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We present a model for vacancy-mediated spontaneous breakdown of free-standing monatomic nanowire based on exclusively random, thermally activated motion of atoms. The model suggests a new two-step vacancy-mediated mechanism for nanowire rupture compared to the more complex three-step hole-mediated mechanism driving the disintegration of nanowire on crystalline surface. It also demonstrates that a free-standing nanowire breaks down much more rapidly than a nanowire on a substrate, because it cannot experience the stabilizing effect of the nanowire/substrate interactions. The rupture mechanism includes single atomic vacancy generation, preceded by appearance of weakly bonded active atoms. The analysis of the simulation data indicates that the active atoms act as a precursor of vacancy formation. These two successive events in the temporal evolution of the nanowire morphology bring the free-standing nanowire into irreversible unstable state, leading to its total disintegration. The present study also manifests an unexpected substantial increase of the nanowire lifetime with diminishing the strength of the atomic interactions between the nanowire atoms. The simulation data reveal three energy regions where a large oscillatory variation of nanowire lifetime is realized. The first region of strong atomic interactions is characterized by tight nanowire rigidity and short lifetime. The next, second region in the consecutive step-down of the attractive interatomic force is characterized by generation of wave-shaped morphology of the atomic chain, enhanced flexibility and dramatic increase of nanowire lifetime. In the last, third region, further weakening of the interactions returns the nanowire again to unstable, short-lifetime state. The observed phenomenon is considered as a “stick-like” to “polymer-like” transition in the nanowire atomic structure as a result of interaction energy variation. The enhanced flexibility reduces the nanowire free energy since it favors and facilitates the rate of entropy propagation in the atomic chain structure. The observed phenomenon opens a way for a new type atomic scale control on the thermal stability of both free-standing nanowire and nanowire on crystalline substrate. The present study also extends the validity of the three-step breakdown mechanism of nanowire on crystalline substrate to the specific case of thermally activated free-standing nanowire rupture not affected by any external forces. [ABSTRACT FROM AUTHOR]

Large single crystals of La 8 Cu 7 O 19 have been grown using the travelling-solvent floating zone method. A rather high oxygen pressure of 9 bar in the growth chamber and a slow growth speed of 0.5 mm/h were among the most important parameters in stabilizing the growth of this incongruently melting compound. Interestingly, a novel growth scenario has been witnessed. The crystal structure of the grown La 8 Cu 7 O 19 crystal has been analyzed using single crystal diffractometry to extract important structural parameters of this compound. We find that La 8 Cu 7 O 19 crystallizes in a monoclinic structure with space group C 2 / c and has the lattice parameters a ≈ 13.83 Å , b ≈ 3.75 Å , c ≈ 34.59 Å , and β ≈ 99.33 ° , in good agreement with the data obtained on polycrystalline samples in the literature. The magnetization shows a highly anisotropic behavior, and an anomaly at T ≈103 K. [ABSTRACT FROM AUTHOR]

Abstract: InSb quantum dots (QDs) and quantum dashes (Q-dashes) were obtained on InAs-rich substrate by both LPE and MOVPE methods. Bimodal mechanism of the formation of the InSb quantum dots was observed on InAs binary surface during the LPE growth. The low-density (5×108 cm−2) big quantum dots with 12nm in height and high-density (1×1010 cm−2) small quantum dots with 4nm in height were found to be present simultaneously. Deposition from the InSb melt over the InAs0.61Sb0.13P0.26 matrix layer lattice-matched with InAs substrate resulted in the uniformity of the InSb QDs. The Q-dashes with density (2.5×109 cm−2) with dimensions of 30nm in height, 500nm in length and 200nm in width were grown by the MOVPE method. The obtained Q-dashes were oriented along the [110] direction. A drastic change in the dot geometry with dependence on III/V ratio of the components in the vapor phase was observed. The shape and the density of the InSb Q-dashes can be determined by the surface chemistry of the InAs(Sb,P) matrix layer. [Copyright &y& Elsevier]

Abstract: We have investigated the structural properties of multi-stacked layers of self-organized In0.4Ga0.6As quantum dots (QDs) embedded with GaN0.007As0.993 strain compensation layers (SCLs) grown on GaAs (311)B substrate by atomic hydrogen-assisted molecular beam epitaxy. Symmetrical lens-shaped QDs are observed along , while their shape is asymmetric along with two different dominant facets. Further, QDs are vertically aligned in the growth direction when viewed along , while the alignment is inclined at an angle of 22° with respect to the growth direction when viewed along . The inclination angle is in good agreement with the result of resonant diffuse X-ray scattering sheets in reciprocal space mapping around GaAs (311) lattice point. We believe that the local strain field around QD extends further outward from the lower-angle facet, thereby the vertical alignment is tilted along the direction of stronger strain field. [Copyright &y& Elsevier]

Abstract: The authors report the formation of two-dimensional InAs quantum dot (QD) arrays by self-organized anisotropic strain engineering of InAs/InGaAsP superlattice (SL) templates on InP (311)B substrates by chemical-beam epitaxy (CBE). The SL template and InAs QD growth conditions are studied in detail for optimized QD ordering. Excellent photoluminescence emission up to room temperature is achieved from buried QD arrays. The emission wavelength is tuned from above 1.9μm to the 1.55μm telecom wavelength region through the insertion of ultrathin GaAs interlayers beneath the QD arrays. [Copyright &y& Elsevier]

Abstract: The transformation of Te nanotubes to CoTe2 nanotubes have been achieved through a solvothermal process in a mixed solvent of ethylene glycol (EG) and oleic acid (OA) at 200°C for 24h. Single crystalline Te nanotubes generated in situ could serve as the Te source and template, and then transformed as self-assembly CoTe2 nanotubes. In the unique reaction system, CoTe2 nanotubes were obtained when the volume ratio of EG and OA (V EG/V OA) was 5/3. The facile approach was extended to prepare other 1D telluride nanostructures, including CdTe, PbTe, Sb2Te3 and Bi2Te3. [Copyright &y& Elsevier]

Abstract: The formation of Ge nanoislands directly on Si(111) surface before the completion of a wetting layer was studied by scanning tunneling microscopy and Raman scattering spectroscopy. The mechanism of the wetting layer formation in the Ge/Si(111) system depends on the rate of Ge deposition. Within the temperature range 350–500°C, with Ge deposition rates of the order of 10−3 bilayers/min, the Ge wetting layer is formed by the multilayer growth mechanism. Therefore, the arrays of Ge islands with the densities of 109–1012 cm−2, depending on the rate of Ge deposition, appear directly on the Si surface during the evolution of the wetting layer. The height of Ge islands is limited by 3 bilayers. The lateral dimensions depend on the coverage of Ge and on the growth temperature. A series of lines related to the quantization of the phonon spectrum along the growth direction [111] was observed in the spectra of Raman scattering by optical phonons of Ge nanoislands. [Copyright &y& Elsevier]

Abstract: We report a comprehensive study into the growth of a 2.9THz quantum cascade laser structure on two different molecular beam epitaxy manufacturers’ systems; within a single growth campaign and over multiple growth campaigns. Device performance figures are compared from all the lasers grown, demonstrating excellent structure reproducibility, not only between each growth campaign, but also between the two MBE systems; including using different combinations and types of group III effusion cells. A small systematic shift in the emission frequency of ∼0.1THz between the two systems was observed. The mechanisms behind this small shift in emission frequency were investigated and partly attributed to differences in the flux profiles associated with the type of aluminium effusion cells used and inhomogeneous broadening in the structure, possibly due to interface roughness. [Copyright &y& Elsevier]

Abstract: We demonstrate the self-assembled generation of nanoholes on AlGaAs surfaces by local droplet etching (LDE). For the etching process, Ga is deposited on the surface, where liquid droplets are formed in a Volmer–Weber-like growth mode. The etching takes place locally at the interface between droplets and substrate and removes a significant amount of substrate material. The structural properties of the LDE nanoholes are studied with atomic force microscopy as function of etching temperature and Ga coverage. A bimodal depth distribution with flat and deep holes is observed. The formation of flat holes can be almost suppressed by optimized etching parameters. The depth of deep holes was adjusted by the process parameters up to a maximum depth of 15nm. The density of deep holes is in the range 5×10−7–1×10−8 cm−2 and depends only slightly on the etching parameters. However, the density can be significantly increased by repeated etching. [Copyright &y& Elsevier]

Abstract: We present the growth and characterization of InAs quantum dots on Al x Ga1− x As surfaces for intersubband devices. This requires the quantum dot energy levels in the Al x Ga1− x As matrix to be above the GaAs bandedge. Using standard As4 fluxes (beam equivalent pressure 8e−6Torr), inhomogeneous broadening of the quantum dot size distribution increases with increasing Al content in the Al x Ga1− x As matrix. Reducing the As4 overpressure during In deposition is found to greatly improve the size distribution of the quantum dots, while producing slightly larger dots and a reduction in the density of small dots (h<1.3nm). Annealing at the higher standard As4 flux for 30s, after the reduced As4 In deposition, produced a negligible change in the quantum dot size distribution. Utilizing surface dots on top of 30 layers of self-assembled quantum dots, the maximum quantum dot height for ground state energies above the GaAs bandedge is determined to be 2nm for Al0.30Ga0.7As and 3nm for Al0.45Ga0.55As. [Copyright &y& Elsevier]

Abstract: Broadband superluminescent diodes incorporating multiple layers of InAs quantum dots (QDs), where the dots height was deliberately varied from one layer to another have been grown and characterized. We used the indium-flush process to accurately control the emission energy of each layer of dots, enabling us to reliability and predictably engineer the bandwidth of the overlapped layers. Photoluminescence spectrum of four combined layers of QDs with full-width at half-maximum of 125nm at peak wavelength energy of 1.06μm was obtained. A 3dB bandwidth emission spectrum of 80nm and output power of 1mW was obtained under CW operation mode at room temperature. [Copyright &y& Elsevier]

Abstract: We have studied the structural and optical properties of 10 stacked layers of self-organized In0.4Ga0.6As quantum dots (QDs) grown on GaAs (311)B substrates by atomic hydrogen-assisted radio frequency (RF)-molecular beam epitaxy. A 40nm-thick GaN0.007As0.993 dilute nitride, which is used to cover each QD layer acts as a strain-compensation layer (SCL). The density of strain-compensated In0.4Ga0.6As QDs on GaAs (311)B can be controlled between 2×1010 and 1×1011 cm−2 by simply changing the growth temperature. Closely spaced In0.4Ga0.6As QDs on GaAs (311)B shows an ordered structure, in which we observe clear peaks in the two-dimensional fast Fourier transformation image. The temperature dependence of photoluminescence (PL) spectra shows a narrower linewidth over the whole temperature range 30−300K for strain-compensated QDs owing to better uniformity in the QD size. [Copyright &y& Elsevier]

Abstract: We have investigated the growth of 10 stacked layers of self-assembled InAs quantum dots (QDs) on GaAs (001) substrates, which were embedded in a combined set of a GaNAs strain-compensating layer (SCL) and an InGaAs strain-reducing layer (SRL). The internal compressive strain induced by each InAs QD layer was compensated by a tensile strain due to a GaNAs SCL. Consequently, the photoluminescence (PL) measured at 30K showed a narrower linewidth of 60.3meV for the sample with GaN0.008As0.992 SCL compared to 94.2meV for InAs/GaAs uncontrolled sample due to an improved QD size uniformity. In order to reduce the nominal lattice mismatch at the heterointerface, we propose to insert an InGaAs SRL between the InAs QD layer and GaNAs SCL. We observed a PL peak redshift up to 1230nm at room temperature, and increased PL intensity for InAs QD/InGaAs SRL/GaNAs SCL samples. [Copyright &y& Elsevier]

Abstract: We investigate the impact of the specific strain gradient on the optical properties of quantum well (QW) structures. This strain gradient emerges if the layer stack is released from the underlying substrate forming a scroll. As the strain state in this configuration changes from compressive to tensile strain the character of the fundamental optical transition in a strained QW is modified. Polarization-dependent low-temperature μ-photoluminescence studies reveal that in all the examined QWs in scrolled structures the valence band has a mixed heavy/light hole like character in agreement with calculations. Therefore, for the interpretation of optical and electronic transport properties of double heterojunctions with a strongly curved geometry the actual built-in strain has to be considered. [Copyright &y& Elsevier]

Abstract: Two-dimensional electron gas (2DEG) in AlGaAs/GaAs heterostructures, grown by molecular beam epitaxy (MBE), has been a favorite template for numerous research in a field of quantum physics during last several decades. While in the early stages the main efforts were devoted to fabricate extremely high-mobility 2DEG by concentrating on the purity of the grown material, nowadays it became clear that the further progress in the field requires new approaches of heterostructures design and the growth procedure. Here we report on the MBE growth of AlGaAs/GaAs heterostructures using a short-period superlattice (SPSL) doping instead of the more standard n-AlGaAs doping. Such doping process allows the use of a low AlAs mole fraction spacer which, in turn, leads to a lower background of impurities as well as a better interface quality. Mobility exceeding 35×106 cm2/Vs was measured in samples with doping introduced on both sides of a quantum well (QW) where the 2DEG was imbedded in. Most importantly the SPSL doping allows introducing “correlations” between ionized donors and allows controlling the potential disorder landscape that governs the appearance of various fractional quantum Hall states. [Copyright &y& Elsevier]

Abstract: Novel radial single-crystalline ZnS nanowire bundles were successfully synthesized via a facile solvothermal route in the presence of triethylenetetramine (TETA). TETA, which was employed for the first time as a growth-orientator for nanoarchitectures, plays a significant role not only for the development of one-dimensional nanostructures, but also in favor of the formation of radial profile. A dynamic ligand-assisted growth mechanism was proposed and demonstrated in detail. Furthermore, the photoluminescence properties of the as-prepared products were studied. The radial ZnS nanowire bundles were found to exhibit enhanced photoluminescence emissions in visible region compared with that of parallel ones and their bulk counterparts, indicating their potential applications for fabricating novel optoelectronic devices. [Copyright &y& Elsevier]

Abstract: We report a facile room-temperature synthesis method for a blue-luminescent silicon nanoparticle, whose surface is stabilized with a hexadecanoxyl monolayer. The synthesis of the nanoparticle was performed by the sodium naphthalenide reduction of silicon tetrachloride. Details of characterization with FTIR and 1H NMR indicated the successful replacement of a surface chloride of the nanoparticle with a hexadecanoxyl group. The use of a surfactant, that is, tetra-n-octylammonium bromide, led to a uniform size distribution, while its absence produced a sample with a large size distribution. The hexadecanoxyl capsule stabilizes the surface of blue-luminescent nanoparticle under ambient conditions even after 1 year. [Copyright &y& Elsevier]

Abstract: Characteristics of InAs quantum dot density on a GaNAs buffer layer grown by metalorganic chemical vapor deposition were investigated using atomic force microscopy, focusing on the growth rate of the buffer layer as a significant growth parameter. High dot density of 1.7×1011 cm−2 was achieved by using the GaNAs buffer with the growth rate of 1.45μm/h. It is found that surface roughness of the buffer layer is a key factor of increasing dot density. Suppression of coalescent dots that are one of the causes of emission intensity degradation was also quantitatively obtained. These results are effective for quantum dot lasers with high modal gain. [Copyright &y& Elsevier]

Abstract: A study of the GaN nanocolumns nucleation and growth by molecular beam epitaxy on Si(111) is presented. Ga droplets with different diameters (340–90nm) were deposited on the substrate, prior to growth, to determine any effect on the nanocolumns size and distribution. Results indicate that there is no difference in nanocolumnar size and density whether Ga droplets are used or not, meaning that Ga droplets do not act as catalysts for the nanocolumns nucleation. In addition, Ga droplets were never observed on the nanocolumn tips upon growth termination. These findings rule out the vapor–liquid–solid mechanism. Instead, driven by a strong lattice mismatch nanocolumnar nucleation occurs spontaneously by Volmer–Weber growth mechanism, whereas nitrogen excess prevents the nucleation sites coalescence. Further nanocolumnar growth proceeds by direct Ga incorporation on the nanocolumns top and by Ga diffusion along the nanocolumns sidewalls up to their apex. Related to this diffusion mechanism, we found that Ga droplets, when used, may act as reservoirs to feed Ga atoms to the neighboring nanocolumns. Nanocolumns preserve a constant diameter if growth conditions are not modified because of a strong metal ad-atom diffusion length along their sidewalls. The effect of using AlN buffer layers on the nanocolumnar growth and morphology is also addressed. [Copyright &y& Elsevier]

Abstract: In this paper we report the synthesis of doped ZnS one-dimensional (1D) nanostructures by well-established technique of chemical vapor deposition using Zn and S powder as precursors. The ZnS 1D nanostructures were grown on the surface of Au particle-filled anodic aluminum oxide templates, catalyst-free graphite sheets and silicon substrates. ZnS 1D nanostructures with Mn, Cu and Fe as dopants were prepared via a rapid process of 15–20min. The morphologies of ZnS nanostructures synthesized on different substrates and at different growth temperatures have distinct dissimilarities. The size of ZnS nanowires originated from the Au catalysts could be varied by altering the size of membrane nanopores as well as the embedded Au particles. Room-temperature photoluminescence measurements reveal strong blue, green and yellow-orange light emissions from the doped ZnS 1D nanostructures. [Copyright &y& Elsevier]

Abstract: The present report describes a model system for the fabrication of crystalline magnetic garnet nanofibers, and provides a universal routine to the fabrication of other ternary inorganic oxide nanofibers. Crystalline bismuth-substituted yttrium iron garnet nanofibers of several micrometers in length and of 100–200nm diameter are prepared by sol–gel and calcination-assisted electrospinning, using a viscous sol–gel precursor solution composed of PVP/(Fe(C11H19O2)3+Y(OOC10H19)3+Bi(TMHD)3). A 15kV DC voltage is applied to the needle, with a 0.5ml/h feeding rate of the precursor solution, during the electrospinning process. Scanning electron microscopy, transmission electron microcopy, X-ray diffraction and magnetization process measurements were performed on the fibers. The composition of the sol–gel precursor solution and the role of the surrounding humidity, which gave optimal results when maintained below 50%, were found to be critical factors during the electrospinning processes. [Copyright &y& Elsevier]

Abstract: Fibrous barium carbonate (BaCO3/witherite) crystals 50–100nm in diameter and several microns in length were grown on calcium carbonate (CaCO3) seeds at temperatures as low as 4°C. The BaCO3 fibers were deposited onto calcite rhombs or CaCO3 films using the polymer-induced liquid-precursor (PILP) process, which was induced with the sodium salt of polyacrylic acid (PAA). The structure and morphology of the resultant fibers were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and polarized light microscopy (PLM). Fibers were successfully grown on calcite seeds of various morphologies, with a range of barium concentrations, and PAA molecular weight and concentration. Two categories of fibers were grown: straight and twisted. Both types of fibers displayed single-crystalline SAED diffraction patterns, but after examining high-resolution TEM lattice images, it was revealed that the fibers were in fact made up of nanocrystalline domains. We postulate that these nanocrystalline domains are well aligned due to a singular nucleation event (i.e., each fiber propagates from a single nucleation event on the seed crystal) with the nanocrystalline domains resulting from stresses caused by dehydration during crystallization of the highly hydrated precursor phase. These BaCO3 fibers grown on calcite substrates further illustrate the robustness and non-specificity of the PILP process. [Copyright &y& Elsevier]

Abstract: Self-assembled InGaN quantum dots (QDs) have been grown using metalorganic vapor-phase epitaxy (MOVPE), without using anti-surfactant. Using 120s annealing, InGaN QDs have been successfully formed with a circular base diameter of 40nm and an average height of 4nm, with QDs density of 4×109 cm−2. The InGaN QDs have peak photoluminescence (PL) wavelengths of 519 and 509nm for samples without and with a GaN upper barrier, respectively. The full-width half-maximum (FWHM) of the PL spectra ranges from 56.6 up to 69.6nm. These results demonstrates that high In-content InGaN QDs can be grown by MOVPE, and can potentially be utilized as the active media for light-emitting diodes (LEDs) and semiconductor laser diodes for green emission. [Copyright &y& Elsevier]

Abstract: Structural and optical properties of multi-stacked self-assembled InAs quantum dots (QDs) on GaAs (001) substrates have been investigated, for which dilute nitride GaN x As1− x layers were used as strain-compensation layers (SCLs). The growth was achieved by atomic hydrogen-assisted radio frequency (RF)-molecular beam epitaxy. The high-quality QD structures were maintained without generation of coalesced islands and dislocations even after 20 layers of stacking. The photoluminescence (PL) peak showed an increasing redshift up to 1.2μm at room temperature with increasing N composition up to 1.0% in GaNAs as a result of the lowering of quantum confinement energy. Furthermore, the PL showed a bimodal size distribution-like feature. The temperature dependence of PL characteristics showed a minimum linewidth at an intermediate temperature range of ∼100K, and existence of the two components obeying the Varshni law. Such behavior can be explained by the dynamics of thermally activated carriers that migrate or tunnel from the smaller-sized QDs to larger QDs via wetting layers. The main reason for the anomalous PL characteristics measured for InAs QDs embedded in GaNAs SCLs is possibly the fluctuations of potential energy in GaNAs layers. [Copyright &y& Elsevier]

Abstract: Square lattice gas models for heteroepitaxial growth are studied by means of kinetic Monte Carlo simulations, in order to find a possible origin of anisotropic island shape observed in growth experiments of long organic molecules. When deposited molecules form clusters irreversibly at their encounter during surface diffusion, islands grow in a ramified dendritic shape, similar to DLA. Introduction of molecular detachment from edges makes islands compact with smooth edges. Tilting of adsorbed long molecules or steps in a vicinal substrate may induce orientation dependence in the detachment rate of edge molecules from an island. In simulations with orientation-dependent detachment rates, a clear anisotropy in an island shape is observed. Shape anisotropy on a vicinal substrate is enhanced as steps get dense, in agreement to the experimental observation. [Copyright &y& Elsevier]

Abstract: An urchin-like ZnO/MgO hierarchical structure was synthesized successfully via one-step thermal evaporation of the mixture of metal Zn and Mg powders under designed conditions. The morphology observations and structure analysis of ZnO/MgO hierarchical structures and the related byproducts revealed that there existed a morphology evolution linkage as MgO spheres—ZnO/MgO hierarchical structures—ZnO flowers. The detailed investigations suggested that the temperature and ZnO x concentration in gas flow played crucial roles in the formation of these structures, especially for the hierarchical structure. The photoluminescence spectra showed a regular change corresponding to the morphology evolution. [Copyright &y& Elsevier]

Abstract: The stabilization of planar In0.4Ga0.6As on GaAs, above thickness typically reported to undergo spontaneous island formation, has been observed. The effect of growth temperature, AsH3 partial pressure, and In0.4Ga0.6As thickness on island size and density was evaluated. Planar films are stabilized by low growth temperatures and high AsH3 partial pressures. Spontaneous island formation is enhanced by high growth temperatures and low AsH3 partial pressures. The results presented are interpreted within the phenomenology of In segregation to the surface, which has been identified previously for the InGaAs/GaAs system. Based on equilibrium models for the critical thickness for island formation, the critical segregation layer thickness for island formation is predicted to be 0.6nm. [Copyright &y& Elsevier]

Abstract: Waveguides formed by (InP)5/(Ga0.47In0.53As)4 short-period superlattices (SPSL) have been grown and characterized for their use as waveguides in InAs self-assembled quantum wires (QWR) lasers. Atomic force microscopy has been used to characterize both the SPSL and the QWR morphology quality. It is demonstrated that the shape of the QWR strongly depends on the roughness of the SPSL surface and that an atomically flat surface is necessary to obtain a uniform QWR size and shape morphology. Photoluminescence (PL) spectroscopy is also employed as a feedback to achieve the optimum growth parameters in order to obtain high-quality QWR confined by SPSL. [Copyright &y& Elsevier]

Abstract: Cobalt oxide (Co3O4) nanocrystals have been synthesized successfully via a facile combustion method. The Li ions incorporated into the Co3O4 lattice should serve as a self-promoter for the crystallization, resulting in the drastic increase of particle size. The Li addition can complex the structure of the energy band gap. The optical absorption spectra indicate that the direct band gap of Co3O4 varied from 3.11 and 1.62 to 3.29–3.98eV after introducing Li ions. This approach provides economically viable route for large-scale synthesis of this kind of nanomaterials. [Copyright &y& Elsevier]

Abstract: Molten sodium salts were studied using in situ diffractiometry and Raman spectroscopy with the aim to establish the composition, arrangement, and tendencies in the temperature evolution of major structural units (SU). The obtained results agree well with the quantum-chemical calculations of the models of corresponding cation–anion associative complexes (AC). A conclusion is made that supports the interpretation of AC with a temperature-dependent association–dissociation constant as a high reactivity SU of polycomponent melts, in contrast with the passive ones, i.e., high-polycondensed fragments of anion groupings. The AC with the configuration predominant in precursor clusters as well as the structure-forming cations can be regarded as elementary crystal growth units. The NMR-spectroscopy of cesium–borate glasses suggests varying structural state and different effects of the structure-forming cations in the polycomponent systems. [Copyright &y& Elsevier]

Abstract: We reported the growth of asymmetric InAs bilayer quantum dots (QD) on GaAs substrate by molecular beam epitaxy. A combination of different InAs growth rates (GR) for the two QD layers was used, respectively, to increase QD density and extend photoluminescence (PL) emission wavelength. A high GR used for the first layer guarantees a high QD density; while a low GR used for the second layer helps to extend the PL emission wavelength due to the dot size increase, which was confirmed by transmission electron microscopy and PL measurements. It was found that this kind of QDs is very sensitive to post-growth annealing procedure due to the dot size increase. By appropriately choosing the growth parameters, InAs bilayer QD laser diodes embedded in a conventional AlGaAs/GaAs waveguide structure were demonstrated. The devices yielded the lowest ever reported threshold current density of 134A/cm2 in the range of 1.5μm wavelength for GaAs-based lasers. [Copyright &y& Elsevier]

Abstract: The Zeeman effect of a hybrid structure consists of a ZnCdMnSe diluted magnetic semiconductor (DMS) quantum well (QW) and superconductor array pattern on the surface was investigated by magneto-photoluminescence (PL) experiment. The superconductor arrays were designed to have width and space of 20 and of 2μm, respectively. The PL from DMS-QW exhibits a large Zeeman shift, a characteristic of DMS system, in the presence of a magnetic field. Significant enhancement of the Zeeman shift, however, was observed in the PL emitted from the superconductor patterned area compared to that observed from un-patterned area of DMS-QW. This indicates that the superconductor arrays pattern enhances the strength of applied magnetic field for local patterned area of the DMS-QW system. [Copyright &y& Elsevier]

Abstract: To form patterned GaInAs hetero-structures on GaAs, we proposed a new formation process using an amorphous As layer as a mask. The process consists of five stages: (1) A GaAs layer is grown at a low temperature about 480°C on a GaAs substrate. The low-temperature-grown layer enhances In diffusion while annealing at the fifth stage. (2) An amorphous As layer is deposited on the GaAs layer as a mask. (3) Designed patterns are drawn on the amorphous As mask by electron beam (EB) lithography. (4) Metallic In is deposited on the patterned amorphous As mask. (5) The sample is annealed for two purposes: one is to re-evaporate the amorphous As mask with metallic In on it and the other is to diffuse In on bare GaAs into the low-temperature-grown GaAs layer. (6) Then, patterned GaInAs/GaAs hetero-structures are formed. In the process, the advantage to use the amorphous As mask is two-fold, i.e., the mask is easily deposited in a normal MBE chamber and is removed by only heating it at an appropriate temperature (about 350oC), all in situ. [Copyright &y& Elsevier]

Abstract: We have investigated evolution of CdSe self-assembled quantum dots (QDs) grown on ZnMnSe diluted magnetic semiconductor (DMSs). In a series of QD systems, CdSe coverage was varied from 1.5 to 2.5ML while constant Mn concentration was kept in the ZnMnSe barrier. The PL peak from CdSe QDs shows systematic red shift with increasing CdSe coverage. This behavior observed in the series of CdSe/ZnMnSe QDs systems indicates systematic evolution of CdSe QD with increasing CdSe coverage. The PL peaks from CdSe QDs and from ZnMnSe barrier show large Zeeman shift, which is a characteristic of DMS systems when a magnetic field is applied. From the ratio of the Zeeman shift observed from CdSe QDs to that observed from ZnMnSe barrier, we are able to extract degree of carrier wave function penetration into the ZnMnSe barrier, which turns out to be systematically decreased with increasing CdSe coverage. [Copyright &y& Elsevier]

Abstract: Carbon implantation effects on self-assembled Ge quantum dots (QDs) have been investigated. Carbon atoms were implanted at different dosage, 9.0×1014, 4.5×1015, and 9.0×1015 ions/cm2 using the same acceleration energy of 20keV. A nominal amount, 6 monolayer (ML), of Ge was grown on the substrate at different growth temperatures ranging from 500 to 600°C using solid source molecular beam epitaxy. The smallest Ge QDs with a 13nm mean lateral diameter, a 1.2nm mean height, and an areal density of 2.0×1011 cm−2 were obtained using the lowest dosage substrate at 550°C. Raman measurement is carried out to investigate the optical phonons and strain. [Copyright &y& Elsevier]

Abstract: The correlation between the negative magnetoresistance and concentration of localized holes in Be/Si pair delta-doped GaAs structures grown by molecular beam epitaxy (MBE) was investigated. The negative magnetoresistance was observed in a high-temperature range. The magnitude of negative magnetoresistance is nearly proportional to the concentration of localized holes. The transition temperatures from the negative magnetoresistance to the positive one decrease with increasing concentration of localized holes. The temperature dependence of the Hall mobility is similar to that of negative magnetoresistance for each sample. The Hall resistance was measured in order to investigate possible ferromagnetic ordering of localized spins at low temperatures. [Copyright &y& Elsevier]

Abstract: Layer-by-layer epitaxial growth of CdSe on ZnSe has been observed at temperatures as low as 170–240°C. Beyond this range, Reflection high energy electron diffraction (RHEED) specular spot intensity oscillations disappear, signifying a multilayer growth mode. While conventional epitaxial growth of CdSe at ∼300°C results in formation of a rough layer-like structure, a method combining the epitaxial growth of a quasi-two-dimensional (2D) CdSe layer at 230°C and subsequent annealing at 310°C induces the formation of discrete CdSe quantum dots (QDs). Here we show that the formation of QDs by this method relies essentially on the layer-by-layer growth of CdSe at 230°C, which allows an induced roughening of the as-grown 2D layer, during the subsequent annealing step. The layer-by-layer growth mode results possibly due to the nucleation of small and irregular precursor 2D clusters during growth at low temperatures, at the kink sites of which potential barriers for downward inter-layer transport of adatoms is low/absent. [Copyright &y& Elsevier]

Abstract: The structural and optical properties of (In,Ga)As/(Al,Ga)As quantum wells grown on GaAs(110) by conventional molecular beam epitaxy as well as by migration-enhanced epitaxy are studied by low-temperature photoluminescence (PL), cathodoluminescence (CL), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The quality of GaAs/(Al,Ga)As quantum wells (QWs) allows to detect spin transport mediated by surface acoustic waves over distances up to 65μm with spin lifetimes of about 22ns. For (In,Ga)As/GaAs QWs, the accumulated strain due to the increase of the In mole fractions or the well thicknesses degrades the structural perfection more dramatically in structures with (110)-orientation than in structures with (001)-orientation. The quality of (In,Ga)As wells is remarkably improved by migration-enhanced epitaxy. [Copyright &y& Elsevier]

Abstract: Ultralong copper submicron wires has been fabricated by a facile hydrothermal route under templateless and surfactantless conditions. Vitamin C served as both the reductant and capping agent that can direct the growth of copper submicron wires. The crystallinity, purity, morphology, and structure features of copper submicron wires were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy and selected area electron diffraction (TEM/SAED). The growth mechanism of the copper submicron wires was studied in detail. [Copyright &y& Elsevier]

Abstract: We discovered a new class of topological crystals, namely linked rings of crystals. Two rings of tantalum triselenide (TaSe3) single crystals were linked to each other while crystal growing. The topology of the crystal form is called a “Hopf link”, which is the simplest link involving just two component unknots linked together exactly once. The feature of the crystals is not covered by the conventional crystallography. [Copyright &y& Elsevier]

Abstract: We propose a 1.3μm high-density InAs quantum dot (QD) structure for optical devices that uses an As2 source and a gradient composition strain reducing layer (GC-SRL). The temperature dependence of the photoluminescence (PL) peak intensity for a temperature increase from 11K to room temperature was very low at . Moreover, the PL peak intensity was ten times greater than that of low-density QDs because of an increase in the QD number, although the PL bandwidth was the same. For the first time, we realized QDs with high-density, uniformity, and quality. This is a promising result since optical devices with QDs exceeding 1.3μm on a GaAs substrate are useful in fiber communications. [Copyright &y& Elsevier]

Abstract: CuO shuttle-like nanocrystals were synthesized by the hydrolysis of cupric acetate (Cu(CH3COO)2·H2O) via a simple surfactant-assisted hydrothermal route at low temperature. It is found that the copper source, reaction temperature, reaction time, and surfactant cetyltrimethylammonium bromide (CTAB) are of importance to form the shuttle-like aggregates made by nanocrystals. A possible oriented-attachment mechanism for these aggregates is proposed based on their shape evolutions. [Copyright &y& Elsevier]

Abstract: Well-crystalline MgO nanocrystals have been synthesized successfully via a facile combustion method with lithium addition. After -doping into the MgO: host, the crystallinity of the sample becomes better, resulting in enhancement of luminescence intensity of the characteristic emission of ions. This approach provides economically viable route for large-scale synthesis of this kind of nanomaterials. [Copyright &y& Elsevier]

Abstract: Vertically aligned ZnO nanorods were successfully synthesized on Si substrates at 700°C through the conventional thermal evaporation method using a ZnO template of thin films instead of metal catalysts. The ZnO nanorods on the ZnO film show a high quality, a large-scale production, and a vertical alignment along the [001]ZnO. The origin of the vertical alignment is ascribed to the preferred orientation of the ZnO template, in which most of the (002) planes are parallel to the ZnO/Si interface. Moreover, the XRD profile shows that the ZnO films play the role of a template layer to fabricate the vertically aligned ZnO nanorods. In addition, this process is cost-effective compared to the thin-film growth system and overcomes the problem of impurity incorporation using metal catalysts. [Copyright &y& Elsevier]

Abstract: Nanowires of beta-Ag0.33V2O5 phase with high aspect ratio have been prepared by hydrothermal method at 180°C for 16h with equal moles of AgNO3 and NH4VO3. Acetic acid was used as an acidifying agent and pH value was between 1.8 and 2.3. X-ray diffraction pattern indicates that the sample is monoclinic phase akin to AgV6O15. Field-emission scanning electron microscopy shows that the nanowires have widths in the range of 70nm, thicknesses of 10nm and lengths of approximately several mm. X-ray photoelectron spectrum measurements further confirm the component of AgV6O15. TEM and HRTEM were further used to characterize the products. The obtained sample might find possible application as an electrode material in lithium ion batteries. [Copyright &y& Elsevier]

Abstract: Design, fabrication, and characterization of monolithically integrated ring diode lasers (RDLs) with relatively large size are reported. Fully functional optoelectronic integrated circuits containing integrated unidirectional RDLs, photodetectors, and coupling waveguides are demonstrated. Multiple switching of lasing direction is observed in RDL with quantum-well active regions, and an S-section or spiral absorbers are used to suppress directional switching and to obtain a more stable unidirectional operation. Unidirectionality of the RDL operation is greatly improved in lasers with quantum-dot active regions. [Copyright &y& Elsevier]

Abstract: Intermixing in InAs quantum dots (QDs) grown by molecular-beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) techniques on GaAs and InP substrates have been investigated by rapid thermal annealing (RTA) and laser-irradiation techniques. In all cases, substantial energy shifts have been observed after RTA and laser annealing. A comparison between the intermixed QD and quantum well (QW) structures shows distinguished differences in photoluminescence (PL) intensity and full-width at half-maximum (FWHM). For QD structures, an increase in PL intensity and a reduction in FWHM were observed after intermixing, whereas for QW structures the FWHM increased and the PL intensity reduced after intermixing, suggesting degradation of the material quality in the QWs after intermixing. Examination of the role of the surrounding matrix in intermixing process shows that InAs QDs placed in a InGaAs QW can retain its good optical quality after high temperature annealing, as the InGaAs QW provides a foundation for the QDs to be fully desorbed in the well. [Copyright &y& Elsevier]

Abstract: The metalorganic vapor-phase epitaxy growth of a highly reflective 24-pair AlGaAsSb/InP-distributed Bragg reflector (DBR) is reported for the first time. The influence of the growth parameters such as the V/III input ratio, the growth temperature and the pressure, the total H2 flow, the gas velocity and the switching sequence of the source gases at the interfaces has been deeply investigated and optimized to achieve stable growth conditions. The DBR achieves a reflectivity as high as 99.5% around 1.55μm, a uniform stable composition, and an excellent crystal quality over the 2inch wafer, with a surface free of crosshatch and a defect density below 1/cm2. For the optical characterizations, measurements of linear and nonlinear reflectivity, transmission, pump-probe and photoluminescence were done. The interfaces and bulk layers of InP/AlGaAsSb/InP heterostructures were analyzed by transmission electron microscopy. High resolution X-ray diffraction measurements were used to determine the composition shift in the growth plane of the DBR. The measurements show the high quality of the growth and demonstrate that thick AlGaAsSb/InP heterostructures can be grown by metalorganic vapor-phase epitaxy (MOVPE), and in particular DBRs above 1.31μm. [Copyright &y& Elsevier]

Abstract: We have investigated the evolution of structural and optical characteristics in self-assembled InAs/GaAs quantum dot (QD) structures with cap layers thinner than or comparable to QD height. Based on cross-sectional QD profiles of atomic force microscopy obtained from incompletely capped samples, we have suggested that the anisotropic image is not a QD structure per se but a complex one combined by QD and sidewall coverage, and schematic models have been illustrated for the structural evolution related with the capping process. As evidence supporting the structural characteristics, the photoluminescence emission spectra showing a crossover of red-to-blue shift of confined QD sublevels at a critical coverage of 5nm close to average QD height are presented. We have proposed energy band diagrams framed by effective potentials of surface barrier that can explain the energy shift phenomena. [Copyright &y& Elsevier]

Abstract: ZnO nanobelts were synthesized by RF sputtering on copper substrates. The sputtering time was 60min, in an argon atmosphere at a pressure of 40mTorr, and with RF power set at 300W. The obtained ZnO nanobelts exhibit a single-crystalline hexagonal structure with a thickness, width and length of about 10, 50nm, and several micrometers, respectively. The TEM analysis suggested that the ZnO nanobelts grew along the and directions on (0001) plane. These ZnO nanobelts have a potential application for use as a nanogas sensor. [Copyright &y& Elsevier]