Structural Phase Transformations of ZnS Nanocrystalline Under High Pressure

In-situ energy dispersive x-ray diffraction on ZnS nanocrystalline was carried out under high pressure by using a diamond anvil cell. Phase transition of wurtzite of 10nm ZnS to rocksalt occurred at 16.0GPa, which was higher than that of the bulk materials. The structures of ZnS nanocrystalline at different pressures were built by using materials studio and the bulk modulus, and the pressure derivative of ZnS nanocrystalline were derived by fitting the equation of Birch-Murnaghan. The resulting modulus was higher than that of the corresponding bulk material, which indicates that the nanomaterial has higher hardness than its bulk materials.     

Synthesis and Optical Properties of ZnO Nanostructures

ZnO nanostructures with different morphologies were fabricated by changing the partial oxygen pressure. The structures, morphologies and optical properties of ZnO nanostructures were investigated by x-ray diffraction, field emission scanning electron microscopy and photoluminescence (PL) spectra at room temperature. All the samples show preferred orientation along the c-axis. The oxygen partial pressure and the annealing atmosphere have important effect on the PL property of ZnO nanostructures. The high oxygen partial pressure during growth of samples and high-temperature annealing of the ZnO samples in oxygen can increase oxygen vacancies and can especially increase antisite oxygen (OZn) defects, which degraded the near band-edge emission. However, the annealing in 1-12 can significantly modify the NBE emission.     

Fabrication and Characterization of Well-Aligned Zn1-xMnxO Nanorods

Well-Migned Zn1-xMnxO nanorods have been synthesized successfully on bare silicon substrates by a simple evaporation method without using any catalyst. X-ray diffraction and electron microscopy studies demonstrate that the as-grown nanorods are of single wurtzite phase with a preferential growth direction along their c- axes, Quantitative energy-dispersive spectrum analysis reveals that the concentration of manganese is around 4 at,%, Magnetic measurements show the single-phase Zn1-xMnxO nanorod arrays exhibiting the paramagnetic behaviour. Photolumlnescence spectra demonstrate that the Zn1-xMnxO nanorods preserve ultraviolet emission at room temperature.     

Study on Synthesis and Gas Sensitivity of SnO2 Nanobelts

Tin dioxide （SnO2 ） nanobelts have been successfully synthesized in bulk quantity by the CVD process based on the thermal evaporation of tin powders. The x-ray diffraction analysis indicates that the nanobelts are the tetragonal futile structure of SnO2. Scanning electron microscopy and transmission electron microscopy observations reveal that the nanobelts are uniform. The selected-area electron diffraction analysis demonstrates that the nanobelts are single crystals. The energy dispersive x-ray analysis of the nanobelt shows that the nanobelts are composed of Sn and O, Gas-sensing components have been manufactured with prepared SnO2 nanobelts. Their performance indicates that SnO2 nanobelts have high sensitivity and selectivity to liquefied petroleum gas with fairly good response-recovery characteristic and stability at 220℃.     

Evaluation of multiaxial stress in textured cubic films by x-ray diffraction

X-ray diffraction is used extensively to determine the residual stress in bulk or thin film materials on the as- sumptions that the material is composed of fine crystals with random orientation and the stress state is biaxial and homogeneous through the x-ray penetrating region. The stress is calculated from the gradient of ε ～ sin^2 φ linear relation. But the method cannot be used in textured films due to nonlinear relation. In this paper, a novel method is proposed for measuring the multiaxial stresses in cubic films with any [hkl] fibre texture. As an example, a detailed analysis is given for measuring three-dimensional stresses in FCC films with [111] fibre texture.     

Growth Mechanism of Vertically Aligned Ag（TCNQ） Nanowires

Highly oriented Ag(TCNQ) nanowires have been prepared on Si(111) wafer at 1O0℃ by the vapour-transport reaction between silver and TCNQ without any other catalyst. X-ray diffraction analysis shows that the composition and crystal structure of the obtained nanostructure were Ag(TCNQ) crystalline. Most Ag(TCNQ) nanowires were grown uniformly and vertically on the substrate with diameters ranging from 50 to 30Onto and the lengths measuring from 2 to 50μm by scanning electron microscopy. Ag particles were observed on the substrate from pure thin Ag film heated under the same conditions as used in synthesizing the nanowires. Nucleation and short Ag(TCNQ) nanowires were prepared by controlling the reaction time, providing direct evidence of the growth mechanism in a nanometre scale. The growth process was explained according to the vapour-liquid-solid model. The gradient of temperature and the densely distributed Ag particles may contribute to the vertically aligned growth. These results will be helpful for the controllable synthesis of Ag(TCNQ) nanowires.     

A Practical Guide for X-Ray Diffraction Characterization of Ga（A1, In）N Alloys

Ca(In, Al)N alloys are used as an active layer or cladding layer in light emitting diodes and laser diodes, x-ray diffraction is extensively used to evaluate the crystalline quality, the chemical composition and the residual strain in Ca(Al,In)N thin films, which directly determine the emission wavelength and the device performance. Due to the minor mismatch in lattice parameters between Ca(Al, In)N alloy and a CaN virtual substrate, x-ray diffraction comes to a problem to separate the signal from Ca(Al,In)N alloy and CaN. We give a detailed comparison on different diffraction planes. In order to balance the intensity and peak separation between Ca(Al,In)N alloy and CaN, (0004) and (1015) planes make the best choice for symmetric scan and asymmetric scan, respectively.     

Atomic and Electronic Structures of Cd0.96Zn0.04Te（l10） Surface

X-Ray diffraction is used to analyse the lattice structure of Cdo.96Zno.o4 Te （CZT）, and the lattice constant is measured to be 0.647nm. The atomic structure of the clean CZT（110） surface obtained by Ar^＋ etching in vacuum is observed by low-energy electron diffraction, where no surface reconstruction is discovered. Angleresolved photoemission spectroscopy was used to characterize the surface state of the clean CZT （110） surface, by which we find a 1.5-eV-wide surface band with the peak at 0.9eV below the Fermi energy containing about 6.9 × 10^14 electrons/cm^2, approximately one electron per surface atom.     

Local structure of NiTi naocrystals studied by EXAFS and XRD

A series of NiTi nanocrystals with different annealing temperatures,prepared by sputtering method,were investigated by extended x-ray absrption fine structure(EXAFS) and x-ray diffraction.It was found that the structure of nano-phase powder is different from bulk NiTi alloy with bcc structure as targent materials.When increasing the annealing temperature,a small fraction of the (Ni,Ti) type nanocrystal with the hexagonal structure was presented except target materials and Ni,and it is atomic occupation in random.Finally there were four Ti and two Ni atoms around central Ni atoms,and the bond length of Ni-Ti and Ni-Ni were 0.2462nm and 0.2585nm at 800℃ annealed.     

Effects of Rapid Recurrent Thermal Annealing on Giant Magnetoresistance NiFe／Ag Multilayers

NiFe/Ag multilayers were prepared by dc sputtering onto glass-ceramic substrates directly at room temperature. The samples were thermally processed by rapid recurrent thermal anneal (RRTA). We studied the effects of RRTA on giant magnetoresistance (GMR) NiFe/Ag multilayer by contro11ing the anneal temperature as well as the rapid anneal cycle. The samples after three RRTA cycles have a similar annealing temperature dependence of GMR responses to the ordinary annealed samples. With the increasing anneal cycle, the GMR response improved at first and then reached an unexpected high value of 9% before descent rapidly. Microstructure study shows that this effect is ascribed to the transformation of continuous NiFe layer into discontinuous one, and then into a granular like film in a step-by-step way.     

Si纳米线的固-液-固可控生长及其形成机理分析

以Au膜作为金属催化剂,直接从n-(111)Si单晶衬底上制备了直径为30—60nm和长度从几微米到几十微米的高质量Si纳米线.实验研究了Au膜层厚、退火温度、N2气流量和生长时间对Si纳米线形成的影响.结果表明,通过合理选择和优化组合上述各种工艺条件,可以实现直径、长度、形状和取向可控的纳米线生长.基于固-液-固生长机理,定性阐述了Si纳米线的形成过程.     

Influence of several factors on the growth of selenium nanowires induced by silver nanoparticles

This paper presents a study on the crystallization and growth mechanism of selenium nanowires induced by silver nanoparticles at ambient conditions with special reference to the effects of factors such as the shapes and size of silver nanoparticles, the induced reaction time, and the molar ratio of Ag⁰ to SeO₃²⁻ ions. The synthesis approach is conducted with no need of any stabilizers, and with no sonochemical process and/or templates. It is found that whether silver spherical particles or colloids can lead to the formation of nanowires with average diameter of 25 nm and lengths up to a few micrometers, and silver nanoplates lead to the formation of flat Se nanostructures. In particular, Au, Cu, Pt, and Pd particles cannot induce the growth of selenium nanowires in aqueous solution at room temperature. The results indicate that silver particles play a critical role in determining the growth of selenium nanowires. The lattice match between hexagonal-Se and orthorhombic- or trigonal-Ag₂Se particles is the major driving force in the growth of such nanostructures. The findings would be useful for design and construction of heterogeneous nanostructures with similar lattice parameter(s).     

Synthesis and attachment of silver nanowires on atomic force microscopy cantilevers for tip‐enhanced Raman spectroscopy

Surface‐enhanced Raman spectroscopy is based on the absorption of light by nanometer‐sized metal particles, resulting in large enhancement of the Raman signal. By replacing the metal particles by a metallic nanotip, the enhancement can be localized. The resulting tip‐enhanced Raman spectroscopy is capable of measuring Raman spectra with high spatial resolution, effectively overcoming the diffraction limit. A successful tip‐enhanced Raman spectroscopy experiment depends heavily on the ability to fabricate tips of a definite metal with the appropriate shape and size, which is still a challenging process. We have prepared silver nanowires with a diameter of 200–300 nm by templated electrochemical deposition and attached them onto atomic force microscope cantilevers by focused electron beam induced deposition. We found that they produce a reproducible enhancement of the Raman signal intensity. Other metals and smaller nanostructures might also be produced, suggesting an interesting development potential for these novel nanoprobes. Copyright © 2011 John Wiley & Sons, Ltd.     

Photochemical decoration of silver nanoparticles on ZnO nanowires as a three‐dimensional substrate for surface‐enhanced Raman scattering measurement

To increase the sensitivity in surface‐enhanced Raman scattering (SERS) measurement, a three‐dimensional (3D) SERS substrate was prepared by the decoration of silver nanoparticles (AgNPs) on the side walls of ZnO nanowires. The prepared 3D SERS substrates provide the advantages of highly loaded density of AgNPs, with a large specific surface area to interact with analytes, and the ease for the analytes to access the surfaces of AgNPs. To prepare the substrates, ZnO nanowires were first grown on a glass plate by wet chemical method. By treating SnCl₂ on the surfaces of ZnO nanowires, Ag seeds could be formed on the side wall of the ZnO nanowires, which were further grown to a suitable size for SERS measurements via photochemical reduction. To optimize and understand the influences of the parameters used in preparation of the substrates, the reaction conditions were systematically adjusted and examined. Results indicated that AgNPs could be successfully decorated on the side wall of the ZnO nanowires only by the assistances of SnCl₂. The size and density of AgNPs were affected by both the concentration of silver nitrate and the irradiation time. With optimized condition, the prepared 3D substrates provided an enhancement factor approaching 7 orders of magnitude compared with conventional Raman intensity. Copyright © 2014 John Wiley & Sons, Ltd.     

Tuning the growth of ZnO nanowires

ZnO nanowires (NWs) with different diameters were obtained by controlling the particles of ZnO sub-layer (SL) exploring hydrothermal method; the diameter of the epitaxial NWs could be tuned from 60 to 146 nm when using SL with a thickness of 70 nm. The thickness of the SL would influence the orientation of the NWs. The top agglomerate NWs could be formed on the SL with a thickness of 10 nm, and the NWs with better orientation were obtained using SL with a thickness of 70 nm. Well aligned ZnO NWs grew perpendicular to the completely stress released SL. The diameter of the NWs was also greatly influenced by the solution concentration; thus ultra fine (diameter∼11 nm) ZnO NWs were obtained through adjusting the solution concentration to 0.001 mol/L. Through our research, we also found that the growth rate of the NWs could also be influenced by the different polarity surface of the SL. In other words, the size of the ZnO NWs could be tuned exactly under optimal conditions.     

十字结构银纳米线的表面等离极化激元分束特性

金属纳米线波导可以将光局域在亚波长尺度内传播, 在纳米光子集成回路方面有着重要的作用. 本文应用有限元方法, 研究了十字结构银纳米线的表面等离极化激元分束特性. 结果表明, 不同模式的表面等离极化激元在十字结构三个分支的输出依赖于端面的几何结构参数. 此外, 研究还发现由于不同模式表面等离极化激元叠加, 在十字结构的分支上出现了周期性电场分布.     

Synthesis of large-scale GaN nanowires by ammoniating Ga2O3 films on Co layer deposited on Si（111） substrates

A mass of GaN nanowires has been successfully synthesized on Si（111） substrates by magnetron sputtering through ammoniating Ga2O3/Co films at 950℃. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscope and Fourier transformed infrared spectra are used to characterize the samples. The results demonstrate that the nanowires are of single-crystal GaN with a hexagonal wurtzite structure and possess relatively smooth surfaces. The growth mechanism of GaN nanowires is also discussed.     

Self‐catalysed growth of InAs nanowires on bare Si substrates by droplet epitaxy

We demonstrate the self‐catalyst growth of vertically aligned InAs nanowires on bare Si(111) by droplet epitaxy. The growth conditions of indium droplets suitable for nucleation and growth of nanowires have been identified. We have then realized vertically aligned and non‐tapered InAs nanowires on bare Si(111) substrates through optimal indium droplets. It was found that the lateral dimensions and density of nano‐wires are defined by the indium droplets. This technique unravels a controllable, cost‐effective and time‐efficient route to fabricating functional monolithic hybrid structures of InAs nanowires on silicon.

     

Aggregation-based growth of silver nanowires at room temperature

We describe an aggregation-based growth mechanism for formation of silver nanowires at room temperature. It is found that the pH of solution and the concentration of l-cysteine capping molecules have an important effect on the formation and growth of nanowires. Characterization by atomic force microscopy (AFM) and UV-vis spectroscopy recorded as time clearly shows that the silver nanowires are grown at the expense of nanoparticles.