Formation of epitaxial erbium-silicide islands on Si(0Â 0Â 1)

Erbium films of 0.5, 2 and 6 nm thickness were evaporated in UHV onto Si(0 0 1) substrates, annealed and characterized in situ by reflected high-energy-electron diffraction (RHEED). The RHEED pattern was streaky for ErSi2−x films at all thicknesses were formed at 400 °C. A heat treatment of the 0.5 and 2 nm thick Er films at 800 °C induced an inhomogeneous surface showing RHEED patterns both of the Si(0 0 1) substrate and the epitaxial ErSi2−x. The same effect was observed after successive repetition of Er depositions, 12 times for the 0.5 nm and three times for the 2 nm thick Er films. In contrast for a 6 nm Er layer the RHEED pattern remained unchanged after the heat treatment at 800 °C. Atomic force microscopy (AFM) indicated the formation of a quasi-continuous layer with roughness independent of the Er film thickness. Cross-sectional transmission electron microscopy (XTEM) showed structures with a “hut like” form. This “continuous-discontinuous” like transformation of the epitaxial ErSi2−x film cannot be explained by only the well known strain effect.