A.N. Aleshin

Study of diffusion in thin AuCu films

Temperature dependences of the volume and grain boundary diffusion coefficients of copper and gold were obtained from Rutherford backscattering spectrometry (RBS) investigations of multilayer CuAu targets. The annealing of films was carried out in vacuum in the temperature range from 448 to 523 K. All stages of annealing of the film targets were tested by He+ RBS (E0=1.5 MeV), and element depth concentration profiles were interpreted on the basis of the Whipple theory and Gilmer-Farrell analysis. Grain boundary diffusion coefficients and the corresponding Arrhenius parameters were obtained.

Segregation effect on grain-boundary diffusion in thin metallic films

The diffusion in Au-Cu and Pt-Cu thin films has been studied by Rutherford backscattering sperctrometry ( RBS ) under the kinetic regimes B (within the temperature interval of 175-290°C and C (room temperature). The 1.5-2.0 MeV He + RBS spectra were taken using 14-18 keV resolution. The RBS spectra were changed to depth-concentration profiles for both bulk and grain boundary (GB) diffusion. Under kinetic regime C the absolute values of GB diffusion coefficients were obtained. Under kinetic regime B the triple products δKD h (δ is the GB width, D b is the GB diffusion coefficient, K is the enrichment ratio) were obtained using the Whipple and Gilmer-Farrell models. The activation energies for GB diffusion of Au into Cu films and Cu into Au films are close to 0.95-0.98 eV atom -1 , whereas the activation energy for GB diffusion of Pt into Cu films is equal to 1.25 eV atom -1 . The comparison between the data on the GB diffusion for kinetic regime B extrapolated to room temperature and the data on the GB diffusion for kinetic regime C enables one to derive the product δK and to separate the contribution of segregation to the parameters of GB diffusion for the systems under study.

Compensation Effect for Grain Boundary Diffusion in a Bicrystalline Experiment

The paper is devoted to the problem of the compensation effect for grain boundary (GB) diffusion, i.e. the linear dependence of the pre-exponential factor of the GB diffusion coefficient on the activation energy. Specific features of GB diffusion as a thermally activated process namely, the influence of segregation factor, K, and variation of the GB width, δ, on the diffusion rate are discussed. A special diffusion experiment was designed to estimate the contribution of the separate component parts of the triple product, KδDGB (DGB is the GB diffusion coefficient). The experiment was performed with Al bicrystals. The variation of the GB width δ, and a value of the segregation factor K, due to GB structure change are estimated. It is concluded that DGB is the main GB structure-sensitive parameter in the triple product. This circumstance allows us to consider the GBs in Al bicrystals as a series of uniform objects and to describe the kinetics of GB diffusion in terms of the compensation temperature Tc and a “barrier” phase. The value of Tc for GB diffusion of Zn and Ge in Al bicrystals is practically the same and equals 709 and 706 K, respectively. The character of the “barrier” phase is discussed.

STUDY OF PT DIFFUSION IN THIN COPPER FILMS UNDER TWO KINETIC REGIMES

The diffusion of platinum in thin copper films has been studied by Rutherford backscattering spectrometry (RBS) under the kinetic conditions B (within the temperature range of 200–290 °C) and C (room temperature). The RBS spectra were modified to concentration curves for both bulk and grain boundary (GB) diffusion. Under the kinetic regime B the triple products KδDb (Db is the GB diffusion coefficient, δ is the GB width, K is the enrichment ratio) were obtained using Whipple’s model. Under the kinetic regime C the absolute value of the GB diffusion coefficient of Pt in Cu films was obtained. A comparison between the data on GB diffusion for the kinetics B extrapolated to room temperature and the data on GB diffusion for the kinetics C enables one to derive the product Kδ and to separate the contribution of segregation into the GB diffusion of Pt in Cu films.

Diffusion in an Ensemble of Intersecting Grain Boundaries

Grain boundary (GB) diffusion in an ensemble of three grain boundaries intersecting in the point of GB triple junction is described on the basis of quasi-steady Fisher’s model. Two versions of the configuration of the ensemble are considered, namely, with different number of GBs adjacent to the surface covered with a diffuser source and with different angle between GB and surface. Analytical expressions for the distribution of diffuser concentration along each GB of an ensemble are derived supposing that the GB diffusion fluxes are equal in the GB triple junction. The expressions for the diffuser concentration distribution along GBs in both ensembles include not only diffusion constants (like GB and bulk diffusion coefficients) but also structural characteristics of the ensemble of grain boundaries (i.e. the depth of the triple junction point under the surface and the angle between GBs in the triple junction point). The specific features of diffusion kinetics in the ensembles of different configuration with an angle of 120o (the equilibrium angle in a polycrystal) were revealed by comparing the diffuser concentration distributions in the ensembles and in the single GB.