title: Compositionally Dependent Nonlinear Optical Bandgap Behavior of Mixed Anodic Oxides in Niobium-Titanium System.
abstract: Optical bandgap mapping of Nb-Ti mixed oxides anodically grown on a thin film parent metallic combinatorial library was performed via variable angle spectroscopic ellipsometry (VASE). A wide Nb-Ti compositional spread ranging from Nb-90 at.% Ti to Nb-15 at.% Ti deposited by cosputtering was used for this purpose. The Nb-Ti library was stepwise anodized at potentials up to 10 V SHE, and the anodic oxides optical properties were mapped along the Nb-Ti library with 2 at.% resolution. The surface dissimilarities along the Nb-Ti compositional gradient were minimized by tuning the deposition parameters, thus allowing a description of the mixed Nb-Ti oxides based on a single Tauc-Lorentz oscillator for data fitting. Mapping of the Nb-Ti oxides optical bandgap along the entire compositional spread showed a clear deviation from the linear model based on mixing individual Nb and Ti electronegativities proportional to their atomic fractions. This is attributed to the strong amorphization and an in-depth compositional gradient of the mixed oxides. A systematic optical bandgap decrease toward values as low as 2.0 eV was identified at approximately 50 at.% Nb. Mixing of Nb2O5and TiO2with both amorphous and crystalline phases is concluded, whereas the possibility of complex NbaTibOyoxide formation during anodization is unlikely.
authors.affiliation: Institute for Chemical Technology of Inorganic Materials, ‡Christian Doppler Laboratory for Combinatorial Oxide Chemistry at the Institute for Chemical Technology of Inorganic Materials, and §Center of Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz , Altenberger Straße 69, 4040 Linz, Austria.
authors.forename: Petra
authors.initials: P
authors.lastname: Bleckenwegner
authors.affiliation: Institute for Chemical Technology of Inorganic Materials, ‡Christian Doppler Laboratory for Combinatorial Oxide Chemistry at the Institute for Chemical Technology of Inorganic Materials, and §Center of Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz , Altenberger Straße 69, 4040 Linz, Austria.
authors.forename: Cezarina Cela
authors.initials: CC
authors.lastname: Mardare
authors.affiliation: Institute for Chemical Technology of Inorganic Materials, ‡Christian Doppler Laboratory for Combinatorial Oxide Chemistry at the Institute for Chemical Technology of Inorganic Materials, and §Center of Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz , Altenberger Straße 69, 4040 Linz, Austria.
authors.forename: Christoph
authors.initials: C
authors.lastname: Cobet
authors.affiliation: Institute for Chemical Technology of Inorganic Materials, ‡Christian Doppler Laboratory for Combinatorial Oxide Chemistry at the Institute for Chemical Technology of Inorganic Materials, and §Center of Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz , Altenberger Straße 69, 4040 Linz, Austria.
authors.forename: Jan Philipp
authors.initials: JP
authors.lastname: Kollender
authors.affiliation: Institute for Chemical Technology of Inorganic Materials, ‡Christian Doppler Laboratory for Combinatorial Oxide Chemistry at the Institute for Chemical Technology of Inorganic Materials, and §Center of Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz , Altenberger Straße 69, 4040 Linz, Austria.
authors.forename: Achim Walter
authors.initials: AW
authors.lastname: Hassel
authors.affiliation: Institute for Chemical Technology of Inorganic Materials, ‡Christian Doppler Laboratory for Combinatorial Oxide Chemistry at the Institute for Chemical Technology of Inorganic Materials, and §Center of Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz , Altenberger Straße 69, 4040 Linz, Austria.
authors.forename: Andrei Ionut
authors.identifier: 0000-0003-4137-1994
authors.initials: AI
authors.lastname: Mardare
mesh_terms: D000497:Alloys / Q000737:chemistry*; D003460:Crystallization; D055664:Electrochemical Techniques; D004566:Electrodes; D009556:Niobium / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D000497:Alloys; D010087:Oxides; D009556:Niobium; C009495:titanium dioxide; D014025:Titanium; C073337:niobium pentoxide
keywords: bandgap; mixed anodic oxides; spectroscopic ellipsometry; thin films; valve metal alloys