J. Walachová

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 3 J cm−2) at several substrate temperatures (200, 250, or 300 °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...

Ballistic electron emission spectroscopy/microscopy of self-assembled InAs quantum dots of different sizes embedded in GaAs∕AlGaAs heterostructure

Self-assembled InAs quantum dots embedded in GaAs∕GaAlAs heterostructure were visualized by ballistic electron emission microscopy. The spectroscopic characteristics on individual quantum dots were examined. Quantum dots had images of elliptical shapes. Their length was from about 10to20nm. Below one-electron p1-like state, one-electron and two-electron ground states and excited two-electron states were observed. The Coulomb interaction and exchange energies between two electrons in quantum dots were determined and compared with the previously published theoretical results.

Study of InAs quantum dots in AlGaAs∕GaAs heterostructure by ballistic electron emission microscopy/spectroscopy

Self-assembled InAs quantum dots in GaAs∕GaAlAs structures were examined by ballistic electron emission microscopy/spectroscopy. The studied structures were grown by metal-organic chemical vapor deposition. Quantum dots with an image of elliptical shape were studied. Ballistic current-voltage characteristics through the quantum dot and outside the quantum dot are compared in the voltage range of 0.55–2V. In the voltage range from 0.55to0.8V examples of ballistic characteristics and their derivatives are given. In a detailed study, measurements with 1mV step in the energy range from 0.55to0.63V are presented.

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.

Thin layers prepared by pulsed laser deposition from Yb0.19Co4Sb12 target

Bulk Yb0.19Co4Sb12 skutterudite prepared by hot pressing was found to be a good high temperature thermoelectric material with a high figure of merit ZT (ZT=1.2 at T=650 K). In this contribution the properties of thin layers prepared by pulsed laser deposition from such target are presented. The target was prepared by hot pressing and was proved to be a skutterudite structure. The thin films were deposited on quartz glass substrates using KrF excimer laser. The substrate temperature during the deposition was 200 degC, 250 degC, 300 degC or 410 degC, the energy density of the laser beam was held at 2 J/cm2, 3 J/cm2 or 5 J/cm 2 for individual experiments. The deposition took place in Ar atmosphere of 13 Pa. The layers from 150 nm up to 440 nm were examined by X-ray diffraction method. Depending on the deposition conditions the layers between amorphous and skutterudite structures were obtained. For some samples, CoSb2 phase and mixed CoSb2 phase with skutterudite structure were also observed. For the layer with skutterudite structure the homogeneity and relative quantity of Yb across the 1cm2 of the surface was examined by secondary ion mass spectrometry. The 60 nm thick layers with skutterudite structure were characterized by Seebeck coefficient and resistivity measurements in the temperature range from 300 K to 550 K. The results are compared with the published results for the bulk material

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.