No abstract

It is shown that current-activated pressure-assisted densification (CAPAD) is sensitive to the Peltier effect. Under CAPAD, the Peltier effect leads to a significant redistribution of heat within the sample during the densification. The densification of highly p-doped silicon nanoparticles during CAPAD and the properties of the obtained samples are investigated experimentally and by computer simulation. Both, simulation and experiments, indicate clearly a higher temperature on the cathode side and a decreasing temperature from the center to the outer shell. Furthermore, computer simulations provide additional insights into the temperature profile which explain the anisotropic properties of the measured sample.

No abstract

Nanocrystalline bulk silicon samples were fabricated using silicon nanoparticles from the gas phase, applying a spark-plasma sintering process. The mean diameter of the crystalline grains after sintering was 30 nm and smaller, the density above 97 % of that of crystalline silicon. Transmission electron microscopy showed a homogenous nanostructure. The thermal conductivity of such an n-type sample with a nominal doping level of 5x10 20 cm -3 was around 11 Wm -1 K -1 at room temperature. With Seebeck-coefficient α = -150 µV/K and specific conductivity σ = 290 S cm -1 , the resulting efficiency ZT is approximately 0.02.

A nanoparticular p-n junction was realized by a field-assisted sintering process, using p-type and n-type doped silicon nanoparticles. A spatially resolved Seebeck microscan showed a broad transition from the positively doped to the negatively doped range. Overshoots on both sides are characteristic for the transition. Despite the tip size being much larger than the mean particle size, information about the dopant distribution between the particles is deduced from modeling the measured data under different assumptions, including the limited spatial resolution of the tip. The best match between measured and modeled data is achieved by the idea of doping compensation, due to the sintering process. Due to a short time at high temperature during the field-assisted sintering process, solid state diffusion is too slow to be solely responsible for the observed compensation of donors and acceptors over a wide range. Therefore, these measurements support a densification mechanism based on (partial) melting and recrystallization.