Shi Pan

Integrate silver colloids with silicon nanowire arrays for surface-enhanced Raman scattering.

A facile method to prepare uniform and reproducible surface-enhanced Raman scattering (SERS) substrates is presented. Quasi-spherical silver colloids prepared by microwave heating and wafer-scale uniform silicon nanowire (SiNW) arrays fabricated via wet chemical etching were united together as SERS substrates. The novel SERS substrates displayed stronger Raman enhancement than conventional silver colloids as well as outstanding uniformity and reproducibility in our experiments. In addition, it was found that the cross section of SiNW arrays possessed stronger enhancement activity than the front side. The enhancement effects of two adjacent SiNWs (as a simplification of SiNW arrays) were evaluated by the finite difference time domain (FDTD) method.

Three powerful research tools from single cells into single molecules: AFM, laser tweezers, and Raman spectroscopy.

By using three physical techniques (atomic force microscopy (AFM), laser tweezers, and Raman spectroscopy), many excellent works in single-cell/molecule research have been accomplished. In this review, we present a brief introduction to the principles of these three techniques, and their capabilities toward single-cell/molecule research are highlighted. Afterward, the advances in single-cell/molecule research that have been facilitated by these three techniques are described. Following this, their complementary assets for single-cell/molecule research are analyzed, and the necessity of integrating the functions of these three techniques into one instrument is proposed.

Plasmonic Effect of a Nanoshell Dimer with Different Gain Materials

Though the plasmonic property for a passive nanoparticle dimer has been studied widely, the performance of a nanoparticle dimer with gain material is still inexplicit to our knowledge. Therefore, in this paper, we focus on the plasmonic effect of a nanoshell dimer, with its core filled with different gain materials, under a polarized plane wave excitation using a three-dimensional finite difference time domain method. It is shown that the gain materials in the core of the nanoshell can compensate the intrinsic absorption of the metal shell, resulting in a local energy enhancement in the junction of the active nanoshell dimer. The physics is supported by the detailed energy distribution of the active nanoshell dimer in each geometry region. It is found that the plasmonic coupling between two active nanoshell particles is more compact than the case of passive ones. The influence of shell thickness on the interaction between two adjacent active nanoshells is also analyzed.

Numerical study on the mechanisms of the SERS of gold-coated pyramidal tip substrates.

In this paper, the physical enhancement mechanisms of the surface-enhanced Raman scattering (SERS) of pyramidal tip substrates are studied theoretically. We structure the periodic square-based arrays of adjacent nanometer pyramidal gold-coated tips on silicon. In order to determine the contribution of plasmonic or diffraction effects on the SERS, three-dimensional (3D) numerical simulations are implemented by taking into account the substrate coated with a gold thin film or a perfect electrical conductor thin film. The tip distance, metal coating thickness and incident light polarization angle are also optimized to investigate whether the further SERS signal can be enhanced.

Carbon nanocoils manipulated by optical tweezers

Carbon nanocoils (CNCs) have attracted much attention due to their unique three-dimensional helix morphology, outstanding mechanical and electronic properties, and potential applications. Compared with carbon nanotubes, CNCs can be dispersed in solvents easily. In this paper, the manipulation of single CNCs by an optical tweezers has been demonstrated. It is found that these CNCs can be trapped, removed and rotated by the manipulation system, resulted from the asymmetrical distribution of optical trapping force generated on the CNCs with chiral features. Furthermore, the length of a single CNC can be adjusted by increasing the power of incident laser beam because the absorbed laser energy can be changed into thermal energy in a CNC. These results suggest that CNCs can be manipulated by an optical tweezers, which is suitable for the alignment of a CNC at a fixed position with a fixed length in electronic devices.

Optical response of bowtie antennas

Optical properties of bowtie antennas are investigated using a numerical method of finite-difference time-domain (FDTD). The optical response in the antenna feed gap is simulated as functions of its geometry parameters (flare angle, arm length, apex width, thickness, gap dimension, as well as the index of substrate), which provide a clear guideline to exploit such antenna structures in practice.

The Structural Characteristics of CIS Thin Films Prepared by Electro-Deposited Method

The properties of the absorber layer of solar cell CuInSe2(CIS) thin film made by electro-depostied method were researched in this article. Different concentration of reactant and voltage was applied to prepare the CIS film. The micro-Raman spectroscopy and X-ray diffraction (XRD) of CIS film was carried out. A correlation between the linewidth A1 mode of Raman spectrum and the XRD line and the voltage of electro-deposition technology was found.

Effective local-field confinement of silver nanoparticle dimer arrays

The optical properties of silver spherical nanoparticle dimer arrays with various incident wavelength are investigated by using the finite difference time domain method. Due to surface plasmon resonance, in the arrays of strongly coupled Ag nanoparticles, the energy of incident light is effectively confined in the gap of penultimate dimer under the influence of surface plasmonic reflection at the end of array structure. Furthermore, the suitable radius of the nanoparticles can be chosen to obtain the resonant peak at the optional position in the range of visible-nearinfrared wavelength. The above effects can be utilized to design effective functional end-structures in integrated optics.

Nano-optical microscopy: now and its industrialization

It is a review about the industrialization of Nano-Optical Microscope (NOM, also referred to as the Near-field Optical Microscope). Two comparisons of AF/PSTM (Transmission Mode) with the first generation commercial A-SNOM and AF/RNOM(Reflective Mode) with A-RNOM have discussed. The commercially used A-SNOM can only obtain a transmissivity image of A-SNOM-T(x,y), but AF/PSTM can obtain the separating the transmissivity image PSTM-T(x,y) and the refractive index imge PSTM-n1(x,y). AF/RNOM can obtain the lower contrast reflective index image but ARNOM cannot. The reason how could Pohl have obtained the first A-SNOM image with a resolution of 20-25nm in 1984 but the commercial A-SNOM-T(x,y) only with the resolution in the 50~100nm range is also discussed. Conclusion on the proposal of AF/PSTM and combined AF/RNOM may be the best candidate for the second generation commercial use of NOM.

Metal nanostrip array for light transmission enhancement in subwavelength slit

Metal nanostrip array for light transmission enhancement in the nanoslit is studied using a finite-difference time-domain method (FDTD). The strips with uniform shape are placed on upper side of a metal film with the nanoslit fabricated in it. It is found that the transmission efficiency can be promoted with an optimization of the strip. Effects of the single strip on the promotion are discussed in detail, a Fabry-Perot resonance model is competent for well understanding the phenomena.