Low Temperature Chemical Vapor Deposition Growth of Graphene ...
Supporting Information for
Low Temperature Chemical Vapor Deposition Growth of Graphene from Toluene on Electropolished Copper Foils
Bin Zhang,a,b Wi Hyoung Lee,a Richard Piner,a Iskandar Kholmanov,a Yaping Wu,a Huifeng Li,a Hengxing Ji,a Rodney S Ruoffa,* *To whom correspondence should be addressed: [email protected]
a
Department of Mechanical Engineering and the Materials Science and Engineering
Program, The University of Texas at Austin, One University Station C2200, Austin, Texas 78712-0292 USA
b
Key Laboratory for Anisotropy and Texture of Materials of Ministry of Education,
School of Materials and Metallurgy, Northeastern University, Shenyang 110819, P. R. China
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Figure S1 illustrates the schematic of the chemical vapor deposition (CVD) setup for growing continuous graphene films. In this vacuum-assisted process, the vapor of liquid toluene flows because the vapor pressure of toluene is higher than the pressure in the reaction chamber.
Figure S1. Schematic of CVD setup for the growth of graphene films using toluene.
Roughness of Cu foils measured by Optical Profilometer The Wyko surface profile system computes four parameters, Ra, Rq, Rz and Rt that provide information about roughness and the surface profile. Ra represents the roughness average, the arithmetic mean of the absolute values of the surface departures from the mean plane. Rq represents the root mean square (RMS) roughness, obtained by squaring each height value in the dataset, then taking the square root of the mean. Rz, average maximum height of the profile, is the average of the ten highest and ten lowest point in the dataset. Rt, maximum height of the surface, is the vertical 2
distance between the hightest and lowest points as calculated over the entire dataset. Figure S2 shows the surface profiler images and the calculation roughness of the Cu foil substrates, (a) before and (b) after electropolishing.
Figure S2. Surface Profiler images and the calculation roughness of the Cu foil substrates. (a) before, (b) after electropolishing.
Comparison of graphene grown on the electropolished and unelectropolished Cu foils under same conditions Figure S3 show the SEM images of graphene on (a) the electropolished Cu foil and (b) unelectropolished Cu foil without the anti-corrosion coating, grown at 550°C for 45 minutes, respectively. 3
Figure S3 SEM images of graphene on (a) the electropolished Cu foil and (b) the unelectropolished Cu foil grown at 550°C for 45 minutes, respectively.
FET devices fabricated using graphene grown at 600 °C. A gold contact was made to the substrate as the back-gate contact. Cr/Au (5nm/50nm) source/drain electrodes were deposited by thermal evaporation with a shadow mask. The graphene channel 4
width and length were 300 µm and 50 µm, respectively. The carrier mobility can be calculated from the ISD-VSG curves in the linear region as[1]:
∆I DS t ox
µ= ε 0ε ox
W VDS ∆VGS L
Where µ is the carrier mobility, ∆IDS is the current change induced by ∆VGS in linear region of the IDS-VGS curve, tox=285 nm is the SiO2 thickness, εox=3.9 is the SiO2 permittivity, ε0 is the vacuum permittivity, W and L are the FET width and length, respectively, and VDS is the source-drain voltage. The linear source-drain current (IDS) versus source-drain voltage (VDS) behavior (Figure S4) indicates a good ohmic contact between the Au/Cr contact pads and the graphene channel.
Figure S4 Graphene FET used for carrier mobility measurement. The channel width and length between the two gold contacts was 300 and 50 µm, respectively. Drain-source current (IDS) vs the drain-source voltage (VDS) under different gate voltages (VGS = -40, -20, 0, 20, 40 V). References 5
[1] Liang, X. et. al. Nano Lett. 2007,7, 3840.
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Low Temperature Chemical Vapor Deposition Growth of Graphene from Toluene on Electropolished Copper Foils
Bin Zhang,a,b Wi Hyoung Lee,a Richard Piner,a Iskandar Kholmanov,a Yaping Wu,a Huifeng Li,a Hengxing Ji,a Rodney S Ruoffa,* *To whom correspondence should be addressed: [email protected]
a
Department of Mechanical Engineering and the Materials Science and Engineering
Program, The University of Texas at Austin, One University Station C2200, Austin, Texas 78712-0292 USA
b
Key Laboratory for Anisotropy and Texture of Materials of Ministry of Education,
School of Materials and Metallurgy, Northeastern University, Shenyang 110819, P. R. China
1
Figure S1 illustrates the schematic of the chemical vapor deposition (CVD) setup for growing continuous graphene films. In this vacuum-assisted process, the vapor of liquid toluene flows because the vapor pressure of toluene is higher than the pressure in the reaction chamber.
Figure S1. Schematic of CVD setup for the growth of graphene films using toluene.
Roughness of Cu foils measured by Optical Profilometer The Wyko surface profile system computes four parameters, Ra, Rq, Rz and Rt that provide information about roughness and the surface profile. Ra represents the roughness average, the arithmetic mean of the absolute values of the surface departures from the mean plane. Rq represents the root mean square (RMS) roughness, obtained by squaring each height value in the dataset, then taking the square root of the mean. Rz, average maximum height of the profile, is the average of the ten highest and ten lowest point in the dataset. Rt, maximum height of the surface, is the vertical 2
distance between the hightest and lowest points as calculated over the entire dataset. Figure S2 shows the surface profiler images and the calculation roughness of the Cu foil substrates, (a) before and (b) after electropolishing.
Figure S2. Surface Profiler images and the calculation roughness of the Cu foil substrates. (a) before, (b) after electropolishing.
Comparison of graphene grown on the electropolished and unelectropolished Cu foils under same conditions Figure S3 show the SEM images of graphene on (a) the electropolished Cu foil and (b) unelectropolished Cu foil without the anti-corrosion coating, grown at 550°C for 45 minutes, respectively. 3
Figure S3 SEM images of graphene on (a) the electropolished Cu foil and (b) the unelectropolished Cu foil grown at 550°C for 45 minutes, respectively.
FET devices fabricated using graphene grown at 600 °C. A gold contact was made to the substrate as the back-gate contact. Cr/Au (5nm/50nm) source/drain electrodes were deposited by thermal evaporation with a shadow mask. The graphene channel 4
width and length were 300 µm and 50 µm, respectively. The carrier mobility can be calculated from the ISD-VSG curves in the linear region as[1]:
∆I DS t ox
µ= ε 0ε ox
W VDS ∆VGS L
Where µ is the carrier mobility, ∆IDS is the current change induced by ∆VGS in linear region of the IDS-VGS curve, tox=285 nm is the SiO2 thickness, εox=3.9 is the SiO2 permittivity, ε0 is the vacuum permittivity, W and L are the FET width and length, respectively, and VDS is the source-drain voltage. The linear source-drain current (IDS) versus source-drain voltage (VDS) behavior (Figure S4) indicates a good ohmic contact between the Au/Cr contact pads and the graphene channel.
Figure S4 Graphene FET used for carrier mobility measurement. The channel width and length between the two gold contacts was 300 and 50 µm, respectively. Drain-source current (IDS) vs the drain-source voltage (VDS) under different gate voltages (VGS = -40, -20, 0, 20, 40 V). References 5
[1] Liang, X. et. al. Nano Lett. 2007,7, 3840.
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