Search

Hydrogen (H2) gas is a green fuel, but its leakage during storage and transportation can lead to disasters due to its explosive nature. Here, a sensitive and selective H2 gas sensor is developed that can detect H2 in H2/CO and H2/NO2 gas mixtures. First, ZnO nanowires (NWs) are grown using vapor–liquid–solid growth. This is followed by atomic layer deposition‐mediated growth of Pd nanoparticles (NPs) on the ZnO NWs and uniform deposition of a thin NiO shell layer (12 nm in thickness) over the Pd‐decorated ZnO NWs. Characterization of the synthesized samples by different methods confirms the desired chemical composition, morphology, and phases. H2 gas sensing studies reveals the highly sensitive and selective response of the optimized gas sensor to H2 at 200 °C. In the presence of H2/CO and H2/NO2 gas mixtures, the NiO‐shelled Pd‐decorated ZnO NW sensor displays good selectivity for H2, but not the Pd‐decorated ZnO NW gas one. The NiO‐shelled Pd‐decorated ZnO NW gas sensor efficiently detected H2 also in the presence of 40% relative humidity and displays good stability even after 1 month. The present results can open the doors to the fabrication of highly selective H2 gas sensors using the described rationale design. [ABSTRACT FROM AUTHOR]

Metal oxide nanowires (NWs) with a high surface area, ease of fabrication, and precise control over diameter and chemical composition are among the best candidates for the realization of resistive gas sensors. Among the different techniques used for the synthesis of materials with NW morphology, approaches based on the vapor–liquid–solid (VLS) mechanism are very popular due to the ease of synthesis, low price of starting materials, and possibility of branching. In this review article, we discuss the gas-sensing features of metal oxide NWs grown by the VLS mechanism, with emphasis on the growth conditions and sensing mechanism. The growth and sensing performance of SnO2, ZnO, In2O3, NiO, CuO, and WO3 materials with NW morphology are discussed. The effects of the catalyst type, growth temperature, and other variables on the morphology and gas-sensing performance of NWs are discussed. [ABSTRACT FROM AUTHOR]

There is an increasing need for the development of low-cost and highly sensitive gas sensors for environmental, commercial, and industrial applications in various areas, such as hazardous gas monitoring, safety, and emission control in combustion processes. Considering this, resistive-based gas sensors using metal oxide semiconductors (MOSs) have gained special attention owing to their high sensing performance, high stability, and low cost of synthesis and fabrication. The relatively low final costs of these gas sensors allow their commercialization; consequently, they are widely used and available at low prices. This review focuses on the important MOSs with different morphologies, including quantum dots, nanowires, nanofibers, nanotubes, hierarchical nanostructures, and other structures for the fabrication of resistive gas sensors. [ABSTRACT FROM AUTHOR]

X-Ray radiation sensors that work at room temperature are in demand. In this study, a novel, low-cost real-time X-ray radiation sensor based on SnO2 nanowires (NWs) was designed and tested. Networked SnO2 NWs were produced via the vapor–liquid–solid technique. X-ray diffraction (XRD), transmission electron microscopy (TEM) and field emission scanning electron microscopy (SEM) analyses were used to explore the crystallinity and morphology of synthesized SnO2 NWs. The fabricated sensor was exposed to X-rays (80 kV, 0.0–2.00 mA) and the leakage current variations were recorded at room temperature. The SnO2 NWs sensor showed a high and relatively linear response with respect to the X-ray intensity. The X-ray sensing results show the potential of networked SnO2 NWs as novel X-ray sensors. [ABSTRACT FROM AUTHOR]

Embedding chemical sensors into mobile devices is an emerging demand in modern information converged technology. The unbearable power consumption to raise the temperature of chemoresitive-type chemical sensors makes it impossible for them to be embedded regardless of their peculiar sensing properties such as low cost, miniaturization, high response, and excellent stability and robustness. In this study, self-heated nanowire sensors were prepared by exploiting the synergic effect of the core–shell structure and catalytic nanoparticles. As a prototype approach, Pt nanoparticle-functionalized SnO 2 –ZnO core–shell nanowires were synthesized, demonstrating extremely striking performance and characteristics. Thicker ZnO shell showed the larger self-heating and higher sensor response. The sensors exhibited excellent selectivity for toluene gas, with negligible responses to other reducing gases. This one possessed a considerable sensing performance at room temperature, even without a significant self-heating. The self-heated sensing of the novel core–shell nanowires developed required only an extremely low power consumption of 31 μW, suggesting their potential in applications as sensors embedded into mobile devices. [ABSTRACT FROM AUTHOR]

One-dimensional, hollow nanostructured materials are among the most promising materials for sensing applications owing to their high surface area that facilitates the adsorption of target gases. Accordingly, for gas sensing studies, hollow ZnO nanowires (NWs) with different surface areas were successfully synthesized herein by using polycarbonate membranes with different pore sizes as templates, and deposition of ZnO via the atomic layer deposition technique. The sensing properties of the synthesized hollow ZnO NWs were examined for CO and NO, revealing their comparative sensing performances with ZnO nanomaterials-based sensors reported in literature. This study highlights a novel way of synthesizing hollow ZnO NWs by using membrane template and their promising sensing properties as well. [ABSTRACT FROM AUTHOR]

We have realized an excellent selective sensing to benzene (C 6 H 6 ) by means of using SnO 2 -ZnO core-shell nanowires functionalized with Pd nanoparticles. We obtained a response of 71 for 100 ppb of C 6 H 6 , which is the highest response reported thus far. The synergistic effects of variation of SnO 2 /ZnO potential barriers and chemical sensitization of Pd are responsible for the highest C 6 H 6 -sensing performance. These results highlight the potential for using Pd functionalized nanowires as a sensing platform in detecting trace concentrations of benzene, which is applicable in the future sensor, including the disease diagnosis and the environmental monitoring. [ABSTRACT FROM AUTHOR]

We sputtered zinc-oxide (ZnO)-branched tin oxide (SnO 2 ) nanowires with a Co shell layer with subsequent annealing to produce cobalt (Co) nanoparticles on the ZnO branches. X-ray diffraction, selected area electron diffraction, and lattice-resolve TEM images showed that the nanoparticles corresponded to a hexagonal Co phase. We further studied the NO 2 sensing performance of Co-decorated ZnO branched structures in the range of 2–10 ppm at 250 °C. Sensor characteristics were examined in terms of sensitivity (i.e., sensor response), response time, and recovery time; we further proposed the possible mechanisms of enhancement of sensing behavior by the attachment of Co nanoparticles. Co-functionalization enhanced the sensor response and significantly decreased the recovery times. The Co-decorated ZnO branched structures showed promising sensing performance toward NO 2 gas at concentrations as low as 2 ppm. [ABSTRACT FROM AUTHOR]

Novel micro-supercapacitors using ZnO nanowire (NW)-grown carbon fibres/carbon papers and SnO NW-grown carbon papers as electrodes are fabricated, and their electrochemical properties are presented. Carbon fibre and carbon paper combined with NW technology could provide insightful strategy to build wearable and flexible fabric-based electronics. Among four device strategies of electrodes (ZnO NWs on carbon fibre, ZnO NWs on carbon paper, bare carbon paper, SnO NWs on carbon paper), electrodes of SnO NW-grown carbon paper exhibited the best electrochemical properties such as the largest area specific capacitance (12 mF cm) and energy density (405 n Wh cm). [ABSTRACT FROM AUTHOR]

Abstract: We have prepared composite nanowires consisting of In2O3 and NiMnGa, in which the In2O3 core was coated with a continuous layer of NiMnGa via pulsed laser deposition technique. We have verified the tubular structure of NiMnGa shell by means of transmission electron microscopy (TEM). X-ray photoelectron spectroscopy revealed the presence of Ni, Mn, and Ga elements and TEM-energy-dispersive X-ray spectroscopy indicated that these elements resided mainly in the shell region. Since X-ray diffraction patterns and lattice-resolved TEM images showed no crystalline NiMnGa phase, with scanning electron microscopy revealing that the shell is sufficiently thick (~55nm), we suggest that the shell layer is amorphous. The ferromagnetic behavior, in terms of coercive field, remanent magnetization, and saturation magnetization in the hysteresis loop, was considerably enhanced by coating the In2O3 core with a NiMnGa shell layer, at the measurement temperature of 300K as well as 5K. We have carried out a comparison study for revealing the mechanisms, by which the ferromagnetism was enhanced by the shell-coating. Although the annealing-induced changes of In2O3 core cannot be ruled out, the presence of NiMnGa phase played a decisive role in enhancing the ferromagnetic behavior of composite nanowires. [Copyright &y& Elsevier]

Abstract: Networked SnO2 nanowire sensors were fabricated on a basis of a selective growth technique. Subsequently, Ar–O2 plasma was applied in order to modify the nanowire surfaces. The NO2 sensing characteristics of the surface-modified SnO2 nanowires were compared to those of pristine SnO2 nanowires at an operating temperature of 300°C. The results showed that the plasma treatment greatly enhanced the response as well as shortened the response and recovery times in SnO2 nanowire-based gas sensors. The enhancement is likely to result from an increase of active surface area for the adsorption of NO2 species by means of the plasma treatment. [Copyright &y& Elsevier]

Vertically well-aligned zinc oxide nanowires (NWs) with high density were successfully synthesized on Si, sapphire and GaN/sapphire substrates by thermal evaporation of zinc powders without catalysts or additives. The growth behavior of ZnO NWs was strongly dependent on the substrate materials. The effects of the substrate position on the structures and properties of ZnO NWs were primarily discussed. The morphology and crystallinity of the resultant NWs were studied by scanning electron microscope, transmission electronic microscope and X-ray diffraction. The photoluminescence (PL) characteristics of the ZnO NWs on the different substrates were studied. The results showed that the as-grown ZnO NWs exhibit a sharp and strong ultraviolet emission at 3.27 eV and a very weak green emission at around 2.48 eV, indicating that the a-synthesized NWs have excellent PL properties with good crystalline quality and can be an ideal candidate for making luminescent devices. By comparison of PL spectra, we revealed that the green-to-UV emission intensity ratios were considerably dependent on the substrate materials, which was explained by the difference in the structural morphology of the produced nanowires. [ABSTRACT FROM AUTHOR]

Abstract: We fabricated MgO/Ag core-shell nanowires, where core nanowires were coated with a conformal layer of Ag via sputtering. By subsequent thermal annealing, we generated Ag nanoparticles. Photoluminescence (PL) studies revealed that Ag-shell coating decreased the intensity of blue emission, whereas that of UV emission remained almost invariant. The subsequent annealing has induced an additional green emission band. We discuss here the possible mechanism by which the PL properties have been tailored by Ag-layer coating and by forming nanoparticles. This approach can be applied to tailor and improve the optical properties of different composite nanostructures. [Copyright &y& Elsevier]

Abstract: ZnO-core/SiOx shell nanowires were successfully fabricated and their morphology, structure, Raman and photoluminescence properties were examined. Not only the sputter-coated product had an one-dimensional morphology, but the tubular structure of SiOx shell was also continuous, smooth, and uniform, along the core nanowires. It was found that two fundamental modes (334, 437 cm−1) and 2 s order modes (1106, 1156 cm−1) of hexagonal ZnO appeared in the Raman spectrum of ZnO-core/SiOx shell nanowires. The photoluminescence (PL) spectrum of the core–shell nanowires were deconvoluted into three Gassian functions, centered at 382, 500, and 758 nm, whether the subsequent thermal annealing was performed or not. The integrated intensities of UV (382 nm) and green (758 nm) emissions were changed by means of the shell-coating and thermal annealing. We have discussed the possible emission mechanisms. [Copyright &y& Elsevier]

Abstract: We have synthesized GaN-core/ZnO-shell nanowires and investigated effects of the ZnO coating. The X-ray diffraction pattern showed that as-synthesized samples are composed of GaN and ZnO. Transmission electron microscopy indicated that the deposited ZnO shell layer is poly-crystalline. The photoluminescence (PL) spectrum of GaN has been changed by the ZnO coating, where emission bands centered at roughly 1.9eV, 2.5eV, and 3.3eV were newly added to the emissions from core GaN nanowires. We found that overall PL intensity has been significantly increased by coating the ZnO shell layers. [Copyright &y& Elsevier]

Abstract: Varying the heating temperature of a mixture of Zn and Ge powders, we have successfully prepared Zn2GeO4 nanowires. We suggest that the 900°C-grown product was mainly grown via a vapor–liquid–solid process, whereas the 800°C-grown product was dominated by a vapor–solid mechanism. For 900°C-grown nanowires, the stem is mainly comprised rhombohedral Zn2GeO4 phase, whereas the tip is characterized by a particle hexagonal GeO2 phase. For 800°C-grown nanowires, both the stem and tip are mainly comprised hexagonal ZnO phase with some additional Zn2GeO4 phase. It was observed that variation of the growth temperature affected the photoluminescence spectra of the nanowires, leading to an overall intensification. We have discussed the possible mechanisms for the observed temperature-induced changes in the PL spectra. [Copyright &y& Elsevier]

Abstract: This paper reports a novel method for fabricating nanotubes, in which the nanowire-templates were removed by simple heating in air. The morphology and structure of the composite nanowires were controlled by varying the heating temperature. High-temperature heating was found to be effective in removing the core TeO2 nanowires. The photoluminescence study indicated that the emission of the core-shell nanowires originated mainly from the ZnO shell. The increased visible emission with increasing heating temperature was attributed to the increase in the number of structural defects in the ZnO shell. The visible emission band was blue-shifted with increasing annealing temperature. [Copyright &y& Elsevier]

Abstract: Composite nanowires consisting of GaN and InN phases were synthesized by heating a mixture of GaN and In powders. The tip nanoparticles also contained GaN and InN phases, in which the InN phases were favored at a lower growth temperature of 600°C. The associated growth mechanisms are believed to involve a self-catalytic vapor–solid–liquid process, in which the composite nanoparticles located at the tips of the nanowires served as a catalyst. Both the Raman and photoluminescence spectra showed GaN- and InN-related peaks, which agrees with the X-ray diffraction and transmission electron microscopy data. [ABSTRACT FROM AUTHOR]

Abstract: Novel In1.94Sn0.06O3 (ITO)/amorphous SiO x core–shell structures were successfully synthesized by simple thermal evaporation. Studies indicated that the core–shell structures typically consisted of a core of crystalline, ITO nanowires surrounded by a shell of amorphous, SiO x tubular structures. We proposed a gold-catalyzed, vapor–liquid–solid process as the dominant mechanism for the growth of the core ITO nanowires, whereas SiO x was grown in a tubular structure by a simultaneous and dynamic process. The possible reason for the preferential formation of the SiO x shells on the outside of the core–shell structures, is discussed. In regard to the core/shell structures, three emission peaks of 2.73, 3.06, and 1.65eV were observed in the room-temperature photoluminescence measurements, and were attributed to the SiO x shell. [ABSTRACT FROM AUTHOR]

Abstract: We have used the simple heating technique for growing TiO2 nanowires. We have changed the thickness of predeposited Au layers on TiAlN substrates, realizing that the thickness of the Au layer influenced the resultant morphology of nanowires. The nanowires were analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence spectroscopy (PL). The resultant nanowires consisted of the tetragonal rutile structure of TiO2. With the nanowire morphology changing with varying the Au layer thickness, we suggest that the associated growth mechanism is a base-growth mode, in which Au played a catalytic role. PL spectra indicated that the TiO2 nanowires exhibited a broad emission band comprising four peaks centered at 3.0, 2.6, 2.3, and 1.5eV. [Copyright &y& Elsevier]

Abstract: GaN-core/Cu-shell nanowires were prepared and their annealing behavior was investigated. The thermal annealing induced the surface-roughening of the hetero-nanowires due to the agglomeration and generation of cluster-like structures from the Cu-shell layers. X-ray diffraction suggested that the thermal annealing generated CuO x phases. The core GaN nanowires exhibited weak ferromagnetism at 5K and their coercivity was increased by Cu-sputtering and subsequent thermal annealing at 800°C. In the Gaussian deconvolution studies, the photoluminescence (PL) spectra exhibited emission bands centered at 2.0 and 3.2eV, irrespective of the Cu-coating and/or thermal annealing. A mechanism is proposed to explain the significant change in the intensity of the ultraviolet (UV) emission by the combination of Cu-sputtering and annealing at 1000°C. [Copyright &y& Elsevier]

Abstract: ZnO nanowires have been synthesized by heating Zn powders under nitrogen (N2) gas atmosphere. The influence of the growth temperature on the morphology, structure, and photoluminescence (PL) properties of ZnO nanowires has been investigated. At the higher-temperature growth process, thinner nanowires have been obtained. Interestingly, it is observed that the variation of growth temperature has significantly affected the photoluminescence spectra of the ZnO nanowires, showing an enhancement in the relative intensity of the green to UV emission bands with the increase of the growth temperature. In addition, the oxygen sensing properties of the as-synthesized ZnO nanowires were tested. [Copyright &y& Elsevier]

Abstract: Al-doped ZnO (AZO) shell layers were coated on core ZnO nanowires to fabricate ZnO/AZO core–shell nanowires. The energy-dispersive X-ray spectra confirmed the presence of Al element in the shell layers, and the lattice resolved transmission electron microscopy image revealed that these layers corresponded to the hexagonal ZnO structure. The X-ray diffraction pattern exhibited a shift of the ZnO peaks, suggesting the substitutive incorporation of Al into the ZnO lattice. The A1(LO) mode line in the Raman spectra was enhanced by the AZO coating. In the photoluminescence measurements, the AZO coating enhanced the intensity ratio of the UV to green emission. [Copyright &y& Elsevier]

Abstract: We reported the preparation and annealing effects of Zinc oxide ZnO/SiO x core–shell nanowires, in which ZnO shell layers were deposited by sputtering. Based on scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and photoluminescence (PL) investigations, we monitored structural and optical changes with respect to the post-annealing process. The samples were mostly amorphous with some crystalline ZnO structure, whereas annealing at 900–1000°C reduced the amount of Zn elements. Thermal annealing induced change in the shape of the PL emission spectra. [Copyright &y& Elsevier]

Abstract: Germanium dioxide (GeO2) nanowires have been synthesized by means of the simple evaporation of solid Ge powders, without using metal catalysts. The nanowires, with a diameter of about 90–200nm, were characterized using scanning electron microscopy (SEM), X-ray diffractometry (XRD), and transmission electron microscopy (TEM). The obtained GeO2 nanowires were crystalline with a hexagonal structure. The growth mechanism was discussed with respect to the vapor–solid process. The photoluminescence measurement revealed two emission peaks at about 2.45eV and 2.91eV at room temperature, opening up a route to potential applications in future optoelectronic nanodevices. Raman measurement of as-synthesized GeO2 nanowires was made at room temperature. [Copyright &y& Elsevier]

Abstract: The structural and optical properties of SnO2–ZnO core–shell nanowires were studied and the effects of thermal annealing were investigated. As-prepared SnO2–ZnO core–shell nanowires exhibited a smooth and continuous shell layer along the nanowire, with a thickness in the range of 5–10nm. While the thin ZnO shell layer disappeared after annealing at 800°C, this did not occur after annealing at 600°C. The as-fabricated SnO2–ZnO core–shell nanowires exhibited yellow emission, presumably from the core SnO2 nanowires. The UV emission from ZnO shell layer was obtained by annealing at 600°C, whereas it was removed by annealing at 800°C. [Copyright &y& Elsevier]

Abstract: GaN-core/Au-shell nanowires were fabricated and the effects of thermal annealing on the structural and photoluminescence (PL) properties were investigated. The surfaces of hetero-nanowires became rough due to the thermal annealing which could be attributed to the agglomeration of Au-shell layers into the cluster-like structures. X-ray diffraction indicated that the thermal annealing enhanced the crystallinity of the Au shell. From Gaussian deconvolution studies, we observed that the Au coating added a green band to the PL spectrum, whereas the thermal annealing enhanced the ultraviolet band. We have discussed the possible emission mechanisms. [Copyright &y& Elsevier]

This paper describes the fabrication of Pd-coated SiOx nanowires via a simple approach and reports the effects of subsequent thermal annealing. While the as-synthesized Pd-coated SiOx nanowires exhibited smooth one-dimensional (1D) nanostructures, the thermal annealing induced a rough surface. X-ray diffraction, selected area electron diffraction, and lattice-resolved transmission electron microscopy coincidentally revealed that the assynthesized Pd-coated SiOx nanowires were comprised of a cubic Pd phase, whereas annealing generated a tetragonal PdO phase. Micro-Raman spectroscopy measurements showed the presence of 630 cm−1-peak, which can be assigned to the B1g mode of single crystal PdO, whether samples had been annealed or not. Although both Pd and PdO phases did not exhibit PL emission, the PL intensity of core SiOx nanowires has been significantly reduced by the Pd-coating, presumably due to the covering effect. [ABSTRACT FROM AUTHOR]

Abstract: We fabricated Co-coated SiO x nanowires and investigated the effects of thermal annealing on their properties. The sputtering process resulted in the formation of a relatively smooth Co shell layer, whereas subsequent thermal annealing generated the Co3O4 phase. The photoluminescence (PL) spectrum was not changed by the Co-coating, whereas the thermal annealing induced new peaks in the yellow and ultraviolet regions. Possible emission mechanisms were discussed. Based on the magnetization measurements of the SiO x -core/Co-shell nanowires, we obtained small and negligible hysteresis loops for the as-fabricated and thermal annealed samples, respectively. [Copyright &y& Elsevier]

Abstract: We prepared ZnO-coated Ga2O3 nanowires and investigated changes in the morphological, structural, and photoluminescence (PL) characteristics resulting from application of a thermal annealing process. With the thermal annealing at 800°C, defect-associated PL peaks (2.2 and 2.6eV) have been intensified with respect to the UV peak, and a new 2.8eV-peak has been generated. Possible emission mechanisms are also discussed. [Copyright &y& Elsevier]

We have reported the preparation of ZnO-coated GaN nanowires and investigated changes in the structural and photoluminescence (PL) properties by the application of a thermal annealing process. For fabricating the core-shell nanowires, Zn target was used to sputter ZnO shell onto GaN core nanowires. X-ray diffraction (XRD) analysis indicated that the annealed core-shell nanowires clearly exhibited the ZnO as well as GaN phase. The transmissoin electron microscopy (TEM) investigation suggested that annealing has induced the crystallization of ZnO shell layer. We have carried out Gaussian deconvolution analysis for the measured PL spectra, revealing that the core GaN nanowires exhibited broad emission which consist of red, yellow, blue, and ultraviolet peaks. ZnO-sputtering induced new peaks in the green region. Thermal annealing reduced the relative intensity of the green emission. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Abstract: By varying the substrate temperature in the range of 800–1000°C, the conditions for the synthesis of AlN nanowires were optimized. Al powders were heated under flowing ammonia gas. The samples were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and photoluminescence (PL) spectroscopy. Based on the absence of tip particles, the growth mechanism of AlN nanowires was considered to follow a vapor–solid process. The overall intensity of the PL spectra was increased by increasing the synthesis temperature, whereas their shapes were changed by varying the synthesis temperature. The associated emission mechanisms are discussed. [Copyright &y& Elsevier]

Abstract: We have demonstrated the fabrication of GaN-core/Ag shell nanowires and investigated their annealing effects. Scanning electron microscopy has revealed that the thermal annealing facilitated the surface-roughening of the heteronanowires. TEM investigations indicated that the thermal annealing has changed the shell morphology from continuous Ag layer to the discrete Au nanoparticles or islands. X-ray diffraction suggested that the thermal annealing has enhanced the crystallinity of Ag shell. Photoluminescence measurements revealed that the Ag-sputtering has induced an UV peak, in addition to the GaN-associated emission peaks. Thermal annealing has further changing the overall shape of the PL spectrum and we have discussed the possible emission mechanisms. [Copyright &y& Elsevier]

The effects of thermal annealing on structural and optical properties of MgO-core-silica (SiO x)-shell nanowires have been investigated. The annealed nanostructures consisted of a crystalline MgO core surrounded by an amorphous SiO x shell layer, whereas the shell surface had become rough and an Mg2SiO4 phase appeared by annealing at a sufficiently high temperature of 800°C. Photoluminescence (PL) measurements of annealed MgO-core/SiO x-shell nanowires indicated that the overall intensities increased on increasing the annealing temperature, with the overall shapes of the emission spectra being independent of the annealing temperature from 600 to 1000°C. This study provides an insight into the annealing studies involving various coaxial nanowires. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: We have fabricated GaN-core/SiOx-sheath nanowires, sheathing the core MgO nanowires by sputtering with Si target. The product has wire-like morphology, regardless of SiO x -sheathing and subsequent annealing. EDX elemental mapping results have coincided with what can be expected for the SiO x -coated GaN nanowires. The core nanowires correspond to a hexagonal GaN structure, whereas the sheath layer is amorphous. Gaussian fitting analysis on the photoluminescence spectra of GaN-core/SiO x -sheath nanowires have exhibited two emission bands peaked at 2.4 eV and 2.9 eV, respectively. We observed that the relative intensity of 2.9 eV-peak to 2.4 eV-peak was increased by the thermal annealing. [Copyright &y& Elsevier]

Abstract: We introduce a simple method of synthesizing SnO2 nanowire-Bi2Sn2O7 nanoparticle composites based on the principle that SnO2 nanowires can be grown by using Bi as catalysts. A mixture of Bi and Sn powders was thermally evaporated, and the effects of growth temperature on the morphology and structure of the products were investigated. We obtained Bi2Sn2O7-tipped SnO2 nanowires at 700°C through a vapor–liquid–solid (VLS) process, whereas particle-free SnO2 nanowires were produced at higher temperatures. We have investigated the oxygen sensing properties of the as-synthesized product. [Copyright &y& Elsevier]

Abstract: Coaxial nanowires of magnesium oxide (MgO) core with zinc oxide (ZnO) shells were synthesized with the assistance of atomic layer deposition method. The diameters of these composite nanowires varied from 50 to 110nm, with sheath thickness in the range of 15–25nm. The sheath layer comprised a hexagonal ZnO phase. We found that the overall shape and peak positions of PL emission spectrum were almost unchanged by the sheath coating with a thin enough ZnO layer. [Copyright &y& Elsevier]

Abstract: This study reported the preparation of ZnO-coated SiO x nanowires and investigated changes in the structural and photoluminescence (PL) characteristics resulting from application of a thermal annealing process. While X-ray diffraction (XRD) analysis revealed the annealing-induced transformation of ZnO to Zn2SiO4, transmission electron microscopy (TEM) observation suggested that shell layer tended to be transformed to nanoparticle-like structures by thermal annealing. Thermal annealing induced the changes in the shape of the PL emission spectrum. [Copyright &y& Elsevier]

Abstract: We have demonstrated the growth of SiO x nanowires by the simple heating of the Cu-coated Si substrates. We have applied X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques to characterize the structure of the samples. The as-synthesized SiO x nanowires had amorphous structures with diameters in the range of 20–80nm. The thickness of the Cu layer affected the resultant sample morphology, favoring the nanowire formation at smaller thickness. Photoluminescence spectra of the nanowires exhibited blue emission. We have proposed the possible growth mechanism. [Copyright &y& Elsevier]

Abstract: This paper presents the use of the simple annealing technique at 1000°C to produce the helical nanostructures of SiO x . We have employed the Co-coated Si substrates, with Co layer and Si substrate utilized as catalyst and Si source, respectively. Beside the ordinary straight nanowires, the helical nanowires such as nanosprings and nanorings were observed. The product was an amorphous structure of SiO x . We have discussed the possible growth mechanism. Photoluminescence spectrum of the SiO x nanostructures showed a blue emission at 428nm and a green emission at 534nm, respectively. [Copyright &y& Elsevier]

Abstract: This study investigated changes in the characteristics of ZnO-coated MgO nanowires resulting from application of a thermal annealing process. Thermal annealing affected the structural morphology, contributing to agglomeration of particle-like structures in the coated ZnO shell. The annealed ZnO was crystalline whereas the as-deposited ZnO was amorphous. Thermal annealing increased the relative photoluminescence intensity of the green light emission. [Copyright &y& Elsevier]

Abstract: We synthesized crystalline MgO nanowires on Au-coated substrates by the heating of MgB2 powders. We carried out the thermal annealing on Au-coated substrates prior to the MgO deposition process, affecting the morphology of the final MgO structures. The produced nanowires were of cubic MgO structures with diameters in the range of 40–200nm. We discussed the possible growth mechanism. Photoluminescence spectrum of the MgO nanowires under excitation at 325nm showed a visible light emission. [Copyright &y& Elsevier]

We have prepared the large-scaled gallium oxide nanowire arrays on sapphire substrates using a reaction of a trimethylgallium (TMGa) and oxygen (O2) mixture. The cross-section of the gallium oxide nanowires had a circular shape with the diameter of about 40–110 nm. Transmission electron microscopy and X-ray diffraction analysis together showed that the nanowires were amorphous phase. Photoluminescence measurements indicated that as-prepared nanowires showed two emission band at 365 and 470 nm. [Copyright &y& Elsevier]

We have synthesized the large-scaled gallium oxide nanowire arrays using a reaction of a trimethylgallium (TMGa) and oxygen (O2) mixture. Scanning electron microscopy revealed that the cross-section of the nanowires had a circular shape with the diameter of about 50–150 nm and the length up to several tens of micrometers. High-resolution transmission electron microscopy showed that the gallium oxide nanowires were of amorphous or polycrystalline nature. [Copyright &y& Elsevier]

Abstract: This paper reports the preparation of Ag-coated SiO x nanowires and analyzes changes in the structural properties and photoluminescence (PL) spectra induced by a thermal annealing process. The thermal induced changes in the sample morphology, generating Ag nanoparticles on the core of SiO x nanowires and crystalline structures were affected, facilitating the generation of the Ag2SiO3 phase. The overall shape of the PL spectrum was changed significantly by both the Ag-coating and the subsequent thermal annealing. Possible emission mechanisms were discussed. This study gives insight into the annealing process regarding various coaxial one-dimensional materials, particularly with metal shell layers. [Copyright &y& Elsevier]

Highlights • For the first time, we fabricated bare and Pd-decorated SnO 2 nanowires for comparative study of hydrogen sensing. • The Pd NPs not only increased the sensitivity of the SnO 2 gas sensor, but also increased its H 2 gas selectivity. • The enhanced sensing properties of the Pd-decorated sensor are related to the Pd NPs' catalytic effect and the formation of Schottcky junctions. Abstract We fabricated bare and Pd-decorated SnO 2 nanowires (NWs) for comparative study of hydrogen sensing. A selective vapor-liquid-solid method was used for fabricating SnO 2 NWs and a UV reduction method was used to decorate Pd NPs on the surfaces of the fabricated NWs. Sensing studies showed that decorating the surfaces of SnO 2 NWs with a noble metal increased the response to 1 ppm H 2 gas from 6.88 to 16.95 at an optimal working temperature of 300 °C. Furthermore, Pd decoration also increased the selectivity. The enhanced sensing properties of the Pd-decorated sensor are related to the Pd NPs' catalytic effect and the formation of Schottcky junctions. This study demonstrated the possibility of a high performance H 2 sensor created by combining metal oxide NWs with a catalyst such as Pd. [ABSTRACT FROM AUTHOR]

We report a novel self-heated CO gas sensor based on Au-functionalized networked SnO 2 -ZnO core-shell nanowires. Increasing the applied voltage particularly enhanced the sensing response due to the self-heating effect within the sensor, and the sensors exhibited good performance without the need for an external heater. The power consumption at 3 and 20 V was estimated to be 11.3 nW and 8.3 μW, respectively. In a sensor with the optimal ZnO shell thickness of 80 nm, the responses for 50 ppm CO were 1.17 and 1.62 at 3 and 20 V, respectively. Also, the important role of ZnO-ZnO homojunctions in the self-heating of the sensor was demonstrated by increasing the ZnO shell thickness, which led to an increase in the sensor response. Furthermore, the optimized sensor exhibited outstanding selectivity toward CO gas. The optimized ZnO shell, the catalytic effect of Au, and the Joule effect contributed to the good, selective response toward CO gas with low power consumption. Since low power consumption is a fundamental requirement for wireless sensors and sensor arrays, this sensor with very low power consumption is a promising choice for such applications. [ABSTRACT FROM AUTHOR]

A novel growth method for CuO-functionalized, branched tin oxide (SnO2) nanowires was developed on the basis of a Cu-triggered tip-growth vapour–liquid–solid (VLS) process during annealing of Cu-coated SnO2 nanowires. The variation in annealing temperature changed the morphology, in which higher temperatures (⩾500 °C) are favourable for the formation of branches. From the observation of tip nanoparticles, we revealed that the growth of branches at 500 and 700 °C was dominated by base-growth and tip-growth VLS processes, respectively. The tip nanoparticles at 700 °C were mainly comprised of a CuO phase. We have demonstrated the potential applicability of the CuO-functionalized, branched SnO2 nanowires to H2S sensors. CuO functionalization significantly enhanced the response to H2S. In sharp contrast, it degraded the response to NO2, suggesting their selective sensing performance to H2S. [ABSTRACT FROM AUTHOR]