Vacuum 80 (2006) 818–822 Electrochemical studies of nano-structured diamond thin-film electrodes grown by microwave plasma CVD Yi-Jiun Chen a,Ã , Tai-Fa Young a,b,c , Shern-Long Lee d , Hsuan-Jung Huang d , Tai-Sung Hsi d , Jun-Gi Chu c , Der-Jun Jang c a Department of Mechanical and Electromechanical Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan, 80424, ROC b Research Center of Nanoscience, National Sun Yat-sen University, Kaohsiung, Taiwan, 80424, ROC c Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan, 80424, ROC d Department of Chemistry, National Sun Yat-sen University, Kaohsiung, Taiwan, 80424, ROC Abstract In this paper, we report the investigation of the electrochemical properties of nano-structured diamond thin-film electrodes on porous silicon (PSi) synthesized by microwave plasma chemical vapor deposition (MPCVD). For the application, boron-doped and undoped diamond thin film has been performed and fabricated into an electrode device, and its microstructure, electrical and chemical properties have been studied. In order to enlarge the surface area of diamond electrodes, a negative bias was applied to the MPCVD process to deposit diamond thin film in a nano-structured form, so that its surface remained rough and nano-fine structured. Diamond thin films were analyzed by Raman spectroscopy and SEM. The morphology of boron-doped diamond thin films on PSi reveals nano-rods in the shape of diamond crystallites. Their electrochemical properties were evaluated by performing cyclic voltammetry (CV) measurement in inorganic K 4 [Fe(CN) 6 ] in a K 2 HPO 4 buffer solution. Boron-doped diamond thin film on PSi has demonstrated good electrochemical properties, with a larger redoxidation current of CV, due to its rough surface, which provides a more active electrochemical interface. r 2005 Elsevier Ltd. All rights reserved. Keywords: Microwave plasma CVD; Nano-structure; Diamond electrode; Cyclic voltammetry 1. Introduction Since the discovery of semiconductive diamond, scien- tists have expected many applications of diamond, and chemical vapor deposition (CVD) as one of the most important methods to synthesize diamond. The conductiv- ity of diamond can be varied across a very wide range through doping with various impurities. For further applications in electronic and electro-chemical engineering, the properties of diamond with doping have been studied extensively. However, the synthesis of low-resistive dia- mond is very difficult. Boron can be doped into diamond by synthesis using CVD to increase its conductivity. Boron- doped diamond (BDD) is a unique material with innumer- able applications because of its unusual physical and chemical properties, including high thermal conductivity, high hardness, and chemical inertness. BDD has been demonstrated to have applications in biotechnology, since diamond electrodes reveal very low catalytic activity in aqueous electrolytes for the evolution of hydrogen and oxygen, and possesses a low background current [1] and a wider potential window than other electrode materials [1,2]. Porous electrodes have gained much attention due to their application in electro-analysis, electro-catalysis, bat- teries, and fuel cells. Fujishima et al. [3] fabricated the porous honeycomb diamond electrode, which exhibited greater capacitance than crystalline BDD electrode’s. Foord et al. [4] reported that the nano-crystalline diamond revealed different electrochemical properties from BDDs. For particular applications, the high surface area BDD has been shown to have superior electrochemical properties [3]. Diamond film growing on porous silicon (PSi) has been shown to influence nucleation, stress and crystal structure. ARTICLE IN PRESS www.elsevier.com/locate/vacuum 0042-207X/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2005.11.036 Ã Corresponding author. E-mail address: bx2@alumni.ccu.edu.tw (Y.-J. Chen).