Supplemental Material for
The Effect of Electron Induced Hydrogenation of Graphene on its Electrical
Transport Properties
Sung Oh Woo 1) and Winfried Teizer 1, 2)
1) Department of Physics and Astronomy, Texas A&M University, College
Station, TX 77843 U.S.A.
2) WPI-Advanced Institute for Materials Research, Tohoku University,
Sendai, Japan
Graphene Field Effect Transistor (GFET) devices were fabricated by mechanical exfoliation. Graphene flakes are transferred from Highly Oriented
Pyrolytic Graphite (HOPG) onto SiO
2
(285nm)/Si. The silicon is highly doped and used as a back gate during the electrical transport measurement. Electrodes were defined by Electron Beam Lithography (EBL) followed by metallization of
Cr(3nm)/Au(50nm) by thermal evaporation. The schematic diagram of a pristine GFET device is shown in Fig. S1(a). PMMA is spun onto the graphene device as shown in Fig. S1(b) and then baked on a hot plate at 165°C for 3 minutes. Then, the PMMA/graphene bilayer was loaded into the EBL chamber, and exposed to an electron beam (Fig. S1(c)). After the electron irradiation on the PMMA/graphene bilayer, the exposed area is confirmed after development by optical microscopy. Finally the PMMA is stripped off in acetone. The electrical transport measurements with a standard 4­probe AC technique are then conducted in high vacuum.

Fig. S1. Schematic diagram of (a) GFET device, (b) PMMA/graphene bilayer, (c) electron irradiation on PMMA/graphene bilayer, and (d) the transport measurement after electron irradiation on PMMA/graphene and subsequent removal of PMMA.
In order to study the Raman background signals from various wafers, we have measured the Raman spectrum from a range of suppliers. The back ground properties differ for various vendors, as shown in Fig. S2. The abnormal
Raman signal background below 2000 cm ­1 originates from the characteristics of the silicon wafer. The Raman peak around 520 cm ­1 is assigned to an optical phonon of silicon, and the peak between 940~990 cm ­1 is the 2 nd order optical phonon of the silicon wafer. The shapes of the 2nd order peak and background signal depend on the silicon dimension 1 and Raman excitation energy 2 .

Fig. S2. Raman spectrum of SiO
2
/Si wafer from different three suppliers.
In order to investigate the chemical binding between graphene and
PMMA fragments generated during electron irradiation on PMMA/graphene bilayer, we conducted an X­ray Photoemission Spectroscopy experiment (Fig.
S3). We purchased large area Chemical Vapor Deposition (CVD) graphene from
ACS materials. PMMA was spun on the large area graphene and baked on a hot plate at 165°C for 3 minutes with the same experimental conditions as for the mechanically exfoliated graphene devices. However, the electron beam current was increased to 2nA to reduce exposure time, and a 2mC/cm 2 dose was irradiated on PMMA/graphene. The exposed area was 2mm by 2mm due to the large incident X­ray beam size (~1mm in diameter) in the XPS equipment.
As shown in Fig. S3, the C 1s signal reveals no remarkable changes from sp 2 to sp 3 or increases of carbon oxide compounds.

Fig. S3. The XPS C 1s signals. The solid line (‘No Irradiation’) was measured without electron irradiation on PMMA/graphene. The dotted line was obtained after electron irradiation on PMMA/graphene and subsequent removal of
PMMA.
References
1.
R­P Wang, G­W Zhou, Y­L Liu, S­H Pan, H­Z Zhang, D­P Yu, and Z.
Zhang, Phys. Rev. B 61, 16827 (2000)
2.
J. B. Renucci, R. N. Tyte, and M. Cardona, Phys. Rev. B 11, 3885 (1975)