Fabrication of Semi-transparent W film Heaters via Phase Transformation

In this study, we prepared highly thermostable semi-transparent heaters composed of W layers with thicknesses of 1-20 nm, on which a 30 nm-thick ZnO layer was deposited to serve as an anti-oxidation barrier. The optical transmittance and sheet resistance of the heaters could be greatly modulated by varying the W layer thickness. For layer thicknesses up to 10 nm, the initial Joule heating above 100 oC significantly reduced the sheet resistance, by 300% for a 6 nm-thick W layer at a fixed voltage for a duration of 400 s. During the test period, heater current and heating capability continuously increased. In subsequent heater operations, the heaters exhibited highly reproducible heating capability. In contrast, for films thicker than 10 nm, the Joule heating process resulted in only a marginal reduction in sheet resistance, i.e., by 4% for a 20 nm-thick W layer. In order to investigate the sharp dependence of heater characteristics on thickness, we performed x-ray diffraction analyses, which revealed that the films thinner than 10 nm were composed of both the equilibrium low-resistivity α-phase and metastable high-resistivity β-phase, and films thicker than 10 nm contained mostly α-phase. The Joule heating process for the thinner films was found to transform the β-phase into α-phase at temperatures above 100 oC, which resulted in significant improvement in the heating capability of the 6 nm-thick W layer. For films thicker than 10 nm, the W layers contained mostly α-phase and no such transformation-induced effects were observed. Finally, W heaters composed of α-phase exhibited highly thermostable and reproducible heater properties, which make the heaters suitable for applications with semi-transparent heaters.

LUMINESCENCE OF Α-WILLEMITE IN THE CATALYTIC OXIDATION OF CARBON MONOXIDE

The interaction of neutral gas particles of thermal energies (molecules and atoms) with the surface of a solid is accompanied by radiation in the visible and I.R. parts of the spectrum. In this case, the surface of a solid body acts as a catalyst for the recombination reactions of gas particles. In this connection, the possibility of exciting luminescence during the catalytic oxidation of carbon monoxide directly by the atomic form of oxygen pre-adsorbed on the surface of a solid is of interest. Kinetic and spectral methods were used to study the luminescence arising from the catalytic oxidation of carbon monoxide by the atomic form of oxygen preadsorbed on the surface of a solid – a sample of α-willemite Zn2SiO4:Mn2+. The main stages in the mechanisms of recombination between adsorbate particles are established. Electronic transitions in adsorption complexes and the activator ion have been identified. During the filling process, the sample temperature was maintained by a constant high-speed electronic control system of the heater current. This made it possible to avoid thermal side effects. The main stages in the mechanisms of recombination between adsorbate particles are established. Electronic transitions in adsorption complexes and the activator ion have been identified. It was found that luminescence excitation proceeds in two main stages, somewhat time-shifted. The two-stage mechanism for the catalytic oxidation of carbon monoxide on the surface of α-willemite with pre-adsorbed atomic oxygen allows a consistent description of the luminescence observed in this case. This type of luminescence has the prospect of using for studying the mechanisms of catalytic oxidation of carbon monoxide.

THERMOELECTRIC EFFECTS IN MESOSCOPIC SUPERCONDUCTOR/FERROMAGNETIC JUNCTIONS

Spin transport properties of a mesoscopic superconductor/ferromagnetic (S/F) junctions of a quantum device are investigated. The thermoelectric voltage as a function of magnetic field oscillations for different heater currents has been calculated. The dependence shows that by increasing the heater current, the oscillation first disappears, and then remarkably reappears inverted compared to low heater current. Also, the value of the thermo-power increases with increasing value of the barrier strength. Our result shows that the degree of spin polarization of the current can be unambiguously determined using Andreev reflection. Our result agrees qualitatively with those in the literature.