Institute of Fundamental Technological Research

The structural, electronic, and magnetic properties of low-energy rhenium implanted c-Si are examined for the first time. The damage created by rhenium ions and the following partial reconstruction of the silicon host matrix after rapid thermal annealing (RTA) are investigated as a function of the fluence. Rutherford backscattering spectrometry (RBS) results reveal that the implanted ions are located in the near-surface region with the distribution maximum at about 23 nm below the surface. The analysis of rhenium-depth distribution using the McChasy code shows that the implanted Re-ions are located in the interstitial lattice positions. The RTA leads to a partial recovery of the silicon crystal structure. According to the RBS results, the formed inclusions are not coherent with the silicon host matrix causing an increase of the lattice distortion. Analysis of channeled RBS/c spectra carried out by the McChasy code revealed different levels of bent channels in damaged regions suggesting bimodal distribution of inclusions in the silicon. Studies of high-resolution X-ray photoelectron spectroscopy (XPS) conducted after the RTA showed the shift of Re 4f7/2 binding energy (BE) by +0.68 and + 0.85 eV with respect to metallic rhenium for the samples with lower/higher fluencies, respectively. Complex XPS, density functional theory (DFT) simulations, and transmission electron microscopy (TEM) data analysis allowed us to conclude that the near-surface layer of the sample (~10 nm) consists of nanoinclusions with cubic and/or hexagonal ReSi. In the middle area of the samples, much larger nanoinclusions (>10/20 nm for higher/lower fluencies, respectively) containing pure metallic rhenium inside are formed. The RTA increases the magnetic moment of the sample with the lower dose nearly 20-fold, whereas in the sample with the higher dose a 3-fold increment is observed only. The magnetic response of the examined systems after the RTA indicates a presence of magnetic interactions between the nanoinclusions resulting in the system exhibiting super-spin glass or super-ferromagnetism.

rhenium-implanted silicon, RBS, XPS, RTA, TEM, DFT