C. David

Evolution, migration and clustering of helium-vacancy complexes in RAFM steel- depth resolved positron annihilation Doppler broadening study

Abstract Indian Reduced Activation Ferritic Martensitic steel is implanted with 130 keV helium ions to a fluence of 5 × 1014 and 1 × 1016 ions/cm2 and investigated using positron annihilation spectroscopy. The samples were characterised by defect sensitive S and W-parameters using depth resolved slow positron beam. A dose dependency is observed in the nucleation and growth of helium bubbles with annealing temperature. An experimental evidence for the migration of smaller helium-vacancy complexes is observed via the variation in thickness/width of irradiated layer with temperature. The S–W plot clearly shows the regions corresponding to defect annealing, bubble nucleation and growth.

Nonlinear effects in defect production by atomic and molecular ion implantation

This report deals with studies concerning vacancy related defects created in silicon due to implantation of 200 keV per atom aluminium and its molecular ions up to a plurality of 4. The depth profiles of vacancy defects in samples in their as implanted condition are carried out by Doppler broadening spectroscopy using low energy positron beams. In contrast to studies in the literature reporting a progressive increase in damage with plurality, implantation of aluminium atomic and molecular ions up to Al3, resulted in production of similar concentration of vacancy defects. However, a drastic increase in vacancy defects is observed due to Al4 implantation. The observed behavioural trend with respect to plurality has even translated to the number of vacancies locked in vacancy clusters, as determined through gold labelling experiments. The impact of aluminium atomic and molecular ions simulated using MD showed a monotonic increase in production of vacancy defects for cluster sizes up to 4. The trend in damage...

Reactive Pulsed Laser Deposition of Titanium Nitride Thin Films: Effect of Reactive Gas Pressure on the Structure, Composition, and Properties

Titanium nitride (TiN) thin films were deposited by reactive pulsed laser deposition (RPLD) technique. For the first time, the composition evaluated from proton elastic backscattering spectrometry, in a quantitative manner, revealed a dependence on the partial pressure of nitrogen from 1 to 10 Pa. Grazing incidence-XRD (GI-XRD) confirmed the formation of predominantly nanocrystalline TiN phase with a crystallite size of around 30 nm. The hardness showed maximum value of ~30 GPa when the composition is near stoichiometric and the friction coefficient was found to be as low as 0.3. In addition, a systematic optical response was observed as a function of deposition pressure from the surface of the TiN films using spectroscopic ellipsometry.

Study of vacancy defects and their thermal stability in MeV Fe ion irradiated RAFM steel using positron beam Doppler broadening spectroscopy

ABSTRACT Indian reduced activation ferritic-martensitic steel was irradiated with 1.1 MeV Fe ions to various doses from 1 to100 dpa at room temperature. The depth profiling of irradiation-induced vacancy-type defects and the defect-recovery under post-irradiation annealing was studied using variable low-energy positron beam Doppler broadening spectroscopy. The influence of irradiation-induced defects on the microstructural properties was studied by glancing incidence x-ray diffraction (GIXRD) and nanoindentation technique. Positron annihilation study showed the signatures of reduced vacancy concentration at the peak damage region due to injected interstitial effect from 30 to 100 dpa and the widening of vacancy-interstitial recombination-rich region towards the end of ion range with the increase in dose. The GIXRD results were analysed by modified Williamson–Hall plot method, and the variation of coherent domain size and micro-strain with irradiation dose was studied. Irradiation-induced hardening was observed in the nanoindentation study. The features observed in the GIXRD and nanoindentation study are correlated with the depth-resolved defect distribution observed in the positron annihilation study.

Annealing Behavior of Ion‐implanted Nitrogen in D9 Steel

Nitrogen isotope N15 was implanted at the sub‐surface of D9 steel. The resonance nuclear reaction analysis was used to probe the implanted nitrogen as a function of depth. The as‐implanted D9 sample was isochronally annealed and by observing the broadening of nitrogen depth profile at various annealing junctures, activation energy for nitrogen diffusion in steel was deduced.