C₆₀/Zeolite Semiconductor Electrode and the Gas Sensing

Sodium Y type zeolite synthesized with homogeneous gels was deposited as thin films on tantalum toothcombs type electrode. C-60 molecules were deposited on the zeolite electrode surface by sublimation in a vacuum and were encapsulated in zeolite supercages by the thermal diffusion. The encapsulation was indicated by a decrease of the pore volume measured by argon gas adsorption. The potassium deposited K-Cb-60/zeolite electrode as well as zeolite and C-60/zeolite electrodes showed the behaviors characteristic to semiconductors in their measurements of currents in dark with temperature. The dependence of their dark currents on temperature was similar, which suggests that carrier formation through thermal band-gap excitation will be mainly caused by zeolite. The C-60/zeolite and K-C-60/zeolite electrodes showed rapid current responses repeatedly at 298 K under UV light irradiation. The introduction of oxygen gas to the C60/zeolite electrode under UV light irradiation resulted in both rapid and slow current decays with time. The current decreased and that remained in the rapid current decay were interpreted as contributions mainly from n-type (80%) and p-type character (20%), respectively. The slow current decay was interpreted by diffusion of oxygen into zeolite supercages. Ethylene sensing on the C-60/zeolite electrode was possible in dark and showed a pressure dependency of Langmuir type isotherm. The result implies that such sensing is caused by compressing ethylene molecules in zeolite supercages.