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BTU
Vanadium dioxide (VO2) features a pronounced, thermally-driven metal-to-insulator transition at 340 K. Employing epitaxial stress on rutile TiO2(001) substrates, the transition can be tuned to occur close to room temperature. Striving for applications in oxide-electronic devices, the lateral homogeneity of such samples must be considered as an important prerequisite for efforts towards miniaturization. Moreover, the preparation of smooth surfaces is crucial for vertically stacked devices and, hence, the design of functional interfaces. Here, the surface morphology of VO2/TiO2(001) films was analyzed by low-energy electron microscopy and diffraction as well as scanning probe microscopy. The formation of large terraces could be achieved under temperature-induced annealing, but also the occurrence of facets was observed and characterized. Further, we report on quasi-periodic arrangements of crack defects which evolve due to thermal stress under cooling. While these might impair some applicational endeavours, they may also present crystallographically well-oriented nano-templates of bulk-like properties for advanced approaches.
The integration of Ge on Si for photonics applications has reached a high level of maturity: Ge photodetectors are available on the Si platform in foundry processes, and Si/Ge heterostructure multiple quantum-well photodiodes are rapidly progressing toward applications in light modulation. These successes result from decades of development of high-quality material growth and integration, which, more recently, has sparked an increasingly broad field of photonic device research based on Si/Ge heterostructures that extends from quantum cascade lasers to sensors. Here, we highlight selected recent structure and device developments as well as possible future trends that are enabled by the maturity of the SiGe material platform
Measuring the Discernibility of Virtual Objects in Conventional and Stylized Augmented Reality
(2006)
Experimental Investigation of Tip Vortex Formation Noise Produced by Wall-Mounted Finite Airfoils
(2021)
Research on the development of bullying is often based upon Bronfenbrenner’s socioecological model (Swearer & Hymel, 2015). Thus, various relevant contextual variables have been identified, including classroom climate and school climate (Thornberg et al., 2018; Zych et al., 2019). School climate has been defined in different ways, mostly including relationships between people in the school environment (Wang et al., 2016). Empirically, only the relationships between students (also summarised within the class as classroom climate) and between teachers and pupils are usually considered. However, teachers have been identified as particularly significant in the bullying process and as role models for students (Colpin et al., 2021). Because of this, it is assumed that relationships among teachers can also be significant risk factors for student bullying. In this study, we investigate communication climate among teachers as part of the school climate and its associations to student bullying. In addition, we follow Bronfenbrenner’s idea of interactions among contextual levels by considering both school climate and classroom climate and investigating moderation effects. Data was collected from more than 550 teachers and 2,000 students in 114 classes at 24 schools in Germany. The analyses involved three-level hierarchical binary
regression analyses and cross-level interaction models. Findings suggest that staff communication climate is not associated directly with students’ experiences with bullying, but that the worse
staff communication climate, the more students bully others in classrooms with high rates of rivalry (cross-level moderation). The associations will further be analysed under consideration of relevant control variables. Final results will be presented at the conference. The study broadens the contextual perspective on bullying by including more than one level at once and supports the importance of a whole-school perspective on bullying.
Unintentional p-type conductivity in intrinsic Ge-rich SiGe/Ge heterostructures grown on Si(001)
(2023)
Direct-band-gap Germanium-Tin alloys (Ge1-xSnx) with high carrier mobilities are promising materials for nano- and optoelectronics. The concentration of open volume defects in the alloy, such as Sn and Ge vacancies, influences the final device performance. In this article, we present an evaluation of the point defects in molecular-beam-epitaxy grown Ge1-xSnx films treated by post-growth nanosecond-range pulsed laser melting (PLM). Doppler broadening – variable energy positron annihilation spectroscopy and variable energy positron annihilation lifetime spectroscopy are used to investigate the defect nanostructure in the Ge1-xSnx films exposed to increasing laser energy density. The experimental results, supported with ATomic SUPerposition calculations, evidence that after PLM, the average size of the open volume defects increases, which represents a raise in concentration of vacancy agglomerations, but the overall defect density is reduced as a function of the PLM fluence. At the same time, the positron annihilation spectroscopy analysis provides information about dislocations and Ge vacancies decorated by Sn atoms. Moreover, it is shown that the PLM reduces the strain in the layer, while dislocations are responsible for trapping of Sn and formation of small Sn-rich-clusters.