WO2017211992A1 - Method for the transfer of graphene - Google Patents
Method for the transfer of graphene Download PDFInfo
- Publication number
- WO2017211992A1 WO2017211992A1 PCT/EP2017/064037 EP2017064037W WO2017211992A1 WO 2017211992 A1 WO2017211992 A1 WO 2017211992A1 EP 2017064037 W EP2017064037 W EP 2017064037W WO 2017211992 A1 WO2017211992 A1 WO 2017211992A1
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- WIPO (PCT)
- Prior art keywords
- graphene
- organic phase
- graphene film
- substrate
- aqueous phase
- Prior art date
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 187
- 229910021389 graphene Inorganic materials 0.000 title claims abstract description 187
- 238000000034 method Methods 0.000 title claims abstract description 84
- 238000012546 transfer Methods 0.000 title description 33
- 239000000758 substrate Substances 0.000 claims abstract description 41
- 239000012074 organic phase Substances 0.000 claims abstract description 40
- 239000008346 aqueous phase Substances 0.000 claims abstract description 26
- 239000012455 biphasic mixture Substances 0.000 claims abstract description 23
- 239000012071 phase Substances 0.000 claims abstract description 22
- 239000007788 liquid Substances 0.000 claims abstract description 12
- 238000005530 etching Methods 0.000 claims abstract description 9
- 230000008018 melting Effects 0.000 claims abstract description 8
- 238000002844 melting Methods 0.000 claims abstract description 8
- 238000001704 evaporation Methods 0.000 claims abstract description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 20
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 17
- 239000010949 copper Substances 0.000 claims description 15
- 229910052802 copper Inorganic materials 0.000 claims description 14
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 12
- ROOXNKNUYICQNP-UHFFFAOYSA-N ammonium persulfate Chemical group [NH4+].[NH4+].[O-]S(=O)(=O)OOS([O-])(=O)=O ROOXNKNUYICQNP-UHFFFAOYSA-N 0.000 claims description 11
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical group [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 10
- 229910052710 silicon Inorganic materials 0.000 claims description 10
- 239000010703 silicon Substances 0.000 claims description 10
- 229910001870 ammonium persulfate Inorganic materials 0.000 claims description 9
- 229910052751 metal Inorganic materials 0.000 claims description 8
- 239000002184 metal Substances 0.000 claims description 8
- 125000000113 cyclohexyl group Chemical group [H]C1([H])C([H])([H])C([H])([H])C([H])(*)C([H])([H])C1([H])[H] 0.000 claims description 6
- 229910052742 iron Inorganic materials 0.000 claims description 6
- 238000001816 cooling Methods 0.000 claims description 5
- FJJYHTVHBVXEEQ-UHFFFAOYSA-N 2,2-dimethylpropanal Chemical compound CC(C)(C)C=O FJJYHTVHBVXEEQ-UHFFFAOYSA-N 0.000 claims description 4
- VOWZNBNDMFLQGM-UHFFFAOYSA-N 2,5-dimethylaniline Chemical compound CC1=CC=C(C)C(N)=C1 VOWZNBNDMFLQGM-UHFFFAOYSA-N 0.000 claims description 4
- UFFBMTHBGFGIHF-UHFFFAOYSA-N 2,6-dimethylaniline Chemical compound CC1=CC=CC(C)=C1N UFFBMTHBGFGIHF-UHFFFAOYSA-N 0.000 claims description 4
- DOLQYFPDPKPQSS-UHFFFAOYSA-N 3,4-dimethylaniline Chemical compound CC1=CC=C(N)C=C1C DOLQYFPDPKPQSS-UHFFFAOYSA-N 0.000 claims description 4
- HRXZRAXKKNUKRF-UHFFFAOYSA-N 4-ethylaniline Chemical compound CCC1=CC=C(N)C=C1 HRXZRAXKKNUKRF-UHFFFAOYSA-N 0.000 claims description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 4
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims description 4
- URLKBWYHVLBVBO-UHFFFAOYSA-N Para-Xylene Chemical group CC1=CC=C(C)C=C1 URLKBWYHVLBVBO-UHFFFAOYSA-N 0.000 claims description 4
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 4
- FGIUAXJPYTZDNR-UHFFFAOYSA-N potassium nitrate Chemical compound [K+].[O-][N+]([O-])=O FGIUAXJPYTZDNR-UHFFFAOYSA-N 0.000 claims description 4
- 230000003197 catalytic effect Effects 0.000 claims description 3
- HPXRVTGHNJAIIH-UHFFFAOYSA-N cyclohexanol Chemical compound OC1CCCCC1 HPXRVTGHNJAIIH-UHFFFAOYSA-N 0.000 claims description 3
- 239000000463 material Substances 0.000 claims description 3
- 238000005406 washing Methods 0.000 claims description 3
- NDVWOBYBJYUSMF-NKWVEPMBSA-N (1r,2s)-2-methylcyclohexan-1-ol Chemical compound C[C@H]1CCCC[C@H]1O NDVWOBYBJYUSMF-NKWVEPMBSA-N 0.000 claims description 2
- HMSVXZJWPVIVIV-UHFFFAOYSA-N 2,2-dimethylpentan-3-ol Chemical compound CCC(O)C(C)(C)C HMSVXZJWPVIVIV-UHFFFAOYSA-N 0.000 claims description 2
- OKXVARYIKDXAEO-UHFFFAOYSA-N 2,3,3-trimethylbutan-2-ol Chemical compound CC(C)(C)C(C)(C)O OKXVARYIKDXAEO-UHFFFAOYSA-N 0.000 claims description 2
- FBWWGYIEJGQWJP-UHFFFAOYSA-N 2,3,3-trimethylpentan-2-ol Chemical compound CCC(C)(C)C(C)(C)O FBWWGYIEJGQWJP-UHFFFAOYSA-N 0.000 claims description 2
- VVAKEQGKZNKUSU-UHFFFAOYSA-N 2,3-dimethylaniline Chemical compound CC1=CC=CC(N)=C1C VVAKEQGKZNKUSU-UHFFFAOYSA-N 0.000 claims description 2
- SXSWMAUXEHKFGX-UHFFFAOYSA-N 2,3-dimethylbutan-1-ol Chemical compound CC(C)C(C)CO SXSWMAUXEHKFGX-UHFFFAOYSA-N 0.000 claims description 2
- LCPVQAHEFVXVKT-UHFFFAOYSA-N 2-(2,4-difluorophenoxy)pyridin-3-amine Chemical compound NC1=CC=CN=C1OC1=CC=C(F)C=C1F LCPVQAHEFVXVKT-UHFFFAOYSA-N 0.000 claims description 2
- RNHKXHKUKJXLAU-UHFFFAOYSA-N 2-(4-methylphenyl)acetonitrile Chemical compound CC1=CC=C(CC#N)C=C1 RNHKXHKUKJXLAU-UHFFFAOYSA-N 0.000 claims description 2
- KLSLBUSXWBJMEC-UHFFFAOYSA-N 4-Propylphenol Chemical compound CCCC1=CC=C(O)C=C1 KLSLBUSXWBJMEC-UHFFFAOYSA-N 0.000 claims description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 2
- WWZKQHOCKIZLMA-UHFFFAOYSA-N Caprylic acid Natural products CCCCCCCC(O)=O WWZKQHOCKIZLMA-UHFFFAOYSA-N 0.000 claims description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims description 2
- 229910002651 NO3 Inorganic materials 0.000 claims description 2
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 2
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 claims description 2
- 229910052581 Si3N4 Inorganic materials 0.000 claims description 2
- 239000000908 ammonium hydroxide Substances 0.000 claims description 2
- GONOPSZTUGRENK-UHFFFAOYSA-N benzyl(trichloro)silane Chemical compound Cl[Si](Cl)(Cl)CC1=CC=CC=C1 GONOPSZTUGRENK-UHFFFAOYSA-N 0.000 claims description 2
- 229910017052 cobalt Inorganic materials 0.000 claims description 2
- 239000010941 cobalt Substances 0.000 claims description 2
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 2
- LMGZGXSXHCMSAA-UHFFFAOYSA-N cyclodecane Chemical compound C1CCCCCCCCC1 LMGZGXSXHCMSAA-UHFFFAOYSA-N 0.000 claims description 2
- VBWIZSYFQSOUFQ-UHFFFAOYSA-N cyclohexanecarbonitrile Chemical compound N#CC1CCCCC1 VBWIZSYFQSOUFQ-UHFFFAOYSA-N 0.000 claims description 2
- GPTJTTCOVDDHER-UHFFFAOYSA-N cyclononane Chemical compound C1CCCCCCCC1 GPTJTTCOVDDHER-UHFFFAOYSA-N 0.000 claims description 2
- WJTCGQSWYFHTAC-UHFFFAOYSA-N cyclooctane Chemical compound C1CCCCCCC1 WJTCGQSWYFHTAC-UHFFFAOYSA-N 0.000 claims description 2
- 239000004914 cyclooctane Substances 0.000 claims description 2
- FHADSMKORVFYOS-UHFFFAOYSA-N cyclooctanol Chemical compound OC1CCCCCCC1 FHADSMKORVFYOS-UHFFFAOYSA-N 0.000 claims description 2
- 239000011521 glass Substances 0.000 claims description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 2
- 229910052737 gold Inorganic materials 0.000 claims description 2
- 239000010931 gold Substances 0.000 claims description 2
- 229910052741 iridium Inorganic materials 0.000 claims description 2
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 claims description 2
- FUZZWVXGSFPDMH-UHFFFAOYSA-N n-hexanoic acid Natural products CCCCCC(O)=O FUZZWVXGSFPDMH-UHFFFAOYSA-N 0.000 claims description 2
- 229910017604 nitric acid Inorganic materials 0.000 claims description 2
- IOQPZZOEVPZRBK-UHFFFAOYSA-N octan-1-amine Chemical compound CCCCCCCCN IOQPZZOEVPZRBK-UHFFFAOYSA-N 0.000 claims description 2
- 229910052763 palladium Inorganic materials 0.000 claims description 2
- 229910052697 platinum Inorganic materials 0.000 claims description 2
- 235000010333 potassium nitrate Nutrition 0.000 claims description 2
- 239000004323 potassium nitrate Substances 0.000 claims description 2
- 229910052702 rhenium Inorganic materials 0.000 claims description 2
- WUAPFZMCVAUBPE-UHFFFAOYSA-N rhenium atom Chemical compound [Re] WUAPFZMCVAUBPE-UHFFFAOYSA-N 0.000 claims description 2
- 229910052703 rhodium Inorganic materials 0.000 claims description 2
- 239000010948 rhodium Substances 0.000 claims description 2
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 claims description 2
- 229910052707 ruthenium Inorganic materials 0.000 claims description 2
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims description 2
- WBHQBSYUUJJSRZ-UHFFFAOYSA-M sodium bisulfate Chemical compound [Na+].OS([O-])(=O)=O WBHQBSYUUJJSRZ-UHFFFAOYSA-M 0.000 claims description 2
- 229910000342 sodium bisulfate Inorganic materials 0.000 claims description 2
- CHQMHPLRPQMAMX-UHFFFAOYSA-L sodium persulfate Substances [Na+].[Na+].[O-]S(=O)(=O)OOS([O-])(=O)=O CHQMHPLRPQMAMX-UHFFFAOYSA-L 0.000 claims description 2
- WMXCDAVJEZZYLT-UHFFFAOYSA-N tert-butylthiol Chemical compound CC(C)(C)S WMXCDAVJEZZYLT-UHFFFAOYSA-N 0.000 claims description 2
- WFRBDWRZVBPBDO-UHFFFAOYSA-N tert-hexyl alcohol Natural products CCCC(C)(C)O WFRBDWRZVBPBDO-UHFFFAOYSA-N 0.000 claims description 2
- 229910000570 Cupronickel Inorganic materials 0.000 claims 1
- 239000000356 contaminant Substances 0.000 claims 1
- YOCUPQPZWBBYIX-UHFFFAOYSA-N copper nickel Chemical compound [Ni].[Cu] YOCUPQPZWBBYIX-UHFFFAOYSA-N 0.000 claims 1
- 238000011065 in-situ storage Methods 0.000 claims 1
- XDTMQSROBMDMFD-UHFFFAOYSA-N Cyclohexane Chemical compound C1CCCCC1 XDTMQSROBMDMFD-UHFFFAOYSA-N 0.000 description 36
- 230000002051 biphasic effect Effects 0.000 description 30
- 230000037303 wrinkles Effects 0.000 description 26
- 229920000642 polymer Polymers 0.000 description 22
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 18
- 235000012431 wafers Nutrition 0.000 description 18
- 229920003229 poly(methyl methacrylate) Polymers 0.000 description 17
- 239000004926 polymethyl methacrylate Substances 0.000 description 17
- 238000005229 chemical vapour deposition Methods 0.000 description 10
- 230000003287 optical effect Effects 0.000 description 10
- 238000013459 approach Methods 0.000 description 9
- 239000000243 solution Substances 0.000 description 8
- 238000004627 transmission electron microscopy Methods 0.000 description 8
- VAZSKTXWXKYQJF-UHFFFAOYSA-N ammonium persulfate Chemical compound [NH4+].[NH4+].[O-]S(=O)OOS([O-])=O VAZSKTXWXKYQJF-UHFFFAOYSA-N 0.000 description 7
- 238000004630 atomic force microscopy Methods 0.000 description 7
- 238000011109 contamination Methods 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 6
- 230000007547 defect Effects 0.000 description 6
- 239000010410 layer Substances 0.000 description 6
- 239000004593 Epoxy Substances 0.000 description 5
- 239000003960 organic solvent Substances 0.000 description 5
- 239000004033 plastic Substances 0.000 description 5
- 239000002356 single layer Substances 0.000 description 5
- 238000001069 Raman spectroscopy Methods 0.000 description 4
- 238000002474 experimental method Methods 0.000 description 4
- 239000011889 copper foil Substances 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 238000001878 scanning electron micrograph Methods 0.000 description 3
- 238000004626 scanning electron microscopy Methods 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 230000005669 field effect Effects 0.000 description 2
- 230000008014 freezing Effects 0.000 description 2
- 238000007710 freezing Methods 0.000 description 2
- JYVHOGDBFNJNMR-UHFFFAOYSA-N hexane;hydrate Chemical compound O.CCCCCC JYVHOGDBFNJNMR-UHFFFAOYSA-N 0.000 description 2
- 230000001939 inductive effect Effects 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 238000000399 optical microscopy Methods 0.000 description 2
- 230000000704 physical effect Effects 0.000 description 2
- 230000003252 repetitive effect Effects 0.000 description 2
- 239000007790 solid phase Substances 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 238000011282 treatment Methods 0.000 description 2
- DZPCYXCBXGQBRN-UHFFFAOYSA-N 2,5-Dimethyl-2,4-hexadiene Chemical compound CC(C)=CC=C(C)C DZPCYXCBXGQBRN-UHFFFAOYSA-N 0.000 description 1
- IRLPACMLTUPBCL-KQYNXXCUSA-N 5'-adenylyl sulfate Chemical compound C1=NC=2C(N)=NC=NC=2N1[C@@H]1O[C@H](COP(O)(=O)OS(O)(=O)=O)[C@@H](O)[C@H]1O IRLPACMLTUPBCL-KQYNXXCUSA-N 0.000 description 1
- 238000001237 Raman spectrum Methods 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 238000000089 atomic force micrograph Methods 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 238000012790 confirmation Methods 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 238000007306 functionalization reaction Methods 0.000 description 1
- -1 graphene ion Chemical class 0.000 description 1
- NEXSMEBSBIABKL-UHFFFAOYSA-N hexamethyldisilane Chemical compound C[Si](C)(C)[Si](C)(C)C NEXSMEBSBIABKL-UHFFFAOYSA-N 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
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- 229920003023 plastic Polymers 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 241000894007 species Species 0.000 description 1
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/15—Nano-sized carbon materials
- C01B32/182—Graphene
- C01B32/194—After-treatment
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
Definitions
- the present invention relates to a method for transferring a graphene sheet to a substrate.
- Graphene is known for its outstanding mechanical, optical and electrical properties.
- Graphene films which have been synthesised by chemical vapor deposition (CVD), have been shown to have uniform structure and be of high quality.
- Copper is one of the many metals which is used to catalyse the growth of graphene.
- the problem with graphene grown on copper is that it tends to crack due to copper oxidation, particularly in water. Therefore, the transfer of graphene films to substrates of interest has been a particular challenge.
- long chain polymers have been used in transfer methods to prevent cracking and to preserve the two- dimensional nature of graphene (Suk et al. "Transfer of CVD-grown monolayer graphene onto arbitrary substrates.," ACS Nano, vol. 5, no.9, pp. 6916-24, Sep 2011 ).
- interfacial caging uses a mixture of an organic solvent and an aqueous solution where graphene floats (is “caged") between the two phases. It is important that the two liquids are immiscible and that the organic solvent has a lower density and higher melting point with respect to the aqueous phase. This enables using this interfacial caging technique for graphene transfer.
- the biphasic mixture serves as a soft and flexible stabilizing medium to prevent the graphene from cracking and results in a flatter graphene surface.
- Figure 1 comprises five photographs showing interfacial caging during the transfer of graphene to TEM grids.
- Figure 2 is a schematic showing the biphasic transfer methods.
- Figure 3 shows optical images showing the characterization of continuality and quality of graphene transferred by the cyclohexane-assisted caging method, the PMMA-assisted method, the top-fishing method and hexane-assisted method.
- Figure 3a shows an optical image of graphene transferred by top-fishing method
- Figure 3b shows an optical image of graphene transferred by the PMMA-assisted method
- Figure 3c shows an optical image of graphene transferred by the hexane-assisted method
- Figure 3d shows an optical image of graphene transferred by the biphasic method following the second approach
- Figure 3e shows a Raman spectra of graphene samples transferred to silicon wafers by cyclohexane-assisted, PMMA-assisted and top-fishing methods
- Figure 3f shows a SEM image of graphene transferred to quantifoil TEM grids by the biphasic method.
- Figure 4 show atomic force microscopy (AFM) images and height profiles of graphene samples transferred to silicon wafer by (a) biphasic method (b) PMMA-assisted method (c) top-fishing method; and (d) hexane-assisted transfer method.
- Figure 5 shows diffraction patterns of graphene taken at the beginning of exposure to electron beam and then after 14 and 15 minutes, respectively.
- Figure 6 shows the electrolyte gate voltage (Vref) dependent sheet conductance (G) of polymer-free graphene at biphasic interface (black) and epoxy substrate (grey).
- a method of transferring a graphene film to a substrate comprising:
- the above methods used to perform the interfacial caging can also be described as "biphasic caging" methods.
- the biphasic mixture comprises at least one aqueous phase and at least one organic phase.
- the phases are immiscible and that the organic phase has a plastic crystal phase of above 0 °C.
- the aqueous phase is water and comprises at least one etchant.
- the organic phase can be selected from a solvent which is less dense than water and is immiscible with water.
- the organic solvent has a melting point between -5°C and 20°C. More preferably, the organic solvent is selected from cyclohexane, cyclooctane, cyclodecane, cyclononane, p-xylene, 2- methyl-2-propanethiol, dimethyl butanol, hexanoic acid, 2,2-dimethyl 3-pentanol, 4- ethylaniline, ⁇ , ⁇ -dimethylaniline, 2,3-dimethylaniline, aminooctane, 2,3,3-trimethyl 2- pentanol, 2,2-dimethylpropanal, cyclohexanecarbonitrile, 2,5-dimethyl- 2,4-hexadiene, cis-2-methylcyclohexanol, 2,5-dimethylaniline, 2,6-d
- the biphasic mixture comprises water as the aqueous phase and cyclohexane as the organic phase.
- Water and cyclohexane are immiscible (solubility of cyclohexane in water is 0.006% at 25°C, solubility of water in cyclohexane is 0.01% at 20°C).
- cyclohexane forms a plastic crystal phase, whereas water is liquid at 0°C.
- Biphasic transfer can be carried out at temperatures between 0°C and 7°C in which cyclohexane is plastic crystal and water is a liquid.
- an etchant is used to completely etch away the support from the graphene which leaves the graphene floating ("caged") in between the two phases.
- the etchant must be capable of etching the support (typically the support is a catalytic metal such as copper) and is selected from, but not limited to, ammonium persulfate, iron(lll) chloride, nitric acid, ammonium hydroxide/hydrogen peroxide, sulfuric acid/hydrogen peroxide, hydrogen peroxide/sodium bisulfate, potassium nitrate/hydrochloric acid, sodium persulfate or iron(lll) nitrate.
- the etchant is insoluble in the organic phase which minimises the interchange of matter between the two phases.
- the etchant is ammonium persulfate.
- the transfer of graphene is executed by cooling the mixture down after etching (see Figure 2).
- the organic phase has a higher freezing point than the aqueous phase.
- the biphasic mixture is cooled down to a temperature such that the organic phase solidifies, but the aqueous phase remains liquid.
- the organic phase is cyclohexane and the aqueous phase is a solution of ammonium persulfate.
- the mixture is cooled down to 2°C. At this temperature, cyclohexane solidifies but the solution of ammonium persulfate remains liquid.
- the graphene sticks to the surface of the solidified cyclohexane. Due to the soft and flexible jelly-like texture of high-temperature solid phase of cyclohexane this step does not induce the formation of cracks in graphene.
- the solidified layer comprising cyclohexane with graphene on it can be easily transferred and placed on a substrate (see Figure 2a).
- cyclohexane is then rinsed with cold water (2°C). In order to remove the solidified cyclohexane, the cyclohexane is left to vaporize (cyclohexane is very volatile, it normally sublimates in 15-90 min depending on the volume).
- the substrate which is suitable for the present invention is selected from a silicon wafer, a TEM quantifoil grid, TEM nanochips, silicon nitride chips or glass chips. Substrates made from other types of materials such as polymers and metals can also be used. The skilled person would be aware of further suitable materials from which the substrate can be made.
- the graphene support is a catalytic metal, preferably wherein the metal is copper, nickel, platinum, gold, palladium, iridium, ruthenium, cobalt, rhodium, rhenium or iron.
- the monolayer graphene films were grown on a 25 pm thick copper foil in a cold wall chemical vapor deposition system (as described in the "Handbook of chemical vapor deposition (CVD)", H. O. Pierson).
- Figure 2 shows schematics of the biphasic transfer a) the first approach.
- Graphene is inserted in the biphasic solution (1 ), the copper is etched (2), the solution is cooled down to 2°C until the cyclohexane phase solidifies (3), and the cyclohexane phase with graphene stuck on it is transferred onto a substrate (4). After that the sample is kept at 2°C until the cyclohexane evaporates (sublimates) b) second approach.
- Graphene is inserted in the biphasic solution together with a wafer on top of it (1 ), the copper is etched (2), the solution is cooled down to 2°C until the cyclohexane phase solidifies (3), and the cyclohexane phase with graphene/wafer stuck on it is removed from the solution (4). After that the sample is rinsed with water to remove the residues of cyclohexane and APS.
- the soft gel-like structure of the plastic solid phase of cyclohexane conforms the surface of graphene preventing mechanical damaging from occurring.
- the same effect has also been observed using hexamethyldisilane, cyclohexanol and combinations thereof. This is because these particular solvents form a plastic crystal phase. Solvents such as these, and in particular cyclohexane, are also highly volatile and this is an additional advantage when reducing the contamination of graphene.
- the transfer process is completely driven by manipulating the physical properties of cyclohexane and doesn't require multiple tools.
- Graphene transferred with the biphasic caging clearly has lower density of wrinkles, and the wrinkles themselves are shorter and narrower as opposed to the other three samples (Figure 3a).
- Image of PMMA- transferred graphene has multiple closed white lines all over the sample ( Figure 3b). Those could be interpreted as wrinkles or as polymer residues segregated on the grain boundaries of graphene.
- Top-fished graphene as expected, exhibits repetitive pattern of bigger, compare to PMMA- and cyclohexane-transferred graphene, parallel wrinkles (white lines with the length of few micrometers and height up to 10 nm, see Figure 3c). This is in a good agreement with the optical images.
- the surface of the hexane-transferred graphene is covered with wrinkles too, but of smaller size with respect to the top-fished sample ( Figure 3d).
- Figures 3f and g show the Scanning Electron Microscopy (SEM) images of the samples transferred in a biphasic method on quantifoil TEM grids. Full coverage has been achieved in large scale. Free standing graphene membranes are free from wrinkles, tearings and visible contaminations (see Figure 3f).
- SEM Scanning Electron Microscopy
- AFM Atomic Force Microscopy
- cyclohexane contrarily to PMMA, is a smaller molecule without conjugated electron system, i.e. not prone to ⁇ - ⁇ stacking on graphene surface, which together with its high volatility make cyclohexane very easy to remove.
- the method allows easy handling without subjecting graphene to harsh treatments. Big areas of graphene can be transferred without inducing defects and big cracks, which was confirmed by Raman spectroscopy, optical, Atomic Force and Scanning Electron microscopy.
- the PMMA-assisted method graphene is supported by a polymer, which allows for controlled further handling and keeps the integrity of graphene.
- the polymer conforms graphene surface and prevents it from formation of large wrinkles.
- the polymer doesn't prevent the graphene from formation of multiple smaller wrinkles.
- Another major drawback of PMMA-based technique is polymer residues. The top-fishing method results in cleaner, but cracked and wrinkled graphene.
- the graphene is softly supported from its both sides, which minimizes such irregularities as wrinkles, crumples and folding's.
- the method allows easy handling without subjecting graphene to harsh treatments. Big areas of graphene can be transferred without inducing defects and big cracks, which was confirmed by Raman spectroscopy, optical, Atomic Force and Scanning Electron microscopy.
- the graphene device at biphasic interface exhibits a significantly higher average carrier mobility (-3470 cm2/Vs, ⁇ 1940 cm2/Vs for hole and -5000 cm2/Vs for electron, see Figure ) compared to -1505 cm2/Vs (-940 cm2/Vs for hole and -2070 cm2/Vs for electron) on epoxy substrate.
- This indicates that the biphasic configuration helps to retain the electrical properties of graphene as the electrical performance of the graphene device is significantly improved. This can be due to the fact that this process reliably results in a graphene layer that has clean surfaces on both side free of polymer contamination. This last point is important because resist residues can prevent surface functionalization and suppress sensing.
- Such a graphene sheet at biphasic interface is, therefore, ideal for sensing applications, especially when a flexible and high-performance graphene devices are needed.
- the floating graphene devices tend to break if the CVD graphene contains too much defects.
- FIG. 6 The electrolyte gate voltage (Vref) dependent sheet conductance (G) of polymer- free graphene at biphasic interface (black) and epoxy substrate (red).
- the gate voltage of the charge neutrality point VCNP 0.16 mV compared to -0.2 mV on epoxy substrate.
- the floating graphene devices tend to break if the CVD graphene contains too many defects.
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Abstract
The present invention relates to a method of transferring a graphene film to a substrate comprising providing a graphene film grown on a support and positioning the supported graphene film at the interface of a biphasic mixture, wherein the biphasic mixture comprises an aqueous phase and an organic phase, and wherein the phases are immiscible, wherein the aqueous phase further comprises an etchant which completely etches the graphene support from the graphene film. After the etching procedure has taken place, the biphasic mixture is cooled to a temperature such that the organic phase solidifies but the aqueous phase remains a liquid, wherein the graphene film sticks to the solidified organic phase. The solidified organic phase is then separated from the aqueous phase and the graphene of the solidified phase is applied to a substrate. The solidified organic phase is then removed by melting, subliming or evaporating the organic phase.
Description
METHOD FOR THE TRANSFER OF GRAPHENE
The present invention relates to a method for transferring a graphene sheet to a substrate. Graphene is known for its outstanding mechanical, optical and electrical properties. Graphene films, which have been synthesised by chemical vapor deposition (CVD), have been shown to have uniform structure and be of high quality.
Copper is one of the many metals which is used to catalyse the growth of graphene. However, the problem with graphene grown on copper is that it tends to crack due to copper oxidation, particularly in water. Therefore, the transfer of graphene films to substrates of interest has been a particular challenge. For years now, long chain polymers have been used in transfer methods to prevent cracking and to preserve the two- dimensional nature of graphene (Suk et al. "Transfer of CVD-grown monolayer graphene onto arbitrary substrates.," ACS Nano, vol. 5, no.9, pp. 6916-24, Sep 2011 ).
Unfortunately, because of their macromolecular structures, the use of polymers in the transfer of graphene is problematic because they stick and irreversibly modify the inherent chemical and physical properties of graphene (Pirckle et al. "The effect of chemical residues on the physical and electrical properties of chemical vapor deposited graphene transferred to Si02, Appl. Phys. Lett., vol. 99, no. 12, p. 122108, 201 1).
Instead of using a polymer, existing polymer-free techniques suggest special frames and holders to keep the integrity of the floating graphene while the water level is carefully lowered down to transfer the graphene onto a substrate (Lin et al "A direct and polymer- free method for transferring graphene grown by chemical vapor deposition to any substrate" ASC Nano no.2, pp. 1784-1791 , 2014). In one example, graphene was transferred to TEM quantifoil grids without using any polymer. The TEM grid was placed on graphene on copper floating in the etchant and a drop of isopropanol was cast on top putting the grid into a direct contact with graphene. However, this technique cannot be used for other substrates that are heavier or have featured morphology (Algara-Siller ef al, "Square ice in graphene nanocapillaries.," Nature, vol. 519, no. 7544, pp. 443-5, Mar. 2015). It is therefore desirable to have a polymer-free method for the transfer of graphene. The Applicant has surprisingly found a technique for transferring grown graphene samples onto various arbitrary substrates without using a polymer. The method of the present invention
is based on the use of a biphasic mixture as an alternative to polymers. While polymers are known to protect graphene from folding during the transfer of graphene, the Applicant has found that organic solvents (such as cyclohexane) can operate similarly but without major contamination or wrinkle formation of the graphene.
This improved technique is called interfacial caging and uses a mixture of an organic solvent and an aqueous solution where graphene floats (is "caged") between the two phases. It is important that the two liquids are immiscible and that the organic solvent has a lower density and higher melting point with respect to the aqueous phase. This enables using this interfacial caging technique for graphene transfer. The biphasic mixture serves as a soft and flexible stabilizing medium to prevent the graphene from cracking and results in a flatter graphene surface.
The present invention will now be described, by way of example, with reference to the accompanying figures in which:
Figure 1 comprises five photographs showing interfacial caging during the transfer of graphene to TEM grids. Figure 2 is a schematic showing the biphasic transfer methods.
Figure 3 shows optical images showing the characterization of continuality and quality of graphene transferred by the cyclohexane-assisted caging method, the PMMA-assisted method, the top-fishing method and hexane-assisted method. Figure 3a shows an optical image of graphene transferred by top-fishing method; Figure 3b shows an optical image of graphene transferred by the PMMA-assisted method; Figure 3c shows an optical image of graphene transferred by the hexane-assisted method; Figure 3d shows an optical image of graphene transferred by the biphasic method following the second approach; Figure 3e shows a Raman spectra of graphene samples transferred to silicon wafers by cyclohexane-assisted, PMMA-assisted and top-fishing methods; and Figure 3f shows a SEM image of graphene transferred to quantifoil TEM grids by the biphasic method.
Figure 4 show atomic force microscopy (AFM) images and height profiles of graphene samples transferred to silicon wafer by (a) biphasic method (b) PMMA-assisted method (c) top-fishing method; and (d) hexane-assisted transfer method.
Figure 5 shows diffraction patterns of graphene taken at the beginning of exposure to electron beam and then after 14 and 15 minutes, respectively.
Figure 6 shows the electrolyte gate voltage (Vref) dependent sheet conductance (G) of polymer-free graphene at biphasic interface (black) and epoxy substrate (grey).
According to the present invention, there is provided a method of transferring a graphene film to a substrate comprising:
(i) providing a graphene film grown on a support;
(ii) positioning the supported graphene film at the interface of a biphasic mixture, wherein the biphasic mixture comprises an aqueous phase and an organic phase, and wherein the phases are immiscible, wherein the aqueous phase further comprises an etchant which completely etches the graphene support from the graphene film;
(iii) after etching has taken place, cooling the biphasic mixture to a temperature such that the organic phase solidifies but the aqueous phase remains a liquid, wherein the graphene film sticks to the solidified organic phase,
(iv) separating the solidified organic phase from the aqueous phase;
(v) applying the graphene of the solidified phase to a substrate; and
(vi) removing the solidified organic phase by melting, subliming or evaporating the organic phase.
In a further aspect of the present invention, there is also provided a method of transferring a graphene film to a substrate comprising:
(i) providing a graphene film grown on a support and placing it on a substrate;
(ii) positioning the supported graphene film substrate at the interface of a biphasic mixture, wherein the biphasic mixture comprises an aqueous phase and an organic phase, and wherein the phases are immiscible, wherein the aqueous phase further comprises an etchant which completely etches the graphene support from the graphene film;
(iii) after etching has taken place, cooling the biphasic mixture to a temperature such that the organic phase solidifies but the aqueous phase remains a liquid, wherein the graphene film sticks to the solidified organic phase,
(iv) removing the solidified organic phase by melting, subliming or evaporating the organic phase.
The above methods used to perform the interfacial caging can also be described as "biphasic caging" methods. The biphasic mixture comprises at least one aqueous phase and at least one organic phase. What is key for the method is that the phases are immiscible and that the organic phase has a plastic crystal phase of above 0 °C. Preferably, the aqueous phase is water and comprises at least one etchant.
In accordance with the present invention, the organic phase can be selected from a solvent which is less dense than water and is immiscible with water. Preferably, the organic solvent has a melting point between -5°C and 20°C. More preferably, the organic solvent is selected from cyclohexane, cyclooctane, cyclodecane, cyclononane, p-xylene, 2- methyl-2-propanethiol, dimethyl butanol, hexanoic acid, 2,2-dimethyl 3-pentanol, 4- ethylaniline, η,η-dimethylaniline, 2,3-dimethylaniline, aminooctane, 2,3,3-trimethyl 2- pentanol, 2,2-dimethylpropanal, cyclohexanecarbonitrile, 2,5-dimethyl- 2,4-hexadiene, cis-2-methylcyclohexanol, 2,5-dimethylaniline, 2,6-dimethylaniline, cyclohexanol, 2,3,3- trimethyl-2-butanol, 3,4-dimethylaniline, cyclooctanol, p-methylbenzylcyanide, 4- propylphenol, or combinations thereof. In a preferred embodiment, the organic phase is cyclohexane.
In a preferred embodiment, the biphasic mixture comprises water as the aqueous phase and cyclohexane as the organic phase. Water and cyclohexane are immiscible (solubility of cyclohexane in water is 0.006% at 25°C, solubility of water in cyclohexane is 0.01% at 20°C). In the temperature window of -87°C<T<7°C cyclohexane forms a plastic crystal phase, whereas water is liquid at 0°C. Biphasic transfer can be carried out at temperatures between 0°C and 7°C in which cyclohexane is plastic crystal and water is a liquid.
As described above, when the graphene film grown on a support and is inserted into the biphasic mixture, an etchant is used to completely etch away the support from the graphene which leaves the graphene floating ("caged") in between the two phases. The etchant must be capable of etching the support (typically the support is a catalytic metal such as copper) and is selected from, but not limited to, ammonium persulfate, iron(lll) chloride, nitric acid, ammonium hydroxide/hydrogen peroxide, sulfuric acid/hydrogen peroxide, hydrogen peroxide/sodium bisulfate, potassium nitrate/hydrochloric acid, sodium persulfate or iron(lll) nitrate. The etchant is insoluble in the organic phase which minimises the interchange of matter between the two phases. Preferably, the etchant is ammonium persulfate.
Once inserted into the biphasic mixture, the sample floats directly at the interface exposing graphene to the cyclohexane phase and exposing copper to the etchant solution. When the copper is completely etched, graphene remains floating between the two phases. The two phases apply pressure from each side of the graphene acting as a firm but flexible shell which limits perturbations and conforms the surface of the graphene.
In one aspect according to the present invention, the transfer of graphene is executed by cooling the mixture down after etching (see Figure 2). The organic phase has a higher freezing point than the aqueous phase. The biphasic mixture is cooled down to a temperature such that the organic phase solidifies, but the aqueous phase remains liquid.
In a preferred embodiment, the organic phase is cyclohexane and the aqueous phase is a solution of ammonium persulfate. After completion of the etching step, the mixture is cooled down to 2°C. At this temperature, cyclohexane solidifies but the solution of ammonium persulfate remains liquid. The graphene sticks to the surface of the solidified cyclohexane. Due to the soft and flexible jelly-like texture of high-temperature solid phase of cyclohexane this step does not induce the formation of cracks in graphene. The solidified layer comprising cyclohexane with graphene on it can be easily transferred and placed on a substrate (see Figure 2a). To avoid residues of ammonium persulfate on graphene, cyclohexane is then rinsed with cold water (2°C). In order to remove the solidified cyclohexane, the cyclohexane is left to vaporize (cyclohexane is very volatile, it normally sublimates in 15-90 min depending on the volume).
In a second approach, the substrate is placed directly on a copper foil covered with graphene (Figure 2b). During etching, due to the interfacial tension between water and cyclohexane, both graphene and the substrate can float at the interface. After solidification, cyclohexane is removed by melting and subsequently washing with water. The fact that graphene was in direct contact with the substrate from the very start of the transfer prevents the formation of ammonium persulfate residues between the graphene and the substrate. The contaminations from the other side of graphene can be removed by rinsing the sample with water.
Having a different affinity to water, copper with graphene and the substrate (for example, a silicon wafer) tend to repel from each other. This problem was overcome by wrapping copper foil around the substrate.
The substrate which is suitable for the present invention is selected from a silicon wafer, a TEM quantifoil grid, TEM nanochips, silicon nitride chips or glass chips. Substrates made from other types of materials such as polymers and metals can also be used. The skilled person would be aware of further suitable materials from which the substrate can be made. The graphene support is a catalytic metal, preferably wherein the metal is copper, nickel, platinum, gold, palladium, iridium, ruthenium, cobalt, rhodium, rhenium or iron. In a preferred embodiment, the monolayer graphene films were grown on a 25 pm thick copper foil in a cold wall chemical vapor deposition system (as described in the "Handbook of chemical vapor deposition (CVD)", H. O. Pierson).
Figure 2 shows schematics of the biphasic transfer a) the first approach. Graphene is inserted in the biphasic solution (1 ), the copper is etched (2), the solution is cooled down to 2°C until the cyclohexane phase solidifies (3), and the cyclohexane phase with graphene stuck on it is transferred onto a substrate (4). After that the sample is kept at 2°C until the cyclohexane evaporates (sublimates) b) second approach. Graphene is inserted in the biphasic solution together with a wafer on top of it (1 ), the copper is etched (2), the solution is cooled down to 2°C until the cyclohexane phase solidifies (3), and the cyclohexane phase with graphene/wafer stuck on it is removed from the solution (4). After that the sample is rinsed with water to remove the residues of cyclohexane and APS.
To prove the necessity of having the layer of solid cyclohexane for the transfer, we also performed three "control" transfers. In the first control transfer the first approach was reproduced and liquid cyclohexane, i.e. at room temperature was used and the graphene was "fished out" directly with a silicon wafer. As a result, no graphene was found on the wafer. In the second control experiment the second approach was reproduced also skipping the freezing step. Again, no graphene was transferred to the substrate, which, therefore, indicates the essential role of the solidification of cyclohexane for transferring graphene. For the third control experiment the second approach transfer method was used without any cyclohexane layer, i.e. simply placed a silicon wafer on top of graphene grown on copper floating on the surface of etchant. No graphene was found on the wafer after the transfer demonstrating the necessity of the supporting upper layer.
The soft gel-like structure of the plastic solid phase of cyclohexane conforms the surface of graphene preventing mechanical damaging from occurring. The same effect has also been observed using hexamethyldisilane, cyclohexanol and combinations thereof. This is because these particular solvents form a plastic crystal phase. Solvents such as these, and in particular cyclohexane, are also highly volatile and this is an additional advantage
when reducing the contamination of graphene. Furthermore, the transfer process is completely driven by manipulating the physical properties of cyclohexane and doesn't require multiple tools. To evaluate the feasibility and relevance of the present invention, a comparison was made with the most commonly used polymer- transfer method, so called polymethyl methacrylate (P MA)-assisted transfer and with the potentially most "clean" method, described herein as "top-fishing", where graphene is simply picked up by a wafer while floating on the surface of the etchant. PMMA protects and conforms the surface of graphene and therefore allows the transfer of large continuous areas of graphene. However, this method has the disadvantage of inevitable contamination of graphene with the polymer. In contrast, the top-fishing transfer method results in cleaner, but discontinuous graphene samples with multiple irregularities (folding's, wrinkles, cracks etc.). The samples, however, have very different topological features. Graphene transferred with the biphasic caging clearly has lower density of wrinkles, and the wrinkles themselves are shorter and narrower as opposed to the other three samples (Figure 3a). Image of PMMA- transferred graphene has multiple closed white lines all over the sample (Figure 3b). Those could be interpreted as wrinkles or as polymer residues segregated on the grain boundaries of graphene. Top-fished graphene, as expected, exhibits repetitive pattern of bigger, compare to PMMA- and cyclohexane-transferred graphene, parallel wrinkles (white lines with the length of few micrometers and height up to 10 nm, see Figure 3c). This is in a good agreement with the optical images. The surface of the hexane-transferred graphene is covered with wrinkles too, but of smaller size with respect to the top-fished sample (Figure 3d).
Among all the different methods of transfer, samples transferred by PMMA-assisted and biphasic technique showed similar continuality and least amounts of cracks; graphene transferred to the silicon wafer through the first approach of biphasic method, however, has traces of residual ammonium persulfate (Figure 3c) which will require a further washing step. Graphene samples transferred with PMMA and second biphasic approach look similar and don't have obvious imperfections (Figure 3d and b). Graphene transferred by top-fishing method is clearly less uniform and has multiple wrinkles, which is clearer in the high magnification image. Those wrinkles originate from the moment when graphene floating on the etchant surface meets the substrate that doesn't conform the graphene surface. The samples transferred with hexane resemble the top-fished samples - during
the scooping of the graphene from the biphasic mixture it broke into smaller pieces and became more wrinkled.
Samples transferred to silicon wafers by three different methods show very similar Raman signatures with the peaks typical for a monolayer graphene sample (Figure 3e), e). Sharp 2D peak, that fits one Lorentz function indicates monolayer graphene (see A. C. Ferrari et al, "Raman spectroscopy as a versatile tool for studying the properties of graphene.," Nat. Nanotechnol., vol. 8, no. 4, pp 235-46, Apr 2013). Negligibly small D peaks indirectly evidence that almost no defects in graphene structure were generated during the transfer processes (again see A. C. Ferrari ef al.,).
Figures 3f and g show the Scanning Electron Microscopy (SEM) images of the samples transferred in a biphasic method on quantifoil TEM grids. Full coverage has been achieved in large scale. Free standing graphene membranes are free from wrinkles, tearings and visible contaminations (see Figure 3f).
SEM of the grids with graphene transferred by the biphasic method performed according to the present invention showed close to full coverage of the grid with graphene. However, inevitably there are areas with cracks and holes, which are seen as uncovered holes in quantifoil film. These defect areas provide a contrast with graphene-covered holes which is necessary for visualization and confirmation of presence of graphene on the grid. In general, no clear distinction between the biphasic transfer and PMMA-assisted method can be made from SEM images. The possible reason for that could be that nonconductive contaminating species can't be visualized with this technique.
Of the experiments performed, most importantly were the Atomic Force Microscopy (AFM) experiments to see if the methods of the present invention resulted in residues, cracks, wrinkles or folding in the graphene sheet. A typical AFM image of graphene transferred to a silicon wafer by PMMA-assisted method has multiple features that correspond to wrinkles, PMMA residues and dust particles (see T. Hallam et al., "Strain, Bubbles, Dirt, and Folds: A Study of Graphene Polymer Assisted-Transfer,", Adv. Mater. Interfaces, vol. 1 , no. 6, p. n/a-n/a, Sep 2014).
The samples, however, have very different topological features. Graphene transferred with the biphasic caging clearly has lower density of wrinkles, and the wrinkles themselves are shorter and narrower as opposed to the other three samples (Figure 4a). Image of PMMA-transferred graphene has multiple closed white lines all over the sample (Figure
4b). Those could be interpreted as wrinkles or as polymer residues segregated on the grain boundaries of graphene. Top-finished graphene, as expected, exhibits repetitive pattern of bigger, compare to PMMA- and cyclohexane-transferred graphene, parallel wrinkles (white lines with the length of few micrometers and height up to 10 nm, see Figure 4c). This is in a good agreement with the optical images. The surface of the hexane- transferred graphene is covered with wrinkles too, but of smaller size with respect to the top-fished sample (Figure 4d).
In conclusion, AFM studies showed better uniformity of graphene transferred by the biphasic method of the present invention. This confirms the advantage of transversal biphasic caging for reducing vibrations and corrugations of graphene surface during the transfer process In addition to that, it's clear that having a top liquid layer on the graphene improves the fishing process (less wrinkles on the sample transferred by hexane-assisted method), but in terms of integrity and smoothness of the surface cannot compete with the polymer-assisted method and the biphasic method reported in this work.
A transmission electron microscopy (TEM) study of graphene transferred to quantifoil grids also showed that the graphene didn't have folding's and wrinkles. The sample exhibited almost no change in diffraction patterns taken over 15 minutes, which indicates, that no noticeable contamination took place on the graphene surface (Figure 5).
The biphasic caging with three principally different transfer methods were compared and summarized the results shown in Table 1. In PMMA-assisted method graphene is supported by a polymer, which allows for controllable further handling and keeps the integrity of graphene. The polymer conforms graphene surface and prevents it from formation of large wrinkles. However, we observed that the polymer doesn't prevent the graphene from formation of multiple smaller wrinkles. Another major drawback of PMMA- based technique is polymer residues. Opposed to it, the top-fishing and hexane-assisted methods result in cleaner, but cracked and wrinkled graphene. Table 1. Analysis of graphene samples transferred with biphasic caging, PMMA-assisted method and top-fishing method
Continuality
the wafer the wafer the wafer the wafer
Density of
low high low high
cracks
2-15 nm high,
2-3 nm high, 2-15 nm high, up >15 nm high,
Size of wrinkles up to 10 pm
0.5-2μηπ long to 10 pm long >10 pm long long
Density of
low medium high high
wrinkles
In the biphasic caging graphene, on the one hand, is softly supported from its both sides, which minimizes such irregularities as wrinkles, crumples and folding's. On the other hand, cyclohexane, contrarily to PMMA, is a smaller molecule without conjugated electron system, i.e. not prone to ττ-π stacking on graphene surface, which together with its high volatility make cyclohexane very easy to remove. The method allows easy handling without subjecting graphene to harsh treatments. Big areas of graphene can be transferred without inducing defects and big cracks, which was confirmed by Raman spectroscopy, optical, Atomic Force and Scanning Electron microscopy.
In conclusion, the PMMA-assisted method graphene is supported by a polymer, which allows for controlled further handling and keeps the integrity of graphene. The polymer conforms graphene surface and prevents it from formation of large wrinkles. However, the polymer doesn't prevent the graphene from formation of multiple smaller wrinkles. Another major drawback of PMMA-based technique is polymer residues. The top-fishing method results in cleaner, but cracked and wrinkled graphene.
In the biphasic caging methods according to the present invention, the graphene is softly supported from its both sides, which minimizes such irregularities as wrinkles, crumples and folding's. Furthermore, using cyclohexane as the organic phase, contrarily to PMMA, is a smaller molecule without conjugated electron system, i.e. not prone to T T stacking on graphene surface, which together with its high volatility make cyclohexane very easy to remove. The method allows easy handling without subjecting graphene to harsh treatments. Big areas of graphene can be transferred without inducing defects and big cracks, which was confirmed by Raman spectroscopy, optical, Atomic Force and Scanning Electron microscopy.
Biphasic electrolyte-gated graphene field-effect transistor
The electrical properties of the free-floating graphene were tested and the results were as follows. While graphene was floating at the organic/water interface, copper electrodes (25 pm Cu) were protected by using PMMA against the etchant, leaving the upper surface for electrical contact. As a control, we also manufactured a monolayer graphene on epoxy as in W. Fu, C. Nef, a Tarasov, M. Wipf, R. Stoop, O. Knopfmacher, M. Weiss, M. Calame, and C. Schonenberger, "High mobility graphene ion-sensitive field-effect transistors by noncovalent functionalization.," Nanoscale, vol. 5, no. 24, pp. 12104-10, Dec. 2013.
The graphene device at biphasic interface exhibits a significantly higher average carrier mobility (-3470 cm2/Vs, ~1940 cm2/Vs for hole and -5000 cm2/Vs for electron, see Figure ) compared to -1505 cm2/Vs (-940 cm2/Vs for hole and -2070 cm2/Vs for electron) on epoxy substrate. This indicates that the biphasic configuration helps to retain the electrical properties of graphene as the electrical performance of the graphene device is significantly improved. This can be due to the fact that this process reliably results in a graphene layer that has clean surfaces on both side free of polymer contamination. This last point is important because resist residues can prevent surface functionalization and suppress sensing. Such a graphene sheet at biphasic interface is, therefore, ideal for sensing applications, especially when a flexible and high-performance graphene devices are needed. We would also like to note here that depending on the quality of the CVD graphene, the floating graphene devices tend to break if the CVD graphene contains too much defects.
Figure 6. The electrolyte gate voltage (Vref) dependent sheet conductance (G) of polymer- free graphene at biphasic interface (black) and epoxy substrate (red). The gate voltage of the charge neutrality point VCNP 0.16 mV compared to -0.2 mV on epoxy substrate. Depending on the quality of the CVD graphene, the floating graphene devices tend to break if the CVD graphene contains too many defects.
Claims
1. A method of transferring a graphene film to a substrate comprising:
(i) providing a graphene film grown on a support;
(ii) positioning the supported graphene film at the interface of a biphasic mixture, wherein the biphasic mixture comprises an aqueous phase and an organic phase, and wherein the phases are immiscible, wherein the aqueous phase further comprises an etchant which completely etches the graphene support from the graphene film;
(iii) after etching has taken place, cooling the biphasic mixture to a temperature such that the organic phase solidifies but the aqueous phase remains a liquid, wherein the graphene film sticks to the solidified organic phase,
(iv) separating the solidified organic phase from the aqueous phase;
(v) applying the graphene of the solidified phase to a substrate; and
(vi) removing the solidified organic phase by melting, subliming or evaporating the organic phase.
2. A method of transferring a graphene film to a substrate comprising:
(i) providing a graphene film grown on a support and placing it on a substrate;
(ii) positioning the supported graphene film substrate at the interface of a biphasic mixture, wherein the biphasic mixture comprises an aqueous phase and an organic phase, and wherein the phases are immiscible, wherein the aqueous phase further comprises an etchant which completely etches the graphene support from the graphene film;
(iii) after etching has taken place, cooling the biphasic mixture to a temperature such that the organic phase solidifies but the aqueous phase remains a liquid, wherein the graphene film sticks to the solidified organic phase,
(iv) removing the solidified organic phase by melting, subliming or evaporating the organic phase.
3. The method according to Claim 1 or Claim 2, wherein the aqueous phase is water.
4. The method according to any preceding claim, wherein the organic phase is selected from cyclohexane, cyclooctane, cyclodecane, cyclononane, p-xylene, 2-methyl- 2-propanethiol, dimethyl butanol, hexanoic acid, 2,2-dimethyl 3-pentanol, 4- ethylaniline, η,η-dimethylaniline, 2,3-dimethylaniline, aminooctane, 2,3,3-trimethyl 2-pentanol, 2,2- dimethylpropanal, cyclohexanecarbonitrile, 2,5-dimethyi- 2,4-hexadiene, cis-2- methylcyclohexanol, 2,5-dimethylaniline, 2,6-dimethylaniline, cyclohexanol, 2,3,3-
trimethyl-2-butanol, 3,4-dimethylaniline, cyclooctanol, p-methylbenzylcyanide, 4- propylphenol or combinations thereof.
5. The method according to any one of Claim 1 or Claim 2, wherein the organic phase is cyclohexane.
6. The method according to any preceding claim, wherein the etchant is selected from ammonium persulfate, iron(lll) chloride, nitric acid, ammonium hydroxide/hydrogen peroxide, sulfuric acid/hydrogen peroxide, hydrogen peroxide/sodium bisulfate, potassium nitrate/hydrochloric acid, sodium persulfate or iron(lll) nitrate.
7. The method according to any one of Claims 1 to 5, wherein the etchant is ammonium persulfate.
8. The method according to Claim 2, wherein the supported graphene film is held in position with the substrate by wrapping extra support material around the supported graphene film and substrate.
9. The method according to any preceding claim, wherein the substrate is selected from silicon wafer, a TEM quantifoil grid, TEM nanochips, silicon nitride chips or glass chips.
10. The method according to any preceding claim, wherein the graphene support is a catalytic metal preferably wherein the metal is selected from copper nickel, platinum, gold, palladium, iridium, ruthenium, cobalt, rhodium, rhenium or iron.
1 1. The method according to Claim 8 wherein the metal is copper.
12. The method according to any preceding claim, wherein the method further comprises a step of washing any contaminants from the graphene film using water.
13. A graphene film substrate obtainable according to any one of the preceding claims. 4. An in-situ sensing application comprising a graphene film substrate according to Claim 13.
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PCT/EP2017/064037 WO2017211992A1 (en) | 2016-06-10 | 2017-06-08 | Method for the transfer of graphene |
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WO (1) | WO2017211992A1 (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
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CN108217627A (en) * | 2018-01-23 | 2018-06-29 | 杭州高烯科技有限公司 | A kind of preparation method of independent self-supporting graphene carbon pipe composite membrane |
GB2593242A (en) * | 2020-03-16 | 2021-09-22 | Vozyakov Igor | Alignment method and apparatus for monomolecular layers |
CN114180558A (en) * | 2021-12-27 | 2022-03-15 | 广东墨睿科技有限公司 | Preparation method of graphene micro-nano cavity superconducting film, related product and application |
CN114959629A (en) * | 2022-05-24 | 2022-08-30 | 中国科学院金属研究所 | Method for transferring two-dimensional material by using higher fatty alcohol or higher fatty acid |
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WO2015196066A2 (en) * | 2014-06-20 | 2015-12-23 | The Regents Of The University Of California | Method for the fabrication and transfer of graphene |
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WO2015196066A2 (en) * | 2014-06-20 | 2015-12-23 | The Regents Of The University Of California | Method for the fabrication and transfer of graphene |
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GUOHUI ZHANG ET AL: "Versatile Polymer-Free Graphene Transfer Method and Applications", ACS APPLIED MATERIALS & INTERFACES, vol. 8, no. 12, 8 March 2016 (2016-03-08), US, pages 8008 - 8016, XP055402803, ISSN: 1944-8244, DOI: 10.1021/acsami.6b00681 * |
LIUBOV A. BELYAEVA ET AL: "Molecular Caging of Graphene with Cyclohexane: Transfer and Electrical Transport", ACS CENTRAL SCIENCE, vol. 2, no. 12, 28 November 2016 (2016-11-28), pages 904 - 909, XP055402800, ISSN: 2374-7943, DOI: 10.1021/acscentsci.6b00236 * |
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Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
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CN108217627A (en) * | 2018-01-23 | 2018-06-29 | 杭州高烯科技有限公司 | A kind of preparation method of independent self-supporting graphene carbon pipe composite membrane |
CN108217627B (en) * | 2018-01-23 | 2020-06-05 | 杭州高烯科技有限公司 | Preparation method of independent self-supporting graphene carbon tube composite membrane |
GB2593242A (en) * | 2020-03-16 | 2021-09-22 | Vozyakov Igor | Alignment method and apparatus for monomolecular layers |
GB2593242B (en) * | 2020-03-16 | 2023-05-31 | Vozyakov Igor | Alignment method and apparatus for monomolecular layers |
CN114180558A (en) * | 2021-12-27 | 2022-03-15 | 广东墨睿科技有限公司 | Preparation method of graphene micro-nano cavity superconducting film, related product and application |
CN114180558B (en) * | 2021-12-27 | 2023-09-08 | 广东墨睿科技有限公司 | Preparation method of graphene micro-nano cavity superconducting film, related product and application |
CN114959629A (en) * | 2022-05-24 | 2022-08-30 | 中国科学院金属研究所 | Method for transferring two-dimensional material by using higher fatty alcohol or higher fatty acid |
CN114959629B (en) * | 2022-05-24 | 2024-01-19 | 中国科学院金属研究所 | Method for transferring two-dimensional material by using higher fatty alcohol or higher fatty acid |
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