Electronic excitation triggered by electron irradiation relaxes in a short time (∼10 fs) with emission of Auger electrons or characteristic x-ray, but in some cases, it may dissociate chemical bonds and hence leads to structural modification of materials. Recent studies revealed that an intermetallic compound, nanoscale α-Pt 2Si, is formed at the Pt/amorphous (a-) SiO x (x∼1.5) thin film interface by electron or photon irradiation [ 1, 2]. Decomposition of a-SiO x via core-hole Auger decay is responsible for the above mentioned Pt 2Si formation. The process has a potential application to a novel processing for a nanoscale silicide formation, including micropatterning by site-selected solid-state reaction.
Fe-Si system forms various silicides that have different stoichiometric compositions. Among these compounds, trigonal Fe 2Si, a ferromagnetic half metal with 100% spin-polarization ratio, is expected as a novel spintronics material, while there are few reports on this topic [ 3, 4]. The advantage of Fe-Si system is that both Fe and Si are abundant resources; however, synthesis of iron silicides generally requires high-temperature processes, and hence, low temperature synthesis of nanoscale silicides via the above-mentioned nonradiative transition is of technologically interest. In this study, we aim to form iron silicide nanosheets at the Fe/a-SiO x thin film interface by electron irradiation and elucidate its microstructure and formation mechanism.
Composite thin films of Fe and a-SiO x (hereafter, a-SiO x/Fe/a-SiO x) were prepared by sequential vacuum vapor deposition of silicon monoxide (SiO) and Fe onto NaCl(001) and Si(111) substrates. The prepared thin films mounted on copper grids were irradiated with 75 keV electrons using a TEM (Hitachi H-7000).