Hansjörg Weis

Structural and optical properties of thin zirconium oxide films prepared by reactive direct current magnetron sputtering

Thin films of zirconium oxide have been deposited onto glass and Si(100) substrates at room temperature by reactive dc magnetron sputtering of a metallic Zr target in an argon–oxygen atmosphere. The films were characterized by Rutherford backscattering spectroscopy, x-ray diffraction, x-ray reflectometry, atomic force microscopy, and optical spectroscopy to investigate the variation of stoichiometry, structure, density, and optical properties upon increasing oxygen partial pressure. The Zr target shows a well-defined hysteresis upon varying the oxygen pressure as determined by quartz crystal microbalance measurements. Rutherford backscattering experiments reveal that the films are metallic with a small amount of oxygen incorporation at oxygen flows well below 2.7 sccm. Stoichiometric ZrO2 films, however, are formed above 2.8 sccm O2 flow (oxidic mode). Grazing angle incidence x-ray diffraction studies show that crystalline ZrO2 films with monoclinic structure grow in this oxygen flow regime. X-ray reflect...

Gasochromic switching of tungsten oxide films: a correlation between film properties and coloration kinetics

Optically switchable coatings based on tungsten oxide offer a wide variety of promising applications, such as the dynamic variation of transmission in smart windows. Our research focuses on the gasochromic switching of amorphous tungsten oxide (WOx) films with a palladium catalyst cap-layer, where coloration takes place in a gas atmosphere with diluted hydrogen and bleaching can be achieved by an oxygen containing gas. The samples are produced by DC-magnetron-sputtering and show a laterally inhomogeneous switching behaviour where the coloration speed varies over more than one order of magnitude. To understand this phenomenon, the films were analyzed by optical spectroscopy with spatial resolution and subsequent simulation of their dielectric function. The switching kinetics of the films could be correlated to the index of refraction n: regions with high n did not switch, whereas regions with lower n showed fast switching behaviour. Since n is linked to the film density via the Lorenz–Lorentz equation, this implies that films with a low-density switch much faster than high-density films. Finally, a model to explain the observed lateral inhomogeneous deposition and coloration velocity is presented.

Defect formation upon reactive direct-current magnetron sputtering of GeO2 films

Defect formation upon reactive direct-current magnetron sputtering of GeO2 films has been studied using x-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive x-ray (EDX) analysis, as well as atomic force microscopy and optical microscopy. The density of the defects shows a clear correlation with oxygen flow rate. High defect densities are observed for flow rates above approximately 27.5 sccm, where a transition of film structure is observed. XRD analysis identifies the defects as Ge crystallites. Defect formation is intimately related to the formation of whiskerlike structures on the target in the vicinity of the erosion zone and arcing in the same area. SEM imaging in conjunction with EDX allows a detailed understanding of defect formation.