S. Dhar

Bio: S. Dhar is an academic researcher from University of Göttingen. The author has contributed to research in topics: Ion & Ion implantation. The author has an hindex of 9, co-authored 28 publications receiving 236 citations.

Ion-beam mixing in Fe/Si bilayers by singly and highly charged ions: evolution of phases, spike mechanism and possible effects of the ion-charge state

Abstract: Silicide formation and ion beam mixing of Fe/Si bilayers due to Ar-, Xe- and Au-ion irradiations at room and liquid-nitrogen temperatures were investigated. For the study of silicide phase formation, the Fe/Si bilayers were irradiated with 100-keV Ar+, 250-keV Xe+, 700-keV Xe2+ or 400-keV Au+ ions at fluences of 1×1015 to 2×1016 ions/cm2. The influence of the ion-charge state on the mixing process was studied in Fe/Si by 100-keV Ar8+-ion implantation, in addition to the corresponding irradiations with singly charged ions at the same energy. Changes in the samples were analyzed by Rutherford backscattering spectroscopy, conversion electron Mossbauer spectroscopy, X-ray diffraction and atomic force microscopy. Pronounced structural changes and the intermixing of the components at the Fe/Si interfaces were measured as a function of the ion species, ion fluence and sample temperature. A linear correlation between the interface broadening and the fluence was observed for all the cases. Mossbauer analysis with enriched 57Fe layers revealed the onset of phase formation out of the solid solution. In order to interpret the mixing rates in this most general case, we considered mixing through thermal local or global spikes and compound formation. The highly charged Ar8+-ion irradiation produced a higher athermal mixing rate compared to singly charged Ar+ ions, and this result could not be explained by the above models.

Atomic mixing and interface reactions in Ta/Si bilayers during noble-gas ion irradiation

Abstract: This article focuses on the influence of chemical driving forces on the mixing and phase formation taking place at the interface of highly reactive metal/semiconductor systems under ion-beam irradiation. Ta/Si bilayers were irradiated with Ar, Kr, and Xe ions to fluences of (0.5-2.5) × 10 1 6 ions/cm 2 and at temperatures between liquid nitrogen and 400°C. The interface mixing and silicide formation were monitored as function of the ion mass and fluence by means of Rutherford backscattering spectrometry and x-ray diffraction. The interface broadening variance was found to depend linearly on the ion fluence and was explained with the help of a compound formation model involving local or global thermal spikes. The results are compared with those found in other silicide and germanide systems. The transition from local to global spikes was found to occur at the critical deposited damage energy of about 2.5 keV/nm.

Direct synthesis of β-FeSi2 by ion beam mixing of Fe/Si bilayers

Abstract: The iron di-silicide β-FeSi2 is a promising direct band gap semiconductor but difficult to produce. Here, the successful direct synthesis of this phase by ion beam mixing of Fe/Si bilayers at temperatures in the range of 450 to 550 °C is reported. The obtained single-phase β-FeSi2 layers and their structure are confirmed by Rutherford backscattering spectrometry, X-ray diffraction and conversion electron Mossbauer spectroscopy.

Xenon irradiation of Ni 3 N / Si bilayers: Surface roughening and interface mixing and reactions

Abstract: The irradiation effects in ${\mathrm{Ni}}_{3}\mathrm{N}/\mathrm{Si}$ bilayers induced by 100--700 keV Xe ions at fluences up to $4\ifmmode\times\else\texttimes\fi{}{10}^{16}$ $\mathrm{ions}/{\mathrm{cm}}^{2}$ were investigated at 80 K and room temperature. The element depth profiles were measured via Rutherford backscattering (Ni,Si) and resonant nuclear reaction (N) analysis, the phase formation at the interface via x-ray diffraction, and the surface roughness by atomic force microscopy. The observed dissociation and preferential sputtering of ${\mathrm{Ni}}_{3}\mathrm{N}$ followed by nitrogen out-diffusion were related to the small binding energy of this compound. Mixing at the ${\mathrm{Ni}}_{3}\mathrm{N}/\mathrm{Si}$ interface occurs via a combination of diffusion and reaction controlled transport processes and the interface broadening varies in second order with the ion fluence. At higher ion fluences, the formation of ${\mathrm{NiSi}}_{2}$ and ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ phases at the interface was found.

Interface mixing in Ta/Si bilayers with Ar ions

Abstract: We report on the room-temperature synthesis of the low-resistivity TaSi2 phase using ion-beam mixing of Ta/Si bilayers with Ar ions. The formation of the silicide phase is observed for different damage energies deposited at the Ta/Si interface. The variance Δσ 2 of the reacted (TaSi2) layer thickness varies linearly with the ion fluence Φ and the reaction rate Δσ 2 /Φ is proportional to the deposited damage energy density FD. The measured mixing/reaction efficiency, Δσ 2 /ΦF D =10±1 nm5/keV, is in agreement with the value calculated by the model of compound formation under local thermal spikes.

Elemental thin film depth profiles by ion beam analysis using simulated annealing - a new tool

Abstract: Rutherford backscattering spectrometry (RBS) and related techniques have long been used to determine the elemental depth profiles in films a few nanometres to a few microns thick. However, although obtaining spectra is very easy, solving the inverse problem of extracting the depth profiles from the spectra is not possible analytically except for special cases. It is because these special cases include important classes of samples, and because skilled analysts are adept at extracting useful qualitative information from the data, that ion beam analysis is still an important technique. We have recently solved this inverse problem using the simulated annealing algorithm. We have implemented the solution in the `IBA DataFurnace' code, which has been developed into a very versatile and general new software tool that analysts can now use to rapidly extract quantitative accurate depth profiles from real samples on an industrial scale. We review the features, applicability and validation of this new code together with other approaches to handling IBA (ion beam analysis) data, with particular attention being given to determining both the absolute accuracy of the depth profiles and statistically accurate error estimates. We include examples of analyses using RBS, non-Rutherford elastic scattering, elastic recoil detection and non-resonant nuclear reactions. High depth resolution and the use of multiple techniques simultaneously are both discussed. There is usually systematic ambiguity in IBA data and Butler's example of ambiguity (1990 Nucl. Instrum. Methods B 45 160–5) is reanalysed. Analyses are shown: of evaporated, sputtered, oxidized, ion implanted, ion beam mixed and annealed materials; of semiconductors, optical and magnetic multilayers, superconductors, tribological films and metals; and of oxides on Si, mixed metal silicides, boron nitride, GaN, SiC, mixed metal oxides, YBCO and polymers.