T.D. Andreadis

Evolve, a time-dependent monte carlo code to simulate the effects of ion-beam-induced atomic mixing

Abstract The sputtering of inhomogeneous multielement targets by medium-energy ions is simulated using the Monte Carlo method. Incident ions as well as the multiple recoil atoms of the cascade produced in the medium are followed until either they escape from the solid or their energy falls below a low cut-off value. Two modes of simulation are demonstrated. In the first mode, the program deals with an undisturbed medium and no change takes place in the medium for the simulation of successive ions; a situation which corresponds to low-dose sputtering experiments. In contrast to previous Monte Carlo codes, the other mode of this program considers atomic-mixing of all species including the implanted beam ions in the medium during the simulation of ion bombardment. This simulation of time-dependent processes can help us to a better understanding of some sputtering phenomena of complicated nature such as the preferential sputtering of certain species within a multielement medium. Furthermore, this simulation d...

Sputter depth profiles of Ni/Cr thin‐film structures obtained from the emission of Auger electrons and x rays

Multilayered thin‐film Ni/Cr/Ni/Cr. . .  structures, prepared by sputter deposition, were depth profiled by argon ion sputtering at energies of both 1 and 3 keV. Compositional depth profiles were obtained by simultaneously detecting the characteristic emission of Auger electrons and x rays that results from bombardment with 5‐keV primary electrons. An ultra‐thin windowed energy‐dispersive Si (Li) detector was used to monitor the emitted Lα x rays of Ni(0.85 keV) and Cr(0.57 keV). Due to the use of a near‐grazing take off angle for x rays, the x‐ray ’’probe depth’’ for 5‐keV primary electrons is somewhat greater than the thickness of an individual thin film (∠70 nm) and results in an x‐ray profile generated by the amount and type of material contained in such a layer thickness. Both Auger and x‐ray measurements indicate that each sputtered film is completely resolved, that little degradation in the interface widths is observed in sputtering through all nine layers of the structure, and that determinations ...

Simulation of recoil mixing in solids produced by energetic atom beams

Abstract A Monte Carlo computer code, called EVOLVE, is used to simulate the concentration changes which result from incident beam atoms and the cascades of recoil atoms. The altered composition of binary alloys is explored under selected conditions. It is observed that when all factors other than mass are removed from consideration, the heavier component in the solid is preferentially moved to deeper locations, producing a deep region enriched in that element.

Simulation of dynamic changes in near-surface composition during ion bombardment

Abstract A Monte Carlo based computer code is used to simulate the concentration changes which develop during ion bombardment as a consequence of the incident beam atoms and the resulting cascades of recoil atoms. This program considers atomic mixing of all species including the implanted beam atoms during the simulation of ion bombardment. Incident ions as well as the recoil atoms of the cascade produced in the medium are followed until either they escape from the solid or their energy falls below a low cutoff value (1.2 eV). The code, EVOLVE, is used to simulate the time dependent sputtering yield of amorphous Si under ion bombardment. The results are compared to experimental data which show an increase in sputtering yield as bombardment progresses. Another dynamic system examined is that of a binary alloy which displays preferential sputtering under ion bombardment.

Ni/Cr interface width dependence on sputtered depth

The composition depth distribution of an interface as determined by Auger sputter depth profiling is dependent, to a large extent, on both the ion‐bombardment‐induced cascade mixing and on the surface topography generated as a result of ion erosion. We assess the relative influence of these two processes on the depth resolution by comparing interface widths obtained by Auger sputter depth profiling (resulting from both the cascade mixing and the topography) to interface widths obtained by computer simulation (due to cascade mixing alone). Depth profiles were measured at eight successive interfaces of a multilayered Ni/Cr/Ni/Cr ⋅⋅⋅ thin‐film structure using both 1‐ and 3‐keV argon ion beams for sputter profiling. These interface widths increase with sputter depth, the increase being more rapid for the 3‐keV bombardment. The calculations with the computer code evolve contain modeling of all contributions to interface broadening, except that of surface topography, thus resulting in constant values of interfa...

Dynamic simulation of changes in near-surface composition during ion bombardment

Abstract A Monte Carlo based computer code, called EVOLVE, is used to simulate the concentration changes which develop as a consequence of the incident beam atoms and the resulting cascades of recoil atoms. During the bombardment, atomic mixing of all species including the implanted beam atoms is simulated. Simulations are utilized to examine several hypotheses of plausible causes of observed dose-dependent sputtering yields. Another dynamic system examined is that of binary alloys which display preferential sputtering under ion bombardment. The altered composition near the surface of such solids is explored by examining depth profiles under selected special conditions.

Model dependence of recoil implantation in binary solid

Abstract Seemingly contradictory results have recently been obtained using the cascade codes EVOLVE and TRIDYN as to whether the heavier or the lighter mass constituent of a two-element target is preferentially recoil implanted deeper into the target. EVOLVE results suggested that heavy atom enrichment occurs in the deeper regions, whereas TRIDYN results have suggested light atom enrichment. This paper explores some of the differences in results. Calculations have been made with MARLOWE(amorphous) and with EVOLVE(modified to match MARLOWE and TRIDYN models) in order to investigate differences between the models. The results support the previous EVOLVE conclusions.

Influence of a multiple‐energy ion beam on the equilibrium profile of a binary alloy

Ion‐bombardment‐induced sputtering of a multielement solid results in a preferential movement of the constituents, producing a composition profile which is dependent upon the beam energy. Recent studies have demonstrated transient changes in surface composition of such samples when the bombarding energy is abruptly changed. It is important to be able to treat multiple‐energy ion beams since most sputtering systems have a contaminant of multiply charged ions with higher energy than the principal component. We have studied the various competing processes that result in the equilibrium profile in order to develop the capability to predict the equilibrium profile which will result, once the parameters of the bombardment have been specified. We find that the equilibrium profile produced by a beam containing two energies cannot be obtained simply by interpolating between the two profiles that would result from the ion components individually. Interpolation is possible only in the near surface region.

Effects of target constituent mass difference on collision cascade induced composition changes in binary alloys

Abstract The cascade simulation code MARLOWE has been used to examine low dose composition changes caused by 5 keV Xe ions normally incident on a homogeneous polycrystalline target composed of 50%-50% Lu and Fe. The depth profile of the collision cascade induced atomic concentration of Lu is calculated and yields an excess of Lu in the surface, in agreement with the published results using the code TRIDYN. Calculation of the distributions of recoil Lu and Fe ions originating in particular layers indicate, however, that the heavier mass ion is driven deeper into the target, on the average, than the lighter mass ion—contrary to general perceptions.

Distribution of origins of sputtered particles and the shape of the target region affected by the cascade recoils

Abstract The recoil cascade resulting from Ar bombardment of Si has been studied by computer simulation. The average behavior of the cascade is determined by combining the results for a large number of incident particle histories. By sorting recoils according to the number of scatterings which precede their production, information is assembled concerning the manner in which the recoil cascade grows in size and shape. Results are also presented concerning the distribution of the origins of the particles which sputter. Here, distributions are given in terms of the transverse distance from the point of incidence of the bombarding ion.