Fluorescence Spectrum Characteristics of Gold Nanorods

Aqueous solutions containing a high yield of suspended gold nanorods with mean aspect ratio 2.5 have been synthesized via an electrochemical method. The fluorescence emission peaks fixed at 37Onm and 670nm are due to the local field enhancement via coupling to the transverse and longitudinal surface plasmon resonance.The quasi-static calculation results indicate that with the increasing aspect ratio of the nanorods, the longer wavelength emission peak decreases and red shifts, whereas the shorter wavelength emission peak blue shifts slightly.     

Electronic Phase Diagram of Mixed-Valence Gold Chloride

A comprehensive electronic phase diagram is derived for mixed-valence gold chloride Cs2Au2Cl6 by means of high-pressure Raman spectroscopy. At all the temperatures investigated (100K≤T≤300 K), applications of pressure induce a phase transition from the mlxed-valence (MV) state to a single-valence (SV) state. In the SV state, a broad Au-Cl stretching band appears at～400 cm^-1 below ～200K. We have interpreted the appearance of the band in terms of formation of the AuX2^--like local lattice distortion, or the bipolarons.     

Self-Assembly of Gold Nanoparticles on Nanometre-Patterned Surface

The self-assembly processes of gold nanoparticles on nanometre-step-patterned Si surface and polished Si surface are investigated by the convective self-assembly method. The convective self-assembly method is used to deposit the colloids dispersed in benzene onto the substrates. The SEM results show that the configurations of the gold arrays depend on the surface morphology of the substrates. On the nanometre-step-patterned Si surface, the nanoparticles self assemble into parallel lines, and the distance between the neighbouring lines is around 35 nm. On the polished Si surface the nanoparticles form compact domains. In each domain the particles are closepacked in a two-dimensional hexagonal superlattice and are separated by uniform distances. The analysis shows that on the nanometre-step-patterned Si surface, the steps play critical roles in the self-assembly process of gold nanoparticles. The capillary force from the steps drives the particles to lines along the steps. Therefore, the particles tend to self-assemble into one-dimensional line structures when the solvent evaporates. For the polished Si substrate there is a little difference that the particles form two-dimensional hexagonal superlattices without the directional confinement.     

Properties and Stability of Nanosecond Optical Limiting of Gold Nanoclusters

Optical limitation(OL) performances of the gold nanoclusters protected by C60-tpy have been investigated with 8 ns pulses at 532nm.The experimental results show that the nanocomposite possesses OL effects superior to C60 in toluene.The main mechanism of OL is attributed to the nonlinear absorption and subsequently induced nonlinear scattering during excitation of the pulse.Ageing of the nanocomposite chloroform solution in air lowers the OL performances by a factor of 2.4,which can be due to the formation of aggregates of large gold particles.     

Detailed Radiative Opacity Studies of a High-Temperature Gold Plasma

The radiative opacity of a gold plasma at a temperature of 360eV and a density of 0.01 g/cm^3 has been studied using a detailed level accounting （DLA） method. Under this plasma condition, the average ionization degree is 50.2. Dominant ion types in the plasma are Au^＋49, Au^＋50 and Au^＋51, which account for 18.3%, 33.1% and 32.6%, respectively. The spectrally resolved opacity shows complex fine structures. The result obtained by the DLA method is compared with that of the average atom model. Detailed analyses are carried out to study the strongest absorption peaks caused by 3d- 4 f transitions near the photon energy of 2600 e V. To better understand the value of the Rosseland mean opacity, the radiative opacity around the energy region of the maximal Rosseland weighting function is also discussed in detail.     

Intensity-Dependent Optical Nonlinear Absorption and Refraction of Gold Nanorods

Au nanorods dispersed in aqueous solution were prepared with the electrochemical method. The absorption spectrum shows two absorption peaks corresponding to the perpendicular and transverse surface plasma resonance absorption of the nanorods. The third-order optical nonlinear properties are investigated by Z-scans. The signs of the nonlinear absorption coemcient and refractive index are reversed as the intensity of incident laser increases, which is due to the shape change of the gold nanoparticles melted by the intense laser pulses.     

Unoccupied Electron States of Ultrathin Films of Thiophene–Phenylene Cooligomers on the Surface of Polycrystalline Gold

Physics of the Solid State - Unoccupied electronic states in the energy range from 5 to 20 eV above the Fermi level have been studied in ultrathin films of dimethyl-substituted...     

Gold nanoparticle growth on self-assembled monolayers of ferrocenyl-substituted terpyridine on graphite

In this contribution we demonstrate that densely packed gold nanoparticles can be grown by Volmer–Weber mode on ferrocenyl functionalized terpyridine (FcTerp) on graphite. FcTerp forms highly ordered and dense self-assembled monolayers (SAMs) on graphite which significantly reduces the diffusion length of gold atoms and increases the sticking coefficient compared to bare graphite. Both effects lead to an increased nucleation and thus, to the growth of densely packed gold nanoparticles with diameters in the nanometer range. The optical properties of the nanoparticles as well as their morphology and the structure of the SAMs were characterized by optical extinction spectroscopy and scanning tunneling microscopy.     

A Sign Alternation of Nonlinear Absorption in Gold Composite Films in Z-Scan

Au-TiO2 composite films with Au atom content varying from about 15% to 82% are prepared by co-sputtering technique. Both open- and closed-aperture Z-scan of the samples are performed in the femtosecond time region. A conversion of the nonlinear absorption from negative to positive is observed as the A u atom content increases due to the saturation of reverse saturable absorption. The nonlinear refractive index γ and effective nonlinear absorption coefficient βeff at the Au atom content of 54% are measured to be 1.6 × 10^-2 cm^2/GW and -2.6 ×10^3 cm/GW, respectively. The corresponding third-order optical nonlinearity X^（3） is about 6.3 × 10^-8 esu.     

Preparation and Characterization of Electroactive Anion‐Exchange Acrylic Polymer–Gold Composites

The characteristics and performance of an ionic polymer–metal composite (IPMC), prepared with an anion‐exchange acrylic copolymer, was examined. The acrylic copolymer was synthesized by the radical copolymerization of fluoroalkyl methacrylate and 2‐(dimethyl amino)ethyl methacrylate(AMA). Effects of the AMA repeating unit's content in the copolymer and effects of the anion type present on the actuation of the IPMC were observed. The optimal content of 19.4 wt% AMA in the IPMC copolymer yielded the best actuation. The actuation also improved according to the type of anion present in the composite, in the following order: Br^???4 ^?.     

Self‐Assembly of Functionalized Gold Nanoparticles with Rigid and Flexible Multifunctional Linkers

The interparticle spacing of carboxyl functionalized gold nanoparticles (Au–COOH) was mediated by rigid cross‐linkers, octa(3‐aminopropyl)octasilsesquioxane (POSS–NH₃ ⁺) and poly(amidoamine) dendrimer terminated with hydroxyl groups (PAMAM–OH), and a flexible polymeric linker, poly(hexanyl viologen) (6‐VP). Regular interparticle spacing was achieved by utilizing POSS–NH₃ ⁺ and PAMAM–OH dendrimer as cross‐linkers, whereas size growth of Au–COOH was observed featuring no interparticle spacing by utilizing 6‐VP as the cross‐linker.     

Mechanism of ion-induced mixing phenomena in Gold–Nickel bilayer on Si substrate

Gold/Nickel bilayer thin films deposited on Si(100) substrates are bombarded by 100 keV ⁴⁰Ar⁺, 260 and 300 keV ⁸⁴Kr²⁺ and 400 keV ¹³²Xe³⁺ ions which deposit maximum energy across the Gold/Nickel interface and hence produce maximum atomic transport within two sides of the interface. However, due to the energy of the projectile ions some Si atoms have also gained energy, which, in turn, displaces the atoms. The atomic displacements caused by the projectile in the system has been analyzed using RBS, XRD, SEM/EDS and AFM/MFM techniques. The relative change in the variance of the intermixed region across the Au–Ni–Si interfaces excluding the irradiation-induced surface roughness has been calculated and it was observed that it increases linearly with ion fluence. The measured athermal mixing rates which vary between 3.7 and 6.9 nm⁴, have been explained by various existing phenomenological models. It shows that local or global thermal spike models are most suitable for explaining the ion beam-induced mixing of systems with strong thermochemical properties of the constituents. The mixing efficiency of this system has been calculated and found to be 1.2 nm⁵/keV.     

Radiation Heat Waves in Gold Plasma

Eight beams 0.35μm laser with pulse duration of about 1.0ns and energy of 260J per beam was injected into a cylindrical cavity to generate intense x-ray radiation on the “Shengguang Ⅱ“ high power laser facility.Gold foils with a thickness in the range of 0.09-0.52μm were attached on the diagnostic hole of the cavity and ablated by the intense x-ray radiation.The propagating radiation heat wave in the high-Z gold plasma was observed clearly.For comparison,we also simulated the experimental results.     

Gold Nanobelt Reorientation by Molecular Dynamics Simulation

The embedded atom method is used to study the structure stability of gold nanobelt. The Au nanobelts have a rectangular cross-section with （100） orientation along the x^-,γ- and z-axes. Free surfaces are used along the x- and y-directions, and periodic boundary condition is used along z-direction. The simulation is performed at different temperatures and cross-section sizes. Our results show that the structure stability of the Au nanobelts depends on the nanobelt size, initial orientation, boundary conditions and temperature. A critical temperature exists for Au nanobelts to transform from initial （100） nanobelt to final （110） nanobelt. The mechanism of the reorientation is the slip and spread of dislocation through the nanobelt under compressive stress caused by tensile surface-stress components.     

Effects of Configuration Interaction on Dielectronic Recombination of Cu-Like Gold Ion through 3d+ e →4l''l'''' Capture Process

Effects of configuration interaction on dielectronic recombination of Cu-fike gold ions through the 3d ＋ e→4l′4l″ capture process are studied in the models of isolated configurations approximation, configuration mixing within 3d^94s4l′4″, and configuration mixing within 3d^94l4l′4l″ （l≥ 0）, employing a relativistic distorted-wave approximation. Nonresonant raditive stabilizing transitions and decays to autoionizing levels followed by radiative cascades, as well as resonant stabilizing transitions from the resonant levels, are taken into account. The additional mixing with 3d^94l4l′4l″ （0 〈 l 〈 l′ 〈l″≤ 3） shifts slightly the peaks of cross section towards low energy. The rate coefficient at low temperature is dramatically changed. The rate coefficient at temperature above 100 eV is enhanced by a factor between 26% and 13%.     

Rhodamine B-Coated Gold Nanoparticles as Effective “Turn-on” Fluorescent Sensors for Detection of Zinc II Ions in Water

We designed a fluorescence resonance energy transfer system consisting of fluorophore Rhodamine B and gold nanoparticles for sensing of zinc ions in aqueous solution. The electrostatic attraction between positively charged N-atoms in Rhodamine molecules and negatively charged citrate corona of gold nanoparticles led to substantial fluorescence quenching. However, the quenching is switched off in the presence of zinc ions and therefore the system can be used as an effective “turn-on” fluorescence sensor. UV-Vis absorption, fluorescence spectroscopy, and transmission electron microscopy were used for sensor evaluation. The approach of “turn-on” fluorescence has real potential for sensing metallic ions in water.     

Complexity of Gold(Ⅲ) Ion With Cefotaxime and Cefepime Drugs: Spectroscopic,Antimicrobial and Antitumor Discussions

The availability of chemical and biological data presented in this paper is the basis for understanding not only the current state of anti-cancer drugs based on gold(Ⅲ), but also the rationale for strategies for future drug design. New Au(Ⅲ) nanosized complexes of cefotaxime(ceph-3) and cefepime(ceph-4) ligands as a 3 rd and 4 th of cephalosporin generation drugs were synthesized. Gold(Ⅲ) complexes were discussed based on the elemental, molar conductance, thermal and magnetic moment measurements as well as spectral(FTIR, ~1HNMR, UV-Vis, and XRD) techniques. FT-IR spectra revealed that the ceph-3 and ceph-4 ligands reacted as a bidentate ligands through carboxylate oxygen and β-lactam oxygen groups. The analytical analysis confirm that the molar ratio is 1∶1(Au~(3+)/ceph) with general formula [Au(L)(Cl)_2] where L=ceph-3 or ceph-4. The structures of Au(Ⅲ) complexes were presence as a square planar geometry. X-ray diffraction patterns referred to a crystalline nature for all synthesized complexes. TEM analyses confirmed that the synthetic gold(Ⅲ) complexes have a nanosized particles. In vitro antimicrobial activities of Au(Ⅲ) complexes were evaluated towards two types of bacteria(G+ G-). The antitumor activities of gold(Ⅲ) complexes are appraised against breast(MCF-7) and colorectal adenocarcinoma(Caco-2) cell lines, which means that the two complexes may consider promising anticancer drugs.     

Bimetallic Silver–Gold Film Waveguide Surface Plasmon Resonance Sensor

Abstract

It is desirable that a surface plasmon resonance (SPR) sensor is highly sensitive to binding interactions within the sensing region, generate evanescent fields with long penetration depths, and utilize a metal film that is very stable even in extreme environmental conditions. In this study, we present the first example of a wavelength-modulated waveguide SPR sensor with a bimetallic silver–gold film for surface plasmon excitation. The underlying silver yields better evanescent field enhancement of the sensing surface, while the overlying gold ensures that the stability of the metallic film is not compromised. It is shown experimentally that in terms of dλ/dn, the bimetallic film waveguide SPR configuration has a sensitivity of 1232 nm/RIU, greater than two times improvement from the 594 nm/RIU achievable with single gold film waveguide SPR sensor. The higher sensitivity, compact nature, and better evanescent field enhancement of this configuration provides the potential to biosensing applications.     

Adsorption of Bipyridine Compounds on Gold Nanoparticle Surfaces Investigated by UV‐Vis Absorbance Spectroscopy and Surface Enhanced Raman Scattering

Adsorption behaviors of 2,2′‐bipyridine (2,2′‐BiPy), 2,4′‐bipyridine (2,4′‐BiPy), and 4,4′‐bipyridine (4,4′‐BiPy) on gold nanoparticle surfaces have been comparatively investigated by means of UV‐vis absorbance spectroscopy and surface‐enhanced Raman scattering (SERS). The three bipyridine compounds are assumed to have a standing geometry on Au surfaces as indicated from several spectral features and relative vibrational intensity factors on the basis of the electromagnetic (EM) selection rule. 2,4′‐BiPy appears to adsorb on Au surfaces via the 4‐pyridyl nitrogen atom as suggested from the stronger enhancement of the vibrational bands ascribed to the 4‐pyridyl ring. The SERS intensities for the three bipyridine compounds on Au could be ascribed to both the electromagnetic (EM) and charge transfer (CT) enhancement mechanism. The charge transfer is assumed to be dissimilar for 2,2′‐BiPy, 2,4′‐BiPy, and 4,4′‐BiPy due to their different positions of the nitrogen atoms as indicated from the disparate ν_8a band enhancements upon adsorption on surfaces.