A novel method for the synthesis of core-shell nanoparticles for functional applications based on long-term confinement in a radio frequency plasma.

A novel combined setup of a Haberland type gas aggregation source and a secondary radio frequency discharge is used to generate, confine, and coat nanoparticles over much longer time scales than traditional in-flight treatment. The process is precisely monitored using localized surface plasmon resonance and Fourier-transform infrared spectroscopy as in situ diagnostics. They indicate that both untreated and treated particles can be confined for extended time periods (at least one hour) with minimal losses. During the entire confinement time, the particle sizes do not show considerable alterations, enabling multiple well-defined modifications of the seed nanoparticles in this synthesis approach. The approach is demonstrated by generating Ag@SiO2 nanoparticles with a well-defined surface coating. The in situ diagnostics provide insights into the growth kinetics of the applied coating and are linked to the coating properties by using ex situ transmission electron microscopy and energy dispersive X-ray spectroscopy. Surface coating is shown to occur in two phases: first, singular seeds appear on the particle surface which then grow to cover the entire particle surface over 3 to 5 minutes. Afterwards, deposition occurs via surface growth which coincides with lower deposition rates. Our setup offers full control for various treatment options, which is demonstrated by coating the nanoparticles with a SiO2 layer followed by the etching of the part of the applied coating using hydrogen. Thus, complex multi-step nanofabrication, e.g., using different monomers, as well as very large coating thicknesses is possible.

Effects of Lithium Polysulfides on the Formation of Solid Electrolyte Interfaces in Silicon Anodes.

Lithium-ion batteries are one of the most important energy storage devices of the future and pave the way for a greener society. In this context, the demand for batteries with high energy density is increasing significantly and is reaching the limits of the technology currently in use. Therefore, intensive research is being conducted to utilize a new class of materials for energy storage. The most promising alternatives to today's nickel-based cathode and graphite anode materials are silicon and sulfur. Both silicon and sulfur are abundant and cheap and possess extremely high theoretical specific capacities of 4200 mAh/gSi and 1675 mAh/gS, respectively. One of the biggest challenges with sulfur-based batteries is the polysulfide shuttle effect, which occurs with sulfur cathodes, leading to an insulating passivation layer, especially on the commonly used lithium metal anodes. Therefore, to replace lithium metal anodes with silicon, it is of major importance to understand the reactivity of polysulfides with silicon. To investigate the effect of lithium polysulfides on the performance of the anodes in the critical formation cycles, mesoporous silicon anodes were galvanostatically cycled in electrolytes containing different concentrations of polysulfides. In this process, the anodes were analyzed after one, five and ten cycles by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy to determine the composition of the SEI. Higher concentrations of polysulfides in the electrolyte result in more inorganic, oxide-containing species in the SEI. Silicon anodes with lower amounts of surface oxide show little or negative effect on the performance in the presence of polysulfides, while anodes with large amounts of surface oxide show higher impedance during cycling, an effect that is enhanced with increasing polysulfide content.

Correlating Optical Reflectance with the Topology of Aluminum Nanocluster Layers Growing on Partially Conjugated Diblock Copolymer Templates.

Large-scale fabrication of metal cluster layers for usage in sensor applications and photovoltaics is a huge challenge. Physical vapor deposition offers large-scale fabrication of metal cluster layers on templates and polymer surfaces. In the case of aluminum (Al), only little is known about the formation and interaction of Al clusters during sputter deposition. Complex polymer surface morphologies can tailor the deposited Al cluster layer. Here, a poly(methyl methacrylate)-block-poly(3-hexylthiophen-2,5-diyl) (PMMA-b-P3HT) diblock copolymer template is used to investigate the nanostructure formation of Al cluster layers on the different polymer domains and to compare it with the respective homopolymers PMMA and P3HT. The optical properties relevant for sensor applications are monitored with ultraviolet-visible (UV-vis) measurements during the sputter deposition. The formation of Al clusters is followed in situ with grazing-incidence small-angle X-ray scattering (GISAXS), and the chemical interaction is revealed by X-ray photoelectron spectroscopy (XPS). Furthermore, atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) yield topographical information about selective wetting of Al on the P3HT domains and embedding in the PMMA domains in the early stages, followed by four distinct growth stages describing the Al nanostructure formation.

Revealing the growth of copper on polystyrene-block-poly(ethylene oxide) diblock copolymer thin films with in situ GISAXS.

Copper (Cu) as an excellent electrical conductor and the amphiphilic diblock copolymer polystyrene-block-poly(ethylene oxide) (PS-b-PEO) as a polymer electrolyte and ionic conductor can be combined with an active material in composite electrodes for polymer lithium-ion batteries (LIBs). As interfaces are a key issue in LIBs, sputter deposition of Cu contacts on PS-b-PEO thin films with high PEO fraction is investigated with in situ grazing-incidence small-angle X-ray scattering (GISAXS) to follow the formation of the Cu layer in real-time. We observe a hierarchical morphology of Cu clusters building larger Cu agglomerates. Two characteristic distances corresponding to the PS-b-PEO microphase separation and the Cu clusters are determined. A selective agglomeration of Cu clusters on the PS domains explains the origin of the persisting hierarchical morphology of the Cu layer even after a complete surface coverage is reached. The spheroidal shape of the Cu clusters growing within the first few nanometers of sputter deposition causes a highly porous Cu-polymer interface. Four growth stages are distinguished corresponding to different kinetics of the cluster growth of Cu on PS-b-PEO thin films: (I) nucleation, (II) diffusion-driven growth, (III) adsorption-driven growth, and (IV) grain growth of Cu clusters. Percolation is reached at an effective Cu layer thickness of 5.75 nm.

Real-time insight into nanostructure evolution during the rapid formation of ultra-thin gold layers on polymers.

Ultra-thin metal layers on polymer thin films attract tremendous research interest for advanced flexible optoelectronic applications, including organic photovoltaics, light emitting diodes and sensors. To realize the large-scale production of such metal-polymer hybrid materials, high rate sputter deposition is of particular interest. Here, we witness the birth of a metal-polymer hybrid material by quantifying in situ with unprecedented time-resolution of 0.5 ms the temporal evolution of interfacial morphology during the rapid formation of ultra-thin gold layers on thin polystyrene films. We monitor average non-equilibrium cluster geometries, transient interface morphologies and the effective near-surface gold diffusion. At 1 s sputter deposition, the polymer matrix has already been enriched with 1% gold and an intermixing layer has formed with a depth of over 3.5 nm. Furthermore, we experimentally observe unexpected changes in aspect ratios of ultra-small gold clusters growing in the vicinity of polymer chains. For the first time, this approach enables four-dimensional insights at atomic scales during the gold growth under non-equilibrium conditions.

Temperature-Dependent Vapor Infiltration of Sulfur into Highly Porous Hierarchical Three-Dimensional Conductive Carbon Networks for Lithium Ion Battery Applications.

Hierarchical, conductive, porous, three-dimensional (3D) carbon networks based on carbon nanotubes are used as a scaffold material for the incorporation of sulfur in the vapor phase to produce carbon nanotube tube/sulfur (CNTT/S) composites for application in lithium ion batteries (LIBs) as a cathode material. The high conductivity of the carbon nanotube-based scaffold material, in combination with vapor infiltration of sulfur, allows for improved utilization of insulating sulfur as the active material in the cathode. When sulfur is evenly distributed throughout the network via vapor infiltration, the carbon scaffold material confines the sulfur, allowing the sulfur to become electrochemically active in the context of an LIB. The electrochemical performance of the sulfur cathode was further investigated as a function of the temperature used for the vapor infiltration of sulfur into the carbon scaffolds (155, 175, and 200 °C) in order to determine the ideal infiltration temperature to maximize sulfur loading and minimize the polysulfide shuttle effect. In addition, the nature of the incorporation of sulfur at the interfaces within the 3D carbon network at the different vapor infiltration temperatures will be investigated via Raman, scanning electron microscopy/energy dispersive X-ray, and X-ray photoelectron spectroscopy. The resulting CNTT/S composites, infiltrated at each temperature, were incorporated into a half-cell using Li metal as a counter electrode and a 0.7 M LiTFSI electrolyte in ether solvents and characterized electrochemically using cyclic voltammetry measurements. The results indicate that the CNTT matrix infiltrated with sulfur at the highest temperature (200 °C) had improved incorporation of sulfur into the carbon network, the best electrochemical performance, and the highest sulfur loading, 8.4 mg/cm2, compared to the CNTT matrices infiltrated at 155 and 175 °C, with sulfur loadings of 4.8 and 6.3 mg/cm2, respectively.

Influence of Cleaning Methods on Resin Bonding to Contaminated Translucent 3Y-TZP ceramic.

PURPOSE: To evaluate the influence of different cleaning methods on the resin bond strength to contaminated translucent 3Y-TZP ceramic. MATERIALS AND METHODS: A total of 133 airborne-particle abraded (0.1 MPa) zirconia specimens were divided into 7 groups. Uncontaminated zirconia specimens were either not cleaned (UN) or cleaned with cleaning paste (Ivoclean) (UP1). After contamination by saliva and blood immersion, zirconia specimens were cleaned using either distilled water rinsing (CW), 99% isopropanol in an ultrasonic bath (CI), cleaning paste according to manufacturer's instructions (CP1), cleaning paste with additional rubbing (CP2), or additional airborne-particle abrasion at 0.1 MPa (CA). Three specimens from each group were examined by x-ray photoelectron spectroscopy (XPS). For each group, sixteen Plexiglas tubes filled with composite resin (Clearfil FII, Kuraray Noritake) were bonded to the zirconia specimens using a primer (Clearfil Ceramic Primer Plus, Kuraray Noritake) and luting composite (Panavia V5, Kuraray Noritake). Before measuring tensile bond strength, specimens were stored in distilled water for 3 or 150 days plus 37,500 thermal cycles. RESULTS: After 3 days, no group showed significantly different TBS compared to the control group UN (p > 0.05). However, groups CW and CI showed significantly lower TBS than all other groups after 150 days (p ≤ 0.05). XPS analysis revealed more organic residue on zirconia surfaces of groups CW and CI than on the other groups. CONCLUSION: Cleaning with the cleaning paste and airborne-particle abrasion were effective in removing saliva and blood contamination and enhancing bond strength.

Photodeposition of Au Nanoclusters for Enhanced Photocatalytic Dye Degradation over TiO2 Thin Film.

Au nanoparticle (NP) decorated heterogeneous TiO2 catalysts are known to be effective in the degradation of various organic pollutants. The photocatalytic performance of such Au-TiO2 structures remarkably depends on the size, morphology, and surface coverage of the Au NPs decorating TiO2. Here we propose an effective way of preparing a highly active Au nanocluster (NC) decorated TiO2 thin film by a novel photodeposition method. By altering the solvent type as well as the illumination time, we achieved well-controlled surface coverage of TiO2 by Au NCs, which directly influences the photocatalytic performance. Here the Au NCs coverage affects both the electron store capacity and the optical absorption of the hybrid Au-TiO2 system. At low surface coverage, 19.2-29.5%, the Au NCs seem to enhance significantly the optical adsorption of TiO2 at UV wavelengths which therefore leads to a higher photocatalytic performance.

Following in Situ the Deposition of Gold Electrodes on Low Band Gap Polymer Films.

Metal top electrodes such as gold are widely used in organic solar cells. The active layer can be optimized by modifications of the polymer band gap via side-chain engineering, and low band gap polymers based on benzodithiophene units such as PTB7 and PTB7-Th are successfully used. The growth of gold contacts on PTB7 and PTB7-Th films is investigated with in situ grazing incidence small-angle X-ray scattering (GISAXS) and grazing incidence wide-angle X-ray scattering (GIWAXS) during the sputter deposition of gold. From GIWAXS, the crystal structure of the gold film is determined. Independent of the type of side chain, gold crystals form in the very early stages and improve in quality during the sputter deposition until the late stages. From GISAXS, the nanoscale structure is determined. Differences in terms of gold cluster size and growth phase limits for the two polymers are caused by the side-chain modification and result in a different surface coverage in the early phases. The changes in the diffusion and coalescence behavior of the forming gold nanoparticles cause differences in the morphology of the gold contact in the fully percolated regime, which is attributed to the different amount of thiophene rings of the side chains acting as nucleation sites.

Wet-Chemical Assembly of 2D Nanomaterials into Lightweight, Microtube-Shaped, and Macroscopic 3D Networks.

Despite tremendous efforts toward fabrication of three-dimensional macrostructures of two-dimensional (2D) materials, the existing approaches still lack sufficient control over microscopic (morphology, porosity, pore size) and macroscopic (shape, size) properties of the resulting structures. In this work, a facile fabrication method for the wet-chemical assembly of carbon 2D nanomaterials into macroscopic networks of interconnected, hollow microtubes is introduced. As demonstrated for electrochemically exfoliated graphene, graphene oxide, and reduced graphene oxide, the approach allows for the preparation of highly porous (> 99.9%) and lightweight (<2 mg cm-3) aeromaterials with tailored porosity and pore size as well as tailorable shape and size. The unique tubelike morphology with high aspect ratio enables ultralow-percolation-threshold graphene composites (0.03 S m-1, 0.05 vol%) which even outperform most of the carbon nanotube-based composites, as well as highly conductive aeronetworks (8 S m-1, 4 mg cm-3). On top of that, long-term compression cycling of the aeronetworks demonstrates remarkable mechanical stability over 10 000 cycles, even though no chemical cross-linking is employed. The developed strategy could pave the way for fabrication of various macrostructures of 2D nanomaterials with defined shape, size, as well as micro- and nanostructure, crucial for numerous applications such as batteries, supercapacitors, and filters.

Pathways to Tailor Photocatalytic Performance of TiO2 Thin Films Deposited by Reactive Magnetron Sputtering.

TiO2 thin films are used extensively for a broad range of applications including environmental remediation, self-cleaning technologies (windows, building exteriors, and textiles), water splitting, antibacterial, and biomedical surfaces. While a broad range of methods such as wet-chemical synthesis techniques, chemical vapor deposition (CVD), and physical vapor deposition (PVD) have been developed for preparation of TiO2 thin films, PVD techniques allow a good control of the homogeneity and thickness as well as provide a good film adhesion. On the other hand, the choice of the PVD technique enormously influences the photocatalytic performance of the TiO2 layer to be deposited. Three important parameters play an important role on the photocatalytic performance of TiO2 thin films: first, the different pathways in crystallization (nucleation and growth); second, anatase/rutile formation; and third, surface area at the interface to the reactants. This study aims to provide a review regarding some strategies developed by our research group in recent years to improve the photocatalytic performance of TiO2 thin films. An innovative approach, which uses thermally induced nanocrack networks as an effective tool to enhance the photocatalytic performance of sputter deposited TiO2 thin films, is presented. Plasmonic and non-plasmonic enhancement of photocatalytic performance by decorating TiO2 thin films with metallic nanostructures are also briefly discussed by case studies. In addition to remediation applications, a new approach, which utilizes highly active photocatalytic TiO2 thin film for micro- and nanostructuring, is also presented.

Durability of resin bonding to zirconia ceramic after contamination and the use of various cleaning methods.

OBJECTIVES: The aim of the study was to evaluate the influence of contamination and different cleaning methods on the tensile bond strength with a phosphate monomer containing luting resin to zirconia ceramic. METHODS: After the contamination with saliva or silicone disclosing agent, 228 polished and airborne-particle abraded zirconia discs were ultrasonically cleaned with 99% isopropanol. In a second step, the specimens were either treated with argon-oxygen plasma, air plasma, enzymatic cleaning agent or did not undergo an additional cleaning process. Uncontaminated zirconia specimens were used as the control group. X-ray photoelectron spectroscopy (XPS) was used for chemical analysis of the bonding surfaces of specimens. Plexiglas tubes filled with composite resin were bonded to zirconia specimens with a phosphate monomer containing luting resin. Tensile bond strength (TBS) was tested after 3 days or 150 days water storage with 37,500 thermal cycles. RESULTS: XPS revealed a decrease of the carbon/oxygen ratio after plasma treatment and an increase after treatment with an enzymatic cleaning agent in all groups. All contaminated specimens showed high and durable TBS after cleaning with a combination of isopropanol and a non-thermal atmospheric plasma. After the cleaning with enzymatic cleaning agent the TBS was significantly reduced in all groups after 150 days thermal cycling. SIGNIFICANCE: The combination of isopropanol and plasma cleaning was effective in removing salvia and disclosing agent contamination. Enzymatic clearing agent was not able to remove contamination effectively and had a negative impact on the TBS of non-contaminated specimens.

Low-Temperature Solution Synthesis of Au-Modified ZnO Nanowires for Highly Efficient Hydrogen Nanosensors.

In this research, the low-temperature single-step electrochemical deposition of arrayed ZnO nanowires (NWs) decorated by Au nanoparticles (NPs) with diameters ranging between 10 and 100 nm is successfully demonstrated for the first time. The AuNPs and ZnO NWs were grown simultaneously in the same growth solution in consideration of the HAuCl4 concentration. Optical, structural, and chemical characterizations were analyzed in detail, proving high crystallinity of the NWs as well as the distribution of Au NPs on the surface of zinc oxide NWs demonstrated by transmission electron microscopy. Individual Au NPs-functionalized ZnO NWs (Au-NP/ZnO-NWs) were incorporated into sensor nanodevices using an focused ion bean/scanning electron microscopy (FIB/SEM) scientific instrument. The gas-sensing investigations demonstrated excellent selectivity to hydrogen gas at room temperature (RT) with a gas response, Igas/Iair, as high as 7.5-100 ppm for Au-NP/ZnO-NWs, possessing a AuNP surface coverage of ∼6.4%. The concentration of HAuCl4 in the electrochemical solution was observed to have no significant impact on the gas-sensing parameters in our experiments. This highlights the significant influence of the total Au/ZnO interfacial area establishing Schottky contacts for the achievement of high performances. The most significant performance of H2 response was observed for gas concentrations higher than 500 ppm of H2 in the environment, which was attributed to the surface metallization of ZnO NWs during exposure to hydrogen. For this case, an ultrahigh response of about 32.9 and 47 to 1000 and 5000 ppm of H2 was obtained, respectively. Spin-polarized periodic density functional theory calculations were realized on Au/ZnO bulk and surface-functionalized models, validating the experimental hypothesis. The combination of H2 gas detection at RT, ultralow power consumption, and reduced dimensions makes these micro-nanodevices excellent candidates for hydrogen gas leakage detection, including hydrogen gas monitoring (less than 1 ppm).

Correlating Nanostructure, Optical and Electronic Properties of Nanogranular Silver Layers during Polymer-Template-Assisted Sputter Deposition.

Tailoring the optical and electronic properties of nanostructured polymer-metal composites demonstrates great potential for efficient fabrication of modern organic optical and electronic devices such as flexible sensors, transistors, diodes, or photovoltaics. Self-assembled polymer-metal nanocomposites offer an excellent perspective for creating hierarchical nanostructures on macroscopic scales by simple bottom-up processes. We investigate the growth processes of nanogranular silver (Ag) layers on diblock copolymer thin film templates during sputter deposition. The Ag growth is strongly driven by self-assembly and selective wetting on the lamella structure of polystyrene-block-poly(methyl methacrylate). We correlate the emerging nanoscale morphologies with collective optical and electronic properties and quantify the difference in Ag growth on the corresponding homopolymer thin films. Thus, we are able to determine the influence of the respective polymer template and observe substrate effects on the Ag cluster percolation threshold, which affects the insulator-to-metal transition (IMT). Optical spectroscopy in the UV-vis regime reveals localized surface plasmon resonance for the metal-polymer composite. Their maximum absorption is observed around the IMT due to the subsequent long-range electron conduction in percolated nanogranular Ag layers. Using X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy, we identify the oxidation of Ag at the acrylate side chains as an essential influencing factor driving the selective wetting behavior in the early growth stages. The results of polymer-templated cluster growth are corroborated by atomic force microscopy and field emission scanning electron microscopy.

Cauliflower-like CeO2-TiO2 hybrid nanostructures with extreme photocatalytic and self-cleaning properties.

In recent years, heterogeneous photocatalysis has gained enormous interest due to increasing concerns about environmental pollution. Here we propose a facile approach to synthesize cauliflower-like CeO2-TiO2 hybrid structures by magnetron reactive sputtering, exhibiting an extremely high photocatalytic activity. While heating and air-quenching of the sputter deposited TiO2 thin film (first layer) triggered the formation of a nanocrack network, the second heat-treatment led to transformation of the CeO2 film (second layer) into CeO2 nanoclusters (NCs). We attribute the resulting high photocatalytic activity to the confined structure of the CeO2 NCs and the CeO2-TiO2 interface, which allows Ce3+/Ce4+ dynamic shifting. In addition to high photocatalytic activity in an aqueous medium, the prepared CeO2-TiO2 hybrid structures exhibited significant self-cleaning properties in air (non-aqueous).

Magnetron-sputtered copper nanoparticles: lost in gas aggregation and found by in situ X-ray scattering.

Magnetron discharge in a cold buffer gas represents a liquid-free approach to the synthesis of metal nanoparticles (NPs) with tailored structure, chemical composition and size. Despite a large number of metal NPs that were successfully produced by this method, the knowledge of the mechanisms of their nucleation and growth in the discharge is still limited, mainly because of the lack of in situ experimental data. In this work, we present the results of in situ Small Angle X-ray Scattering measurements performed in the vicinity of a Cu magnetron target with Ar used as a buffer gas. Condensation of atomic metal vapours is found to occur mainly at several mm distance from the target plane. The NPs are found to be captured preferentially within a region circumscribed by the magnetron plasma ring. In this capture zone, the NPs grow to the size of 90 nm whereas smaller ones sized 10-20 nm may escape and constitute a NP beam. Time-resolved measurements of the discharge indicate that the electrostatic force acting on the charged NPs may be largely responsible for their capturing nearby the magnetron.

Efficacy of Plasma Treatment for Decontaminating Zirconia.

PURPOSE: To evaluate the influence of contamination and plasma treatment on the bond strength of resin to zirconia ceramic. MATERIALS AND METHODS: After immersion in saliva or the use of a silicone disclosing agent, polished and airborne-particle abraded zirconia specimens were cleaned either ultrasonically in 99% isopropanol or with nonthermal plasma. Uncontaminated zirconia specimens were used as control. For chemical analysis, specimens of all groups were examined with x-ray photoelectron spectroscopy (XPS). Plexiglas tubes filled with composite resin were bonded to ceramic specimens with a phosphate-monomer-containing luting resin. The influence of contamination and cleaning methods on ceramic bond durability was examined by tensile testing after 3 and 150 days of water storage, with an additional 37,500 thermocycles during the 150-day storage. RESULTS: XPS showed an increase in the amount of oxygen and a decrease in the amount of carbon on the zirconia surface after plasma treatment. After contamination with silicone, XPS revealed a high amount of Si residue on the surface that none of the investigated cleaning processes could completely remove. The tensile bond strength to uncontaminated zirconia ceramic was durable, but was significantly reduced by contamination. CONCLUSION: Plasma treatment was effective in removing salivary contamination but not silicone disclosing agent residue from the bonding surface of zirconia.

PdO/PdO2 functionalized ZnO : Pd films for lower operating temperature H2 gas sensing.

Noble metals and their oxide nano-clusters are considered to be the most promising candidates for fabricating advanced H2 gas sensors. Through this work, we propose a novel strategy to grow and modulate the density of PdO/PdO2 nanoparticles uniformly on nanostructured Pd-doped ZnO (ZnO : Pd) films by a one-step solution approach followed by thermal annealing at 650 °C, and thus to detect ppm-level H2 gas in a selective manner. The gas sensing properties of such hybridized materials showed that the PdO-functionalized ZnO samples offer significantly improved H2 gas sensing properties in an operating temperature range of 25-200 °C. The deposition of ZnO : Pd films via a simple synthesis from chemical solutions (SCS) approach with an aqueous bath (at relatively low temperatures, <95 °C) is reported. Furthermore, the functionalization of palladium oxide nanoclusters by a simple but highly effective approach on ZnO : Pd film surfaces was performed and is reported here for the first time. The morphological, structural, vibrational, optical, chemical, and electronic properties were studied in detail and the mixed phases of palladium oxide nanoclusters on the ZnO surface were found. Sensor studies of the ZnO : Pd samples (in the range of 25-350 °C operating temperature) showed good selectivity to H2 gas, especially in the range of higher temperatures (>150 °C, up to 350 °C); however, the PdO/PdO2 mixed phases of the nanocluster-modified surface ZnO : Pd films showed a much better selectivity to H2 gas, even at a lower operating temperature, in the range of 25-150 °C. For such PdO-functionalized ZnO : Pd films, even at room temperature, a gas response of ∼12.7 to 1000 ppm of H2 gas was obtained, without response to any other reducing gases or tested vapors. The large recovery time of the samples at room temperatures (>500 s) can be drastically reduced by applying higher bias voltages. Furthermore, we propose and discuss the gas sensing mechanism for these structures in detail. Our study demonstrates that surface functionalization with PdO/PdO2 mixed phase nanoclusters-nanoparticles (NPs) is much more effective than only the Pd doping of nanostructured ZnO films for selective sensing applications. This approach will pave a new way for the controlled functionalization of PdO/PdO2 nanoclusters on ZnO : Pd surfaces to the exact detection of highly explosive H2 gas under various atmospheres by using solid state gas sensors.

Single-step generation of metal-plasma polymer multicore@shell nanoparticles from the gas phase.

Nanoparticles composed of multiple silver cores and a plasma polymer shell (multicore@shell) were prepared in a single step with a gas aggregation cluster source operating with Ar/hexamethyldisiloxane mixtures and optionally oxygen. The size distribution of the metal inclusions as well as the chemical composition and the thickness of the shells were found to be controlled by the composition of the working gas mixture. Shell matrices ranging from organosilicon plasma polymer to nearly stoichiometric SiO2 were obtained. The method allows facile fabrication of multicore@shell nanoparticles with tailored functional properties, as demonstrated here with the optical response.

Single target sputter deposition of alloy nanoparticles with adjustable composition via a gas aggregation cluster source.

Alloy nanoparticles with variable compositions add a new dimension to nanoscience and have many applications. Here we suggest a novel approach for the fabrication of variable composition alloy nanoparticles that is based on a Haberland type gas aggregation cluster source with a custom-made multicomponent target for magnetron sputtering. The approach, which was demonstrated here for gold-rich AgAu nanoparticles, combines a narrow nanoparticle size distribution with in operando variation of composition via the gas pressure as well as highly efficient usage of target material. The latter is particularly attractive for precious metals. Varying argon pressure during deposition, we achieved in operando changes of AgAu alloy nanoparticle composition of more than 13 at%. The alloy nanoparticles were characterized by x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy. The characteristic plasmon resonances of multilayer nanoparticle composites were analyzed by UV-vis spectroscopy. Tuning of the number of particles per unit area (particle densities) within individual layers showed an additional degree of freedom to tailor the optical properties of multilayer nanocomposites. By extension of this technique to more complex systems, the presented results are expected to encourage and simplify further research based on plasmonic multi-element nanoparticles. The present method is by no means restricted to plasmonics or nanoparticle based applications, but is also highly relevant for conventional magnetron sputtering of alloys and can be extended to in operando control of alloy concentration by magnetic field.