Tailoring preferable orientation relationship and shape of α-FeSi2 nanocrystals on Si(001): impact of gold and Si/Fe flux ratio, and origin of α/Si boundaries
The growth of α-FeSi2 nanocrystal ensembles on gold-activated and gold-free Si(001) surface under different Si/Fe flux ratio by molecular beam epitaxy is reported. The study reveals the utilisation of gold as a catalyst regulates the preferable orientation relationship (OR) of the nanocrystals to silicon and their morphology at given Si/Fe flux ratio. α-FeSi2 free-standing crystals with continuously tuned size from 30 nm up to several micrometres can be grown with α(001)//Si(001) basic OR at the gold-assisted condition and at the gold free growth with α(111)//Si(001) OR on Si(001) surface. The preferred morphology of nanocrystals with a particular OR can be altered through the changes of Si/Fe flux ratio. Herein, the microstructure and basic OR between the silicide nanocrystals and the silicon substrate, formation of nanocrystals facets were analysed in detail with the help of microscopic techniques and simulation method based on analysis of near coincidence site (NCS) distribution at silicide/silicon interfaces. On the basis of the simulation used we managed to reveal the nature of the interfaces observed for the main types of α-FeSi2 nanocrystals grown. Three types of interfaces typical for nanoplates with α(001)//Si(001) basic OR, which are (i) stepped, (ii) stressed and (iii) flat, are explained by a tendency to increase the NCS density at interface. The results presented reveal the potential of the bottom-up fabrication of α-FeSi2 nanocrystals with tuned physical properties as a potentially important contact material and building blocks for future nanoelectronic devices.