Absolute Seebeck coefficient of thin platinum films

The influence of size effects on the thermoelectric properties of thin platinum films is investigated and compared to the bulk. Structural properties, like the film thickness and the grain size, are varied. We correlate the electron mean free path with the temperature dependence of the electrical conductivity and the absolute Seebeck coefficient $S_{\text{Pt}}$ of platinum. We use a measurement platform as a standardized method to determine $S_{\text{Pt}}$ and show that $S_{\text{Pt,film}}$ is reduced compared to $S_{\text{Pt,bulk}}$. Boundary and surface scattering reduce the thermodiffusion and the phonon drag contribution to $S_{\text{Pt,film}}$ by nearly the same factor. A detailed discussion and a model to describe the temperature dependence of the absolute Seebeck coefficient and the influence of size effects of electron-phonon and phonon-phonon interaction on $S_{\text{Pt}}$ is given

Systematic X-ray absorption study of hole doping in BSCCO - phases

X-ray absorption spectroscopy (XAS) on the O 1s threshold was applied to Bi-based, single crystalline high temperature superconductors (HTc's), whose hole densities in the CuO2 planes was varied by different methods. XAS gives the intensity of the so-called pre-peak of the O 1s line due to the unoccupied part of the Zhang-Rice (ZR) singlet state. The effects of variation of the number n of CuO2 - planes per unit cell (n = 1,2,3) and the effect of La-substitution for Sr for the n = 1 and n = 2 phase were studied systematically. Furthermore the symmetry of the states could be probed by the polarization of the impinging radiation.Comment: 4 pages, 2 figures, to appear in the proceedings of SCES2001, Ann Arbor, August 6-10, 200

LUMINESCENCE CHARACTERIZATION OF GaAs SINGLE QUANTUM WELLS

The peculiarities of the photo- and cathodoluminescence of MOVPE grown single quantum wells containing impurities are investigated. The investigations reveal monolayerfluctuations with a lateral extension of about 10 µm. The incorporation of carbon in the thicker islands is shown using micrographs of spectrally resolved cathodoluminescence. Extrinsic radiative transitions involving the impurities are found also in the barrier above that islands which contain impurities. These inhomogenities are proposed to be connected with dislocations emanating from the substrate and penetrating the sandwiched layer structure

Absolute Seebeck coefficient of thin platinum films

The influence of size effects on the thermoelectric properties of thin platinum films is investigated and compared to the bulk. Structural properties, like the film thickness and the grain size, are varied. We correlate the electron mean free path with the temperature dependence of the electrical conductivity and the absolute Seebeck coefficient SPt of platinum. A measurement platform was developed as a standardized method to determine SPt and show that SPt,film is reduced compared to SPt,bulk. Boundary and surface scattering reduce the thermodiffusion and the phonon drag contribution to SPt,film by nearly the same factor. We discuss in detail on behalf of a model, which describes the temperature dependence of the absolute Seebeck coefficient, the influence of size effects of electron-phonon and phonon-phonon interaction on SPt

Temperature dependent thermal conductivity in Mg doped and undoped beta Ga2O3 bulk crystals

For $\beta$-$\mathrm{Ga_2O_3}$ only little information exist concerning the thermal properties, especially the thermal conductivity $\lambda$. Here, the thermal conductivity is measured by applying the electrical 3$\omega$-method on Czochralski-grown $\beta$-$\mathrm{Ga_2O_3}$ bulk crystals, which have a thickness of $200~\mathrm{\mu m}$ and $800~\mathrm{\mu m}$. At room temperature the thermal conductivity along the [100]-direction in Mg-doped electrical insulating and undoped semiconducting $\beta$-$\mathrm{Ga_2O_3}$ is confirmed as $13\pm 1~\mathrm{Wm^{-1}K^{-1}}$ for both crystals. The thermal conductivity increases for decreasing temperature down to $25~\mathrm{K}$ to $\lambda(25~\mathrm{K})=(5.3\pm 0.6)\cdot 10^2~\mathrm{Wm^{-1}K^{-1}}$. The phonon contribution of $\lambda$ dominates over the electron contribution below room temperature. The observed function $\lambda(T)$ is in accord with phonon-phonon-Umklapp scattering and the Debye-model for the specific heat at $T\gtrsim 90~\mathrm{K}$ which is about $0.1$ fold of the Debye-temperature $\theta_\mathrm{D}$. Here a detailed discussion of the phonon-phonon-Umklapp scattering for $T< \theta_\mathrm{D}$ is carried out. The influence of point defect scattering is considered for $T<100~\mathrm{K}$.Comment: 11 pages, 6 figure

Thermal and electrical conductivity of single crystalline kesterite Cu₂ZnSnS₄

Abstract For single crystalline sulfur-based kesterite Cu2ZnSnS4 the electrical and thermal conductivity are measured from 20 K to 320 K. The electrical conductivity decreases exponentially with decreasing temperature. The temperature dependence can be assigned to Mott-variable-range-hopping, an electrical transport process within an impurity band in the band gap. With the 3ω-method a thermal conductivity room temperature value of 5.1 ± 0.5 Wm−1K−1 and a maximal value of 8.0 ± 0.5 Wm−1K−1 at 100 K are found. Phonon-phonon-umklapp-scattering can explain the high temperature range from 100 K to 320 K. The low temperature values of the thermal conductivity are dominated by the temperature-dependence of the specific heat capacity, due to a reduced phonon-mean-free-path, owing to phonon-impurity-scattering.</jats:p