A Mössbauer Study on Solid Krypton Precipitates in Aluminium and Silicon

Abstract

ABSTRACTMössbauer spectroscopy on the 9.4 keV transition in 83Kr is used to study inert gases in metals and semiconductors. An absorber was made by implanting 83Kr at 110 keV in Al foils to a total dose of 1.7· 1016 Kr cm−2, leading to the formation of small precipitates (bubbles). Spectra on the as-implanted sample were taken as a function of temperature for three 83RbI sources which differ in line shape due to a different water content. A model is presented to extract the absorber parameters from the spectra in a consistent way, in spite of the different sources used. The spectra of Kr bubbles in Al produced by high dose implantation show two components: a single line from Kr inside the bubble and a quadrupole split component from Kr at the Kr-Al interface. The total absorption area could be fitted very well assuming a simple Debye model, yielding a Debye temperature of ΘDT = 101(2) K. For the individual components we obtained Debye temperatures of ΘDQ = 98(6) K and ΘDS = 90(10) K. The isomer shift of the bulk fraction is significantly larger than that of a solid Kr layer at ambient pressure, reflecting the fact that the s-density increases under compression. The size of the precipitates can be estimated to be 1.5–1.8 nm. Thin KrSi films, produced by Kr plasma sputter deposition, were characterized using cross-sectional X-ray analysis. The results clearly show two different layers. Presumably, the film grows at first as c-Si with a low Kr concentration, but after having reached a certain critical thickness, further growth proceeds as a-Si with a high Kr concentration. For Mössbauer spectroscopy an absorber of 83KrSi was made by plasma deposition on an Al foil. The spectra can be fitted with a single line and a quadrupole component, both with isomer shifts much larger than found in the case of small Kr bubbles in Al. No change in the total absorbed area was observed from 4.2 to 200 K indicating a lower limit of 250 k for the Debye temperature. Both observations indicate that the Kr resides in very small clusters.