Organic Capping Research Articles

Metallic nanoparticles irradiated by low-energy protons for radiation therapy: Are there significant physical effects to enhance the dose delivery?

To identify which physical properties of nanoparticles are correlated with the survival fraction of cells exposed in vitro to low-energy protons in combination with nanoparticles. The Geant4 simulation toolkit (version 10.3) was used to model nanoparticles of different sizes (5-50 nm) and materials (Ti, Zr, Hf, Ta, Au, Pt), with or without an organic capping ensuring biocompatibility and to irradiate them with 1.3 or 4 MeV protons and 5.3 MeV alpha particles. The spectra of secondary electrons inside and at the nanoparticle surface were computed, as well as electron yields, Auger and organic capping contribution, trapping in metal bulk and linear energy transfer profiles as a function of distance from the nanoparticle center. In a next step, an in silico cell model was designed and loaded with gold nanoparticles, according to experimental uptake values. Dose to the cell was evaluated macroscopically and microscopically in 100 × 100 × 100 nm³ voxels for different radiation qualities. The cell geometry showed that radiation enhancement is negligible for the gold concentration used and for any radiation quality. However, when the single nanoparticle geometry is considered, we observed a local LET in its vicinity considerably higher than for the water equivalent case (up to 5 keV/μm at the titanium nanoparticle surface compared to 2.5 keV/μm in the water case). The yield of secondary electrons per primary interaction with 1.3 MeV protons was found to be most favorable for titanium (1.54), platinum (1.44), and gold (1.32), although results for higher Z metals are probably underestimated due to the incomplete simulation of de-excitation cascade in outer shells. It was also found that the organic capping contributed mostly to the production of low-energy electrons, adding a spike of dose near the nanoparticle surface. Indeed, the yield for the coated gold nanoparticle increased to 1.53 when exposed to 1.3 MeV protons. Although most electrons are retained inside larger nanoparticles (50 nm), it was shown that their yield is comparable to smaller sizes and that the linear energy transfer profile is better. From a combination of ballistic and nanoparticle size factors, it was concluded that 10-nm gold nanoparticles were better inducers of additional cell killing than 5-nm gold nanoparticles, matching our previous in vitro study. Although effects from a physical standpoint are limited, the high linear energy transfer profile at the nanoparticle surface generates detrimental events in the cell, in particular ROS-induced damage and local heating.

Compound Quantum Dot-Perovskite Optical Absorbers on Graphene Enhancing Short-Wave Infrared Photodetection.

Colloidal quantum dots (QDs) combined with a graphene charge transducer promise to provide a photoconducting platform with high quantum efficiency and large intrinsic gain, yet compatible with cost-efficient polymer substrates. The response time in these devices is limited, however, and fast switching is only possible by sacrificing the high sensitivity. Furthermore, tuning the QD size toward infrared absorption using conventional organic capping ligands progressively reduces the device performance characteristics. Here we demonstrate methods to couple large QDs (>6 nm in diameter) with organometal halide perovskites, enabling hybrid graphene phototransistor arrays on plastic foils that simultaneously exhibit a specific detectivity of 5 × 1012 Jones and high video-frame-rate performance. PbI2 and CH3NH3I co-mediated ligand exchange in PbS QDs improves surface passivation and facilitates electronic transport, yielding faster charge recovery, whereas PbS QDs embedded into a CH3NH3PbI3 matrix produce spatially separated photocarriers leading to large gain.

Comparison between silver and gold nanoparticles stabilized with negatively charged hydrophilic thiols: SR-XPS and SERS as probes for structural differences and similarities

The electronic and molecular structure, as well as the chemical nature of noble metal (silver, gold) nanoparticles (AgNPs, AuNPs) stabilized by the negatively charged hydrophilic organic thiol Sodium 3-mercapto-1-propanesulfonate (3-MPS) has been probed combining Synchrotron Radiation-induced X-ray Photoelectron Spectroscopy (SR-XPS) and Surface Enhanced Raman Spectroscopy (SERS). Complementary information about the electronic, chemical and molecular structure is obtained combining SERS and XPS data, allowing to evidence structural similarities and differences related to the noble metal choice. These results coherently suggest the effective 3-MPS chemical absorption onto the nanoparticle surface, which allows to obtain a stable and biocompatible system, suitable for ad hoc further functionalization as required for several applications in biotechnology. It was observed that the NPs molecular overlayer is made up by covalent bonds between thiols and metallic surface atoms, without degradation of the molecule. The metals SR-XPS spectra analysis collected on the silver and gold nanoparticles points out a small surface to volume atomic percent ratio, as a consequence of the NPs size (≥5nm). Surface-enhanced Raman Scattering (SERS) spectroscopy was employed for the investigation of the NP molecular conjugation. SERS spectra acquired on the capped Ag and AuNPs are in very good agreement and suggest that the same organic layer is covering the NPs. The conjugation with 3-MPS is confirmed by comparing SERS data with the conventional Raman signature of the ligand. The reproducibility of SERS measurements overall points out the high purity and homogeneity of the system and the good integrity of the organic capping layer.

A Novel Photochemical Method for the Synthesis of Au Triangular Nanoplates inside Nanocavity of Mesoporous Silica Shells

We report a new photochemical method for tuning the shapes of gold nanoparticles inside nanocavity of mesoporous silica shells (mHSS) using Ag+ ions without using any convential organic capping ligands. mHSS acts as a nanocontainer and is used for entrapping the chloroauric acid molecules along with Ag+ ions. The shape of gold nanoparticles is tuned from spheres to triangular nanoplates inside mHSS by varying the molar ratio of [AuCl4–]/[Ag+] in the reaction. The results confirm that the presence of Ag+ ions promotes the growth of Au triangular nanoplates inside mHSS. The Au triangular nanoplates demonstrate superior catalytic activity than spherical Au nanoparticles.

Non-Colloidal Nanocatalysts Fabricated Using Arc Plasma Deposition and Their Application in Heterogenous Catalysis and Photocatalysis

To understand technologically complex catalytic systems and to tailor both activity and selectivity in heterogeneous catalysis and photocatalysis, there is the challenge of bridging the materials gap that exists between two- and three-dimensional model catalytic systems and real catalysts, which are comprised of highly dispersed, oxide-supported metal nanoparticles. While colloid nanoparticles synthesized using wet chemistry have the potential for tuning size, shape, and composition, there are complexities related to the organic capping layers. Therefore, the development of new model catalysts without a capping layer is crucial. Coaxial vacuum arc plasma deposition (APD) is a method to fabricate non-colloidal nanocatalysts that has the potential for large-scale synthesis of nanocatalysts and, at the same time, allows for systematic investigation of intrinsic factors that affect catalytic activity. In this article, we describe the fabrication of catalytic nanoparticles using APD, and their application in heterogeneous catalysis and photocatalysis research. Direct vaporization of metallic materials to deposit active materials on two-dimensional or three-dimensional oxide supports has drawn considerable interest due to its simplicity, high reproducibility, and the possibility for large-scale production. We highlight recent studies on metal–support interactions, the effect of doping on the oxide, and hot electron-driven chemical reactions. In the case of photocatalysis, APD was used to fabricate metal nanoparticles on a hierarchically porous oxide; enhanced hydrogen evolution by doping and porosity was also demonstrated. Therefore, the materials gap in catalysis can be bridged by the potential for large-scale synthesis of a variety of catalysts using APD.

Plasmonic Ag/AgCl‐modified bismuth subcarbonate with enhanced visible light photocatalytic activity

Plasmonic Ag/AgCl‐modified bismuth subcarbonate (Bi2O2CO3) composites were prepared by a multistep process with hydrothermal, deposition, and photoreduction in the absence of organic capping agents. The properties of the obtained Ag/AgCl/Bi2O2CO3 samples were characterized using X‐ray diffraction, field emission scanning electron microscopy and X‐ray photoelectron, UV–visible diffuse reflectance, and photoluminescence spectroscopies. The results reveal that Ag/AgCl nanoparticles are dispersed on the Bi2O2CO3 surface to achieve plasmonic Ag/AgCl/Bi2O2CO3. The Ag/AgCl/Bi2O2CO3 nanocomposites show improved rhodamine B (RhB) adsorption capacity and photocatalytic activity compared with pure Bi2O2CO3 and Ag/AgCl. In addition, the Ag/AgCl/Bi2O2CO3 composite with 20 wt% Ag/AgCl exhibits the highest photocatalytic activity and remains stable for the photodegradation of RhB under visible light. The enhanced photocatalytic activity of Ag/AgCl/Bi2O2CO3 may be attributed to the surface plasmon resonance effect of in situ generated Ag nanoparticles and synergistic effect of Ag/AgCl and Bi2O2CO3, which increase the separation efficiency of photogenerated electron–hole pairs under visible light irradiation.

Elemental mercury vapor chemoresistors employing TIO2 nanofibers photocatalytically decorated with Au-nanoparticles

The toxicity of mercury, its ubiquitous presence and the complexity of its cycle in the environment push for urgent actions at both local and global level to develop detection and monitoring systems characterized by fast responses, low cost, low maintenance and ease of use. As a result of the combination of gold affinity for mercury with the nanoscale size of the frameworks, gold nanostructures look the most promising nanomaterials for creating novel sensors with sensing features comparable to those of commercial complex and expensive analytical systems currently available. Composite nanofibrous electrospun layers of titania decorated with gold nanoparticles (AuNPs) were fabricated to obtain nanostructured materials capable of adsorbing elemental mercury. Linker-free gold nanoparticles were grown on the electrospun titania nanofibers through the photocatalytic reduction of tetrachloroauric acid carried out by UV-irradiated nanofibers of titania in the presence of an organic capping reagent. Chemoresistors employing such decorated nanomaterials were then created in order to detect mercury vapors in the atmosphere. Various decorations of titania nanofibers with gold nanoparticles deposited onto distinct substrates were morphologically investigated at nanoscale. The electrical properties of the resulting chemoresistors were assessed. The capacity of chemoresistors employing various amounts of AuNPs for detecting low concentrations of mercury vapors (tens of ppt) in both static and dynamic (i.e. under a carrier gas flow – synthetic air) conditions was tested. The potential of the resulting sensors in environmental monitoring of elemental mercury vapors is discussed.

Dense-plasma-driven ultrafast formation of FePt organization on silicon substrate

This article demonstrates the removal of organic capping and promotion of long-range 2D organization of chemically synthesized FePt nanoparticles dispersed on Si 〈100 〉 substrate by means of pulsed H+ energetic ion irradiation using a dense plasma focus (DPF) device. The irradiation of energetic H+ ions on FePt nanoparticles clearly resulted in enhanced structural and magnetic behaviour of the FePt nanoparticles as a function of plasma focused irradiation shots. Transmission electron microscopy (TEM)/scanning electron microscopy (SEM) images of the FePt nanoparticles clearly show a marked enhancement in average particle size from 2.5 nm for non-irradiated sample to about 28 nm for four plasma focus shots irradiation. The gradual removal of organic capping over chemically synthesized FePt nanoparticles with increasing plasma focus shots exposure is confirmed using Raman spectroscopy. A uniform 2D organization of bimetallic FePt nanoparticles over 1 cm × 1 cm silicon substrate is obtained with three plasma focus shots with better magnetic properties as compared with plasma-untreated FePt nanoparticles. Plasma focused irradiation shots

Tunable Room-Temperature Synthesis of Coinage Metal Chalcogenide Nanocrystals from N-Heterocyclic Carbene Synthons

We present a new toolset of precursors for semiconductor nanocrystal synthesis, N-heterocyclic carbene (NHC)-metal halide complexes, which enables a tunable molecular platform for the preparation of coinage metal chalcogenide quantum dots (QDs). Phase-pure and highly monodisperse coinage metal chalcogenide (Ag2E, Cu2–xE; E = S, Se) QDs are readily synthesized from the direct reaction of an NHC-MBr synthon (where M = Ag, Cu) with alkylsilyl chalcogenide reagents at room temperature. We demonstrate that the size of the resulting QDs is well-tailored by the electron-donating ability of the L-type NHC ligands, which are further confirmed to be the only organic capping ligands on the QD surface, imparting excellent colloidal stability. Local superstructures of the NHC-capped Ag2S QDs are observed by TEM, further demonstrating their potential for synthesizing monodisperse ensembles and mediating self-assembly.

Phonons in Hybrid Lamellar Supercrystals

Phonons in hybrid lamellar supercrystals are investigated by Raman scattering. Special attention is paid to low-frequency vibrations as a mean to shed some light onto the structure at the nanometer scale. In particular, little is known about the structure of the organic capping agents in supercrystals made of colloidal nanopoarticles. This is due to the fact that characterization tools such as electron microscopy and X-ray diffraction are mostly sensitive to the inorganic phase due to its larger electronic density. Raman scattering does not suffer from this limitation. In this class of materials, synthesized following the “benzyl alcohol route”, the inorganic layers are kept together by π–π conjugated interactions. Low-frequency Raman spectra have been measured for yttrium and neodymium oxide-based lamellar organic–inorganic supercrystals synthesized with three benzyl alcohol derivatives. The spectra strongly depend on the nature of both the inorganic and organic phase despite the resulting lamellar struc...

Regulating the Catalytic Function of Reduced Graphene Oxides Using Capping Agents for Metal-Free Catalysis.

Reduced graphene oxide (rGO) functionalized with organic capping agents has gained increasing attention as a promising metal-free catalyst. To optimize the properties of rGO for target applications, comprehending the link between the catalytic function of rGO and the chemical and structural characteristics of capping agents is critical. Herein, we report a systematic study on the effect of capping agents on the catalytic function of rGO for redox reactions using nitrogen-containing surface modifiers with distinctly different chemical structures, such as poly(diallyldimethylammonium chloride), cetyltrimethylammonium chloride, and poly(allylamine hydrochloride), which have the capability to endow rGO with improved suspension stability, enhanced reactant adsorption, and modified electronic properties. Functionalized rGOs were facilely prepared by the reduction of graphene oxide with hydrazine in the presence of the capping agents. The results of model redox reactions, that is, 4-nitrophenol and ferricyanide reduction reactions, catalyzed by the functionalized rGOs corroborated that the way the capping agents functionalize rGO, which is highly correlated with their chemical structure, drastically influences the overall reaction kinetics, including induction time, reduction rate, total reaction time, and reaction order. This strongly suggests that the judicious selection of capping agents is crucial to fully harness the catalytic function of rGO and thus to design novel rGO-based non-metallic catalysts with controllable reaction kinetics.

Nature of Active Sites and Their Quantitative Measurement in Two-Dimensional Pt Metal Catalysts

Quantitative measurement of the number of active surface sites on two-dimensional (2D) catalysts is one of the most crucial points in heterogeneous catalysis because it is used to determine the turnover frequency (TOF), which refers to the catalytic activity of model catalysts. However, because of the difficulty in identifying the effective active surface area on 2D heterogeneous catalysts, there is still the assumption that each metal atom is an active site. To shed light on these issues and to bridge the activity gaps between 2D and three-dimensional (3D) heterogeneous catalysts, we present an experimental approach that uses Pt nanoparticle (NP) arrays on a thin silicon wafer probed with CO pulse chemisorption, a widely used surface-sensitive technique, to determine the number of active sites and the area of the effective active surface. A Pt thin film and Pt NP arrays with two different NP sizes (i.e., 2.1 and 4.5 nm) were prepared as model systems for 2D catalysts. The effective active metal surface area determined using CO pulse chemisorption for these 2D catalysts is 53–79% of the apparent metal surface area that was obtained by measuring the surface area based on scanning electron microscopy images. This discrepancy between the active and apparent surface area is attributed to the presence of hydrocarbon contamination and organic capping layers on the catalysts. The results indicate that estimating the active sites of 2D catalysts by apparent surface area is reasonably in agreement with the number measured by chemisorption that is used to characterize 3D nanocatalysts. This experimental technique on 2D catalysts can be expected to provide information for extracting the true TOF of product molecules on 2D catalysts in gas-phase catalytic reactions.

Surface Functionalization of Metal Nanoparticles by Conjugated Metal-Ligand Interfacial Bonds: Impacts on Intraparticle Charge Transfer.

Noble metal nanoparticles represent a unique class of functional nanomaterials with physical and chemical properties that deviate markedly from those of their atomic and bulk forms. In order to stabilize the nanoparticles and further manipulate the materials properties, surface functionalization with organic molecules has been utilized as a powerful tool. Among those, mercapto derivatives have been used extensively as the ligands of choice for nanoparticle surface functionalization by taking advantage of the strong affinity of thiol moieties to transition metal surfaces forming (polar) metal-thiolate linkages. Yet, the nanoparticle material properties are generally discussed within the context of the two structural components, the metal cores and the organic capping layers, whereas the impacts of the metal-sulfur interfacial bonds are largely ignored because of the lack of interesting chemistry. In recent years, it has been found that metal nanoparticles may also be functionalized by stable metal-carbon (or even -nitrogen) covalent bonds. Because of the formation of dπ-pπ interactions between the transition-metal nanoparticles and terminal carbon moieties, the interfacial resistance at the metal-ligand interface is markedly reduced, leading to the emergence of unprecedented optical and electronic properties. In this Account, we summarize recent progress in the studies of metal nanoparticles functionalized by conjugated metal-ligand interfacial bonds that include metal-carbene (M═C) and metal-acetylide (M-C≡)/metal-vinylidene (M═C═C) bonds. Such interfacial bonds are readily formed by ligand self-assembly onto nanoparticle metal cores. The resulting nanoparticles exhibit apparent intraparticle charge delocalization between the particle-bound functional moieties, leading to the emergence of optical and electronic properties that are analogous to those of their dimeric counterparts, as manifested in spectroscopic and electrochemical measurements. This is first highlighted by ferrocene-functionalized nanoparticles that exhibit nanoparticle-mediated intervalence charge transfer (IVCT) among the particle-bound ferrocenyl moieties, as manifested in electrochemical and spectroscopic measurements. Such intraparticle charge delocalization has also been observed with other functional moieties such as pyrene and anthracene, where the photoluminescence emissions are consistent with those of their dimeric derivatives. Importantly, as such electronic communication occurs via a through-bond pathway, it may be readily manipulated by the valence states of the nanoparticle cores as well as specific binding of selective molecules/ions to the organic capping shells. These fundamental insights may be exploited for diverse applications, ranging from chemical sensing to (nano)electronics and fuel cell electrochemistry. Several examples are included, such as sensitive detection of nitroaromatic derivatives, metal cations, and fluoride anions by fluorophore-functionalized metal nanoparticles, fabrication of nanoparticle-bridged molecular dyads by, for instance, using nanoparticles cofunctionalized with 4-ethynyl-N,N-diphenyl-aniline (electron donor) and 9-vinylanthracene (electron acceptor), and enhanced electrocatalytic activity of acetylene derivatives-functionalized metal/alloy nanoparticles for oxygen reduction reaction by manipulation of the metal core electron density and hence interactions with reaction intermediates. We conclude this Account with a perspective where inspiration from conventional organometallic chemistry may be exploited for more complicated nanoparticle surface functionalization through the formation of diverse metal-nonmetal bonds. This is a unique platform for ready manipulation of nanoparticle properties and applications.

Enhanced electrocatalytic performance of an ultrafine AuPt nanoalloy framework embedded in graphene towards epinephrine sensing

A novel hierarchical nanoporous thin film of AuPt alloy embedded in graphene (AuPt@GR) was successfully synthesized through the self-assembly of ultrafine AuPt nanoparticles (~3nm) within GR sheets by means of a facile chemical vapor deposition (CVD) procedure without the use of any external organic capping agent and reducing agent. A binder-free sensor based on the AuPt@GR hybrid material was fabricated and its electrocatalytic activity was evaluated by using it to determine epinephrine (EP) in PBS solution (pH=7.4) and in human serum spiked PBS solution. Amperometric measurements of the sensor response showed an extremely low limit of detection (0.9nM at a signal-to-noise ratio of 3), high sensitivity (1628µAmM−1cm−2), wide linear detection range (1.5×10−9–9.6×10−6M), and negligible response to interferents. At the same time, the sensor also exhibited very long-term amperometric stability (4000s), cyclic voltammetric stability (500 cycles), good reproducibility, and highly accurate detection of EP in real samples. The excellent electrochemical performance was attributed to synergistic effects of Au, Pt, and GR as well as to the formation of a unique nanoporous structure that provided enhanced electrocatalytic activity, a highly electroactive surface, and fast mass transport. These results suggest strong potential of the AuPt@GR hybrids for use in biosensors and bioelectronic devices.

Porous Carbon-Supported Gold Nanoparticles for Oxygen Reduction Reaction: Effects of Nanoparticle Size.

Porous carbon-supported gold nanoparticles of varied sizes were prepared using thiolate-capped molecular Au25, Au38, and Au144 nanoclusters as precursors. The organic capping ligands were removed by pyrolysis at controlled temperatures, resulting in good dispersion of gold nanoparticles within the porous carbons, although the nanoparticle sizes were somewhat larger than those of the respective nanocluster precursors. The resulting nanocomposites displayed apparent activity in the electroreduction of oxygen in alkaline solutions, which increased with decreasing nanoparticle dimensions. Among the series of samples tested, the nanocomposite prepared with Au25 nanoclusters displayed the best activity, as manifested by the positive onset potential at +0.95 V vs RHE, remarkable sustainable stability, and high numbers of electron transfer at (3.60-3.92) at potentials from +0.50 to +0.80 V. The performance is comparable to that of commercial 20 wt % Pt/C. The results demonstrated the unique feasibility of porous carbon-supported gold nanoparticles as high-efficiency ORR catalysts.

Improved photoluminescence quantum yield and stability of CdSe-TOP, CdSe-ODA-TOPO, CdSe/CdS and CdSe/EP nanocomposites

Size-controllable monodisperse CdSe nanocrystals with different organic capping were prepared based on the hot-injection method. The effective separation of nucleation and growth was achieved by rapidly mixing two highly reactive precursors. As a contrast, we prepared CdSe/CdS nanocrystals (NCs) successfully based on the selective ion layer adsorption and reaction (SILAR) technique. This inorganic capping obtained higher photoluminescence quantum yield (PLQY) of 59.3% compared with organic capping of 40.8%. Furthermore, the CdSe-epoxy resin (EP) composites were prepared by adopting a flexible ex situ method, and showed excellent stability in the ambient environment for one year. So the composites with both high PLQY of nanocrystals and excellent stability are very promising to device application.

Silicon Quantum Dot Nanoparticles with Antifouling Coatings for Immunostaining on Live Cancer Cells.

Fluorescent silicon quantum dots (SiQDs) have shown a great potential as antiphotobleaching, nontoxic and biodegradable labels for various in vitro and in vivo applications. However, fabricating SiQDs with high water-solubility and high photoluminescence quantum yield (PLQY) remains a challenge. Furthermore, for targeted imaging, their surface chemistry has to be capable of conjugating to antibodies, as well as sufficiently antifouling. Herein, antibody-conjugated SiQD nanoparticles (SiQD-NPs) with antifouling coatings composed of bovine serum albumin (BSA) and polyethylene glycol (PEG) are demonstrated for immunostaining on live cancer cells. The monodisperse SiQD-NPs of diameter about 130 nm are synthesized by a novel top-down method, including electrochemical etching, photochemical hydrosilylation, high energy ball milling, and "selective-etching" in HNO3 and HF. Subsequently, the BSA and PEG are covalently grafted on to the SiQD-NP surface through presynthesized chemical linkers, resulting in a stable, hydrophilic, and antifouling organic capping layer with isothiocyanates as the terminal functional groups for facile conjugation to the antibodies. The in vitro cell viability assay reveals that the BSA-coated SiQD-NPs had exceptional biocompatibility, with minimal cytotoxicity at concentration up to 1600 μg mL(-1). Under 365 nm excitation, the SiQD-NP colloid emits bright reddish photoluminescence with PLQY = 45-55% in organic solvent and 5-10% in aqueous buffer. Finally, through confocal fluorescent imaging and flow cytometry analysis, the anti-HER2 conjugated SiQD-NPs show obvious specific binding to the HER2-overexpressing SKOV3 cells and negligible nonspecific binding to the HER2-nonexpressing CHO cells. Under similar experimental conditions, the immunofluorescence results obtained with the SiQD-NPs are comparable to those using conventional fluorescein isothiocyanate (FITC).

Porous Au–Ag Nanospheres with High-Density and Highly Accessible Hotspots for SERS Analysis

Colloidal plasmonic metal nanoparticles have enabled surface-enhanced Raman scattering (SERS) for a variety of analytical applications. While great efforts have been made to create hotspots for amplifying Raman signals, it remains a great challenge to ensure their high density and accessibility for improved sensitivity of the analysis. Here we report a dealloying process for the fabrication of porous Au-Ag alloy nanoparticles containing abundant inherent hotspots, which were encased in ultrathin hollow silica shells so that the need of conventional organic capping ligands for stabilization is eliminated, producing colloidal plasmonic nanoparticles with clean surface and thus high accessibility of the hotspots. As a result, these novel nanostructures show excellent SERS activity with an enhancement factor of ∼1.3 × 10(7) on a single particle basis (off-resonant condition), promising high applicability in many SERS-based analytical and biomedical applications.

Hydrogenation of nitroarenes into aromatic amines over Ag@BCN colloidal catalysts

The present work reports that two-dimension layered ternary boron carbon nitrogen nanosheets can serve as good carriers to support and disperse noble metal nanoparticles. The Ag@BCN colloids have thus been prepared by attaching Ag nanoparticles on the surfaces of BCN nanosheets. The detailed structures of the Ag@BCN samples were investigated by X-ray diffraction, transmission electron microscopy, atomic force microscope, infrared, and X-ray photoelectron spectroscopy. It is found that the surface NH groups of BCN nanosheets are beneficial for the attachment of Ag nanopaprticles. Compared with the conventional organic capping compounds, the two dimensional planar BCN nanosheets endow the attached nanoparticle with the high active surfaces. Moreover, the hydrogenation of nitroarenes into the corresponding aromatic amines can be highly achieved over Ag@BCN colloids by NaBH4. In particular, the apparent activation energy of the conversion reaction of p-nitroaniline to p-phenylenediamine was found to be 76.0kJ/mol over the Ag@BCN colloids with 3wt% Ag content. Our results may provide a new approach for the design noble metal based composites and find the practical application for the hydrogenation of nitroarenes.

Temperature and layer thickness dependent in situ investigations on epindolidione organic thin-film transistors

We report on in situ performance evaluations as a function of layer thickness and substrate temperature for bottom-gate, bottom-gold contact epindolidione organic thin-film transistors on various gate dielectrics. Experiments were carried out under ultra-high vacuum conditions, enabling quasi-simultaneous electrical and surface analysis. Auger electron spectroscopy and thermal desorption spectroscopy (TDS) were applied to characterize the quality of the substrate surface and the thermal stability of the organic films. Ex situ atomic force microscopy (AFM) was used to gain additional information on the layer formation and surface morphology of the hydrogen-bonded organic pigment. The examined gate dielectrics included SiO2, in its untreated and sputtered forms, as well as the spin-coated organic capping layers poly(vinyl-cinnamate) (PVCi) and poly((±)endo,exo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, diphenylester) (PNDPE, from the class of polynorbornenes). TDS and AFM revealed Volmer-Weber island growth dominated film formation with no evidence of a subjacent wetting layer. This growth mode is responsible for the comparably high coverage required for transistor behavior at 90–95% of a monolayer composed of standing molecules. Surface sputtering and an increased sample temperature during epindolidione deposition augmented the surface diffusion of adsorbing molecules and therefore led to a lower number of better-ordered islands. Consequently, while the onset of charge transport was delayed, higher saturation mobility was obtained. The highest, bottom-contact configuration, mobilities of approximately 2.5×10−3cm2/Vs were found for high coverages (50nm) on sputtered samples. The coverage dependence of the mobility showed very different characteristics for the different gate dielectrics, while the change of the threshold voltage with coverage was approximately the same for all systems. An apparent decrease of the mobility with increasing coverage on the less polar PNDPE was attributed to a change in molecular orientation from upright standing in the thin-film phase to tilted in the bulk phase. From temperature-dependent mobility measurements we calculated activation barriers for the charge transport between 110meV and 160meV, depending on the dielectric configuration.