R.E. Benenson

Computer simulation of helium-induced forward-recoil proton spectra for hydrogen concentration determinations☆

Abstract The availability of accurate p-4He elastic scattering cross sections with values which can be generated in a computer program means that, with proper attention to energy loss, helium-induced forward recoil proton spectra can be simulated for arbitrary hydrogen concentrations. Such simulated spectra can be used to fit data either in transmission or glancing-angle geometry. The method of calculating forward-recoil cross sections for incident 4He or 3He are explained and representative values tabulated. The spectrum simulation calculation without, and with. straggling and the effects of multiple scattering and kinematics are illustrated for transmission geometry.

High sensitivity hydrogen analysis using elastic recoil

Abstract The high sensitivity analysis of H and D in thin foils (25 μm or less) using 4He induced elastic recoils is described. Using 4–6 MeV He ions, background count rates corresponding to hydrogen concentrations of approximately 1 ppm (atomic) are demonstrated for both isotopes.

Backscattering analysis for oxygen profiling using 16O(α, α)16O 3.05 MeV resonance parameters

The well-known 16O(α, α)16O scattering resonance near 3.05 MeV permits oxygen to be identified in the presence of heavy elements being analyzed by Rutherford backscattering. We investigate explicit use of published resonance parameters and the best presently available stopping powers to make computer simulations of backscattering energy spectra in order to make quantitative measurements of near surface oxygen profiles in bulk oxides and thin films. Simulations of bulk Al2O3, Y2O3, YBa2Cu3O7−ϵ, and thin films of ZrO2 on silicon are compared with actual data, and found to be generally in excellent agreement.

Ion-beam mixing in micron-size widths

Abstract Experiments are described which are intended to lay the groundwork for producing ion-beam-mixed alloys as narrow lines, using a microbeam. Two methods have been examined: direct use of a 400 keV Ar microbeam on Sb and Ag films evaporated on Si wafers, and mixing of a layer of Sn on Si by a conventional 140 keV Kr beam through a 1000-mesh Cu grid. Results are presented as mappings of RBS spectrum regions, which presently show no diffusion outside the irradiated area. Suggestions for more quantitative measurements are included.

Comparison of strain and damage profiles induced by implantation of Xe+, Ne+ and H2+ ions in yttrium iron garnet

Abstract Ions of 120 keV Xe + , 100 keV Ne + and 120 keV H + 2 have been implanted to various doses in 2.6 μm epitaxial layers of yttrium iron garnet (Y 3 Fe 5 O 4 ) grown on 〈111〉 single crystal gadolinium gallium garnet. Rutherford backscattering and resonant 16 O(α, α) 16 O scattering of channeled 3.07 MeV 4 He + ions have been measured to study crystal distortions induced during room temperature implantation. Strain close to the surface was obtained from the angle change between 〈110〉 and 〈100〉 axes as measured by channeling in implanted and unimplanted parts of the crystal. The damage profile was obtained directly from the energy spectrum of backscattered particles. A simple method to evaluate strain profiles from the measured RBS (Rutherford Backscattering) spectra has been used.

Radiation of MeV electrons axially channeled in Ni

Abstract Forward radiation spectra of electrons channeled along the 〈111〉 and 〈110〉 axes of a Ni single crystal (5000 A thick) have been measured with a semiconductor detector for beam energies of 2.2 to 3.0 MeV and various crystal tilt angles θ. In the 〈111〉 case, the 2p-1s transition of channeling states can be identified. At E = 2.96 MeV, the line energy is 4.72 keV with a fwhm width of ~ 50%. The broad linewidth and the absence of a dip in the observed line intensity variation with tilt angle are reflections of large scattering effect. Such scattering effects will be larger for the more tightly bound states such as those in the 〈110〉 direction, and this explains the absence of resolved channeling radiation lines in the measured spectra for 〈110〉.

Microbeam Beam Heating Analysis of Thin Foils Using Heat Conduction Theory

The temperature distribution in and near the scan region of an ion microbeam is estimated using heat conduction theory. In the calculation, the energy deposited by a beam spot on a thin foil is treated as a point energy source. The spatial and time dependent temperature contributions from energy deposited by the ion beam rastering in a square scan pattern were then computed. The results showed that for poor conductors, the temperature of the material under the scan region can rise rapidly by up to two orders of magnitude, while that of good conductors remains virtually unchanged. The calculated results were consistent with experimental data where Mylar foils were scanned using an He microbeam and the time for melt through was measured. Radiational cooling effects were also investigated and found to contribute little to the heat losses at typical microbeam beam powers.

Analysis of proton channeling by lead fluoride

Abstract Recent proton axial channeling measurements have endeavored to help explain the fast-ionic conduction mechanism of PbF2, but lattice location programs have been unavailable. As a start on this problem, and for the CaF2 structure in general, a computer simulation of angular scans is described in which thermally spread string potentials are used to establish the potential fields across, respectively, the (100) and (110) planes. The particle flux calculations assume statistical equilibrium. The axial channeling angular scan half-widths as a function of temperature give quite good agreement with experiment, but the apparent disappearance of 〈100〉-axis channeling at T > 700 K is not yet explained.

Axial channeling by an intersecting plane potential

Abstract A model for 〈100〉 axial channeling based on the electrostatic potential of two mutually perpendicular sets of intersecting parallel planes is used to calculate the close-encounter probability between incident particles and planar lattice atoms. The development of the model was in the context of extending channeling calculations to octahedron clusters. Assumptions and geometrical constraints are discussed, and the results of the calculations are compared with recent experimental angular scans for the B atoms in LaB6.

Channeling study of the co-operative Jahn-Teller effect in nickel chromite single crystal by backscattering and resonant nuclear scattering of helium ions☆

Abstract Using the channeling technique, the co-operative Jahn-Teller effect in nickel chromite single crystals has been studied by helium ion backscattering and the resonant nuclear scattering of O 16 (α,α)O 16 at E α = 3.056 MeV. The results have shown that the chan dips for Ni + Cr and O atoms around 〈110〉, 〈111〉 and 〈111〉 axes become shallow at temperatures below the dynamic to static Jahn-Teller transition, which has been attributed to extra dechanneling due to the domain effect and explained by the (110) twin model. Also there is some indication that the Ni or Cr atoms (or both) are laterally displaced from the 〈111〉 or 〈111〉 axis at temperatures lower than the transition temperature. This differs from the usual expectation for the co-operative Jahn-Teller effect.