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991.
Secondary electron emission yieldδ was measured for thin films of alumina prepared byrf sputtering technique. Single pulse method was used along with 4-gridleed optics system to determineδ. Maximum value of 4·3 was obtained at primary energy of 350 eV. The Dionne’s theory was used to analyse the results and the
emission probability escape depth and absorption coefficient of secondaries were also estimated. Fairly good correlation is
observed between experimental and theoretical values ofδ for beam energies upto 1 keV. 相似文献
992.
993.
994.
We have measured the complex film impedance 1/σd (σ conductivity, d film thickness) of three YBaCuO thin films with d = 44, 115, and 168 nm on MgO substrates at 10.2 GHz in the temperature range between 300 and 4 K. Below Tc, the experimental results are discussed in terms of the two-fluid model and the BCS theory. The residual resistance decreases with the film thickness. The thinnest film has a residual surface resistance of 3 · 10?4 Ω. For this film, the complex microwave conductivity is calculated and compared with the models. Apart from the residual resistance, the measured conductivity is in agreement with the peak caused by the energy gap of the BCS theory. All measurements were performed with a cavity perturbation method which we have to our knowledge applied for the first time to superconducting thin films. The method allows to determine the complex impedance of films with arbitrary thickness. In particular, films with thicknesses small compared to the skin depth δ or the London penetration depth λ can be measured. Therefore, we are able to measure the impedance both in the normal and superconducting state. 相似文献
995.
The microstructure and transport properties of various 90° grain boundaries in (103) oriented YBa2Cu3O7(YBCO) thin films grown epitaxially in situ by 90° off-axis sputtering are compared. The (103) films grown on (101) LaAlO3 and (101) SrTiO3 substrates have specific sets of 90° grain boundaries in both principal in-plane directions: 90° [010] twist boundaries along the [101] direction, and 90° [010] symmetrical tilt boundaries and 90° [010] basal-plane-faced tilt boundaries along the (301) direction. No weak-link behavior is observed across some of these boundaries by transport critical current density and normalized magnetic field dependence of J
c measurements along both those in-plane directions. High-resolution transmission electron microscopy reveals variations in the structure and microfaceting of the 90° boundaries, which may contribute to the absence of weak-link behavior. These results have important implications for understanding the behavior of step-edge Josephson junctions. 相似文献
996.
Copper sulphide films prepared by reactive evaporation, when heated in air at 500 K, oxidized to Cu2O after a series of intermediate chemical transitions. Golden yellow coloured Cu2O films showed a large absorption before the fundamental absorption edge. The optical band gap was found to be (2.29±0.02)eV.
When these Cu2O films were further heated they got converted to CuO and the optical band gap was found to be (2.17±0.02)eV. 相似文献
997.
Amorphous silicon oxide thin films were prepared by co-evaporation of Si and SiO in ultra-high vacuum. Different compositions were obtained by changing the evaporation rate of silicon. After thermal annealing treatments, the dissociation of the silicon oxide in pure silicon and silicon dioxide leads to the formation of silicon clusters embedded in a silicon oxide matrix. Thus the samples were annealed to different temperatures up to 950°C. Depending on the annealing temperature and on the composition, different cluster sizes were obtained. The photoluminescence (PL) energy depends on the cluster size and a large range of wavelengths is obtained from 500 to 750 nm. The PL, attributed to a confinement effect of the electron–hole pairs in the silicon particles, is studied as a function of the temperature. It is demonstrated that the continuous decrease of PL intensity with the temperature from 77 to 500 K depends on the structure of the samples. For samples with well-separated clusters, the PL decreases rapidly with the temperature. For samples containing clusters separated by a small distance, the PL weakly depends on the temperature. No shift of the energy is observed. The results are discussed by taking into account the competition between the radiative recombination in the silicon clusters and the non-radiative escape of the carriers via a hopping mechanism. 相似文献
998.
D. Grosso F. Babonneau C. Sanchez G.J. de A.A. Soler-Illia E.L. Crepaldi P.A. Albouy H. Amenitsch A.R. Balkenende A. Brunet-Bruneau 《Journal of Sol-Gel Science and Technology》2003,26(1-3):561-565
Since mesoporous materials can be prepared by combining the sol-gel chemistry and the structuring effect of surfactants, they have attracted attention for application in various high technology fields. The present work deals with the analyses of the mechanisms involved in the formation of SiO2 and TiO2 highly organised 2D-hexagonal meso-structured films using Brij 58 as surfactant. The preparation of such films by dip-coating involves rapid evaporation which makes the different steps difficult to control. Simultaneous in-situ SAXS (synchrotron) and interferometry analyses have been performed to get a first understanding of the self-assembly process. SiO2 and TiO2 materials have a different chemical reactivity (kinetics and coordination aspects). However, we show that the mechanisms involved during dip-coating are quite similar : the self-assembly leading to the organised phase takes place at a final stage of the drying process, involves the formation of a disorganised intermediate phase and depends also on the presence of micellar interfaces in addition to film/air and film/substrate interfaces. 相似文献
999.
Highly transparent conductive Al2O3 doped zinc oxide (AZO) thin films have been deposited on the glass substrate by pulsed laser deposition technique. The effects of substrate temperature and post-deposition annealing treatment on structural, electrical and optical properties of AZO thin films were investigated. The experimental results show that the electrical resistivity of films deposited at 240 °C is 6.1 × 10−4 Ω cm, which can be further reduced to as low as 4.7 × 10−4 Ω cm by post-deposition annealing at 400 °C for 2 h in argon. The average transmission of AZO films in the visible range is 90%. The optical direct band gap of films was dependent on the substrate temperature and the annealing treatment in argon. The optical direct band gap value of AZO films increased with increasing annealing temperature. 相似文献
1000.
Summary The electrical-conductivity frequency dependence of reactive-evaporation-depositeda-Si:H films has been measured in the temperature range (100÷450)K. The influence of the substrate temperature, of the hydrogen
ions energy and of post-deposition thermal treatments has also been investigated. The results show that, depending on the
material quality, three different conduction mechanisms associated with gap states, band or band tail states and to hopping
processes near the Fermi level are observed. 相似文献