Investigation of pre-structured GaAs surfaces for subsequent site-selective InAs quantum dot growth

In this study, we investigated pre-structured (100) GaAs sample surfaces with respect to subsequent site-selective quantum dot growth. Defects occurring in the GaAs buffer layer grown after pre-structuring are attributed to insufficient cleaning of the samples prior to regrowth. Successive cleaning steps were analyzed and optimized. A UV-ozone cleaning is performed at the end of sample preparation in order to get rid of remaining organic contamination

Investigation of pre-structured GaAs surfaces for subsequent site-selective InAs quantum dot growth

<p>Abstract</p> <p>In this study, we investigated pre-structured (100) GaAs sample surfaces with respect to subsequent site-selective quantum dot growth. Defects occurring in the GaAs buffer layer grown after pre-structuring are attributed to insufficient cleaning of the samples prior to regrowth. Successive cleaning steps were analyzed and optimized. A UV-ozone cleaning is performed at the end of sample preparation in order to get rid of remaining organic contamination.</p

Ultraviolet photoluminescence of ZnO quantum dots sputtered at room-temperature

We observe ultraviolet photoluminescence from sputtered ZnO quantum dots which are fabricated with no annealing steps. The nanocrystals are embedded in amorphous SiO2 and exhibit a narrow size distribution of 3.5 ± 0.6 nm. Photoluminescence and transmittance measurements show a shift of ultraviolet emission and absorption of the dots compared to bulk ZnO material. This work paves the way for cheap nanooptical devices in the ultraviolet which are fabricated in a single sputtering run

Melting-Induced Evolution of Morphology, Entanglement Density, and Ultradrawability of Solution-Crystallized Ultrahigh-Molecular-Weight Polyethylene

The melting-induced change in the density of physical network junctions, which are formed by chain entanglements and network junctions due to anchoring of chain segments to crystals, is studied by 1H NMR T2 relaxometry for solution- and melt-crystallized ultrahigh-molecular-weight polyethylene (UHMWPE), sc-UH, and mc-UH, respectively. The NMR results are complemented by real-time synchrotron wide- and small-angle X-ray scattering (WAXS and SAXS) analyses to extract the sizes of the crystalline lamellae and intercrystalline domains. Below the melting temperature, the network of physical junctions is denser in the amorphous phase of mc-UH than the one in sc-UH owing to a lower entanglement density and a smaller number of physical junctions from polymer crystals in sc-UH. However, the difference in the total density of physical junctions between mc-UH and sc-UH films decreases with decreasing crystallinity during melting. At the end of the melting trajectory, at vanishing crystallinity, the volume-average entanglement density, as characterized by the NMR method, is approximately the same in sc- and mc-UH. This indicates that the entanglement density in sc-UH films increases during melting owing to the fast buildup of local chain entanglements. These entanglements are formed by segments of the same chain, neighboring chains, or both due to a displacement of chain fragments upon lamellar thickening and due to the so-called “chain explosion” that occurs locally in the amorphous domains. The increase in the entanglement density in sc-UH is additionally confirmed by the solid-state drawability of sc-UH films that were annealed in the melting region but below the end of melting. The maximum draw ratio decreases and the drawing stress increases with the increasing annealing temperature