On the extinction multipole plasmons in gold nanorods

On the basis of the T-matrix formalism and numerical simulations, we derive an explicit rule for partial multipole contributions to the plasmon resonances of gold nanorods at a fixed or random orientation. The parity of a given spectral resonance number n coincides with the parity of their multipole contributions l, where l is equal to or greater than n, and the total resonance magnitude is determined by the lowest multipole contribution. We also investigate the dependence of multipole plasmons on the size, shape, and orientation of nanorods with respect to the polarized incident light. It is shown that the multipole resonance wavelengths as a function of the aspect ratio divided by the resonance number collapse onto one linear scaling curve. This scaling is explained by using the plasmon standing wave concept introduced by Schider et al. [Plasmon dispersion relation of Au and Ag nanowires. Phys Rev B 2003;68:155427].     

金纳米棒核/贵金属壳杂化纳米结构的可控制备和性质调控

贵金属纳米颗粒由于其独特的光学及催化性能引起了人们的广泛关注,而这些性能与纳米颗粒的尺寸、形貌、结构组成等密切相关.目前如何有意识地控制晶体生长过程,以得到人们需要的纳米结构和组成,仍具有相当大的挑战性.文章重点介绍了利用具有特定形貌和晶面组成的金纳米棒(Au nanorods)作为种子,借助形成核/壳结构,诱导了Ag, Pd, Pt棒状纳米结构的形成,并实现了对杂化纳米结构光学和催化性能的调控,进一步扩展了贵金属纳米结构的应用范围.作者的研究结果表明,形成杂化纳米结构是性能调控的一种有效方式.     

金纳米棒核/贵金属壳杂化纳米结构的可控制备和性质调控

贵金属纳米颗粒由于其独特的光学及催化性能引起了人们的广泛关注,而这些性能与纳米颗粒的尺寸、形貌、结构组成等密切相关.目前如何有意识地控制晶体生长过程,以得到人们需要的纳米结构和组成,仍具有相当大的挑战性.文章重点介绍了利用具有特定形貌和晶面组成的金纳米棒（Au nanorods）作为种子,借助形成核/壳结构,诱导了Ag...     

Surface-enhanced Raman scattering properties of highly ordered self-assemblies of gold nanorods with different aspect ratios

Gold nanorods with aspect ratios of from 1 (particles) to 31.6 were synthesized by the seed-mediated method and packed in a highly ordered structure on a large scale on silicon substrates through capillary force induced self-assembly behaviour during solvent evaporation.The gold nanorod surface exhibits a strong enhancing effect on Raman scattering spectroscopy.The enhancement of Raman scattering for two model molecules (2-naphthalenethiol and rhodamine 6G) is about 5-6 orders of magnitude.By changing the aspect ratio of the Au nanorods,we found that the enhancement factors decreased with the increase of aspect ratios.The observed Raman scattering enhancement is strong and should be ascribed to the surface plasmon coupling between closely packed nanorods,which may result in huge local electromagnetic field enhancements in those confined junctions.     

表面等离激元探针的高介电灵敏度与液体折射率测定

利用金纳米棒在光照射下激发表面等离激元的性质,实验研究了其在不同介电环境下的吸收光谱.通过分析纵向等离子体共振吸收峰峰位随介质折射率的变化,获得了金纳米棒表面等离激元探针测量介质折射率的经验公式为n=(385.59)-1(λ/nm-290.56).利用金纳米棒表面等离激元探针的高介电灵敏度,测试了一些未知液体的折射率,并与阿贝折射仪测量法的结果相比较.结果与分析表明,本方法较之阿贝折射仪测量介质折射率的方法具有更高的精密度.因此,表面等离探针可用于拓展大学物理实验中的介质折射率测量实验.     

Complexation of bovine serum albumin and gold nanorods revealed by plasmon-enhanced light scattering spectroscopy

Complexation of bovine serum albumin (BSA) and gold nanorods has been investigated by plasmon-enhanced light scattering spectroscopy under external stimuli such as the changes in hydrogen ion concentration value and ionic strength, with addition of ethanol. The results indicated that the BSA chains tend to adopt a coil conformation by decreasing hydrogen ion concentration value. Scattering intensity of the gold nanorods–BSA system gradually decreases because BSA chains tend to adopt a coil conformation with addition of sodium chloride. This work will further extend the application range of this method due to its simplicity, rapidity, and sensitivity.     

Preparation of monodisperse bimetallic nanorods with gold nanorod core and silver shell and their plasmonic property and SERS efficiency

In this study, monodisperse bimetallic nanorods with gold (Au) nanorod core and silver (Ag) shell (Au@AgNRs) were synthesized through seed‐mediated growth process by reduction of AgNO₃ using Au nanorods with narrow size and shape distribution as seeds. With increasing the used amount of AgNO₃, the Ag shell thickness of their lateral facets is raised faster than that of their two tips, leading to a decrease of their aspect ratios. Four plasmon bands are observable on the extinction spectra of Au@AgNRs, which are attributed to the longitudinal dipolar plasmon mode, transverse dipolar plasmon mode, and octupolar plasmon mode of the core‐shell structured bimetallic nanorods, respectively. As their Ag shell thickness increases, their longitudinal plasmon band blue‐shifts notably with the transverse plasmon band blue‐shifting and the two octupolar plasmon bands red‐shifting slightly, due to the decrease of their aspect ratios and enhancement of Ag plasmon resonance contribution. When used as surface‐enhanced Raman scattering (SERS) substrate for probing minute amounts of 4‐mercaptobenzoic acid in aqueous solution, Au@AgNRs have much stronger SERS activity than Au nanorods, and the obtained Raman signals are highly reproducible arising from their excellent monodispersity. Their SERS activity is remarkably increased with their Ag shell thickness thanks to the enhancing surface electric field and the chemical enhancement associated with electronic ligand effect. Copyright © 2014 John Wiley & Sons, Ltd.     

Tunable plasmon resonance wavelength of the periodic gold film with converging and diverging shaped slits and grooves

We investigate a periodic slit-groove metal array with converging and diverging shaped channels by using the finite-difference time-domain (FDTD) method. We show that the peaks and dips of the transmission spectra can be tuned by the geometry parameters of the groove. And the resonance modes are strongly correlated with the groove depth and width of both ends of the groove, and the transmission dip between the resonance modes can be modulated by these parameters. However, the distance between the slit and the groove has little influence on the transmission. We show that the periodic slit-groove with diverging and converging shaped channels is useful for the design of plasmonic devices.     

Enhanced Device Performances of Blue‐Emitting PLEDs Coupled with Silver‐Nanoicosahedrons

Silver‐nanoicosahedron particles (AgNIPs) are produced by chemical reduction and photochemical methods and doped into the hole transport layer (HTL) or emissive layer (EML) of blue‐emitting polymer light‐emitting diodes (PLEDs) to improve their luminous efficiency. The optimal distributed‐densities of the AgNIPs are determined from current density–voltage–luminance measurements at different doping concentrations. The AgNIP dopant doses that maximize the average luminous efficiency of the proposed PLED are 6.71 µg cm^?2 in EML (achieving 3.48 cd A^?1) and 6.88 µg cm^?2 in HTL (achieving 3.35 cd A^?1). Although the luminous efficiencies of the blue‐emitting PLEDs fabricated by both doping methods are not significantly different, the maximum plasmonic enhancement (around 30‐fold) of the blue‐emitting PLED with AgNIPs in EML is red‐shifted to the green region (≈530 nm in the electroluminescence spectrum), seriously degrading the luminescent monochromaticity of the blue‐emitting PLED. The maximum plasmonic enhancement (around 33‐fold) of blue‐emitting PLED with AgNIPs in HTL occurred at 430 nm, overlapping the localized surface‐plasmon resonance extinctions of the AgNIPs in HTL (425 nm), thus favoring the enhancement of fluorescence emission. Therefore, to enhance the large‐area emission of blue‐emitting PLEDs, the AgNIPs should be doped in the HTL rather than the EML.     

Evaluating the surface density and heterogeneity of a dithiobis (succinimidylpropionate) self-assembled monolayer on gold and its coupling with DNA embedded within a matrix

The homogeneity of a self-assembled monolayer (SAM) on a surface is an important parameter which affects the ability of a SAM to fulfill its intended function. As an example, SAMs formed from octanethiols can form an impermeable surface, while SAMs based on a bifunctional coupling reagent can form a surface with uniform reactivity. Exposure of gold nanoparticles or gold surfaces to solutions of dithiobis (succinimidylpropionate) (DSP) gives rise to a surface which can react with DNA. Atomic force microscopy, UV-vis and gel electrophoresis experiments indicate that a self-assembled monolayer of DSP on gold nanoparticles can attenuate aggregation, inhibit the “lying down” of covalently-bound single-stranded (ss) DNA and promote more efficient hybridization. The determination of the point of aggregation after reacting DSP with colloidal gold yields 2.86 × 10⁻¹⁰ mol/cm² or 42% of the value determined from molecular modeling. Cyclic voltammetry experiments validate that DSP on a gold quartz crystal (6.3 × 10⁻¹⁰ mol/cm²) forms a fairly uniform SAM that is within 94% of maximum coverage when compared with results obtained from molecular modeling (6.67 × 10⁻¹⁰ mol/cm²). Surface plasmon resonance experiments indicate that the reaction of a DSP coated gold surface with (ss) DNA yields 2.4 × 10⁻¹² mol/cm² or reaction with about 1% of the available surface area. Subsequent reactions of the DSP surface with the filler, n-boc-1,4-phenylene diamine (n-boc), yield a total surface coverage of 1.8 × 10⁻¹¹ mol/cm². The surrounded (ss) DNA yields a surface with 97% hybridization efficiency toward the complement.     

Size dependent reaction kinetics of small gold clusters with carbon monoxide: Influence of internal degrees of freedom and carbonyl complex stability

The reactions of free gold clusters Au^–, , and with carbon monoxide are studied in an rf-octopole ion trap experiment at cryogenic temperatures. While Au^– is unreactive toward CO over the whole temperature range investigated, the two and three atom cluster anions show a maximum adsorption of two CO molecules at temperatures below 250 K. From time resolved trapping experiments the strongly cluster size dependent reaction kinetics are obtained and a distinct reaction mechanism is deduced. The size dependence of the measured rate coefficients reveals the preferred formation and particular stability of the carbonyl complex . Through RRK analysis of the absolute termolecular rate coefficients we are able to estimate the binding energy of CO to and .