Results 1 - 10 of 12060
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[en] The effect of two-dimensional diatomic-island nucleation on the linear stability of the step morphology during molecular beam epitaxy is investigated numerically via shooting methods. It is found that the effect of diatomic islands on the step morphological stability is significant. The greater the effects of diatomic islands, the more stable the step morphology. Increasing capture efficiency can decrease the critical surface capillary length and shift the critical wave number toward short-wavelength regimes. The unstable region is shrunk with increasing capture efficiency. Further, increasing flux coverage and/or surface coverage can decrease the critical surface capillary length and shift the critical wave number toward short-wavelength regimes. (orig.)
[en] In the present paper the authors describe results of computer calculations of intensity distribution of beams by effusion holes. The calculation aims to determine intensity distribution of molecular beams in exposed target surface. 10 refs, 6 figs
[en] The molecular beam epitaxy, MBE, is a physical technique of synthesis in which a sheet of a solid increases, in a chamber of ultra-high vacuum, the reaction of atomic or molecular beams of its elementary components in the vapor phase, the impact these on a monocrystalline substrate which is kept at proper temperature. Using this technique, films are obtained high purity and excellent crystalline quality, in which the composition and can be alternating layers control up to a limit of one atomic layer. In the beginning was dedicated only to the manufacture of III-V semiconductor heterostructures, but quickly transcended other material systems. It is an ideal technique for heterostructures considered as model systems in solid state physics (quantum wells, superlattices, quantum wires and dots ...) and for manufacturing devices with advanced new design. In addition, the current convergence of disciplines to the ubiquitous nano technology, the deep knowledge gained on the fundamental phenomena involved in MBE growth of very different systems materials, allows use of the technique beyond its intrinsic ability to control the process in the direction of growth, and apply it to obtain ordered nano structures and networks grounds on the nano scale. (author) 12 refs.
[en] We investigate the influence of modified growth conditions during the spontaneous formation of GaN nanowires (NWs) on Si(111) in plasma-assisted molecular beam epitaxy. We find that a two-step growth approach, where the substrate temperature is increased during the nucleation stage, is an efficient method to gain control over the area coverage, average diameter, and coalescence degree of GaN NW ensembles. Furthermore, we also demonstrate that the growth conditions employed during the incubation time that precedes nanowire nucleation do not influence the properties of the final nanowire ensemble. Therefore, when growing GaN NWs at elevated temperatures or with low Ga/N ratios, the total growth time can be reduced significantly by using more favorable growth conditions for nanowire nucleation during the incubation time. (paper)
[en] We investigate experimentally and theoretically the band structure of the (In0.53Ga0.47As)1−z (In0.52Al0.48As)z digital alloy grown by using molecular beam epitaxy as a function of z, where z is defined by the thickness fraction of the InGaAs and the InAlAs layers lattice-matched to InP. To calculate the band structures of the InGaAs/InAlAs digital alloy, we used the 4 × 4 k·p method; then, we compared these band structures with the photoluminescence experimental results. These experimental and theoretical results show that the InGaAs/InAlAs digital alloy not only can contribute to the method of band-gap engineering by using various types of thickness combinations but also can cover the wavelength gap of 1.2 μm (1.1 μm (GaAs) <λ< 1.3 μm InP)), that only the quantum dot can cover. We also propose a quantum-well structure that is able to cover the wavelength gap.
[en] A rotor apparatus intended for the study of gas/surface interaction processes is presently nearing completion. The carbon fiber rotors under consideration are constructed with shapes derived from long thin cylindrical rods oriented with the longest axis in a horizontal plane, and spun in a horizontal plane about an axis which is perpendicular to the long axis and passes through the mid-point of the cylinder. The beam formation processes are discussed and rotor diagrams presented. Performance of these types of high speed rotor show them to have a very important future as sources of intermediate energy molecular beams
[en] For the Ga-assisted growth of GaAs nanowires on Si(111) substrates by molecular beam epitaxy, growth temperature, As flux, and Ga flux have been systematically varied across the entire window of growth conditions that result in the formation of nanowires. A range of GaAs structures was observed, progressing from pure Ga droplets under negligible As flux through horizontal nanowires, tilted nanowires, vertical nanowires, and nanowires without droplets to crystallites as the As flux was increased. Quantitative analysis of the resulting sample morphology was performed in terms of nanowire number and volume density, number yield and volume yield of vertical nanowires, diameter, length, as well as the number and volume density of parasitic growth. The result is a growth map that comprehensively describes all nanowire and parasitic growth morphologies and hence enables growth of nanowire samples in a predictive manner. Further analysis indicates the combination of global Ga flux and growth temperature determines the total density of all objects, whereas the global As/Ga flux ratio independently determines the resultant sample morphology. Several dependencies observed here imply that all objects present on the substrate surface, i.e. both nanowires and parasitic structures, originate from Ga droplets. (paper)
[en] Polarons are critical to our understanding of many condensed matter systems, but are difficult to observe and characterize. By combining cathodoluminescence spectroscopy measurements with insights from first-principles calculations, we have identified transitions involving two distinct and simultaneous polaronic states in relaxed Ba_xSr_1_−_xTiO_3 films grown by molecular beam epitaxy. These polaronic optical transitions arise from two discrete Ti-O-Ti bonding configurations simultaneously present in the system, one with a 180° bond angle and the other with buckled geometry due to octahedral tilting. By compositional modulation, we show that we can semi-quantitatively probe the population of each bonding configuration.
[en] We successfully grow high-quality wurtzite InAs nanowires on GaAs substrates. The influences of growth temperature and orientations of GaAs substrates on the morphology and microstructure of InAs nanowires are also investigated. We find that a low growth temperature (330°C) is beneficial to the synthesis of uniform defect-free InAs nanowires. Meanwhile, InAs nanowires along 〈111〉B direction are always dominated despite the variation of GaAs substrate orientations. (cross-disciplinary physics and related areas of science and technology)