Field emission characteristics of fast grown nanocrystalline diamond/amorphous carbon composite films by microwave plasma-enhanced chemical deposition method Wen-Jen Liu a, ⁎, Xing-Jian Guo b , Chi-Lung Chang c , Cheng-Hsun Li a , Chia-Wei Hsu a a Department of Material Science and Engineering, I-Shou University, Kaohsiung, Taiwan, 840 ROC b High Voltage Electron Microscopy Station, National Institute for Materials Science (NIMS), 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan c Department of Materials Science and Engineering, MingDao University, Taiwan, ROC abstract article info Available online 11 February 2009 Keywords: Nanocrystalline diamond Diamond Chemical vapor deposition Nano-materials Field emission This study synthesized the nanocrystalline diamond/amorphous carbon (NCD/a-C) composite films by the microwave plasma-enhanced chemical vapor deposition (MPCVD) system with Ar/CH 4 /N 2 mixtures. A localized rectangular-type jet-electrode with high density plasma was used to enhance the formation of NCD/a-C films, and a maximum growth rate of 105.6 μm/h was achieved. The content variations of sp 2 and sp 3 phases via varying nitrogen gas flow rates were investigated by using Raman spectroscopy. The NCD/a-C film which synthesized with 6% nitrogen concentration and no hydrogen plasma etching treatment possessed a low turn-on electric field of 3.1 V/μm at the emission current of 0.01 μA. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Nanocrystalline diamond (NCD), ultrananocrystalline diamond (UNCD) or amorphous carbon (a-C) embedded NCD (NCD/a-C) films, with advantages of having higher surface flatness than polycrystalline CVD diamond, high hardness, high wear resistance, high thermal conductivity, low friction coefficient, high electrical resistance, high optical transparency, high electron emission efficiency and excellent chemical inertness, have attracted great attention in researches [1–5]. NCD films with nano-sized diamond grains have been extensively investigated for field emission (FE) applications because their larger grain boundary area can serve as the electron conduction channel for easier electrons field emission. In the electron conduction model, the nano-sized diamond grain boundary, which consists of sp 2 phase, plays an important role. The regions with sp 2 phase that have low electrical resistance property and act as an electron transport path can promote the FE phenomena [6]. Microwave plasma-enhanced chemical vapor deposition (MPCVD) system, which adopts Ar/CH 4 , H 2 /CH 4 , Ar/H 2 /CH 4 /N 2 or Ar/H 2 /CH 4 mixtures, has been widely used to deposit NCD or UNCD films [1–4]. However, the increase of the growth rate needs to be further improved in real application, and related researches are rarely reported. In this study, fast growth rate NCD/a-C films were synthesized by using the MPCVD system via Ar/CH 4 /N 2 gas mixtures with a novel electrode design. The addition of N 2 gas in synthesis of NCD/a-C films and the usage of H 2 gas for plasma etching treatment of the deposited NCD/a-C films were considered to adjust the sp 2 and sp 3 phases content. Hydrogen plasma treatment could effectively remove amorphous carbon and graphite atoms on the NCD/a-C films surface, and this process would not change the nano-sized diamond grain size in the films. Therefore, the purpose of the study is to investigate the effects of the N 2 concentrations and hydrogen plasma etching treatment on the sp 2 and sp 3 phase fractions, the microstructure, and the field emission characteristics of NCD/a-C films. 2. Experimental details This study used a MPCVD system with a novel rectangular-type plasma generation region, including a microwave generator, a stainless steel jet-electrode for ultra-high density plasma generation, a Ar/CH 4 /N 2 gas mixtures feeding line, and an etching gas (H 2 ) line, as shown in Fig. 1 . The NCD/a-C films were synthesized by using the stainless steel jet-electrode to transfer plasma shape from a ball-type to a localized rectangular-type. The area of rectangular-type plasma was about 30 mm×10 mm, and it could effectively increase the plasma density in the vicinity of the substrate. The deposition distance between sample and the electrode exit was fixed at 5 mm. Ar gas, CH 4 gas and N 2 gas were used as a main working gas a for NCD/a-C films deposition. The total main working gas and the CH 4 gas flow rates were fixed at 100 sccm and 1 sccm, respectively. The N 2 gas flow rates could vary within the range of 0–8 sccm. Ar gas was adopted to ignite plasma, and CH 4 gas was introduced into electrode for mainly providing C + and H + species to synthesize NCD/a-C films. N 2 gas was used to control the fractions variations of sp 2 and sp 3 phases. The substrate temperature was controlled at 650 °C on the samples holder Thin Solid Films 517 (2009) 4031–4034 ⁎ Corresponding author. Tel.: +886 7 6577262; fax: +886 7 6578444. E-mail address: jurgen@isu.edu.tw (W.-J. Liu). 0040-6090/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2009.01.183 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf