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Vanadium dioxide with superior thermal sensitivity is one of the most preferred materials used in microbolometer, and the B phase of VO2 is particularly prominent. However, conventional VO2 (B) undergoes low temperature-coefficient of resistance (TCR) values and large resistances. In this paper, simple controllable composite films of vertical graphene nanowalls/VO2 (B) (i.e., VGNWs/VO2 (B)) with a suitable square resistance (12.98 kΩ) and a better temperature-coefficient of resistance (TCR) (−3.2%/K) were prepared via low pressure chemical vapor deposition. The VGNWs can provide a fast channel for electron transport and enhance the conductivity of VO2 (B). This preparation method can provide a low cost, facile and simple pathway for the design and fabrication of high performance VO2 (B) thin films with superior electrical properties for its application in uncooled infrared detectors. Keywords: Vertical graphene nanowalls, VO2 (B) films, Chemical vapor deposition, Uncooled infrared detectors

The influence factors on the defect types in vertical graphene nanosheets (VGNs) are widely researched while few systematic research has been reported on the growth temperature, which should play an important role in the transformation of defects types. In this work, VGNs were grown via plasma enhanced chemical vapor deposition (PECVD) method in the atmosphere of CH4, H2 and Ar. Based on SEM, Raman, XPS, NEXAFS and UPS spectrum analysis, we found that the types of defects in VGNs have clearly transformed from vacancy-like to boundary-like, corresponding to the rising growth temperature. Moreover, NEXAFS suggests that features near 7.7 eV are attributed to boundary-like defects, as well as −6.7 eV in UPS, providing an intuitive and half-quantitative direction to characterize boundary-like defects in VGNs. Additionally, the sheet resistance (from 1386 to 175 Ohm/Sq) and the wetting angle (from 148° to 121°) decrease as the temperature rises. It shows that changing the growth temperature, as the easy and effective method, is crucial of modulating the properties of VGNs owning to the transition of defects types from vacancy-like to boundary-like.

This work first reports the controllable preparation of rGO/VO2(B) intercalation films via a simple sol-gel method at relative low temperature (420 °C). The excellent conductance and thermal conductivity of rGO could significantly enhance the performance and sensitivity of VO2(B) films to be used for uncooled infrared detectors. Aluminum (Al) reduction is introduced to reduce the oxygen-containing functional groups of graphene oxide (GO) and V2O5 of GO/V2O5 intercalation films in a two-zone furnace. According to our results, the reduced-GO (rGO), as a fast channel for electron transport, was inserted into the VO2(B) film, and thus the electron transfer between rGO/VO2(B) intercalation films occurs much faster than in pure VO2(B) films. The film preparation processes were optimized through adjusting the doping concentration of rGO, and rGO/VO2(B) intercalation films with applicable temperature coefficient of resistance (TCR) (−2.78%/K) and square-resistance (21.22 kΩ) were achieved. Our work provided a promising and feasible technique to convict the cost and complexity of high vacuum method used to fabricate the VO2 thermal sensing thin films.

A comparative study of anti-reflection microstructures (ARMs) and ARMs with Al2O3 coatings (Al2O3/ARMs) on zinc selenide (ZnSe) has been carried out. The transmittance and electric field intensities were analyzed and presented using finite-difference time-domain (FDTD) simulations. ARMs were successfully fabricated on ZnSe surfaces by reactive ion etching and an Al2O3 layer was deposited onto the ARMs by an ion beam sputtering method. The theoretical analysis and experimental results showed that the transmittance of Al2O3/ARMs-treated ZnSe had a close relationship with the thickness of Al2O3 layer and was higher than that of ARMs-treated ZnSe in the 2–5 μm wavelength range, which was due to the fact that the Al2O3/ARMs had a better graded refractive index profile. The angle-dependent reflectance of ZnSe with Al2O3/ARMs was lower than that with ARMs. A difference of the spatial distribution of the electric field intensity between ARMs and Al2O3/ARMs was observed due to the surface Al2O3 coating, which predicted qualitative laser damage thresholds for both structures. The results of this study provide potential applications in high-efficiency IR optoelectronic devices and high power mid-infrared laser systems.

Endowing vanadium dioxide (VO2) thin films with excellent thermal sensitive performance is greatly desired for application in uncooled infrared (IR) detectors. Here, we demonstrate a strategy of co-doping by using a simple and feasible CVD method to synthesize Mo-Al-doped VO2(B) thin films with high temperature-coefficient-of-resistance (TCR, −3.6%/K) and favorable square resistances (16.2 kΩ). Both the TCR and resistance are superior to that of undoped and Al-doped VO2(B) thin film, and the TCR is larger than that of Mo-doped VO2(B) thin film. The underlying microscopic mechanism for the performance improvement might be that Mo-Al co-doping creates less lattice deformation, strain and inhomogeneity of carrier concentration due to dimension and charge compensation than that of single-doping and the partly release of 3d electrons around V4+-V4+ pairs in co-doping films. Besides, the special two-dimensional octahedral structure of monoclinic (C2/m) VO2(B) favors the strain control with doping. The films have been subjected to synchrotron radiation based X-ray photoelectron spectroscopy (SRPES) and X-ray absorption near edge structure (XANES) techniques to study the local atomic and electronic structure around V ions. The results indicated that the dopants of Mo and Al were incorporated into the VO2 lattice and occupied some of the V lattice sites, resulting in the formation of the V1-x-yMoxAlyO2 substitution solid solution. V L-edge and O K-edge XAS results identically verified that Mo-Al co-doping might create the least lattice deformation in films. Hence, the high performance of films proves that the co-doping strategy is suitable for uncooled infrared detector applications.

Eco-friendly “green” electronics are attracting increasing interests in recent years. Here, biodegradable organic/inorganic hybrid indium-tin-oxide electric double layer (EDL) transistors were fabricated on plastic substrates. Solution processed chitosan based polysaccharide films were used as gate dielectrics. Due to extremely high EDL capacitances of the chitosan-based electrolytes, the oxide EDL transistors exhibit good performances. Resistor loaded inverters were also built, exhibiting full-swing characteristics and high voltage gains at low operation voltages. Wave-type conversions were realized including conversions from sinusoid waves into rectangular waves and from noise signals into two-bit outputs. Furthermore, the organic/inorganic hybrid transistors can be dissolved in water easily. The proposed organic/inorganic hybrid oxide transistors may have potential applications in “green” portable devices.

Due to the high lattice symmetry and special three-dimensional crystal channel, sulvanite Cu3VSe4 is predicted to be a new type of thermoelectric material with good performance. In this work, the energy band diagram and phonon spectrum of Cu3VSe4 with sulvanite structure were calculated using density functional theory, and Cu3VSe4 pure phase was experimentally synthesized through the combination of the elements using conventional solid-state reactions. Surprisingly, the thermoelectric characterization reveals that Cu3VSe4 is a semiconductor with electron-hole co-transport feature, which results in the poor thermoelectric performance due to the recombination of electrons and holes at low temperature. While holes gradually dominate with the increase of temperature and Cu3VSe4 possesses a high Seebeck coefficient of 558 μV/K at 571 K. Our results may serve as the groundwork for future research on the structure and thermoelectric properties of Cu3VSe4.

Batteries with fast recharge rates while maintaining sufficient capacity are highly attractive for applications such as electric transportation and electrical storage of renewable sources. Designing an electrode structure that enables facile transport of lithium ions and electrons is an effective way to enhance capacity retention at fast charge and discharge rates. Here, we report a LiFePO4 (LFP) cathode as the model electrode with directional microstructure using an in-house developed freeze tape casting (FTC) technique. The microstructure and electrochemical performance of the electrodes with different freeze velocity and solid content were investigated, and an optimized directional electrode microstructure was obtained. The optimized LFP electrode exhibited competitive discharge capacities of 123.8 and 40.7 mA h g−1 at 0.1 and 15 C respectively, where 15 C represents ~4 min charge or discharge. For comparison, the capacity of conventional LFP cathodes containing typical tortuous porous microstructures often drops to negligible levels at the fast charge and discharge rate of 15 C. A relatively large cathode (~10 cm × 5 cm) containing the directional microstructure was fabricated, demonstrating the scalability of the FTC technique.

This work reports a new method for low-temperature, cost-effective fabrication of VO2(B) thin films, which is assumed to be the preferred phase structure for the application in uncooled infrared detectors using chemical vapor deposition (CVD) in a three-zone furnace. While high-vacuum techniques are extensively used nowadays which together with high temperature post-annealing are very complicated in operation and expensive, our method successively achieves the facile and scalable synthesis of thermal sensitive VO2(B) thin films with high TCRs (from −2.4%/K to −2.89%/K) and favorable square resistances (10 kΩ–40 kΩ) at a growth temperature range of 375–450 °C. The output results are comparable to the reported values of the high-vacuum synthesized VO2(B) thin films, proved our method suitable for uncooled infrared detector applications.

Nanocomposites of (1-x)CuFe2O4/xNiO (x = 10% to 50 wt %) have been synthesized utilizing a chemical co-precipitation method. In order to obtain the required phase, the samples have been annealed at 600 °C for 6 h. The x-ray Diffraction (XRD) technique has been used for the crystallographic structure analysis which not only confirms the coexistent of both copper ferrite (CuFe2O4) and nickel oxide (NiO) phases in all samples but also verifies the absence of any impurity phases. The average crystallite size as estimated via XRD patterns show that the average size lies in the range of 22–36 nm which has also been confirmed by TEM. The FTIR absorbance spectra also show the characteristic vibration modes of cation at tetrahedral and octahedral sites. The electrical properties like A.C. conductivity, impedance, Dielectric constant, and Tangent loss has been measured by LCR meter. The results show that with the increase in NiO concentration, electrical conductivity increases for all concentration while dielectric constant decreases up to 30% NiO wt% and increases with further addition of NiO. The real and imaginary parts of impedance depict same dispersion i.e the impedance decreases at higher frequency due to increase in conductivity. Moreover the magnetic characterizations performed by VSM, reveal that the hysteresis loops exhibit normal behavior of ferromagnetic/ferrimagnetic materials for all compositions but the coercivity (Hc), and saturation magnetization (Ms) decreases with the increase in NiO contents that transform the material in to soft magnetic.

In this study, the influence of Si ions irradiations (12 MeV energetic) on structural and optical characteristics of InGaN/GaN thin film has been investigated. Irradiation was performed at different Si ions fluences in the range of 1×10 13 to 1×10 15 ions/cm 2 . X-ray diffraction (XRD) pattern of pristine film indicates only the (0 0 2) oriented crystallites of InGaN while the irradiated films patterns showed other phases (InN and GaN) as well. Ion irradiations at different dose rates have shown no or negligible effect on grain size of InGaN except a shift in the peak position which demonstrates the development of tensile stresses. The existence of other phases in the irradiated films patterns is the indication of InGaN phase separation. Defects produced due to irradiation were also confirmed from peak shifting and appearance of new peak at 669 cm −1 in Raman spectra. A decrease in optical bandgap with the increase of ion irradiation dose rate is being reported in this work.

The Nanocomposites of CuFe 2 O 4 /ZnO have been synthesized by two steps wet chemical coprecipitation method under optimum condition. The crystal structure, particle size, and morphology of the synthesized samples have been characterized by X-ray Diffraction (XRD) and electron microscopy techniques. The XRD measurements have depicted the formation of required phases of nanocomposites and no impurity phases are being observed. The FTIR analysis confirm the presence of vibration bands at the surface of synthesized materials. The magnetic properties have been measured by Vibrating Sample Magnetometer (VSM) under applied field of ±2 T, all the samples except pristine ZnO have shown superparamagnetic behaviour for all concentration with decreasing saturation magnetization. The electromagnetic wave (EMW) absorption properties have been studied by reflectometer under frequency range of 2–10 GHz. The maximum absorption of 42.35 dB has been achieved at frequency of 8.35 GHz with 30% ZnO. Moreover with concentration ≥40% of ZnO whole frequency band below −10 dB has been covered. The observed results show that these nanocomposites have excellent microwaves absorption properties due to the compatibility of dielectric and magnetic properties.

The nanocomposites of (SnO 2 ) x (CuFe 2 O 4 ) (1−x) (where x=0–100 wt%) have been successfully synthesized via two steps chemical method. XRD pattern has revealed the formation of inverse spinal phases with tetragonal crystal structure without any impurity phases for CuFe 2 O 4 sample. The thermodynamic solubility limit of SnO 2 in CuFe 2 O 4 matrix has been found to be 30 wt% and above this percentage crystal phases related to SnO 2 started to appear. The average particle size and shape of CuFe 2 O 4 nanoparticles have been strongly influenced by addition of SnO 2 as depicted by TEM results. FTIR results have confirmed the existence of cation vibration bands at tetrahedral and octahedral sites along with Sn-O vibration band at higher concentrations, which also validates the formation of nanocomposites. Furthermore, the dielectric constant, tangent loss and conductivity of CuFe 2 O 4 nanoparticles have been found to increase up to 30 wt% addition of SnO 2 and then decreases with further increase which is attributed to variations in resistivity and space charge carriers. Magnetic measurements have shown that saturation magnetization decreases from 35.68 emu/gm to 10.26 emu/gm with the addition of SnO 2 content.

The nanocomposites of MgO/CuFe 2 O 4 has been prepared by two steps co-precipitation method at low temperature. The crystal structure, morphology and particle size have been characterized by X-ray Diffraction (XRD) and Transmission electron microscopy (TEM). The average crystallite size lies in the range of 20–32 nm and XRD pattern also confirms the coexistent of both phases without impurity related phases. The TEM images reveal that spherical CuFe 2 O 4 magnetic nanoparticles are embedded in MgO Matrix. The Fourier Transform Infrared Spectroscopy (FTIR) results show the stretching and bending vibrations of tetrahedral and octahedral sites of ferrites along with vibration mode of MgO. The magnetic characterization has been performed by Vibrating Sample Magnetometer (VSM) at room temperature under the applied field of ±2T. The M-H loop of MgO shows ferromagnetic behavior at low field value of ±0.5 T due to oxygen vacancies defects and diamagnetic behavior at higher field value. On the other hand, the CuFe 2 O 4 nanoparticles shows normal superparamagnetic behavior with 30.78emu/gm saturation magnetization. Morever with the increase in concentration of MgO, the coercivity remains same but saturation magnetization decreases due to decrease in volume percent of magnetic contents. The electromagnetic wave absorption properties has been measured by vector analyzer in the frequency range of 2–10 GHz and best absorption reach to −25.35 dB at frequency of 8.38 GHz. Furthermore at higher concentration of MgO ≥40%, it covers the whole frequency band below −10 dB. This excellence microwave absorption may be due to the effective complementarities between dielectric and magnetic loss in this novel MgO/CuFe 2 O 4 nanocomposites.

VO 2 (B) is currently a preferred phase structure for the application as bolometer material, which, however, suffers from low temperature-coefficient-of-resistance (TCR) values and large resistances. Here we present the combined experimental and first-principles calculations study on both doped and undoped VO 2 (B) thin films enabling us to attain high TCR (−3.9%/k) and suitable square-resistance (32.7 kΩ) by controlled W doping employing the widely used magnetron sputtering technique. The TCR value is 50% larger than reported ones at the similar resistance. The underlying microscopic mechanism for the performance improvement was studied and results indicated that the introduction of extra electrons and the variation in the band structure resulting from the incorporation of W 6+ ions in the VO 2 (B) crystal lattice contribute to the enhancement of the electronic conductivity. Moreover, the special two-dimensional octahedral structure of monoclinic ( C 2/m) B-phase VO 2 favors the strain control with W-doping for achieving a large TCR, which overcomes the analogous predicament between the high conductivity and large TCR generated by dopants in the M-phase VO 2 . The present findings provides a facile and simple pathway for the design and fabrication of high performance W-doped VO 2 (B) thin films rendering superior optical and electrical properties for its wide applications in thermo-opto-electro sensing devices.

Monoclinic vanadium dioxide is a thermochromic material for advanced applications to smart optoelectronic devices. However, the poor visible-light transmission and high phase transition temperature (Tc) of VO2 hinder its practical use. Our first-principles calculations show that group IV elements (Si, Ge, Sn, Pb) doping may be an efficient way to reduce the Tc of VO2, which is coupled with the changes in the geometry and electronic structures, i.e., the decrease in Tc is associated with the correlation between the volume and the β angle, and the variable band gaps between eg and t2g are narrowed by 0.05–0.37 eV after doping. In addition, group IV elements (Si, Ge, Sn, Pb) doping can improve the absorption and transmittance of light in the low energy region, favoring the efficient utilization of sunlight in the infrared region. Our findings would provide a useful guidance for fabrication of high quality VO2 based thermochromic materials.

Introduction of broadband antireflection coatings (ARCs) is a promising method to enhance efficiency of solar cells. In this paper, the TiO 2 –SiO 2 stack coatings with refractive-index-grade structure are proposed and have been successfully fabricated via sol–gel dip-coating technique. The structure, morphology, optical properties and wettability of TiO 2 –SiO 2 stack coatings were systemically investigated. The broadband antireflection performance is improved over the solar spectrum with increase of solar transmittance by 7.80% and maximum transmittance of 99.16% at 550 nm on glass slide substrates. The responding reflectance is largely reduced and the minimum values in visible and near-infrared regions are 0.40% and 0.05%, respectively. By introducing broadband ARCs, the efficiency of Cu(In,Ga)Se 2 solar cells is increased from 11.20% to 12.15%, which reveals superiority and importance of TiO 2 –SiO 2 stack coating as an outstanding antireflection material, having high potential for practical applications.

Graphene/ceramic composites are proposed by directly depositing graphene on the insulating Al2O3 particles by chemical vapor deposition without any metal catalysts. Carbothermic reduction occurring at the Al2O3 surface is vital during the initial stage of graphene nucleation and the graphene sheet can connect with neighboring sheets to completely cover Al2O3 particles. The quality and layer number of graphene on Al2O3 can be finely tailored by changing the growth temperature and gas ratio. Graphene coated Al2O3 (G-Al2O3) composites are used as effective fillers of stearic acid (SA) to increase the thermal transport property. By the optimization of the layer number of graphene, size of Al2O3 particles and ratio of G-Al2O3/SA in a quantitative, their thermal conductivities significantly increase up to 11 folds from 0.15 to 1.65 W m−1 K−1. The great improvement is attributed to the high thermal transfer performance of graphene and excellent wettability between graphene and SA. When the G-Al2O3/SA composites with the graphene coated porous Al2O3 foam, the thermal conductivity further reaches to 2.39 W m−1 K−1, and the corresponding latent heat is 38 J g−1. It demonstrates the potential applications of graphene in thermal transport and thermal energy storage devices.

Direct growth of graphene on Al2O3 film is successfully achieved assisted with NiAl2O4 film on a SiO2 substrate by chemical vapor deposition at 800 °C. The Ni particles are first uniformly separated out on the substrate, and play an important role in capturing carbon atoms and accelerating the nucleation to grow high quality graphene rooting on insulating Al2O3 film. The thickness of graphene films can be tuned from two layers to few layers (

A phase change material consisting of three-dimensional graphene aerogel (GA) and octadecanoic acid (OA) was produced. The GA was assembled from the sheets of graphene oxide in a hydrothermal reaction. The pore sizes of the network were several micrometers and the pore walls consisted of thin layers of stacked graphene sheets. OA was impregnated into GA by capillary forces, with the GA acting as the support. The GA/OA composite had a thermal conductivity about 2.635 W/m K at a GA loading fraction of ∼20 vol%, which was about 14 times that of the OA (0.184 W/m K). The transient heating and cooling responses of the material were investigated for thermal energy storage. The GA had a low bulk density so that the weight percent of the GA in the composite was only about 15%. The composite presents a high heat storage capacity of 181.8 J/g, which was very close to the value of the OA alone (186.1 J/g).

Tungsten bronze compounds M 2 KNb 5 O 15 ( M =Ca, Sr, Ba) were successfully synthesized, and the luminescence properties were investigated. Among the three compounds, Ca 2 KNb 5 O 15 showed an obviously broad band of host luminescence at 460 nm with exciting at 269 nm. By doping Eu 3+ into the M sites, Ca 2 KNb 5 O 15 :Eu 3+ displayed strong red emission from Eu 3+ ions characteristic transitions, nearly four times higher than Sr 2 KNb 5 O 15 :Eu 3+ and seven times higher than Ba 2 KNb 5 O 15 :Eu 3+ . Crystal packing factor (PF) was introduced to account for this luminescence difference, lower PF being correlated to higher luminescence intensity for perovskite-related structure. Both the as-prepared compounds and the literature examples were proved to fit this correlation. This can be explained through the influence of the structural packing on the environment distortion and crystal field splitting of the doping site.

A novel two-step process combining surface catalyzed process with segregation growth was used to prepare single crystal hexagonal bilayer graphene domains on Cu metal substrates by ambient pressure chemical vapor deposition. Carbon atoms are first dissolved into the quasi-melting Cu metal at 1080 °C and then segregated on the Cu surface to form nucleation centers of single-layer graphene during cooling. The graphene crystallites spontaneously act as templates to induce the carbon atoms to form hexagonal bilayer graphene domains. The bilayer graphene domains are size-tunable by controlling the growth conditions. The yield of the bilayer graphene is over 90% and the defect-free domains reach ∼100 μm in size, greater than the reported single-layer domains.

Red emission of monoclinic Zr (1−2 x ) Eu x M x O 2 ( M = Nb, Ta; x = 0.05) was enhanced by the M addition, about five times higher than Zr 0.95 Eu 0.05 O 2 excited by 395 nm or 469 nm at room temperature. The corresponding quantum yield improves 2–4 times, achieving ∼13%. The luminescence enhancement is attributed to that the codoped Eu 3+ and M 5+ ions result in the seven-coordinated Eu 3+ activators with the low symmetry C 1 , compared with the eight-coordinated high symmetric (D 2d ) Eu 3+ ions coexisted with oxygen vacancies in Zr (1−x) Eu x O 2 . The thin film of Zr 0.90 Eu 0.05 Nb 0.05 O 2 , deposited by radio frequency magnetron sputtering method, also shows intensely red emission.

In this paper, three-dimensional (3D) graphene network was prepared by chemical vapor deposition (CVD) on 3D porous Ni template. The as-prepared 3D graphene showed high conductivity of ∼600 S cm −1 and low square resistance of 1.6 Ω sq −1 . With the aid of 3D graphene network, the poorly conductive LiFePO 4 exhibited high conductivity and good rate performance of 109 mA h g −1 at 10 C, indicating potential application in high rate lithium ion batteries.

Double perovskite Ca 2 LaSbO 6 , successfully synthesized by solid state reaction method, was identified by Rietveld refinements to crystallize in the monoclinic space group P 2 1 / n , which is isostructural to Ca 2 La M O 6 ( M =Nb, Ta). Excellent red luminescence of Eu-doped Ca 2 La M O 6 ( M =Sb, Nb, Ta) can be obtained and no luminescence quenching effect was observed when Eu-doping level reached 40%. For Ca 2 La 0.6 NbO 6 :0.4Eu 3+ , quantum efficiencies of 20.9% and 27.7% were reached to show high light conversion and bright red emission excited at 465 nm (blue light) and 534 nm (green light), respectively, comparable to the commercial phosphors. Through systemic investigation for the series of double perovskite compounds, the excellent red emission in Ca 2 LaMO 6 is attributed to highly distorted polyhedra of EuO 8 (low tolerance factor of the pervoskite), and large bond distances of La−O (low crystal field effect of the activator).

In a traditional hot-filament chemical vapor deposition (HF-CVD) system, highly (111)-textured diamond film was deposited on Si (111) substrate treated by diamond powder ultrasonic scratching or other methods. The relationship between the (111)-textured diamond film growth and the nucleation density has been discussed. The morphologies and structures of the films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy.

Rings of single-walled carbon nanotubes (SWNTs) with a high yield of 30-50% have been fabricated through a floating catalytic chemical vapor deposition (FCCVD) method. The SWNT rings, which were characterized as the self-looping nanotube coils, feature a relative small diameter of 100-300 nm and a thin thickness of 1-8 nm. The high yield of the SWNT rings has been ascribed to the unique experimental configuration which could favor the as-synthesized straight SWNTs to bend freely and easily to form the coil-shaped structures. The technique presented here may advance the new understanding to bulk-prepare the nanotube rings. (c) 2006 Elsevier B.V. All rights reserved.

A new experimental technique has been presented to investigate the surface-enhanced Raman scattering (SERS) on “individual and untouched” single-walled carbon nanotubes (SWNTs) deposited onto gold or silver film-covered substrate through a direct CVD method. It was found that the radial breathing mode for SERS shows a narrower linewidth than the normal Raman spectroscopy (NRS). Relative to NRS, the SERS spectra also revealed a preferable contribution to some metallic component of the G line. However no obvious difference for D and G′ between SERS and NRS has been revealed, which is different from the previous results on bulk SWNT samples.

In this letter, the ordered FeS2 (pyrite) nanowire arrays were firstly fabricated by sulfurizing the Fe nanowires that were electrodeposited in the pores of anonic aluminum oxide (AAO). The results revealed that pyrite nanowires are well formed when sulfurized at 450 degrees C for 8 h. The FeS2 nanowire arrays are highly ordered and have high wire packing densities. The successfully fabricated pyrite semiconducting nanowire arrays should be of significant interest in practical applications as the semiconductor electrodes especially for photovoltaic solar cells. (c) 2005 Elsevier B.V. All rights reserved.

Nanocrystalline ZnS films have been prepared by sulfidation of the reactive magnetron sputtered ZnO films. The structure, composition and optical properties of the sulfurized ZnO films as a function of the sulfidation temperature (TS) have been systematically studied. It is found that at TS ⩾ 400 °C ZnO is completely converted to ZnS with the hexagonal structure. The ZnS films have a strongly (0 0 2) preferred orientation and an optical transparency of about 80% in the visible region. In addition, at TS

Branching structures in nanometer level are of great importance in developing nanoscale science and functional electrical devices. In this letter, multidimensional magnesium oxide structures with cone-shaped branching have been mass-produced using a simple chemical vapor deposition method. The dominant structures in the product include two-dimensional ‘+’, ‘T’, or ‘Γ’ assemblies, and three-dimensional complex configurations. The results presented here enrich the nanoscale community with new basic materials for the fabrication of functional electrical and chemical sensing devices.

Synchrotron radiation with surface X-ray diffraction is conducted to study pyrite FeS2 films on Si (10 0) wafers. The results show that the "strong (2 0 0) reflection" for the FeS2/Si(1 0 0) sample primarily comes from the stress peak of the silicon substrate, other than the effect of the preferred orientation of pyrite crystal grains which has been assumed previously. On the contrary, the FeS2/Si(1 0 0) sample actually indicates a strong preferred growth along (3 1 1) orientation, and this preferential growth of pyrite films becomes intenser with the prolonged annealing time. (C) 2004 Elsevier B.V. All rights reserved.

Positron annihilation spectroscopy (PAS) was conducted to study microstructure defects in pyrite FeS2 films deposited on glass and Si substrates. PAS provides unique information that the main defects existing in pyrite films sulfurized at 300°C are sulfur vacancies, and pyrite films with better crystallization are obtained when sulfurized at 400°C as a consequence of the reduction of the number of sulfur vacancies present in the films. On increasing the sulfurizing temperature higher than 400°C, the obvious 3γ decay shows that much nanoscale pores must appear in the films, which might worsen the performance of the pyrite films. Also our research indicates that a thin transition layer might be formed in the interface region resulted from the epitaxial growth and thermal diffusion for pyrite films deposited on Si substrates.

The effect of sulfur vapor pressure in preparing the FeS2 films has been discussed and some incongruous views about sulfur pressure have been clarified in this paper based on experimental results and theoretical analysis. It is shown that lower sulfur pressures than the saturation value only result in poorer crystallization and worse performances, and in other words the FeS2 films could be optimized through improving the sulfur pressure till the saturation point. However for a certain temperature the sulfur pressure is limited by its saturated vapor pressure, and further increase of the sulfur quantity reacted with Fe films has little influence on the structure and properties of the pyrite films. (C) 2003 Elsevier B.V. All rights reserved.

Single-crystalline beta-Ga2O3 nanobelts were synthesized by a simple physical evaporation method in argon atmosphere with the starting materials of Ga. The beta-Ga2O3 nanobelts have a width of 50-100 nm and width-to-thickness ratios of 5-10, and length of up to a few millimeters, which may have potential applications in nanosize sensors or optoelectronic nanodevices. (c) 2006 Elsevier Ltd. All rights reserved.