A model of the formation of a p-type surface conductive layer on deposited diamond films is proposed. According to the model, the ionization of acid in water produces oxonium ion ( H3O+) which reacts with hydrogen on diamond films and causes the creation of holes in diamond films. The model also explains the disappearance of the p-type surface conductive layer by the action of alkaline substances. The experimental results concerning the change in electrical resistance at the surface of diamond films can be explained using the proposed model.
The semiclassical approximation is extended to the case of ionisation of atoms by relativistic charged particles. The theory is formulated both for a relativistic and a non-relativistic electron description. For total cross sections the theory is shown to be equivalent to the relativistic plane-wave Born approximation. Numerical results for the impact parameter distribution of the ionisation probability for the K shell are given.
The electrical surface resistance of diamond films deposited by the hot-filament chemical vapor deposition (CVD) method is measured in oxidizing and reducing atmospheres. The electrical surface resistance decreases in NO2, HCl and O3 gases. On the other hand, it increases in NH3 gas. The mechanism of change in electrical resistance is explained by the formation mechanism of a p-type surface conductive layer. The realization of a gas sensor will be discussed considering the experimentally obtained results.
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