with an acid solution (4: 1: 0.05 sulfuric acid, nitric acid and potassium permanganate) for 48-96 hours. After completion of the reaction, the mixture was poured into deionized water and filtered. The intercalated MCMB was washed repeatedly in a 5% HCl solution to remove most of the sulfate ions. Next, the sample was repeatedly washed with deionized water until the pH of the filtrate was 4.5 or higher. Next, this slurry was subjected to ultrasonic treatment for 10 to 100 minutes to obtain a GO suspension. In TEM and atomic force microscopy studies, most GO sheets were single layer graphene when the oxidation treatment was over 72 hours, and two or three layer graphene when the oxidation time was 48-72 hours. It has been shown.

The GO sheet has a ratio of oxygen of about 35% to 47% by weight for an oxidation treatment time of 48 to 96 hours. The suspension was then coated onto the PET polymer surface using reverse roll transfer coating and another comma coating procedure to create an oriented GO film. The resulting GO film has a thickness that can vary from about 0.5 to 500 μm after removing the liquid. The halogenation treatment was performed before the feed step (using HF acid) and after (eg, F ₂ and Br ₂ plasma, discussed further below).

Example 3 Preparation of Graphene Oxide (GO) Suspension and GO Gel from Natural Graphite 30 ° C. with a Liquid Oxidant Consisting of Sulfuric Acid, Sodium Nitrate and Potassium Permanganate in a Ratio of 4: 1: 0.05 Oxidized graphite was prepared by oxidizing graphite flakes. When natural graphite flakes (14 μm particle size) are soaked and dispersed in the liquid oxidant mixture for 48 hours, the suspension or slurry appears optically opaque and dark and is maintained. After 48 hours, the reaction mass was washed three times with water and adjusted to a pH value of at least 3.0. The final amount of water was then added to prepare a series of GO-water suspensions. The inventors have confirmed that when the GO sheet occupies a weight fraction of> 3%, typically 5% to 15%, the GO sheet forms a liquid crystal phase.

  For comparison purposes, we also prepared GO gel samples by extending the oxidation time to about 96 hours. With continued vigorous oxidation, the dark and opaque suspension obtained after 48 hours of oxidation turns into a translucent, brown-yellowish solution after some water washing.

  Using both reverse roll coating and slot die coating, we apply a GO suspension or GO gel onto a PET film to coat and remove the liquid medium from the coated film, which allows us to dry. A thin film of graphene oxide was obtained. Next, various heat treatments and halogenation treatments were performed on the GO film. These heat treatments typically include an aging treatment at 45 ° C. to 150 ° C. for 1 to 10 hours. Halogenation is discussed in Examples 4 and 5.

  Scanned electron microscope (SEM), transmission electron microscope (TEM) photograph of graphene layer and image of limited field electron diffraction (SAD), bright field (BF) and dark field (DF) Was used to characterize the structure of the integrated layer. For measurement of the film cross-section, the sample was embedded in a polymer matrix, sliced using an ultramicrotome, and etched with Ar plasma.

  By close examination and comparison of FIGS. 6A, 6A and 7B, the graphene layers in the halogenated GO film made according to the present invention are oriented substantially parallel to each other. Although shown, this is not the case with flexible graphite foil and GO or GH paper. The tilt angle between the two identifiable layers in the integrated film of halogenated graphene is mainly less than 5 degrees. In contrast, because there are many folded graphite flakes, twists and misorientations in flexible graphite, many of the angles between the two graphite flakes are greater than 10 degrees and some are as large as 45 degrees. (FIG. 6B). Although not defective, the misorientation between graphene platelets in graphene paper (FIG. 7B) is also large (on average >> 10 to 20 °), and there are many gaps between the platelets. The integrated halogenated graphene film is substantially free of gaps.

Example 4: Halogenation of GO after deposition of GO layer Chlorination of GO platelets using chloroform (CF) and chlorobenzene (CB) separately at a temperature of 50-100 ° C for 1-10 hours. Went. The degree of GO chlorination was evaluated by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). In order to investigate the effect of CF or CB treatment on the dielectric performance of the resulting chlorinated GO, a film about 70 nm to 2 μm thick was made.

Fluorination of reduced graphene oxide sheets (single layer and multilayer) can be performed in plasma containing CF ₄ , SF ₆ , XeF ₂ , fluoropolymer or Ar / F ₂ as a fluorinating agent. By changing the plasma treatment time and the type of fluorinating agent, the fluorine content of the resulting fluorinated graphene can be changed.

A number of techniques were used for fluorination of graphene oxide, including exposure to F ₂ gas at intermediate temperatures (400-600 ° C.) and treatment with F-based plasma. XeF ₂ is a strong fluorinating agent for graphene oxide without etching and thus provides an easy route for graphene halogenation. The characterization of this method by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, corresponds to 25-50% coverage (Formula _C 4 _{F~C 2} F in the case of one-side exposure by fluorination at room temperature ) And in the case of double-sided exposure, it becomes clear to be saturated with CF. Due to its high electronegativity, fluorine causes a strong chemical shift in the carbon 1s binding energy, thus allowing X-ray photoelectron spectroscopy (XPS) to be used to determine composition and bond type.

Fluorination was also performed by plasma enhanced chemical vapor deposition (PECVD). In a typical procedure, the PECVD chamber was evacuated to about 5 mTorr and the temperature was increased from room temperature to 200 ° C. Next, CF ₄ gas was introduced into the chamber at a controlled gas flow rate and pressure. The degree of fluorination of the GO sample was adjusted by changing the exposure time. A suitable CF ₄ plasma exposure time was found to be 3-7 minutes per 1 nm of Go layer thickness. For example, when the GO layer was 10 nm thick, the exposure time was 30-70 minutes.

Bromination and iodination of Go were performed in a similar procedure using Br ₂ , I ₂ , BrI, CBr ₄ and / or CCl ₄ gas or plasma under equivalent conditions.

Example 5: Preparation of various halogenated graphene oxide sheets / molecules prior to the feed and deposition steps Sonication in the presence of sulfolane, dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP) A graphene fluoride suspension was obtained by chemical etching of (commercially available) fluorinated graphite particles. During this process, solvent molecules intercalate between the graphene layers, weakening the van der Waals force between adjacent layers, and promoting the formation of a graphene fluoride suspension by peeling off the fluorinated graphite. The GF suspension is applied onto the surface of the PET film under high shear conditions (eg faster linear velocity ratio 2/1 to 5/1) using comma coating, slot die coating or preferably reverse roll transfer coating. Direct coating was possible.

  Through the chemical reaction between graphene oxide and hydrofluoric acid, graphene fluoride having various fluorine contents could be easily obtained. Fluorination of graphene oxide can be performed by exposure of graphene oxide to anhydrous HF vapor at various temperatures, or can be performed photochemically at room temperature using an HF solution. These procedures were performed on GO sheets or molecules before the feed and deposition steps.

  By UV light irradiation in a liquid chlorine medium, both single layer graphene and several layer graphene can be chlorinated up to 56-74% by weight. Bromination of both single-layer and few-layer graphene can be performed under equivalent conditions.

As an example, GO (15 mg) was mixed with 30 mL of carbon tetrachloride and sonicated for 20 minutes using a chip sonicator. The resulting suspension was transferred into a 500 mL quartz vessel fitted with a condenser maintained at 277 ° C. The reaction chamber was purged with high purity nitrogen for 30 minutes and chlorine gas was passed through the chamber. Gaseous chlorine condensed in the quartz container. A quartz container containing about 20 mL of liquid chlorine was heated to 250 ° C. and simultaneously irradiated with UV light (250 watt high pressure Hg vapor lamp) for 1.5 hours. Removal of the solvent and excess chlorine left a transparent film on the quartz vessel wall. This solid was dispersed in absolute alcohol under sonication, filtered and washed with distilled water and absolute alcohol. The filtrate was then redispersed in 40 ml of distilled water, sonicated for 2 minutes and centrifuged. The resulting black supernatant was separated and filtered using a PVDF membrane (200 nm pore size). The yield from a 15 mg GO sample was about 7-10 mg. Dispersion of the chlorinated graphene sheet in a solvent (eg, CCl ₄ ) can form a suspension for supply and deposition.

In the case of bromination, 12 mg of graphene was mixed in a quartz container, and 20 mL of liquid bromine was added thereto. The mixture was sonicated for 10 minutes using a sonicator. To this was added 0.5 g of carbon tetrabromide. Next, the quartz container was heated to 250 ° C. and simultaneously irradiated with UV light as in the case of chlorination. Excess bromine was removed and the product was washed with sodium thiosulfate. The solid residue was then washed several times with water and absolute alcohol to remove sodium thiosulfate, then dispersed in 40 mL distilled water and centrifuged. The resulting black supernatant was separated and filtered using a PVDF membrane (200 nm pore size). The yield from a 12 mg sample was about 5-7 mg. The brominated graphene sheet can be dispersed in a solvent (eg, CBr ₄ ) to form a suspension for supply and deposition.

  A desired amount of halogenated GO sheet / molecule can be added to the GO suspension or GO gel prior to the feed / deposition step to form a GO / halogenated GO mixed suspension or gel. Typically, the weight ratio of halogenated GO to GO is 10/1 to 1/10 (in selected liquid media such as DMF and NMP), more typically 1/1 to 1/10 (liquid When the medium is water).

Example 6: Properties of halogenated graphene integrated layer Methods for measuring dielectric strength, dielectric constant, volume resistivity (reciprocal of electrical conductivity) are well known in the art. The studies of the present invention followed standardized methods: dielectric strength (ASTM D-149-91), dielectric constant (ASTM D-150-92) and volume resistivity (ASTM D-257-91).

  FIG. 8 shows the dielectric breakdown strength of the GO film, the GO-derived integrated fluorinated graphene film according to the present invention (made by the reverse roll transfer coating method) and the prior art polyimide film plotted as a function of film thickness. These data show that the halogenated graphene film according to the present invention exhibits a very high breakdown strength (> 12 MV / cm) even at large film thicknesses of 25-125 μm (unusually unexpected) Is). The breakdown strength value was found to be relatively independent of film thickness. In contrast, for the same thickness range, the graphene oxide film withstands a dielectric strength of 0.62 to 1.1 MV / cm and is an order of magnitude smaller. For comparison purposes, a commercially available polyimide film (du Pont Kapton film) has a dielectric strength of 1.54 to 3.03 MV / cm.

  The dielectric breakdown strength of GO-derived fluorinated graphene film and chlorinated graphene film (both prepared by reverse roll transfer procedure and separately by casting procedure) is expressed as fluorination degree (atom allocation F / (F + O) or chlorination degree (atom The ratio, as a function of Cl / (Cl + O), is plotted in Figure 9. Although the casting procedure did not include any significant amount of shear stress, the reverse roll coating method produced high shear in the orientation of GO and halogenated GO films. These data show that for the same 100 nm thickness, the dielectric strength of the GO film is 2.6 MV / cm for the pure GO film (no fluorination or zero fluorination degree), and the complete fluorine It is shown that it increased to 22.2 MV / cm in the case of the modified film. If even, by fluorination, show that can impart greatly improved dielectric strength GO film. This is unexpected. Composite film of chlorinated GO film also has the same tendency.

  Most notably and unexpectedly, due to orientation induced by shearing of fluorinated or non-fluorinated GO sheets or molecules, an integral film is made to insulate the non-oriented or less-oriented equivalent made by conventional casting. It can withstand dielectric breakdown strength (2.6-22.2 MV / cm) much higher than the breakdown strength (1.1-7.2 MV / cm). Similarly, highly oriented chlorinated GO sheets or integral films of molecules can provide much higher dielectric strength compared to their casting equivalents where the sheets / molecules are not properly oriented. This is a very important discovery, which provides a versatile way to achieve the exceptional dielectric strength of graphene materials.

  GO-derived fluorination produced by GO-derived fluorinated graphene film (prepared by reverse roll transfer procedure) and conventional papermaking procedure (vacuum-assisted filtration) plotted as a function of degree of fluorination with respect to atomic ratio F / (F + O) The dielectric breakdown strength of graphene paper is summarized in FIG. These data show that the dielectric strength (1.1 to 1.45 MV / cm) of the GO paper film prepared by the conventional method of vacuum assisted filtration of a plurality of fluorinated GO sheets is relatively low, and compared with the degree of fluorination. It shows that it is unrelated. Some orientation is achieved in this way, but the dielectric strength remains very low. Defects, voids, twists, and breaks in the fluorinated GO sheet are the concentration at which breakdown begins at these imperfections at a relatively low overall (average) low voltage level and then rapidly propagates throughout the sample. It seems to be a local drop site of the electric field. The method according to the invention eliminates these imperfections.

The dielectric constants of GO-derived fluorinated graphene films and brominated graphene films plotted as a function of degree of fluorination (atomic assignment F / (F + O) or degree of bromination (atomic ratio Br / (Br + O)) are summarized in FIG. As the degree of fluorination or bromination increases, the dielectric constant of the halogenated graphene integrated film increases to reach its maximum value, and then decreases when the degree of fluorination or bromination exceeds 0.6. Most notable is the partially halogenated GO film (C ₆ Z _x O _y , where Z is a halogen element selected from F, Cl, Br, I, and x = 0.01 to 6.0, y = 0 to 5.0 and x + y ≦ 6.0) can exhibit a dielectric constant of 3.9 to 22.2, and an integrated layer of GO (x = 0; C ₆ O dielectric constant value 2.3 in the case of _y ) It is a measurement result that is in contrast.

In summary, an integrated film of halogenated graphene (highly oriented GO-derived halogenated graphene film, GOGH) made from the original graphene oxide suspension or GO gel using a shear stress based method of controlling orientation Has the following characteristics:
(1) An integrated halogenated graphene film (thin or thick) is typically an integrated halogenated graphene oxide or a halogenated graphene structure substantially free of oxygen, which is polycrystalline with large crystal grains It is. The film has a wide or long chemically bonded graphene surface, all oriented substantially parallel to each other. In other words, the crystallographic c-axis directions of all the constituent graphene surfaces in all the crystal grains are oriented in substantially the same direction. In other words, an integrated layer is a plurality of constituent halogenated graphene surfaces that are substantially parallel to one another along one direction, and those halogenated surfaces that are less than 10 degrees (more typically less than 5 degrees). It has a plurality of constituent halogenated graphene surfaces having an average deviation angle of the graphene surface.

  (2) The reverse roll coating is very effective for realizing a high degree of graphene plane orientation and crystal perfection of halogenated graphene.

  (3) The presence of halogen and oxygen in the integrated halogenated GO layer provides an unexpected synergistic effect in the production of high dielectric constant films.

  (4) A single graphene element that is completely integrated and substantially free of voids, containing no distinguishable individual flakes or platelets that were present in the original GO suspension. Or a monolith. In contrast, a paper or film of halogenated graphene or GO platelets (each platelet <100 nm) is a simple unbound aggregate / laminate of multiple individual platelets of GO or halogenated GO. The platelets in these paper / films are poorly oriented and have a large number of twists, curves and wrinkles. Since many voids or other defects are present in these paper / film structures, the breakdown strength is low.

  (5) In the prior art method, the individual graphene or GO sheets (<< 100 nm, typically <10 nm) that make up the original structure of the graphite particles can be obtained by a process of expansion, exfoliation and separation. did it. By simply mixing these individual sheets / flakes and recompressing them into bulk objects, it was possible to attempt to orient these sheets / flakes along one direction, preferably by compression. However, with these conventional methods, the resulting aggregate-constituting flakes or sheets can be easily identified or clearly observed even with the naked eye or under a low magnification optical microscope (100-1000x) Remain as individual flakes / sheets / platelets that can be made.

  In contrast, the fabrication of a monolithic film of halogenated graphene according to the present invention results in the fact that all the original graphene surfaces are oxidized and separated from each other, resulting in highly reactive functional groups (eg, —OH,> O and — Including the step of vigorously oxidizing the original graphite particles to the extent that they become individual graphene surfaces or molecules having COOH) at the edges or on the surface of the graphene surface. These individual hydrocarbon molecules (containing elements such as O and H in addition to carbon atoms) are dispersed in a liquid medium (eg, a mixture of water and alcohol) to form a GO dispersion. The dispersion is then reverse roll coated onto a smooth substrate surface, and then the liquid component is removed to form a dry GO layer. With slight heating or aging, these highly reactive molecules react with each other, mostly laterally along the graphene surface (in an edge-to-edge fashion with increasing length and width) and possibly even between graphene surfaces. And chemically bond.

  FIG. 7 (D) shows a possible chemical linking mechanism where multiple GO molecules can be chemically linked together to form a film, but only two aligned GO molecules are shown as an example. ing. Furthermore, chemical connections can occur not only between edges, but also between faces. These ligation and coalescence reactions proceed in such a way that the molecules are chemically coalesced, ligated and integrated into a single material. These molecules or “sheets” become very long and wide. These molecules (GO sheets) are completely lost in their original properties and are no longer individual sheets / platelets / flakes. There is only one monolayer structure that is a substantial network of interconnected macromolecules having a substantially infinite molecular weight. This can also be described as graphene polycrystals (having several grains, but typically not having distinguishable well-defined grain boundaries). All constituent graphene surfaces have very large lateral dimensions (length and width) and are arranged parallel to each other.

More detailed studies using a combination of SEM, TEM, limited field diffraction, X-ray diffraction, AFM, Raman spectroscopy and FTIR have shown that graphite films have several giant graphene surfaces (typically length / width>> 100 μm, more typically >> 1 mm). These giant graphene surfaces are often stacked and bonded along the thickness direction (crystallographic c-axis direction) not only by van der Waals forces (like conventional graphite microcrystals) but also by covalent bonds. . In these cases, though not wishing to be limited by theory, Raman and FTIR spectroscopy studies have shown that not only conventional sp ² but also sp ² (dominant) and sp ³ (weak but weak) in graphite. It seems to indicate the coexistence of electron configuration.

  (6) This integrated GOGH film is not made by bonding or bonding individual flakes / platelets together using a resin binder, linker or adhesive. Instead, the GO or halogenated GO sheets (molecules) in the dispersion or gel coalesce with each other by the formation of linkages or covalent bonds to form an integrated graphene element, and any linker or binder molecules added externally and No polymer is used. These GO or halogenated GO molecules are “living” molecules that can be linked together in a manner similar to the living polymer chain where “recombination” occurs (eg, a 1,000 monomer unit living chain and 2,000 molecules). Another living chain of monomer units is linked or linked to form a 3,000 unit polymer chain). For example, a 3,000 unit chain can be combined with a 4,000 unit chain to form a 7,000 unit huge chain.

(7) The integrated film typically has incomplete grain boundaries and typically large grains with crystallographic c-axes in all grains substantially parallel to each other. It is a polycrystal composed of This element is derived essentially from a GO suspension or GO gel obtained from natural graphite or artificial graphite particles having a plurality of graphite microcrystals. Prior to chemical oxidation, these starting graphite microcrystals have an initial length (L _{a in the} crystallographic a-axis direction), an initial width (L _{b in the} b-axis direction) and a thickness (L _{c in the} c-axis direction). Have When vigorously oxidized, these initial individual graphite particles are chemically converted into highly aromatic graphene oxide molecules with high concentrations of edge or surface functional groups (eg, —OH, —COOH, etc.). The These aromatic halogenated GO molecules in the GO suspension have lost the original property of being part of graphite particles or flakes. After removing the liquid components from the suspension and performing thermal aging, the resulting GO molecules are chemically coalesced and linked into highly oriented single or monolithic graphene elements.

Single graphene element resulting typically have a much greater length or width than L _a and L _b of the original crystallites. Length / width of the graphite film is much larger than L _a and L _b of the original crystallites. Even individual crystal grains of the polycrystalline graphite film in, have a much greater length or width than L _a and L _b of the original crystallites.

  (8) Their unique chemical composition (including oxygen content), morphology, crystal structure (including graphene spacing) and structural features (eg, high orientation, few defects, chemical bonds and gaps between graphene sheets) Highly oriented graphene oxide-derived halogenated GO films have a unique combination of significant dielectric constant and breakdown strength.

  In conclusion, the inventors have successfully developed a monolithic integrated film of highly oriented graphene halide monoliths that are completely new, novel and unexpectedly distinct and distinct types of dielectric materials. Chemical composition (oxygen and halogen content), structure (crystal integrity, grain size, defect population, etc.), crystal orientation, achievable thickness, morphology, manufacturing method and high orientation of this new class of materials and The properties are fundamentally different and clearly different from any known graphene material. These halogenated graphene films can be used as dielectric material components in a variety of microelectronic devices.

Claims (41)

An integrated layer of oriented halogenated graphene having a thickness of 10 nm to 500 μm and a chemical formula of C ₆ Z _x O _y , wherein Z is a halogen selected from F, Cl, Br, I or combinations thereof Element, x = 0.01-6.0, y = 0-5.0 and x + y ≦ 6.0), and 0.35 nm to 1. An integrated layer of oriented halogenated graphene having a surface spacing d002 of 2 nm.   The integrated layer of oriented halogenated graphene according to claim 1, wherein the interplanar spacing d002 is 0.40 nm to 1.0 nm.   The integrated layer of oriented halogenated graphene according to claim 1, wherein the interplanar spacing d002 is 0.50 nm to 0.90 nm.   A plurality of halogenated graphene surfaces substantially parallel to each other along one direction, the plurality of halogenated graphene surfaces having an average deviation angle of the halogenated graphene surface of less than 10 degrees The integrated layer of oriented halogenated graphene according to claim 1, comprising:   The integrated layer of oriented halogenated graphene according to claim 1, wherein the average deviation angle of the halogenated graphene surface is less than 5 degrees.   The integrated layer of oriented halogenated graphene according to claim 1, having a thickness of 20 nm to 200 μm.   The integrated layer of oriented halogenated graphene according to claim 1, having a thickness of 100 nm to 100 μm.   The integrated layer of oriented halogenated graphene according to claim 1, having a thickness of 1 μm to 100 μm.   The oriented halogenated graphene of claim 1 having a dielectric constant greater than 4.0, an electrical resistivity greater than 108 Ω-cm or a dielectric breakdown strength greater than 5 MV / cm when measured at a layer thickness of 100 nm. Integrated layer.   Integration of oriented halogenated graphenes according to claim 1, having a dielectric constant greater than 10 when measured at a layer thickness of 100 nm, an electrical resistivity greater than 1010 Ω-cm or a breakdown strength greater than 10 MV / cm. layer.   The oriented layer of graphene halide according to claim 1, having a dielectric constant greater than 15 or a dielectric breakdown strength greater than 12 MV / cm when measured at a layer thickness of 100 nm.   The oriented layer of graphene halide according to claim 1, wherein y = 0 and x = 0.01 to 6.0.   The integrated layer of oriented halogenated graphene according to claim 1, wherein y = 0.1 and x = 0.1 to 5.0.   A microelectronic device comprising the integrated layer of graphene halide according to claim 1 as a dielectric component. A method for producing a highly oriented sheet of halogenated graphene or an integrated layer of molecules comprising:
a. Preparing either a graphene oxide dispersion having a graphene oxide sheet dispersed in a fluid medium or a graphene oxide gel having graphene oxide molecules dissolved in a fluid medium, the graphene oxide sheet or the oxidation The graphene molecules contain an amount of oxygen greater than 5% by weight;
b. Supplying and depositing a layer of the graphene oxide dispersion or the graphene oxide gel on a surface of a supporting substrate under shear stress conditions, the supplying and depositing step comprising graphene oxide on the supporting substrate Thinning induced by shearing of the graphene oxide dispersion or the graphene oxide gel to form a wet layer of the film, and orientation induced by shearing of the graphene oxide sheet or the graphene oxide molecules; ;
c. Chemical formula of C ₆ Z _x O _y (wherein Z is a halogen element selected from F, Cl, Br, I, or a combination thereof, x = 0.01 to 6.0, y = 0 to 5) . And x + y ≦ 6.0) and a dry integrated layer of graphene halide having an interplanar spacing d _{002 of} 0.35 nm to 1.2 nm as measured by X-ray diffraction For this purpose, (i) a halogenating agent is introduced into the wet layer of the graphene oxide, and a chemical reaction is caused between the halogenating agent and the graphene oxide sheet or the graphene oxide molecule. Forming a wetting layer and removing the flowing medium from the wetted layer of graphene halide, or (ii) removing the flowing medium from the wetted layer of graphene oxide to remove the graphene oxide Either of forming a dry layer and introducing a halogenating agent into the dry layer of the graphene oxide and causing a chemical reaction between the halogenating agent and the graphene oxide sheet or the graphene oxide molecule Comprising the steps of: A method for producing a highly oriented sheet of halogenated graphene or an integrated layer of molecules comprising:
a. Preparing either a graphene oxide dispersion having a graphene oxide sheet dispersed in a fluid medium or a graphene oxide gel having graphene oxide molecules dissolved in a fluid medium, the graphene oxide sheet or the oxidation The graphene molecules contain an amount of oxygen greater than 5% by weight;
b. Dispersion of the halogenated graphene sheet by introducing a halogenating agent into the graphene oxide dispersion or the graphene oxide gel and causing a chemical reaction between the halogenating agent and the graphene oxide sheet or graphene oxide molecule Forming a graphene or gel of halogenated graphene molecules, wherein the halogenated graphene sheet has a chemical formula of C ₆ Z _x O _y (wherein Z is selected from F, Cl, Br, I, or a combination thereof) A halogen element, wherein x = 0.01-6.0, y = 0-5.0 and x + y ≦ 6.0);
c. Providing and depositing a layer of the halogenated graphene dispersion or gel on a surface of a supporting substrate under shear stress conditions, wherein the supplying and depositing step comprises wetting graphene oxide on the supporting substrate; Comprising: thinning induced by shearing of a dispersion or gel of halogenated graphene to form a layer; and orientation induced by shearing of said halogenated graphene sheet or molecule;
d. The flowing medium is removed from the wetted graphene halide layer to form an integrated layer of halogenated graphene having an interplanar spacing d _{002 of} 0.35 nm to 1.2 nm as measured by X-ray diffraction. Including a step.   The method according to claim 15, wherein the graphene oxide sheet contains single-layer graphene oxide or several-layer graphene oxide sheets each having 2 to 10 graphene oxide surfaces.   16. The method of claim 15, wherein the fluorinating agent comprises a liquid, gaseous or plasma species containing a halogen element selected from F, Cl, Br, I or combinations thereof.   17. A method according to claim 16, wherein the fluorinating agent comprises a liquid, gaseous or plasma species containing a halogen element selected from F, Cl, Br, I or combinations thereof. The fluorinating agent is hydrofluoric acid, hexafluorophosphoric acid or HPF ₆ , XeF ₂ , F ₂ gas, F ₂ / Ar plasma, CF ₄ plasma, SF ₆ plasma, HCl, HPCl ₆ , XeCl ₂ , Cl ₂ Gas, Cl ₂ / Ar plasma, CCl ₄ plasma, SCl ₆ plasma, HBr, XeBr ₂ , Br ₂ gas, Br ₂ / Ar plasma, CBr ₄ plasma, SBr ₆ plasma, HI, XeI ₂ , I ₂ , I ₂ / 16. The method of claim 15, wherein the method is selected from Ar plasma, CI ₄ plasma, SI ₆ plasma, or combinations thereof. The fluorinating agent is hydrofluoric acid, hexafluorophosphoric acid or HPF ₆ , XeF ₂ , F ₂ gas, F ₂ / Ar plasma, CF ₄ plasma, SF ₆ plasma, HCl, HPCl ₆ , XeCl ₂ , Cl ₂ Gas, Cl ₂ / Ar plasma, CCl ₄ plasma, SCl ₆ plasma, HBr, XeBr ₂ , Br ₂ gas, Br ₂ / Ar plasma, CBr ₄ plasma, SBr ₆ plasma, HI, XeI ₂ , I ₂ , I ₂ / The method of claim 16, wherein the method is selected from Ar plasma, CI ₄ plasma, SI ₆ plasma, or combinations thereof.   16. The method of claim 15, wherein the supplying and depositing step comprises a printing, spraying, coating and / or casting procedure combined with a shear stress procedure.   The method of claim 15, wherein the supplying and depositing step comprises a reverse roll transfer coating procedure.   The method of claim 15, wherein the supplying and depositing step comprises a slot die coating or comma coating procedure.   The feeding and depositing step feeds the graphene oxide dispersion or graphene oxide gel layer onto a surface of a coating roller rotating in a first direction at a first linear velocity to form a graphene oxide applicator layer The applicator roller transfers the applicator layer of graphene oxide to a surface of a support film driven at a second linear velocity in a second direction opposite to the first direction; The method according to claim 15, wherein a wet layer of the graphene oxide is formed on the support film.   26. The method of claim 25, wherein the support film is driven by a reversing support roller disposed at a working distance from the application roller and rotating in the second direction opposite the first direction.   The step of supplying the graphene oxide dispersion or graphene oxide gel onto the surface of the application roller comprises using a metering roller and / or a doctor blade to apply a desired thickness of the graphene oxide on the application roller surface. 26. The method of claim 25, comprising providing an applicator layer.   26. A method according to claim 25, comprising manipulating 2, 3 or 4 rollers.   The support film is supplied from a feed roller, and the dried layer of halogenated graphene supported by the support film is wound on a take-up roller, and the method is performed in a roll-to-roll manner. 26. The method according to 25.   26. The method of claim 25, wherein a speed ratio defined as (second linear velocity) / (first linear velocity) is 1/5 to 5/1.   31. The method of claim 30, wherein the speed ratio is greater than 1/1 and less than 5/1.   Aging the wet layer of graphene oxide after step (b) over an aging time of 1 hour to 7 days in an aging chamber at an aging temperature of 25 ° C. to 100 ° C. and a humidity level of 20% to 99%, 16. The method of claim 15, further comprising the step of (c) aging the wetted graphene halide layer afterwards or aging the halogenated graphene integrated layer after step (d). At a first heat treatment temperature of more than 100 ° C. but not more than 3,200 ° C., the aligned halogenated graphene integrated layer is heat-treated for a desired length of time to obtain an interplanar spacing d ₀₀₂ and 1 of less than 0.4 nm. 16. The method of claim 15, further comprising the step (e) of producing a graphite film having a total oxygen / halogen content of less than wt%.   The method of claim 15, wherein the fluid medium comprises water, alcohol, a mixture of water and alcohol, or an organic solvent.   16. The method of claim 15, further comprising a compression step during or after step (d) to reduce the thickness of the integral layer.   34. The method of claim 33, further comprising a compression step during or after the heat treatment step to reduce the thickness of the graphite film.   The graphene oxide dispersion or graphene oxide gel in a reaction vessel at a reaction temperature for a length of time sufficient to obtain the graphite material in powder or fiber form to obtain the graphene oxide dispersion or graphene oxide gel. Prepared by immersing in an oxidizing liquid, the graphite material is natural graphite, artificial graphite, intermediate phase carbon, intermediate phase pitch, mesocarbon microbeads, soft carbon, hard carbon, coke, carbon fiber, carbon nanofiber, The method of claim 15, wherein the method is selected from carbon nanotubes or combinations thereof.   The graphene oxide dispersion or graphene oxide gel is obtained from a graphite material having the largest original graphite grain size, and the integrated layer of graphene halide has a grain size larger than the largest original grain size The method according to claim 15, which has a polycrystalline graphene structure.   The graphene oxide dispersion or graphene oxide gel is obtained from a graphite material having a plurality of graphite microcrystals that do not exhibit a preferred crystal orientation when measured by X-ray diffraction or electron diffraction, and the integrated graphene halide The method according to claim 15, wherein the crystallization layer is a polycrystalline graphene structure having a preferred crystal orientation as measured by the X-ray diffraction method or electron diffraction method. 33. The method of claim 32, wherein the aging step induces chemical linking, coalescence or chemical bonding of the graphene oxide sheet or graphene oxide molecules in an edge-to-edge manner. A method for producing an integrated layer of highly oriented graphene halide and graphene oxide,
a. Preparing either a graphene oxide dispersion having a graphene oxide sheet dispersed in a fluid medium or a graphene oxide gel having graphene oxide molecules dissolved in a fluid medium, the graphene oxide sheet or the oxidation The graphene molecules contain an amount of oxygen greater than 5% by weight;
b. Mixing a desired amount of graphene halide sheet into the graphene oxide suspension or gel to form a mixed suspension;
c. Supplying and depositing a layer of the mixed suspension on a surface of a supporting substrate under shear stress conditions, the supplying and depositing procedure comprising a halogenated graphene-graphene oxide mixture on the supporting substrate Including thinning induced by shearing of the mixed suspension to form a wet layer of and a orientation induced by shearing of the halogenated graphene and graphene oxide sheets or molecules;
d. Removing the fluid medium from the wet layer to form an integrated layer of the graphene halide and graphene oxide.

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