Embedded Au Nanoparticles Research Articles

Schottky barrier height engineering of Al contacts on Si by embedded Au nanoparticles

Embedding metal nanoparticles (NPs) into metal contacts at metal–Si (MS) interface is an alternative method for modification of Schottky barrier height (SBH) and compared with traditional methods that might result in an undesired alteration of the MS interface, offers a tremendous simplification and adaptation in processing steps. There is a direct link between the type, size and density of NPs and their interaction with contact/semiconductor and the improved electrical characteristics. A comprehensive analysis of the NPs effect at MS interface is required to make appropriate and efficient selection of contact/NPs combination as well as deposition of NPs and fabrication of nanostructured contact. In this work, multiple successive deposition of colloidal Au NPs by spin-coating is used as an alternative and simple method to deposit Au NPs on n- and p-Si substrates. Electrical parameters of Au NPs/Al nanostructured contacts including SBH and ideality factor are in turn extracted from current–voltage characteristics. Two models of inhomogeneity in SBH and enhanced tunneling at triple interface are then invoked for further analysis of the NPs effect on electrical properties of contacts. The best model proposed to describe this phenomenology is the enhanced tunneling at triple interface.

Electrical behavior of amorphous indium–gallium–zinc oxide thin film transistors by embedding Au nanoparticles in the channel layer

We reported the effects on the electrical behavior of amorphous indium–gallium–zinc oxide (a-IGZO) thin film transistors (TFTs) after introducing various positions and sizes of Au nanoparticles (NPs) in the channel layer. These TFTs showed an off-current increase and threshold voltage (Vth) shift compared to conventional a-IGZO TFTs. The effects of Au NPs are explained to form the carrier conduction path which causes the current leakage in the channel layer, and act as either electron injection sites or trap sites. Therefore, this study demonstrates that the optimized control of size and position of Au NPs in the channel layer is crucial for its application in the electrical stability improvement and Vth control of a-IGZO TFTs.

High-efficiency inverted polymer solar cells via dual effects of introducing the high boiling point solvent and the high conductive PEDOT:PSS layer

Polymer solar cells (PSCs) are of great interest in the past decade owing to their potentially low-cost in the manufacturing by the solution-based roll to roll method. In this paper, a novel inverted device structure was introduced by inserting a high conductive PEDOT:PSS (hcPEDOT:PSS) layer between the Au nanoparticles (NPs)-embedded hole transport layer (PEDOT:PSS) and the top electrode layer. Power conversion efficiency (PCE) initially reached up to 4.51%, illustrating ∼10% higher compared with the device similarly enhanced by Au NPs plasmonics where only one PEDOT:PSS layer with the embedded Au NPs was used in single bulk heterojunction inverted PSCs based on the poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methylester (P3HT:PCBM). The PCE was further improved from 4.51% to 5.01% by adding the high-boiling point solvent of 1,8-diiodooctane (DD) into the active layer, presenting ∼20% enhancement in PCE through dual effects of introducing the high boiling point solvent and the high conductive PEDOT:PSS layer. Morphologies of the active layers were characterised by SEM and AFM separately in the paper.

Electron emission of Au nanoparticles embedded in ZnO for highly conductive oxide

We investigated the effect of embedded Au nanoparticles (Au NPs) on electrical properties of zinc oxide (ZnO) for highly conductive oxide semiconductor. Au NPs in ZnO films influenced both the structural and electrical properties of the mixture films. The electrical resistivity decreases by as much as five orders of magnitude. This is explained by the electron emission from Au NPs to the ZnO matrix. Temperature-dependent Hall effect measurements show that an electron emission mechanism changes from tunneling to thermionic emission at T = 180 K. The electron mobility in the mixture film is mainly limited by the grain boundaries at lower temperature (80-180 K), and the Au/ZnO heterogeneous interface at higher temperature (180-340 K). In addition to the electron emission, embedded Au NPs alter the ZnO matrix microstructure and improve the electron mobility. Compared to the undoped ZnO film, the carrier concentration of the Au NP-embedded ZnO film can be increased by as much as six orders of magnitude with a small change in the carrier mobility. This result suggests a way to circumvent the inherent tradeoff between the carrier concentration and the carrier mobility in transparent conductive oxide (TCO) materials.

Controlled shape modification of embedded Au nanoparticles by 3 MeV Au2+-ion irradiation

Shape modification of embedded Au nanoparticles by 3 MeV Au2+-ion irradiation has been studied by cross-sectional transmission electron microscopy (XTEM). The ion irradiation on spherical Au nanoparticles shallowly-embedded in SiO2 caused a well-controlled transformation of shape to ellipsoidal. Satellite nanoparticles of smaller sizes were found to nucleate around the ellipsoids. Rapid growth of the ellipsoidal nanoparticles was observed as the applied fluence increased from 3 × 1015 to 7 × 1015 ions cm−2. The XTEM study also revealed the crystallinity of the ellipsoids formed by MeV ion irradiation. Reduction in the surface plasmon resonance (SPR) peak intensity in the optical absorption spectrum indicates partial dissolution of the spherical nanoparticles by ion irradiation. We have thus obtained a unique near-surface structure of ellipsoidal nanoparticles. The results are discussed in terms of effects of ion energy deposition and inverse Ostwald ripening.

Controllable Localized Surface Plasmonic Resonance Phenomena in Reduced Gold Oxide Films

In this study, we used reactive sputtering to prepare large-area, homogeneous gold oxide (AuOx) films, which we then subjected to reduction processes under ambient conditions at room temperature to obtain reduced AuOx films featuring embedded Au nanoparticles (NPs). We analyzed these films in terms of both their material characteristics and optical properties. For the first time, we obtained the optical constants of AuOx films directly deposited on glass and Si substrates. Moreover, we observed localized surface plasmon resonance (LSPR) phenomena from the visible to the near-infrared (NIR) during the formation of the Au NPs in the AuOx film. The plasmonic properties of the Au NPs embedded in the AuOx films were much different from those of chemically synthesized Au NPs. We found that the LSPR wavelength of the Au NPs embedded in the AuOx films could be tuned from 700 to 980 nm by varying the duration of the reduction process. Moreover, the reduced AuOx films could be applied as surface-enhanced Raman spectroscopy (SERS)-active substrates. The minimum detection was achieved down to a concentration of 10–10 M (R6G) when using the reduced AuOx film-based substrate–a level comparable with those of other kinds of SERS substrates prepared using more complicated methods. The rapid method proposed herein provides large-areas films with tunable resonance wavelengths for applications as SERS-active substrates in optical and chemical sensing.

Synthesis of embedded Au nanostructures by ion irradiation: influence of ion induced viscous flow and sputtering

The ion-irradiation induced synthesis of embedded Au nanoparticles (NPs) into glass from islands of Au on a glass substrate is studied in the context of recoiling atoms, sputtering and viscous flow. Cross sectional transmission electron microscopy studies revealed the formation of Au NPs embedded in the glass substrates by the 50 keV Si− ion irradiation of irregularly shaped Au nanostructures on the glass surfaces at a fluence of 3 × 1016 ions/cm2. The depth profiles of Au in the samples were obtained from high-resolution Rutherford backscattering spectrometry studies. The results from TRIDYN simulation reveal the role of various ion-induced processes during the synthesis of the embedded Au NPs, viz. sputtering and recoiling atoms. Simulation and experimental results suggest that the viscous flow is one of the major factors that are responsible for the embedding of Au nanoparticles into the glass substrate.

Three-Phase Co-assembly: In Situ Incorporation of Nanoparticles into Tunable, Highly Ordered, Porous Silica Films

We present a reproducible, one-pot colloidal co-assembly approach that results in large-scale, highly ordered porous silica films with embedded, uniformly distributed, accessible gold nanoparticles. The unique coloration of these inverse opal films combines iridescence with plasmonic effects. The coupled optical properties are easily tunable either by changing the concentration of added nanoparticles to the solution before assembly or by localized growth of the embedded Au nanoparticles upon exposure to tetrachloroauric acid solution, after colloidal template removal. The presence of the selectively absorbing particles furthermore enhances the hue and saturation of the inverse opals’ color by suppressing incoherent diffuse scattering. The composition and optical properties of these films are demonstrated to be locally tunable using selective functionalization of the doped opals.

Gold nanoparticles deposited on linker-free silicon substrate and embedded in aluminum Schottky contact

Given the enormous importance of Au nanoparticles (NPs) deposition on Si substrates as the precursor for various applications, we present an alternative approach to deposit Au NPs on linker-free n- and p-type Si substrates. It is demonstrated that, all conditions being similar, there is a significant difference between densities of the deposited NPs on both substrates. The Zeta-potential and polarity of charges surrounding the hydroxylamine reduced seeded growth Au NPs, are determined by a Zetasizer. To investigate the surface properties of Si substrates, contact angle measurement is performed. Field-emission scanning electron microscope is then utilized to distinguish the NPs density on the substrates. Finally, Al/Si Schottky barrier diodes with embedded Au NPs are fabricated, and their structural and electrical characteristics are further evaluated using an energy-filtered transmission electron microscope and current–voltage measurements, respectively. The results reveal that the density of NPs is significantly higher on n-type Si substrate and consequently has more pronounced effects on the electrical characteristics of the diode. It is concluded that protonation of Si–OH group on Si surface in low pH is responsible for the immobilization of Au NPs, which eventually contributes to the lowering of barrier height and enhances the electrical characteristics.

Smart Photothermal-Triggered Bilayer Phase Transition in AuNPs–Liposomes to Release Drug

Novel thermosensitive liposomes with embedded Au nanoparticles (AuNPs) in the liposome bilayer were prepared by a combination method of film build and supercritical CO(2) incubation. These AuNPs-liposomes possess AuNPs that are embedded in the bilayer and a drug that is encapsulated in the central aqueous compartment. The AuNPs in the liposomes can strongly absorb light energy and efficiently convert the absorbed energy to heat. The localized heat induces a phase transition in the liposome bilayer and releases the drug. The drug release from the AuNPs-liposomes can be controlled by the irradiation time and AuNPs concentration in the AuNPs-liposomes at room temperature, where the AuNPs function as a nanoswitch for triggering drug release both spatially and temporally. The results suggest that drug release from the AuNPs-liposomes is due to a photothermic effect that induces phase transition of the liposomes rather than destruction of the liposome bilayer.

Au-TiO2Nanocomposites and Efficient Photocatalytic Hydrogen Production under UV-Visible and Visible Light Illuminations: A Comparison of Different Crystalline Forms of TiO2

nanocomposites were prepared by the solvated metal atom dispersion (SMAD) method, and the as-prepared samples were characterized by diffuse reflectance UV-visible spectroscopy, powder XRD, BET surface analysis measurements, and transmission electron microscopy bright field imaging. The particle size of the embedded Au nanoparticles ranged from 1 to 10 nm. These Au/TiO2 nanocomposites were used for photocatalytic hydrogen production in the presence of a sacrificial electron donor like ethanol or methanol under UV-visible and visible light illumination. These nanocomposites showed very good photocatalytic activity toward hydrogen production under UV-visible conditions, whereas under visible light illumination, there was considerably less hydrogen produced. Au/P25 gave a hydrogen evolution rate of 1600 μmol/h in the presence of ethanol (5 volume %) under UV-visible illumination. In the case of Au/TiO2 prepared by the SMAD method, the presence of Au nanoparticles serves two purposes: as an electron sink gathering electrons from the conduction band (CB) of TiO2 and as a reactive site for water/ethanol reduction to generate hydrogen gas. We also observed hydrogen production by water splitting in the absence of a sacrificial electron donor using Au/TiO2 nanocomposites under UV-visible illumination.

Optimized hydrogen sensing properties of nanocomposite NiO:Au thin films grown by dual pulsed laser deposition

Nanocomposite NiO:Au thin films, formed by gold nanoparticles embedded in a nickel oxide matrix, have been grown by reactive pulsed laser deposition (R-PLD). Two actively synchronized nanosecond laser sources, a KrF excimer laser (248 nm) and a Nd:YAG laser (355 nm), were used for the simultaneous ablation of nickel and gold targets in oxygen ambient. The morphology, composition, and optical properties of the obtained nanocomposites were investigated and were found to correlate with the concentration of Au nanoparticles. Further, the NiO:Au nanocomposites have been tested as hydrogen sensors. Embedding Au nanoparticles into the NiO film matrix reduced the sensors operating temperature and improved their performance by orders of magnitude.

Electrodes of Poly(N‐methyl pyrrole)/Au and Poly(m‐aminobenzene sulfonic acid)‐Functionalized Multiwalled Carbon Nanotubes for Supercapacitor Applications

AbstractAn assembly of poly(N‐methyl pyrrole) (PMP) doped with poly(3‐styrene sulfonate) with embedded Au nanoparticles (PMP/Au) was grown by electropolymerization of the monomer (MP) followed by adsorption of a Au colloid. Multiwalled carbon nanotubes were functionalized with poly(m‐aminobenzene sulfonic acid) (MWCNT/PABS) and deposited electrophoretically over conducting substrates. X‐ray diffraction (XRD) and Raman studies confirmed the successful functionalization of the MWCNTs by PABS. A new asymmetric supercapacitor design incorporating PMP/Au and MWCNT/PABS as electrodes was implemented for the first time, and the cell delivered a reversible specific capacitance of 967 F g−1 and a maximum energy density of 174 Wh Kg−1, which was superior to a PMP‐MWCNT/PABS cell (167 F g−1) and higher than many reported capacitances of poly(pyrrole)‐based supercapacitors. The PMP/Au electrode outperformed pristine PMP, graphite, and MWCNT/PABS electrodes in a study of different symmetric and asymmetric cells employing these electrodes. Scanning spreading resistance microscopy (SSRM) and conducting atomic force microscopy (C‐AFM) showed a lower spreading resistance and a larger nanoscale electronic conductivity for the PMP/Au electrode than for the pristine PMP electrode; these attributes allow unhindered charge transport both in the radial direction and across the cross‐section of the PMP/Au electrode. The facile electron propagation in the PMP/Au electrode, enabled by the presence of localized conducting domains of Au nanoparticles implanted in the PMP electrode, effectively translates into an enhanced specific capacitance of PMP/Au‐based cells relative to PMP. The results demonstrate that asymmetrically designed cells offer an exciting way to boost the overall performance of supercapacitors.

Optical absorptive response of platinum doped TiO2 transparent thin films with Au nanoparticles

In this paper different optical absorption bands associated to the surface plasmon of resonance of a nanoparticle containing sample were achieved by a sol–gel processing route. We study the linear and nonlinear optical absorptive properties of a titanium dioxide thin film with superficial Au nanoparticles. A chaotic behavior related with modification of the optical absorption by a multi-wave mixing interaction was investigated. A characteristic Mandelbrot group tendency was used to describe the possibility of a resulting absorptive response. The analysis of the observations showed that an excitation at 488nm wavelength in the nanocomposite can originate a measurable change in the absorptive properties for the propagation of optical beams at 532nm and at 650nm. However, the inhibition of this condition exhibited by the film can be obtained by the shift of its plasmonic response. It is considered that the near resonance participation of the Au nanoparticles is mainly responsible for avoiding the photodarkening contribution to the optical absorptive response of the sol–gel TiO2 film with embedded Au nanoparticles. Potential applications of the samples are proposed for development of optical sensors or transparent thin films for filtering functions.

Enhanced optical and electrical gas sensing response of sol–gel based NiO–Au and ZnO–Au nanostructured thin films

NiO and ZnO thin films of about 40–50nm thickness with embedded Au nanoparticles have been synthesized with a simple and reliable sol–gel procedure. The nanocomposites films are crystalline and porous and they show optical absorptions in the visible range according to Au nanoparticles concentration. These films have been tested as optical and electrical sensors for pollutant gases detection. A fast and reversible response has been detected for hydrogen, CO and NO2. Au nanoparticles have been found to improve the optical sensing properties of both NiO and ZnO films over the Au surface plasmon resonance peak wavelength range, but also to enhance the ZnO optical response in the near UV range, where Au nanoparticles are optically inactive. Moreover, combining the observed shift in the surface plasmon resonance peak and the different semiconductive type of the two oxides, it has been proved that reducing gases inject electrons into the oxide and then afterward the charge variation is detected by Au nanoparticles. Electrical tests confirm the n-type behavior of ZnO and p-type behavior of NiO, and show good performances at lower temperatures. Moreover, an enhancing effect of Au nanoparticles in the overall sensing performances is observed also in electrical tests.

Annealing effect on the structural and optical properties of embedded Au nanoparticles in silicon suboxide films

Au/SiOx nanocomposite films have been fabricated by co-sputtering Au wires and SiO2 target using an RF magnetron co-sputtering system before the thermal annealing process at different temperatures. The structural and optical properties of the samples were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), optical transmission, and reflection spectroscopy. XPS analysis confirms that the as-prepared SiOx films are silicon-rich suboxide films. FESEM images reveal that with an increase in annealing temperature, the embedded Au NPs tend to diffuse toward the surface of the SiOx films. In IR spectra, the intensity of the Si–O–Si absorption band increases with the annealing temperature. Optical spectra reveal that the position and intensity of the surface plasmon resonance (SPR) peak are dominated by the effect of the inter-particle distance and size of the Au NPs embedded in the SiOx films, respectively. The SPR absorption peak shows the blue-shift from 672 to 600 nm with an increase in annealing temperature. The growth of silica nanowires (SiOx NWs) is observed in the film prepared on a c-Si substrate instead of a quartz substrate and annealed at temperatures of 1000 °C.

Enhancing the device performance of Sb2S3-sensitized heterojunction solar cells by embedding Au nanoparticles in the hole-conducting polymer layer

Performance of Sb(2)S(3)-sensitized heterojunction solar cells is enhanced by embedding Au nanoparticles in the poly-3-hexylthiophene (P3HT) hole-conducting polymer layer. The improved charge transfer/transport at the Sb(2)S(3)/P3HT/Au interface by extended interface area of the P3HT/Au counter electrode and the re-absorption of the backscattering light from the embedded Au nanoparticles enhanced the device performance: J(sc) 11.0 to 12.8 mA cm(-2), V(oc) 606 to 626 mV, fill factor (FF) 60.5 to 61.2%, and power conversion efficiency (η) 4.0 to 4.9%. Simultaneous enhancement of V(oc), J(sc), and FF in Au nanoparticle-embedded systems is mainly attributed to the improved charge collection efficiency and light harvesting efficiency of Sb(2)S(3) due to the improved charge transfer/transport in the Sb(2)S(3)/P3HT/Au interface.

Enhancement of Visible-Light Photocatalytic Activity of Mesoporous Au-TiO2Nanocomposites by Surface Plasmon Resonance

Mesoporous Au-TiO2nanocomposite plasmonic photocatalyst with visible-light photoactivity was prepared by a simple spray hydrolytic method using photoreduction technique at90∘C. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N2adsorption-desorption isotherms. The formation of hydroxyl radicals (•OH) on the surface of visible-light illuminated Au-TiO2nanocomposites was detected by the luminescence technique using terephthalic acid as probe molecules. The photocatalytic activity was evaluated by photocatalytic decolorization of Rhodamine-B (RhB) aqueous solution under visible-light irradiation (λ > 420 nm). The results revealed that the TiO2could be crystallizedviaspray hydrolysis method, and the photoreduction technique was facilitated to prepare Au nanoparticles in the mesoporous TiO2at90∘C. The light absorption, the formation rate of hydroxyl radicals, and photocatalytic decolorization of Rhodamine-B aqueous solution were significantly enhanced by those embedded Au nanoparticles in the Au-TiO2nanocomposites. The prepared Au-TiO2nanocomposites exhibit a highly visible-light photocatalytic activity for photocatalytic degradation of RhB in water, and their photocatalytic activity is higher than that of the pristine TiO2nanoparticles due to the surface plasmon resonance.

Boronate self-assemblies with embedded Au nanoparticles: preparation, characterization and their catalytic activities for the reduction of nitroaromatic compounds

Sequential boronate esterification of benzene-1,4-diboronic acid with pentaerythritol induced hierarchical molecular self-assembly to produce mono-dispersed flower-like microparticles. ATR-FT-IR, PXRD, 13C-CP-MAS and 11B-DD-MAS NMR spectra indicate that the particles consist of zigzag-shaped packing structures of polymeric 2,4,8,10-tetraoxa-3,9-diboraspiro[5.5]undecane. Au nanoparticles (Au NPs) with a mean diameter of 2.7 nm were successfully deposited on the microparticles by the deposition reduction (DR) method. It is noteworthy that the resulting novel hybrids exhibited an efficient catalytic activity for the reduction of nitroaromatic compounds; in particular, high chemoselectivity in the hydrogenation of 4-nitrostyrene to the corresponding aniline was attained without reduction of the vinyl bond. Careful investigation of the catalyst suggested a synergistic effect between Au NPs and the boronate support in the selective hydrogenation. These findings strongly suggest that boronate self-assemblies are advantageous as support materials for preparation of heterogeneous catalysts based on polymer–Au hybrids.

One-pot synthesis of responsive catalytic Au@PVP hybrid nanogels

Responsive catalytic hybrid nanogels with Au nanoparticle cores and a polyvinylpyrrolidone (PVP) based gel shell are prepared through a novel one-pot approach. The embedded Au nanoparticles demonstrate both a pH-modulated catalytic activity and anti-aggregation properties upon recycling.