K Milants

Trapping of ion-implanted 57Co to cavities in c-Si: a qualitative study

Abstract We observe a pronounced dose dependence in the trapping of Co to the internal surface of nanosized cavities in c-Si. Mossbauer spectroscopy shows that cavity trapping is most explicit for low Co contamination levels ( 5 × 1014 at/cm2), silicide formation becomes predominant at first and then subsequently partially dissolves upon prolonged annealing at temperatures exceeding 750°C. In the intermediate region, a clear starting situation is only reached after several annealing steps. Again Co gets trapped at the cavities, reaching essentially an identical level as for the low dose case. For the low and intermediate dose case, the onset of cavity trapping is followed in detail, showing that a large initial fraction of weakly surface bound Co depopulates in favor of the formation of small CoSi2 precipitates in the vicinity of the voids. Subsequently, this CoSi2 phase then partially dissolves in favor of strongly surface bound Co.

Study of the trapping of CoFe impurities at the internal wall of nanosized Si voids

The trapping of transition metal impurities to cavities in c-Si recently attracted much interest, stemming from the possibility to use the process for proximity gettering. Mossbauer spectroscopy is employed on ion-implanted 57Co57Fe to elucidate the nature of the site of the impurity atom at the internal surface of the voids. We observe a trapping effect upon thermal treatment, hampering normal silicide formation. Also a pre-existing silicide phase can be partially dissolved in favour of cavity trapping. The binding energy for cavity trapping is found to be lower than for silicide formation.

A Mossbauer study of Co cluster nucleation in Ag

In the present study we aim to investigate the onset of Co cluster formation in Ag by Mossbauer spectroscopy. Hyperfine interaction techniques are very powerful in determining the onset of formation of very small clusters because they probe the atomic environment present at the radioactive probe atoms site. We employed different sample preparation techniques and discuss the differences between them. We could establish the proper conditions for obtaining a large fraction of Co dimers. The behaviour of the different components in the Mossbauer spectra as a function of the Co concentration allows us to estimate the typical trapping radius for Co dimer formation.

A combined Mössbauer and Rutherford backscattering spectroscopy analysis of the influence of nanosized cavities on CoSi2 formation

For Co in Si, the competition between CoSi2 formation and cavity trapping is studied by Rutherford backscattering and Mossbauer spectroscopy. The presence of nanosized voids hampers the formation of a buried epitaxial silicide layer in its initial phase, preventing the small CoSi2 particles from forming a bulk layer. The Mossbauer spectra show that a pre‐existing silicide phase can be partially dissolved in favor of cavity trapping. In addition, channeling measurements provide qualitative information about the voids, showing that the thermal stability of the voids is much higher than for defects resulting from self‐implantation.

X-ray diffraction, Rutherford backscattering and channeling measurements on Pb inclusions in Si

Pb inclusions have been formed in Si 〈111〉 single crystals by ion implantation to doses of 1015, 5 × 1015 and 1016 at./cm2. Combining Rutherford backscattering spectrometry (RBS), channeling and X-ray diffraction (XRD) results, we obtain information about the pressure in the inclusions, their epitaxy to the host lattice and the dependence of these properties on implantation dose and annealing temperature.

Tetramethyl tin in frozen rare gases. A study of impurity-host binding

Abstract The Mossbauer effect in 119 Sn was applied to obtain information on the local dynamical properties in frozen rare gases. The results show a hardening of th phonon spectrum for the matrix isolated tetramethyl tin molecule in neon and argon. No such enhancement is observed for the matrices of solid krypton and xenon. An explanation based on geometrical considerations is proposed.

Nanosized Metallic Sn Precipitates in Si, Formed Upon Ion Implantation

In this work we firstly established the optimal conditions to preferentially form nanosized β-Sn inclusions from a supersaturated solid solution of Sn in Si, formed by a high dose ion implantation. Afterwards we tried to elucidate the origin of the strongly enhanced recoilless fraction of Sn nuclei inside these precipitates, thereby making a link to the observed shift in isomer shift value. This is tentatively interpreted in terms of a local compression of the inclusion to about 200 kbar.

Study of the formation of Cs inclusions in refractory bcc metals by133Xe(Cs) Mössbauer resonance

The formation and properties of Cs inclusions in Mo and W are observed through a preimplanted133Xe(Cs) local probe, which is found to reside in three sites: a substitutional site, an interfacial one and a further site which is not detectable directly, but the presence of which can be inferred from the Mössbauer measurements. The location of the probe at the interface of small Cs inclusions is characterized by large Debye temperatures of around 200 K, a quadrupole interaction of +1.86(15) mms−1, which is close to known surface site values, and an isomer shift of −0.33(12) mms−1. From the latter value an approximate local pressure of 5 GPa is deduced. In W the site populations are followed as a function of Cs dose. The observed interchange of populations in the low dose range is thought to represent the initial formation of the second phase inclusions.