Fig 1

Contamination on the surface of CVD-derived graphene 56, 58. (a) Schematic of the formation of contamination on the surface of graphene during the high-temperature CVD growth; (b) AFM image of freshly prepared graphene grown on Cu foil; (c) TEM image of unclean graphene. Inset: High-resolution transmission electron microscopy (HRTEM) image of unclean graphene film; (d, e) High angle annular dark field (HAADF)-scanning TEM (STEM) (d) and HAADF-STEM plus energy-dispersive X-ray (EDX) map of C element (e) of graphene transferred onto TEM grid; (f, g) HRTEM image of unclean graphene (f) and structure of amorphous carbon contamination after removing graphene lattice beneath based on fast Fourier transform mask filter (g). (a–c) Adapted with permission from Ref. 56. Copyright 2019, Springer Nature. (d–g) Adapted with permission from Ref. 58. Copyright 2019, Wiley-VCH."

Fig 2

Structure of contamination on the surface of graphene 58. (a–c) Statistics of the size of nano-domains (a), C–C bonding angle (b), and bonding length (c) of amorphous carbon. Adapted with permission from Ref. 58. Copyright 2019, Wiley-VCH."

Fig 3

Formation of contamination during CVD growth of graphene 56. (a) TERS spectra of clean (red) and unclean (blue) graphene regions, and in-situ far-field Raman spectrum (dark cyan) of the unclean graphene at the same region. Inset: TERS mapping of D band intensity of unclean graphene; (b) Statistics of the D and G band positions of graphene grown by 12CH4 and 13CH4; Inset: typical TERS spectra of 13C-labelled unclean graphene; (c) ToF−SIMS spectra of 12C-labelled (blue) and 13C-labelled (red) graphene. Adapted with permission from Ref. 56. Copyright 2019, Springer Nature."

Fig 4

Schematic diagram of the formation mechanism of amorphous carbon on graphene surface during the high-temperature growth process."

Fig 5

Reduced polymer residues on clean graphene surface after transfer 26, 56. (a) Schematic of contamination on the surface of graphene after transfer; (b, c) AFM images of unclean (b) and clean (c) graphene transferred onto SiO2/Si substrates; (d) ToF-SIMS spectra of transferred unclean graphene (blue) and clean graphene (red) on SiO2/Si substrates with the assistance of 2H-labelled PMMA. Inset: Structure of 2H-labelled PMMA. (a) Adapted with permission from Ref. 26. Copyright 2020, American Chemical Society. (b–d) Adapted with permission from Ref. 56. Copyright 2019, Springer Nature."

Fig 6

Growth of superclean graphene with the assistance of Cu foam 56. (a) Schematic of the Cu foil-foam stacked structure for the growth of superclean graphene; (b) AFM image of the freshly prepared clean graphene grown on Cu; (c) TEM image of the superclean graphene. Inset: HRTEM image of clean graphene with atomic-scale resolution; (d) Photograph of the quartz substrates before and after collecting the species in the boundary layer during high-temperature graphene growth with and without Cu foam; (e) Scanning electron microscopy (SEM) image of the Cu nanoparticles collected by quartz substrate; (f) Raman spectra of the carbon species formed during graphene growth with (red) and without (blue) Cu foam. Adapted with permission from Ref. 56. Copyright 2019, Springer Nature."

Fig 7

Growth of superclean graphene using Cu(OAc)2 as carbon source 78. (a) Schematic diagram for the growth of graphene using CH4 and Cu(OAc)2 as the carbon sources; (b, c) TEM images of unclean graphene (b) and clean graphene (c). Inset of (b): FFT image of the region marked in white square; Inset of (c): FFT image of the region marked in white square (top) and TEM image with atomic resolution (bottom); (d) Theoretical calculation of hydrogenation barrier of CH4 with (red) and without (blue) Cu catalyst; (e) Raman spectra of the carbon species formed in the boundary layer during graphene growth using CH4 (blue) and Cu(OAc)2 (red). Adapted with permission from Ref. 78. Copyright 2019, American Chemical Society."

Fig 8

Growth of superclean graphene by cold-wall CVD 79. (a) Schematic diagram of growth of the superclean graphene in cold-wall CVD (CW-CVD) system; (b) Computational fluid dynamics simulation result of the temperature distribution in CW-CVD system; (c) Profiles of distance change between carbon atoms during the formation of C4H10; (d) The formation of carbon clusters by capturing carbon species at low temperature (up) and high temperature (down). Adapted with permission from Ref. 79. Copyright 2020, Wiley-VCH."

Fig 9

Preparation of superclean graphene via selective of etching amorphous carbon with CO2 58. (a) Schematic diagram of the formation and elimination of amorphous carbon on CVD-grown graphene surface; (b) The reaction barriers of CO2 etching graphene (blue) and amorphous carbon (red); (c) The reaction barriers of CO2 etching amorphous carbon (red) and graphene (blue); (d) Reaction rates of CO2 etching amorphous carbon (red) and graphene (blue). Note that in this work, 5-8-5, 555-777, and 55-77 topological defects are used as the simplified model structures of the amorphous carbon contamination on graphene surface. Adapted with permission from Ref. 58. Copyright 2019, Wiley-VCH."

Fig 10

Preparation of superclean graphene with the assistance of activated carbon-coated lint roller 80. (a) Schematic of the activated carbon-coated lint roller for the cleaning of amorphous carbon on graphene surface; (b) Cross-sectional EDX mapping result of the contact region between graphene and activated carbon; (c) TEM image of superclean graphene. Inset: HRTEM image of graphene lattice; (d) Statistics of the adhesion force of Camorphous-Grapehene (blue) and Camorphous-Cactivated (red). Adapted with permission from Ref. 80. Copyright 2019, Wiley-VCH."

Fig 11

The superior properties of superclean graphene 56, 58. (a) Measured resistance of superclean graphene as a function of the gate voltage at 1.9 K (red) and room temperature (blue); (b) Measured contact resistance of superclean graphene as a function of gate bias; Inset: False-colored SEM image of the TLM device; (c) UV-Vis spectra of monolayer (red), bilayer (orange) and trilayer (blue) superclean graphene; Inset: Photograph of clean (left) and unclean (right) graphene transferred onto quartz substrates. (d) Statistics of the measured thermal conductivity of clean and unclean graphene. (a, b, d) Adapted with permission from Ref. 56. Copyright 2019, Springer Nature. (c) Adapted with permission from Ref. 58. Copyright 2019, Wiley-VCH."