Inspired via the dandelion structure which has multi-dimensional channels facilitating the transport of fluids, bilayer TS-1@dandelion-SiO.sub.2 and hollow HTS@dandelion-SiO.sub.2 were successfully ...synthesized via an hydrothermal strategy including core TS-1 or HTS particles synthesis and an epitaxial growth of regular SiO.sub.2 shell. TS-1@dandelion-SiO.sub.2 or hollow HTS@dandelion-SiO.sub.2 possessed a ca. 300 nm core with ca. 100-200 nm of SiO.sub.2 shell with perpendicular channels, this hierarchical structure facilitated reactants/products transportation, and the structured SiO.sub.2 shell triggered the size of TS-1 or HTS and increased to ~ 800 nm, which was beneficial for nanosized crystals separation and recovery from the reaction system. Particularly, the epitaxial SiO.sub.2 shell increased Lewis acid sties on TS-1 and HTS external surface enhancing cyclohexene conversion. Further, the relationship between SiO.sub.2 shell morphology and catalytic activity was explored through the synthesis of HTS@inordinance-SiO.sub.2 with irregular SiO.sub.2 shell indicating the superiority of oriented channels originated from regular SiO.sub.2 shell.
Fast near-IR (NIR) emitters are highly valuable in telecommunications and biological imaging. The most established NIR emitters are epitaxially grown Insub.xGasub.1−xAs quantum dots (QDs), but ...epitaxial growth has several disadvantages. Colloidal synthesis is a viable alternative that produces a few NIR-emitting materials, but they suffer from long photoluminescence (PL) times. These long PL times are intrinsic in some NIR materials (PbS, PbSe) but are attributed to emission from bright trapped carrier states in others. We show that Cdsub.3Psub.2 QDs possess substantial trap emission with radiative times >10sup.1 ns. Surface passivation through shell growth or coordination of Lewis acids is shown to accelerate the NIR emission from Cdsub.3Psub.2 QDs by decreasing the amount of trap emission. This finding brings us one step closer to the application of colloidally synthesized QDs as quantum emitters.
Three-dimensional topological insulators (3D-TIs) are a new generation of materials with insulating bulk and exotic metallic surface states that facilitate a wide variety of ground-breaking ...applications. However, utilization of the surface channels is often hampered by the presence of crystal defects, such as antisites, vacancies, and twin domains. For terahertz device applications, twinning is shown to be highly deleterious. Previous attempts to reduce twins using technologically important InP(111) substrates have been promising, but have failed to completely suppress twin domains while preserving high structural quality. Here we report growth of twin-free molecular beam epitaxial Bisub.2Sesub.3 and Sbsub.2Tesub.3 structures on ultra-thin Insub.2Sesub.3 layers formed by a novel selenium passivation technique during the oxide desorption of smooth, non-vicinal InP(111)B substrates, without the use of an indium source. The formation of un-twinned Insub.2Sesub.3 provides a favorable template to fully suppress twin domains in 3D-TIs, greatly broadening novel device applications in the terahertz regime.
The n.sup.+-InAs/n.sup.0-InAs.sub.1 - .sub.ySb.sub.y/p-InAsSbP heterostructures with asymmetric band offsets at the heteroboundaries of the active region have been grown by vapor-phase epitaxy from ...organometallic compounds on InAs substrates. The forward branch of the current-voltage characteristics of the obtained heterostructures at low temperatures has segments with the tunneling conduction. The energy-band diagram of the double InAs/InAs.sub.1 - .sub.ySb.sub.y/InAsSbP heterostructure is calculated in the range of compositions (y < 0.2) of the narrow-gap active region. The InAs.sub.1 - .sub.ySb.sub.y/InAsSbP heterojunction is shown to be a II type heterojunction in this composition range. The electroluminescence observed in the experiment for the n.sup.+-InAs/n.sup.0-InAs.sub.1 â .sub.ySb.sub.y/p-InAsSbP heterostructures with the active region in compositions y > 0.14 is due to interface radiative transitions with participation of localized hole states at the II type heteroboundary.
In this study, the structural and electrical properties of orthorhombic κ-Gasub.2Osub.3 films prepared using Halide Vapor Phase Epitaxy (HVPE) on AlN/Si and GaN/sapphire templates were studied. For ...κ-Gasub.2Osub.3/AlN/Si structures, the formation of two-dimensional hole layers in the Gasub.2Osub.3 was studied and, based on theoretical calculations, was explained by the impact of the difference in the spontaneous polarizations of κ-Gasub.2Osub.3 and AlN. Structural studies indicated that in the thickest κ-Gasub.2Osub.3/GaN/sapphire layer used, the formation of rotational nanodomains was suppressed. For thick (23 μm and 86 μm) κ-Gasub.2Osub.3 films grown on GaN/sapphire, the good rectifying characteristics of Ni Schottky diodes were observed. In addition, deep trap spectra and electron beam-induced current measurements were performed for the first time in this polytype. These experiments show that the uppermost 2 µm layer of the grown films contains a high density of rather deep electron traps near Esub.c − 0.3 eV and Esub.c − 0.7 eV, whose presence results in the relatively high series resistance of the structures. The diffusion length of the excess charge carriers was measured for the first time in κ-Gasub.2Osub.3. The film with the greatest thickness of 86 μm was irradiated with protons and the carrier removal rate was about 10 cmsup.−1, which is considerably lower than that for β-Gasub.2Osub.3.
Asymmetric n-InAs/InAs.sub.(1 - .sub.y)Sb.sub.y/p-InAsSbP heterostructures with a narrow-gap active layer and a composition range y = 0.09-0.16 were grown by vapor phase epitaxy from metalorganic ...compounds. Room-temperature electroluminescence was observed at a wavelength of up to lambda = 5.1 m at a spectral maximum. The study of low-temperature electroluminescence spectra provided the possibility to establish the existence of two radiative recombination channels caused by the nature of the InAsSb/InAsSbP heterointerface. The effect produced by the chemistry of the active layer on the composition of the grown barrier layer and the formation of the InAsSb/InAsSbP heterojunction with an increase in the antimony content in the InAsSb solid solution was demonstrated.
High-quality VO.sub.2 films with precisely controlled thicknesses were grown on sapphire substrates by plasma-assisted oxide molecular beam epitaxy (MBE). To evaluate the degradation of ...semiconductor-metal transition (SMT) behavior of VO.sub.2 films under solar radiation, the temperature-driven SMT was investigated by measuring the electrical resistance during heating and cooling processes under solar simulator AM1.5, which provided illumination approximately matching the natural sunlight. The distinct reversible SMTs were observed for all the samples, whereas a remarkably conflicting trend in resistance change for extremely thin and thick samples was observed after exposure to the sunlight soaking system. The corresponding mechanism was proposed based on sunlight-induced resistance changes due to the transformation in the electron correlation and structural symmetry. The results might be especially attractive for some specific applications of VO.sub.2 films where solar radiation was inevitable.
For ABO.sub.3 perovskites, the magnetic and electronic properties couple strongly to the BO.sub.6 octahedral rotations and distortions. Therefore, precise control of the octahedral rotations and ...distortions via epitaxial strain and interfacial octahedral connectivity has become the key for engineering novel functionalities in ABO.sub.3 heterostructures and superlattices. In this paper, we investigated the local octahedral rotations in a (1 unit cell (u.c.)//4 u.c.) x 13 LaNiO.sub.3/LaGaO.sub.3 superlattice grown on a (001) SrTiO.sub.3 substrate. By using aberration-corrected high-resolution transmission electron microscopy, we found that the octahedral rotations of NiO.sub.6 adopted the same 100 and 010 rotational magnitudes as the neighboring GaO.sub.6 till the surface of the superlattice. Our results indicate that in LaNiO.sub.3-based superlattices, the NiO.sub.6 rotations can be precisely controlled via interfacial octahedral connectivity when the thickness of the LaNiO.sub.3 layer is only 1 unit cell.
