Wilhelm G. Wolfer

On the role of ions in the formation of cubic boron nitride films by ion-assisted deposition

We have investigated how ion irradiation can selectively promote formation of dense [ital sp][sup 3]-bonded cubic [ital c]BN over the graphite-like [ital sp][sup 2]-bonded phases. Experiments used ion-assisted pulsed laser deposition in which either the ion mass (m[sub ion]) or ion energy (E) was varied in conjunction with ratio of ion flux to depositing atom flux (J/a). For a fixed ion energy and mass, there is a critical J/a above which [ital c]BN formation is initiated, a window of J/a values in which large [ital c]BN percentages are obtained, and a point at which J/a is so large that the resputter and deposition rates balance and there is no net film deposition, in agreement with Kester and Messier. As do Kester and Messier, we find that [ital c]BN formation is controlled by a combination of experimental parameters that scale with the momentum of the ions. However, unlike Kester and Messier, we do not find that [ital c]BN formation scales with the maximum momentum that can be transferred in a single binary collision, as either incorrectly formulated by Targove and Macleod and used by Kester and Messier, or as correctly formulated. Instead we observe that [ital c]BN formation best scales withmorexa0» the total momentum of the incident ions, (m[sub ion]E)[sup 1/2]. We also consider the mechanistic origins of this (m[sub ion]E)[sup 1/2] dependence. Computer simulations of the interaction of ions with BN show that [ital c]BN formation cannot be simply scaled to parameters such as the number of atomic displacements or the number of vacancies produced by the ion irradiation. A critical examination of the literature shows that none of the proposed models satisfactorily accounts for the observed (m[sub ion]E)[sup 1/2] dependence. We present a quantitative model that describes the generation of stress during ion-assisted film growth.«xa0less

Self-diffusion and impurity diffusion of fee metals using the five-frequency model and the Embedded Atom Method

The activation energies for self-diffusion of transition metal (Au, Ag, Cu, Ni, Pd, Pt) have been calculated with the Embedded Atom Method (EAM); the results agree well with available experimental data for both mono-vacancy and di-vacancy mechanisms. The EAM was also used to calculate activation energies for vacancy migration near dilute impurities. These energies determine the atomic jump frequencies of the classic five-frequency formula, which yields the diffusion rates of impurities by a mono-vacancy mechanism. These calculations were found to agree fairly well with experiment and with Neumann and Hirschwalds T/sub m/ model.

Self-Diffusion and Impurity Diffusion of FCC Metals Using the Embedded Atom Method

Diffusion in FCC metals at medium and high temperatures occurs primarily by a vacancy mechanism. Diffusion is dominated by the contribution of mono-vacancies, but the contribution of di-vacancies is significant at high temperatures.