Radek Zeipl

Properties of thin N-type Yb0.14Co4Sb12 and P-type Ce0.09Fe0.67Co3.33Sb12 skutterudite layers prepared by laser ablation

The properties of thin thermoelectric layers (about 60 nm in thickness) prepared by pulsed laser deposition are presented. Hot pressed targets were made from “middle” temperature range thermoelectric bulk materials with the potential high figure of merit ZT. P-type and N-type layers were prepared from Yb0.19Co4Sb12 and Ce0.1Fe0.7Co3.3Sb12 targets, respectively. The thin films were deposited on quartz glass substrates using KrF excimer laser. The individual layers were prepared by applying different laser beam energy densities (2 or 3u2002Ju2009cm−2) at several substrate temperatures (200, 250, or 300u2009°C). Crystallinity and composition of the layers were examined by x-ray diffraction and wavelength dispersive analysis, respectively. Homogeneity of Yb across a surface of the Yb filled film was explored by secondary ion mass spectrometry. The thermoelectric properties, the Seebeck coefficient, the electrical resistivity, and the power factor, for the best prepared P and N layer are presented in the temperature range...

Study of Yb-Doped CoSb3 Thermoelectric Thin Films Prepared by Laser

Thin films of Yb filled CoSb3 were prepared on fused silica substrates using pulsed laser deposition method. The stoichiometric Yb0.19Co4Sb12 target was prepared by hot pressing method. The deposition conditions were changed with the goal to reach layers of smooth morphology. The target-to substrate distance was kept equal to 4 cm. The ambient argon pressure moved from 0.5 Pa to 13 Pa, laser repetition rate from 3 Hz to 10 Hz, and substrate temperature from 250 °C to 400 °C. We tested laser fluencies from 0.8 J·cm-2 to 5 J·cm-2. Films roughness was determined by mechanical profilometer and by atomic force microscopy. The lowest roughness of about 5 nm – 10 nm was reached for low laser fluencies but mechanical quality of films was poor and growth rate low (about 0.1 A/pulse). From WDX analysis follows that there is an excess of Yb and Sb compared to Yb0.19Co4Sb12 target.

Scanning Thermal Microscopy of Thermoelectric Nanostructures

We present the development and results of a new simple method for thermal conductivity characterization of thin films and thermoelectric structures using a scanning thermal microscope in pulsed current mode. The presented method does not allow measurement of absolute thermal conductivity of the studied system, but only relative to the Si substrate. We present the results of the method on the Si substrate/layer step boundary. The nano-layers of different thickness and different materials were prepared for the experiments by the pulsed laser deposition from hot-pressed targets.

Characterization of laser prepared Bi2Te3 nano-layers

A method for relative thermal conductivity characterization of thin thermoelectric layers and multi-layered structures in nanometre range using a scanning thermal microscope working in an active constant current mode is suggested. The method requires a very smooth and high quality surface of the studied thermoelectric system. To fulfil these requirements a study of the influence of principal deposition conditions including substrate temperature and laser beam density on surface quality of Bi2Te3 layers prepared by pulsed laser deposition was performed and its results are presented.

Very Smooth FeSb2Te and Ce0.1Fe0.7Co3.3Sb12 Layers Prepared by Modified PLD

We report on the preparation of thermoelectric layers of FeSb2Te and Ce0.1Fe0.7Co3.3Sb12 on silicon (100) and fused silica substrates via a combination of pulsed laser deposition (PLD) and rapid thermal annealing methods. A wide range of deposition conditions were tested including on- and off-axis approaches and variation of the annealing temperature profile. Wavelength dispersive x-ray spectroscopy was used to determine stoichiometry. An optical microscope, mechanical profilometer, and atomic force microscopy served to map layer topology. For the FeSb2Te layers, Sa was between 1.4xa0nm and 6xa0nm, with Sq ranging from 2.1xa0nm to 7.8xa0nm. For Ce0.1Fe0.7Co3.3Sb12 layers, Sa was from 1.3xa0nm to 4.2xa0nm and Sq between 1.7xa0nm and 6.2xa0nm. Crystalline structure was determined by x-ray diffraction. The best layers (in terms of smooth surface and crystalline structure) prepared using a modified off-axis PLD arrangement were then characterized for thermoelectric properties. The smooth, stoichiometric and crystalline layers of both types were prepared at an annealing temperature of 423xa0K for 10xa0min. All experiments were conducted with the aim of finding the deposition condition providing smooth and crystalline layers. These conditions should be used for the deposition of multilayered systems composed of the FeSb2Te and Ce0.1Fe0.7Co3.3Sb12 layers with a period of about 1xa0nm, where there could be layer roughness comparable to the period.

Physical Properties of Bi2Te3 Nanolayers

The properties of very thin Bi2Te3 (nano-) layers of different thickness prepared by pulsed laser deposition at different fluences are presented. Thermoelectric properties such as the thermal conductivity, the in-plain electrical conductivity, the Seebeck coefficient and also crystallinity, composition and morphology are presented. The surface properties were studied by atomic force microscopy.

Properties of thermoelectric Ce0.09Fe0.67Co3.33Sb12/FeSb2Te multi-layered structures prepared by laser ablation

Multi-layered Ce0.09Fe0.67Co3.33Sb12/FeSb2.1Te structures composed of thin equidistant layers were prepared by Pulsed Laser Deposition on fused silica quartz glass substrates. The structures were prepared at different substrate temperatures (230 °C or 250 °C) applying the laser beam energy density of 3 Jcm−2. In the contribution we present some thermoelectric properties such as the in-plane electrical conductivity, the Seebeck coefficient and the power factor for the multi-layered structures in the temperature range from 300 K to 500 K. Comparison of multi-layered structures thermoelectric properties with single thin Ce0.09Fe0.67Co3.33Sb12 and FeSb2.1Te layers is given. A cross sectional picture of the multi-layered structure made by Scanning Electron Microscope is presented for the thicker multi-layered structure.

Properties of pulsed laser deposited Bi2(m+n)Te3 thin films

The Bi2Te3 thin films with various thicknesses were prepared by laser ablation in vacuum using the KrF excimer laser. The energy density of laser was set at 5 J/cm2 (resp. at 2 J/cm2 in the second experiment). The substrate temperature was held at 410 °C. The influence of thickness on the Hall mobility and conductivity at room temperature is presented.