Discrete Dipole Approximation Simulation of Nearly Touching Plasmonic Au Dimers and Influence of Particle Shape Assembly on Optical Response.

The method Discrete Dipole Approximation (DDA) is used to calculate the extinction spectra and field distribution of three types of dimers. In the paper we provide a systematic analysis of the optical response of different nanoscopic dimer structures with relatively small gap distances. A description is given about how the energy and excitation cross sections of dimer plasmons depend on nanoparticle separation. Resonance peaks of dimers show red-shift compared with single nanoparticle. Dimers formed by different single particle display distinct optical response. Interaction junctions in dimers can serve as hot spots for field enhancement. Field distribution in gaps made of two flat planes is nearly continuous. Changing gaps between two particles in dimers can tune the resonance wavelength effectively as well as different particle ensembles. Existence of sharp corners can attract and change field distribution. It is not effective volume but the effective cross-section that dominates the extinction efficiency.

[An Analysis of Combustion Emission Spectrum and Combustion Products of KClO4/Zr in the Quartz Tubes].

Aiming at understanding the light radiation properties of KClO4/Zr combusting under different conditions, emission spectrum and combustion products for KClO4/Zr combusting in open air and closed quartz tubes were studied respectively. Energy distribution of the light radiation signal and the emission intensity evolution with time were measured with fiber optic spectrometer, and photo-diode and oscilloscope. Spectral efficiency within (590±10), (750±10) and (808±10) nm were analyzed respectively according to the obtained flame emission spectrum. Morphology of the combustion products of KClO4/Zr were observed with scanning electronic microscopy (SEM). Results showed that the flame emission spectrum of KClO4/Zr distributed within the visible and near infrared width wave band, whiel the strongest radiation appeared within 730 nm to 820 nm band. When burning in closed quartz tubes, detected combustion emission spectrum intensity decreased significantly with the decrease in size of the tube. Also, the energy distribution of the emission spectrum showed different variation trends, and to deal with flame emission spectrum distribution, as the change of volume of quartz tubes, (590±10), (750±10) and (808±10) nm bands' spectral efficiency are also present different change rules. Generally, increasing the diameter of the quarts tube favored the increase of the effective light radiation energy detected outside of the tube, and decreasing the diameter of the quartz tubes favored the peak emission intensity of KClO4/Zr. With the increase of tube diameter, KClO4 burning more fully, the product particle size is smaller; the morphology is the rule of the globular. And the change of tube length is not too large effect in the reaction results.

The influence of edge and corner evolution on plasmon properties and resonant edge effect in gold nanoplatelets.

In this paper a simulation of the properties of surface plasmons on gold nanoplatelets with various cross-sections inscribed in a circle and an investigation of their field distributions to assign multiple SPRs are described. The manipulated propagation can be obtained through the evolution of edges and corners. Furthermore, the particle morphology and the associated spectral positions alone do not uniquely reflect the important details of the local field distribution or the resonance modes. The plasmon modes were investigated and found to be mainly excited along the edges and in the side and sloped side surfaces. The strong field distributions can generally be found around the corners and how the plasmons transmit through the corners to adjacent edges was also investigated. Besides the plasmons excited along the edges as were found for the triangular nanoplatelets, plasmons were excited in the interior region of the triangular surfaces and were also investigated. Despite this in the infrared region, plasmon modes were found to be along the edges for the hexagonal nanoplatelets. Also, it can be seen that the change of nanoplatelet thickness can support different plasmon modes ranging from dipolar resonance mode to quadrupole resonance mode. The thickness far below the skin depth can display complex plasmon modes along the edges and on the side and sloping side surfaces as well as the strong coupling between the top and bottom surfaces. The observed plasmon resonance modes in this simulation reflect the interference of all these contributions including the plasmons along the edges and on the side surfaces. This is an essential step towards a thorough understanding of plasmon modes and the effect of edge and corner evolution in polygonous nanoplatelets.

[Study of density functional theory for surface-enhanced Raman spectra of furfural].

In the present paper, DFT method at the B3LYP/6-31+G* * (C, H, O)/LANL2DZ(Ag) level was used to optimize molecular configurations of furfural. Based on the optimized structure, the normal Raman spectrum (NRS) of FUR and the surface-enhanced Raman spectrum (SERS) of FUR adsorbed on Ag, Ag2 and Ag4 were all calculated, which were compared with the experimental values. The calculation results indicated that a good conformity was found between the computed and the experimental results. The results of furfural adsorbed on Ag4 were more approximate to the ever reported experimental date than those of furfural adsorbed on Ag and Ag2. At the end, detailed analysis of the Raman spectrum and more comprehensive assignments of the vibration mode for furfural were studied by the software of GaussView. The data of the SERS by comparing with the one of NRS show that furfural molecule and Ag atoms interact with each other. And we suppose that the molecular plane with the ring of adsorbed furfural molecule is vertically orientated to the silver surface. The work in this paper offers a theory evidence for detection and trace analysis of drinks containing furfural.

[Study of density functional theory for surface-enhanced Raman spectra of p-aminothiophenol].

In the present paper, DFT method at the B3LYP/6-31++G** (C, H, N, S)/LANL2DZ(Ag) level was used to optimize molecular configurations of p-aminothiophenol. Based on the optimized structure, the normal Raman scattering (NRS) spectrum of PATP and the surface-enhanced Raman scattering(SERS) spectrum of PATP adsorbed on Ag and Ag2 were both calculated, and were compared with the results of other literatures values. The calculation results indicated that a good conformity was found between the computed and experimental results. The results of PATP adsorbed on Ag2 were more approximate to the ever reported experimental data than those of PATP adsorbed on Ag. At the end, detailed analysis of the Raman spectrum and more comprehensive assignments of the vibration mode for p-aminothiophenol were studied by the software of GaussView. In comparison with SERS spectrum and NRS spectrum of PATP molecule, the authors observed the stretching vibration bands in the SERS spectrum at about 213 cm(-1), which is due to Ag-S stretching vibration mode. The work in this paper has greatly directive value in understanding and explaining some experiment phenomenon, and helps to study the mechanism of surface-enhanced Raman scattering of PATP.

Correlations of the stability, static dipole polarizabilities, and electronic properties of yttrium clusters.

Static dipole polarizabilities for the ground-state geometries of yttrium clusters (Yn, n < or = 15) are investigated by using the numerically finite field method in the framework of density functional theory. The structural size dependence of electronic properties, such as the highest occupied molecular orbital-lowest occupied molecular orbital (HOMO-LUMO) gap, ionization energy, electron affinity, chemical hardness and softness, etc., has been determined for yttrium clusters. The energetic analysis, minimum polarizability principle, and principle of maximum hardness are used to characterize the stability of yttrium clusters. The correlations of stability, static dipole polarizabilities, and electronic properties are analyzed especially. The results show that static polarizability and electronic structure can reflect obviously the stability of yttrium clusters. The static polarizability per atom decreases slowly with an increase in the cluster size and exhibits a local minimum at the magic number cluster. The ratio of the mean static polarizability to the HOMO-LUMO gap has a much lower value for the most stable clusters. The static dipole polarizabilities of yttrium clusters are highly dependent on their electronic properties and are also partly related to their geometrical characteristics. A large HOMO-LUMO gap of an yttrium cluster usually corresponds to a large dipole moment. Strong correlative relationships of the ionization potential, softness, and static dipole polarizability are observed for yttrium clusters.