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Abstract: We present a comparative study of InAs quantum dots grown on Si-doped GaAs (100) substrates, Si-doped GaAs (100) vicinal substrates, and semi-insulating GaAs (100) substrates. The density and size distribution of quantum dots varied greatly with the different substrates used. While dots on exact substrates showed only one dominant size, a clear bimodal size distribution of the InAs quantum dots was observed on GaAs vicinal substrates, which is attributed to the reduced surface diffusion due to the presence of multiatomic steps. The emission wavelength is blueshifted during the growth of GaAs cap layer with a significant narrowing of FWHM. We found that the blueshift is smaller for QDs grown on GaAs (100) vicinal substrates than that for dots on exact GaAs (100) substrates. This is attributed to the energy barrier formed at the multiatomic step kinks which prohibits the migration of In adatoms during the early stage of cap layer growth. [Copyright &y& Elsevier]

Abstract: One-dimensional Sb2S3 and Sb2Se3 crystals with straw-tied-like architectures have been successfully prepared in high yield by a one-pot hydrothermal method using water-soluble potassium antimony tartrate as antimony source. X-ray powder diffraction results and electron diffraction (ED) analysis show that the Sb2S3 wires and Sb2Se3 rods have a preferential growth direction along their c-axis. The peculiarities of the one-dimensional (1-D) growth mechanism are discussed. [Copyright &y& Elsevier]

Abstract: Si-rich silicon oxide (SiO x , 1<x<2) films were prepared by RF magnetron reactive sputtering or co-sputtering on the Si(111) substrates. X-ray diffraction patterns showed that the peak of silicon nanocrystals (NCs), separated from SiO x films, had (111) preferred orientation. The results of scanning electron microscopy indicated the Si NCs uniting into clusters. We demonstrated that the photoluminescence (PL) peaks at 650nm was caused by defect center. In particular, we discussed the correlation between the PL and the structure of SiO x films. The mean size of the Si NCs was estimated to be about 3nm by the PL peak position. [Copyright &y& Elsevier]

Abstract: An organic-assistant chemical vapor transport and condensation method is introduced to synthesize well-aligned ZnS nanowires. By means of decomposition of organics, a risen flow is generated that drives the ZnS nanowires growth direction upwards. From SEM images, the diameters of nanowires are uniform and nanowires are well-aligned and vertical to the surface of the silicon substrate. XRD pattern, TEM image and SAED suggest that the structure of ZnS nanowires is hexagonal and single crystalline. The growth orientation of nanowires is toward 〈002〉. In RAMAN spectrum, the E 1 (LO) mode resulting from the lateral morphology of ZnS nanowires is also observed in our sample. It restricts the phonon propagation direction to parallel the c-axis. A blue-light emission band is revealed in the PL spectrum which can be attributed to vacancies and surface states. [Copyright &y& Elsevier]

Abstract: Alterations of carbon particles carrying Pt clusters were studied by means of transmission electron microscopy (TEM). Carbon particles of size 20–30nm produced in a He gas atmosphere by the conventional arc-discharge method changed into carbon tubes or ribbon-like spherules based on an onion-like structure by heating in air at 300°C. In the case of carbon particles carrying Pt clusters, the alteration of carbon particles took place gradually at 300°C, and the Pt clusters become partially exposed to the air as they were no longer covered by the carbon layer. The generation of electricity by using Pt clusters in fuel cell is proposed as an application for the Pt clusters. [Copyright &y& Elsevier]

Abstract: We report molecular beam epitaxy (MBE) growth and device performance of 1.3μm GaInNAs/GaNAs single-quantum well lasers on GaAs substrates. Record low threshold current densities of 300, 320 and 360A/cm2 for cavity lengths of 1200, 1000 and 800μm, respectively, and a transparency current density of only 84A/cm2 are achieved for the 100μm wide broad area lasers. A characteristic temperature of 108K is measured in the temperature range of 8–70°C for a laser with a cavity length of 1000μm. We find that optimization of the RF nitrogen source during the MBE growth plays a crucial role in reducing the threshold current density. [Copyright &y& Elsevier]

Abstract: High electron mobility transistor (HEMT) structures consisting of: GaAs (buffer layer)/i-AlGaAs(spacer layer)/n-AlGaAs(barrier layer)/n-GaAs(cap layer) were grown by MBE on GaAs substrates. The optical properties of the HEMT structures were studied by photoreflectance (PR) spectroscopy at different temperatures. We observed in the PR spectra transitions located approximately at 1.41 and 1.85eV, associated with the energy band edges of GaAs and AlGaAs, respectively. Oscillatory signals slightly above these energies were recognized as Franz–Keldysh oscillations (FKO). By employing lasers with different wavelengths as modulation sources, and by varying the thickness of the layers in the heterostructures we were able to identify the origin of the PR signals in the spectra. The FKO close to the GaAs band gap originate at the GaAs buffer/i-AlGaAs heterojunction where the two-dimensional electron gas is localized. Finally, low-temperature PR experiments indicate that the oscillatory signal observed above the AlGaAs band edge is formed by two overlapped signals, one of which originates in the GaAs(cap)/n-AlGaAs interface. [Copyright &y& Elsevier]

Abstract: Self-assembled quantum dash (QDash) lasers based on InP with an emission wavelength of about 1.5μm were grown by molecular beam epitaxy with solid-state sources. Two different approaches were investigated to further extend the broad gain bandwidth of QDash structures. One approach is based on layer thickness variations in a stacked QDash structure with thick barriers to avoid vertical strain coupling. In the alternative structure, the barrier thickness is reduced to allow strain coupling which modifies automatically the QDash size from layer to layer. With both approaches, the gain bandwidth could be significantly increased in comparison to structures with a single QDash layer. However, lasers based on active regions with reduced barrier widths show additionally a significant improvement of the device performance. Ridge waveguide lasers based on this new material show continuous wave (cw) operation up to 75°C. At 20°C, a threshold current of 65mA was obtained for 2mm long devices with 2.5μm wide ridges. [Copyright &y& Elsevier]

Abstract: High-performance (high optical output power, high efficiency), GaAs-based Quantum Dots (QD) edge emitting laser (EEL) results are presented. The active region is based on multiple stacks of InAs/GaInAs/GaAs QD. The whole structure has been grown in a multiwafer production MBE system (using substrate holders). Threshold current density of and high differential quantum efficiency of 70% were obtained at room temperature. These excellent values in addition to good I–V characteristics (1.1V turn on voltage and series resistance as low as ) led to record continuous wave (CW) output power of 4.2W for broad area devices ( wide, long). [Copyright &y& Elsevier]

Abstract: We present a modified growth procedure used to control the emission wavelength of InAs quantum dots in a GaInAsP matrix grown on InP(311)B substrates by gas source molecular beam epitaxy. In this procedure, the quantum dots are grown on a GaInAsP buffer layer and partially capped with the same GaInAsp alloy. Then As/P exchanges during a growth interruption are used in order to reduce quantum dots height and thus to control the emission wavelength. Two GaInAsP quaternary alloys composition have been studied in this work. Both could be used as optical waveguide in 1.55μm laser diodes. We present and compare photoluminescence results on test structures with these two quaternary alloys. Finally, the new growth procedure is successfully applied and we demonstrate a quantum dot laser emission at 1.58–1.61μm at 300K. [Copyright &y& Elsevier]

Abstract: Wurtzite quasi-alloys of MgZnO with MgO/ZnO superlattices have been grown by molecular beam epitaxy on sapphire substrates on high-quality ZnO buffer layers. The equivalent band gap energy of the quasi-ternary MgZnO was successfully tuned from 3.3 to 4.65eV by changing the thicknesses of the MgO and ZnO layers. The near-band-edge cathodoluminescence was obtained from the MgO/ZnO superlattice without noticeable deep-level emissions and the multiple quantum well structures with MgO/ZnO superlattice quasi-ternary alloys were definitely fabricated, being capable of emitting ultraviolet (UV) luminescence from the well layers. These results suggest the promising potential of their optical functions for deep UV light emission and/or detection applications. [Copyright &y& Elsevier]

Abstract: The electrical properties in highly doped, weakly strained (In,Ga)(As,N)/(Al,Ga)As MQWs are studied by Hall measurements at various temperatures. With increasing N content in the well and Al content in the barrier, the electron mobility is strongly reduced. Magnetoresistance measurements are performed at low temperatures revealing carrier localization induced by the incorporation of N. From Raman spectroscopy, a preferential incorporation of N at the interface with the (Al,Ga)As barrier is found. Intersubband absorption experiments show only a small shift of the signal with increasing N content, but a strongly reduced and broadened absorption peak. [Copyright &y& Elsevier]

Abstract: The excitation power dependent photoluminescence (PL) of self-assembled In0.7Ga0.3As1− x N x () quantum dots (QDs) has been investigated in the excitation power density ranged from 3.0kW/cm2 to 50mW/cm2. As the excitation power increases, the emission peak of In0.7Ga0.3As0.98N0.02 QDs shifts to shorter wavelengths, while the peak of In0.7Ga0.3As QDs remains at the same wavelength. In the low-excitation cases, the PL peak of the In0.7Ga0.3As0.98N0.02 QDs has a tail on the lower energy side, on the other hand, that of the In0.7Ga0.3As QDs shows a symmetrical shape. Since the dot size distribution of the In0.7Ga0.3As0.98N0.02 QDs is similar to that of the In0.7Ga0.3As QDs, this blue-shift and the lower energy tail of the PL peak of the In0.7Ga0.3As0.98N0.02 QDs are attributed to the nitrogen-related states below the conduction band edge as are observed in the case of InGaAsN quantum wells (QWs). [Copyright &y& Elsevier]

Abstract: The resonant tunneling process of electrons through a single self-assembled InAs quantum dot (QD) has been studied by conductive-tip atomic force microscopy. The unique structure employed here consists of two layers of InAs QDs, which are separated by 5-nm-thick undoped GaAs layer. The conductive tip is placed in contact with the surface InAs QD which functions as a nano-sized electrode to measure the flow of electrons from the n+-GaAs substrate via a buried QD. A conductance structure attributed to resonant electron tunneling through the quantized level of QD is observed in the current–voltage characteristics. The resonant voltage is larger than the usual flat band voltage, indicative of a considerable voltage loss caused by the Fermi level pinning around the nano-sized electrode. [Copyright &y& Elsevier]

Abstract: We present an effective method to tune the emission wavelength of InAs/InP(100) quantum dots (QDs) in the wavelength region. The InAs QDs are embedded in lattice-matched GaInAsP which is the waveguide core material in InP-based photonic devices. By inserting ultrathin GaAs (0.3–2.5 monolayers (MLs)) or GaP (0.3–1.1MLs) layers between the QDs and the GaInAsP buffer, continuous wavelength tuning from above to below at room temperature is demonstrated by varying solely one growth parameter, i.e., the interlayer thickness. The thin GaAs and GaP interlayers play an important role in suppressing As/P exchange and consuming surface-segregated In, leading to drastic reduction of the emission wavelength of the InAs QDs. [Copyright &y& Elsevier]

Abstract: The influence of growth parameters and substrate material on the basic processes during strain-induced InAs-quantum dot (QD) formation and the resulting structural properties of the QDs is studied with reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM), and X-ray diffraction. The process of strain-induced QD formation is strongly influenced by the intermixing with substrate material and the desorption of indium at high temperatures. From the experimental results, we conclude that the strain-energy modification due to temperature-dependent intermixing has a larger influence on QD formation than temperature-dependent kinetic processes at the surface. Interestingly, we also find that the maximum growth temperature limited by desorption depends on the growth speed. [Copyright &y& Elsevier]

Abstract: A systematic study of the morphology of self-organized islands in the InAs/GaAs(001) and Ge/Si(001) systems is presented, based on high-resolution scanning tunneling microscopy measurements. We demonstrate that in both cases two main island families coexist: smaller pyramids bound by one type of shallow facets and larger multifaceted domes. Their structure and facet orientation are precisely determined, thus solving a highly debated argument in the case of InAs/GaAs(001). The comparison between the two material systems reveals the existence of striking similarities that extend even to the nature of island precursors and to the islands that form when depositing InGaAs or GeSi alloys. The implications of these observations on a possible universal description of the Stranski–Krastanow growth mode are discussed with respect to recent theoretical results. [Copyright &y& Elsevier]

Abstract: Thin layers embedded in ZnTe matrix have been grown on GaAs (100) substrate by hot-wall epitaxy technique with varying growth time. Their optical properties have been investigated by photoluminescence (PL) measurements at low temperature and by temperature-dependent PL measurements. PL measurements show that the quantum dots (QDs) related peak at lower energy side with a broad full-widths at half-maximum (FWHM) and the two-dimensional (2D) layer related peak at higher energy side with a narrow FWHM are clearly resolved and their energies shift to lower energies as the growth time increases. It is also found from temperature-dependent PL measurements that the activation energy of QDs is almost two times larger than that of 2D layer. Atomic force microscopy confirms their quantum dot formation. [Copyright &y& Elsevier]

Abstract: We report on the formation of (In,Ga)As self-assembled quantum structures grown on different orientations of GaAs along one side of the stereographic triangle between (100) and (111)A. The samples were characterized by atomic force microscopy. A systematic transition from zero-dimensional (In,Ga)As quantum dots to one-dimensional quantum wires was observed as the substrate was varied along the side of the triangle between (100) and (111)A. An explanation for the role of the substrate in determining the size of the nanostructure is proposed. [Copyright &y& Elsevier]

Abstract: Many group II sulphides semiconductors have the rocksalt structure as their stable crystal structure. In the case of MgS and MnS, it has been demonstrated that these compounds can be grown in the metastable zinc-blende structure using a simple MBE growth procedure that can increase the thickness of these metastable layers to over 130nm. In this paper, we review the growth method and features which arise during the growth of both MgS and MnS, namely the development parallel surface ridges and the loss of the zinc-blende crystal structure. [Copyright &y& Elsevier]

Abstract: We present the control of the emission wavelength of InAs quantum dots in a GaInAsP matrix grown on InP(311)B substrates by gas source molecular beam epitaxy. By growing the capping layer in two steps, the control of the dot height and thus of the emission wavelength is achieved. The dot height is tuned using As/P exchange during a growth interrupt. We have studied the changes induced by the nature of the overpressure (As, P, As and P) during the growth interrupt. Photoluminescence spectra at room temperature show the effects of the different growth parameters on the peak energy and width. [Copyright &y& Elsevier]

Abstract: The growth of thin InGaN epilayers on GaN by metal-organic vapour-phase epitaxy has been investigated by atomic force microscopy. The effect of increasing the NH3 flow rate on films growing in a 2D growth mode has been examined, and a transition from 2D island nucleation to step-flow growth with increasing NH3 flow tentatively attributed to a decrease in the barrier to adatom incorporation at step edges. Furthermore, increasing the overall reactor pressure, and hence the NH3 partial pressure, has been shown to encourage the formation of 3D nanostructures. This transition from 2D to 3D growth is linked to surface kinetic or thermodynamic effects rather than a change in the composition of the film. [Copyright &y& Elsevier]

Abstract: The tri-methyl-Sb flow and the surfactant time dependence of photocurrent (PC) spectra was studied on InGaAsN/GaAs-strained multiple quantum wells (MQWs) structures grown by using metalorganic chemical vapor deposition (MOCVD). The structural properties of InGaAsN/GaAs-strained MQWs were investigated by using high-resolution X-ray diffraction (HRXRD). In the case of InGaAsN/GaAs-strained MQWs, an increase in compressive strain from an analysis of the satellite peaks in HRXRD was observed on increasing the tri-methyl-Sb flow and the surfactant time. For InGaAsN/GaAs-strained MQWs, the peaks observed in the photocurrent spectra were preliminarily assigned to electron–heavy hole (–hh) and electron–light hole (–lh) fundamental excitonic transitions. Their peaks are red-shifted with increasing tri-methyl-Sb flow and surfactant time. But the photocurrent peak is blue-shifted at the surfactant time of . It seems to be due to the improvement of structure properties at interface owing to a surfactant-suppressing surface diffusion phenomenon during growth. We compared this with the result of the experimental energies for InGaAsN/GaAs-strained MQWs. [Copyright &y& Elsevier]

We report photoluminescence (PL) spectra associated with bimodal size-distribution observed in a series of self-assembled InAs/GaAs quantum-dot (QD) heterostructures with different InAs coverages. The PL spectra exhibit a well-defined doublet-like QD peak with invariable energy positions regardless of the coverage attributed to large and small QD groups. The excitation-power dependence reveals that the high-energy peak is composed by two contributions, one from the excited state of large QDs and the other from the ground state of small QDs. The power- and the temperature-dependent plots on the integrated PL-intensity ratios show distinctive features supporting an evolution of bimodal size-distribution on the InAs coverage variation in the QD ensembles. These suggest that, in as-grown InAs QD ensembles with appropriate InAs coverage grown under an optimized condition, there can exist a specific bimodal size-distribution consisting of two groups of large and small QDs whose sizes are fixed, but whose numbers vary with the amount of InAs coverage with no rearrangement of the overall size-distribution profile. [Copyright &y& Elsevier]

A particle with a CdTe core and carbon mantle was produced by the advanced carbon-coating method which enables direct coverage with a carbon layer using an electron microscope. The coagulated particles containing approximately 30–200 CdTe particles produced by the gas evaporation method were covered with a carbon layer of about 7 nm thickness at 300°C. By heating these particles above 500°C, the sublimation process of a part of the CdTe particle can be directly captured by high-resolution transmission electron microscopy and recorded in real time on videotape. Sublimation on the CdTe(1 1 1) surfaces occurred in the step flow mode of two (1 1 1) layers. It was observed that two (1 1 1) zinc-blende layers changed to the (0 0 0 2) wu¨rtzite configuration unit just before sublimation. The condensation of CdTe on the sublimated particle surface and growth of CdTe in the carbon layers were also captured in the video image. These sublimation processes were discussed in terms of the existence of the polarity of II–VI compounds. [Copyright &y& Elsevier]

The formation of InAs self-assembled islands on the InP(3 1 1)B surface in Stranski–Krastanow growth mode is investigated. First, we study the island nucleation on (1 0 0) and (3 1 1)B surfaces by means of low-temperature photoluminescence. We show that the InAs deposition at a substrate temperature of 480°C leads to formation of islands during the deposition on (3 1 1)B InP surface. On the other hand, morphological transformation occurs only during an annealing stage on (1 0 0) surfaces. Such a difference is related to the lower surface energy cost of island formation on InP(3 1 1)B. Then, we study the island characteristics as a function of substrate temperature and growth rate. Smaller islands are achieved at lower growth temperature. It should be related to a fast nucleation step, followed by a diffusion controlled island growth stage. Finally, we investigate the island stability by performing annealing after growth. The island height increases and density decreases as a function of the annealing time. This implies that Oswald ripening takes place and thus island arrays on (3 1 1)B surface do not correspond to a free energy minimum. We conclude that the island formation on InP(3 1 1)B is mainly governed by kinetic effects. [Copyright &y& Elsevier]

Ordered arrays of self-assembled ErSi2−x, SmSi2−x, and DySi2−x nanowires aligned along Si [1 1 0] have been grown at 600°C on Si(0 0 1) vicinal substrates. The nanowires grow perpendicular to the Si dimer rows and are 1.5–5 nm wide, approximately 2 monolayers high and up to 1 μm long. These nanowires were characterized in situ with scanning tunneling microscopy. [Copyright &y& Elsevier]

Intermixing with Ga from the substrate, and In over Ga segregation during strain-induced formation of InGaAs quantum dots are studied experimentally with electron diffraction (RHEED) and theoretically with a kinetic rate equations-based growth model. Our growth model yields the temperature-dependent critical time for quantum dot formation. The results reproduce our RHEED data very well. Furthermore, the quantum dot volume calculated with the model agrees with independent measurements. Calculations of the time-dependent strain energy inside the quantum dots establish strain-relaxation by quantum dot formation. [Copyright &y& Elsevier]

Bi20TiO32 in the form of nanocones are reported for the first time, which have been found during the formation of Bi2Ti2O7 nanocrystals. Bi20TiO32 nanocones were prepared by metalorganic decomposition technique. From X-ray patterns, it was found that Bi20TiO32 is a metastable phase, and can transform gradually into Bi2Ti2O7 phase with the annealing time increasing at a temperature of 550°C. The image of field emission scanning electron microscopy shows that the lengths of the nanocones are up to several micrometers and the diameters of cusps range from 20 to 200 nm. The studies of transmission electron microscopy show that the nanocones are crystalline Bi20TiO32. The growth mechanism of Bi20TiO32 nanocones has been proposed, which is similar to the vapor–liquid–solid growth mechanism. [Copyright &y& Elsevier]

MnTe/ZnTe and MnSe/ZnSe superlattices are grown by molecular beam epitaxy (MBE) on GaAs(1 0 0) substrates 5°vicinal toward [0 &1macr; 1] direction. Crystal structures, lateral lattice spacings, and atomic step arrays on the growing surface are investigated by in situ reflection high energy electron diffraction (RHEED). The superlattices are grown on ZnTe or ZnSe buffer layers which are lattice relaxed with respect to the GaAs substrate and have uniform array of atomic steps on the surface. MnTe and MnSe layers grow coherently, respectively, on the ZnTe and ZnSe buffer layers and show RHEED patterns indicating a uniform array of atomic steps when their thicknesses are smaller than 1–2 ML. High-quality (MnTe/ZnTe)60 and (MnSe/ZnSe)60 vicinal superlattices can be prepared for the MnTe or MnSe layers thinner than 1–2 ML. [Copyright &y& Elsevier]

Abstract: Au-assisted growth of InAs nanowire by molecular beam epitaxy is highly governed by the surface diffusion kinetics on the surface and the sidewalls of the growing nanowire. In this paper, we discuss the effects of growth temperature, As/In flux ratio, substrate orientation on the growth of InAs nanowire by MBE technique and their influence on the length, growth rate and density of the obtained nanowires. The obtained results show that while increasing V/III ratio, the density and length of the grown nanowires increases. Also it has been found that the growth rate of the nanowires has been improved remarkably at higher V/III ratios. Moreover, the thickness of nanowire is found to decrease with increasing V/III ratio. [Copyright &y& Elsevier]

Abstract: We report on the particle diameter dependence of the growth rate of the InSb segment of InAs-InSb heterostructured nanowires grown by chemical beam epitaxy. The analysis of the growth rate reveals that the growth is limited by the Gibbs–Thomson effect and the effect of NW lateral dimensions on the nucleation rate during the layer by layer growth. In the temperature range explored, the surface diffusion of adatoms toward the particle and the growth temperature are not affecting the growth rate. [Copyright &y& Elsevier]

Abstract: A novel approach to fabricating a highly aligned one-dimensional (1D) surface nanostructure on the surface of Fe/ZnSe bilayers grown on GaAs (001) substrates is reported. The resulting 1D nano-grooves were found to align along the [110] direction with a spacing of about 7–10nm and a height of about 1–2nm, resulting in a circular arc reflection high-energy electron diffraction (RHEED) pattern when the e-beam is aligned with them. We present a model based on Ewald construction to explain the unusual RHEED observation. The formation mechanism of the 1D nano-grooves is possibly related to an Fe–Se exchange interaction and Fe-induced decomposition of several top ZnSe atomic layers with regional selection during high-temperature annealing. [Copyright &y& Elsevier]

Abstract: Modulation doping using Mn as an acceptor has been applied to the molecular beam epitaxial grown compressively strained InAs channels. Strain engineering has been accomplished by the growth of a graded, fully relaxed In x Al1− x As buffer layer on GaAs(001) substrates in which the In content x was increased from 0% to 75%. Transmission electron microscopical investigation of the heterostructures reveals the high quality of the heterostructures grown on top of the metamorphic buffer layer. Significant segregation and diffusion of the Mn doping profile is confirmed by secondary ion mass spectroscopical analysis. Both normal as well as inverted doped quantum well structures show pronounced Shubnikov-de Haas oscillations and quantum Hall effect plateaus. However, for the inverted heterostructures where a significant Mn concentration within the InAs channel can be detected, a strong resistance maximum at B=0T accompanied by a hysteretic behaviour and reproducible resistance jumps indicative of ferromagnetic ordering is observed. [Copyright &y& Elsevier]

Abstract: We study the formation of GaAs quantum dots (QDs) by droplet epitaxy on various GaAs surfaces. The fabrication process consists of two steps. First, liquid Ga droplets are grown in a Volmer-Weber-like mode. This is followed by crystallization under As pressure. We demonstrate fabrication of droplet epitaxial GaAs QDs on (001), vicinal (001), (110), and (311)A GaAs surfaces. On (311)A GaAs, QDs are formed with higher density and smaller height compared to (001) and (110), which is attributed to a higher energy barrier for surface diffusion. Values of the surface diffusion barrier are determined and its influence on temperature-dependent QD density is studied by means of a QD growth model. On vicinal (001) surfaces, step bunches are found to act as preferred nucleation sites for GaAs QDs which opens the possibility for a lateral positioning of the QDs by pre-patterning. [Copyright &y& Elsevier]

Abstract: It is known that by capping InAs/GaAs quantum dots (QDs), photoluminescence (PL) exhibits blue shift because InAs QD shrinks by intermixing of InAs with GaAs matrix. Moreover, stacked structure of InAs QDs on GaAs, which was preferable for QD lasers and vertical cavity surface emitting lasers (VCSELs), shows increased full-width at half-maximum (FWHM) of PL spectrum because QDs expand due to increase in this intermixing effect with the increase in number of stacking of QD/GaAs layers. Here, suppression of this intermixing was successfully tried by inserting an ultra-thin AlAs at the interfaces between InAs and GaAs layers. As experimental results, PL emission exhibited red shift. Furthermore, the size expansion of stacked QD was suppressed, which was confirmed by UHV-AFM. [Copyright &y& Elsevier]

Abstract: We introduce high mobility two-dimensional hole systems (2DHSs) in AlGaAs/GaAs heterosystems grown by molecular beam epitaxy (MBE). Utilizing a carbon filament source, two-dimensional hole gases (2DHGs) were fabricated on the (001) and (110) crystal plan. These samples exhibit low-temperature mobilities beyond 106 cm2/Vs at densities varying from 0.6 to 2.3×1011 cm−2. In order to explore the subband structure as a function of carrier density, aluminum top gates were deposited on the samples. The carrier density was found to show a hysteretic behavior when tuned with an external electric field. The origin of this effect will be discussed. It opens a way to adjust the hole density in a wide range within a single sample in the absence of an externally applied electric field. [Copyright &y& Elsevier]

Abstract: Na2Ti n O2 n +1 typed whiskers has been extensively used for frictional materials, reinforcement materials and high insulators, and TiO2 whiskers can be applied for catalyst support and photocatalysts. Na2Ti6O13 whiskers were easily synthesized by hydrothermal treatment of the mixed solution of spherical TiO2 powder with anatase structure and NaOH solution at 250°C for 4h. The sodium titanate (Na2Ti6O13) whiskers obtained had a smooth surface and high aspect ratio of 100nm below in diameter and 100μm above in length. TiO2 whiskers were obtained by acid treatment of the Na2Ti6O13 whiskers in 0.5M HCl solution at 100°C for 48h. This suggests that Na ions in the Na2Ti6O13 structure were extracted during acid treatment and the formed TiO2·nH2O hydrate was turned to the TiO2 whisker with anatase phase. [Copyright &y& Elsevier]

Abstract: We have studied the effect of coupling on spin polarization in two asymmetric double-layer quantum dot (DLQD) systems consisting of adjacent CdSe and CdZnSe layers. The thickness of the ZnSe barrier separating the CdSe QDs from the CdZnSe QDs in the DLQD structures was 20 monolayer (ML) and 60ML respectively. Experiments as a function of excitation power reveal that the inter-dot coupling is relatively strong in DLQD with the 20ML barrier, while it is rather weak when the barrier is thick (60). When a magnetic field is applied, the PL emitted by CdSe and CdZnSe QDs is partially circularly polarized due to the Zeeman splitting of the spin states in each layer material. While the degree of circular polarization emitted by the two layers was approximately the same when the barrier separating the layers was thick (60ML), a large difference in the degree of polarization between the PL emitted by the CdSe and by the CdZnSe QD layers was observed in the sample with the 20ML barrier. This barrier-dependent difference observed in the two DLQD structures is discussed in terms of coupling-dependent spin interaction between carriers localized in the adjacent QD layers. [Copyright &y& Elsevier]

Abstract: We have performed polarization-selective magneto-photoluminescence (PL) experiments on a self-assembled CdSe quantum dot (QD) system to investigate the spin relaxation time of the exciton. The intensities of the PL peak exhibited significant differences for the two circular polarizations when a magnetic field was applied. The degree of polarization at each energy within the broad PL line strongly depends on the separation of that energy position from the LO-phonon resonance condition. We have used a simple two-level rate equation model, including spin-flip time and exciton recombination time , to analyze the observed polarization of the PL. In this model, we are able to fit the magnetic field dependence of the spin polarization within the QD (which produces the PL polarization) by using as a fitting parameter. The fitting reveals that the parameter ranges from 2 to 8, and that it strongly depends on the energy separation between the PL emitted by specific dots of the QD ensemble and the LO-phonon resonance line. Thus, the spin relaxation time is much longer than the exciton recombination time, but the value of the ratio of the two times is a sensitive function of how close the PL emission is to the resonant excitation. [Copyright &y& Elsevier]

Abstract: The growth of self-organized dots of Mn-doped GaN on AlN by plasma-assisted molecular beam epitaxy was studied. The observations of reflection high-energy electron diffraction (RHEED) revealed that the transition of the growth mode from 2D to 3D was delayed by adding a small amount of Mn flux and it disappeared with the further increase in Mn flux. By atomic force microscope (AFM) measurement on a surface with uncapped dots, it was found that the 2D–3D transition occurs with the formation of high dots density only when a tiny amount of Mn flux was added. A possible mechanism for the suppression of the dot formation by additional Mn atoms is discussed. [Copyright &y& Elsevier]

Abstract: Single crystals of spin ladder-like compound CaCu2O3 (2-leg) have been grown by the traveling-solvent floating-zone method. It was shown that crystal quality depends much on the starting composition to form solvent (flux), oxygen pressure and growth rate. Large-size, inclusion-free CaCu2O3 crystals were grown under high oxygen pressure (7bar) using CuO-poor starting composition (CaO:CuO=2:1) to form the solvent. Ca(Cu1− x Zn x )2O3 (x=0.035, 0.07, 0.14) crystals grown under identical conditions contained inclusions such as Ca2CuO3 or CaO. Compositional analyses by energy-dispersive X-ray spectroscopy (EDXS) indicate that the Zn-ions are substituted at both Ca- and Cu-sites. All samples show antiferromagnetic behavior. [Copyright &y& Elsevier]

Abstract: The vapor-phase epitaxy (VPE) deposition of CdTe on III–V heterosubstrates was performed in order to investigate the formation of micro-pixels usable in X-ray and thermo-photovoltaic converters. InSb and (Ga)InSb layers grown by molecular beam epitaxy on semi-insulating GaAs (100) wafers were employed as substrates. In these layers, the presence of Ga- and In-rich dots (200–500nm in diameter) was detected using AFM and SEM-EDAX techniques. We found that these dots, which are in liquid phase at the VPE growth temperature (450°C), act as nucleation points during the VPE process and prompt the selective area deposition of CdTe leading to the formation of columnar structures. Two important trends related to the growth morphology were established. First, the group V element does not affect the growth of CdTe columnar structures, i.e. the formation of these structures is independent of As or Sb. Second, the In-rich dots prompt the formation of CdTe columnar structures than the Ga-rich dots better. [Copyright &y& Elsevier]

Abstract: Investigation into phenomenology and essence of the natural differentiation of borate melt components and its effect on nucleation and crystal growth were performed using differential-thermal and X-ray powder diffraction analyses, testing of molten state, and crystallization procedures, including seeding and growth of barium metaborate (BBO) crystals. The major reason of quasi-stable partial differentiation of components in this type of medium is the active polycondensation of their boron-oxygen anion units. This leads to a change in the ratio of actively interacting components and might change the composition and structure of complex anions as well as the configuration of cation–anion associative complexes that are primary elements for crystal genesis. These changes are responsible for the occurrence of subphases and glassy segregations in a wide range of volume ratios. The character of seeding and crystal growth in TSSG configuration correlates with the partial differentiation of melt components. The composites of the quasi-binary BaO–B2O3 and ternary BaO–B2O3–Na2O systems as well as the low-temperature phase of BBO (β-BaB2O4) were chosen as model objects. [Copyright &y& Elsevier]