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Many strategies have been adopted to improve the photoinduced features of zinc oxide nanostructures for different application fields. In this work, zinc oxide has been synthesised and decorated by plasmonic metal nanoparticles to enhance its photocatalytic activity in the visible range. Furthermore, an insulating layer of SiO

cm/s) surface carrier recombination ve-locity of GaAs and the nanowire large surface-to-volume ratios, effective and long-term stable passivation of GaAs surface states is however, necessary. A common approach is to overgrow a wider bandgap AlGaAs shell around GaAs nanowires. GaAs–AlGaAs core–shell nanowires thus show strong enhancement of luminescence intensity, improved minority carrier diffusion lenghts, and recombi-nation lifetimes with respect to bare GaAs nanowires [3, 4]. Also, the small lattice mismatch between the two materials may induce elastic strain fields and piezo-electric effects along the nanowire [111] axial direction; recently, Hocevar et al. [4] demonstrated the occurrence of systematic red-shifts in the core luminescence of molecular beam epitaxy (MBE) grown GaAs–Al

Group III–V compound semiconductor nanowires with radial modulation of the materials composition and/or doping in the form of core–shell and core–multishell nanowire heterostructures show promise as novel and high-performance nano-scale light emitting diodes, lasers, photodetectors and solar cells. Strict control over the growth of such radially heterostructured nanowires is, however, necessary. We report the experimental dependence of AlGaAs shell growth by metalorganic vapor phase epitaxy (MOVPE) around free-standing Au-catalysed GaAs nanowires on the relevant sizes and densities of the nanostructures. A model based on (i) the vapor mass transport of group III species, and (ii) perfect conformality between the nanowires and the substrate of AlGaAs deposition is proposed and validated, describing the observed MOVPE growth dynamics of the shell material around dense ensembles of GaAs nanowires. We predict the complex (non-linear) dependence of the shell growth rate on the initial GaAs nanowire diameters (i.e., initial Au catalyst nanoparticle size), heights, local densities on the substrate, and deposition time, which is in very good agreement with experimental data; in particular, a monotonic decrease of AlGaAs shell thickness is expected and observed with increasing nanowire density.

This work deals with the deposition of lead (Pb) thin films by the UV pulsed laser ablation technique, for their further use as photocathode devices in superconducting radio frequency guns. Scanning electron microscopy and atomic force microscopy analyses were performed to study the morphological features of Pb thin films deposited on Si (100) and Nb substrates. The films showed a granular structure with a nearly fully covered surface only for that one deposited on Nb substrate. X-ray diffraction measurements indicate the growth of polycrystalline Pb thin films with a preferential orientation along (111) planes. Results of the photoemission performance of Pb thin film deposited on Nb substrate showed a very encouraging average value of quantum efficiency of 6 x 10(-5) through a single-photon absorption process, promoting further studies in the realisation of Pb photocathodes by this technique

We report on the pyrolytic metalorganic vapour phase epitaxy of ZnSe, ZnS and ZnSSe by using diethyldisulphide [(C 2 H 5 ) 2 S 2 ] and dimethyldiselenide [(CH 3 ) 2 Se 2 ], these dialkyls being suitable for the low (

In this work, we report on the microstructural and morphological characterization of III-V semiconductor nanowires (NWs) epitaxially grown on (111)B-GaAs substrates by Au-catalyst assisted metalorganic vapor phase epitaxy. As-grown dense (108-109 cm-2) arrays of few-micron long vertically-aligned (i.e. parallel to the crystallographic axis) GaAs, AlxGa1-xAs and core-shell GaAs-AlxGa1-xAs NWs were investigated, carrying out HRXRD measurements on different (hkl) reflections and by recording reciprocal space maps (RSMs) around the materials (111) reciprocal lattice points (relps). We show that NW diffraction peaks are visible in the RSM by means of characteristic halos. In the case of GaAs NWs, the halo is located at the (111) relp indicating that the NWs are grown along the direction and parallel to the axis of the GaAs substrate. On the contrary, for AlxGa1-xAs NWs or intentional core-shell GaAs-AlxGa1-xAs NWs the halo is displaced (along the momentum transfer normal to the surface, Qz) with respect to the GaAs (111) relp due to the elastic lattice strain associated with the compositional variation, e.g. the Al molar fraction in the AlxGa1-xAs alloy, within the nanostructures.

The stoichiometry of single ternary III-V semiconductor nanowires was analyzed by Raman spectroscopy. Free-standing AlxGa1-xAs nanowires were obtained through metal organic vapor phase epitaxy (MOVPE) by the vapor liquid solid (VLS) mechanism on GaAs substrates. The as-grown nanowires were studied with a scanning confocal Raman spectrometer (spatial resolution approximate to 300 nm). They were located by Rayleigh imaging and individual nanowires selected for Raman spectroscopy. The acquired spectra exhibit 2-mode behavior. The stoichiometry of single nanowires was determined based on the frequencies of the GaAs- and AlAs-like transversal optical (TO) and longitudinal optical (LO) peaks with an accuracy of below 10%. Measurements at different positions along the axis revealed variations of the composition within single nanowires. This non-uniformity evidences that the nanowires possess an internal structure.

Quasi 1-dimensional (quasi-1D) semiconductor nano-crystals (so-called nanowires) represent the forefront of today’s solid state physics and technology. These systems, having two of their dimensions comparable to the wavelengths of the electronic or phononic wavefunctions, are expected to show a variety of quantum confinement effects, such as density of state singularities, molecular-like states extending over large distances, high luminescence efficiencies and low lasing threshold: these properties have led to consider quasi-1D nanostructures as the fundamental building blocks for the realization of novel types of photonic and electronic nano-devices. The high surface-to-volume ratio of these nanostructures allows also to exploit the role of surface states (and their ambient-driven changes) in determining the nanostructure carrier transport and optical excitation/recombination properties. Despite the abovementioned attractive physical and technological assets, until very recently, not too many studies were performed on quasi-1D semiconductor systems, whilst twodimensional (2D) structures − quantum wells − have been under study already for more than three decades and quasi zero-dimensional (0D) objects − quantum dots, QDs − have been in the focus of researchers for nearly two decades. The main reason for such discrepancy resides in the difficulty of fabricating these nanostructures. In the recent past, quasi-1D nanostructures of III-V compound semiconductors have been generally grown on three-dimensional patterned (V-grooved) substrates (Kapon, 1994), or on high-index (such as {n11}-oriented) substrate planes (Notzel & Ploog, 2000). In such cases the major nanowire dimension was running in the substrate plane, with the consequence, however, that interactions with the substrate may dominate over 1D effects. These difficulties have lead to consider free-standing quasi-1D nano-crystals having negligible interaction with the substrate. Free-standing nanowires based on III-V compound semiconductors are nowadays in the focus of intense research activities throughout the world; this in reason of the prominent role of these compounds in the optoelectronic arena. Demonstration of resonant tunnelling diodes (Bjork et al. 2002; Wensorra et al., 2005), single electron transistors (Thelander et al., 2003; Thelander et al., 2005), and photodetectors (Pettersson et al., 2006) based on quasi-1D nanostructures of III-V compounds have been reported. Also intense single photon sources have been fabricated by embedding InGaP quantum dots in free-standing GaP nanowires Source: Nanowires, Book edited by: Paola Prete, ISBN 978-953-7619-79-4, pp. 414, March 2010, INTECH, Croatia, downloaded from SCIYO.COM

Optical reflection, transmission, and absorption in arrays of GaAs and GaAs/AlGaAs core-shell nanowires are studied using transfer matrix and photonic bandgap formalisms, analyzing the effects of size, geometry, height, packing density, and polarization. Energy dependence of the spectra demonstrates optical modes in the dielectric, similar to guided resonant modes, and also the air bands. Simulation of polarization dependence verifies higher absorption with the electric field along the wire axis. Higher absorption at much lower volume compared to thin film, combined with excellent charge transport, make core-shell nanowire arrays excellent candidates for optoelectronics applications.

We report a detailed calculation of the effects of residual lattice and thermal strains on the electronic states of nearly pseudomorphic ZnSe/ZnS short-period superlattices (SLs). Comparison is made with experimental electronic transitions derived from 10K absorption spectroscopy measurements performed on 30 periods ZnSe/ZnS SLs, having well and barrier thickness Lw=1.4 nm and Lb=5.7 nm, respectively. ZnSe/ZnS SLs were grown by metalorganic vapour phase epitaxy (MOVPE) on a 500 nm thick ZnS buffer layer and capped with a 210 nm thick ZnS epilayer. The whole structures were deposited on (100)GaAs. The intrinsic conduction to valence band offset ratio is finally found to be 8:92 for the above SL structure. The impact of the weak electron confinement on the SLs optical and electronic properties, with special attention to laser applications, is also discussed.

This work reports on the structural characterization of Au nanocrystals directly prepared on the surface of (100)Si and 150 nm-thick SiO2 deposited (100)Si substrates, by a physical self-assembly method, consisting in the UHV evaporation of a thin Au film and its successive high temperature annealing. The morphology, orientation, and crystalline structure of Au nanocrystals were characterized by scanning and high-resolution transmission electron microscopy and X-ray diffraction, respectively. Experimental results show that the nature of the substrate strongly influences the process of Au nanocrystal formation upon heat treatment, by affecting the interaction of deposited Au with the underlying material. In the case of clean (100)Si substrates the Au strongly interacts with Si, so that Au nanoislands are obtained with a well defined epitaxial relationships with the substrate, i.e. [100]AuÐÐ[110]Si and [110]AuÐÐ[311]Si. The nanoisland shape is affected by faceting at the Au/Si interface, the Au nanocrystal being limited by the {111}, {311}, {711} and {-111} planes of Si. In the case of SiO2/(100)Si substrates spherical shaped Au nanoparticles with random crystal orientation are instead, produced.