Correction for ‘Systematic investigation of the SERS efficiency and SERS hotspots in gas-phase deposited Ag nanoparticle assemblies’ by L. B. He et al., Phys. Chem. Chem. Phys., 2017, 19, 5091–5101.

•Pd nanoparticles with small size and good dispersion prepared by gas phase cluster beam deposition exhibit excellent catalytic activity for methanol oxidation.•3D MWCNTs/FLG hybrids provided larger surface area and higher electron conductivity.•The Pd NPs/MWCNTs/FLG reveals enhanced ECSA and mass specific current corresponds for methanol oxidation.Pd nanoparticles with a mean diameter of 6.7 nm are prepared by gas phase cluster beam deposition. The Pd nanoparticle films exhibit excellent catalytic activity and stability for methanol oxidation. 3D hybrid nanostructures combined with multi-walled carbon nanotubes and few-layer graphene sheets are used as supports to further enhance the methanol electro-oxidation activity of the Pd nanoparticle catalysts by a factor of more than 2.7. The catalytic activity towards methanol electro-oxidation is characterized with cyclic voltammetry measurements. An ultrahigh electrochemical active surface area (ECSA) as large as 311 m2 g−1pd and a mass specific current corresponding to methanol oxidation levels as high as 4038 mA mg−1pd are realized. These results can be attributed to the high electrochemical activity of the Pd nanoparticles and the unique conductive structure of the multi-walled carbon nanotubes/few-layer graphene sheets.Download high-res image (183KB)Download full-size image

Gas-phase deposited Ag nanoparticle assemblies are one of the most commonly used plasmonic substrates benefiting from their remarkable advantages such as clean particle surface, tunable particle density, available inter-particle gaps, low-cost and scalable fabrication, and excellent industry compatibility. However, their performance efficiencies are difficult to optimize due to the lack of knowledge of the hotspots inside their structures. We here report a design of delicate rainbow-like Ag nanoparticle assemblies, based on which the hotspots can be revealed through a combinatorial approach. The findings show that the hotspots in gas-phase deposited Ag nanoparticle assemblies are uniquely entangled by the excitation energy and specific inter-particle gaps, differing from the matching conditions in periodic arrays. For Ag nanoparticle assemblies deposited on Formvar-filmed substrates, the mean particle size is maintained around 10 nm, while the particle density can be widely tuned. The one possessing the highest SERS efficiency (under 473 nm excitation) have a particle number density of around 7100 μm−2. Gaps with an inter-particle spacing of around 3 nm are found to serve as SERS hotspots, and these hotspots contribute to 68% of the overall SERS intensity. For Ag nanoparticle assemblies fabricated on carbon-filmed substrates, the mean particle size can be feasibly tuned. The one possessing the highest SERS efficiency under 473 nm excitation has a particle number density of around 460 μm−2 and a mean particle size of around 42.1 nm. The construction of Ag–analyte–Ag sandwich-like nanoparticle assemblies by a two-step-deposition method slightly improves the SERS efficiency when the particle number density is low, but suppresses the SERS efficiency when the particle number density is high.

Both fabrication of Au nano-objects and the nonlinear optical properties of Au nano-objects are the focus of research. In the present work, Au nanoparticles with different mean sizes (18, 32, 42, and 70 nm) are controllably fabricated in ethanol by changing the concentration of poly(vinylpyrrolidone) (PVP) and HAuCl4, as well as the power of continuous wave UV light at 365 nm. PVP acts as both reducing and protective agent. The mechanism of photoreduction of PVP to HAuCl4 is proposed. PVP undergoes a series of chemical reactions which include the attack of the hydrogen atom on the tertiary carbon atom at the α-position of the nitrogen atom, production of a hydroxyl radical, and chain scission. The hydroxyl radical combines with the hydrogen atom produced through the dissociation of HAuCl4, which facilitates the decomposition of HAuCl4. The fabrication mechanism of Au nanoparticles is discussed. The nonlinear absorption of these Au nanoparticles is investigated; all of them exhibit saturable absorption, and the saturable absorption dominates the nonlinear absorption with the increase of laser energy. The dominance of saturable absorption in the nonlinear absorption is due to the stronger single-photon absorbed intraband absorption from the ground state to the first excited state in the conduction band, the weaker excited state absorption in the conduction band, and the weaker two-photon absorption from the d band to the conduction band.

•Pd–Ni alloy nanoparticles were synthesized with a gas aggregation process.•Quantum conductance-based H2 sensors were fabricated from Pd–Ni nanoparticle films.•The effect of Ni content on the α-β phase transition behavior of PdHx was studied.•The H2 response characteristics of Pd–Ni nanoparticle films were studied.•The optimal Ni content was determined to fabricate excellent H2 sensors.Pd–Ni alloy nanocrystals, with a controlled Ni atom content ranging from 0 to 60%, were synthesized with a gas aggregation process. The mean size of the alloy nanoparticles was found to decrease with Ni content. Quantum conductance-based hydrogen sensors were fabricated by depositing films of closely spaced Pd–Ni nanoparticles in gas phase with a well-controlled coverage, on the surface of silicon chips prefabricated with interdigital electrodes. Significant changes on the α- β phase transition behavior of PdHx and hence the hydrogen response characteristics of the nanoparticle-based sensors, induced by the incorporation of Ni into the Pd nanoparticles, were demonstrated. An optimal Ni content of 16% was suggested to make excellent H2 sensors with rapid response, high sensitivity as well as good linearity and reliability in a wide hydrogen pressure range.

•The self focusing of Pd NPs increases with the hydriding.•The nonlinear absorption of Pd NPs changes from SA to RSA with the hydriding.•The acoustic breathing movement of Pd NPs damps obviously with the hydriding.•The contact between the NPs and the substrate becomes loose with the hydriding.Pd nanoparticles are deposited on one surface of a quartz sheet. Their optical nonlinearity and ultrafast dynamics in air and in hydrogen environment are investigated. The Pd nanoparticles exhibit self focusing and saturable absorption in air. In hydrogen environment with increasing hydrogen, the NPs maintain self focusing, however their nonlinear refraction index increases; and their nonlinear absorption changes from saturable absorption to reverse saturable absorption. In hydrogen environment, the acoustic breathing movement of these NPs damps more obviously and the contact between the NPs and quartz sheet is looser, comparing to that in air.

Polystyrene(PS)/ZnO micronano hierarchical structures were fabricated on a flat surface by depositing ZnO nanoparticles from a cluster beam at oblique incidence on the surface predeposited with PS microspheres. The hierarchical structure was composed of submicron-sized PS particle layers covered with dense films of columnar ZnO nanoparticle piles separated with nanoscale pores. It was demonstrated that the cooperative effect that combines the microlens function of the PS microspheres and the enhanced Rayleigh scattering of the ZnO nanoparticle porous layers can be used to greatly reduce the total internal reflection at the medium–air interface. The PS/ZnO hierarchical structures were fabricated on the surface of GaN-based light-emitting diode (LED) chips to enhance the light-extraction efficiency. A 77.7% improvement on the light-output power was realized, which was much greater than that obtained with the PS microstructures alone.Keywords: cluster beam; hierarchical structures; light extraction; light-emitting device; ZnO nanoparticles

•Ag nanoparticles were deposited on InGaN QWs to enhance photoluminescence.•The complex mechanisms of surface plasmon enhanced photoluminescence were analyzed.•The influence of localized surface plasmons on carrier dynamics in QWs was studied.•We show carrier localization enhancement by localized surface plasmon coupling.An analysis of the complex mechanisms of enhanced photoluminescence (PL) from InGaN/GaN quantum wells (QWs) by surface plasmon (SP) coupling is reported. Silver nanoparticles were deposited on the QWs to generate a wide surface plasmon resonance (SPR) band covering both PL excitation and emission wavelengths. Significant enhancement of the integrated PL intensity, a blue shift of the PL peak wavelength, a suppression of the relative contribution of PL from In-rich quantum dot-like structures, and an increased PL decay time were observed in temperature-dependent and time-resolved PL spectroscopy. In addition to an enhanced radiative recombination rate by resonant coupling the spontaneous emissions to SPs, QW carrier dynamics can be significantly affected by SPR-enhanced, light-induced local fields. The latter occurs because of screening of the quantum-confined Stark effect and the enhanced localization of carriers.Graphical abstract

TiO2 nanoparticle layers composed of columnar TiO2 nanoparticle piles separated with nanoscale pores were fabricated on the bottom surface of the hemispherical glass prism by performing gas phase cluster beam deposition at glancing incidence. The porosity as well as the refractive index of the nanoparticle layer was precisely tuned by the incident angle. Effective extraction of the light trapped in the substrate due to total internal reflection with the TiO2 nanoparticle layers was demonstrated and the extraction efficiency was found to increase with the porosity. An enhanced Rayleigh scattering mechanism, which results from the columnar aggregation of the nanoparticles as well as the strong contrast in the refractive index between pores and TiO2 nanoparticles in the nanoporous structures, was proposed. The porous TiO2 nanoparticle coatings were fabricated on the surface of GaN LEDs to enhance their light output. A nearly 92% PL enhancement as well as a 30% EL enhancement was observed. For LED applications, the enhanced light extraction with the TiO2 nanoparticle porous layers can be a supplement to the microscale texturing process for light extraction enhancement.

We demonstrate a promising method to fabricate highly adhesive silver nanoparticle coating on glass carbon electrode with good dispersity by using gas phase cluster beam deposition. The fabricated nanoparticles have clean surface and show enhanced electrocatalytic activity toward the reduction of H2O2 with a considerably decreased overpotential. A nonenzyme sensing platform for stable detection of H2O2 with a very rapid response time (less than 1 s), high sensitivity (63 μA/mM) as well as a low detection limit (1.3 μM) is realized from the silver nanoparticle based electrode with a optimized nanoparticle coverage.

The response time of the quantum conductance-based hydrogen sensor fabricated from films consisting of closely spaced palladium nanoparticles formed with cluster beam deposition was investigated. The dependence of the response time on the coverage-regulated nanoparticle size, as well as the hydrogen pressure, was determined. At low hydrogen pressure, the response time is dominated by the hydriding time of the larger Pd nanoparticles. Fast response as short as 3 s to 1,000 Pa H2 could be realized with the lower coverage nanoparticle film, with a sensitive change of the relative conductance as high as 70 %. At 10 kPa hydrogen pressure, subsecond hydrogen response could be realized. With the increase of the hydrogen pressure, the response time of the devices becomes longer and longer as determined by the hydriding time of the Pd nanoparticles involved in the smaller size population of the size distribution, and approaches the same value for the hydrogen sensors with different nanoparticle coverages. The abnormal increase of the response time accompanied by the formation of the α + β coexistence phase of PdHx was also investigated.

Closely spaced palladium nanoparticle arrays were fabricated in between a pair of interdigital electrodes by means of gas phase cluster beam deposition with controlled coverage. The quantum conductance change induced by hydrogen absorption was used for hydrogen sensing. The hydrogen response behavior of a sensor chip was investigated in N2 + H2 mixture gas. The sensor could be calibrated with three linear response hydrogen concentration regimes. A sub-second fast response was shown at 2.2% H2 concentration. The influence of the temperature variation to the quantitative hydrogen concentration measurement with this sensor was discussed.

Few-layer graphene sheets were prepared by splitting expanded graphite using high-power sonication. Atomic-level calibrated scanning transmission electron microscopy was used to obtain efficient layer statistics, enabling optimization of the experimental conditions. This resulted in a two-step splitting mechanism in which the mean number of layers was first reduced to less than 20 by heating to 1100 °C and then to a few-layer region by a 5-min 104 W L−1 – power-density sonication. Raman spectroscopic analysis confirms the above mechanism and demonstrates that the sheets are largely free of defects and functional groups.

The response of quantum-conductance-based hydrogen sensors fabricated by controllable deposition of closely spaced Pd nanoparticle films between interdigital electrodes was investigated. Three typical response regions with different conductance–hydrogen pressure correlations were observed. The response characteristics of the devices were found to depend strongly on the nanoparticle coverage. In the low H2 pressure region, higher coverage gives higher sensitivity. In the high H2 pressure region, quantitative sensing can only be realized with low nanoparticle coverage. Optimizing the coverage allows the attainment of highly sensitive hydrogen sensors with a very wide quantitative working range, extending far beyond the hydrogen pressure region associated with the α-to-β phase transition of Pd.

Periodic nanoring arrays are prepared by self-assembled poly styrene-block-polymethylmethacrylate (PS-b-PMMA) diblock copolymer under rapid solvent-annealing. The dimension of the nanorings can be modified by controlling the solvent-annealing time.

Well-ordered Ag nanoparticle arrays with high particle density were fabricated by photochemical reduction of domain-selective Ag+-loading on hydrophobic polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) self-assembled diblock copolymer templates.

Well-ordered Ag nanoparticle arrays with high particle density were fabricated by photochemical reduction of domain-selective Ag+-loading on hydrophobic polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) self-assembled diblock copolymer templates.

Correction for ‘Systematic investigation of the SERS efficiency and SERS hotspots in gas-phase deposited Ag nanoparticle assemblies’ by L. B. He et al., Phys. Chem. Chem. Phys., 2017, 19, 5091–5101.

Both fabrication of Au nano-objects and the nonlinear optical properties of Au nano-objects are the focus of research. In the present work, Au nanoparticles with different mean sizes (18, 32, 42, and 70 nm) are controllably fabricated in ethanol by changing the concentration of poly(vinylpyrrolidone) (PVP) and HAuCl4, as well as the power of continuous wave UV light at 365 nm. PVP acts as both reducing and protective agent. The mechanism of photoreduction of PVP to HAuCl4 is proposed. PVP undergoes a series of chemical reactions which include the attack of the hydrogen atom on the tertiary carbon atom at the α-position of the nitrogen atom, production of a hydroxyl radical, and chain scission. The hydroxyl radical combines with the hydrogen atom produced through the dissociation of HAuCl4, which facilitates the decomposition of HAuCl4. The fabrication mechanism of Au nanoparticles is discussed. The nonlinear absorption of these Au nanoparticles is investigated; all of them exhibit saturable absorption, and the saturable absorption dominates the nonlinear absorption with the increase of laser energy. The dominance of saturable absorption in the nonlinear absorption is due to the stronger single-photon absorbed intraband absorption from the ground state to the first excited state in the conduction band, the weaker excited state absorption in the conduction band, and the weaker two-photon absorption from the d band to the conduction band.

Gas-phase deposited Ag nanoparticle assemblies are one of the most commonly used plasmonic substrates benefiting from their remarkable advantages such as clean particle surface, tunable particle density, available inter-particle gaps, low-cost and scalable fabrication, and excellent industry compatibility. However, their performance efficiencies are difficult to optimize due to the lack of knowledge of the hotspots inside their structures. We here report a design of delicate rainbow-like Ag nanoparticle assemblies, based on which the hotspots can be revealed through a combinatorial approach. The findings show that the hotspots in gas-phase deposited Ag nanoparticle assemblies are uniquely entangled by the excitation energy and specific inter-particle gaps, differing from the matching conditions in periodic arrays. For Ag nanoparticle assemblies deposited on Formvar-filmed substrates, the mean particle size is maintained around 10 nm, while the particle density can be widely tuned. The one possessing the highest SERS efficiency (under 473 nm excitation) have a particle number density of around 7100 μm−2. Gaps with an inter-particle spacing of around 3 nm are found to serve as SERS hotspots, and these hotspots contribute to 68% of the overall SERS intensity. For Ag nanoparticle assemblies fabricated on carbon-filmed substrates, the mean particle size can be feasibly tuned. The one possessing the highest SERS efficiency under 473 nm excitation has a particle number density of around 460 μm−2 and a mean particle size of around 42.1 nm. The construction of Ag–analyte–Ag sandwich-like nanoparticle assemblies by a two-step-deposition method slightly improves the SERS efficiency when the particle number density is low, but suppresses the SERS efficiency when the particle number density is high.