• Energy Research
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AbstractHeterojunction CdS/CdTe thin film solar cells were fabricated with a superstrate structure consisting of the successive layers: soda lime glass/ITO/CdS/CdTe/back contact. ZnTe:Cu films were deposited on the back surface of the CdTe layer presenting as ohmic back contact. The substrate was soda lime glass coated with ITO films by rf magnetron sputtering serving as the transparent front contact. A thin layer of CdS with thickness about 80nm was applied by chemical bath deposition. Close-spaced sublimation of the CdTe films was accomplished by placing a CdTe source in a close proximity (6mm) to the substrate in vacuum chamber with low pressure about 3×10-2 mbar. The source was heated to 550 ∘C and the substrate to 450 ∘C. This arrangement causes Cd and Te to sublime from source and diffuse to the substrate. The fabricated cells were investigated using current-voltage (I-V) in the temperature range 20-300K under a standard AM1.5 illumination in order to define the transport mechanism in the heterojunction. Tunnelling enhanced interface recombination has been found to dominate carrier transport mechanism in the junction at all investigated temperatures.

A method is presented for calculating the electromagnetic forces on the end windings of turbine generators for both the steady state and transient modes of operation. Part 1 of this paper deals with the basic concepts of the force calculation and gives several examples of steady state forces and how they vary with load and power factor. PartII deals with several types of transient operation. The currents and fields which these transients produce are discussed and forces are found for various cases such as short circuits, synchronizing out of phase and transmission line switching.

The paper describes a two dimensional numerical model for analysis of the local and integral characteristics of linear electromagnetic pumps, such as magnetic field distribution, pressure developed, amplitude of pressure pulsation with double supply frequency and distribution of liquid metal velocity over the azimuth. Numerical results are compared with experimental ones.

AbstractIron-acceptor (FeAc) pair association has been studied in compensated n-type silicon. A dynamic approach, based on the charge carrier recombination rates over the Fei trap level, leads to an explanation of the observed FeAc pairing reaction in compensated n-type silicon and extends the understanding of FeAc pairing kinetics. Association kinetics was used to measure a height dependent acceptor concentration profile. Even in compensated n-type silicon good agreement with expected concentrations is found.

Characteristics of Tm:YAG ceramic for high efficient 2-μm lasers are analyzed. Efficient diode end-pumped continuous-wave and Q-switched Tm:YAG ceramic lasers are demonstrated. At the absorbed pump power of 53.2W, the maximum continuous wave (cw) output power of 17.2 W around 2016 nm was obtained with the output transmission of 5%. The optical conversion efficiency is 32.3%, corresponding to a slope efficiency of 36.5%. For Q-switched operation, the shortest width of 69 ns was achieved with the pulse repetition frequency of 500 Hz and single pulse energy of 20.4 mJ, which indicates excellent energy storage capability of the Tm:YAG ceramic.

Abstract Ti-doped ZnO (ZnO/Ti) thin films were grown on indium tin oxide substrates by a facile electrodeposition route. The morphology, crystal structure and resistive switching properties were examined, respectively. The morphology reveals that grains are composed of small crystals. The (002) preferential growth along c-axis of ZnO/Ti could be observed from structural analysis. The XPS study shows the presence of oxygen vacancies in the prepared films. Typical bipolar and reversible resistance switching effects were observed. High R OFF/R ON ratios (approximately 14) and low operation voltages within 100 switching cycles are obtained. The filament theory and the interface effect are suggested to be responsible for the resistive switching phenomenon.

We investigate the effect of slowly-varying parameter on the energy transfer in a system of weakly coupled nonlinear oscillators, with special attention to a mathematical analogy between the classical energy transfer and quantum transitions. For definiteness, we consider a system of two weakly coupled oscillators with cubic nonlinearity, in which the oscillator with constant parameters is excited by an initial impulse, while a coupled oscillator with slowly-varying parameters is initially at rest. It is proved that the equations of the slow passage through resonance in this system are identical to equations of the nonlinear Landau-Zener (LZ) tunneling. Three types of dynamical behavior are distinguished, namely, quasi-linear, moderately nonlinear and strongly nonlinear. The quasi-linear systems exhibit a gradual energy transfer from the excited to the attached oscillator, while the moderately nonlinear systems are characterized by an abrupt transition from the energy localization on the excited oscillator to the localization on the attached oscillator. In the strongly nonlinear systems, the transition from the energy localization to strong energy exchange between the oscillators is revealed. A special case of the rapid irreversible energy transfer in the strongly nonlinear system with slowly-varying parameters is also investigated. The conditions providing different types of the dynamical behavior are derived. Explicit approximate solutions describing the transient processes in moderately and strongly nonlinear systems are suggested. Correctness of the constructed approximations is confirmed by numerical results.

Abstract Thin films of vanadium oxide were deposited on glass substrates at 450 o C by atmospheric pressure chemical vapour deposition. The effect of the vanadium tetrachloride to water precursor ratio on the structural and morphological properties of the films was investigated. The water concentration was observed to strongly affect the vanadium oxidation state and the morphological characteristics of the films. The importance of achieving single-phase of a particular oxidation state towards the improvement of the electrochemical performance of thin films grown by atmospheric pressure CVD is highlighted.