Supplemental Material
UV/Ozone treatment to reduce metal-graphene contact resistanceWei Li1,2, Yiran Liang1, Dangmin Yu1, Lianmao Peng1, Kurt P. Pernstich2, Tian Shen2,
A. R. Hight Walker2, Guangjun Cheng2, Christina A. Hacker2, Curt A. Richter2,
Qiliang Li3, David J. Gundlach2,*, and Xuelei Liang1,*
1. Key Laboratory for the Physics and Chemistry of Nanodevices and Department of
Electronics, Peking University, Beijing, 100871, China
2. Physical Measurement Laboratory, National Institute of Standards and Technology,
Gaithersburg, MD 20899, USA
3. Department of Electrical and Computer Engineering, George Mason University,
Fairfax, VA 22030, USA
E-mail: liangxl@pku.edu.cn; david.gundlach@nist.gov
Ultraviolet ozone (UVO) treatment details:
The UVO cleaning process is relatively simple. Results from three commercial UVO
systems were analyzed in the course of this study. One system is new and was
installed at Peking University (China), and the other systems (newer and older models)
are at NIST (USA). The electrical characteristics, Raman spectroscopy, and atomic
force microscopy (AFM) results were obtained on samples processed at Peking
University. Additional Raman and X-ray photoelectron spectroscopy (XPS) studies
were performed on nominally identical transferred CVD-grown graphene layers
processed in the systems at NIST. The specific configuration (e.g. exhaust rate, feed
gas, sample-to-grid lamp distance, and lamp intensity) differ between systems.
However, the trends from results obtained on all of the systems show the UVO
cleaning of the contamination on graphene surface has a wide process window and
can be easy to control.
Figure S1. Surface roughness vs. UVO treatment process. Root mean square (RMS)
surface roughness values were taken from an analysis of the AFM images in Figure 2
of the main text. The resist residue was introduced during both the transfer and
photo-lithography steps. Most of the residue was removed in the first 5-10 minutes
treatment.
Figure S2. The integrated D-to-G peak intensity ratio obtained by a Lorentian fit to
the data in Figure 3 of the main text. The ratio remains at a low value and a significant
increase is not observed until 22 min.