AVS 54th International Symposium
    Thin Film Tuesday Sessions
       Session TF-TuM

Paper TF-TuM2
Evaluation and Control of Electric Conduction of Carbon Nanowalls Fabricated by Plasma-Enhanced CVD

Tuesday, October 16, 2007, 8:20 am, Room 613/614

Session: Two-Dimensional Carbon Nanostructures
Presenter: W. Takeuchi, Nagoya University, Japan
Authors: W. Takeuchi, Nagoya University, Japan
M. Ura, Nagoya University, Japan
Y. Tokuda, Aichi Institute of Technology, Japan
M. Hiramatsu, Meijo University, Japan
H. Kano, NU Eco-Engineering Co.,Ltd., Japan
M. Hori, Nagoya University, Japan
Correspondent: Click to Email

Carbon nanowalls (CNWs), two-dimensional (2-D) carbon nanostructure, consisting of graphite sheets standing vertically on the substrate, have attracted much attention for several applications, including field emitter arrays, gas storage, and membranes for electrochemical energy storage. Recently, it was reported that 2-D multilayer graphene sheet offers high mobility and huge sustainable currents. Therefore, CNW films potentially would possess high mobility and huge sustainable current density, since the CNWs are basically graphene sheet. Considering the practical applications of CNWs, further investigations are required to clarify the growth mechanism and to control their structure and properties. In this study, we focused on the evaluation and control of electric properties of CNWs. CNWs were fabricated on the quartz substrate by the plasma enhanced CVD with H radical injection employing a mixture of C2F6/H2. We investigated the influence of N2 or O2 addition to the process gas mixture on the morphology and electric properties of CNWs. Hall measurement and Raman spectroscopy were used to evaluate the electric properties and structure of CNWs. The Hall coefficient was positive for the CNW film grown without additives. When O2 was added to the plasma, it was still positive. In the case of N2 addition, it displayed negative value. The positive or negative value of the Hall coefficient implies p- or n-type, respectively. Therefore, it was found that the conduction type of CNW films was controllable by adding N2 or O2 to the C2F6/H2 plasma. Morphology and crystallinity of CNWs were also changed by the addition of N2 and O2. In the Raman spectroscopy, all samples have a strong peak at 1590 cm-1 (G-band) indicating the formation of a graphitized structure, and another peak around at 1350 cm-1 corresponding to the disorder-induced phonon mode (D-band). The G-band width in the Raman spectrum increased when N2 was added. In the case of O2 addition, G-band width and peak intensity ratio of D band to G band of CNWs decreased. These results indicate that nitrogen would be included in CNWs and act as a donar, while accompanied by the slight degradation of graphite crystallinity. On the other hand, oxygen would play a role of etching of amorphous carbon content and contribute to the higher graphitization, while conduction type of CNW films would not change.