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Comprehensive structural studies of thin island Al films with a thickness of 20–50 nm deposited by magnetron sputtering on Si(111) substrates in an argon plasma at a pressure of 6 × 10–3 mbar and a temperature ranging from 20 to 500°C are presented. The morphology and microstructure of the films are studied using XRD, SEM, EDS, and TEM methods. It is found that most of the islands are Al {001} and Al {111} crystallites with lateral sizes of 10–100 nm, differently conjugated with the Si(111) substrate. At room temperature of the substrate, only Al {001} crystallites are epitaxially formed on it. The epitaxial growth of Al {111} crystallites is predominant as the substrate temperature increases above 400°C. The influence of the temperature of the Si(111) substrate on the process of epitaxial growth of crystallites, the dynamics of their shape, and structural perfection is shown. It is found that crystallites epitaxially connected to the substrate experience deformation at ε = 7 × 10–3 and ε = –2 × 10–3 for Al {001} and Al {111}, respectively. It is shown that for thin island Al films on Si(111), the dependence of the number of crystallization centers and the particle growth rate on the supercooling temperature is consistent with the band model of crystallization. At the same time, a shift in the characteristic temperatures for the zone boundaries is observed due to the properties of the substrate. This must be taken into account when engineering the surface morphology and structural perfection of crystallites in Al island magnetron films. [ABSTRACT FROM AUTHOR]

Temperature-gradient metalorganic chemical vapor deposition (MOCVD) was used to deposit InxGa1-xN/GaN multiple quantum well (MQW) structures with a concentration gradient of indium across the wafer. These MQW structures were deposited on low defect density (2 x 108 cm-2) GaN template layers for investigation of microstructural properties and V-defect (pinhole) formation. Room temperature (RT) photoluminescence (PL) and photomodulated transmission (PT)were used for optical characterization, which show a systematic decrease in emission energy for a decrease in growth temperature. Triple-axis x-ray diffraction (XRD), scanning electron microscopy, and cross-sectional transmission electron microscopy were used to obtain microstructural properties of different regions across the wafer. Results show that there is a decrease in crystal quality and an increase in V-defect formation with increasing indium concentration. A direct correlation was found between V-defect density and growth temperature due to increased strain and indium segregation for increasing indium concentration. [ABSTRACT FROM AUTHOR]

A corner-overgrown GaAs/AlGaAs heterostructure is investigated with transmission and scanning transmission electron microscopy, demonstrating self-limiting growth of an extremely sharp corner profile 3.5 nm wide. In the AlGaAs layers, we observe self-ordered diagonal stripes, precipitating exactly at the corner, which show increased Al content measured with x-ray spectroscopy. A quantitative model for self-limited growth is adapted to the present case of faceted molecular beam epitaxial growth, and the corner sharpness is discussed in relation to quantum confined structures. We note that corner overgrowth maintains nanometer sharpness after microns of growth, allowing corner-shaped nanostructures. [ABSTRACT FROM AUTHOR]

Ion-beam-synthesized 74Ge nanocrystals embedded in an amorphous silica matrix exhibit large compressive stresses in the as-grown state. The compressive stress is determined quantitatively by evaluating the Raman line shift referenced to the line position of free-standing nanocrystals. Postgrowth thermal treatments lead to stress reduction. The stress relief process is shown to be governed by the diffusive flux of matrix atoms away from the local nanocrystal growth region. A theoretical model that quantitatively describes this process is presented. [ABSTRACT FROM AUTHOR]

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012. [ABSTRACT FROM PUBLISHER]

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010. [ABSTRACT FROM PUBLISHER]

In situ transmission electron microscopy observations of nanowire morphologies indicate that during Au-catalyzed Ge nanowire growth, Ge facets can rapidly form along the nanowire sidewalls when the source gas (here, digermane) flux is decreased or the temperature is increased. This sidewall faceting is accompanied by continuous catalyst loss as Au diffuses from the droplet to the wire surface. We suggest that high digermane flux and low temperatures promote effective surface passivation of Ge nanowires with H or other digermane fragments inhibiting diffusion and attachment of Au and Ge on the sidewalls. These results illustrate the essential roles of the precursor gas and substrate temperature in maintaining nanowire sidewall passivation, necessary to ensure the growth of straight, untapered, 〈111〉-oriented nanowires. [ABSTRACT FROM AUTHOR]

We report a systematic and quantitative study of near-infrared intersubband absorption in strained AlGaN/GaN and lattice-matched AHnN/GaN superlattices grown by plasma-assisted molecular-beam epitaxy as a function of Si-doping profile with and without S doping. For AlGaN/GaN, we obtained good theoretical agreement with experimental measurements of transition energy, integrated absorbance and linewidth by considering many-body effects, interface roughness, and calculations of the transition lifetime that include dephasing. For the AHnN/GaN system, experimental measurements of the integrated absorbance due to the superlattice transitions produced values more than one order of magnitude lower than AlGaN/GaN heterostructures at similar doping levels. Furthermore, observed transition energies were roughly 150 meV higher than expected. The weak absorption and high transition energies measured in these structures is attributed to columnar alloy inhomogeneity in the AlInN barriers observed in high-angle annular dark-field scanning transmission electron microscopy. We simulated the effect of these inhomogeneities using three-dimensional band-structure calculations. The inhomogeneities were modeled as AlInN nanorods with radially varying In composition embedded in the barrier material of the superlattice. We show that inclusion of the nanorods leads to the depletion of the quantum wells (QWs) due to localization of charge carriers in high-in-containing regions. The higher energy of the intersubband transitions was attributed to the relatively uniform regions of the QWs surrounded by high Al (95%) composition barriers. The calculated transition energy assuming Al0.95ln0.05 N barriers was in good agreement with experimental results. [ABSTRACT FROM AUTHOR]

Ion-beam-synthesized 74Ge nanocrystals embedded in an amorphous silica matrix exhibit large compressive stresses in the as-grown state. The compressive stress is determined quantitatively by evaluating the Raman line shift referenced to the line position of free-standing nanocrystals. Postgrowth thermal treatments lead to stress reduction. The stress relief process is shown to be governed by the diffusive flux of matrix atoms away from the local nanocrystal growth region. A theoretical model that quantitatively describes this process is presented. [ABSTRACT FROM AUTHOR]