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Molecular beam epitaxy technique has been used to deposit a single layer and a bilayer of MoSe 2 on sapphire. Extensive characterizations including in-situ and ex-situ measurements show that the layered MoSe 2 grows in a scalable manner on the substrate and reveals characteristics of a stoichiometric 2H-phase. The layered MoSe 2 exhibits polycrystalline features with domains separated by defects and boundaries. Temperature and magnetic field dependent resistivity measurements unveil a carrier hopping character described within two-dimensional variable range hopping mechanism. Moreover, a negative magnetoresistance was observed, stressing a fascinating feature of the charge transport under the application of a magnetic field in the layered MoSe 2 system. This negative magnetoresistance observed at millimeter-scale is similar to that observed recently at room temperature inWS2 flakes at a micrometer scale [Zhang et al., Appl. Phys. Lett. 108, 153114 (2016)]. This scalability highlights the fact that the underlying physical mechanism is intrinsic to these two-dimensional materials and occurs at very short scale., 15 pages, 6 figures

We investigate both theoretically and experimentally the effects of the In surface segregation in InGaN/GaN quantum wells (QWs). It is shown that this phenomenon induces a blue-shift of the QW photoluminescence (PL) energy, which does not depend on the QW width, at least for well thicknesses larger than 1.5 nm. The oscillator strength of the QW optical transitions decreases when the segregation process increases due to the spatial separation of the electron and hole pairs by the internal electric field. The surface segregation phenomenon has been studied by reflection high-energy electron diffraction in the case of molecular beam epitaxy growth with NH3 as the nitrogen source. Evidence for surface segregation is given by comparing PL results and data deduced from a careful analysis of the growth rate variation of GaN deposited on an In covered surface. (C) 2003 Elsevier Science B.V. All rights reserved.

The polarity of GaN epilayers grown by molecular beam epitaxy is controlled using Mg. This is achieved by simultaneously exposing the surface to Mg and NH3 fluxes during growth interruption. Reflection high-energy electron diffraction (RHEED) indicates the formation of a Mg3N2, layer. Overgrowing GaN on this surface leads to a polarity inversion either from Ga to N or N to Ga. The change of the polarity is followed in situ by RHEED via surface reconstructions of the GaN surface. The polarity inversion is further confirmed by convergent beam electron diffraction experiments. Finally, high-resolution transmission electron microscopy images show different interface morphologies between Ga/N and N/Ga polarity boundaries. The control of the GaN polarity opens the way for novel periodic polarity structures dedicated to non-linear optics. (C) 2002 Elsevier Science B.V. All rights reserved.

We report the growth of InAs/InAs1-xSbx single and double heterostructured nanowires by Au-assisted chemical beam epitaxy. The InAs1-xSbx nanowire segments have been characterized in a wide range of antimony compositions. Significant lateral growth is observed at intermediate compositions (x similar to 0.5), and the nucleation and step-flow mechanism leading to this lateral growth has been identified and described. Additionally, CuPt ordering of the alloy has been observed with high resolution transmission electron microscopy, and it is correlated to the lateral growth process. We also show that it is possible to regrow InAs above the InAsSb alloy segment, at least up to an intermediate antimony composition. Such double heterostructures might find applications both as mid-infrared detectors and as building blocks of electronic devices taking advantage of the outstanding electronic and thermal properties of antimonide compound semiconductors.

GaAs was used as the target material for the deposition of GaN films by reactive sputtering. The films were grown at different compositions of the sputtering gas mixture (0-100% nitrogen in argon) at substrate temperatures of 450 and 550 degrees C. The films were studied using XRD and XPS techniques. Even a small quantity of nitrogen in the sputtering medium was found to prevent the formation of GaAs on the substrate. Films grown at 550 degrees C using 100% nitrogen as the sputtering-reactive gas were found to be single phase (0002) oriented hexagonal gallium nitride and revealed complete absence of arsenic. (C) 1998 Elsevier Science S.A. .

Laser-assisted deposition: The discovery of chemical vapor deposition (CVD) conditions under which the growth rate is a decreasing function of the precursor flux has the potential to boost the resolution of laser-assisted CVD processes whereas flux- and desorption-limited conditions appear to be the ideal environment for spatially addressable combinatorial experiments (see picture). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zinc phosphide (Zn3P2) is an ideal absorber candidate for solar cells thanks to its direct bandgap, earth-abundance, and optoelectronic characteristics, albeit it has been insufficiently investigated due to limitations in the fabrication of high-quality material. It is possible to overcome these factors by obtaining the material as nanostructures, e.g. via the selective area epitaxy approach, enabling additional strain relaxation mechanisms and minimizing the interface area. We demonstrate that Zn3P2 nanowires grow mostly defect-free when growth is oriented along the [100] and [110] of the crystal, which is obtained in nanoscale openings along the [110] and [010] on InP(100). We detect the presence of two stable rotated crystal domains that coexist in the structure. They are due to a change in the growth facet, which originates either from the island formation and merging in the initial stages of growth or lateral overgrowth. These domains have been visualized through 3D atomic models and confirmed with image simulations of the atomic scale electron micrographs. Density functional theory simulations describe the rotated domains' formation mechanism and demonstrate their lattice-matched epitaxial relation. In addition, the energies of the shallow states predicted closely agree with transition energies observed by experimental studies and offer a potential origin for these defect transitions. Our study represents an important step forward in the understanding of Zn3P2 and thus for the realisation of solar cells to respond to the present call for sustainable photovoltaic technology., We acknowledge Martin Friedl, Didem Dede, Nicholas Morgan, and Wonjong Kim for helpful discussions regarding selective area growth and the substrate patterning procedures. M. C. S., S. M. S., P. T. V. and J. A. acknowledge funding from Generalitat de Catalunya 2017 SGR 327. ICN2 is supported by the Severo Ochoa programme from Spanish MINECO (Grant No. SEV-2017-0706) and is funded by the CERCA Programme/Generalitat de Catalunya. M. C. Spadaro has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 754510 (PROBIST) and the Severo Ochoa programme. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 823717 – ESTEEM3. Authors acknowledge the use of instrumentation provided by the National Facility ELECMI ICTS, node “Laboratorio de Microscopías Avanzadas” at University of Zaragoza. S. E. S., E. Z. S., M. Z., R. P., J. B. L. and A. F. i M. were supported by SNSF Consolidator grant BSCGI0-157705 and the Max-Planck-EPFL-Center for Molecular Nanoscience and Technology. N. Y. D. acknowledges the UK Engineering and Physical Sciences Research Council (EPSRC) for funding (Grant No. EP/S001395/1). The DFT calculations were performed using the computational facilities of the Advanced Research Computing @ Cardiff(ARCCA) Division, Cardiff University.

GaN and InGaN layers are grown by molecular beam epitaxy using ammonia as nitrogen precursor. The lattice mismatch between InN and GaN is very large and a Stranski-Krastanov (SK) growth mode transition can occur above a critical In composition. However, changing the growth conditions, namely increasing the NH3 flux, allows one to promote the 2D growth. This phenomenon can be ascribed to a surfactant effect of hydrogen atoms (or NHx radicals) present at the growth surface. The optical properties of InGaN/GaN quantum dots, made by SK growth mode, and InGaN/GaN quantum wells are compared. (C) 2001 Elsevier Science B.V. All rights reserved.

By means of Raman and photoluminescence measurements we have studied the effect of strain and confinement on the optical phonon spectrum of single InAs quantum wells. The frequency region of longitudinal optical phonons confined in both the InAs well and InP barrier layer has been studied. Simple modelling of the effects of the strain and the confinement on the InAs phonon is able to explain the dependence of the phonon frequencies on the layer thickness. Experimental evidence of vibrations localized at the InAs/InP interface is also reported and discussed. Finally, confinement of InP phonons in the layer between the InAs slab and the sample surface is observed and related to the structural features of the InAs well as deduced from photoluminescence measurements.