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Germanium dioxide (GeO2) is a versatile material with several different crystalline polymorphs and interesting applications in, e.g., optics, microelectronics, and Li-ion batteries. In particular, many of the material's properties depend on the size of the prepared crystallites, and thus, nanocrystalline GeO2 is of special interest. Here, GeO2 nanoparticles are prepared via sol–gel processes by the hydrolysis of Ge isopropoxide (Ge(OCH(CH3)2)4). The precipitated powders are dried at room temperature and annealed in ambient air using temperatures between 500 °C and 1000 °C from 3 to 24 h. The samples were characterized by X-ray diffraction, X-ray absorption fine structure spectroscopy, and scanning electron microscopy, providing the crystalline structures, the phase composition, as well as the morphology and crystallite size of the formed particles and their changes upon heating. According to the structural analysis, the samples are crystalline with a dominant β- (low temperature) quartz phase without any heat treatment directly after drying and increasing contributions of α- (high-temperature modification) quartz and quartz-like GeO2 structures with increasing temperature and annealing time were found. According to electron microscopy and the X-ray analysis, the particle size ranges from about 40 to 50 nm for the pristine particles and to about 100 nm and more for the annealed materials. [ABSTRACT FROM AUTHOR]

The sputter deposition and the growth of thin copper films on float glass substrates are in situ studied using grazing incidence, reflection mode X‐ray absorption fine structure spectroscopy with subsecond time resolution. The experimental data are compared with model calculations, assuming the presence of crystalline, face‐centered cubic metallic Cu nanostructures. From a detailed analysis of the measured spectra, the film thickness as well as the surface roughness is determined, leading to a detailed understanding of the films growth as a function of the sputter deposition time. In particular, different stages of film growth can clearly be distinguished from the fits of the experimental data. The results suggest the formation of isolated, approximately nm‐sized copper clusters in the initial phase of the film deposition for the first few seconds, a coalescence phase with a nominal thickness of ≈1.5−2.8 nm, constant roughness of about 1.4 nm for the subsequent ≈5 s, and finally 3D growth of the Cu crystallites in the film for later stages of film growth. Further prospects of the methodology are given. [ABSTRACT FROM AUTHOR]

The molecular second order nonlinear optical properties of lanthanate complexes serving as counteranion to a hemicyanine chromophore as nonlinearity moiety is determined. The relative impact of f-orbital filling and ligands on the molecular second-order nonlinear optical response of lanthanate complexes is reported.

The fast solid-solid transformations with millisecond time resolution is investigated using piezo X-ray absorption spectra (XAFS) technique in combination with an in situ cell. The technique records X-ray absorption spectra in a continuous mode by making use of piezo tilt tables in the X-ray monochromator, which are actuated by an oscillatory high voltage.

Cu2ZnSnS4 solar cells deposited by thermal co-evaporation have been characterized structurally and electronically to determine the dependence of the electronic properties on the elemental composition of the kesterite phase, which can significantly deviate from the total sample composition. To this end, the kesterite phase content and composition were determined by a combination of X-ray fluorescence and X-ray absorption measurements. The electronic properties, such as carrier density and minority carrier diffusion length, were determined by electron beam induced current measurements and capacitance-voltage profiling. The charge-carrier transport properties are found to strongly depend on the Cu/(Sn+Zn) ratio of the kesterite phase. For the Cu-poor sample, a minority carrier diffusion length of 270 nm and a total collection length of approx. 500 nm are deduced, indicating that current collection should not be an issue in thin devices. [ABSTRACT FROM AUTHOR]

The methanation of CO2 within the power-to-gas concept was investigated under fluctuating reaction conditions to gather detailed insight into the structural dynamics of the catalyst. A 10 wt % Ni/Al2O3 catalyst with uniform 3.7 nm metal particles and a dispersion of 21% suitable to investigate structural changes also in a surface-sensitive way was prepared and characterized in detail. Operando quick-scanning X-ray absorption spectroscopy (XAS/QEXAFS) studies were performed to analyze the influence of 30 s and 300 s H2 interruptions during the methanation of CO2 in the presence of O2 impurities (technical CO2). These conditions represent the fluctuating supply of H2 from renewable energies for the decentralized methanation. Short-term H2 interruptions led to oxidation of the most reactive low-coordinated metallic Ni sites, which could not be re-reduced fully during the subsequent methanation cycle and accordingly caused deactivation. Detailed evaluation of the extended X-ray absorption fine structure (EXAFS) spectra showed surface oxidation/reduction processes, whereas the core of the Ni particles remained reduced. The 300-s H2 interruptions resulted in bulk oxidation already after the first cycle and a more pronounced deactivation. These results clearly show the importance and opportunities of investigating the structural dynamics of catalysts to identify their mechanism, especially in power-to-chemicals processes using renewable H2. [ABSTRACT FROM AUTHOR]