Papers by Author: Hubert Scherrer

Abstract: The short-time-consumption melting and hot pressing processes were used to synthesize n-type and p-type Bi-Sb-Te thermoelectric materials. The synthesis materials were characterized and used for the module fabrication. The aluminium substrate was used instead of alumina substrate because it is easy to cut and to avoid fragility of the module. The performance of 20 x 20 mm2 prototype thermoelectric module consists of 7 pairs of n-type and p-type Bi-Sb-Te thermoelectric materials was investigated and then compared its performance to 40 mm x 40 mm commercial module. The output power densities as a function of temperature difference across the devices and open circuit voltages from the module are reported.

Abstract: Literature data on (self-)diffusion in transition metal borides are extremely sparse due to the low atomic mobility of the constituents and due to the fact that for B there exist no suitable radioactive tracers and only two stable isotopes with a high natural abundance of 19 % (10B) and 81 % (11B), respectively. The present paper reviews our experiments on the tracer diffusion of transition metals and boron in TiB2, WB2+x, and (TixWyCrz)B2 which were carried out using stable isotopes and secondary ion mass spectrometry (SIMS). For tracer deposition, ion implantation and magnetron sputtering were used. In order to measure boron diffusion, a specially designed experiment was build up where a TiB2 layer was sputtered on an isotope-enriched Ti11B2 bulk ceramic sample. In addition, first results on chemical interdiffusion in the system (TixWyCrz)B2 will be presented. Here, a method based on magnetron sputtered layers and secondary neutral mass spectrometry (SNMS) was used which allows to determine much lower diffusivities (down to 10-19 m2/s) than the conventional EDX line-scan method on cross-sectional samples.

Abstract: The self-diffusion of nitrogen is investigated in polycrystalline thin silicon nitride films using a gas-exchange method (14N2/Si3 15N4) in comparison to Si3 14N4/Si3 15N4/Si3 14N4 isotope heterostructures. The films are produced by reactive r. f. magnetron sputtering. Depth profile analysis is carried out with secondary ion mass spectrometry (SIMS), secondary neutral mass spectrometry (SNMS), and nuclear resonant reaction analysis (NRRA). The nitrogen diffusivities determined with the use of isotope heterostructures follow an Arrhenius law in the temperature range between 1200 and 1700 °C with an activation enthalpy of DH = 4.9 eV and a pre-exponential factor of D0 = 1 x 10-6 m2/s, indicating a conventional diffusion mechanism via localized point defects. Using the gas-exchange method, the nitrogen diffusivities could be obtained only in the temperature range between 1600 and 1700 °C. This is due to the fact that at temperatures below 1600 °C the surface exchange process with its high activation enthalpy (about 10 eV) is rate limiting, leading to non detectable diffusion profiles. The application of the different methods of depth profiling leads to the same diffusivities within estimated errors.