Papers by Keyword: Tellurium

Abstract: Nanocomposites of tellurium and sodium nitrate were synthesized via a simple thermal dissolution of polycrystalline tellurium powder in nitric acid, followed by tellurium reduction in the presence of sodium dithionite solution. Thin solid films based on these composites have been fabricated and characterized. The morphology, composition and structure of the films were investigated by SEM, EDS, and XRD methods and the possible chemical reactions for the synthesis of relevant nanocomposites were formulated. It has been established that composites consist of nanowires with a diameter of ~100 nm and lengths up to 1,0 micrometers and nanoparticles of 100 ÷ 300 nanometers comprising about 35 at% Te and 7.0 at% of sodium nitrate. It is expected that nanocomposites synthesized via this method can be of interest in producing functional thin films, having both electronic and ionic conductivity.

Abstract: Tuning the bandgap of superlattice structures creates devices with unique optical, electronic and mechanical properties. Designing solar cells with superlattice structures increases the range of light energy absorbed from the solar spectrum in the device. A superlattice is a nanostructure composed of alternating thin layers of two materials. The thickness of the constituent materials alters the optical bandgap of the superlattice. This paper discusses a mathematical model which computes the effective bandgap of a CdTe/PbTe superlattice based on a given thickness of the CdTe and PbTe films. The output of this model is verified by fabricating superlattices with different thickness and measuring their effective bandgaps. The electrochemical atomic layer deposition method is used to fabricate the superlattice structures. The advantage of this method over other vacuum techniques is that it is inexpensive and operates at room temperature. This paper also discusses a method to mitigate the lattice mismatch between the substrate and the superlattice. The optical bandgaps, crystallinity, grain size and chemical composition of the structures are measured using a spectrometer, diffractometer, transmission electron microscope and scanning electron microscope, respectively. The bandgaps of the fabricated superlattices were in agreement with the simulated values. This model can be used for designing the bandgaps of superlattices which can be incorporated in solar cells.

Abstract: A model based on the k.p perturbation theory to compute the energy bands in a CdTe/PbTe superlattice structure is developed. The model uses the dispersion relations for the heavy hole, light hole and the split off bands to compute the effective bandgap in a CdTe/PbTe superlattice structure. Given a certain thickness of the layers composing the superlattice the model computes the effective bandgap. This model will be used towards understanding the relationship between film thickness and optical bandgaps in a CdTe/PbTe superlattice. The end goal is to tailor the optical bandgap of a CdTe/PbTe superlattice to result in maximum efficiency when used in a solar cell.

Abstract: Glutathione peroxidase (GPX) is a well-known selenoenzyme that can protect cells against oxidative damage. A novel dicyclodextrinyl ditelluride (2-TeCD) compound was devised as a functional mimic of the GPX. The antioxidant effect of 2-TeCD was evaluated by its ability to protect mitochondria from oxidative damage. 2-TeCD could also suppress the TNF-α induced inflammatory effect on HUVECs surface in a dose-dependent manner. Meanwhile, 2-TeCD exhibited anti-proliferative property both in vitro and in vivo. These results indicate that 2-TeCD may be useful for developing medical agents in many pathological conditions such as cataract­, age-related diseases­, atherosclerosis, cancer and so on.

Abstract: A long pulsed laser ablation with a moving target at high speed technique was applied to prepare tellurium nanoparticles from a tellurium target under argon gas at atmospheric pressure. The prepared nanoparticles were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), and X-ray diffraction (XRD). The influence of the moving speed of the target on the size, morphology and crystallographic structure of the nanoparticles was investigeated. The results show that for the target moving at high speed without burning of the target the production of isolated nanoparticles is obtained. The diameter of the nanoparticles is ranging from 30 to 200 nm.

Abstract: A Bi2Te3-based thermoelectric semiconductor was subjected by high pressure torsion (HPT). Sample disks of p-type Bi0.5Sb1.5Te3.0 were cut from sintered compacts that were made by mechanically alloying (MA) followed by hot pressing. Disks were subjected by HPT with 1, 5 and 10 turns at 473 K under 6.0 GPa of pressure. Crystal orientation was investigated by X-ray diffraction. Microstructures were characterized using scanning electron microscopy. Results indicated that HPT disks after 5 turns had a preferred orientation and a fine grain compared with pre-HPT disks while the orientation factor was decreased after HPT using 10 turns. The power factor had a maximum value at 5 turns as determined by measuring its thermoelectric properties. A maximum power factor of 4.30×10-3 Wm-1K-2 was obtained for HPT disks after 5 turns. This value was larger than that for the pre-HPT disk. The over-HPT of 10 turns was found to have caused a decrease in the preferred orientation leading to a low power factor.

Abstract: Selenium (Se) and tellurium (Te) ions are implanted into n-type 6H-, 4H- and 3C-SiC epilayers. Double-correlated deep level transient spectroscopy investigations reveal that both Se and Te atoms form double donors in SiC. The number of double donors observed corresponds to the number of inequivalent lattice sites of the particular SiC polytype. This observation is a strong hint that Se and Te atoms reside on lattice sites. The activation energies FEa of Te double donors are larger than the corresponding ones of Se double donors.

Abstract: The high sensitivity of the low temperature electrical properties of p-type pure tellurium (Te) to impurities, structural boundaries, point defects and dislocations allows to investigate the structural imperfection profiles in crystals grown under different conditions. Our interest was focused on studying the influence of grain boundaries on the electrical properties of the samples that were remelted and directionally solidified in space (µg) without a seed (W-µg), in comparison with the sample grown under the normal earth conditions (1g0) and a nanocluster sample obtained by filling with melted Te of dielectric opal matrix voids (Opal sample). The W-µg ingot of Te was prepared in the "Crystallizator" furnace under microgravity conditions aboard the "Mir" space station [1]. The concentration variation of electrically active defects and neutral defects along the samples were studied by galvanomagnetic methods (Hall effect and electrical resistivity) in a wide temperature range from 0.4 to 300 K. In these measurements, the following effects caused by the micro- and nano- crystalline structure were found: low hole mobility, high concentration of neutral defects, and anomalous positive magnetoresistance in low magnetic fields at low temperatures. Besides, the specific resistivity of the space sample was found to oscillate (up to 20%) along the length which can be correlated with the presence of a few contact points of the melt with the ampoule wall. This ingot was formed as a result of rapid homogeneous spontaneous solidification, accompanied by forming a micro-block structure. The appearance of the anomalous positive magnetoresistance was observed in the micro-block W- sample and the nanocluster Opal sample. It is a consequence of intensive hole scattering at the grain boundaries which leads to an increase of the intervalley transition probability and to a change of the spin sign of holes in a low symmetry Te crystal. According to the weak localization theory [2], the spin variation during the scattering results in a positive magnetoresistance of the sample in low magnetic fields, in contrast to bulk Te crystals.