title: Real-time in situ Mueller matrix ellipsometry of GaSb nanopillars: observation of anisotropic local alignment.
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.
authors.affiliation: Physics Department, Norwegian University of Science and Technology (NTNU) NO-7491 Norway. ingar.nerbo@ntnu.no
authors.forename: Ingar Stian
authors.initials: IS
authors.lastname: Nerbø
authors.forename: Sebastien
authors.initials: S
authors.lastname: Le Roy
authors.forename: Martin
authors.initials: M
authors.lastname: Foldyna
authors.forename: Elin
authors.initials: E
authors.lastname: Søndergård
authors.forename: Morten
authors.initials: M
authors.lastname: Kildemo
mesh_terms: D016880:Anisotropy; D000965:Antimony / Q000737:chemistry*; D005708:Gallium / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D008859:Microscopy, Polarization / Q000379:methods*; D008962:Models, Theoretical; D049329:Nanostructures; D036103:Nanotechnology / Q000379:methods*
chemical_list: D000965:Antimony; D005708:Gallium