Bleckenwegner Petra, Mardare Cezarina Cela, Cobet Christoph, Kollender Jan Philipp, Hassel Achim Walter, Mardare Andrei Ionut
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.
ACS Comb Sci. 2017 Feb 13;19(2):121-129. doi: 10.1021/acscombsci.6b00162. Epub 2017 Jan 3.
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 NbO and TiO with both amorphous and crystalline phases is concluded, whereas the possibility of complex NbTiO oxide formation during anodization is unlikely.
通过可变角度光谱椭偏仪（VASE）对在薄膜母体金属组合库上阳极生长的Nb-Ti混合氧化物进行光学带隙映射。为此，使用了通过共溅射沉积的从Nb-90原子百分比Ti到Nb-15原子百分比Ti的宽Nb-Ti成分范围。Nb-Ti库在高达10V SHE的电位下逐步进行阳极氧化，并且以2原子百分比的分辨率沿着Nb-Ti库映射阳极氧化物的光学性质。通过调整沉积参数，使沿着Nb-Ti成分梯度的表面差异最小化，从而允许基于单个Tauc-Lorentz振荡器对混合Nb-Ti氧化物进行数据拟合描述。沿着整个成分范围对Nb-Ti氧化物光学带隙进行映射显示，与基于按原子分数比例混合单个Nb和Ti电负性的线性模型存在明显偏差。这归因于混合氧化物的强烈非晶化和深度成分梯度。在大约50原子百分比的Nb处，确定了光学带隙系统地降低至低至2.0eV的值。得出结论，NbO和TiO在非晶相和晶相中均发生混合，而在阳极氧化过程中形成复杂NbTiO氧化物的可能性不大。
