Self-Ordered Voids Formation in SiO2 Matrix by Ge Outdiffusion

The annealing behavior of very thin SiO2/Ge multilayers deposited on Si substrate by e-gun deposition in high vacuum was explored. It is shown that, after annealing at moderate temperatures (800°C) in inert atmosphere, Ge is completely outdiffused from the SiO2 matrix leaving small (about 3 nm) spherical voids embedded in the SiO2 matrix. These voids are very well correlated and formed at distances governed by the preexisting multilayer structure (in vertical direction) and self-organization (in horizontal direction). The formed films produce intensive photoluminescence (PL) with a peak at 500 nm. The explored dynamics of the PL decay show the existence of a very rapid process similar to the one found at Ge/SiO2 defected interface layers

A Grazing-Incidence Small-Angle X-Ray Scattering View of Vertically Aligned ZnO Nanowires

We report a grazing-incidence small-angle X-ray scattering study of ZnO films with vertically aligned and randomly distributed nanowires, grown through a hydrothermal growth process on nanostructured ZnO seeding coatings and deposited by electron beam evaporation on silicon and glass, respectively. The comparison of the scattering patterns of seeding coatings and nanowires showed that the scattering of vertically aligned nanowires exhibited a specific feature: the dominant characteristic of their scattering patterns is the appearance of fine structure effects around the specular peak. These effects were clarified by the combined reflection and scattering phenomena, suggested for the aligned nanowires-substrate system. Furthermore, they enabled the calculation of the average gyration radius of nanowires in horizontal direction. The calculated value was in good agreement with the radii of nanowires estimated by surface electron microscopy. Therefore, the observed feature in the scattering pattern can serve as evidence of the aligned growth of nanowires

GISAXS/GIXRD View of ZnO Films with Hierarchical Structural Elements

ZnO films constituted of porous sheet-like structures, formed by calcination of precursor, were examined using scanning electron microscopy and simultaneous small-angle scattering and diffraction of the synchrotron-sourced X-rays, under the grazing-incidence conditions. The presented analysis enabled insight into the complexity of the film morphology, which revealed substrate sensitivity on the microscopic and nanoscopic length scales. The average size and spatial arrangement of nanoparticles, single-crystal domains, and the average size and features of nanopores in sheet-like structures were determined for films deposited on glass, polycrystalline ZnO layer, and silicon

Stress Evolution during Ge Nanoparticles Growth in a SiO₂ Matrix

Superstructures are explored that were obtained by multilayer magnetron deposition at room temperature of 20 SiO2 and SiO2:Ge bilayers, each 2 × 4 nm thick, and subsequently annealed in inert N2 atmosphere at different temperatures in the range of 500–750 °C. The structural and optical changes induced by annealing and the formation and growth of Ge nanoparticles (nps) from early clusters to their full growth and final dissolution were studied by the simultaneous grazing-incidence small- and wide-angle X-ray scattering, transmission electron microscopy, and (time-resolved) photoluminescence (PL). It is shown that in as-deposited multilayers aggregation of small clusters already occurred, and the clusters were reasonably well intercorrelated in the lateral plane. During annealing at Ta = 550 °C or higher temperatures, Ge nps start to form and remain partly amorphous at lower Ta but crystallize completely at about 600 °C. At even higher temperatures, the Ge nps dissolve and Ge diffuses out almost completely, leaving voids in the SiO2 matrix. Visible PL from the samples was detected and attributed to defects in the nps/matrix interface layers rather than to the nps itself because PL persisted even after Ge nps dissolution

Formation of isolated Ge nanoparticles in thin continuous Ge/SiO₂ multilayers

A simple and reliable e-gun assisted physical vapor deposition technique was used to deposit alternatively amorphous thin (2 nm) continuous layers of Ge and SiO2 in high vacuum. Our goal was to explore whether annealing of these multilayers in inert atmosphere at rather low temperature (525 °C) will produce isolated sphere-like Ge nanoparticles embedded in amorphous SiO2 matrix suitable for solar cell applications, and which analyzing technique will provide the most comprehensive information on this composite material. All samples were characterized by the following complementary techniques: grazing incidence X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM) and grazing incidence small-angle X-ray scattering (GISAXS). All techniques confirm Ge nanoparticles formation. It was demonstrated that GISAXS provides the most detailed description of the particle size and shape on a macroscopic scale. © 2020 Elsevier Lt