Low-temperature ion beam mixing of Pt and Si markers in Ge

The mixing of Pt and Si marker atoms in Ge during 750-keV Xe irradiation was measured at temperatures between 6 and 500 K. The low-temperature measurements show that the mixing parameter for Pt is nearly twice that for Si. This result is in strong contradiction to the collisional theory of ion beam mixing. A weak temperature dependence in the mixing is found for both markers

Effect of dose rate on ion beam mixing in Nb-Si

The influence of dose rate, i.e., ion flux, on ion beam mixing in Nb‐Si bilayer samples was measured at room temperature and 325 °C. At the higher temperature, an increase in dose rate of a factor of 20 caused a decrease in the thickness of the mixed layer by a factor of 1.6 for equal total doses. At room temperature, the same change in flux had no effect on mixing. These results are consistent with radiation‐enhanced diffusion theory in the recombination‐limited regime

Threshold displacement and interstitial-atom formation energies in Ni3Al

Threshold displacement energies for atomic displacements along 110, 100, and 111 directions, and formation enthalpies of several symmetric interstitial atom configurations were calculated for Ni3Al by computer simulation using "embedded atom method” potentials. The Ni-Ni (100) dumbbell in the plane containing only Ni atoms has the lowest interstitial-atom enthalpy although the enthalpies of other configurations are similar. Interstitial configurations involving Al atoms all have much higher enthalpies. The anisotropy of the threshold energies in Ni3Al is similar to pure metals and no significant difference in threshold energy was observed for 110 replacement chains in rows containing all Ni atoms or alternating Ni-Al atoms. Various metastable interstitial atom configurations were observed, including crowd-ions. In addition, the spontaneous recombination volume for some configurations can be much smaller than in pure metals. The consequences of these results for radiation induced segregation and amorphization are discusse

Strong mass effect on ion beam mixing in metal bilayers

Molecular dynamics simulations have been used to study the mechanism of ion beam mixing in metal bilayers. We are able to explain the ion induced low-temperature phase stability and melting behavior of bilayers using only a simple ballistic picture up to 10 keV ion energies. The atomic mass ratio of the overlayer and the substrate constituents seems to be a key quantity in understanding atomic mixing. The critical bilayer mass ratio of $\delta < 0.33$ is required for the occurrence of a thermal spike (local melting) with a lifetime of $\tau > 0.3$ ps at low-energy ion irradiation (1 keV) due to a ballistic mechanism. The existing experimental data follow the same trend as the simulated values.Comment: 4 pages, 4 figures, preprin

Convection-induced compositional patterning at grain boundaries in irradiated alloys

We consider the stability of precipitates formed at grain boundaries (GBs) by radiation-induced segregation in dilute alloys subjected to irradiation. The effects of grain size and misorientation of symmetric-tilt GBs are quantified using phase field modeling. A novel regime is identified where, at long times, GBs are decorated by precipitate patterns that resist coarsening. Maps of the diffusional P\'eclet number indicate that arrested coarsening takes place when solute advection dominates over thermal diffusion right up to the precipitate/matrix interface, overwhelming capillary effects. This contrasts with liquid-solid mixtures where convection only accelerates coarsening.Comment: 29 pages, main text with 3 figures, 1 table, 1 supplemental information documen

Ion Beam Mixing in Ag-Pd Alloys

Ion beam mixing during 750 keV Kr+ irradiation at 80 K was measured on a series of Ag‐Pd alloys using Au marker atoms. The mixing in pure Ag was the greatest and it decreased monotonically with increasing Pd content, being a factor of 10 higher in pure Ag than in pure Pd. This large difference in mixing cannot be explained by the difference in cohesion energy between Ag and Pd in the thermodynamic model of ion beam mixing proposed by Johnson et al. [W. L. Johnson, Y. T. Cheng, M. Van Rossum, and M‐A. Nicolet, Nucl. Instrum. Methods B 7/8, 657 (1985)]. An alternative model based on local melting in the cascade is shown to account for the ion beam mixing results in Ag and Pd

Ion mixing and thermochemical properties of tracers in Ag

Very thin films of Ni, Ta, W, Pb, and Bi in a Ag matrix were irradiated at 77 K with 330 keV Kr ions at doses from 3 to 7×10^15 ions/cm^2 and analyzed at room temperature by backscattering of 1.9 MeV He + . The measured mixing efficiencies, Dt/phiFD, for the various tracers correlate with their respective tracer impurity diffusion coefficients and impurity-vacancy binding energies in Ag. The results concur with previous ones with a Cu matrix and further support the idea that the parameters that are important for thermal diffusion are also important for ion mixing in a thermal spike

Defect production and electronic stopping for light ions in metals

A method for determining effective electronic stopping powers in metals is presented. The method involves measuring damage rates in thin films as a function of ion energy. The experimental results are compared with predictions based on Monte Carlo computer simulations. Results are presented for H, D, He, and Li projectiles on Cu, Ag, and Ni. The implication of these results for defect production is discussed

Crystalline-to-amorphous phase transition in irradiated silicon

The amorphous(a)-to-crystalline (c) phase transition has been studied in electron(e ) and/or ion irradiated silicon (Si). The irradiations were performed in situ in the Argonne High Voltage Microscope-Tandem Facility. The irradiation of Si, at <10K, with 1-MeV e to a fluence of 14 dpa failed to induce the c-to-a transition. Whereas an irradiation, at <10K, with 1.0 or 1.5-MeV Kr+ ions induced the c-to-a transition by a fluence of approx.0.37 dpa. Alternatively a dual irradiation, at 10K, with 1.0-MeV e and 1.0 or 1.5-MeV Kr+ to a Kr+ fluence of 1.5 dpa - where the ratio of the displacement rates for e to ions was approx.0.5 - resulted in the Si specimen retaining a degree of crystallinity. These results are discussed in terms of the degree of dispersion of point defects in the primary state of damage and the mobilities of point defects

Mechanism and kinetics of radiation-induced segregation in Ni-Si alloys

Rutherford-backscattering and Auger chemical-depth-profiling measurements show that films of the ..gamma..'-Ni/sub 3/Si phase produced on the ion-bombarded surfaces of Ni-Si alloys obey simple parabolic growth kinetics. At low temperatures the film growth-rate constant exhibits Arrhenius behavior and varies with the fourth root of the dose rate. The apparent activation energy in this low-temperature region is approx. 0.3 eV. At high temperatures the growth constant is independent of the dose rate. The results are consistent with a diffusion-controlled growth model, which assumes Si atoms migrate in the form of a fast-diffusing Si-interstitial complex