Modulation of lattice constants by changing the composition and strain in incommensurate Nowotny chimney-ladder phase FeGeγ epitaxially grown on Si

Abstract

Abstract The single phase FeGeγ nanocrystals (NCs) with incommensurate Nowotny chimney-ladder structure were epitaxially grown on Si substrates by reaction between deposited Fe atoms and Ge nanostructured layers on Si. The Ge nanostructured layers worked as blocking layers of the Fe diffusion to Si substrates. We used the two kinds of the Ge nanostructured layers: Ge wetting layers formed by direct Ge deposition on Si and Ge NCs formed by Ge deposition on ultrathin SiO2 films with ultrasmall nanowindows on Si. In the case of Ge wetting layers, the FeGeγ NCs were directly formed on Si, where there was a-axis strain due to the 2.9% lattice mismatch between FeGeγ and Si. On the other hand, in the case of Ge NCs, formed FeGeγ NCs were elastically-strain-relaxed due to the small contact with Si substrates through nanowindows in the ultrathin SiO2 films. Furthermore, the c-axis lattice constant in the epitaxial FeGeγ NCs changed due to the variation of the Fe-Ge composition. These results demonstrated that a-axis lattice constant was modulated by strain control of FeGeγ NCs due to the change of contact area with Si substrate and that c-axis lattice constant of FeGeγ NCs with incommensurate Nowotny chimney-ladder structure was modulated by manipulating Fe-Ge composition. These modulation of lattice constants will open a road for manipulating phonon group velocity related to the lattice constant and managing the waste heat in various devices implemented on Si substrates.