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 tellurium nanotubes by galvanic displacement
Abstract Tellurium nanotubes with controlled diameter and wall thickness were synthesized by galvanic displacement of cobalt nanowires and their temperature dependent field effect transistor and magnetoresistance properties were systematically investigated. The nanotube diameter was slightly larger than the sacrificial cobalt nanowire diameter with a wall thickness of range from 15 to 30 nm depending on the diameter of cobalt nanowires. Te nanotubes show p-type semiconducting property with the field effect carrier mobility of approx. 0.01 cm 2 /V s which is relatively lower than other 1D nanostructure. Low mobility might be attributed to porous morphology with small grain size (
Early Stage Diagnosis of Parkinson’s Disease Using HOS Features of EEG Signals
Parkinson’s disease (PD) is a common neurodegenerative disease that causes involuntary muscle movements and tremor among other symptoms. One approach to diagnosing this disease is by analyzing the electroencephalography (EEG) signals of the patients. However, due to the complexity of this type of signal, more advanced feature extraction and classification methods are required. The goal of this study is to combine six well-known features in EEG analysis with eight higher order statistical features and use them for classification of early stage PD (1st and 2nd stage) from a healthy control group. After extracting the required features, eight classifiers are employed to classify the signals.