We report on an enhanced thermoelectric figure of merit ZT=sigmaS(2)T/lambda (where sigma is electrical conductivity, S is thermopower, T is absolute temperature, and lambda is thermal conductivity) for PbTe/PbSe0.20Te0.80 superlattices (SLs) and PbTe doping SLs due to a reduction of the thermal conductivity lambda parallel to the layer planes. Despite a small decrease of the power factors sigmaS(2) due to a reduction of sigma in these superlattices, the figure of merit is higher as compared to the corresponding bulk materials and reaches maximum values in the temperature range between 400 and 570 K

We have investigated the strain and composition distribution in uncapped SiGe islands grown on Si (001) by x-ray diffraction. In order to be sensitive to the dot layer on the sample surface, and at the same time being able to measure in-plane strain and strain in growth direction, we utilized a scattering geometry at grazing incidence angles, but with high exit angles. The measured intensity distribution is compared to simulations based on the strain distribution calculated by a finite element method. Although pure Ge has been deposited during island growth by molecular beam epitaxy, the Ge composition varies from 0.5 at the island base to 1.0 at the top of the islands. Even at this top, the elastic relaxation reaches only about 50%.

Fast highly-sensitive room-temperature semiconductor gas sensor based on the nanoscale Pt-TiO 2 -Pt sandwich, Sensors and Actuators B: Chemical (2014), http://dx. AbstractDevelopment of fast highly-sensitive semiconductor gas sensors operating at room temperature, which would be compatible with semiconductor technology, remains a challenge for researchers.Here we present such sensor based on a nanoscale Pt-TiO 2 -Pt sandwich. The sensor consists of a thin (~30 nm) nanocrystalline TiO 2 layer with ~10 nm grains, placed between the bottom Pt electrode layer and top Pt electrode shaped as a long narrow (width w down to 80 nm) stripe. If we decrease w to ~100 nm and below, the sensor exposed to air with 1% H 2 exhibits the increase of response (R air / ) up to ~ 10 7 and decrease of the reaction time to only a few seconds even at room temperature. The sensitivity increase is due to a nontrivial non-ohmic effect, a sudden decrease (by three orders of magnitude) of the electrical resistance with decreasing w for w ~ 100nm. This non-ohmic effect is explained as a consequence of two nanoscale-related effects: the hydrogen-diffusion-controlled spatially-inhomogeneous resistivity of the TiO 2 layer, combinedPage 2 of 41 A c c e p t e d M a n u s c r i p t 2 with onset of the hot-electron-temperature instability when the tiny grains are subjected to high electric field.

We present a method and results based on x-ray scattering capable of resolving the shape and strain distribution in buried islands, as well as their vertical composition gradient. As an example, results are presented obtained for a single layer of SiGe dome-shaped islands capped by a 160-nm Si layer. For a growth temperature of 700°C, a significant decrease of the average Ge content from about xϭ0.78 before overgrowth to about xϭ0.37 is found. The diameter of the islands increases from 110 to about 180 nm, their height shrinks from about 13 nm to 6 nm. This significant change of the island shape and content is accompanied by a pronounced change of their average in-plane lattice constant. The strain status of the overgrown flat islands is close to that of an embedded SiGe quantum well, i.e., with respect to the relaxation status of the uncapped islands a considerable strain redistribution takes place.

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