Discrete Dipole Approximation Aided Design Method for Nanostructure Arrays

A discrete dipole approximation （DDA） aided design method is proposed to determine the parameters of nanostructure arrays. The relationship between the thickness, period and extinction efficiency of nanostructure arrays for the given shape can be calculated using the DDA. Based on the calculated curves, the main parameters of the nanostructure arrays such as thickness and period can be determined. Using this aided method, a rhombic sliver nanostructure array is designed with the determinant parameters of thickness （40 nm） and period （440 nm）. We further fabricate the rhombic sliver nanostructure arrays and testify the character of the extinction spectra. The obtained extinction spectra is within the visible range and the full width at half maximum is 99nm, as is expected.     

The octa-twin tetraleg ZnO nanostructures

We have developed a simple solid-vapor approach for controlled growth of the tetraleg ZnO nanostructure at high yield. The length of the tetraleg is 2-3 μm and the edge size of its centering nucleus is 70-200 nm. Our electron microscopy study gives the first direct evidence about the existence of the octahedral multiple twin nucleus, which is confirmed to be responsible for the formation of the tetraleg ZnO nanostructure. The tetraleg ZnO nanostructure is likely to be a candidate as building blocks for contructing photonic crystals.     

Directional Nanoslit-Bump Coupler for Surface Plasmon Polaritons

We investigate a p-polarized plane wave transmitted through a metallic slit-bump nanostructure using the finite difference time domain simulation. It is found that narrow bumps with suitable separation can diffract surface plasmons into highly directional collimating beams. The number and directionality of the beams can be controlled by adjusting the geometry parameters of the nanostructure. The structure with optimized parameters may be interesting for practical applications as directional nanoslit SPP-light coupler in integrated photonic devices.     

Effect of Media on the Electric Field of a Rhombic Nanostructure Array

Electric field distribution is an important parameter for nanostructure arrays in nanobiosensing appfications. It can influence the sensitivity and the resolution of nanobiosensors. We focus on the effect of media on the electric field distribution of a rhombic silver nanostructure array. The finite-difference time-domain algorithm- based numerical calculation method is used to monitor the electric field distribution of the silver nanostructures when the refractive index of the medium around the nanostructure array is changed. The calculated results show that tuning the refractive index of the medium around silver can have a considerable influence on the electric field distribution in the reflection and transmission directions. This effect can be used to increase the extinction efficiency and to improve the resolution of the spectra for nanobiosensing.     

“Sputtered-atom assembly” of carbon nanostructures during ion bombardment

We report the observation of a carbon nanostructure grown on a graphite surface by Ar⁺ ion bombardment. We demonstrate experimentally that, in view of transmission electron microscopy (TEM)-based evidence, some of these carbon nanostructures emerged the whiskerlike protrusion and/or the sputtered-surface, suggesting a new growth model for nanocarbon, distinctly different from that found in arc-discharge and many other methods. Received: 14 April 2000 / Accepted: 17 April 2000 / Published online: 13 July 2000     

Carrier-envelope phase-dependent electron tunneling in a coupled double-quantum-dot system driven by a few-cycle laser pulse

We theoretically investigate the dependence of the electron tunneling on the carrier-envelope phase of a few-cycle laser pulse in a coupled double-quantum-dot system, and we show that the electron tunneling between coupled quantum dots is very sensitive to the carrier-envelope phase under a change of the parameters of the system. This in turn provides an additional means to measure the carrier-envelope phase of a laser pulse at lower laser intensity regime in the solid-state nanostructure.     

The effect of periodic magnetic-electric barriers on electron transport in a nanostructure

Using the transfer matrix method, the transmission probability, the spin polarization and the electron conductance of a ballistic electron are studied in detail in a nanostructure. We observe that these quantities sensitively depend on the number of periodic magnetic-electric barriers. As the number of periods increases, the resonance splitting increases, the number of the resonance peaks increases and the peaks become sharper as well as the spin polarization being enhanced. Surprisingly, a polarization of nearly 100% can be achieved by spin-dependent resonant tunneling in this structure, although the average magnetic field of the structure is zero.     

Surface Plasmon Resonance and Field Enhancement of Au/Ag Alloyed Hollow Nanoshells

We investigate the nanostructure, surface plasmon resonance （SPR） absorption and nonlinear enhancement of Au/Ag alloyed hollow nanoshells prepared by the replacement reaction of Ag nanoparticles in a HAuCI4 aqueous solution. As the volume of HAuCl4 increases from OmL to 0.S mL, the SPR band of the Au/Ag alloyed nanoshells is tuned from 430nm to 780nm, and the third-order nonlinear optical susceptibility is enhanced nearly by an order of magnitude, which indicates a large enhancement of local field in the Au/Ag alloyed hollow nanoshells with hole defects.     

Application of Ru(bpy)3 in control and formation of gold surface nanostructure through oxidation-reduction cycling

It was studied that the nanostructure formed on a gold surface via a simple oxidation-reduction cycles (ORC) in 0.1 M KCl containing Ru(bpy)₃²⁺ with different concentrations. Atomic force microscopy (AFM) and energy-dispersed spectroscopy (EDS) were used to characterize the nanostructure formed on the gold surface. Sweep-step voltammetry and corresponding electroluminescence (ECL) response, in situ electrochemical quartz crystal microbalance (EQCM) measurement were used to monitor the ORC procedure. It was found that the surface structure became more uniform in the presence of Ru(bpy)₃²⁺, and the surface roughness was decreasing with the increasing of Ru(bpy)₃²⁺ concentration, suggesting a simple and effective method to control the formation of nanostructure on the gold surface.     

Novel self-assembled nanostructured alumina array with nanoscale grooves

A unique novel self-assembled nanostructured alumina array with nanoscale grooves can be induced and controlled in nanometer dimension by a general electrochemical oxidation of aluminum in sulfuric acid. Almost inter-perpendicular self-assembled alumina nanostructure arrays separated by a few tens nanometer thick interface sheet were also observed in many domains. And the formation of this nanostructured array is considered as the result of the special competition balance between electrochemical oxidation and etching. Because of similarities of aluminum anodization with semiconductor anodization, our results may be proved useful for Si or GaAs nanostructure synthesis.     

Bilayer ZnO nanostructure fabricated by chemical bath and its application in quantum dot sensitized solar cell

Chemical bath method was used to synthesize bilayer ZnO nanostructure on ITO glass in the alkaline solution. As revealed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), the product consists of a layered structure of ZnO nanorods at the bottom and nanoflower atop. The as-prepared sample was assembled in quantum dot sensitized solar cell (QDSSC), which obtained the incident photon to current conversion efficiency (IPCE) of 15% at 400 nm and power conversion efficiency (PCE) of 0.45%. Therefore, this novel bilayer ZnO nanostructure has the potential for application in solar cell device as the photoelectrode.     

Synthesis of ZnO compound nanostructures via a chemical route for photovoltaic applications

A facile, low-temperature, and low-cost chemical route has been developed to prepare ZnO nanowire and nanosphere compound structures. The morphology, structure, and composition of the yielded products have been examined by field-emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction measurements. We have systematically investigated the optical properties of the ZnO nanostructures by micro-Raman, photoluminescence, and transmission spectroscopy. The results demonstrate that the yielded ZnO nanostructures possess good optical quality with high light absorption. We have further successfully employed the obtained ZnO compound nanostructures in dye-sensitized solar cells. The light-to-electricity conversion results show that the compound nanostructure exhibits a significant enhancement of short-circuit current density due to the increased surface area and light scattering in the compound nanostructures. The present chemical route provides a simple way to synthesize various compound nanostructures with high surface area for nanodevice applications.     

Towards laser-manipulated deposition for atom-scale technologies

We have developed an apparatus for nanostructure fabrication based on direct deposition of laser-manipulated cesium vapors onto pyrolitic graphite. Key features of our apparatus are production and manipulation of a longitudinally cooled atom beam, which allows for straightforward operation in the moderate to low flux density conditions. Both unstructured and structured low surface coverage depositions have been carried out and samples carefully analyzed at the atom scale by in situ tunneling microscopy. Results represent a step forward to the realization of a novel technology for space-controlled deposition of few, eventually single, atoms.     

Polymerization of Silicon-Doped Heterofullerenes： an Ab Initio Study

We perform the calculations on geometric and electronic structures of Si-doped heterofullerene C5oSi10 and its derivatives, a C40Si20-C40Si20 dimer and a C40Si20-based nanowire by using density-functional theory, The optimized configuration of the C40Si20-based nanowire exhibits a regular dumbbell-shaped chain nanostructure. The electronic structure calculations indicate that the HOMO-LUMO gaps of the heterofullerene-based materials can be greatly modified by substitutionally doping with Si atoms and show a decreasing trend with increase cluster size. Unlike the band structures of the conventional wide band gap silicon carbide nanomaterials, the C40Si20- based nanowire has a very narrow direct band gap of 0.087eV.     

Tunneling mechanism through the nonlinear electrical transport in Co/CoO particles with core-shell nanostructure

We investigate the nonlinear electrical transport as a function of temperature in Co/CoO nanoparticles having core-shell nanostructure. Nanoparticle was synthesized by sol-gel citrate precursor technique where core-shell nanostructure is confirmed by the high resolution Transmission Electron Microscopy. Current-voltage (I-V) characteristics are measured over the temperature range 20-295 K. I-V curve exhibits ohmic behaviour at 295 K. Nonlinear electrical transport is observed at low temperature (T) for T?275 K. Electrical transport properties have been interpreted in terms of tunneling mechanism where tunneling between ferromagnetic Co nanoparticles takes place through the antiferromagnetic CoO layer. Analysis of dynamic conductance (G=dI/dV) indicates that the inelastic tunneling via localized states of antiferromagnetic CoO layers is dominant in the transport mechanism at low temperature.     

Coherent laser-induced optical behaviors in three-coupled-quantum wells and their application to terahertz signal detection

We investigate quantum optical behaviors of a weak-probe laser field in an asymmetric semiconductor three-coupled-quantum wells (TCQW) structure based on intersubband transitions (ISBTs) via switch-on/off of terahertz (TH) signal radiation under the application of a control laser field. A scheme for TH signal detection and its strength measurement based on this probe absorption characteristic also are put forward, where TH signal field does not interact directly with electron, but significantly affects the coherent optical absorption properties of such a weak-probe laser field. Consequently, the proposed TCQW nanostructure may be used for reducing and cancelling out the important thermionic dark current component in the process of TH signal detection, measurement and photodetector design.     

Magnetic properties of (Fe, Fe–B)/γ-Fe2O3 core shell nanostructure

Temperature-dependent magnetic properties of a core/shell nanostructure are reported employing magnetometry and electron magnetic resonance (EMR) spectroscopy. Structural characterization of the sample synthesized by NaBH₄ reduction of FeCl₃ was done by x-ray diffraction, TEM and Mössbauer spectroscopy and showed a core/shell nanostructure with a core of diameter D?20 nm consisting of α-Fe and amorphous Fe–B alloy and a shell of 7 nm thickness made up of principally γ-Fe₂O₃. Temperature-dependent EMR studies at 9.28 GHz show a narrow line with g?2.01 superimposed on a broad line with g?2.20. The narrow line assigned to the oxide shell disappears below about 60 K, in agreement with a blocking temperature T_B?30 K measured in SQUID magnetometry. The EMR parameters of the broad EMR line are similar to those reported for α-Fe nanoparticles imbedded in amorphous SiO₂ matrix. The magnitude of the saturation magnetization M_S=70 emu/g of the nanostructure is smaller than that of bulk α-Fe (M_S=220 emu/g) and bulk γ-Fe₂O₃ (M_S=88 emu/g). Size dependence is used to interpret the absence of exchange-bias in the field-cooled sample of the nanostructure.