The energy loss of medium-energy He+ ions backscattered from a Cu(100) surface

A model is presented for the shape of the surface peak in the energy spectrum of backscattered ions in a channeling and blocking experiment. The elastic energy loss distribution of the ions is calculated by use of Monte Carlo simulation. The inelastic energy loss distribution is calculated by use of data obtained from gas phase ion-atom collisions. The model for the shape of the surface peak is applied to the analysis of energy spectra of 175 keV He+ ions backscattered from a Cu(100) surface. It is found that, under channeling and blocking conditions, the inelastic energy loss in surface layers can be almost three times higher than under normal (i.e. random-incidence and -detection) conditions. It is therefore concluded that the inelastic energy loss depends strongly on the impact parameter of the collision

A search for luminescence of the trivalent manganese ion in solid aluminates

As an alternative way of examining the prospects of the trivalent manganese ion as a luminescent centre in glasses, Al2O3:Mn, ZnAl2O4:Mn and LaAlO3:Mn were investigated by means of spectrofluorometry. The luminescent species identified were divalent and tetravalent manganese and impurities (chromium), whereas trivalent manganese did not show luminescence at wavelengths ≤ 800 nm in LaAlO3:Mn and ZnAl2O4:Mn and ≤ 1000 nm in Al2O3:Mn for T down to liquid helium temperature. It is argued that both a strong crystal field and a large Jahn-Teller splitting quench the luminescence of trivalent manganese and these results lower the benefits for using this ion in glasses

Calibration of the cross section of the 18O(p, [alpha])15N nuclear reaction at Ep = 1700-1775 keV

The differential cross section of the 18O(p, α)15N nuclear reaction has been calibrated at proton energies between 1700 and 1775 keV and at a detection angle of 155°. For the calibration, two silicon reference samples and a nickel sample were partially oxidized in enriched 18O. The absolute 18O-content in the grown oxide films is measured with RBS by direct comparison with a Bi-implanted silicon calibration standard. The measured resonance curve is fitted with a split Breit-Wigner function. The maximal cross section of the resonance at 1766 keV is found to be 135 ± 5 mb/sr. Its width is 4.5 ± 0.3 keV

Ion beam studies of oxygen exposed Ni(100)

A clean Ni(100) surface and a surface exposed to 18O2, have been studied by high-energy ion scattering and nuclear reaction analysis. The structure of the clean and the exposed surfaces is studied by 750 keV He+ ion scattering in combination with channeling and blocking. The results are consistent with results obtained by medium-energy ion scattering. Absolute oxygen contents are measured using the 18O(p, α)15N nuclear resonance at Ep=1766 keV. It is found that the oxygen content of the surface for which the c(2×2) LEED pattern is observed, is 0.42±0.04 of a Ni(100) monolayer. The oxygen content of a saturated oxide layer is 2.4±0.2 of a monolayer. Furthermore, it is concluded that the saturated oxide layer consists of stoichiometric NiO

Deposition rate in modulated radio-frequency silane plasmas

Plasma-enhanced chemical-vapor deposition of amorphous silicon by a square-wave amplitude-modulated radio-frequency excitation has been studied by optical emission spectroscopy and plasma modeling. By the modulation, the deposition rate is increased or reduced, depending on the plasma parameters. The increase in the deposition rate in powder-free (alpha-regime) plasmas is explained by the behavior of the electrons. High-energy electrons cause a large production of radicals at the onset of the plasma, as evidenced by an overshoot in optical emission. This is confirmed by a one-dimensional fluid model. An optimum in the deposition rate at a modulation frequency of about 100 kHz is determined by the decay time of the electron density. (C) 2000 American Institute of Physics. [S0003-6951(00)02515-8]