Spectroscopic Analysis of Nitrogen-Doped Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared By Coaxial Arc Plasma Deposition

Abstract

Ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) is a new candidate carbon semiconductor applicable to electrical devices. It has been investigated that nitrogen-doping for diamond is ineffective for realizing n-type conduction at room temperature, because nitrogen form a deep donor level of 1.7 eV below the bottom of a conduction band in diamond. For a-C:H, n-type conduction is realized by nitrogen doping, however it is difficult for the carrier density to be controlled widely. On the other hand, it has been reported that nitrogen doping is effective for UNCD/a-C:H prepared by chemical vapor deposition (CVD) and pulsed laser deposition (PLD)1), 2), the doping mechanism for UNCD/a-C:H seems to differ from those for diamond and a-C:H. In this study, UNCD/a-C:H films were prepared by coaxial arc plasma deposition (CAPD) with nitrogen atmosphere and the effects of the nitrogen doping on the UNCD crystallite formation were structurally investigated. X-ray photoemission spectra (XPS), which were measured with MgKα line, of the UNCD/a-C:H films prepared at different inflow ratio of nitrogen and hydrogen (IN/H ). N1s peaks strengthened with an increase in the IN/H , which evidently indicates that the nitrogen content in the film increased with the IN/H . The nitrogen contents of the films deposited at IN/H of 0.25, 0.5, 1.0 and 1.5 were estimated to be 3, 5, 6 and 8 at. %, respectively. Near-edge X-ray absorption fine structure (NEXAFS), spectral shape of the nitrogen-doped films different from the undoped film were obtained. By increasing the doping amount, the intensity of the π*C=N increased, while the intensity of the σ*C-C is decreased. Which refers to strengthen in sp2 bonds and weaken in sp3 bonds. Furthermore, increasing the electrical conductivity by increasing the nitrogen-doping amount can be ascribed to contribute of sp2bonds. The details will be reported at the conference. 1) Dai, et al.: Phys. Rev. B 71, 075421 (2005). 2) T. Yoshitake, et al.: Jpn. J. Appl. Phys 49, 015503 (2010).