Abstract: A process for producing a thermoelectric material comprises molding a material powder comprising two or more elements selected from the group consisting of bismuth, tellurium, antimony and selenium and having average diameter in the range from 0.05 to 100 .mu.m and sintering the molded material powder with or without hot isostatic pressing. The material powder may be calcinated before the molding. A process for producing a thermoelectric element comprises cutting out pieces of a pillar-like shape from each of a p-type thermoelectric material and a n-type thermoelectric material, connecting the pieces cut out from the p-type thermoelectric material and the pieces cut out from the n-type thermoelectric material alternately with electrodes at the upper faces or the lower faces of the pieces and attaching insulating base plates to the surfaces of the electrodes. The p-type thermoelectric material and the n-type thermoelectric material are respectively produced by the process described above.

Abstract: A microwave plasma generating apparatus for generating plasma by radiating microwave into a space in which electric discharge takes place contains a plurality of microwave radiating means for radiating a plurality of microwaves having different directions of electric fields from each other. This microwave plasma generating apparatus can produce a diamond thin film by exciting a carbon source gas supplied into the space and bringing the excited gas into contact with a substrate to be formed thereon with the diamond thin film, the substrate being disposed in the space in which the electric discharge is performed. This apparatus can produce a large volume of plasma in a stable fashion and, as a result, provide a diamond thin film in a large area as a whole.