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[Display omitted] • Polarity of GaN wurtzite was controlled by thermal ALD and ALA. • ALA buffer layer improved crystallinity of GaN thermal ALD. • 50 nm of high-quality GaN ALD with preferred orientation were deposited. • Self-limiting reaction of GaN was achieved within ALD growth rate regime. Ga-polar GaN thin films and N-polar GaN thin films were fabricated by using thermal ALD and plasma assisted ALA processes, respectively. The polarity of GaN wurtzite thin films was determined by cross-sectional STEM analysis of as-deposited films and top-view SEM images after KOH wet-etching. The crystallinity and grain size of thermal ALD GaN were drastically increased with the GaN ALA buffer layer. The ALA Ar plasma pulse in each ALD cycle decreased the oxygen and carbon impurity content and improved the crystallinity of GaN thin films by removing organic ligands. High purity GaN thin films were successfully deposited on oxide-free Si (1 1 1) substrate by using the ALA process with 100 ms of TDMAGa with push gas, 3 × 800 ms of N 2 H 4 , and 15 s of 25 W ALA plasma pulse with −25 V stage DC bias at 275 °C. The lowest FWHM value (0.59°), smooth surface morphology (RMS=1.0 nm), and 10–20 nm grain size of columnar GaN thin films were obtained by tuning process parameters. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ar+ bombardment and subsequent annealing treatment resulted in Ga atom segregation in the Ga doped single crystals of ZnO with the dopant concentration of ∼0.005 %. • Plentiful atomic reconstructions were successfully prepared on ZnO(0001) surface. • Three distinct evolutionary pathways from disorder to (2 × 8) reconstruction were observed. Preparing atomic reconstructions and tracking their evolutionary pathways on polar surfaces of wurtzite ionic crystals remain a big challenge in surface science. Here, we addressed this challenge by introducing Ga surface segregation through Ar+ bombardment and subsequent annealing treatment. By employing ZnO(0001) surface as a model system for wurtzite ionic crystals, we generated various atomic reconstructions and observed three distinct evolutionary pathways. These pathways involved complex dynamic processes including atom desorption and movement, and each pathway started with a disordered surface and ended with a (2 × 8) reconstruction. Tracking all the pathways, the overall reconstruction route can be put in order as "disorder → (√3 × √3)R30° → (2 × 2) → (2 × 4) → (2 × 8)", as the surface Ga concentration is increased. These atomic reconstructions are proposed to originate from the alternations in the valence state of cation and the influence of surface segregation on the vacant states of dangling bonds. Our discoveries present a comprehensive framework for generating a multitude of atomic reconstructions and elucidating their evolutionary pathway on intricate polar surfaces of wurtzite ionic crystals. [ABSTRACT FROM AUTHOR]

ZnO ultrathin films supported on Cu, Ag or Au are attracting increasing interest because they can form under special conditions on commercial Cu/ZnO/Al 2 O 3 catalysts for methanol synthesis, or can be used as alternative materials for catalysis, or as prototypes of the so-called inverse catalysts. In the present study, we have investigated the thickness dependence of the structure and electronic properties of free standing and Cu(111) supported ZnO ultrathin films by means of DFT + U calculations. On the free-standing films, a flat graphitic-like morphology is observed up to 10 layers, where a transition to wurtzite-like structures occurs. On Cu(111), a slightly corrugated graphitic structure is obtained for ZnO films up to 4 layers. From 5 layers on, the rumpling becomes substantial and a phase transition to wurtzite takes place. The driving force behind the destabilization of flat graphitic films on Cu(111) is the charge transfer from the underlying Cu support to the film. This finding rationalizes the experimental observations that the transformation from graphitic to wurtzite polymorph of ZnO films on Cu takes place above 5-layer thickness. Unlabelled Image • Thickness dependence of structural and electronic properties of ZnO and ZnO/Cu(111) films • Charge transfer from Cu support to the ZnO film governs film morphology. • The transformation of ZnO/Cu(111) films from graphitic-like to wurtzite occurs at 5 layers thickness. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Sn doped ZnO nanowires wrapped by non-polar (2 1 ¯ 1 ¯ 0) surface and (0001) and (1 0 1 ¯ 1) polar surfaces. • Strain concentration around planar defects lowered the energy in the wurtzite lattice. • Lowered Oxygen vacancy (Vo) concentration after doping led to reduced deep level emission. Abstract Polar surface dominated Sn doped ZnO nanowires (NWs) with an octagonal shaped cross section have been fabricated by chemical vapor deposition method. The NWs grew along [01 1 ¯ 0] direction, and were wrapped by non-polar surface (2 1 ¯ 1 ¯ 0) and polar surfaces (0001) and (1 0 1 ¯ 1). Planar defects in (0001) plane were formed in the middle of the doped NWs, and strain concentration occurred around the planar defects, which might lower the energy in the wurtzite lattice and thus maintain polar surface dominated configuration. X-ray photoelectron spectroscopy (XPS) and Raman tests reveal that the concentration of Oxygen vacancy (V O) was significantly lowered after doping, which led to the reduced deep level emission (DLE). [ABSTRACT FROM AUTHOR]

[Display omitted] • Mg-doped zincblende GaN thin film samples were grown on GaAs substrates by plasma-assisted MBE. • Ga-rich regime conditions at the surface on the growth front yields nearly 100 % zincblende phase purity. • Higher Mg doping cell temperatures and N-rich conditions prompt wurtzite formation and twinning on the 〈 111 〉 faces. Zincblende (zb) GaN thin films doped with Mg were grown by molecular beam epitaxy on GaAs under Ga- and N-rich conditions and different Mg cell temperatures. X-ray diffraction and electron-backscatter diffraction determined the ideal orientation of the zb-GaN, its textural relationship to the substrate, wurtzite and twin content, and their interfaces with the GaN matrix. A comparison to pole figure simulations allowed a thorough description of orientation of wurtzite inclusions and twins, forming interfaces along the 〈 111 〉 directions of the matrix. The results revealed zincblende volumetric purities as high as 99.9 % and twinning as low as 1.3 %. Ga-rich conditions and lower doping cell temperatures led to the highest phase purities. Moreover, crystalline and surface quality are also deeply linked to the wurtzite inclusions and twinning obtained. Films with the least amounts of these displayed the highest quality. This is likely due to excess Ga atoms on the surface helping the Mg doping atoms incorporate more orderly into the growing film. The results from this investigation provide a deeper understanding of the effects of Mg doping on the crystalline structure of zb-GaN films, paving the way for practical applications of zincblende nitrides in modern optoelectronic devices. [ABSTRACT FROM AUTHOR]

We demonstrate pure wurtzite InAs nanowires over a wide diameter range. The nanowires are grown on an InP (1 1 1)B substrate by Au-catalyzed metal organic chemical vapor deposition. The crystal structure of nanowires strongly depends on the growth temperature and V/III ratio. Under optimized growth condition, pure wurtzite phase is obtained over the full length of the tens-of-micrometer-long nanowire, covering a broad diameter range of 70–420 nm. The broad diameter range of wurtzite phase is attributed to a high actual V/III ratio due to a reduction of In amount because of the InP substrate. The pure wurtzite nanowires exhibit much higher electron mobility than those with dense stacking faults, showing great potential in high-speed electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Wurtzite BAlN alloy with large bandgap is an emerging material system for UV optoelectronic and power devices. In this study, the BAlN/GaN heterojunction with a sharp interface and uniform distribution of the elements was formed by careful control of epitaxial conditions to avoid GaN desorption and parasitic reactions whose band alignment was then measured for the first time. The valence band offset (VBO) was found to be nearly-zero, i.e. −0.2 ± 0.2 eV, in the B 0.14 Al 0.86 N/GaN heterojunction by X-ray photoelectron spectroscopy. Additionally, the conduction band offset (CBO) is estimated at 2.1 ± 0.2 eV, which is the largest reported CBO among epitaxial GaN-based heterojunctions. In comparison to the type-I Al 0.75 Ga 0.25 N/GaN heterojunction (both Al 0.75 Ga 0.25 N and B 0.14 Al 0.86 N alloy have the same bandgap of 5.7 eV), the CBO and VBO of the B 0.14 Al 0.86 N/GaN heterostructure are significantly larger and smaller, respectively. The nearly-zero VBO and the very large CBO of the B 0.14 Al 0.86 N/GaN heterojunction could potentially lead to considerable performance enhancement for GaN optoelectronics and power electronics devices. [ABSTRACT FROM AUTHOR]

ZnO nanowire (ZNW) arrays were in-situ grown on the sensing electrode via a facile hydrothermal route for NO 2 sensing application. ZNW arrays were prepared by a seed layer deposition on the surface of the sensing electrode using a dipping process in a Zn(CH 3 COO) 2 ·2H 2 O ethanol solution followed by a seed growth using a hydrothermal route in the Zn(NO 3 ) 2 ·6H 2 O-HMTA (C 6 H 12 N 4 ) system. The microstructural characterizations of the ZNW arrays by means of XRD, FESEM, TEM, FTIR and XPS showed that ZnO nanowires with the diameters of 80–90 nm and the lengths of 0.6–1 μm had a single crystal hexagonal wurtzite structure. Gas sensing properties demonstrated the response of the sensor based on the ZNW arrays was linearly proportional to the NO 2 concentration in the range of 1–30 ppm with good reproducibility and selectivity. The maximum sensor response to NO 2 was obtained at an operating temperature of 250 °C. The response and recovery times reduced rapidly with increasing the operating temperature. The growth mechanism and sensing mechanism of the ZNW arrays were discussed in accordance with the deposition of the seed layer and the modulation of the depletion layer, respectively. [ABSTRACT FROM AUTHOR]

Effects of lattice and polar/nonpolar mismatch between the GaP layer and Ge(111) substrate are investigated by spatially resolved Raman spectroscopy. The red shifted transverse optical (TO) and longitudinal optical (LO) phonons due to residual strain, along with asymmetry to TO phonon ∼358 cm −1 are observed in GaP/Ge(111). The peak intensity variation of mode ∼358 cm −1 with respect to TO phonon across the crystallographic morphed surface of GaP micro structures is associated with the topographical variations using atomic force microscopy mapping and Raman spectroscopy performed on both in plane and cross-sectional surface. Co-existence of GaP allotropes, i.e. wurtzite phase near heterojunction interface and dominant zinc-blende phase near surface is established using the spatially resolved polarized Raman spectroscopy from the cross sectional surface of heterostructures. This consistently explains effect of surface morphology on Raman spectroscopy from GaP(111). The study shows the way to identify crystalline phases in other advanced semiconductor heterostructures without any specific sample preparation. [ABSTRACT FROM AUTHOR]

We report an investigation of the optical and structural properties of wurtzite phase Al x Ga 1− x N/AlN structure grown on Si(111) within the compositional range of 0 ≤ x ≤ 1. The study focuses on providing essential physical quantities for the fabrication process control, namely the composition dependence of phonon mode energy and refractive index. Three complementary techniques, infrared ellipsometry, Raman spectroscopy and X-ray diffraction, have been used to minimize uncertainties in our analysis. Based on the high quality and nearly strain-free Al x Ga 1− x N/AlN double layer samples, we determined the calibration curve for the A 1 (LO) phonon mode. We have also constructed the ellipsometry model which uses a-priori knowledge of experimentally measured A 1 (TO) phonon mode frequencies. From the best model fit to the collected ellipsometry spectra of the entire sample series, we obtained the anisotropic refractive indices of the Al x Ga 1− x N alloys with a very satisfactory accuracy. [ABSTRACT FROM AUTHOR]

Zn-Ti-O thin films with different concentrations of titanium were deposited by reactive magnetron co-sputtering in a reactive Ar/O 2 atmosphere from zinc and titanium targets. It was found that with increasing Ti content the structure of the films gradually changes from a fully crystalline pure ZnO wurtzite structure with a strongly preferred columnar orientation to an amorphous Zn-Ti-O material with 12.5 at.% Ti. The optical parameters (spectral refractive index and extinction coefficient, optical band gap) and thickness of the films were analysed by the combined evaluation of ellipsometric measurements and measurements of transmittance on a UV–vis spectrophotometer. For evaluation of optical parameters was used Cody-Lorentz dispersion model. [ABSTRACT FROM AUTHOR]

Mg doped ZnO films with hexagonal wurtzite structure were deposited on c-cut sapphire Al 2 O 3 substrates by pulsed laser deposition. Both room temperature ferromagnetism and band gap of the films simultaneously tuned by the concentration of oxygen vacancies were performed. Our results further reveal that the singly occupied oxygen vacancies should be responsible for the room temperature ferromagnetism and band gap narrowing. Singly occupied oxygen vacancies having the localized magnetic moments form bound magnetic polarons, which results in a long-range ferromagnetic ordering due to Mg doping. Moreover, band gap narrowing of the films is probably due to the formation of impurity band in the vicinity of valence band, originating from singly occupied oxygen vacancies. These results may build a bridge to understand the relationship between the magnetic and optical properties in oxide semiconductor, and are promising to integrate multiple functions in one system. [ABSTRACT FROM AUTHOR]

Undoped and F-doped CdS thin films were succesfully grown on the glass substrates by the spray prolysis method. X-ray diffraction results showed that all the samples had hexagonal wurtzite structure with the (1 0 1) preferred orientation. It was found from scanning electron microscopy that an increase in the grain size was observed after F-doping. The band gap value of CdS thin films increased from 2.38 eV to 2.42 eV with the increase of F concentration from 0 to 6 at.%. The intensity of room temperature photoluminescence spectrum of undoped CdS thin films enhanced with the increment of F-doping amount that is related to the increase of point defects formed by the flourine atoms. Electrical measurements showed that the carrier concentration increased from 1.93 × 10 12 cm −3 to 7.62 × 10 12 cm −3 when CdS thin films were doped with 2 at.% F. However, further increase in F amount up to 6 at.% caused a decrease in the carrier concentration. On the other hand, resistivity value first decreased from 1.26 × 10 5 Ω cm to 8.54 × 10 4 Ω cm with the increase of F-doping up to 2 at.% and then increased to 1.65 × 10 5 Ω cm for 6 at.% F-doping. It can be concluded that 2 at.% F-doped CdS thin films exhibited the best electrical and optical properties, which is suitable for the application of thin film solar cells. [ABSTRACT FROM AUTHOR]

In this work, ZnO microrods were produced by hydrothermal synthesis. DNA was extracted from pork spleen cells by cellular lysis, deproteinization and precipitation. The analysis of the DNA binding to the ZnO was performed using Raman spectroscopy a technique that allowed for the evaluation of the effect that the presence of the ZnO in the complex has on the DNA structure. Vibrational spectral bands from the DNA molecule and hexagonal wurtzite ZnO were observed and classified as E 2 (M), A 1 (TO), E 2 (High), E 1 (LO) and 2LO. The Raman signals from the vibrational bands corresponding to the phosphodiester bond 5′-C-O-P-O-C-3′ and bond stretching of the PO 2 − group, as well as ring vibrations of the nitrogenous bases of the DNA, were enhanced by the presence of the ZnO microrods. The bands from the modes corresponding to the C-O and O P O − molecules of the DNA backbone were observed to exhibit larger spectral shifts due to the compression and tensile stresses generated at the ZnO/DNA interface, respectively. In addition, the relative vibrational mode intensities of the nitrogenous bases increased. [ABSTRACT FROM AUTHOR]

[Display omitted] • Quasi-ternary ZnO/MgO alloys are grown by MBE as an alternative to random alloys. • The highest mean Mg concentration is reaching 72%. • Critical thickness of Mg layers for retaining wurtzite crystallinity is established. • HAADF images confirmed thicknesses of ZnO and MgO layers assessed with two approaches of simulation of XRD diffractograms. • Biaxial strains at interfaces are partly responsible for creation of ZnMgO region, which influences WZ structure retainment. The analysis of heteroepitaxially grown ZnO/MgO superlattices on a -oriented ZnO substrates was described. The influence of unalike natural crystalline structures of ZnO and MgO on the interface's abruptness and retaining wurtzite crystallinity was studied. Wurtzite structure was found to be retained in the MgO thin barriers up to 1.5 nm, but creation of nonuniform biaxial strains and some interdiffusion of Mg from barriers to ZnO QW's seemed to be inevitable. The complex strain/composition heterogeneities can be explained by the difference of vapor pressure between Mg (p = 1.93 Pa) and Zn (p = 0.22 Pa) elements at growth temperatures and high mobility of Mg atoms, which are gladly incorporated into ZnO matrix. As a result, a subtle three monolayers in size ZnMgO film was created at the interfaces, which was partly responsible for retaining the wurtzite structure of coherently grown MgO layers. [ABSTRACT FROM AUTHOR]

The nitrogen 1 s near edge X-ray absorption fine structure (NEXAFS) of gallium nitride (GaN) shows a strong natural linear dichroism that arises from its anisotropic wurtzite structure. An additional spectroscopic variation arises from lattice strain in epitaxially grown GaN thin films. This variation is directly proportional to the degree of strain for some spectroscopic features. This strain variation is interpreted with the aid of density functional theory calculations. [ABSTRACT FROM AUTHOR]

Photoelectron diffraction is proposed to determine nondestructively the polarity of wurtzite crystals with polar surfaces ( c -plane). Small segments of polar plots of photoemission from anion core levels in the ( 1 0 1 ¯ 0 ) azimuthal plane are qualitatively different for two polarities around the polar angle 20°. The magnitude of the ratio of electron photoemission intensities at two polar angles I 20 / I 23 can be utilized as a simple criterion determining the crystal polarity. [ABSTRACT FROM AUTHOR]

Highlights: [•] A simple one-pot colloidal approach has been developed to prepare CuInS2 nanoplates. [•] The as-obtained CuInS2 nanoplates possess a wurtzite phase. [•] Higher temperature and time extension can facilitate the growth of CuInS2 nanoplates through the cation inter-diffusion. [•] The as-obtained CuInS2 nanoplates can self-assemble into face-to-face columns. [ABSTRACT FROM AUTHOR]

Highlights: [•] (La,Sr)MnO3-ZnO 1D heterostructures were successfully fabricated using the cross-linked inclined ZnO nanostructures as a template. [•] (La,Sr)MnO3 nanolayers experience grain coarseness during high-temperature annealing. [•] High-temperature thermal annealing at 950°C in an oxygen-rich ambient reduces crystal defects in the (La,Sr)MnO3 nanolayer. [ABSTRACT FROM AUTHOR]

Abstract: Deposition of cadmium sulfide (CdS) thin film on BK7 glass substrates has been prepared by a dry and in situ fabrication process with ion-beam sputtering deposition at room temperature. The structural, optical and electrical properties of CdS thin film were investigated. X-ray diffraction (XRD) analysis indicates the formation of polycrystalline CdS film with the mixed structure of cubic and hexagonal wurtzite phase. The Raman peaks are observed at 304cm−1 and 606cm−1, and these peaks are identified as the first and second order LO optical phonons form of the CdS film. Energy dispersive X-ray Spectrometer (EDS) shows no other impurity elements, except Cd and S. The as-deposited film exhibits good transfer of the sintered target material with almost the same Cd/S ratio. Scan electron microscopy (SEM) and atomic force microscopy (AFM) reveal that the CdS thin film has a smooth surface and exhibited an obvious columnar growth indicating the c-axis preferred orientation. The detected room-mean-square (RMS) roughness by AFM is 0.76nm. Optical transmission and absorption spectroscopy measurement reveal high absorption and energy band gap is of about 2.32eV. The CdS thin film is of n-type conductivity and the resistivity is found to be in the order of 104 Ωcm. The CdS films annealed at 100°C were demonstrated to be improvement in structural, electrical and optical properties. [Copyright &y& Elsevier]

Abstract: The carbon thin films were grown on different substrates with different buffer layers by laser molecular beam epitaxy (LMBE) with a high purity graphite carbon target. A UV pulsed KrF excimer laser with a wavelength of 248nm was used as laser source. The structure, surface morphology and other properties of the carbon thin films were characterized by Raman spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED) and atomic force microscopy (AFM). The results show that the properties of the carbon thin films and the formation of the graphene film have a strong relation to the structure and properties of the substrate. The substrate with a hexagonal wurtzite structure which is similar to the hexagonal honeycomb structure of the carbon atoms arranged in the graphene is more beneficial for the formation of the graphene thin film. In our experiment conditions, the carbon films grown on sapphire substrates with different buffer layers have an ordered structure and a smooth surface, and form high quality tri-layer graphene films. [Copyright &y& Elsevier]

Abstract: In this study, ZnO nanostructures were grown on various ultra-thin layers coated (100)-oriented SrTiO3 (STO) single-crystal substrates using thermal evaporation of metallic zinc at 600°C. This study used the ZnO seed layer and/or metal catalyst layer to grow high-density ZnO nanostructures on STO substrates. X-ray diffraction and scanning electron microscopy (SEM) measurements showed that the use of Au and Ag catalysts is crucial in producing ZnO nanostructures with a preferential c-axis direction. The as-grown ZnO nanostructures had a hexagonal facet. Among various STO substrates (Au/STO, Ag/STO, ZnO/STO, Au/ZnO/STO, and Ag/ZnO/STO), the ZnO nanostructures grown on the Au/STO substrate had the highest degree of vertical alignment, and the intensity ratio of the UV to visible emission band reached 55. Conversely, the ZnO nanostructures grown on the ZnO seed layer-coated STO substrate were more randomly oriented, and the intensity ratio of the UV to visible emission band was only 9.5. The cathodoluminescence (CL) results showed that higher vertically aligned ZnO nanostructures have lower-density crystal defects. The current–voltage measurements supported the structural analysis. [Copyright &y& Elsevier]

Abstract: Undoped and Mg-doped ZnO thin films were deposited on Si(100) and quartz substrates by the sol–gel method. The thin films were annealed at 873K for 60min. Microstructure, surface topography and optical properties of the thin films have been measured by X-ray diffraction (XRD), atomic force microscope (AFM), UV–vis spectrophotometer, and fluorophotometer (FL), respectively. The XRD results show that the polycrystalline with hexagonal wurtzite structure are observed for the ZnO thin film with Mg:Zn=0.0, 0.02, and 0.04, while a secondary phase of MgO is evolved for the thin film with Mg:Zn=0.08. The ZnO:Mg-2% thin film exhibits high c-axis preferred orientation. AFM studies reveal that rms roughness of the thin films changes from 7.89nm to 16.9nm with increasing Mg concentrations. PL spectra show that the UV–violet emission band around 386–402nm and the blue emission peak about 460nm are observed. The optical band gap calculated from absorption spectra and the resistivity of the ZnO thin films increase with increasing Mg concentration. In addition, the effects of Mg concentrations on microstructure, surface topography, PL spectra and electrical properties are discussed. [Copyright &y& Elsevier]

Abstract: This paper presents the investigation of the properties of GaN nanowires synthesized from Ni-catalyzed chemical vapour deposition method under various growth temperatures. The influence of the growth temperatures on the morphological, structural and optical characteristics of the synthesized GaN nanowires was investigated in this work. Field-emission scanning electron microscopy images revealed that the 950°C was the optimal growth temperature for synthesizing uniform, straight and smooth morphology of GaN nanowires. X-ray diffraction results demonstrated that the synthesized low dimensional GaN structures have the hexagonal wurtzite structure. Ultraviolet and blue emissions were detected from photoluminescence measurements. In addition, phonon replicas with the energy separation of 90meV have been observed at the lower energy of the blue emission region in photoluminescence spectra. [Copyright &y& Elsevier]

Abstract: The Zn0.9Co0.1O films are fabricated by chemical solution deposition method. All the films have the ZnO wurtzite structure with a preferential orientation along the c-axis. The analysis of X-ray near-edge absorption spectroscopy and X-ray photoelectron spectroscopy indicates that the valence of Co is +2, and there are oxygen vacancies in Zn0.9Co0.1O films annealed in Ar atmosphere. Extended X-ray absorption fine structure results reveal that Co2+ ions have dissolved into ZnO and substituted for Zn2+ ions. Magnetization measurements show that the film annealed in Ar exhibits ferromagnetism which can be explained by the formation of bound magnetic polarons. [Copyright &y& Elsevier]

Abstract: Polycrystalline In x Ga1−x N thin films were prepared by mixed source modified activated reactive evaporation (MARE) technique. The films were deposited at room temperature on glass substrates without any buffer layer. All the films crystallize in the hexagonal wurtzite structure. The indium concentration calculated from XRD peak shift using Vegard''s law was found to be varying from 2% to 92%. The band gap varies from 1.72eV to 3.2eV for different indium compositions. The indium rich films have higher refractive indices as compared to the gallium rich films. The near infra-red absorption decreases with gallium incorporation into InN lattice which is mainly due to decrease in the free carrier concentration in the alloy system. This fact is further supported from Hall effect measurements. MARE turns out to be a promising technique to grow In x Ga1−x N films over the entire composition range at room temperature. [Copyright &y& Elsevier]

Abstract: Wurtzite zinc oxides films (ZnO) were deposited on silicon (001) and corning glass substrates using the pulsed laser deposition technique. The laser fluence, target–substrate distance, substrate temperature of 300°C were fixed while varying oxygen pressures from 2 to 500Pa were used. It is observed that the structural properties of ZnO films depend strongly on the oxygen pressure and the substrate nature. The film crystallinity improves with decreasing oxygen pressure. At high oxygen pressure, the films are randomly oriented, whereas, at low oxygen pressures they are well oriented along [001] axis for Si substrates and along [103] axis for glass substrates. A honeycomb structure is obtained at low oxygen pressures, whereas microcrystalline structures were obtained at high oxygen pressures. The effect of oxygen pressure on film transparency, band gap E g and Urbach energies was investigated. [Copyright &y& Elsevier]

Abstract: The Cu-doped ZnO and pure ZnO powders were synthesized by sol–gel method. The structural properties of the samples were investigated by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. All the results confirmed that copper ions were well incorporated into the ZnO lattices by substituting Zn sites without changing the wurtzite structure and no secondary phase existed in Cu-doped ZnO nanoparticles. The Zn0.97Cu0.03O nanoparticles exhibited ferromagnetism at room temperature, as established by the vibrating sample magnetometer analysis. [Copyright &y& Elsevier]

Abstract: The properties of ZnO quantum dots (QDs) synthesized by the sol–gel process are reported. The primary focus is on investigating the origin of the visible emission from ZnO QDs by the annealing process. The X-ray diffraction results show that ZnO QDs have hexagonal wurtzite structure and the QD diameter estimated from Debye–Scherrer formula is 8.9nm, which has a good agreement with the results from transmission electron microscopy images and the theoretical calculation based on the Potential Morphing Method. The room-temperature photoluminescence spectra reveal that the ultraviolet excitation band has a red shift. Meanwhile, the main band of the visible emission shifts to the green luminescence band from the yellow luminescence one with the increase of the annealing temperature. A lot of oxygen atoms enter into Zn vacancies and form oxygen antisites with increasing temperature. That is probably the reason for the change of the visible emission band. [Copyright &y& Elsevier]

Abstract: Room temperature soft chemical deposition route has been utilized to grow thin films of ZnO on glass substrate. Annealing at 673K removed zinc hydroxide phase and nanofibrous ZnO films with wurtzite crystal structure were obtained. Decrease in the room temperature electrical resistivity from 107 to 104 Ωcm was observed after annealing. The nanofibrous ZnO thin films were sensitive to the explosive liquefied petroleum gas (LPG) and the maximum response of 17% at 698K under the exposure of 6500ppm of LPG was obtained. [Copyright &y& Elsevier]

Abstract: Free standing nanoparticles of ZnO doped with transition metal ion Mn have been prepared by solid state reaction method at 500°C. X-ray diffraction (XRD) analysis confirmed high quality monophasic wurtzite hexagonal structure with particle size of 50nm and no signature of dopant as separate phase. Incorporation of Mn has been confirmed with EDS. Bio-inorganic interface was created by capping the nanoparticles with heteromultifunctional organic stabilizer mercaptosuccinic acid (MSA). The surface morphological studies by scanning electron microscopy (SEM) showed formation of spherical particles and the nanoballs grow in size uniformly with MSA capping. MSA capping has been confirmed with thermo gravimetric analysis (TGA) and FTIR. Photoluminescence (PL) studies show that the ZnO:Mn2+ particles are excitable by blue light and emits in orange and red. Occurrence of room temperature ferromagnetism in Mn doped ZnO makes such biocompatible luminescent magnetic nanoparticles very promising material. [Copyright &y& Elsevier]

Abstract: We investigated the microstructure and optical properties of Zn1−x Mn x O films synthesized by the magnetron sputtering technique. Structural analyses suggest that Mn occupied the Zn sites successfully and did not change the wurtzite structure of ZnO. In addition, nanoscale columnar grain arrays were found in the Mn-doped ZnO films. The experimental results indicate that moderate Mn doping could enhance the photoluminescence emission of ZnO. The possible origin of the emissions from our samples was also explored. [Copyright &y& Elsevier]

Abstract: The Cu/ZnO nanocomposite films have been synthesized by cathodic electrodeposition and characterized using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), photoluminescence (PL) and field emission microscope (FEM). The XRD pattern shows a set of well defined diffraction peaks, which could be indexed to the wurtzite hexagonal phase of ZnO. In addition, characteristic diffraction peaks corresponding to Cu and Zn are also observed. The SEM image shows formation of two-dimensional (2D) hexagonal sheets randomly distributed and aligned almost normal to the substrate. Uniformly distributed small clusters of Cu nanoparticles possessing average diameter of ∼25nm, as revealed from the TEM image, are seen to be present on these 2D ZnO sheets. The selected area electron diffraction (SAED) image confirms the nanocrystalline nature of the Cu particles. From the field emission studies, carried out at the base pressure of ∼1×10−8 mbar, the turn-on field required for an emission current density of 0.1μA/cm2 is found to be 1.56V/μm and emission current density of ∼100μA/cm2 has been drawn at an applied field of 3.12V/μm. The Cu/ZnO nanocomposite film exhibits good emission current stability at the pre-set value of ∼10μA over a duration of 5h. The simplicity of the synthesis route coupled with the better emission properties propose the electrochemically synthesized Cu/ZnO nanocomposite film emitter as a promising electron source for high current density applications. [Copyright &y& Elsevier]

Abstract: ZnO thin films with thikness d =100nm were deposited onto different substrates such as glass, kapton, and silicon by radio frequency magnetron sputtering. The structural analyses of the films indicate they are polycrystalline and have a wurtzite (hexagonal) structure. The ZnO layer deposited on kapton substrate shows a stronger orientation of the crystallites with (002) plane parallel to the substrate surface, as compared with the other two samples of ZnO deposited on glass and silicon, respectively. All three layers have nanometer-scale values for roughness, namely 1.7nm for ZnO/glass, 2.4nm for ZnO/silicon, and 6.8nm for ZnO/kapton. The higher value for the ZnO layer deposited on kapton substrate makes this sample suitable for solar cells applications. Transmission spectra of these thin films are strongly influenced by deposition conditions. With our deposition conditions the transparent conducting ZnO layer has a good transmission (78–88%) in VIS and NIR domains. The values of the energy gap calculated from the absorption spectra are 3.23eV for ZnO sample deposited onto glass substrate and 3.30eV for the ZnO sample deposited onto kapton polymer foil substrate. The influence of deposition arrangement and oxidation conditions on the structural, morphological, and optical properties of the ZnO films is discussed in the present paper. [Copyright &y& Elsevier]

Abstract: Well-aligned ZnO nanorod arrays were synthesized by low-temperature wet chemical bath deposition (CBD) method on Si substrate under different conditions. Results illustrated that dense ZnO nanorods with hexagonal wurtzite structure were vertically well-aligned and uniformly distributed on the substrate. The effects of precursor concentration, growth temperature and time on nanorods morphology were investigated systematically. The mechanism for the effect of preparation parameters was elucidated based on the chemical process of CBD and basic nucleation theory. It is demonstrated that the controllable growth of well-aligned ZnO nanorods can be realized by readily adjusting the preparation parameters. Strong near-band edge ultraviolet (UV) emission were observed in room temperature photoluminescence (PL) spectra for the samples prepared under optimized parameters, yet the usually observed defect related deep level emissions were nearly undetectable, indicating high optical quality ZnO nanorod arrays could be achieved via this easy process chemical approach at low temperature. [Copyright &y& Elsevier]

Abstract: The structural stability of GaP nanowires (NWs) with facets including twin planes is systematically investigated using our empirical potentials which incorporate the electrostatic interaction between surface cations and anions. The cohesive energy of GaP NWs for diameter of 30nm demonstrates that the wurtzite structure is the most stable over entire diameter range. This is because the electrostatic interaction between surface cations and anions is dominant around twin planes, resulting in the small energy deficit compared to that on polar facets. By comparing the cohesive energy of GaP NWs consisting of facets with that of facets, the NWs consisting of facets are found to be favorable than those consisting of facets over entire diameter range. These results imply that growth processes such as vapor–liquid–solid mechanism could affect on the formation of NWs consisting of facets. [Copyright &y& Elsevier]

Abstract: In–N codoped ZnMgO films have been prepared on glass substrates by direct current reactive magnetron sputtering. The p-type conduction could be obtained in ZnMgO films by adjusting the N2O partial pressures. The lowest resistivity was found to be 4.6Ωcm for the p-type ZnMgO film deposited under an optimized N2O partial pressure of 2.3mTorr, with a Hall mobility of 1.4cm2/Vs and a hole concentration of 9.6×1017 cm−3 at room temperature. The films were of good crystal quality with a high c-axis orientation of wurtzite ZnO structure. The presence of In–N bonds was identified by X-ray photoelectron spectroscopy, which may enhance the nitrogen incorporation and respond for the realization of good p-type behavior in In–N codoped ZnMgO films. Furthermore, the ZnMgO-based p–n homojunction was fabricated by deposition of an In-doped n-type ZnMgO layer on an In–N codoped p-type ZnMgO layer. The p–n homostructural diode exhibits electrical rectification behavior of a typical p–n junction. [Copyright &y& Elsevier]

Abstract: We proposed in the present work that large-scale synthesis of sensitive ZnO–SnO2 nanofibres which can be obtained via a simple electrospinning method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction patterns (XRD) showed the average diameter of ZnO–SnO2 nanofibres ranging between 100 and 200nm, the mixture of wurtzite (ZnO) and rutile (SnO2) structure in the composite fibers. The sensitivity of the obtained ZnO–SnO2 nanofibres to toluene was also investigated. The results showed that under optimal conditions, the calibration curve of response versus toluene concentration was linear in the range of 10–300ppm, the response and recovery time were only several seconds, and sensitivity for toluene was desirable. [Copyright &y& Elsevier]

Abstract: Mg x Zn1−x O (x =0.0–0.20) thin films have been deposited by sol–gel technique on glass substrates and the effect of growth ambient (air and oxygen) on the structural, and optical properties have been investigated. The films synthesized in both ambient have hexagonal wurtzite structure. The c-axis lattice constant decreases linearly with the Mg content (x) up to x =0.05, and 0.10 respectively for air- and oxygen-treated films, above which up to x =0.20, the values vary irregularly with x. The change in the optical band gap values and the ultraviolet (UV) peak positions of Mg x Zn1−x O films show the similar change with x. These results suggest that the formation of solid solution and thus the structural and optical properties of Mg x Zn1−x O thin films are affected by the growth ambient. [Copyright &y& Elsevier]

Abstract: ZnO:Al(AZO) thin films with different Al-doped concentration were developed under different temperature. The effects of the temperature and Al-doped concentration on the infrared emissivity were investigated. Results show that the crystalline phase of the AZO films is hexagonal wurtzite which is the same as that of the un-doped ZnO film. The crystalline size become larger and the particle shapes become more regular with the increase of temperature, which lead to the increase of resistivity and the decreases of the infrared emissivity. [Copyright &y& Elsevier]

Abstract: Zinc oxide (ZnO) nanocrystals doped with different groups of impurities, e.g., Li, Na, Cu, Pr and Mg synthesized by solid-state reaction method under similar conditions exhibit different morphology. XRD showed monophasic wurtzite structure but change in lattice parameters and Zn–O bond length indicates incorporation of dopant ion in ZnO lattice. The morphology of ZnO nanocrystals exhibited striking dependence on type of dopant ion with the shape changing from nanorods, spherical to petal like particles. Photoluminescence (PL) shows pronounced UV emission and negligible visible emission for Li, Na and Cu doped ZnO nanocrystals with peak positions coinciding with that of undoped ZnO. Whereas signature emission of Pr3+ ion as well as broad visible emission from Mg doped ZnO revealed the role of intra gap metastable states formed by the dopant ion in the emission process. [Copyright &y& Elsevier]

Abstract: Zinc oxide (ZnO) thin films were deposited on microscope glass substrates by sol–gel spin coating method. Zinc acetate (ZnAc) dehydrate was used as the starting salt material source. A homogeneous and stable solution was prepared by dissolving ZnAc in the solution of monoethanolamine (MEA). ZnO thin films were obtained after preheating the spin coated thin films at 250°C for 5min after each coating. The films, after the deposition of the eighth layer, were annealed in air at temperatures of 300°C, 400°C and 500°C for 1h. The effect of thermal annealing in air on the physical properties of the sol–gel derived ZnO thin films are studied. The powder and its thin film were characterized by X-ray diffractometer (XRD) method. XRD analysis revealed that the annealed ZnO thin films consist of single phase ZnO with wurtzite structure (JCPDS 36-1451) and show the c-axis grain orientation. Increasing annealing temperature increased the c-axis orientation and the crystallite size of the film. The annealed films are highly transparent with average transmission exceeding 80% in the visible range (400–700nm). The measured optical band gap values of the ZnO thin films were between 3.26eV and 3.28eV, which were in the range of band gap values of intrinsic ZnO (3.2–3.3eV). SEM analysis of annealed thin films has shown a completely different surface morphology behavior. [Copyright &y& Elsevier]

Abstract: The zinc blende (ZB)–wurtzite (W) polytypism of GaAs layers at the Au/GaAs(111)B interfaces is investigated based on total-energy electronic-structure calculations within density functional theory. The calculations for the abrupt interfaces including a GaAs top layer with ZB and W stacking sequences reveal that the ZB sequence is energetically favorable, but the energy of W sequence with an interstitial Au atom at the top GaAs layer of the interface is lower than that of ZB sequence. This is because electrons accumulate around the interstitial region due to the hybridization between Au-6s and As-4p orbitals, resulting in the reduction of Ga–As bond charges. As a result, the relative stability at the top GaAs layer is determined by the electrostatic energy due to ionic charges. The results imply that the stabilization of W sequence at the Au catalyst–semiconductor interfaces as well as that on the nanowire faces are the origins for the appearance of W segments in NWs, qualitatively consistent with experiments. [Copyright &y& Elsevier]

Abstract: Structural trends in group III–V semiconductor nanowires (NWs) are systematically investigated based on Monte-Carlo simulations using our empirical potential calculations. The calculated NW stacking sequences for the selective area growth demonstrate that the averaged periodicity between wurtzite segments, which is independent of the NW size, decreases with increasing ionicity of semiconductors . It is also found that the periodicity is affected by the nucleus size of NWs: The calculated periodicity in InP (InAs) NWs with the nucleus size consisting of 10 atoms are 0.76 (0.86) nm, reasonably consistent with the experimentally reported one. On the other hand, the nucleus size to reproduce the experimentally reported periodicity in GaAs NWs is estimated to be more than 70 atoms. These results thus imply that the nucleus size as well as is of importance in determining the averaged periodicity between wurtzite segments. [Copyright &y& Elsevier]

Near-field photoluminescence (PL) was measured from ZnO film, composed of nanocrystallites with zinc-blend (ZB) and wurtzite (W) structures, on a sapphire (0 0 0 1) substrate at room temperature (RT). The size of nanocrystallites was in the range of 30–50 nm. Using a fiber probe with aperture size of 80 nm, two near-field emission peaks attributed to one ZB and one W structures were observed. The difference in the emission energies was 0.10 eV close to the calculated bandgap difference between ZB and W structures. The intensity of emission peak from ZB structure with lower energy was stronger than that from W structure, which is supposed to be resulted from the quenched excitonic effect of W structure. [Copyright &y& Elsevier]

[Display omitted] • The work function of polytypic GaP nanowires was studied via Kelvin probe microscopy. • The work function is different for wurtzite (4.2 eV) and zinc blende (4.34 eV) GaP. • Flat defects act like wurtzite insets decreasing the work function of zinc blende GaP. • Sub-monolayer arsenic shell increases the work function up to 4.75 eV. In this work we investigate effects of the crystal phase, twinning defects and shell formation on the work function distribution over the surface of axially heterostructured GaP/GaPAs/GaP nanowires via frequency-modulated Kelvin probe force microscopy. Analysis of experimental data is supported by theoretical model based on density functional theory and Schrodinger–Poisson calculations. The study revealed that the work function of pure (110) ZB and (11 2 ¯ 0) WZ GaP is 4.34 eV and 4.20 eV respectively. The work function is found to be sensitive to the lattice twinning period which can additionally shift it between the value of WZ and ZB. Formation of a sub-monolayer thick GaPAs shell results in drastic increase of the work function (up to 4.75 eV). Thus, in this work we introduce several techniques for manipulating GaP nanowire work function. The ability to distinguish different crystal phases of the same material by means of Kelvin probe microscopy is shown for the first time. [ABSTRACT FROM AUTHOR]

[Display omitted] • The heterophase junction of WS accelerates the separation and transfer of photogenerated carriers; • The internal electric field of wurtzite' (0 0 2) active facets improves photogenerated carriers' separation; • the synergistic effects of the exposed active facets, heterophase interface and inherent defects increase vacancies in WS; • The cost of photocatalysts can be greatly reduced using natural sphalerite as raw material. The development of stable and efficient photocatalysts is a basic requirement for photocatalytic treatment of heavy metal pollutants. For this study, a composite photocatalyst (W x S 1-x) consisting of hierarchical nano-sphere wurtzite with exposed active facets and natural sphalerite was constructed. Optimized as W 0.4 S 0.6 , it was able to reduce Cr (VI) at an efficiency of 97.11% in 30 min via photocatalysis, which was 4.20 times that of natural sphalerite. The key factors enhancing the photocatalytic performance of WS are the exposed active facets of wurtzite, the heterogeneous transition layer and the inherent mineralization defects of natural sphalerite, all combining to increase vacancies. Furthermore, the separation of photogenerated electrons and holes is more efficient thanks to the built-in electric field induced by the active facets and the heterophase junction, which contributes to the material's overall photocatalytic efficiency. Multiple characterizations were done, revealing the photocatalytic mechanism that was just outlined. This study provides a new approach to constructing high-efficiency and low-cost photocatalysts by combining defect engineering and heterojunction design. [ABSTRACT FROM AUTHOR]

Abstract: Mg-doped ZnO thin films were fabricated by laser ablation of Zn:Mg targets consisting of Mg metallic strips and Zn disk in oxygen atmosphere with a goal to facilitate convenient control of Mg contents in the films. The characteristics of the deposited films were examined by analyzing their photoluminescence (PL), X-ray diffraction and X-ray photoelectron spectroscopy (XPS) spectra. Mg contents as analyzed by XPS indicate that the target composition is fairly transferred to the deposited films. The wurtzite structure of ZnO was conserved even for the highly doped ZnO films and there was no Mg- or MgO-related XRD peaks. With increase in the Mg content, the bandgap and PL peak energy shifted to blue and the Stokes shift became larger. [Copyright &y& Elsevier]

Abstract: A variational approach is used to study the surface states of an electron in a semi-infinite wurtzite nitride semiconductor. The surface-state energy of the electron is calculated, by taking the effects of the electron–surface optical phonon interaction and structure anisotropy into account. The numerical computation has been performed for the energies of the electronic surface states as a function of the surface potential V 0 for wurtzite GaN, AlN, and InN, respectively. The results show that the electron–phonon interaction lowers the surface state energy. It is also found that the energies of the electronic surface-state in wurtzite structures are lower than that in the zinc-blende structures by hundreds of meV for the materials calculated. The influence of e–p-interactions on the surface state of electron cannot be neglected. [Copyright &y& Elsevier]