| The goal of the research was to develop and characterize the optical and electrochemical properties of boron-doped diamond thin film on quartz to better exploit the superb optical and material stability properties of diamond in the UV-Vis range. Adherent boron-doped diamond thin films were reproducibly deposited on quartz using microwave plasma chemical vapor deposition, with a 0.5% CH4/H2 source gas mixture containing 1 to 10 ppm B2H6 (200 sccm total gas flow), a system pressure of 45 Torr, and a microwave power of 800 W. Polishing of the quartz with a diamond powder/water slurry resulted in a high density of surface striations which promoted a high instantaneous nucleation density, leading to deposition of a continuous film of small microcrystallites (100--300 nm, 13 nm rms roughness) in a short growth time (1 to 2 h). The useful optical window in the UV-visible region ranged from ca. 225 to 900 nm. Loss of transmitted light was due mostly to reflection and absorption (due to nitrogen impurities and the boron dopant band). The diamond/quartz OTE had a carrier concentration of 1020 cm-3 (holes), and low electrical resistivity (0.058 O-cm) laterally through the grains and grain boundaries. The electrochemical properties included a wide potential window of nearly 3 V in aqueous solution, a low and stable background current, and fast electrochemical responsiveness for Fe(CN)6-3/-4, Ru(NH 3)6+2/+3, and CPZ0/•+. The spectroelectrochemical performance of the diamond OTE was evaluated in a specially designed, thin-layer cell, using chlorpromazine. Well-defined, thin-layer voltammetry was observed with Qpox values independent of scan rate, as expected for thin-layer behavior. The linear dynamic range was from 20 to 100 muM with a limit of detection of 0.5 muM (S/N = 3). A linear Nernst plot was observed with a slope of 56.9 mV (n = 1), and an ordinate intercept of 0.41 V. The diamond/quartz OTE possesses material property stability far superior to that of a commonly used OTE material, ITO. After potential cycling in 1 M NaOH and 1 M HNO3 for over two hours each, optical properties, film morphology, and resistivity of the films were unaffected, and the electrochemistry of Fe(CN)6 -3/-4 and Ru(NH3)6+2/+3 at these electrodes remained active after the polarization treatment. (Abstract shortened by UMI.)... |
