Gold Nanoparticle Arrays Research Articles

In situ synthesis of directional gold nanoparticle arrays along ridge cracks of PDMS wrinkles

The synthesis of gold nanoparticles (AuNPs) on polydimethylsiloxane (PDMS) substrates is generally influenced by the condition of the exposed PDMS surfaces. AuNPs are usually synthesized on native PDMS surfaces because it is difficult to do so on PDMS surfaces that have been treated by oxygen plasma. In this study, wrinkled PDMS substrates were generated by oxygen-plasma treatment under stretching and AuNPs were selectively formed on the ridge of the PDMS wrinkles by in situ reduction with gold chloride. To investigate the mechanism of the formation of AuNPs, the prepared wrinkled PDMS substrates were observed by liquid-mode atomic force microscopy. The synthesized AuNPs on the PDMS wrinkles were characterized using scanning electron microscopy. This study provides valuable insight into the synthesis of AuNPs on wrinkled PDMS surfaces, which can be applied to biosensors and optical devices.

One-dimensional array of small tunnel junctions fabricated using 30-nm-diameter gold nanoparticles placed in a 140-nm-wide resist groove

We present percolative arrays of gold nanoparticles (NPs) formed in a resist groove. To enhance the connection probability, the width of the resist groove (140 nm) was designed to be approximately five times larger than the diameter of gold NPs (30 nm). Two-stage deposition of gold NPs was employed to form bridge connections between the source and drain electrodes. Dithiol molecules coated on surfaces of gold NPs worked as tunnel barriers. 5 of 12 samples exhibited Coulomb blockade characteristics, in one of which the gate response was confirmed.

Self-assembled quasi-hexagonal arrays of gold nanoparticles with small gaps for surface-enhanced Raman spectroscopy.

The fabrication and optical characterization of self-assembled arrangements of rough gold nanoparticles with a high area coverage and narrow gaps for surface-enhanced Raman spectroscopy (SERS) are reported. A combination of micellar nanolithography and electroless deposition (ED) enables the tuning of the spacing and size of the noble metal nanoparticles. Long-range ordered quasi-hexagonal arrays of gold nanoparticles on silicon substrates with a variation of the particle sizes from about 20 nm to 120 nm are demonstrated. By increasing the particle sizes for the homogeneously spaced particles, a large number of narrow gaps is created, which together with the rough surface of the particles induces a high density of intense hotspots. This makes the surfaces interesting for future applications in near-field-enhanced bio-analytics of molecules. SERS was demonstrated by measuring Raman spectra of 4-MBA on the gold nanoparticles. It was verified that a smaller inter-particle distance leads to an increased SERS signal.

Investigation of optical properties by localized surface plasmon excitation of nanoparticle arrays in photodetectors

We investigate absorption in the active medium by localized surface plasmon excitation of metal nanoparticle arrays. Calculations show for each specific application of the photodetector, which size of the metal nanoparticles should be deposited on photodetector. We show that the power absorption in the active medium in the presence of silver nanoparticle arrays in a certain wavelength range is more than gold nanoparticle arrays. Presence of nanoparticle arrays on surface of active medium can lead to dependence of absorption on wavelength and distance from nanoparticle arrays. Absorption cross-section in active medium strongly depends on distance from nanoparticle array that should be considered in design of embedded semiconductor quantum dots in the active medium.

Multi-band sensing characteristics of optical waveguide based on gold nanoparticles arrays

According to the optical waveguide theory, a hybrid waveguide-plasmon system consisting of gold nanoparticles arrays on top of a planar optical waveguide structure is proposed. Due to the interactions between the LSPs (Localized Surface Plasmons) and the waveguide modes, the transmission spectra generates multiple resonance peak. Based on this fact, the refractive index sensing characteristics of the array structure are analyzed. The full width at half maximum of the transmission spectra is very narrow, so the structure has excellent sensitivity and a high figure of merit.

Highly efficient production of ordered wafer-scale gold nanoparticle arrays film by simple heat treatment based on colloidal monolayer

Periodic hexagonal gold crystal spherical nanoparticle arrays with controllable size and periodicity are fabricated by physical vapor deposition and further heat treatment based on monolayer colloidal crystal template. The size and center-to-center spacing of nanoparticles (NPs) were manipulated conveniently by tuning the deposition thickness of Au film and the size of colloidal spheres of the template, respectively. The thickness range of deposited Au film dependent on the size of colloidal spheres was investigated comprehensively. Dewetting model was established and employed to analyze the whole process of the evolution from gold film to spherical nanoparticle with uniform size. Additionally, localized surface plasmon resonance (LSPR) responses of these Au nanoparticle arrays were systematically measured. It is found that the extinction properties are significantly influenced by the particle size and periodicity of arrays. With the increase of particle size, the LSPR peak shows a red shift due to the quantum size effect of the nanoscaled Au particle. Meanwhile, the diffraction peaks also show small red shift due to a slight increase of average refractive index of arrays. This is highly helpful to improve its practical applications for detecting biochemical molecules based on LSPR and diffraction peak sensing.

One-dimensional array of gold nanoparticles fabricated using biotemplate and its application to fine FET

By synthesizing AuS nanoparticles (NPs) with spherical shell protein (ferritin) and using a V-groove, a one-dimensional array of NPs was formed at the bottom of the V-groove. It has been reported that AuS NPs are converted to Au NPs by UV/ozone treatment. Floating gate memory (FGM) was fabricated by applying this one-dimensional array to V-grooved junctionless (JL) FETs, V-grooved nin-like-type FETs, and pip-like-type FETs, which are fine FETs. In JL-FETs, it is considered that conversion occurred because of good charge storage efficiency, and operation in the opposite direction to normal FGM operation was seen. In the nin-like and pip-like types devices, the same operation as in conventional FGM was shown, and the width of the memory window was about the same size as when one electron entered one NP. The one-dimensional arrangement of the metal NPs used in this study is considered to be applicable to various fields of nanotechnology.

Dynamic optical properties of gold nanoparticles/cholesteric liquid crystal arrays

Abstract

Tailoring uniform gold nanoparticle arrays and nanoporous films for next-generation optoelectronic devices

High-density arrays of gold nanodots and nanoholes on indium tin oxide (ITO)-coated glass surfaces are fabricated using a nanoporous template fabricated by the self-assembly of diblock copolymers of poly (styrene-block-methyl methacrylate) (PS-b-PMMA) structures. By balancing the interfacial interactions between the polymer blocks and the substrate using random copolymer, cylindrical block copolymer microdomains oriented perpendicular to the plane of the substrate have been obtained. Nanoporous PS films are created by selectively etching PMMA cylinders, a straightforward route to form highly ordered nanoscale porous films. Deposition of gold on the template followed by lift off and sonication leaves a highly dense array of gold nanodots. These materials can serve as templates for the vapor-liquid-solid (VLS) growth of semiconductor nanorod arrays for next generation hybrid optoelectronic applications.

Goos–Hänchen and Imbert–Fedorov shifts in a two-dimensional array of gold nanoparticles

Using an oblique linearly polarized laser beam, Goos–Hanchen (GH) and Imbert–Fedorov (IF) reflection shifts of a two-dimensional array of gold nanoparticles (NPs) on water substrate are investigated within the framework of a theoretical model. The dependences of spatial ( Δ ) and angular ( Θ ) shifts on the angle of radiation, the polarity of light, the size, and concentration of particles have been studied in detail. It is shown that a grazing p-wave light yields to the highest negative amount of GH shifts, while a 45-deg polarization that radiates at 45 deg would maximize IF shifts. The deviations are sensitive to the particle size linearly and decrease using larger NPs except in the angular out-of-plane shift ΘIF, which has a critical point where its sign and trend change. The curves of ΔGH, ΘGH, and ΘIF for various lattice constant exhibit peaks for a specific arrangement that moves toward smaller values as the particle size increases. On the other hand, ΔIF always has an additive behavior. Accurate monitoring of these parameters may serve as a precise method to determine thickness and aggregation of nanostructured films.

Guided Assembly of Two-Dimensional Arrays of Gold Nanoparticles on a Polycrystalline Gold Electrode for Electrochemical Surface-Enhanced Raman Spectroscopy

Development of a reproducible two-dimensional array of gold nanoparticles (AuNPs) through a guided assembly approach and sequentially using an electrochemical cleaning procedure to remove all cappi...

Fabrication and photosensitivity of structures based on CdS:Au nano-particles nanocomposite

In order to improve the light trapping in CdS/CdTe thin-film solar cells, the metallic nano-particles embedding can increase the photoabsorption as a result of the enhanced electric field and forward-scattering upon excitation of the surface plasmon resonance (SPR). This paper investigates how chemically deposited gold nano-particles array affects the CdS film optical properties. The surface morphology, and absorption of the CdS thin films decorated on top or inside with Au nano-particles array were studied in subsequent stages of the technological process. The SPR effect, an enhanced light absorption and photosensitivity in the visible range of spectrum for CdS:Au nano-particles nanocomposite films was shown. The spectral responsivity region for the ITO/CdS:Au NPs/Ag surface barrier structures was found to be extended to the long-wavelengths. Using Finite Element Method simulations, the plasmon resonance wavelength for fabricated Au nano-particles geometries was calculated and compared with experimental data. The results of this paper will contribute to the optimization of plasmonic CdS/CdTe solar cell and will pave the way for the development of highly efficient solar cell devices.

Ordered mesoporous Au/TiO2 nanospheres for solvent-free visible-light-driven plasmonic oxidative coupling reactions of amines

Imines are important intermediates for the synthesis of fine chemicals and pharmaceuticals. Design of a “green” oxidation catalyst to promote the direct oxidation of amines to imines by dioxygen have attracted great attention. Herein, we designed a catalyst of ordered mesoporous Au/M-TiO2 nanoparticles using a template-based approach. The as-prepared Au/M-TiO2 nanoarrays of anatase crystalline structure, with high specific surface area (222 m2/g), small pore size (∼2.1 nm) and ordered arrangements, gave dense array of ultrasmall pore-confined gold nanoparticles. The mesoporous Au/M-TiO2 exhibits particularly high visible light activity for photocatalytic selective aerobic oxidation of benzylamine to N-benzylidene benzylamine in a green approach by utilizing dioxygen as an oxidant in solvent-free conditions. The yield of N-benzylidene benzylamine can reach 1.73 mmol (TOF = 178.6 h−1, based on Au) in Au/M-TiO2 system, which is 1.5 and 1.6 times higher than that of the Au/P25 and Au/Acros anatase photocatalysts, respectively. Furthermore, we can also achieve high yield of N-benzylidene benzylamine (1.30 mmol, TOF = 134.2 h−1, based on Au) in air atmosphere. The confinement effect of the mesopores in Au/M-TiO2 facilitate the formation of O2− radicals and make the bi-molecular reaction highly preferred for promoting the high selectivity and conversion in plasmonic photocatalysis. Meanwhile, the Au/M-TiO2 with mesoporous structure can facilitate the efficient contact between the solvent and the nanomaterial, while possessing sufficient interfacial area for active oxidation reactions. This work paves a promising way to develop visible light-responsive TiO2-based photocatalysts with high specific surface area for highly efficient green oxidative organic synthesis.

Plasmonic Screening Effect of Gold Nanoparticles Array on Light Absorption in Poly(3-hexyl)Thiophene Thin Film.

The localized surface plasmon (LSP) photophysical phenomenon occurring in metal nanostructures is often presented as a way to effectively couple light into sub-wavelength-scale photovoltaic devices, which would otherwise suffer from a weak light absorption. The simultaneous complementary effect of localized optical field depletion receives far less attention. We studied a system consisting of a planar gold nanoparticles array (AuNP) deposited at the surface of a semiconducting polymer thin film (P3HT). By comparing the UV-vis spectra of P3HT with and without the AuNP array, we have estimated that the AuNPs screen the optical absorption in the interfacial layer of about 3.8 nm effective thickness due the near-field depletion effect. It suggests that the AuNP array may be used to practically "hide" a thin semiconductor layer, e.g., in order to tune the perceived color of the photovoltaic cell embedded in architecture, or in wearable devices.

Merely Measuring the UV-Visible Spectrum of Gold Nanoparticles Can Change Their Charge State.

Metallic nanostructures exhibit a strong plasmon resonance at a wavelength whose value is sensitive to the charge density in the nanostructure, its size, shape, interparticle coupling, and the dielectric properties of its surrounding medium. Here we use UV-visible transmission and reflectance spectroscopy to track the shifts of the plasmon resonance in an array of gold nanoparticles buried under metal-oxide layers of varying thickness produced using atomic layer deposition (ALD) and then coated with bulk layers of one of three metals: aluminum, silver, or gold. A significant shift in the plasmon resonance was observed and a precise value of ωp, the plasmon frequency of the gold comprising the nanoparticles, was determined by modeling the composite of gold nanoparticles and metal-oxide layer as an optically homogeneous film of core-shell particles bounded by two substrates: one of quartz and the other being one of the aforementioned metals, then using a Maxwell-Garnett effective medium expression to extract ωp for the gold nanoparticles before and after coating with the bulk metals. Under illumination, the change in the charge density of the gold nanoparticles per particle determined from the change in the values of ωp is found to be some 50-fold greater than what traditional electrostatic contact electrification models compute based on the work function difference of the two conductive materials. Moreover, when using bulk gold as the capping layer, which should have resulted in a negligible charge exchange between the gold nanoparticles and the bulk gold, a significant charge transfer from the bulk gold layer to the nanoparticles was observed as with the other metals. We explain these observations in terms of the "plasmoelectric effect", recently described by Atwater and co-workers, in which the gold nanoparticles modify their charge density to allow their resonant wavelength to match that of the incident light, thereby achieving, a lower value of the chemical potential due to the entropy increase resulting from the conversion of the plasmon's energy to heat. We conclude that even the act of registering the spectrum of nanoparticles is at times sufficient to alter their charge densities and hence their UV-visible spectra.

Dielectric waveguide-enhanced localized surface plasmon resonance refractive index sensing

We theoretically show a high-performance refractive index (RI) sensor that consists of a two-dimensional (2D) gold nanoparticle array lying on a dielectric slab waveguide. The sensor has high RI sensitivity and figure of merit (FOM), reaching 250 nm/RIU and 28, respectively. Such a high RI sensitivity and FOM result from a sharp fanolike resonance, which is caused by the interference between the localized surface plasmon resonances (LSPRs) excited on individual gold nanoparticles and the waveguide mode propagating in the adjacent dielectric slab. The interference condition is that the electric field of the waveguide mode must be parallel to the polarization direction of the LSPRs. Our work may have potential applications in ultra-compact biomedical sensing.

Improved localized surface plasmon resonance index sensitivity based on chemically-synthesized gold nanoparticles on indium tin oxide surfaces

The results of this reported work indicated that gold nanoparticle arrays self-assembled on indium tin oxide (ITO) glasses can obtain broader localized surface plasmon resonance (LSPR) wavelength range and higher sensitivity than the bare quartz. The results of surface electric field calculated using finite difference time domain showed that the electric field of nanoparticles on ITO glasses is enhanced and the repulsive forces within each particle is weakened. According to the dipolar interaction mechanism, a weakened repulsive forces within each particle lead to a lower resonance frequency and a strong redshift of the LSPR spectra.

Simple optical method to determine the scattering properties of non- deterministic array of nanoparticles in visible spectrum

A simple optical method has been designed to determine the scattering properties of non-deterministic nanoparticle array in the visible spectrum. Specifically the scattering properties of gold nanoparticles have been investigated in this paper. We have fabricated the gold nanoparticles by sputtering thin layers of gold followed by annealing. For a non-deterministic array of gold nanoparticles having diameter of 80-100 nm, the optical measurement shows that the maximum scattering occurs for a helium spectrum line of wavelength 492 nm. The experimental results agree well with the FDTD simulation results which have been carried out by importing the fabricated geometry into the simulation tool. The optical method thus provides us with simple yet novel experimental technique to directly estimate the wavelength dependent scattering properties (in the visible spectrum) of any nanoparticle array irrespective of the material, its shape, size, coverage as well as the distribution pattern. This would help us to tune the fabrication process for maximizing the scattering efficiency of any suitable nanoparticle array at a particular wavelength.

Effects of particle size and annealing on plasmon-induced charge separation at self-assembled gold nanoparticle arrays.

Two-dimensional periodic Au nanoparticle arrays were constructed on TiO2 thin films by a micelle lithography method and seed-mediated photoelectrochemical growth. Their adjustable interparticle distance allows investigation of a particle size effect on plasmon-induced charge separation (PICS) efficiencies without interference from particle aggregation or plasmon coupling. External or internal PICS efficiencies were found to increase and decrease, respectively, with an increase in particle diameter from 25 to 38 nm. Improvement of the contact between Au nanoparticles and TiO2 by annealing enhanced the intensity of a plasmonic interface mode and both external and internal PICS efficiencies.

Surface-enhanced Raman scattering active gold nanoparticle/nanohole arrays fabricated through electron beam lithography

Effective surface-enhanced Raman scattering (SERS)-active substrates from gold nanoparticle and gold nanohole arrays were successfully fabricated through electron beam lithography with precise computer-aided control of the unit size and intergap distance. Their SERS performance was evaluated using 4-mercaptobenzoic acid (4-MBA). These gold arrays yielded strong SERS signals under 785 nm laser excitation. The enhancement factors for 4-MBA molecules on the prepared gold nanoparticle and nanohole arrays maxed at 1.08 × 107 and 8.61 × 106, respectively. The observed increase in SERS enhancement was attributed to the localized surface plasmon resonance (LSPR) wavelength shifting toward the near-infrared regime when the gold nanohole diameter increased, in agreement with the theoretical prediction in this study. The contribution of LSPR to the Raman enhancement from nanohole arrays deposited on fluorine-doped tin oxide glass was elucidated by comparing SERS and transmission spectra. This simple fabrication procedure, which entails employing electron beam lithography and the controllability of the intergap distance, suggests highly promising uses of nanohole arrays as functional components in sensing and photonic devices.