In situdiffraction studies of the initial growth processes of textured icosahedral quasicrystalline thin films

Abstract

The seeding and morphology of quasicrystalline ${\mathrm{Ti}}_{x}{\mathrm{Ni}}_{y}{\mathrm{Zr}}_{1\ensuremath{-}x\ensuremath{-}y}$ thin films grown by pulsed-laser deposition on ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}(0001)$ have been investigated in situ, using in-plane x-ray diffraction and reflectivity with synchrotron radiation. The crystallinity of the final films was further studied ex situ using a laboratory x-ray source. Local icosahedral order becomes established after a film thickness of $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, which is followed by an abrupt change in the growth rate after a film thickness of approximately $5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, as long-range quasicrystalline order begins to become energetically favorable. The films grow two-dimensionally even up to thicknesses of over $100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and are highly textured, consisting of columnar grains with one of their fivefold symmetry axes perpendicular to the substrate surface.