Papers

ICMCTF2005 Session D4: Diamond-Based Materials and Devices

Tuesday, May 3, 2005 4:10 PM in Room Royal Palm 1-3

Tuesday Afternoon

Start	Invited?	Item
4:10 PM		D4-9 The Use of CVD Diamond Electrodes in the Oxidation of Organics P.M. Natishan (US Naval Research Laboratory); F.J. Martin (Geo Centers, Inc.); B.R. Stoner (MCNC); J. Farrell (University of Arizona); H.B. Martin (Case Western Reserve University); P.L. Hagans, W.E. O'Grady (US Naval Research Laboratory) Boron-doped diamond (BDD) electrodes prepared by chemical vapor deposition were used to electrochemically oxidize organic compounds such as phenol. Cyclic voltammetry showed that phenol was oxidized by the diamond electrodes and that the electrodes remained electroactive after multiple cycles. Experiments that were carried out with a flow cell showed that phenol in an aqueous stream was converted completely to CO₂. Also in this work, the presence of a short-lived species (SLS) produced by anodic polarization of BDD electrodes was observed and investigated. Anodic potentials greater than 1.5 V with respect to the standard hydrogen electrode (SHE) were required to generate the SLS. Increasing anodic potentials between 1.5 and 3.0 V/SHE resulted in increasing concentrations of the SLS, until a saturation point was reached. Normal pulse voltammetry experiments showed that anodically produced SLS survive for less than 50 ms under open circuit conditions. We believe that the SLS is important to the oxidation of organic compounds.
4:50 PM		D4-11 Diamond/Nanodiamond Vacuum Field Emission Devices J.L. Davidson, W.P. Kang, R. Takalkara, K. Subramanian (Vanderbilt University) Chemical vapor deposited (CVD) diamond and related carbon materials are excellent materials for electron field emitters because of their low or negative affinity (NEA) and excellent mechanical and chemical properties such as high hardness and ability to withstand ion bombardment. The NEA property of diamond, unlike other materials, is retained in a residual gas ambient. In addition to these properties, diamond has the highest thermal conductivity and can have high electrical conductivity, enabling diamond devices to operate at high temperatures and high power. This makes diamond field emitters potentially advantageous in vacuum microelectronics. In this paper, we report the development of (a) vertical and (b) lateral diamond vacuum field emission devices with excellent field emission characteristics. These diamond field emission devices, diode and triode, were fabricated using a self-aligning gate formation technique from silicon-on-insulator wafers using conventional silicon micropatterning and etching techniques. High emission current > 0.1 amp was achieved from the vertical diamond field emission diode with an indented anode design. The gated diamond triode in vertical configuration displayed excellent transistor characteristics with high DC gain of ~800 and large AC output voltage of ~100 V p-p. Lateral diamond field emission diodes with cathode-anode spacing less than 2 microns were fabricated. The lateral diamond emitter exhibited a low turn-on voltage of ~5 V (field ~3 V/micron) and a high emission current of 6 microamps. The low turn-on voltage and high emission characteristics are the best of reported lateral field emitter structures. These devices have been packaged and tested and their performance as freestanding, conventionally configured electronic devices will be reported.
5:10 PM		D4-12 Plasma Enhanced Synthesis of Diamond Nanocones Films Q. Yang (University of Saskatchewan, Canada) The property of negative electron affinity (NEA) makes diamond a promising electron field emission material. Diamond with an aligned nanotip structure has been thought to have much better field emission properties. Furthermore, diamond nanotips with micro or submicro scale roots may have greater rigidity, subjecting less mounting difficulties, compared with carbon nanotubes, when used for scanning probe microscopy. In this paper, three plasma processes developed to fabricate diamond nanocones in hot filament reactor includes: (1) plasma enhanced hot filament CVD, (2) graphite etched by hydrogen, and (3) hydrogen plasma treatment of the diamond films pre-coated on the silicon substrate. During the above processes, a dc glow discharge was initiated between the filament (anode) and the substrate holder (cathode). In the first process, conventional hot filament chemical vapor deposition using a gas mixture of hydrogen and 1 vol % methane was used. In the second process, a graphite plate was placed below the substrate and only hydrogen was supplied. In this case, the graphite etched by hydrogen is the carbon resource for diamond growth. In the third process, pure hydrogen plasma (without any carbon resource in the system) was used. In the above three processes, all the other process parameters were similar. Diamond nanocones were formed on diamond-coated silicon substrate through all three processes while graphitic nanocones were observed on polished P-type (100)-oriented silicon wafers through the first two processes, and no thing were formed on silion wafers through the third process. The cones are solid with nanometer-size tips and submicron scale roots, and are well aligned with various orientation angles depending on the location on the substrates. The orientation of the cones appears to be determined by the direction of the electric field lines on the sample surface.
5:30 PM		D4-13 Preparation of Highly Stable, Low Capacitance, Active Carbon by Polymer Blend J.Y. Hwang, J.H. Wang (National Taiwan University, Taiwan); O.M. Chyan (University of North Texas); L.C. Chen, C.-H. Shen, C.W. Chen (National Taiwan University, Taiwan); K.H. Chen (Academic Sinica, Taiwan) Polymer blend has been widely used to prepare porous carbon, but the studies on preparing electrode materials and catalyst support by this process are few. In this paper, the high mesoporosity and electrochemical activity, needed as catalyst support, were observed. It is found that the surface area and pore size, as analyzed by the Scanning Electron Microscopy (SEM) and BET methods, were controlled by changing the chemical concentration and carbonization temperature. Besides, the electrochemical properties were measured by the Cyclic Voltammetry (CV) method in H₂SO₄ solution containing K₃[Fe(CN)₆] as the electrolyte. The results were compared with those of commercialized activated carbons, XC72 and BP2000. The high mesoporosity, stability and low capacitance all suggested the potential application for electrode materials and catalytic metal support. Finally, loading of platinum and ruthenium, as the prime catalysts for fuel cell, will be carried out by ion-exchange technique. The efficiency of the process and the characteristically electrochemical properties of these carbon-metal nanocomposites will be discussed.