In situspecular and diffuse x-ray reflectivity study of growth dynamics in quench-condensed xenon films

Abstract

Specular and diffuse reflectivity and diffraction of x rays are used to probe polycrystalline films of xenon quench condensed onto a ${\mathrm{SiO}}_{2}\mathrm{}/\mathrm{S}\mathrm{i}\mathrm{}$ substrate. Measurements during deposition complement more extensive static measurements. Stable nonequilibrium structures are observed. We interpret our observations in terms of island growth and coalescence. Island separation and ultimate size are strongly temperature dependent. Coalescence has a pronounced effect at the lowest temperature studied (17 K) where islands are small and have large surface-to-volume ratios. We observe a concurrent increase in roughness and reduction in diffuse scattering, indicating a change in surface morphology. Continued deposition yields a highly disordered, porous structure on top of the dense coalesced layer. At 25 and 35 K bulk density films grow with a surface morphology that evolves only slowly from that determined before coalescence. Bulk diffusion allows intermixing and prevents a composite film structure like that observed at lower temperatures.