Supplementary material
Thermoelectric power of graphene as surface charge doping indicator
Anton N. Sidorov1,a), Andriy Sherehiy2, Ruwantha Jayasinghe2, Robert Stallard2, Daniel K.
Benjamin1, Qingkai Yu3, Zhihong Liu3, Wei Wu4, Helin Cao5, Yong P. Chen5, Zhigang Jiang1,b),
and Gamini U. Sumanasekera2,c)
1
School of Physics, Georgia Institute of Technology, Atlanta, GA 30332
2
3
Department of Physics, University of Louisville, Louisville, KY 40292
Ingram School of Engineering, and Materials Science, Engineering and Commercialization
Program, Texas State University, San Marcos, TX 78666
4
Center for Advanced Materials, and Department of Electrical and Computer Engineering,
University of Houston, Houston, TX 77204
5
Department of Physics, Purdue University, West Lafayette, IN 47907
Details on chemical vapor deposition graphene growth, Raman spectroscopy identification
and Seebeck coefficient measurement
The graphene specimens measured in this work were synthesized by the chemical vapor
deposition (CVD) method at ambient pressure on polycrystalline Cu foils, with thickness of 25
µm, and purity better than 99.8% (as described in Ref. [S1]). 70 ppm CH4 was used as the
precursor gas, carried by a H2:Ar =1:30 gas mixture, with total flow of 310 sccm at atmosphere.
The graphene formation time was 10 min, at 1000 ⁰C. After the growth, the graphene film was
a)
Electronic mail: asidorov3@mail.gatech.edu
b)
Electronic mail: zhigang.jiang@physics.gatech.edu
c)
Electronic mail: gusuma01@louisville.edu
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coated with a protective layer of polymethyl methacrylate (PMMA), and placed in an aqueous
solution of iron(III) nitrate to etch off the Cu foil. Afterwards, the graphene film was scooped out
onto a Si/SiO2 substrate, and then rinsed with DI water several times.
Figure S1: (Right panel) Two-dimensional (2D) Raman spectroscopy mapping of a graphene
sample over a 1010 m2 area. The color contrast represents the ratio of peak intensites,
I(G’)/I(G), where values of ~2 or larger are characteristic of monolayer graphene. (Left panel, ac) Selected Raman spectra from three places on the 2D map (marked by circles).
The CVD-grown graphene samples are found to be monolayers over a large area. To
confirm this, we performed Raman spectroscopy mapping over a 1010 m2 area of the sample
(see Fig. S1) using a Horiba HR800 micro Raman system with a 532.1 nm wavelength laser (1
m spot size). Figure S1(a-c) plot three individual spectra obtained at selected places in the 2D
map (marked by circles), and these spectra show all the signature Raman peaks of graphene, i.e.,
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the G’-band ~2680 cm-1, the G-band ~1588 cm-1 and the D-band ~1345 cm-1. There is a
relatively small intensity D peak indicating some disorder. This is most likely explained by the
presence of chemical residue from the transfer to the Si/SiO2 substrate. The color contrast of the
2D map represents the numerical ratio of the peak intensities of the G’ and the G bands,
I(G’)/I(G). The presence of the G’ band of single-Lorentzian lineshape and the ratio of peak
intensities I(G’)/I(G) > 2 are characteristic of a graphene monolayer. A large area (200200 µm2)
mapping of a similar gramphene film was demonstrated previously in Ref. [S1].
After transferring onto the Si/SiO2 substrate, the graphene sample is mounted on a
ceramic holder connected to a measurement probe. The probe is loaded into a quartz reactor
placed inside a tube furnace. Two Chromel-Alumel thermocouples are attached to the sample
with small amounts of silver epoxy, and a small platinum resistive heater is placed (also by silver
epoxy) at one of the ends of the device, as shown in Fig. S2. For four-probe resistance
measurements, two extra copper wires are attached as current leads. The reactor is evacuated to a
base pressure below 10-6 Torr using a turbo molecular pump and degassed at 500 K, while the
time evolution of the Seebeck coefficient and the four-point resistance are recorded
concomitantly. Then the reactor is cooled down to room temperature under high vacuum. To
measure the Seebeck coefficient, a temperature difference (ΔT  1 K) is generated across the
sample by applying a voltage pulse to the heater. The typical heating power is ~10 mW, and the
pulse duration is 3-5 seconds. The slope of the thermo-emf (ΔV) vs. temperature difference (ΔT)
plot, during the heating and cooling, is used to obtain the Seebeck coeffiicient at a given
temperature. The thermo-emf was measured with a Keithley 2182 nanovoltmeter, while the fourprobe resistance measurements were performed using a Keithley 2400 source meter with an
excitation current ~100 A. Further experimental details are described in Ref. [S2].
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Figure S2: (a) Schematic of the Seebeck coefficient measurement set-up consisting of a layer of
graphene deposited on a Si/SiO2 substrate with two K-type thermocouples and a platinum
resistive heater (side-view). (b) The circuit diagram showing the relevant voltages used to
determine the thermo-emf and the temperature difference in response to a voltage pulse on the
heater. I+ and I- indicate the current leads used to measure the four-probe resistance of the
device simultaneously.
References
[S1] H. L. Cao, Q. K. Yu, L. A. Jauregui, J. Tian, W. Wu, Z. Liu, R. Jalilian, D. K. Benjamin, Z.
Jiang, J. Bao, S. S. Pei, and Y. P. Chen, Applied Physics Letters 96, 122106 (2010).
[S2] G. U. Sumanasekera, L. Grigorian, and P. C. Eklund, Measurement Science and
Technology 11, 273 (2000).
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