We consider ion mixing in the low temperature regime, where it is insensitive to temperature. Mixing of most thin markers is Gaussian, independent of irradiation flux, and varies linearly with fluence. However, the mixing in some media varies widely between markers of similar mass and appears to correlate with thermal diffusion constants. In bilayer systems, the profile of long-range mixing is exponential, and the number of mixed atoms scales linearly with fluence. This can be modeled successfully with simple collisional theory. Short range mixing scales with the square root of the fluence, but again shows strong correlations with known bulk chemical properties. We conclude that chemical driving forces and low energy transport mechanisms such as interstitial migration play major roles in ion mixing, even at low temperatures.

In addition to the accumulation of the implanted species, a considerable number of processes can affect the composition of an alloy in the surface region during ion bombardment. Collisions of energetic ions with atoms of the alloy induce local rearrangement of atoms by displacements, replacement sequences and by spontaneous migration and recombination of defects within cascades. Point defects form clusters, voids, dislocation loops and networks. Preferential sputtering of elements changes the composition of the surface. At temperatures sufficient for thermal migration of point defects, radiation-enhanced diffusion promotes alloy component redistribution within and beyond the damage layer. Fluxes of interstitials and vacancies toward the surface and into the interior of the target induces fluxes of alloying elements leading to depthdependent compositional changes. Moreover, Gibbsian surface segregation may affect the preferential loss of alloy components by sputtering when the kinetics of equilibration of the surface composition becomes competitive with the sputtering rate. Temperature, time, current density and ion energy can be used to influence the individual processes contributing to compositional changes and, thus, produce a rich variety of composition profiles near surfaces.

Ion beam mixing in Pt-Si bilayered samples was measured during irradiation with projectiles ranging in mass from 4 amu (He) to 131 amu (Xe) at 10 K, 300 K and 373 K. Using deposited damage energy as a basis for comparing the different irradiations, it was found that the beavier ions were more efficient than the lighter ones for inducing mixing. Moreover, it was observed that the mixing was essentially independent of temperature below 373 K. These results are interpreted on the basis that the mixing is caused by the stimulated motion of defects during the cooling phase of energetic cascades.

A Model for Ion Mixing of Bilayer systems in a thermal spike is described. Normal thermal reactions, at a constant average temperature, are assumed for the duration of the spike. New experimental results on mixing of a Nb/Si couple with Xe ions are shown to agree with the prediction of the model that the apparent activation energy in ion mixing can depend upon the ion species. Calculations of spike mixing for Cr and Ni with Si are presented which show that a substantial part of the experimentally observed mixing rates, and their temperature dependence, can be attributed to thermal spike effects.

Root-mean-square diffusion distances for both vacancy and interstitial defects in metals can be very large at elevated temperatures, e.g. several μm's in one second at 500°C. Consequently, defects that escape the implanted region at elevated temperature can produce compositional and microstructural changes to depths which are much larger than the ion range. Because of the high defect mobilities, and of the fact that diffusion processes must compete with the rate of surface recession, the effects of defect production (ballistic mixing), radiation-enhanced diffusion and radiation- induced segregation become spatially separated during ion bombardment at elevated temperature. Results of such experimental studies in a Cu-Ni alloy are presented, discussed and compared with predictions of a phenomenological model. Contributions to the subsurface compositional changes from radiation-enhanced diffusion and radiation- induced segregation are clearly identified.

Experimental investigations of the redistribution of a thin (1nm) Sn marker layer lying between two thicker dissimilar layers (Ge and Si) during 360 keV As ion irradiation are reported. Several permutations of layer arrangements were tested, i.e. Si/Sn/Ge, Ge/Sn/Si, Si/Sn/Si and Ge/Sn/Ge. It was also found that in the dissimilar “diffusion” couples, the Sn drifts in the Ge rich direction, regardless of whether the Ge is on the surface side or the substrate side of the marker. This phenomemon of anisotropic transport is interpreted as a drift induced by a gradient in the “diffusion” coefficient. The radiation resistance of concentrated alloys is discussed in the light of this phenomenon.

Mixing effects induced by Kr++ bombardment in the Au-Fe and Pt-Fe metallic systems have been studied by Rutherford backscattering and X-ray diffraction techniques. The mixed amount of Fe atoms shows a linear dependence on the square root of the Kr do se for both systems. The induced mixing appears more efficient for the Pt-Fe with respect to the Au-Fe system. In the case of Pt-Fe mixing is much more efficient when the initial bilayer structure has Pt on the top. The X-ray diffraction analysis reveals the formation of an extended solid solution of Fe in Pt, having the Fe40 Pt60 composition.

Ion beam irradiation of metal film/SiO2 interfaces causes reactions when the metals are those chemically capable of reducing SiO2. These reactions result in the formation of metal rich silicides in the region of the interface and an increase in the adhesion of the film to the substrate. For other nonreactive metals ion irradiation causes lateral transport of metal atoms resulting in the formation of an island structure. The results obtained by ion irradiation are compared with previous studies of high temperature thermal processing of metal films on SiO2.

Ion implantation causes alkali migration to the surface in alkali silicate glasses. Rutherford backscattering spectrometry was used to follow this depletion. Room temperature implantations of 5×1016 250 keV Xe/cm2 in 12M20·88SiO2 (M = Li,Na,K,Rb,Cs) removes approximately equal numbers (within a factor of 2) of alkali from the glass. Low temperature (77K) implants significantly reduce the alkali loss. These results imply a radiationenhanced diffusion mechanism in which the alkali interchanges with the products of the collision cascade, with the kinetics being limited by the radiation damage components. The results for mixed-alkali glasses ((12−x)M2O·xCs20·88Si02) give further evidence for this process. In glass/'metal couples, radiation enhanced diffusion allows the interchange of glass network components with deposited metals. Rutherford backscattering spectrometry was used to follow the interchange of silicate and phosphate glass components with metal ions near the heavy-ion implanted interface between glass substrate and metal (Al,Zr) films.

A new approach is developed, employing “in situ” electrical resistivity measurements, as a tool to study ion beam mixing of evaporated metal-metal multi or bilayers. The electrical resistivity variations measured continuously during the ion bombardment exhibit a monotonical increase and a tendency toward a saturation process allowing to detect precisely the total mixing of the film. The volume fraction of intermixed atoms can be determined within the framework of a simple conduction model. Experimental results are given in the case of Fe-Al and Al-Ag multilayers.

The rate of ion induced mixing of 700 Å Au layers vapor deposited on amorphous and single crystalline Si substrates held at room temperature was measured as a function of dose using 300 key Si, 350 keV Ar, and 525 keV Kr ion beams.Mixing profiles were measured at various fluences by Rutherford backscattering techniques and were found to be consistent with mixed layers whose thicknesses increased with ion dose. Mixing compositions, which were stoichiometric over the entire mixed region at Au-28.5 at.% Si, were found to be independent of ion species or implant fluence. For all ion species the dose dependence of mixing was closer to linear than the square root power law reported previously [1]. In addition, the mixing rate for Au on single crystalline substrates was significantly higher than Au n substrates amorphised by Si (self-ion) implantation at liquid nitrogen temperature. No difference was found between the mixing rates when the amorphous substrates were prepared by room temperature implantation. Preliminary results indicate similar behavior for the Au/Ge couple.

Changes in the subsurface composition of Ni-40 at.% Cu alloys during 3-keV Ne+ bombardment at temperatures between 25 and 700°C were studied by means of ion scattering spectroscopy.Both the time evolution of the composition in the surface atom layer during ion bombardment and subsurface concentration profiles after rapid specimen cooling to room temperature were measured as a function of temperature. Radiation-enhanced diffusion coefficients were derived from the effective altered-layer thicknesses obtained. A comparison of the experimental measurements with theoretical calculations based on a phenomenological model enabled the identification of processes and kinetics responsible for subsurface compositional modifications.

Nickel substrates were coated with a thin Sn film and implanted with 100 keV Xe+ to fluences between 3 and 7.1015 ions/cm2. Surface chemistry changes were monitored using Auger and Mfssbauer spectroscopies. By comparing between profiles of un-implanted and implanted specimens, it was found that ion implantation through the film caused Ni to move into the Sn film and Sn to penetrate into the Ni substrate. The Mdssbauer analysis disclosed the presence of new surface phases. A substantial increase in the tarnishing resistance of Ni was found by using this treatment.

The Boltzmann transport equation is used to describe a beam of ions of atomic species 1 (1-atoms) bombarding a target modelled as an amorphous mixture of 2-atoms and 3-atoms. In a manner familiar in nuclear reactor theory, the method of characteristics is used to integrate the resulting transport equations. An exact expression for the migration flux J3 of 3-atoms is obtained in closed form. This expression can be evaluated in terms of a power series in a distance parameter s. For the case of slowly varying density N3 of 3-atoms, Fick's law, relating J3 to the gradient of N3, is derived from this expression; it is given by the lowest order term of the power series. J3 is shown to be proportional to the bombarding flux. Concomittantly, a closed expression for the mixing parameter in Fick 's law is obtained, which allows a calculation of this quantity for realistic interatomic potentials. A model Kinchin-Pease displacement cascade is proposed, which is expected to allow a reasonable first approximation calculation of the mixing parameter in Fick's law. It is deduced that the mixing parameter will depend sensitively on the lattice displacement energy. This dependence constitutes a physical mechanism for chemical effect in cascade mixing, as well as for fluence and temperature dependence of cascade mixing.

The kineticsof phase formation and growth in Au-Al and Cu-Al thin film bilayers under ion beam bombardment was investigated in detail for the dependence on the beam energy. The experimental data can be interpreted within the radiation enhanced diffusion description, taking into proper account the target configuration, the growth of a new phase and the deposited energy density distribution.

Atomic mixing effects of sputter depth-profiles are modeled by a diffusion theory with a depth-dependent diffusion constant D. The model is compared to SIMS depth profiles, using 5 keV Ar+ bombardment of dilute thin-film multilayers of Al, Ag, Ti and Mo in silicon. The experimental values of D can be explained by cascade mixing and radiation enhanced diffusion within the cascade for Al, Ag and Ti markers but not for the Mo marker.

We report on our studies of Ni transport induced by 290 keV Xe irradiation of thin Ni films evaporated on thermally grown SiO2 at Xe fluences of 1015–1016 cm−2 and at temperatures of 77–750 K during irradiation. A simple etching technique was used to remove the free Ni leaving the SiO2 layer with incorporated Xe and Ni, whose profiles are directly measured using 2 MeV He+ backscattering spectrometry.

Marker experiments are used to verify the selectivity of the etching procedure. An apparent discontinuity in the Ni concentration across the Ni-SiO2 interface may produce the high selectivity observed within our etching process. Features associated with both cascade mixing and recoil implantation are readily discernible in the residual metal profiles. An exponential tail is evident beyond ∼ 500 Å of the SiO2 and is insensitive to temperature. within 500 Å of the surface the Ni profile demonstrates a strong temperature dependence which affects both the cascade mixing and recoil implantation processes. These profiles show favorable agreement with theory for samples implanted at temperatures of ≤ 300 K, while deviations in the high temperature behavior suggest a way chemical effects may alter the collision processes.

The chemical and microstructural changes caused by the direct implantation of solutes into metals are examined. The particular case involving Al+-ion implantation into nickel is treated in detail. Chemical composition profiles measured using Auger spectroscopy and Rutherford backscattering, and average near-surface chemical composition measured using an analytical electron microscope, are compared with model calculations. The microstructures that develop during implantation are investigated using transmission electron microscopy. For low fluences implanted near room temperature, these microstructures contain dislocations and dislocation loops. Dislocation loops, dislocations, and voids result from implantations at temperatures near 500°C. Higher fluences at these elevated temperatures produce precipitates when the composition of implanted solute lies in a two-phase region of the phase diagram. Implanted concentrations corresponding to intermetallic compounds produce continuous layers of these compounds. Room temperature, as compared to elevated temperature, implantation may produce the same phases at the appropriate concentrations, e.g. β'-NiAl, or different phases, depending on the relative stability of the phases involved.

We have compared the formation of amorphous alloys from Ni-Hf multilayer films by ion mixing and solid state diffusion. We find that ion mixing and solid state reaction produce significant differences in the composition range of the amorphous phase inside the mixed samples. Moreover, the thermochemical parameters which are of primary importance for the solid state reaction also influence the behavior of the Ni-Hf system under ion mixing.

Evaporated bilayers and multilayers of Fe and Al have been studied during ion beam mixing with Xe ions using in-situ electrical resistivity measurements. Experiments have been performed in the composition range 40 – 58 at.% Al and at both temperatures 77 K and 300 K. A semi-empirical model is proposed to explain the observed kinetics. At low doses, a square root dependence of the mixed volume fraction on dose is found at 77 K but not at 300 K. The results are discussed by comparison with the different models proposed for ion beam mixing.