Shrinking kinetics by vacancy diffusion of a pure element hollow nanosphere

In this paper, shrinking via the vacancy mechanism of a hollow mono-atomic nanosphere is described. Using Gibbs–Thomson boundary conditions, an exact solution is obtained for the kinetic equation in quasi steady-state at the linear approximation. Collapse time as a function of the geometrical size of a hollow nanosphere is found. An extension to hollow binary alloy nanospheres is also made. Previous Monte Carlo simulations of this problem are discussed.     

Specific Heat of Hollow Nanosphere Coupled to Substrate： Quantum Size Effects

With the help of the elastic wave theory in the perturbed approximation the density-of-states for vibrational modes and the specific heat are studied for different hollow Si nanospheres, coupled with a semi-infinite substrate. We find that the modes of such coupled hollow spheres are significantly broadened and shifted toward low frequencies. The specific heat of the coupled hollow nanosphere is bigger than an isolated one due to the coupling interaction and quantum size effects. The predicted coupling and size enhancements on specific heat are probed in thermal experiments.     

Preparation and optical properties of Cu2O hollow microsphere film and hollow nanosphere powder via a simple liquid reduction approach

In this work, we report a simple liquid reduction approach to prepare Cu₂O hollow microsphere film and hollow nanosphere powder with Cu(OH)₂ nanorods as precursor and ascorbic acid as the reductant at 60 °C. When Cu(OH)₂ nanorod array film grown on a copper foil is used as the precursor, Cu₂O thin film made up of hollow microspheres with average diameter of 1.2 μm is successfully prepared. When the Cu(OH)₂ nanorods are scraped from the copper foil and then used as the precursor, Cu₂O hollow nanosphere powder with the average diameter of 270 nm is obtained. The samples are characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and ultraviolet-vis light (UV-vis) absorption spectra. A possible formation mechanism of Cu₂O hollow spheres is discussed.     

Laser tattoo removal as an ablation process monitored by acoustical and optical methods

Monodisperse hollow silica nanospheres have been prepared by using a polystyrene nanosphere template-assistant approach and their potential as antireflection (AR) coatings for window applications has been discussed. The as-prepared hollow silica nanospheres have a typical inner diameter of 200 nm and a shell thickness of 15–20 nm. The AR effect over the ultraviolet-visible-near infrared spectral region has been observed for the hollow silica nanospheres, with a minimized reflection of about 5.2 % at 500 nm, compared to 8.5 % of a plain float glass substrate. By modifying the structural features of the hollow silica nanospheres, their AR properties can be further enhanced.     

Wake potential and stopping power for a charged particle moving outside a nanosphere

The interaction of a charged particle with a nanosphere is studied based on the dielectric response theory. We obtain the analytical expressions of the induced potential and stopping power, as the charged particle moving outside the nanosphere with a constant velocity. From our results, since the spherical shape limitation, the well-known V-shaped wake effect tracing the particle cannot be observed clearly no matter at the nanosphere surface or in the bulk. Besides, we also find that the particle can even gain energy from the electron polarization as the particle moves to the nanosphere at relatively low velocity.     

Carbon-coated hollow CoO microporous nanospheres synthesized by CoF<Subscript>2</Subscript> as the intermediates as anode materials for lithium-ion batteries

Uniformly carbon-coated hollow CoO microporous nanospheres have been successfully synthesized by the facile hydrothermal method using CoF₂ as the intermediates and glucose as the carbon source. The whole synthesis process can avoid using the toxic surfactant additives and tedious post-processing. The glucose-derived carbon not only suppresses the aggregation of CoO nanoparticles, but also plays an important role on the stabilization of hollow CoO microporous nanosphere structure. The specific structure can largely improve the electronic conductivity and accommodate the volume change of CoO electrode in the electrochemical processes. When used as anode materials of lithium ion batteries, the hollow CoO/C microporous composites exhibit exceptionally high-rate performances, high-specific capacity, and improved cycle performances. This study may provide a new approach for the synthesis of carbon-coated hollow microporous architecture electrode for high-performance batteries.     

A visible-near infrared tunable waveguide based on plasmonic gold nanoshell

A tunable plasmonic waveguide via gold nanoshells immerged in a silica base is proposed and simulated by using the finite difference time-domain （FDTD） method. For waveguides based on near-field coupling, transmission frequencies can be tuned in a wide region from 660 to 900 nm in wavelength by varying shell thicknesses. After exploring the steady distributions of electric fields in these waveguides, we find that their decay lengths are about 5.948-12.83 dB/1000 nm, which is superior to the decay length （8.947 dB/1000 nm） of a gold nanosphere plasmonic waveguide. These excellent tunability and transmittability are mainly due to the unique hollow structure. These gold nanoshell waveguides should be fabricated in laboratory.     

Y_2O_3∶Eu~(3+)纳米球的可控合成及尺寸效应所影响的发光性质

采用均匀沉淀法,通过改变稀土离子与尿素的量比成功合成了粒径分别为80,55,40 nm的Y_2O_3∶Eu~(3+)纳米球样品。通过X射线衍射(XRD)、场发射扫描电镜(FE-SEM)和发光光谱对不同尺寸纳米球的晶体结构、微观形貌和发光性质做了分析,对Y_2O_3∶Eu~(3+)纳米球的生长过程进行了研究。根据Judd-Ofelt理论,利用Eu~(3+)的发射光谱和荧光衰减等数据,计算了5D0→7FJ能级的辐射跃迁速率和荧光分支比,计算得到Y_2O_3基质材料的折射率为1.80以及不同粒径样品的光学跃迁强度参数。最后分析了5D0能级荧光发射与温度之间的依赖关系,结果证明了荧光温度猝灭行为符合Crossover过程,并通过阿伦尼乌斯公式非线性拟合获得了激活能,粒径为80,55,40 nm的Y_2O_3∶Eu~(3+)纳米球样品的活化能分别为0.201,0.193,0.200 eV。     

基于直接胶体晶体刻蚀技术的高度有序纳米硅阵列的尺寸及形貌控制

以自组装单层胶体小球阵列为掩模，采用直接胶体晶体刻蚀技术在硅表面制备二维有序尺寸可控的纳米结构.在样品制备过程中，首先通过自组装法在硅表面制备了直径200nm的单层聚苯乙烯(PS)胶体小球的二维有序阵列；然后对样品直接进行反应离子刻蚀(RIE)，以氧气为气源，利用氧等离子体对聚苯乙烯小球和对硅的选择性刻蚀作用，通过改变刻蚀时间，制备出不同尺寸的PS胶体小球的有序单层阵列；接着以此二维PS胶体单层膜为掩模，以四氟化碳为气源对样品进行刻蚀；最后去除胶体球后得到二维有序的硅柱阵列.SEM和AFM的测量结果表明：改变氧等离子体对胶体球的刻蚀时间和四氟化碳对硅的刻蚀时间，可以控制硅柱的尺寸以及形貌，而硅柱阵列的周期取决于原始胶体球的直径. 关键词： 胶体晶体刻蚀 纳米硅柱阵列     

Oxygen Electroreduction by Single PtPd Nanocubes Encaged in Hollow Carbon Nanospheres: Improved Durability and Strong Effect of Carbon‐Shell Thickness

As a cathode reaction in fuel cells, oxygen reduction reaction (ORR) plays a critical role in determining the overall performance of a fuel cell. It is still a big challenge to find effective ways to improve the catalytic activity, efficiency, and especially stability of ORR electrocatalysts. In the present study, single nanoparticle electrocatalysis for ORR is realized for the first time by encaging PtPd nanocube in hollow and porous carbon nanosphere (PtPd@HCS). Through tuning the carbon‐shell thickness by carbonization temperature, the effects of carbon‐shell thickness on ORR catalytic performance of PtPd@HCS are systematically investigated. The PtPd@HCS calcinated at 800 °C (PtPd@HCS‐800) with the thinnest carbon shell (3.52 nm) and rich pore structure exhibits enhanced ORR catalytic activity and stability. The strategy mentioned here is expected to provide a new method to design single nanoparticle electrocatalysts for fuel cells with high catalytic performance and reduced loading of precious metals.     

Versatile nanosphere lithography technique combining multiple-exposure nanosphere lens lithography and nanosphere template lithography

A versatile nanosphere composite lithography(NSCL) combining both the advantages of multiple-exposure nanosphere lens lithography(MENSLL) and nanosphere template lithography(NSTL) is demonstrated. By well controlling the development, washing and the drying processes, the nanosphere monolayer can be well retained on the substrate after developing and washing. Thus the NSTL can be performed based on MENSLL to fabricate nanoring, nanocrescent and hierarchical multiple structures. The pattern size and the shape can be systemically tuned by shrinking nanospheres by using dry etching and adjusting the tilted angle. It is a natural nanopattern alignment process and possesses a great potential in the scope of nano-science due to its low cost,simplicity, and versatility for variuos nano-fabrications.     

Mechanism for the Self-Assembly of Hollow Micelles from Rod-Coil Block Copolymers

The mechanism for the self-assembly of hollow micelles from rod-coil diblock copolymers is proposed. In a coilselective solvent, the diblock copolymers self-assemble into a layered structure. It is assumed that the rigid rods form an elastic shell whose properties are dictated by a bending energy. For a hollow micelle, the coils outside the micelle form a brush, while the coils inside the micelle can be in two different states, a brush or an adsorption layer, corresponding to symmetric or asymmetric configurations, respectively. The total energy density of a hollow micelle is calculated by combining the interfacial energy, elastic bending energy and the stretching energy of the brushes. For the asymmetric configuration with a polymer brush on one side, the competition between the elastic bending energy and the brush stretching energy leads to a finite spontaneous curvature, stabilizing hollow spherical micelles. Comparison of the free energy density for different geometries demonstrates that transitions for the different geometry micelles are controlled by the degree of polymerization of the coils and the length of the rods. These results are in agreement with the experimental results.     

Determination of electron density and energy influx in a hollow cathode glow discharge used for powder modification

The electron density and energy influx in an argon hollow cathode glow discharge were determined to obtain adequate parameters for subsequent surface modification of low density polyethylene (LDPE) powder to change the wettability. The electron density was studied by Langmuir probe measurement in dependence on process gas pressure and hollow cathode material. Besides the determination of the rate of increasing electron density with input power an optimal experimental pressure was determined. The energy influx was studied by thermal probe measurements in dependence on process gas pressure, bias voltage, axial position and hollow cathode material. Inside the hollow cathode the energy influx is nearly constant along the whole cathode length. With increasing pressure the energy influx decreased. At biased thermal probe the energy influx was observed to decrease up to the floating potential and beyond it increases with increasing voltage. Using different hollow cathode materials the electron density as well as the energy influx reach higher values for aluminum than for copper and stainless steel.     

Triple‐Yolked ZnO/CdS Hollow Spheres for Semiconductor‐Sensitized Solar Cells

A new kind of complex hollow structure, ZnO/CdS triple‐yolked hollow spheres (TYs), is prepared using a facile method. The formation mechanism is described in terms of a combined effect of the bubble‐assisted Ostwald ripening and appropriate ion‐exchange processes. The structural effect of ZnO hollow microspheres on the energy conversion efficiency is investigated. The uniqueness of TYs morphology leads to a 37% enhancement in energy conversion efficiency for SSSCs, as compared with single‐shelled hollow spheres. The method using controlled ZnO/CdS yolk‐in‐shell structures in SSSCs presents obvious advantages in the generation of light scattering and makes full use of the internal structures of the photoelectrode. It also provides a feasible synthetic approach for fabrication of other complex hollow structures made of multicomponent functional heteromaterials.     

位错联系的应力场对晶体生长影响的蒙特-卡罗模拟

本文运用van der Hoek等人提出的应力能函数,进行晶体生长的蒙特-卡罗模拟,研究了位错空核的形成,发现固—流键平均形成能ω和过饱和度△μ都对空核形成有很大的影响。本文还讨论了台阶及二维扩散与空核半径之间的关系。模拟表明位错空核将延缓直台阶的推进。 关键词：     

倾斜L形手性结构的制备以及圆二色性

在单层聚苯乙烯小球模板上,制备了大面积倾斜L形手性结构.通过倾斜角沉积技术,在小球的一侧生长二氧化硅,在二氧化硅上面沉积金属层;在垂直方向沉积另一金属层,使两个金属层具有不同高度从而形成倾斜L形手性结构.研究发现,通过控制二氧化硅的厚度,可以实现倾斜L形手性结构的圆二色性的调控.数值模拟结果表明,倾斜L形手性结构的圆二色性机制符合Born-Kuhn模型理论.     

Plasmon resonance in a nanosphere

The phenomenon of plasmon resonance in a nanosphere and a nanospheroid is considered. As is known, this phenomenon does not depend explicitly on the size of these nanoparticles. However, it is shown that, actually, the resonance conditions are determined by the diameter of the nanosphere and by the length of the major axis of the nanospheroid.     

Electrodynamic response of a nanosphere

The electrodynamic response of electron gas on the surface of a nanosphere in a weak magnetic field is studied. The case of the photon polarization vector oriented parallel to the magnetic field (the Faraday geometry) is considered. An analytic expression for the coefficient of electromagnetic-radiation absorption by the nanosphere is derived. It is shown that, at low temperatures, the absorption curve has, in the general case, two resonance peaks. The curve also exhibits breaks.     

应用球形和海胆状金混合SERS基底检测高环多环芳烃

合成了海胆状金银复合纳米材料,并与球形金纳米材料混合作为表面增强拉曼活性基底实现了对水中高环多环芳烃的痕量检测。对海胆状材料进行表征,粒径大小约为300～400 nm,表面有40～100 nm明显的刺状凸起。与球形金溶胶混合后并优化pH值及混合比例等参数,产生了优于球形金溶胶2～3倍的增强效果。利用此增强基底检测了危害严重的高环多环芳烃污染物——芘(四环)、苯并蒽(四环)、苯并芘(五环),得到的光谱数据反映出混合SERS基底有良好的重复性和稳定性,对测得光谱进行特征峰归属分析,固体拉曼光谱与水溶液SERS光谱有确定的对应关系,并且在低浓度范围多环芳烃特征峰峰强与其水溶液浓度有良好的线性关系。经计算,芘(四环)、苯并蒽(四环)、苯并芘(五环)的检测限分别为0.44,2.92和1.64 nmol·L-1。该研究的创新点为合成了海胆金纳米颗粒,与球形金溶胶混合后制成新型高效SERS检测基底;选用自制高效SERS基底,实现了高环PAHs痕量检测。结果表明,利用该方法制备的活性基底,可实现对水中高环多环芳烃的痕量检测,为检测水中高环多环芳烃提供了实验室依据。