Au Nanoparticle Films Research Articles

Electrical percolation through a discontinuous Au nanoparticle film

Au thin films of thicknesses ranging from 5 to 20 nm were grown in UHV through physical vapour deposition on glass substrates decorated with Pt interdigitated electrodes with 5 μm separation. As expected, a gradual decrease in the electrical resistance of the films was observed as growth proceeded; however, when the average film thickness was greater than around 11 nm, the resistance decrease was not smooth but occurred in discrete steps. These resistance steps are attributed to the formation of electrical percolation pathways connecting the electrodes. The samples were then annealed at temperatures between 200 °C and 500 °C for periods of 1 to 22 h with the aim of producing insulating nanoparticle films. Dewetting of the Au films produces nanoparticles whose size and separation depend on annealing temperature and time, as well as the initial thickness of the Au film. The complex electrical resistance behaviour of the film was also monitored during the dewetting process.

Facile method for detecting C 23 H 25 ClN 2 in fish using Au nanoparticle films as SERS substrates on glass

Facile method for detecting C ₂₃ H ₂₅ ClN ₂ in fish using Au nanoparticle films as SERS substrates on glass

Mechanism of large optical nonlinearity in gold nanoparticle films.

The Z-scan technique, using femtosecond (fs) laser pulses at 1480nm laser pulses, was used to measure the nonlinear optical properties of gold (Au) nanoparticle (NP) films made by both nanosecond (ns) and fs pulsed laser deposition (PLD) in vacuum. At irradiance levels of 1×1012 Wm-2, the ns-PLD films displayed induced absorption with β=4×10-5 mW-1, and a negative lensing effect with n2=-4.7×10-11 m2 W-1 with somewhat smaller values for the fs-PLD films. These values of n2 imply an unphysically large change in the real part of the refractive index, demonstrating the need to take account of nonlinear changes of the Fresnel coefficients and multiple beam interference in Z-scan measurements on nanoscale films. Following this approach, the Z-scan observations were analyzed to determine the effective complex refractive index of the NP film at high irradiance. It appears that at high irradiance the NP film behaves as a metal, while at low irradiance it behaves as a low-loss dielectric. Thus, it is conjectured that, for high irradiance near the waist of the Z-scan laser beam, laser driven electron tunneling between NPs gives rise to metal-like optical behavior.

Evaluation of cigarette flavoring quality via surface-enhanced Raman spectroscopy.

Herein, surface-enhanced Raman spectroscopy (SERS) combined with principal component analysis (PCA) has been successfully applied in the evaluation of cigarette flavoring quality using monolayer films of Au nanoparticles as substrates. With such a method, even a slight difference in the formula of the essence that cannot be directly identified by SERS can be distinguished.

Tuning the interactions between chiral plasmonic films and living\xa0cells

Designing chiral materials to manipulate the biological activities of cells has been an important area not only in chemistry and material science, but also in cell biology and biomedicine. Here, we introduce monolayer plasmonic chiral Au nanoparticle (NP) films modified with l- or d-penicillamine (Pen) to be developed for cell growth, differentiation, and retrieval. The monolayer films display high chiroptical activity, with circular dichroism values of 3.5 mdeg at 550 nm and 26.8 mdeg at 775 nm. The l-Pen-NP films accelerate cell proliferation, whereas the d-Pen-NP films have the opposite effect. Remote irradiation with light is chosen to noninvasively collect the cells. The results demonstrate that left circularly polarized light improves the efficiency of cell detachment up to 91.2% for l-Pen-NP films. These findings will facilitate the development of cell culture in biomedical application and help to understand natural homochirality.

Surface-Enhanced Resonance Raman Scattering of Rhodamine 6G in Dispersions and on Films of Confeito-Like Au Nanoparticles.

Surface-enhanced resonance Raman scattering (SERRS) of rhodamine 6G was measured on confeito-like Au nanoparticles (CAuNPs). The large CAuNPs (100 nm in diameter) in aqueous dispersion systems showed stronger enhancing effect (analytical enhancement factor: over 105) of SERRS than the small CAuNPs (50 nm in diameter), while the spherical Au nanoparticles (20 nm in diameter) displayed rather weak intensities. Especially, minor bands in 1400–1600 cm−1 were uniquely enhanced by the resonance effect of CAuNPs. The enhancement factors revealed a concentration dependence of the enhancing effect at low concentration of rhodamine 6G. This dependency was due to a large capacity of hot-spots on CAuNPs, which were formed without agglomeration. The surface-enhancing behaviour in the film systems was similar to that in the dispersions, although the large CAuNPs had lower enhancing effect in the films, and the small CAuNPs and the spherical Au nanoparticles were more effective in their films. These results suggest that the CAuNPs have an advantage in ultrasensitive devices both in dispersions and films, compared to the agglomerate of spherical Au nanoparticles.

Enhanced thermal stability of boron nitride-coated Au nanoparticles for surface enhanced Raman spectroscopy

During the past decades, researchers have made great efforts towards ideal surface enhanced Raman spectroscopy (SERS) substrate, which is supposed to be reliable, sensitive and reusable. Boron nitride (BN) is electrically insulator and can sustain up to 600 °C, which makes it possible that BN acts as a barrier layer to eliminate metal-induced disturbances for SERS and provide more reliable signals of the analyte. Here, we synthesis BN via chemical vapor deposition (CVD) method, investigated its oxidation resistance and prepare BN-coated gold nanoparticles (BN/Au). Although electromagnetic enhancement decreases exponentially with distance, the SERS performance of BN/Au substrate is comparable to bare Au after being annealed at proper temperature. Moreover, Cycle tests results indicated that the introduction of BN as a coating layer could improve the stability of the SERS substrate compared to bare Au nanoparticles film. Our SERS substrate of BN/Au was obtained via CVD method, which could ensure scalable synthesis and applications.

Approach to Fabricating a Compact Gold Nanoparticle Film with the Assistance of a Surfactant.

We report a facile method to fabricate a compact Au nanoparticle film with the assistance of surfactants. First, the dodecanethiol-coated Au nanoparticles were floated on the surface of the toluene/acetonitrile solvent mixture and adjusted to an expanded dispersion by changing the mixture ratio. Silicone oil was then added as a surfactant to compress the floating nanoparticles from the original loose status to a closely packed arrangement that produced a compact nanoparticle film. The relationship of the compressed film area to the silicone oil concentration was plotted and compared to the surface tension curve of silicone oil. The results were quite consistent, suggesting that the surface location of the surfactant induced the nanoparticles' compression. The resulting nanoparticle film was uniform and sufficiently robust to be transferred to the solid substrate. Moreover, it could be applied to catalyze the reduction of 4-nitrophenol. Our study indicated that the utilization of surfactants to compress the well-dispersed nanoparticles on the liquid surface is a simple, fast, and adaptable method of fabricateing compact nanoparticle films with great promise for future applications.

Answer to comments on “Fabrication and photovoltaic conversion enhancement of graphene/n-Si Schottky barrier solar cells by electrophoretic deposition”

Here, we reply to comments by Valentic et al. on our paper published in Electrochimica Acta (2014, 130: 279). They commented that Au nanoparticles played the dominant role on the whole cell's performances in our improved graphene/Si solar cell. We argued that our devices are Au-doped graphene/n-Si Schottky barrier devices, not Au nanoparticles (film)/n-Si Schottky barrier devices. During the doping process, most of the Au nanopatricles covered the surfaces of the graphene. Schottky barriers between doped graphene and n-Si dominate the total cells properties. Through doping, by adjusting and tailoring the Fermi level of the graphene, the Fermi level of n-Si can be shifted down in the graphene/Si Schottky barrier cell. They also argued that the instability of our devices were related to variation in series resistance reduced at the beginning due to slightly lowered Fermi level and increased at the end by the self-compensation by deep in-diffusion of Au nanoparticles. But for our fabricated devices, we know that an oxide layer covered the Si surface, which makes it difficult for the Au ions to diffuse into the Si layer, due to the continuous growth of SiO layer on the Si surface which resulted in series resistance decreasing at first and increasing in the end.

A high-sensitive ultraviolet photodetector composed of double-layered TiO2 nanostructure and Au nanoparticles film based on Schottky junction

In this study, a Schottky-type ultraviolet (UV) photodetector based on double-layered nanostructured TiO2/Au films was fabricated. Double-layered titanium dioxide (TiO2) nanostructures composed of one layer of TiO2 nano-flowers on one layer of TiO2 nanorods on fluorine-doped tin oxide (FTO) pre-coated glass substrates were synthesized via a convenient hydrothermal method using titanium butoxide and hydrochloric acid as the starting precursor, without involving the use of any other surfactants and catalysts. A granular-shaped thin-layer of Au film using vacuum sputter coating technique was subsequently deposited on TiO2 for the formation of Schottky-type photodetector. The as-fabricated Schottky device showed various photocurrent responses when irradiated with different wavelength of UV light. This suggests that the newly-developed photodetectors have promising potential for identifying different UV light wavelengths.

Noble metal nanostructures for double plasmon resonance with tunable properties

We report and compare two vacuum-based strategies to produce Ag/Au materials characterized by double plasmon resonance peaks: magnetron sputtering and method based on the use of gas aggregation sources (GAS) of nanoparticles. It was observed that the double plasmon resonance peaks may be achieved by both of these methods and that the intensities of individual localized surface plasmon resonance peaks may be tuned by deposition conditions. However, in the case of sputter deposition it was necessary to introduce a separation dielectric interlayer in between individual Ag and Au nanoparticle films which was not the case of films prepared by GAS systems. The differences in the optical properties of sputter deposited bimetallic Ag/Au films and coatings consisted of individual Ag and Au nanoparticles produced by GAS is ascribed to the divers mechanisms of nanoparticles formation.

Experimental investigation of energy transfer between CdSe/ZnS quantum dots and different-sized gold nanoparticles

Hybrid nanostructures of quantum dots(QDs) and metallic nanostructure are attractive for future use in a variety of optoelectronic devices. For photodetection applications, it is important that the photoluminescence (PL) of QDs is quenched by the metallic nanostructures. Here, the quenching efficiency of CdSe/ZnS core-shell quantum dots (QDs) with different sized gold nanoparticles (NPs) films through energy transfer is investigated by measuring the PL intensity of the hybrid nanostructures. In our research, the gold NPs films are formed by the post-annealing of the deposited Au films on the quartz substrate. We find that the energy transfer from the QDs to the Au NPs strongly depends on the sizes of the Au NPs. For CdSe/ZnS QDs direct contact with the Au NPs films, the largest energy transfer efficiency are detected when the resonance absorption peak of the Au NPs is nearest to the emission peak of the CdSe/ZnS QDs. However, when there is a PMMA spacer between the QDs layer and the Au NPs films, firstly, we find that the energy transfer efficiency is weakened, and the largest energy transfer efficiency is obtained when the resonant absorption peak of the Au NPs is farthest to the emission peak wavelength of CdSe/ZnS QDs. These results will be useful for the potential design of the high efficiency QDs optoelectronic devices.

Ordered Hexagonal Nanoplasmonic Au Nanoparticle Arrays: AAO-Assisted Thermal Treatment Synthesis and Application as Surface-Enhanced Raman Scattering Substrates

We have reported on the synthesis of ordered hexagonal Au nanoparticle (NPs) arrays by anodic alumina oxide templates (AAO)-assisted thermal treatment. This simple process has led to the formation of an ordered hexagonal array of Au NPs on the surface of AAO. SERS properties of the ordered hexagonal Au NPs could be obtained by varying the size of Au NPs. Compared with the Au thin film on AAO, the SERS intensity of rhodamine adsorbed on the ordered hexagonal Au NPs was about 1000 times stronger. And the hexagonal Au NPs array films have had stronger Raman-enhanced signal compared to the disorder Au NPs films. Simulations according to the three-dimensional finite-difference time domain (3D-FDTD) have displayed that these electric field enhancements of the ordered hexagonal Au NPs are strongly dependent on the gap distance. Plasmonic ordered hexagonal Au NPs could provide us new platforms to realize novel optoelectronic devices.

Strong coupling of localized surface plasmons and ensembles of dye molecules.

We have studied strong exciton-plasmon coupling in the films of Ag nanoislands as well as in the layer-by-layer (LBL) deposited films of Au nanoparticles (NPs) coated with highly concentrated rhodamine 6G (R6G) dye. Their absorbance and the reflectance spectra featured the peaks or dips, which were not characteristic of dye or NPs/nanoislands taken separately. The positions of the spectral maxima (or minima) in the dye-doped films, plotted against those in pristine Ag nanoislands films, resulted in the dispersion curves comprised of three branches. They could be described by the analytical model based on the Hamiltonian accounting for the unperturbed energies of the surface plasmon (SP) resonance, the two bands composing the absorption spectrum of R6G dye, and the exciton-plasmon coupling energy Δ. Its value was larger in Ag nanoislands films deposited on hyperbolic metamaterials (0.221 eV) than on glass (0.165 eV). The minimal gap between the upper and the lower branches was equal to ≈3Δ. The dispersion curves in the Au NPs LBL films could be described with the Hamiltonian equation at relatively small dye concentrations. At larger concentrations of R6G molecules, the spectral peaks shifted and became more pronounced. The corresponding dispersion curve could not be described in terms of the existing model, indicating the need for further theoretical studies.

Electrolyte-gated charge transport in molecularly linked gold nanoparticle films: The transition from a Mott insulator to an exotic metal with strong electron-electron interactions.

Strong electron-electron interactions experienced by electrons as they delocalize are widely believed to play a key role in a range of remarkable phenomena such as high Tc superconductivity, colossal magnetoresistance, and others. Strongly correlated electrons are often described by the Hubbard model, which is the simplest description of a correlated system and captures important gross features of phase diagrams of strongly correlated materials. However, open challenges in this field include experimentally mapping correlated electron phenomena beyond those captured by the Hubbard model, and extending the model accordingly. Here we use electrolyte gating to study a metal-insulator transition (MIT) in a new class of strongly correlated material, namely, nanostructured materials, using 1,4-butanedithiol-linked Au nanoparticle films (NPFs) as an example. Electrolyte gating provides a means for tuning the chemical potential of the materials over a wide range, without significantly modifying film morphology. On the insulating side of the transition, we observe Efros-Shklovskii variable range hopping and a soft Coulomb gap, evidencing the importance of Coulomb barriers. On the metallic side of the transition, we observe signatures of strong disorder mediated electron-electron correlations. Gating films near MIT also reveal a zero-bias conductance peak, which we attribute to a resonance at the Fermi level predicted by the Hubbard and Anderson impurity models when electrons delocalize and experience strong Coulomb electron-electron interactions. This study shows that by enabling large changes in carrier density, electrolyte gating of Au NPFs is a powerful means for tuning through the Hubbard MIT in NPFs. By revealing the range of behaviours that strongly correlated electrons can exhibit, this platform can guide the development of an improved understanding of correlated materials.

Novel “signal-on” electrochemiluminescence biosensor for the detection of PSA based on resonance energy transfer

Here, we propose a simple and novel “signal-on” electrochemiluminescence (ECL) biosensor based on resonance energy transfer (RET) for detection of prostate specific antigen (PSA). The system is composed of Multi-walled carbon nanotubes (MWCNT), polyamidoamine (PAMAM) dendrimer and Au nanoparticles (NPs) film on glassy carbon electrode (GCE) to improve the electron transfer, provide abundant amine group for the immobilization of biomolecules, and amplify the ECL signal. After that, Au nanorods (Au NRs) labeled peptide is modified on electrode surface to serve as ECL-RET acceptor due to the excellent overlap between the ECL emission spectrum of Ru(bpy)32+ and the absorption spectrum of Au NRs, leading to the significant decrement of ECL signal. Upon the sensing cleavage of peptide with PSA, both Au NRs and peptide are released from electrode surface, resulting in the high recovery efficiency of ECL signal. The proposed approach exhibits a wide linear range from 0.1pg/mL to 10ng/mL with a detection limit of 0.03pg/mL. Results revealed that the recoveries were in a range from 95% to 108%, indicating good accuracy of the proposed method for PSA detection. In addition, the proposed biosensor exhibited well specificity for the detection of PSA.

Self-Assembled Large-Scale Monolayer of Au Nanoparticles at the Air/Water Interface Used as a SERS Substrate.

Self-assembly of metal nanoparticles has attracted considerable attention because of its unique applications in technologies such as plasmonics, surface-enhanced optics, sensors, and catalysts. However, fabrication of ordered nanoparticle structures remains a significant challenge. Thus, developing an efficient approach for the assembly of large-scale Au nanoparticles films for theoretical studies and for various applications is highly desired. In this paper, a facial approach for fabricating a monolayer film of Au nanoparticles was developed successfully. Using the surfactant polyvinylpyrrolidone (PVP), a large-scale monolayer film of well-ordered, uniform-sized Au nanoparticles was fabricated at the air/water interface. The film exhibited a two-dimensional (2D) hexagonal close-packed (HCP) structure having interparticle gaps smaller than 2 nm. These gaps generated numerous uniform "hot spots" for surface-enhanced Raman scattering (SERS) activity. The as-prepared monolayer film could be transferred to a solid substrate for use as a suitable SERS substrate with high activity, high uniformity, and high stability. The low spot-to-spot and substrate-to-substrate variations of intensity (<10%), the large surface enhancement factor (∼10(6)), and the high stability (∼45 days) make the substrate suitable for SERS measurements. Transfer of the monolayer film onto a glassy carbon electrode produced an Au electrode with clean, well-defined nanostructure suitable for electrochemical SERS measurements. The adsorption process of ionic liquids on the electrode with the monolayer film is similar to that on bulk metal electrodes. The present strategy provides an effective way for self-assembly of Au nanoparticles into well-defined nanostructures that may form optimal reproducible SERS substrates for quantitative analysis. It also provides an electrode with clean, well-defined nanostructure for electrochemical investigations.

Observation of a scrolled graphene nanoribbons with gap-plasmonic system

We report an observation of a scrolled graphene nanoribbon (sGNR) produced via a chemical vapor deposition. The sandwiched sGNR between Au nanoparticle and Au thin film system can be identified by the remarkable enhancement of G peak accompanied with a subsequent splitting (G+ and G−) with strong Radial Breading Like Mode enhancement. Because the weak adhesion force between graphene monolayer and target Au substrate during transfer maybe result in a sparse distribution of sGNR with a z-directional curvature-induced G peak splitting. Reproducibility and mass production with a nanometer scale circuit devices may be anticipated from this work.

In‐situ Synthesis of Stabilizer‐Free Gold Nanocrystals with Controllable Shape on Substrates as Highly Active Catalysts for Multiple Use

AbstractRecyclable gold nanocatalysts with controllable morphology are in‐situ formed on the solid substrate by a facile ultrasonic spray pyrolysis method. The Au nanoparticles on Mo substrates form spheres, while on Si icosahedra, or after addition of Cu ions to the precursor solution, decahedra are obtained. The catalytic properties are studied for the reduction of 4‐nitrophenol as a model reaction and compared with those of several stabilized colloidal Au catalysts. Due to the absence of any stabilizers on the surface and the good adhesion to the solid support, the substrate‐immobilized Au nanoparticles exhibit excellent catalytic activity and stability as well as simple reuse without activity loss and easy recyclability. Furthermore, it is shown that by this spray pyrolysis process also the inner walls of a tube can easily be coated. The efficiency of this resulting flow‐through reactor is investigated. Finally, naked Au nanoparticle films enable a unique comparative investigation of the catalytic reaction rate in the presence of typical ligands used for the stabilization of colloidal nanoparticle catalysts. Only with the films of naked Au nanoparticles is a constant Au base available, while different ligands lead to different sizes and probably shapes of colloidal particles thus not allowing an exact comparison. It turns out that all investigated stabilizers reduce the catalytic efficiency.magnified image

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.