Thermoelectric Properties of Films and Monocrystalline Whiskers of Tellurium
Tellurium is an interesting semiconductor for thermoelectric applications because its thermopower is high (500 muV/K). Its figure of merit is low in the bulk because it has high thermal conductivity. However, in confined geometries, the phonon conductivity decreases due to phonon scattering. Therefore we have investigated the thermoelectric properties of Te films and whiskers. We report a study of the thermoelectric properties of Te films obtained by vacuum-condensation method on glass, polyamide, mica at various temperatures of condensation. The crystallographic structure of the films is characterized by the distribution function of the grain major axis. It is shown that the films condensed at 433 K possess the highest mobility. Te whiskers were grown from the paragas phase and they were single crystals in the form of hexahedral cylinder having cavities inside. When deposited on cold substrate, the cylinders had no cavities. The direction of the whisker crystal growth was always [0001] with respect to the whiskers length. It is shown that in films with the thickness of ~1 mum, the room temperature thermopower S is 330 muV/K and increases with temperature increasing (S = 450 muV/K at 450 K). The resistivity decreases with the temperature growth, as a result the power factor alpha2sigma increases by almost a factor of two. The 77 K electric conductivity of Te whiskers is 2-to-3 order-of-magnitude higher than in bulk crystals, presumably due to high structural perfection of whisker crystals. The thermopower in the range of 300 K is S = 400-750 muV/K
Synthesis of Te-Bi core-shell nanowires by two-step electrodeposition in ionic liquids
Abstract Te-Bi core-shell nanowires were synthesized by electrochemical deposition in ionic liquids without using a template. The nanowires were synthesized in two steps: self-standing single crystal Te nanowires with a diameter of 76.2 ± 28.4 nm and a length of a few microns were electrodeposited first, taking advantage of the templating properties of the mixture of ionic liquids EOPipTFSI:EOPipBr 95:5 mole%. The Bi shell was then deposited on the Te core in EOPipTFSI. The influence of various experimental parameters on Bi shell deposition was studied. Thanks to the higher viscosity of the electrolyte compared to an aqueous medium, a lower growth rate is observed, leading to a thin layer of bismuth. In addition, High Resolution Transmission Electronic Microscopy shows that under optimal conditions the Te nanowires are entirely covered by a homogeneous, compact and polycrystalline Bi shell and that the core/shell interface is smooth.
Relationships Between Food Preferences and Food Acceptance Ratings
A study was conducted to assess relationships between food preference ratings and food acceptability ratings. Acceptability ratings for each of two discriminably different samples of nine food items were obtained using the 9-point hedonic scale. Regression analysis indicated that no linear relationship existed between these ratings and either hedonic or frequency preference ratings of the foods. In addition, the range of acceptability ratings was smaller than the range of corresponding’preference ratings. Panelists’expressed preferences had no effect on their assignment of differential acceptance ratings to different samples of the items. Correlations between preference ratings of laboratory panelists and military field panelists were good, in spite of higher absolute preference ratings assigned by the laboratory panel.