K.K. Bourdelle

Damage and aluminum distributions in sic during ion implantation and annealing

Abstract Damage buildup in SiC during ion implantation of Al + with an energy of 90 keV and flucnces of 10 13 –10 16 ions/cm 2 at room temperature was studied. It was observed that the surface concentration of displaced host atoms and χ min increase rapidly in the fluence range of 3 × 10 13 –10 15 cm −2 and change weakly outside this range. The amorphization of the surface layer occurred at a fluence of φ c ≈ 8 × 10 14 cm −2 . The thickness of the amorphous layer as well as the depth and the width of the Al-atoms profile exceed the values calculated lor an amorphous target. The possibility of recrystallizing the damaged layer depended on the ion fluence. The precipitation of Al-atoms at structural defects was observed.

Monte Carlo simulation of ion-beam channeling in YBa2Cu3O7

Abstract A Monte Carlo program (UPIC) for the simulation of ion channeling in crystals with complex structure is described. The program is applied to simulate the channeling of 1.5 MeV He+ and 1 MeV D+ near the [001] axis of YBa2Cu3O7 assuming strongly correlated atomic displacements along the [001] Cu-O rows in the superconducting state. The values for the abrupt change in the half-width of the channeling dip observed in experiments [R.P. Sharma et al., Phys. Rev. B 38 (1988) 9287] at the temperature of the superconducting transition, Tc, are reproduced in the simulations with correlation coefficients of 0.8–0.9. The increase in the minimum channeling yield at Tc found in measurements [T. Haga et al., Phys. Rev. B 41 (1990) 826] can be qualitatively explained by the increase in dechanneling rate due to correlations.

A channeling study of ion-produced disorder in silicon carbide

Abstract The RBS/C technique is used to study the disorder buildup in silicon carbide (SiC) produced by Al+ and Ga+ ions with energies of 40 and 90 keV. The damage rate increases sharply in the fluence range near the critical value for amorphization, Φ ≈ 1 × 1014 cm−2 and = 8×1014 cm−2 for Ga+ and Al+ ions, respectively. The defect concentration rises slowly with fluence outside this range. At fluences Φ > Φc, the concept of elastic energy loss density is used in the analysis of the amorphous layer thickness. A strong decrease of the critical energy loss density, Wc, is observed when the amorphous layer expands due to fluence accumulation.

SiC amorphlzation as a result of Ga+ implantation

Abstract The ion implantation of 40 and 90 keV Ga+ ions at high doses into silicon carbide was studied. The thickness of layers randomized by ion implantation determined as a function of the ion dose and energy was compared with that expected from the theory of energy loss in elastic collisons. It was found that the data for two implantation energies could not be described by one value of critical energy deposition. Two factors are proposed to be responsible for the discrepancy: buffer layer formation and beam annealing.

Evolution of lead precipitates in ion implanted aluminium

Abstract Aluminium-lead alloys are characterized by extremely low miscibility in the solid phase across the entire equilibrium phase diagram. Ion implantation of lead into aluminium at room temperature therefore results in spontaneous phase separation and formation of nm-size lead precipitates growing in topotactical alignment (epitaxy in three dimensions) with the aluminium matrix with a cube/cube orientation relationship. Transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS) and channeling techniques were used to analyze the formation and evolution of lead precipitates during implantation and subsequent annealing. Implantations at room temperature induce a microstructure characterized by very small (2–5 nm) precipitates embedded in a heavily damaged matrix. Only ∼50% of the implanted lead atoms are retained in precipitates while the rest are in supersaturated solution or in small (

RBS analysis of diffusion and evaporation of implanted lead in aluminium

Abstract The diffusion of non-equilibrium concentrations of Pb implanted into Al crystals has been analyzed by fitting experimentally measured profiles to the solution of the diffusion equation with the boundary condition that the outward flux at the surface is proportional to the surface concentration. This solution contains two free parameters, namely diffusivity and evaporation constant, which were found by the fitting. There are some systematic differences between the measured and fitted profiles, but the fitting procedure provides fairly constant values of the diffusion coefficient and the evaporation rate, with the diffusion coefficients obeying an Arrhenius relation. For some of the experimental conditions the differences became so large in the later stage of annealing that the process is not adequately described by the simple diffusion equation. The systematic differences are believed to be related to effects of a surface oxide layer, radiation induced damage, surface segregation and lead inclusions.

Channeling in RBa2Cu3O7 − x single crystals

Abstract The results of He + ion channeling in RBa 2 Cu 3 O 7 − x (RBaCuO) single crystals (where R = Y , Pr ) are reported. The channeling effects in Pr + Ba and Cu sublattices of the tetragonal PrBaCuO crystals are compared. The normalized yield of the backscattered particles from the channeling in the Cu sublattice is higher and the width of the angular dependence of the RBS yield is lower than those in the Pr + Ba sublattice. The experimental aligned spectra are compared with the calculated ones. The calculations take into account the diffusion in the transverse motion and energy loss of the particles. The results of channeling in orthorhombic YBaCuO crystals are also briefly discussed.

Channeling study of the orientational dependence of laser-induced damage in GaAs and GaP

Abstract Channeling was used for the study of laser-induced damage in GaAs and GaP samples with different crystallographic orientations of the surface. The greatest damage was observed for (111) GaAs and (111) GaP samples. Possible mechanisms for the damage production are discussed.