An oxide/silicon core/shell nanowire metal-oxide semiconductor field-effect transistor

This paper studies an oxide/silicon core/shell nanowire MOSFET(OS-CSNM).Through three-dimensional device simulations,we have demonstrated that the OS-CSNM has a lower leakage current and higher I on /I off ratio after introducing the oxide core into a traditional nanowire MOSFET(TNM).The oxide/silicon OS-CSNM structure suppresses threshold voltage roll-off,drain induced barrier lowering and subthreshold swing degradation.Smaller intrinsic device delay is also observed in OS-CSNM in comparison with that of TNM.     

Synthesis and magnetic properties of Mn doped CuO nanowires

Study of diluted magnetic semiconductor nanowires is one of the important topics in materials science. By using Mn-Cu alloy as the starting material, Mn doped CuO nanowire arrays have been synthesized in air at the temperature of 550 °C. X-ray diffraction measurements and scanning electron microscopic study shows that the nanowires were grown on Cu₂O substrate. Transmission electron microscopic study shows the single crystal property of the nanowires. Magnetic measurements show ferromagnetic property in the Mn doped CuO nanowires with the critical temperature higher than 80 K.     

A redox reaction model for self-heating and aging prediction of Al/CuO multilayers

Sputter-deposited Al/CuO multilayers capable of highly energetic reactions have been the subject of intense studies for tunable initiation and actuation. Designing high performance Al/CuO-based initiator devices definitively requires reliable prediction of their ignition and reaction kinetics including self-heating or ageing as a function of heating rate and environmental conditions. The paper proposes a heterogeneous reaction model integrating an ensemble of basic mechanisms (oxygen diffusion, structural transformations, polymorphic phase changes) that have been collected from recent experimental investigations. The reaction model assumes that the rate of reaction is limited by the transport of oxygen across the growing layer of Al₂O₃ separating Al and CuO. Importantly, we show that the model predicts reasonably all exotherms through a wide range of temperature (ambient – 1000°C), all resulting from a pure diffusion process as experimentally observed for such Al/CuO multilayers. The model shows how the temperature ramp affects the structure of the multilayer and especially the growth of alumina-based interfacial regions. It highlights the importance of the interfacial chemistry evolution such as the native mixture of Al_xCu_yO_z transformation into a thin amorphous alumina, and the polymorphic phase transformation of this latter. The first one occurring at ～350°C results in a loss of continuity of the interface leading to the accelerated redox reaction whereas the second one occurring between 500 and 600°C produces a denser barrier to oxygen diffusion leading to the stop of redox reaction. We finally use the model to simulate thermal annealing as usually performed in accelerated ageing experiments. We theoretically observe and experimentally validate that a two weeks exposure of the multilayers at 200°C starts degrading the multilayers thermal properties whereas when the temperature remains below 200°C, the material keeps its entire integrity.     

ZnO/CuO 核壳结构纳米线光致发光性能 与CuO壳层厚度的关系

通过分别生长核层与壳层制备出了ZnO/CuO核壳结构的纳米线。形貌和结构分析表明,ZnO核为单晶纳米线而CuO则以多晶形式覆盖在核层表面上。光致发光(PL)研究表明,ZnO纳米线PL强度随CuO壳层厚度的变化而变化。当壳层比较薄时ZnO的PL强度增大,这主要是由于CuO壳层对ZnO核层的修饰减少了表面态,而当壳层厚度增加到一定程度时,ZnO的PL强度不再变化,这主要是由于在核壳结构中形成了type-I型结构的原因。我们对这一现象做了详细的讨论。     

CuO/Al2O3、CuO/CeO2-Al2O3和CuO/La2O3-Al2O3催化剂中CuO物种被CO氧化的比较

用浸渍法制备了CuO/Al2O3 (Cu/Al)、CuO/CeO2- Al2O3 (Cu/CeAl)和CuO/La2O3-Al2O3(Cu/LaAl)催化剂. 通过原位XRD、Raman和H2-TPR方法， 对催化剂中的CuO物种以及CuO-Al2O3的固-固相反应进行了表征. 结果表明，对于Cu/Al催化剂，CuAl2O4存在于CuO与Al2O3层之间，CuO以高分散和晶相两种相态存在于催化剂的表层；对于Cu/CeAl催化剂，除了少量高分散和晶相的CuO存在于表层外，大部分CuO迁移到了CeO2的内层，     

Diverse nanowires activated self-scrolling of graphene nanoribbons

Diverse nanowires (NWs) activating the self-scrolling of planar graphene (GN) nanoribbons have been studied by using molecular dynamics (MD) simulations. Once the NWs’ radiuses reach a threshold, all the seven NWs, acting as an external force, can initiate the conformational change of the GN nanoribbons, and finally form the core/shell composite NWs. Our simulation found that van der Waals (vdW) force plays an important role in the process of forming core/shell composite NWs. This preparation method of the core/shell composite NWs will open a further development of a broad new class of metal/GN core/shell composite NWs with enhanced properties. And these core/shell structures can be the building blocks of functional nanodevices with unique mechanical, electrical, or optical properties.     

Synthesis and magnetic properties of carbon-coated Ni/SiO_2 core/shell nanocomposites

A simple method for the synthesis of carbon-coated Ni/SiO2 core/shell nanocomposites is reported. The Ni nanoparticles were coated with silica layers via a combined procedure of sol-gel fabrication and hydrogen reduction prior to carbon coating via acetylene decomposition at an appropriate temperature. It was found that the anti-acid ability of the Ni/SiO2 composites was greatly enhanced after carbon coating. The results of magnetization measurement show that the real part (μ′) of complex permeability of the as-obtained sample is almost independent of frequency, and the imaginary part (μ″) stays small up to a frequency of 1 GHz. The encapsulation of Ni particles with SiO2 results in the rise of Ni nanoparticles resistivity. The outcome is the reduction in effect of eddy current at high frequency, making the real part μ′ almost constant and the imaginary part μ″ very small. Thus, this simple method may be effective for preparing composites of soft magnetic properties, especially in the high-frequency range.     

Synthesis and magnetic properties of carbon-coated Ni/SiO2 core/shell nanocomposites

A simple method for the synthesis of carbon-coated Ni/SiO₂ core/shell nanocomposites is reported. The Ni nanoparticles were coated with silica layers via a combined procedure of sol-gel fabrication and hydrogen reduction prior to carbon coating via acetylene decomposition at an appropriate temperature. It was found that the anti-acid ability of the Ni/SiO₂ composites was greatly enhanced after carbon coating. The results of magnetization measurement show that the real part (μ′) of complex permeability of the as-obtained sample is almost independent of frequency, and the imaginary part (μ″) stays small up to a frequency of 1 GHz. The encapsulation of Ni particles with SiO₂ results in the rise of Ni nanoparticles resistivity. The outcome is the reduction in effect of eddy current at high frequency, making the real part μ′ almost constant and the imaginary part μ″ very small. Thus, this simple method may be effective for preparing composites of soft magnetic properties, especially in the high-frequency range. Supported by the Jiangsu Postdoctoral Foundation of Jiangsu Province and the Major Project of National Basic Research Program of China (Grant No. 2005CB623605)     

Synthesis and Raman signature for the formation of CdO/MnO2 (core/shell) nanostructures

In the present report, bare CdO and CdO/MnO₂ core/shell nanostructures of various cores and different shell sizes were synthesized using co‐precipitation method. The phase, size, shape and structural details of the bare CdO and CdO/MnO₂ nanostructures were investigated by X‐ray diffraction, transmission electron microscopy (TEM), and Raman spectroscopy measurements. TEM micrographs confirm the formation of core/shell nanostructures. The presence of CdO (core) and MnO₂ (shell) crystal phases was determined by analyzing the Raman data of bare CdO and CdO/MnO₂ core/shell nanostructures. The Raman spectra of bare CdO nanostructures contain one broad intense convoluted envelop of three bands in the spectral range of 200–500 cm⁻¹ and a weaker band located at ~940 cm⁻¹. The intensity of these two Raman bands is decreased with the increase of shell size and disappeared completely for the shell size 5.3 ± 1 nm. Further, two new Raman bands appeared at ~451 and ~665 cm⁻¹ for the shell size 1.3 ± 0.1 nm. These two Raman bands are assigned to the deformation of Mn–O–Mn and Mn–O stretching modes of MnO₂. The intensity of these two Raman bands is enhanced with the increase of shell size and attains a maximum value for the shell size 5.3 ± 1 nm. The disappearance of characteristics Raman bands of CdO phase and the appearance of characteristics Raman bands corresponding to MnO₂ phase for nanostructures of shell size 5.3 ± 1 nm authenticate the presence of CdO as core and MnO₂ as shell in the core/shell nanostructures. Copyright © 2014 John Wiley & Sons, Ltd.     

Cu/C核/壳纳米结构的气相合成、形成机理及其光学性能研究

采用乙酰丙酮铜为原料, 通过化学气相沉积大批量制备出Cu/C核/壳纳米颗粒和纳米线. 研究结果表明, 通过控制沉积温度可对Cu/C核/壳纳米材料的形貌和结构进行很好的控制. 比如, 沉积温度为400 ℃时可获得直径约200 nm的Cu/C核/壳纳米线, 沉积温度为450 ℃ 时可获得直径约200 nm的Cu/C核/壳纳米颗粒和纳米棒的混合产物, 沉积温度为600 ℃时可获得直径约22 nm的Cu/C核/壳纳米颗粒. 获得的Cu/C核/壳纳米结构是由一个新颖的凝聚机理形成的, 而这种机理不同于著名的溶解-析出机理. 紫外-可见光谱和荧光光谱分析结果表明: Cu/C核/壳纳米线和纳米颗粒均在225 nm处出现Cu的吸收峰, 同时在620 和616 nm处分别出现了纳米线和纳米颗粒的表面等离子共振吸收峰. Cu/C核/壳纳米线在312 和348 nm处、 Cu/C核/壳纳米颗粒在304 和345 nm处出现荧光发射谱峰. 关键词： Cu/C核/壳结构 纳米线 纳米颗粒 光学性能     

小粒径同质/异质壳层结构NaGdF_4:3%Nd~(3+)纳米颗粒的近红外发光特性

采用共沉淀法制备了粒径小于5 nm的六方相NaGdF_4:3%Nd~(3+)纳米颗粒.纳米颗粒表面缺陷会使发光中心产生严重的淬灭,对其表面包覆适当厚度的壳层可以有效地减少发光淬灭,提高发光性能.对NaGdF_4:3%Nd~(3+)核心纳米颗粒分别进行同质和异质包覆并且通过调节核壳比制备了不同壳层厚度的NaGdF_4:3%Nd~(3+)@NaGdF_4和NaGdF_4:3%Nd~(3+)@Na YF4纳米颗粒,研究了不同的壳层厚度对核心纳米颗粒发光的影响,并对两种不同核壳结构纳米颗粒的发光性能进行了对比.在808 nm近红外光激发下,NaGdF_4:3%Nd~(3+)纳米颗粒发射出位于约866,893,1060 nm的近红外发射.与核心纳米颗粒相比,核壳结构的纳米颗粒的荧光强度增强,荧光寿命增长,并且随着壳厚的增加,荧光强度出现先增强后减弱、荧光寿命逐步增长的趋势.与相同条件下同质包覆的NaGdF_4:3%Nd~(3+)@NaGdF_4纳米颗粒相比,异质包覆的NaGdF_4:3%Nd~(3+)@NaYF_4纳米颗粒光谱荧光强度增强,寿命增长.     

Preparation and characterization of core/shell particles with siloxane in the shell

The core/shell particles consisting of polystyrene core and 3-(methacryloxypropyl)-trimethoxysilane (MPS) shell were prepared in the present study by successive seeding polymerization under kinetically controlled conditions and were characterized by particle size analyser, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM image indicated that the particles containing organic siloxane presented an evident core/shell structure. Additionally, the study of XPS also revealed that MPS could be grafted onto the surface of polystyrene microspheres and the atomic ratio of C/Si on the surface of the core/shell particles (MPS-40) was very close to the ratio of C/Si in the molecule of MPS. The surface properties of the films produced from the core/shell particles were also investigated by the static contact angle method. Compared with the homopolymer of PS, the core/shell particles were more effective to create hydrophobic surface, so, the introduction of MPS was capable of obvious increase in water repellency.     

Synthesis of robust water-soluble ZnS:Mn/SiO2 core/shell nanoparticles

Water-soluble Mn doped ZnS (ZnS:Mn) nanocrystals synthesized by using 3-mercaptopropionic acid (MPA) as stabilizer were homogeneously coated with a dense silica shell through a multi-step procedure. First, 3-mercaptopropyl triethoxy silane (MPS) was used to replace MPA on the particle surface to form a vitreophilic layer for further silica deposition under optimal experimental conditions. Then a two-step silica deposition was performed to form the final water-soluble ZnS:Mn/SiO₂ core/shell nanoparticles. The as-prepared core/shell nanoparticles show little change in fluorescence intensity in a wide range of pH value.     

内核/壳层微结构上应力驱动的三角和斐波纳契数花样

自然界中三角和斐波纳契数的叶序花样随处可见.通过控制几何条件以及冷却之后产生的应力,这些花样能在Ag内核/SiOx壳层微结构(约10μm大小)上予以实现.在这种内核/壳结构表面上,大小形状十分一致的小球通过自组装是形成斐波纳契数花样(我们观察到5×8,8×13和13×21三种)还是三角花样,取决于基座面的几何构形.作者工作的意义在于揭示了在适当的几何约束下,自组装形成的花样是总应变能最小的结果.这对叶序花样的形成来源提出了一种非遗传的机理.此外,作者的研究表明,高度有序的、甚至含有内禀缺陷的微结构可以通过应力工程在大面积范围内同时得到.     

Controlling the electrostatic discharge ignition sensitivity of composite energetic materials using carbon nanotube additives

Powder energetic materials are highly sensitive to electrostatic discharge (ESD) ignition. This study shows that small concentrations of carbon nanotubes (CNT) added to the highly reactive mixture of aluminum and copper oxide (Al + CuO) significantly reduces ESD ignition sensitivity. CNT act as a conduit for electric energy, bypassing energy buildup and desensitizing the mixture to ESD ignition. The lowest CNT concentration needed to desensitize ignition is 3.8 vol.% corresponding to percolation corresponding to an electrical conductivity of 0.04 S/cm. Conversely, added CNT increased Al + CuO thermal ignition sensitivity to a hot wire igniter.     

Radial heterostructure and interface effects on thermoelectric transport properties of Bi/Sn and Bi/Sb core/shell nanowires

The thermoelectric transport properties of Bi/Sn and Bi/Sb core/shell (C/S) nanowires grown by the method of on-film formation of nanowires were systematically investigated. The electrical conductivity and Seebeck coefficient of nanowires with different diameters were measured as a function of the temperature. The contribution of Sn and Sb shells to the total transport in the C/S nanowires was determined using analytical fitting based on the parallel combination of the conductive system model. The carrier-interface boundary scattering at the C/S interface was quantitatively evaluated as the sheet resistance. In addition, the effect of hole doping on the transport properties was also observed in the Bi/Sn C/S nanowires.     

Magnetic properties of Ni/Au core/shell studied by Monte Carlo simulations

The magnetic properties of ferromagnetic Ni/Au core/shell have been studied using Monte Carlo simulations within the Ising model framework. The considered Hamiltonian includes the exchange interactions between Ni–Ni, Au–Au and Ni–Au and the external magnetic field. The thermal total magnetizations and total magnetic susceptibilities of core/shell Ni/Au are computed. The critical temperature is deduced. The exchange interaction between Ni and Au atoms is obtained. In addition, the total magnetizations versus the external magnetic field and crystal filed for different temperature are also established.     

Dependence of flame propagation on pressure and pressurizing gas for an Al/CuO nanoscale thermite

The pressure dependence of flame propagation in an Al/CuO nanoscale thermite was studied. Experiments were performed by loosely packing the Al/CuO mixture in an instrumented burn tube, which was placed in a large volume, constant pressure chamber with optical windows. A high-speed camera was used to take photographic data, and six pressure transducers equally spaced along the length of the burn tube were used to measure the local transient pressure. Ambient pressures were varied between 0 and 15 MPa, and three different pressurizing gases were used: argon, helium, and nitrogen. Three modes of propagation were observed. The pressure at which the mode of propagation changed was similar for argon and nitrogen, however, when pressurized with helium, transition occurred at lower pressures. In the low-pressure regime (0–2 MPa) a constant velocity mode with speeds on the order of 1000 m/s was observed. In this region, a convective mode of propagation was dominant. An accelerating regime was observed for a pressure range of approximately 2–5 MPa in argon and nitrogen, with speeds ranging from 100 to 800 m/s. In helium, however, if an accelerating region existed it occurred over a narrow pressure range which was not observed in the present experiments. An oscillating regime was observed in all three gases, in a pressure range of 5–9 MPa for argon and nitrogen, and a range of 2–4 MPa for helium. Velocities in this region are bimodal, and differ by orders of magnitude, suggesting that the propagation mechanism was oscillating between convective and conductive. At relatively high ambient pressures, a constant velocity mode with speeds on the order of 1 m/s was observed for all three gases. The conductive mode of propagation was likely dominant in this region.     

High performance Au/Ag core/shell bipyramids for determination of thiram based on surface‐enhanced Raman scattering

Au/Ag core/shell bipyramids were used as surface‐enhanced Raman scattering (SERS) substrates to determine the thiram. The metallic substrates showed high SERS performance and are very suitable for the analytical sensors. The fabrication and characterization of the Au/Ag core/shell bipyramids were described. The influence of experimental parameters, such as the thickness of Ag shell of the bipyramids, sodium chloride concentration, and pH value on SERS of thiram was examined and optimized. Under the optimum conditions, thiram molecules were effectively adsorbed onto bipyramids and the SERS intensity is proportional to the concentration of thiram in the range of 3.3 to 400.0 ng mL^–1. The corresponding correlation coefficient of the linear equation is 0.997, which indicates that there is a good linear relationship between SERS intensity and thiram concentration. The limit of detection for thiram is 2.0 ng mL^–1. The experimental results indicate that the proposed method is a viable method for determination of thiram. Some environmental water samples were analyzed and the analytical results were satisfactory. Copyright © 2012 John Wiley & Sons, Ltd.     

Hysteresis loops and susceptibility of a transverse Ising nanowire

In this work, the magnetization, susceptibility, and hysteresis loops of a magnetic nanowire are described by the transverse Ising model using the effective field theory within a probability distribution technique. The effects of the exchange interaction between core/shell and the external fields on the magnetization and the susceptibility of the system are examined. Some characteristic phenomena are found in the thermal variations, depending on the ratios of the physical parameters in the shell and the core.