Au Nanoparticle Films Research Articles

Irradiation Wavelength-Dependent Photocurrent Sensing Characteristics of AuNPs/P3HT Composites on Volatile Vapor

Gas sensing characteristics of Au nanoparticles (AuNPs)/3-hexylthiophene-2, 5-diyl (P3HT) composite based on photocurrent detection under different irradiation wavelengths were investigated. AuNPs with different structures were prepared either by the vacuum sputtering/annealing method or by the wet chemical synthesis based on seed growth. AuNPs/P3HT composites were prepared by the dip coating method. The optical features of P3HT and Au nanostructure/P3HT composite were investigated. The optical absorption increase of AuNPs film was observed after P3HT coating, which was attributed to the interaction between the P3HT and the Au nano-islands. New shoulder peaks and the phenomenon of one spectral peak splitting into two were observed in the absorption spectra of the composite film, which confirmed the interaction between the AuNPs and the P3HT further. The photoconductivity characteristics of the P3HT and AuNPs with spectral peak position at 580-nm (AuNPs580)/P3HT composite films were investigated utilizing LED light source with different dominate wavelengths. The wavelength-dependent photocurrent change ratio I/I0 of both the P3HT and the AuNPs580/P3HT composite films was observed. The maximum I/I0 of the P3HT and AuNPs580 composite films emerged under LED irradiation with a dominate wavelength 590 nm, which was mainly ascribed to the antenna effect from the Au nano-islands, the carrier injection from nanostucture to P3HT, localized surface plasmon resonance coupling among Au nanostructures, and plasmon coupling between the Au nano-islands and the P3HT molecules. The response of Au nano-island/P3HT composite to ethanol vapor showed that the response and recovery time was shorter than 2 s. Furthermore, gas sensing characteristics were verified to be irradiation wavelength dependent. Irradiation light source with a dominate wavelength 590 nm produced the largest I/I0 1.07.

Growth of thiol-coated Au-nanoparticle Langmuir monolayers through a 2D-network of disk-like islands

Formation of 2D-networked structures of disk-like islands for ultrathin Langmuir–Schaefer (LS) films of thiol-coated Au-nanoparticles (DT-AuNPs) on H-passivated Si substrates is evidenced for the first time, by X-ray scattering data and AFM images.

Charge transfer process at the Ag/MPH/TiO2 interface by SERS: alignment of the Fermi level.

A nanoscale metal-molecule-semiconductor assembly (Ag/4-mercaptophenol/TiO2) has been fabricated over Au nanoparticle (NP) films as a model to study the interfacial charge transfer (CT) effects involved in Ag/MPH/TiO2. Due to the interaction between Au NPs and Ag NPs, some distinct differences occur in the SERS spectra. We also measured the SERS of Ag/MPH (4-mercaptophenol), Ag/MPH/TiO2, and Au/Ag/MPH/TiO2 assemblies at excitation wavelengths of 477, 514, 532, 633, and 785 nm. We found that the changes in the CT process, caused by the introduction of TiO2 and Au, can be reflected in SERS. Then in combination with other detection methods, we proposed a possible CT process involved in the Ag/MPH, Ag/MPH/TiO2, and Au/Ag/MPH/TiO2 assemblies. A Pt/Ag/MPH/TiO2 assembly was also constructed to verify our proposed CT mechanism. This work not only provides more details about CT between metal-molecule-semiconductor interfaces but also aids in constructing nanoscale models to study interfacial problems with the SERS technique.

Preparation and characterization of nanostructured thin films of Au and Ag nanoparticles synthesized by ascorbic acid on modified glass surface

Preparation and characterization of nanostructured thin films of Au and Ag nanoparticles synthesized by ascorbic acid on modified glass surface

Fabrication of periodical Ag-Au compound nanostructure films with controllable Ag nanoparticle aggregate patterns: a study on surface-enhanced Raman scattering

The Ag–Au compound nanostructure films with controllable patterns of Ag nanoparticle (NP) aggregates were fabricated. A strategy of two‐step synthesis was employed toward the target products. Firstly, the precursor Au NP (17 nm) films were synthesized as templates. Secondly, the Ag NPs (45 nm) were deposited on the precursor films. Three types of Ag NP aggregates were obtained including discrete Ag NPs (discrete type), necklace‐like Ag NP aggregates (necklace type), and huddle‐like Ag NP aggregates (huddle type). The surface‐enhanced Raman scattering (SERS) property was studied on these nanostructures by using the probing molecule of rhodamine 6G under the excitation laser of 514.5 nm. Interestingly, the different types of samples showed different enhancement abilities. A statistical method was employed to assess the enhancement. The relative enhancement factor for each Ag NP was estimated quantitatively under the ratio of 1 : 25 : 18 for the discrete‐type, necklace‐type, and huddle‐type samples at the given concentration of 10−8 mol/l. This research shows that the enhancement ability of each Ag NP is dependent on the aggregate morphology. Moreover, the different enhancement abilities displayed different limit detection concentrations up to 10−8, 10−11, and 10−9 mol/l, separately. The understanding of the relationship between the defined nanostructures and the SERS enhancement is very meaningful for the design of new SERS substrates with better performance. Copyright © 2015 John Wiley & Sons, Ltd.

Pulsed Electrodeposition of Gold Nanoparticles on Fluorine-Doped Tin Oxide Glass and Absorption-Based Surface Plasmon Resonance Evaluation

Synthesis and immobilization of Au nanoparticles (AuNPs) was performed on transparent fluorine-doped tin oxide (FTO) substrate by pulse electrodeposition method. The method was cost effective, simple and capable of producing nanoparticles strongly attached to the substrate. Effects of several influencing factors such as duty cycle, pulse frequency, current density, solution concentration, deposition period and annealing procedure on the optical properties of AuNPs-FTO electrode were investigated. AuNPs-FTO electrodes were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and UV-Vis absorption analysis. Controllability of the plasmon absorption of the electrodeposited film by tuning of the electrodeposition conditions and thermal annealing procedure was important achievements helpful to the progress of the AuNP film applications in the tunable localized surface plasmon resonance spectroscopy (LSPR) manufacturing industry.

Inhibiting plasmon catalyzed conversion of para-nitrothiophenol on monolayer film of Au nanoparticles probed by surface enhanced Raman spectroscopy

The plasmon catalyzed surface reaction has been attracted considerable attention due to its promising application in heterogeneous catalysis. This kind of plasmon catalysis played bilateral roles in driving the unconventional reactions or destructing the surface molecule layer. The acceleration or inhibition on this catalysis is still remained significant challenge. In this paper, monolayer film of Au nanoparticles was fabricated at air/water interface as substrates both for surface enhanced Raman spectroscopy (SERS) and plasmon catalyzed surface reaction. The influence from several issues, involving surfactants, coadsorption species, the solvent and water, were systemically investigated to probe the acceleration and inhibition on the plasmon catalysis reaction. The concentration and molecular weight of surfactant polyvinylpyrrolidone (PVP) exhibited significant influence in the reactive activity for the plasmon catalyzed dimerization of para-nitrothiophenol (PNTP) to p,p′-dimercaptoazobenzene (DMAB). A suitable molecular weight of 10,000 and concentration of 10mg/mL were beneficial for improving the conversion efficiency of PNTP to DMAB. The higher molar ratio of coadsorbed 1-octanethiol and the aprotic solvents resulted in the inhibition of dimerization because 1-octanethiol occupied the surface sites to isolate the adsorbed PNTP molecules with a larger distance and lack of proton source. The plasmon catalysis occurred in ionic liquids suggested that water was essential for the dimerization of PNTP, in which it was used to accelerate the reaction rate and severed as the hydrogen source.

Real-Time Monitoring Distance Changes in Surfactant-Coated Au Nanoparticle Films upon Volatile Organic Compounds (VOCs)

We explore into the role of the organic ligands composition surrounding Au nanoparticles (NPs) toward internanoparticles distance changes and film structure during vapor sensing by the use of in situ grazing-incidence small-angle X-ray scattering (GISAXS) and other relevant techniques. We observed distinct changes in core-to-core distance and film structure upon measured concentrations of polar ethanol (EtOH) and nonpolar toluene (Tol) vapors. As-formed tetraoctylammonium bromide (TOABr)-coated Au NPs (SNPs) film exhibited ∼0.4 nm core-to-core increase in distance and improved SNPs correlation upon 80% Tol. In the presence of EtOH, SNPs distance seems not to change and correlation critically diminishes, leading to an amorphous film. As-formed films were exchanged with nonanedithiol (NDT) and exposed to 100% Tol vapor. Interestingly, the incorporation of NDT increased distance between NPs and rendered film flexibility. It is determine that just a small number of S, from NDT ligands, binds to Au NPs, and those exchanged alkanedithiol chains adopted a loop conformation around the Au NPs as evidenced by X-ray absorption near-edge structure (XANES) and kink defects by Fourier transformed infrared (FT-IR) experiments, respectively. These findings may solve some fundamental questions about internanoparticle distance-dependent phenomena such as electron transport in chemiresistors and coupling effects in localized surface plasmon resonance (LSPR) solid-state sensors.

Novel Fabrication of Au Nanoparticle Film on a Polyelectrolyte‐coated Glass for Efficient Surface‐enhanced Raman Scattering#

In this paper, we report a novel method for the growth of gold nanoparticles on a polyelectrolyte‐coated glass and its application as a surface‐enhanced Raman scattering (SERS) substrate. Gold nanoparticles were readily grown on a polyelectrolyte‐coated substrate using butylamine as the reductant of HAuCl4 . The Au nanoparticles formed on the polyelectrolyte‐coated substrate exhibited superior SERS activity compared to an electrochemically roughened Au substrate or a vacuum‐evaporated Au film. In addition, our Au substrate shows excellent reproducibility and noticeable stability as an SERS substrate. The proposed strategy is simple, cost effective, and reproducible for the mass production of gold nanoparticles films, irrespective of the type of the underlying substrates, which therefore are useful in the development of plasmonics and SERS‐based analytical devices.

Design of TiO2/Au nanoparticle films with controlled crack formation and different architectures using a centrifugal strategy

Centrifugal strategy is demonstrated to enable the design of hybrid nanocomposite films with controllable architecture, porosity, crack density and thickness.

Adsorption and conformation variation of BSA protein with the size variation of the metallic nanoparticles in LB film

Abstract Adsorption and conformation variation of globular protein bovine serum albumin (BSA) on the surfaces of different sized gold nanoparticle Langmuir–Blodgett (LB) films have been studied by using atomic force microscopy, UV–vis and FTIR spectroscopy. Films of Au nanoparticles of different sizes were prepared on the quartz substrates by the LB method. Our study reveals that the protein adsorption increases on the nanoparticle covered quartz surfaces with the increase of the nanoparticle size. Moreover, modifications in the secondary conformations of the adsorbed protein occur on the surfaces of the nanoparticles in comparison with the bare quartz surface. Interparticle gap area and gap volume dependent protein adsorption and conformation variation have been proposed.

Enzymatic glucose sensor based on Au nanoparticle and plant-like ZnO film modified electrode.

A novel electrochemical glucose sensor was developed by employing a composite film of plant-like Zinc oxide (ZnO) and chitosan stabilized spherical gold nanoparticles (AuNPs) on which Glucose oxidaze (GOx) was immobilized. The ZnO was deposited on an indium tin oxide (ITO) coated glass and the AuNPs of average diameter of 23 nm were loaded on ZnO as the second layer. The prepared ITO/ZnO/AuNPs/GOx bioelectrode exhibited a low value of Michaelis-Menten constant of 1.70 mM indicating a good bio-matrix for GOx. The studies of electrochemical properties of the electrode using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed that, the presence of AuNPs provides significant enhancement of the electron transfer rate during redox reactions. The linear sweep voltammetry (LSV) shows that the ITO/ZnO/AuNPs/GOx based sensor has a high sensitivity of 3.12 μA·mM(-1)·cm(-2) in the range of 50 mg/dL to 400 mg/dL glucose concentration. The results show promising application of the gold nanoparticle modified plant-like ZnO composite bioelectrode for electrochemical sensing of glucose.

Two-dimensional colloidal crystal assisted formation of conductive porous gold films with flexible structural controllability

Two-dimensional (2D) colloidal crystals of polystyrene (PS) particles were used as a structure-controlling template to fabricate conductive Au films with an ordered array of nanoholes. The fabrication mainly involved the functionalization of the supporting substrate with polyelectrolyte (PE) functional layers, self-assembly of Au nanoparticles, and electroless deposition of gold. The self-assembly of Au nanoparticles and electroless deposition of gold were macroscopically monitored using ultraviolet–visible (UV–vis) spectroscopy based on the changes in both the extinction spectra of Au nanoparticles and the optical responses of ordered arrays of PS particles. By scanning electron microscopy (SEM) characterization, it was found that Au nanoparticles were assembled into a film structure with orderly dispersed nanoholes and the deposition of gold was confined to the preformed Au nanoparticle films. During the formation of Au films, PE layer structure, Au nanoparticle size and heating treatment applied to the PS template could influence the structures of conductive porous Au films such as the hole diameter, film thickness, and hole diameter/wall thickness ratio (D/W). In addition, this paper also described electrochemical cyclic voltammetry (CV) employed to demonstrate the porosity of the ultimate Au films.

Transient competition between photocatalysis and carrier recombination in TiO2 nanotube film loaded with Au nanoparticles

Highly ordered TiO2 nanotube array (TNA) films are fabricated by using an anodic oxidation method. Au nanoparticles (NPs) films are decorated onto the top of TNA films with the aid of ion-sputtering and thermal annealing. An enhanced photocatalytic activity under ultraviolet C (UVC, 266 nm) light irradiation is obtained compared with that of the pristine TNA, which is shown by the steady-state photoluminescence (PL) spectra. Furthermore, a distinct blue shift in the nanosecond time-resolved transient photoluminescence (NTRT-PL) spectra is observed. Such a phenomenon could be well explained by considering the competition between the surface photocatalytic process and the recombination of the photo-generated carriers. The enhanced UV photocatalytic activities of the Au—TNA composite are evaluated through photo-degradation of methyl orange (MO) in an aqueous solution with ultraviolet—visible absorption spectrometry. Our current work may provide a simple strategy to synthesize defect-related composite photocatalytic devices.

Particle lithography-based patterning of polyelectrolyte template films and their application in fabrication of gold/silver nanoparticle assembly

The site-specific deposition of polyelectrolytes (PEs) or PE/noble metallic nanoparticle (NP) composites at nanoscale is highly desirable owing to their diverse applications in nanodevices. Herein, we demonstrated a simple yet effective method to fabricate different types of surface micropatterns with PE/noble metallic NP composites via particle lithography. The positively charged PE of poly(diallyldimethylammonium chloride) and negatively charged NPs of gold/silver (Au/Ag) were used as a model system. The layer-by-layer self-assembly technique was employed as the fabricating strategy. The final nanostructures, consisting of Au NP films with inlaid circular vacant island microarrays or Au NP films with inlaid circular Ag NP island microarrays, were fabricated, respectively. Scanning electron microscopy and atomic force microscopy were used to investigate the structural morphology, microstructure, and the NP growth. Furthermore, the surface-enhanced Raman scattering performance has been obtained based on the as-prepared Au/Ag nanopatterns. Our method displayed an excellent opportunity for the simple and effective production of nanopatterns on the surfaces demonstrating significant advantages in designing novel nanodevices.

Scale effects of nanomechanical properties and deformation behavior of Au nanoparticle and thin film using depth sensing nanoindentation.

Nanoscale research of bulk solid surfaces, thin films and micro- and nano-objects has shown that mechanical properties are enhanced at smaller scales. Experimental studies that directly compare local with global deformation are lacking. In this research, spherical Au nanoparticles, 500 nm in diameter and 100 nm thick Au films were selected. Nanoindentation (local deformation) and compression tests (global deformation) were performed with a nanoindenter using a sharp Berkovich tip and a flat punch, respectively. Data from nanoindentation studies were compared with bulk to study scale effects. Nanoscale hardness of the film was found to be higher than the nanoparticles with both being higher than bulk. Both nanoparticles and film showed increasing hardness for decreasing penetration depth. For the film, creep and strain rate effects were observed. In comparison of nanoindentation and compression tests, more pop-ins during loading were observed during the nanoindentation of nanoparticles. Repeated compression tests of nanoparticles were performed that showed a strain hardening effect and increased pop-ins during subsequent loads.

Growth of Au nanoparticle films and the effect of nanoparticle shape on plasmon peak wavelength

Metal nanoparticles (NPs) exhibit localized surface plasmon resonance (LSPR) and thus have potential for use in a wide range of applications. A facile technique for the preparation of NP films using an electron-cyclotron-resonance plasma sputtering method without a dewetting process is described. Field emission scanning electron microscopy (FE-SEM) observations revealed that the Au NPs grew independently as island-like particles during the first stage of sputtering and then coalesced with one another as sputtering time increased to ultimately form a continuous film. A plasmon absorption peak was observed via optical measurement of absorption efficiency. The LSPR peak shifted toward longer wavelengths (red shift) with an increase in sputtering time. The cause of this plasmon peak shift was theoretically investigated using the finite-difference time-domain calculation method. A realistic statistical distribution of the particle shapes based on FE-SEM observations was applied for the analysis, which has not been previously reported. It was determined that the change in the shape of the NPs from spheroidal to oval or slender due to coalescence with neighbouring NPs caused the LSPR peak shift. These results may enable the design of LSPR devices by controlling the characteristics of the nanoparticles, such as their size, shape, number density, and coverage.

Fe3+ to Fe2+ Conversion by Plasmonically Generated Hot Electrons from Ag Nanoparticles: Surface-Enhanced Raman Scattering Evidence

We have demonstrated using surface-enhanced Raman scattering (SERS) of cyanide that “hot” electrons can be plasmonically generated from nanostructured Ag and/or Au substrates. For this, we first fabricated poly(ethylenimine) (PEI)-capped Ag and Au nanoparticle films onto glass slides. Cyanide was then adsorbed (via the carbon lone-pair electrons) onto the films to obtain the NC/Ag and NC/Au systems. Subsequently, Fe3+ or Fe2+ ions were bound to the pendant nitrogen atoms to obtain the corresponding Fe3+/NC/Ag and Fe3+/NC/Au systems or the Fe2+/NC/Ag and Fe2+/NC/Au systems. All these systems were stable under laser light illumination at 632.8 nm, with CN stretching bands at 2159 and 2143 cm–1 for the Fe3+/NC/Ag and Fe2+/NC/Ag systems, respectively, and at 2180 and 2158 cm–1 for the Fe3+/NC/Au and Fe2+/NC/Au systems, respectively. Under the laser light illumination at 514.5 nm, the Fe3+/NC/Ag system was gradually converted to the Fe2+/NC/Ag system, with the CN stretching band shifting from 2159 to 2143 cm–1...

Distance-dependent fluorescence of tris(bipyridine)ruthenium(II) on supported plasmonic gold nanoparticle ensembles.

Metal surfaces and nanostructures interact with fluorescent materials, enhancing or quenching the fluorescence intensity, modifying the fluorescent lifetime, and changing the emission frequency and linewidth. These interactions occur via several mechanisms, including radiationless energy transfer, electric field enhancement, and photonic mode density modification. The interactions display a strong dependence on the distance between the fluorophore and the metal structures. Here we study the distance-dependent effects of two types of plasmonic gold nano-island films on the emission intensity, wavelength, linewidth and lifetime of a fluorophore layer, separated from the film by a dielectric spacer 2-348 nm thick. The distance dependence is found to be unrelated to the plasmonic field decay lengths. In some cases fluorescence intensity enhancement is seen even at 200 nm metal-fluorophore separation, indicating far-field effects. We report, for the first time, a distance-dependent oscillation in the emission peak wavelength and linewidth, attributed to interference-based oscillations in the intensity of the electric field. We find that the studied nanoparticle (NP) films do not display the previously reported distance profile of single NPs, but rather behave in a collective fashion similar to continuous metal surfaces.

Synchrotron X-ray Studies of Rapidly Evolving Morphology of Self-Assembled Nanoparticle Films under Lateral Compression

Interfacial nanostructures represent a class of systems that are highly relevant to studies of quasi-2D phases, chemical self-assembly, surfactant behavior, and biologically relevant membranes. Previous studies have shown that under lateral compression a Langmuir film of gold (Au) nanoparticles assembled at the liquid-air interface exhibits rich mechanical behavior: it undergoes a rapid structural and morphological evolution from a monolayer to a trilayer via an intermediate hash-like phase. We report the results of studying this structural evolution using grazing incidence X-ray off-specular scattering (GIXOS). We utilize GIXOS to obtain a quantitative mapping of electron density profile normal to the liquid surface with a subnanometer resolution and follow the structural evolution of the Au nanoparticle film under lateral compression with a subminute temporal resolution. As the surface pressure is increased, the self-assembled nanoparticle monolayer first crinkles into a double-layer phase before forming a trilayer. This study reveals the existence of a transient bilayer phase and provides a microscopic picture of the particle-level crinkling phenomena of ultrathin films. These studies were previously impossible due to the relatively short time scales involved in crinkling formation of these transient phases and their intrinsically inhomogeneous nature.