Structure and ultrafast ethanol sensing properties of In2O3-capped Zn-doped Fe2O3 nanorods

This paper reports the facile synthesis of In₂O₃-capped Zn-doped Fe₂O₃ nanorods along with their ethanol gas sensing properties. A two-stage process involving thermal oxidation of Fe foils and Zn powders in air and the sputter-deposition of In₂O₃ was used to synthesize these nanostructures. The nanorods synthesized using this method were ∼5 μm in length and 50–120 nm in diameter with a shell layer thickness of 10–15 nm. The multiple-networked In₂O₃-capped Zn-doped Fe₂O₃ nanorod sensor showed a significantly enhanced and ultrafast response to ethanol gas. The enhanced sensing performance was explained by modulation of the potential barrier height and the strong catalytic activity of In₂O₃ for ethanol oxidation.     

Synthesis and characterization of Ag/PVA nanorods by chemical reduction method

Silver (Ag) nanorods with the average length of 280 nm and diameters of around 25 nm were synthesized by a simple reduction process of silver nitrate in the presence of polyvinyl alcohol (PVA) and investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission-electron microscopy (TEM) and UV–vis spectrum. It was found out that both temperature and reaction time are the important factors in determining the morphology and aspect ratios of nanorods. TEM images showed the prepared Ag nanorods have a face centered shape (fcc) with fivefold symmetry consisting of multiply twinned face centered cubes as revealed in the cross-section observations. The fivefold axis, i.e. the growth direction, normally goes along the (1 1 1) zone axis direction of the basic fcc Ag-structure. Preferred crystallographic orientation along the (1 1 1), (2 0 0) or (2 2 0) crystallographic planes and the crystallite size of the Ag nanorods are briefly analyzed.     

Adsorption-controlled transition of the electrical properties realized in Hematite（alpha-Fe2O3） nanorods ethanol sensing

Alpha-Fe2O3 nanorods are synthesized through a hydrothermal method with no surfactant introduced and ethanol sensors are fabricated from these nanorods.The device can respond to ethanol vapour in a concentration range from 1 to 1500 parts per million and shows both p-type and n-type responding characteristics during the investigation of the ethanol sensing.The sensor displays a p-type characteristic when the ethanol concentration is low and converted into an n-type characteristic as the concentration exceeds a certain value.Such a phenomenon is attributed to the chemisorbed oxygen,which leads to different modifications of the energy band at the surface,namely,depletion layer or inversion layer.     

Synthesis of Au-functionalized SnO2 nanotubes using TeO2 nanowires as templates and their enhanced gas sensing properties

Au-functionalized SnO₂ nanotubes were prepared for use as gas sensors using TeO₂ nanowires as templates. Transmission electron microscopy revealed tube diameters, tube lengths and tube wall thicknesses ranging from 50 to 200 nm, 5 to 50 μm, and 13 to 18 nm, respectively. The Au-functionalized SnO₂ nanotube sensors showed responses of 179–473 % to 1–5 ppm NO₂ at 300 ^°C. These values are much higher than those obtained using bare SnO₂ nanotubes synthesized in this study and most other SnO₂ one-dimensional nanostructure-based sensors reported in the literature. The NO₂ gas sensing mechanism of the Au-functionalized SnO₂ nanotube sensors is also discussed.     

Enhanced NO2 gas sensing properties of WO3 nanorods encapsulated with ZnO

The influence of the encapsulation of WO₃ nanorods with ZnO on the NO₂ gas sensing properties was examined. WO₃-core/ZnO-shell nanorods were fabricated by a two-step process comprising the catalyst-free thermal evaporation of a mixture of WO₃ and graphite powders in an oxidizing atmosphere and atomic layer deposition of ZnO. Multiple networked WO₃-core/ZnO-shell nanorod sensors showed the response of 281?% at 5 ppm NO₂ at 300?°C. This response value was approximately 9 times larger than that of bare WO₃ nanorod sensors at 5 ppm NO₂. The response values obtained from the WO₃-core/ZnO-shell nanorods in this study were more than 5 times higher than those obtained previously from the SnO₂-core/ZnO-shell nanofibers at the same NO₂ concentration range. The significant enhancement in the response of WO₃ nanorods to NO₂ gas by encapsulating them with ZnO can be accounted for based on the space-charge model.     

Fabrication of diamond nanorods for gas sensing applications

Diamond nanorods were fabricated for a sensing device by utilizing reactive ion etching in CF₄/O₂ radio frequency plasma. The length of the nanorods has been controlled by the ion etching time. The obtained morphologies were investigated by scanning electron microscopy. The gas sensing properties of the H-terminated diamond-based sensor structures are indicating that we have achieved high sensitivity to detect phosgene gas. Also, our sensor exhibited good selectivity between humid air and phosgene gas if the measurement is conducted at elevated temperatures, such as 140 °C. Furthermore, such sensor response rating could reach as high value as 4344 for the phosgene gas, which was evaluated for the sample consisting of the longest nanorods (up to 200 nm).     

Enhancement of the ultraviolet emission of ZnO nanorods by terphenyl liquid-crystalline ligands modification

We have developed a novel method to modifying the surface of ZnO nanorods (ZnO NRs) using p-hexoxyterphenylol (HTph-OH) as liquid crystal ligands. The structure and morphology of the modified ZnO NRs were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and atomic force microscopy (AFM). AFM measurement showed that the dispersion of ZnO NRs could be dramatically improved by the surface modification of HTph-OH and further annealing treatment at its liquid crystal state temperature (150 °C). The remarkable decrease of the annealed composite film roughness is because the HTph-OH chains self-organize into more ordered structure induced by mesogens after annealing treatment, which may push the ZnO NRs to form oriented nano-dispersing structure. The optical properties of the modified ZnO NRs were investigated by UV-vis absorption spectroscopy and photoluminescence spectroscopy (PL). Markedly enhanced band-edge ultraviolet photoluminescence and significantly reduced defect-related emission were observed. We attribute this observation to the nearly perfect surface passivation of the ZnO NRs by the HTph-OH molecules. Meanwhile, UV emission of modified ZnO NRs could be further enhanced by increasing the concentration of HTph-OH and annealing treatment at its liquid crystal state temperature.     

银/二氧化钛核壳纳米颗粒对碲化镉纳米晶的荧光增强研究

利用新合成的复合纳米结构银/二氧化钛核壳纳米颗粒,研究了金属银纳米颗粒对碲化镉纳米晶层荧光的增强情况.结果表明,这种新型复合金属纳米结构能极大地增强发光纳米晶层的荧光强度.银/二氧化钛核壳纳米颗粒是以水合肼、硝酸银和四异丙氧基钛为原材料,利用胶体化学法在水溶液中合成.透射电子显微镜图片表明这种新合成的银/二氧化钛纳米材料基本上呈球形,有较为明显的核壳结构,中间黑色的核是银纳米颗粒,外层颜色较浅部分是二氧化钛壳层.另外,包裹二氧化钛壳层后,银纳米颗粒的表面等离子吸收带从409 nm红移至430 nm,也证实了这种新型核壳纳米材料的形成.将此合成方法得到的银/二氧化钛纳米颗粒和碲化镉纳米晶用旋转涂覆方法进行直接组合后,得到了银纳米颗粒对碲化镉纳米晶荧光的明显增强,并对其增强的物理过程进行了讨论.这种能够增强荧光团发光的新型复合银纳米结构将在发光器件、荧光成像、生物探测等方面具有一定的应用价值.     

SiO_2/Ag核壳结构纳米粒子的制备及其表面荧光增强

以罗丹明B掺杂的SiO2球为核,通过化学还原的方法制备了二氧化硅/银核壳结构复合纳米粒子。采用透射电镜(TEM)、紫外-可见-近红外(UV-Vis-NIR)分光光度计和荧光分光光度计对二氧化硅/银核壳结构纳米粒子的表面形貌、表面等离子共振和表面荧光增强特性进行了研究和表征。结果表明,二氧化硅/银核壳结构纳米粒子的表面等离子共振峰具有明显的可调谐性,且其表面荧光增强强烈依赖于银壳层的表面等离子共振,随银壳层厚度的增大而增强。     

Improvement of a novel anode material TeO2 by chlorine doping

A simple and versatile method for the preparation of chlorine-doped TeO₂ was developed via thermal decomposition of Te₆O₁₁Cl₂ in situ. Te₆O₁₁Cl₂ was prepared with TeCl₄ and ethanol as reagents, while TeO₂ was fabricated with water as a solvent. The morphology, surface, and electrochemical performances of the obtained materials were systematically studied. It was found that chlorine-doped TeO₂ demonstrated the highest cycling efficiency and stability than Te₆O₁₁Cl₂ and TeO₂. The presence of Te–Cl bond is expected to contribute to the reversible capacity and Li inserting process.     

Electromechanical nonlinearity of Bi2TeO5

The electromechanical nonlinearity of a bismuth tellurite single crystal (Bi₂TeO₅) is investigated. It is revealed that the noncentral forces of interatomic interaction dominate in this material. The relation between the structural features of Bi₂TeO₅ and its elastic properties is analyzed.     

UV-activated gas sensing properties of ZnS nanorods functionalized with Pd

Pd-functionalized ZnS nanorods were prepared for use as gas sensors. Scanning electron microscopy revealed the diameters and lengths of the nanorods ranging from 30 to 80 nm and from 2 to 5 μm, respectively. The diameter of Pd nanoparticles ranged from 2 to 5 nm. Transmission electron microscopy revealed that ZnS nanorods and Pd nanoparticles were monocrystalline and amorphous, respectively. The responses of multiple networked ZnS nanorods sensors to 1–5 ppm NO₂ were increased substantially by a combination of Pd functionalization and UV irradiation. Pristine ZnS nanorod sensors at room temperature in the dark showed a response (∼100%) almost independent of NO₂ concentration in a NO₂ concentration range of 1–5 ppm. Pristine ZnS nanorod sensors showed enhanced responses of 214–603% to 1–5 ppm NO₂ at room temperature under UV illumination. Pd-functionalized ZnS nanorods sensors showed further enhanced responses of 355–1511% to 1–5 ppm NO₂ at room temperature under UV illumination. The NO₂ gas sensing mechanism of the Pd-functionalized ZnS nanorods sensors under UV illumination is discussed in depth.     

反常氧化碲声光偏转器控制理论研究

根据晶体的声光特性以及反常布喇格衍射的Dixon方程,得出了氧化碲声光偏转器在反常布拉格衍射条件下的参量矢量关系.分析了超声波方向、入射光角度、衍射光角度与声波频率之间的关系.针对卫星光通信中衍射角固定的应用情况,通过数值求解和参量拟合,建立了一个基于平面方程的简单控制模型.利用该模型可以很快得到超声控制频率,使衍射角固定不变.     

Excellent ethanol sensing properties based on Er_2O_3-Fe_2O_3 nanotubes

In this work, pure α-Fe2O3 and Er2O3-Fe2O3 nanotubes were synthesized by a simple single-capillary electrospinning technology followed by calcination treatment. The morphologies and crystal structures of the as-prepared samples were characterized by scanning electron microscopy and x-ray diffraction, respectively. The gas-sensing properties of the as-prepared samples have been researched, and the result shows that the Er2O3-Fe2O3 nanotubes exhibit much better sensitivity to ethanol. The response value of Er2O3-Fe2O3 nanotubes to 10 ppm ethanol is 21 at the operating temperature240?, which is 14 times larger than that of pure α-Fe2O3 nanotubes(response value is 1.5). The ethanol sensing properties of α-Fe2O3 nanotubes are remarkably enhanced by doping Er, and the lowest detection limit of Er2O3-Fe2O3 nanotubes is300 ppb, to which the response value is about 2. The response and recovery times are about 4 s and 70 s to 10 ppm ethanol,respectively. In addition, the Er2O3-Fe2O3 nanotubes possess good selectivity and long-term stability.     

Controllable synthesis of Ag nanorods using a porous anodic aluminum oxide template

This paper describes a new approach to the synthesis of Ag nanorods. A solvothermal method was used to make Ag nanoparticles inside anodic aluminum oxide (AAO) templates. The nanoparticles were then annealed at 300 °C to produce Ag nanorods. The size of AAO templates, which is focused on in this study, would determine the diameter of Ag nanorods. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In this study, a nanorod growth mechanism is deduced, and understanding of the growth of nanorods inside AAO templates is furthered. This work demonstrates that it is possible to make crystalline nanorods that the size can be varied.     

Chemical synthesis of zinc oxide nanorods for enhanced hydrogen gas sensing

Zinc oxide(ZnO) nanorods are prepared using equimolar solution of zinc nitrate((Zn(NO3)2) and hexamethylenetetramine(C6H12N4) by the hydrothermal technique at 80 C for 12 h. Epitaxial growth is explored by X-ray diffraction(XRD) patterns, revealing that the ZnO nanorods have a hexagonal(wurtzite) structure. Absorption spectra of ZnO are measured by UV–visible spectrometer. The surface morphology is investigated by field emission scanning electron microscopy(FESEM). The synthesized ZnO nanorods are used for detecting the 150 C hydrogen gas with a concentration over 1000 ppm. The obtained results show a reversible response. The influence of operating temperature on hydrogen gas detecting characteristic of ZnO nanorods is also investigated.     

银纳米粒子/碳纳米管阵列SERS基底增强因子分析和实验

为了直观、准确地定量分析表面拉曼增强散射基底结构的拉曼增强,利用磁控溅射和高温退火的方法制备了银纳米粒子修饰垂直排列的碳纳米管阵列三维复合结构样品;实验采用罗丹明6G(R6G)溶剂作为探针分子,结合共聚焦显微拉曼系统,开展了表面增强拉曼增强因子(EF)分析计算的相关实验。SEM结果表明：在有序碳纳米管阵列的表面和外壁均匀地负载了大量银纳米粒子。对退火温度为450 ℃,退火时间为30 min的样品进行了EF计算,得到其增强因子约为2.2×103,并分析了EF值低的原因主要是：在碳纳米管上溅射的银膜膜厚不均匀,导致退火后银颗粒分布不均,使得样品粗糙度值偏大,EF值较低;实验中所用的激励光源并非银纳米颗粒的优化光源。     

Electronic structure of rutile SnO2, GeO2 and TeO2

The electronic structure of SnO₂, GeO₂ and TeO₂ in the rutile crystal structure is calculated using the scalar-relativistic linear muffin-tin-orbital method. Good accordance between the calculated energy bands and experimental information is found. Some important qualitative discrepancies remain, demonstrating the delicacy of the problem of obtaining the electron energies of relatively low symmetry ionic crystals from first principles. The crystal charge distribution reveals a significant admixture of covalency in the bonding of the rutile dioxides, and the appropriate charge state of the cation turns out to be far from the ideal ionic + 4 configuration. This has an important impact on the interpretation of Mössbauer experiments with the ¹¹⁹Sn and ⁷³Ge isotopes as the valence contribution to the electron density on the nuclear site is substantial.     

Holographic performance of photorefractive Bi 2 TeO 5 crystals

Bismuth tellurite - Bi 2 TeO 5 is a new photorefractive material recently available for optical memory investigations. Analogue volume holograms of a two-dimensional test pattern were recorded in undoped Bi 2 TeO 5 crystals by using a cw Nd:YAG laser at 532 v nm. The quality, dark decay and durability during permanent reading of the image were studied and compared to those of the reference LiNbO 3 :Fe crystals. The holograms in the two crystals were of comparable quality, and they were less vulnerable for strong laser exposure in Bi 2 TeO 5 than in the LiNbO 3 :Fe crystals by a factor of 50.