We report the first successful preparation of thin films of Y-Ba-Cu-O superconductors using pulsed excimer laser evaporation of a single bulk material target in vacuum. Rutherford backscattering spectrometry showed the composition of these films to be close to that of the bulk material. Growth rates were typically 0.1 nm per laser shot. After an annealing treatment in oxygen the films exhibited superconductivity with an onset at 95 K and zero resistance at 85 and 75 K on SrTiO3 and Al2O3 substrates, respectively. This new deposition method is relatively simple, very versatile, and does not require the use of ultrahigh vacuum techniques.

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In this paper an introduction is given to secondary electron emission properties. It is shown that the reduced secondary emission yield 15/b, as a function of the reduced primary energy Ep/Em can be described by a universal curve. It is found that it is easier to use the measurement of the maximum secondary electron emission 6, and the energy E,,, at which this maximum is reached to determine the suitability of a coating for use in the display than direct measurement of the first crossover energy EI. The value of 6, and E,,, can be used to derive EI. Furthermore, it is observed that in any material the elastic fraction of the secondary electrons exhibits a universal behaviour as a function of Ep. Fits to S(EJ and the energy distribution of the secondary electrons are proposed which can be used in Monte Carlo simulations.

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Initial stages of Si epitaxial growth on vicinal Si (001) substrates were investigated using scanning tunneling microscopy. For a growth temperature of about 750 K it was found that initial growth occurs almost exclusively at one of the two nonequivalent types of step edge. This leads to the formation of a single-domain surface with an array of evenly spaced straight steps with biatomic height. This structure can be preserved by quenching the sample to room temperature. PACS numbers: 61.50.Cj, 68.55.Bd, 82.40.DmThe interest in the use of silicon molecular-beam epitaxy (Si MBE) on Si(001) surfaces for the production of novel electronic devices has motivated many studies of the initial stages of growth and the influence of the preceding cleaning treatment. One topic of interest has been the preparation of single-domain surfaces, where the steps between adjacent terraces have a height of an even number of monolayers (ML). This is important in reducing the amount of antiphase boundaries in III-V films grown on Si substrates. 1 It has been reported in the literature that a prolonged annealing of samples with a misorientation less than 0.2° at about 1250 K may result in a single-domain surface. 2 " 5 On samples with a misorientation of more than about 4° towards [110], biatomic height steps were found after cleaning and annealing at about 1150 K. 6 " 8 During MBE on a sample with a misorientation of 0.5° towards [110], a single-domain reflection high-energy electron diffraction pattern was observed. 9,10 However, Sakamoto et al. 10 mentioned that this single-domain surface is not stable. When growth is terminated and the sample is kept at the growth temperature of about 750 K, this surface changes back into a two-domain surface within a few minutes. 10 We present scanning-tunneling-microscope (STM) images of epitaxially grown single-domain Si (001) surfaces that were quenched to room temperature immediately after termination of growth.The STM uses a mechanical approach 11 and is described in more detail elsewhere. 12,13 It is mounted in an ultrahigh-vacuum chamber with a base pressure of lxlO -8 Pa, together with a low-energy electron diffraction (LEED) system. Si can be evaporated in situ from resistively heated Si strips at a growth rate of about 1 ML/min, as calibrated with Rutherford backscattering spectrometry on carbon substrates, and at a pressure better than 2xl0" 7 Pa. The 5x20-mm 2 substrates were cut from commercially available wafers (Wacker, floating zone, n type, 1 a cm) and ultrasonically rinsed in ethanol before loading into the vacuum chamber. The misorientation, as determined by x-ray diffraction, was 0.52° in the [110] and 0.09° in the [TlO] directions, respectively. Inside the chamber the samples were heated resistively. Temperatures were measured with an infrared pyrometer with an accuracy of 50 K. After outgassing the sample and the holder for several hours, the sample was thermally cleaned at 1450 K for 2 min and cooled at an average rate of 25 K/min. Si films have been deposited on these clean s...

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High Tc superconducting thin films prepared by pulsed Nd:YAG laser ablation AIP Conf.