Thermoelectric properties of Bi2Te3-PbTe pseudo binary near the eutectic composition.

(Bi2Te3)(1-x)(PbTe)(x) binary systems near eutectic composition were prepared by melting of elemental metals and a sequential water quenching process and their microstructures and thermoelectric properties were investigated. Multiple phases such as Bi2Te3, BiPbTe and PbTe were observed due to phase separation when the composition x was higher than the eutectic point. Also the electrical conduction type of the alloys converted from p-type to n-type in the phase separated alloys. The lattice thermal conductivities in the phase-separated alloys are lower than those in alloys without phase separation, attributable to increased boundary scattering.

Growth and thermoelectric properties of multilayer thin film of bismuth telluride and indium selenide via rf magnetron sputtering.

A bismuth telluride (BT)/indium selenide (IS) multilayer film was deposited at room temperature by rf magnetron sputtering on a sapphire substrate in order to investigate how the multilayered structure affects the microstructure and thermoelectric properties. The effect of annealing at different temperatures was also studied. The results were compared with those from a BT film with the same thickness. A TEM study showed that the interface between the BT and IS layers became vague as the annealing temperature increased, and the BT layer crystallized while the IS layer did not. The presence of thin IS layers can help to limit the evaporation of Te from the BT/IS multilayer film, thus increasing the amount of Bi2Te3 phase in the multilayer film as compared with that of the BT film. An abrupt increase in the Seebeck coefficient of the multilayer film was observed when annealed at 300 degrees C, and the resistivity of the annealed multilayer film was high compared to that of the BT film. This result can also be explained by the proposed role of the IS layer, which limits the evaporation of Te at high temperature. The highest power factor of -3.9 x 10(-6) W/K2 cm was obtained at room temperature from the multilayer film annealed at 300 degrees C.

Thermoelectric properties of Bi2Te3-In2Se3 composite thin films prepared by co-sputtering.

Bi2Te3-In2Se3 films were prepared by co-sputtering followed by annealing, and their structural and thermoelectric properties were investigated. The immiscible nature of the two alloys results in precipitation of the second phase, thus leading to structures with self-assembled dots that are a few nanometers in scale. HAADF-STEM and HRTEM were used to confirm that In2Se3 nanodots that were a few nanometers in size did indeed form in the Bi2Te3 thin film. It was found that the incorporation of these nanodots can reduce the thermal conductivity of the thin film.

Fabrication of carbon nanotube-emitters on Ag-Cu alloy film by thermal welding.

A field emission electron source was fabricated on a Si substrate using Ag-Cu alloy (ACa) and carbon nanotubes (CNTs). The ACa was adopted as a binder material due to its excellent electrical conductivity, oxidation stability, and suitable melting point (783 degrees C). The surface morphology of the ACa-film was improved by introducing an Nb layer as an adhesion layer between the ACa-film and the Si substrate. The ACa-film thickness was varied from 100 to 500 nm. The spray method was employed to deposit a CNT film on the ACa/Nb/Si substrate for large area fabrication. After annealing the substrate at 700 degrees C for 10 min, the CNT film was tightly welded on the ACa-films, and the CNT-emitters fabricated on the 400-nm-thick ACa-film exhibited high current density and stability with a low turn-on voltage. It is worth noting that ACa could be applied to the glass substrate because the CNT-emitters fabricated at 500 degrees C exhibited good field emission characteristics.

Synthesis of bandgap-controlled semiconducting single-walled carbon nanotubes.

Bandgap-controlled semiconducting single-walled carbon nanotubes (s-SWNTs) were synthesized using a uniquely designed catalytic layer (Al(2)O(3)/Fe/Al(2)O(3)) and conventional thermal chemical vapor deposition. Homogeneously sized Fe catalytic nanoparticles were prepared on the Al(2)O(3) layer and their sizes were controlled by simply modulating the annealing time via heat-driven diffusion and subsequent evaporation of Fe at 800 degrees C. Transmission electron microscopy and Raman spectroscopy revealed that the synthesized SWNTs diameter was manipulated from 1.4 to 0.8 nm with an extremely narrow diameter distribution below 0.1 nm as the annealing time is increased. As a result, the bandgap of semiconducting SWNTs was successfully controlled, ranging from 0.53 to 0.83 eV, with a sufficiently narrow energy distribution, which can be applied to field-effect transistors based on SWNTs.

Correlation between photoluminescence and Fourier transform infrared spectra in tetra-ethyl-ortho-silicate thin films.

We report strong visible photoluminescence (PL) from thermally treated tetra-ethyl-ortho-silicate (TEOS) thin films at room temperature. High-resolution transmission electron microscope (HRTEM) studies showed that the PL originated from nanocrystalline-Si (nc-Si). HRTEM images showed that as-grown TEOS thin films had quasi-static amorphous (QSA) SiO(2) phases instead of the typical amorphous (TA) SiO(2) phases, and that they divided into small pieces of nc-Si after thermal treatment. In addition, Fourier transform infrared (FTIR) investigations showed that the QSA-SiO(2) phases were composed of three types of bonding modes (i.e., Si-O-Si bending, Si-O bending, and Si-O-Si stretching), which play important roles in the formation of the nc-Si at relatively lower annealing temperatures.