The incommensurate nature of epitaxial titanium disilicide islands on Si(001)

Much of traditional metallurgy depends on manipulating thermodynamic and kinetic constraints to achieve the desired microstructure. It is becoming apparent that it may be possible to exploit similar principles to achieve designer self-assembled nanostructures on surfaces. A key question in determining equilibrium island sizes is whether epitaxial growth occurs with commensurate lattice parameters (with corresponding elastic strain), or whether the islands are relaxed. In the case of TiSi2 islands on Si(001), we can show both by STM and by TEM that the C49 phase is incommensurate, and that the islands have the relaxed silicide lattice parameters. The STM images show this both from the dimensions of surface reconstructions and from subtle current imaging contrast that we attribute to the periodic nature of the island/substrate interface. The TEM evidence comes primarily from analysis of moiré fringes, and the electron diffraction data confirm the presence of the C49 phase.