Abstract
The formation of GaSb nanopillars by low energy ion sputtering is studied in real-time by spectroscopic Mueller matrix ellipsometry, from the initial formation in the smooth substrate until nanopillars with a height of 200-300 nm are formed. As the nanopillar height increased above 100 nm, coupling between orthogonal polarization modes was observed. Ex situ angle resolved Mueller polarimetry measurements revealed a 180° azimuth rotation symmetry in the off-diagonal Mueller elements, which can be explained by a biaxial material with different dielectric functions εx and εy in a plane parallel to the substrate. This polarization coupling can be caused by a tendency for local direction dependent alignment of the pillars, and such a tendency is confirmed by scanning electron microscopy. Such observations have not been made for GaSb nanopillars shorter than 100 nm, which have optical properties that can be modeled as a uniaxial effective medium.
Highlights
Spectroscopic ellipsometry (SE) has proved to be an efficient tool for real-time observation of the formation of nanostructured surfaces, e.g. the height evolution of GaSb nanopillars has been monitored during ion sputtering [1]
In this study we report real-time in situ spectroscopic Mueller matrix measurements of GaSb during ion sputtering: from the initial formation in the smooth substrate, until pillars with heights of 200 − 300 nm are formed
The formation of GaSb nanopillars by sputtering with 500 eV Ar+ ions has been monitored in real-time by Mueller matrix ellipsometry
Summary
Spectroscopic ellipsometry (SE) has proved to be an efficient tool for real-time observation of the formation of nanostructured surfaces, e.g. the height evolution of GaSb nanopillars has been monitored during ion sputtering [1]. For reflections from an anisotropic material, there will in general be coupling between orthogonal field components To fully characterize this coupling it is necessary to do generalized ellipsometry or Mueller matrix ellipsometry [4]. GaSb nanopillars prepared by sputtering with normal ion incidence, with a height less than 100 nm, have earlier been reported not to result in coupling between orthogonal polarization components, and to be modelled as a uniaxial effective material with the optic axis normal to the substrate [1]. In this study we report real-time in situ spectroscopic Mueller matrix measurements of GaSb during ion sputtering: from the initial formation in the smooth substrate, until pillars with heights of 200 − 300 nm are formed. To our knowledge, generalized ellipsometry or Mueller matrix ellipsometry studies of an anisotropic nanostructured surface have not been performed in real-time before
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