Search

We report solid iodine as a precursor additive for achieving purified organometallic perovskite crystals. By adding iodine, we found that the reaction can be pushed toward pure iodine phase rather than the kinetically favored chlorine phase. This approach can be applied in large crystalline perovskite solar cells and improved the average efficiency from 9.83% to 15.58%.

The gelation behavior of Nafion dispersions was investigated using small-angle neutron scattering to better understand the mechanical toughness of dispersion-cast Nafion membranes. Three types of gelation were observed, depending on dispersing fluids: (i) homogeneous, thermally reversible gelation that was present in most aprotic polar dispersing fluids; (ii) inhomogeneous, thermally irreversible gelation as films, found in alcohols; and (iii) inhomogeneous, thermally irreversible gelation which precipitates in water/monohydric alcohol mixtures. The mechanical toughness of dispersion-cast Nafion membranes depends on the dispersing fluid, varying by more than 4 orders of magnitude. Excellent correlation between the critical gelation concentration and mechanical toughness was demonstrated with the Nafion membranes cast at 140 °C. Additional thermal effects among Nafion membranes cast at 190 °C were qualitatively related to the boiling point of dispersing fluids. Little correlation between mechanical toughne...

Increased oxygen reduction reaction (ORR) kinetics, improved CO tolerance, and more efficient water and heat management represent significant advantages that high-temperature polymer electrolyte fuel cells (HT-PEFCs) operating with a phosphoric acid-doped polybenzimidazole (PBI) membrane offer over traditional Nafion-based, low-temperature PEFCs. However, before such HT-PEFCs become viable, the detrimental effect of phosphate chemisorption on the performance of state-of-the-art Pt-based cathode catalysts needs to be addressed. In this study, we propose a solution to the severe poisoning of Pt-based PEFC cathode catalysts with phosphates (H2PO4– and HPO42–) by replacing standard Pt/C catalysts with phosphate-tolerant, nonprecious metal catalyst (NPMC) formulations. Catalysts with a very high surface area (845 m2 g–1) were synthesized in this work from polyaniline (PANI), iron, and carbon using a high-temperature approach. The effects of metal precursors and metal loading on the morphology, structure, and O...

Structure-property-performance relationships of disulfonated poly(arylene ether sulfone) multiblock copolymer membranes were investigated for their use in direct methanol fuel cell (DMFC) applications. Multiple series of reactive polysulfone, polyketone, and polynitrile hydrophobic block segments having different block lengths and molecular composition were synthesized and reacted with a disulfonated poly(arylene ether sulfone) hydrophilic block segment by a coupling reaction. Large-scale morphological order of the multiblock copolymers evolved with the increase of block size that gave notable influence on mechanical toughness, water uptake, and proton/methanol transport. Chemical structural changes of the hydrophobic blocks through polar group, fluorination, and bisphenol type allowed further control of the specific properties. DMFC performance was analyzed to elicit the impact of structural variations of the multiblock copolymers. Finally, DMFC performances of selected multiblock copolymers were compared against that of the industrial standard Nafion in the DMFC system.

A composite anode consisting of hollow SnO2 microspheres covered by glass-like B2O3 layers was prepared via a combined hydrothermal-impregnation method, which results in much improved electrochemical performance in lithium ion batteries, relative to pristine SnO2 anodes. The cycling and rate capabilities of the SnO2–B2O3 composite anodes were investigated as a function of B2O3 content. The balance between increased electron-acceptor effect and compromised electronic conductivity due to addition of B2O3 is maximized around 20 wt% B2O3 loading. The best performing SnO2–B2O3 composite anode exhibits a specific capacity of 622.7 mAh g−1 up to 160 cycles, and is able to maintain a capacity above 528.6 mAh g−1 at rate of 5C. These enhanced performance characteristics are attributed to the unique composite structures consisting of the hollow SnO2 cores and the B2O3 buffer layers, which likely are beneficial for reducing the overall volume changes. Importantly, the decreased charge transfer resistance and increased Li+ diffusion coefficient, resulting from B2O3 coating, lead to overall improvement of rate performance for the composite anodes. Such-fabricated composite structures are stable during the Li+ insertion/extraction, thereby promoting cycling stability.

In contrast to neat ammonia-borane (AB), the thermal decomposition of AB with N-substituted amine-boranes yields a liquid product after extended heating and H2 release. NMR and GPC data indicate that co-oligomerization has occurred. These results show promise for developing high energy density AB-based fuel formulations for automotive applications.

A major, unprecedented improvement in the durability of polymer electrolyte membrane fuel cells is obtained by tuning the properties of the interface between the catalyst and the ionomer by choosing the appropriate dispersing medium. While a fuel cell cathode prepared from aqueous dispersion showed 90 mV loss at 0.8 A cm(-2) after 30,000 potential cycles (0.6-1.0 V), a fuel cell cathode prepared from glycerol dispersion exhibited only 20 mV loss after 70,000 cycles. This minimum performance loss occurs even though there was an over 80% reduction of electrochemical surface area of the Pt catalyst. These findings indicate that a proper understanding and control of the catalyst-water-ionomer (three-phase) interfaces is even more important for maintaining fuel cell durability in typical electrodes than catalyst agglomeration, and this opens up a novel path for tailoring the functional properties of electrified interfaces.

Using thick-shell or "giant" CdSe/CdS nanocrystal quantum dots (g-NQDs), characterized by strongly suppressed Auger recombination, we studied the influence of plasmonic interactions on multiexciton emission. Specifically, we assessed the separate effects of plasmonic absorption and plasmonic emission enhancement by a systematic analysis of the pump fluence dependence of low-temperature photoluminescence (low-T PL) derived from individual CdSe/CdS g-NQDs deposited on nanoroughened silver films. Our study reveals that (1) the multiexciton (MX) emissions in g-NQD coupled to silver films were enhanced not only through the creation of more excitons via enhancement of absorption but also through the direct modification of the competition between the radiative and nonradiative recombination processes of MXs; (2) strong enhancement in absorption is not necessary for strong multiexciton emission; and (3) the emission of MXs can become stronger with the increase of multiexciton order. We also exploited the strong enhancement of MX emission to perform second-order photon correlation and cross-correlation experiments using very low pump fluences and observed a strong photon bunching that decays with increasing pump fluence.

Removal of intercalated water within graphitic sheets is critical to achieving high-performing oxygen reduction reaction catalysts., Graphitic materials are essential in energy conversion and storage because of their excellent chemical and electrical properties. The strategy for obtaining functional graphitic materials involves graphite oxidation and subsequent dissolution in aqueous media, forming graphene-oxide nanosheets (GNs). Restacked GNs contain substantial intercalated water that can react with heteroatom dopants or the graphene lattice during reduction. We demonstrate that removal of intercalated water using simple solvent treatments causes significant structural reorganization, substantially affecting the oxygen reduction reaction (ORR) activity and stability of nitrogen-doped graphitic systems. Amid contrasting reports describing the ORR activity of GN-based catalysts in alkaline electrolytes, we demonstrate superior activity in an acidic electrolyte with an onset potential of ~0.9 V, a half-wave potential (E½) of 0.71 V, and a selectivity for four-electron reduction of >95%. Further, durability testing showed E½ retention >95% in N2- and O2-saturated solutions after 2000 cycles, demonstrating the highest ORR activity and stability reported to date for GN-based electrocatalysts in acidic media.

Macrophage Cells Secrete Specific Cytokines and Accumulate Activated Interferon Regulatory Factor 3 after Multi-Walled Carbon Nanotube Exposure The health consequences of human exposure to carbon-based nanomaterials are not fully understood and the effects that such materials have on the immune system have not been adequately characterized. To determine if the innate immune system is modulated by exposure to carbon-based nanomaterials, the extracellular accumulation of an array of cytokines was measured in cell culture media obtained from mouse macrophage cells (RAW264.7) following exposure to carbon nanotubes (CNTs) or fullerene (C60). Accumulation of a specific subset of cytokines was observed after exposure to multi-walled CNTs (MWCNT), but was not observed when cells were exposed to single-walled CNTs (SWCNTs) or C60. Additionally, the accumulation of the activated (phosphorylated) form of the interferon regulatory factor 3 (IRF3) transcription factor and associated interferon beta (IFNβ) was observed after MWCNT exposure. These data suggest that IRF3 is a mediator of MWCNTactivated signal transduction pathways in macrophage cells. Furthermore, our data show that MWCNTs induce an innate immune response at subtoxic doses and suggests that MWCNT exposure may result in chronic inflammation and compromised immunity.

Rapidly dip-coating a silicon substrate in an acetaminophen solution creates a thin film of polymorphic nuclei, and the relative amounts of each polymorph vary with the type of solvent. Polarized light microscopy (PLM) revealed that all films were initially amorphous and gradually crystallized over time scales of minutes to hours. Fourier transform infrared spectroscopy (FTIR) was used to identify the polymorphic form during crystallization and weeks after apparent stabilization of growth. Crystallites that initially nucleated from the amorphous films were found to be the metastable orthorhombic form. Over time, the orthorhombic crystallites stopped growing and the remaining amorphous regions transformed to the stable monoclinic form. The choice of solvent determined how fast the orthorhombic crystallites grew and thus controlled the polymorphic character of the film. For example, dip-coating from an ethanol solution produced a largely orthorhombic film, while water yielded a film with mixed character. Ki...

In this work, we present a synthesis approach for nitrogen-doped graphene-sheet-like nanostructures via the graphitization of a heteroatom polymer, in particular, polyaniline, under the catalysis of a cobalt species using multiwalled carbon nanotubes (MWNTs) as a supporting template. The graphene-rich composite catalysts (Co-N-MWNTs) exhibit substantially improved activity for oxygen reduction in nonaqueous lithium-ion electrolyte as compared to those of currently used carbon blacks and Pt/carbon catalysts, evidenced by both rotating disk electrode and Li-O(2) battery experiments. The synthesis-structure-activity correlations for the graphene nanostructures were explored by tuning their synthetic chemistry (support, nitrogen precursor, heating temperature, and transition metal type and content) to investigate how the resulting morphology and nitrogen-doping functionalities (e.g., pyridinic, pyrrolic, and quaternary) influence the catalyst activity. In particular, an optimal temperature for heat treatment during synthesis is critical to creating a high-surface-area catalyst with favorable nitrogen doping. The sole Co phase, Co(9)S(8), was present in the catalyst but plays a negligible role in ORR. Nevertheless, the addition of Co species in the synthesis is indispensable for achieving high activity, due to its effects on the final catalyst morphology and structure, including surface area, nitrogen doping, and graphene formation. This new route for the preparation of a nitrogen-doped graphene nanocomposite with carbon nanotube offers synthetic control of morphology and nitrogen functionality and shows promise for applications in nonaqueous oxygen reduction electrocatalysis for Li-O(2) battery cathodes.

Conducting polymer (polyaniline) sheets are shown to be active substrates to promote the growth of nanostructured silver thin films with highly tunable morphologies. Using the spontaneous electroless deposition of silver, we show that a range of nanostructured metallic features can be controllably and reproducibly formed over large surface areas. The structural morphology of the resulting metal-polymer nanocomposite is demonstrated to be sensitive to experimental parameters such as ion concentration, temperature, and polymer processing and can range from densely packed oblate nanosheets to bulk crystalline metals. The deposition mechanisms are explained using a diffusion-limited aggregation (DLA) model to describe the semi-fractal-like growth of the metal nanostructures. We find these composite films to exhibit strong surface-enhanced Raman (SERS) activity, and the nanostructured features are optimized with respect to SERS activity using a self-assembled monolayer of mercapto-benzoic acid as a model Raman reporter. SERS enhancements are estimated to be on the order of 10(7). Through micro-Raman SERS mapping, these materials are shown to exhibit uniform SERS responses over macroscopic areas. These metal-polymer nanocomposites benefit from the underlying polymer's processability to yield SERS-active materials of almost limitless shape and size and show significant promise for future SERS-based sensing and detection schemes.

We report here an efficient noncovalent chemical route to dense and uniform assembly of magnetic nanoparticles onto multi-walled carbon nanotubes within a single-layer configuration. While preserving the electrical conduction behavior of the nanotube network itself, the resulting carbon nanotube derivatives exhibit a distinct superparamagnetism, and can be magnetically manipulated via a quick and reversible mode.

We describe here a one-step synthesis of hybrid metal nanoparticles (MNPs) and polymer composites on glass substrates using poly(vinyl pyrrolidone) (PVP) as both the reducing agent and polymer matrix. With this method, it takes only one minute to produce a nanocomposite thin film that contains MNPs with controlled size and morphology. The size and morphology of gold nanoparticles can be manipulated by simply modulating the ratio between the PVP and the Au precursor, while the nearly monodispersed spherical silver nanoparticles are insensitive to the reaction conditions, which is believed to result from a better control over the crystal structure of the Ag seeds than that of the Au seeds in the presence of PVP. Moreover, the resulting MNP–polymer composites are high-quality thin films with tunable optical properties—the λmax of absorption spectra changes from 480 nm to greater than 580 nm (from blue to red color). This environmentally friendly synthetic technique may open up a new avenue for facile nanomaterial synthesis that is not accessible by conventional solution chemistry.

SERS-active silver hierarchical assemblies are synthesized in solution by the assistance of small acid molecules. We here demonstrate the acid-directed self-assembly of metal nanoparticles (MNPs) into large systems with complex structures, without the application of any polymer surfactant or capping agent. It is verified that small acid molecules (citric acid, mandelic acid, etc.) incorporated into conventional solution chemistry can direct the assembly of MNPs into well-defined hierarchical structures. The constructed assembled structures with highly roughened surfaces can be highly sensitive SERS platforms, and the fabricated core–shell Ag wires show especially high SERS sensitivity toward the analyte melamine. The prepared Ag particles with hierarchical structures show no evident polarization-dependent SERS behavior, and this isotropic feature may be an advantage for highly sensitive SERS tags, since no certain incident polarization is required for molecule detection. We believe the subsequent addition of acid to induce formation of self-assembled structures can be a general synthetic platform to fabricate metal structures with complex morphologies.

We report a facile synthesis of large-area homogeneous three-dimensional (3D) Ag nanostructures on Au-supported polyaniline (PANI) membranes through a direct chemical reduction of metal ions by PANI. The citric acid absorbed on the Au nuclei that are prefabricated on PANI membranes directs Ag nanoaprticles (AgNPs) to self-assemble into 3D Ag nanosheet structures. The fabricated hybrid metal nanostructures display uniform surface-enhanced Raman scattering (SERS) responses throughout the whole surface area, with an average enhancement factor of 10(6)-10(7). The nanocavities formed by the stereotypical stacking of these Ag nanosheets and the junctions and gaps between two neighboring AgNPs are believed to be responsible for the strong SERS response upon plasmon absorption. These homogeneous metal nanostructure decorated PANI membranes can be used as highly efficient SERS substrates for sensitive detection of chemical and biological analytes.

We report a facile synthesis of silver nanoparticles (AgNPs) by using a new reducing agent, pretreated N-methyl-pyrrolidone (NMP*). The resulting AgNPs are characterized by using UV−vis, TEM, and X-ray spectroscopy. These AgNPs exhibit strong surface enhanced Raman scattering response on addition of 4-mercaptobenzoic acid. A possible redox mechanism involving silver ion and NMP* was proposed. The oxidized species resulting from thermally treated NMP/O2 were analyzed by nuclear magnetic resonance and gas chromatography techniques, and it was determined that 5-hydroxy-N-methyl-2-pyrrolidone played the role of reducing agent. The facile synthesis of functional metal nanoparticles via an environmentally friendly procedure with control in particle size, and understanding of the reaction mechanisms pave the ways to further developing metal nanoparticles for chemical and biological detections.

Electrode structure within PEFCs, including the Pt-ionomer interface, is created while making electrodes from catalyst inks based on ionomer dispersed in solvent. The relationship between final electrode structure and processing conditions is poorly understood. We have varied the solvent used in cathode catalyst inks, and then subjected the resulting MEAs to hydrogen-air performance and durability testing. Specifically, cathodes cast from inks based on inonomer dispersions in water-propanol-isopropanol (W/P cathode) initially perform better than cathodes cast from glycerol-based dispersions (Gly cathode), but are far less durable. After 10,000 potential cycles from 0.60 V to 1.0 V in N2, the performance on air of the W/P cathode falls significantly below that of the Gly cathode. NMR and neutron scattering measurements of ionomer dispersions, as well as AFM and TEM data from cast ionomer films, offer insight into how the effect of solvent choice on the ionomer structure may impact durability.

We present a strategy for the synthesis of multiplexed spectral encoder beads based on combinations of different surface enhanced Raman (SERS) signatures generated by dye-functionalized Ag nanoparticle tags. A key problem in SERS-based multiplexing arises in balancing the competitive binding of different signal generating dyes to the nanoparticle surfaces, which leads to difficulty in generating final summation spectra by design. We avoid this complication by decoupling the formation of individual tags from multiplexing of their spectra by self-assembly of different tag combinations onto SiO(2) microbead supports via biotin-avidin binding. Linear combinations of individual nanoparticle tag spectra are generated in precursor solutions and are found to directly translate to the final encoder bead fingerprint spectrum in a 1:1 binding stoichiometry that preserves the original solution ratios. The result is an ability to multiplex spectral signatures in both frequency and intensity space to generate a large number of unique encoder signatures from a limited number of initial tag spectra. Raman microscopy of 75 individual beads shows that spectral response is highly uniform from bead-to-bead, making the encoder assemblies suitable for highly multiplexed bioassay applications and as model systems for cellular surface labeling studies for imaging and immunoassays.

We report here the preparation of nanostructured polypyrroles (PPys) with different morphologies (nanospherical or nanofibrillar) through a surfactant-assisted oxidative polymerization route. Nanofibrillar PPy has a higher redox current, presumably due to a higher surface area accessible to the electrolytes and a lower charge transfer resistance compared to that of the spherical PPy. The impedance spectrum of spherical PPy at lower frequencies suggests a semi-infinite diffusion process, while nanofibrillar PPy displays barrier diffusion and capacitor characteristics. Electrodeless (chemical) deposition of Au particles from AuCl 4 − aqueous solution using nanostructured PPy also shows different morphologies, presumably due to a difference in growth kinetics dominated by the differences in surface area and surface chemistry. Our work demonstrates control over the electrochemical responses and charge transfer mechanisms of these conducting polymers. This control arises from their unique length scale geometries and surface areas that allows for the fabrication of Au nanoparticles with tunable morphologies. Our work in the controlled synthesis of nanostructured conducting polymers and metal nanoparticles opens up new opportunities for nanofiber-based electronic and sensory devices.

We describe a plasmonic crystal device possessing utility for optically transducing chemical forces. The device couples complex plasmonic fields to chemical changes via a chemoresponsive, surface-bound hydrogel. We find that this architecture significantly enhances the spectroscopic responses seen at visible wavelengths while enabling capacities for sensitive signal transduction, even in cases that involve essentially no change in refractive index, thus allowing analytical detection via colorimetric assays in both imaging and spectroscopic modes.

Isolation and purification of single-walled carbon nanotubes (SWCNTs) are prerequisites for their implementation in various applications. In this work, we present a fast (similar to 5 min), low-cost, and easily scalable bench-top approach to the extraction of high-quality isolated SWCNTs from bundles and impurities in an aqueous dispersion. The extraction procedure, based on aqueous two-phase (ATP) separation, is widely applicable to any SWCNT source (tested on samples up to 1.7 nm in diameter) and independent of defect density, purity, diameter, and length. The extracted dispersions demonstrate that the removal of large aggregates, small bundles, and impurities is comparable to that by density gradient ultracentrifugation, but without the need for high-end instrumentation. Raman and fluorescence-excitation spectroscopy, single-nanotube fluorescence imaging, atomic force and transmission electron microscopy, and thermogravimetric analysis all confirm the high purity of the isolated SWCNTs. By predispersing the SWCNTs without sonication (only gentle stirring), full-length, pristine SWCNTs can be isolated (tested up to 20 mu m). Hence, this simple ATP method will find immediate application in the generation of SWCNT materials for all levels of nanotube research and applications, from fundamental studies to high-performance devices.

We developed a class of quasi-3D plasmonic crystal that consists of multilayered, regular arrays of subwavelength metal nanostructures. The complex, highly sensitive structure of the optical transmission spectra of these crystals makes them especially well suited for sensing applications. Coupled with quantitative electrodynamics modeling of their optical response, they enable full multiwavelength spectroscopic detection of molecular binding events with sensitivities that correspond to small fractions of a monolayer. The high degree of spatial uniformity of the crystals, formed by a soft nanoimprint technique, provides the ability to image binding events over large areas with micrometer spatial resolution. These features, together with compact form factors, low-cost fabrication procedures, simple readout apparatus, and ability for direct integration into microfluidic networks and arrays, suggest promise for these devices in label-free bioanalytical detection systems.

Secondary electron emission is developed as a means to quantify and image protein binding to Au surfaces modified with patterned organic thin-film arrays. Alkane thiols were patterned via microcontact printing on gold, and their effects on the secondary electron (SE) yield of the surface, systematically quantified. We show that a self-assembled monolayer (SAM) of hexadecane thiol significantly increases the SE yield over the native gold surface, a yield that increases as a function of alkane chain length (C8−C16). This effect is linearly correlated with the surface potentials and wetting properties of these SAMs. Surface layers comprised of poly(ethylene glycol) (PEG) grafted polyacrylamide polymers behave differently, affecting the SE yield by attenuation according to the polymer thickness. These results demonstrate the relative contributions of factors related to the adsorbate molecular structures that serve to strongly mediate the SE yield, providing a foundation for exploiting them as a quantitative e...

We describe a theoretical analysis of the structures of self-organizing nanoparticles formed by Pt and Ru-Pt on carbon support. The calculations provide insights into the nature of these metal particle systems-ones of current interest for use as the electrocatalytic materials of direct oxidation fuel cells-and clarify complex behaviors noted in earlier experimental studies. With clusters deposited via metallo-organic Pt or PtRu(5) complexes, previous experiments [Nashner et al. J. Am. Chem. Soc. 1997, 119, 7760; Nashner et al. J. Am. Chem. Soc. 1998, 120, 8093; Frenkel et al. J. Phys. Chem. B 2001, 105, 12689] showed that the Pt and Pt-Ru based clusters are formed with fcc(111)-stacked cuboctahedral geometry and essentially bulklike metal-metal bond lengths, even for the smallest (few atom) nanoparticles for which the average coordination number is much smaller than that in the bulk, and that Pt in bimetallic [PtRu(5)] clusters segregates to the ambient surface of the supported nanoparticles. We explain these observations and characterize the cluster structures and bond length distributions using density functional theory calculations with graphite as a model for the support. The present study reveals the origin of the observed metal-metal bond length disorder, distinctively different for each system, and demonstrates the profound consequences that result from the cluster/carbon-support interactions and their key role in the structure and electronic properties of supported metallic nanoparticles.

We describe in this report the preparation, structural characterization, and phase behaviors exhibited by supported metallic and bimetallic nanoparticles. Homometallic nanoparticles of either Pt or Ru were synthesized by the reduction of various precursors ((CH3)2Pt(COD), H2PtCl6, and RuCl3) onto different carbon supports: Vulcan XC-72 (VXC) and Shawinigan Acetylene Black (SAB). The choice of precursor has a large structural influence on the reductive condensation of the Pt metal particles. All of the various precursors and supports produced particles with very similar size distributions, with the exception of (CH3)2Pt(COD), which formed a complex distribution of small (20 A) and large (>50 A) particles. The centerpiece of this study is the characterization of the growth behaviors seen in the synthesis of binary Pt−Ru nanoparticles. These heterometallic particles were synthesized via a seeded reductive condensation of one metal precursor onto pre-supported nanoparticles of a second metal; the latter serv...

An apparatus is described for the automated collection of luminescence emission decay curves over a wide range of analyte concentrations. The decay curves allow for determination of the excited-state lifetime or calculated steady-state intensity of a luminophore as a function of the analyte concentration. The data presented here demonstrate the use of the apparatus for pH titrations.

Surface plasmon assisted catalysis (SPAC) reactions of 4-aminothiophenol (4ATP) to and back from 4,4'-dimercaptoazobenzene (DMAB) have been investigated by single particle surface enhanced Raman spectroscopy, using a self-designed gas flow cell to control the reductive/oxidative environment over the reactions. Conversion of 4ATP into DMAB is induced by energy transfer (plasmonic heating) from surface plasmon resonance to 4ATP, where O₂ (as an electron acceptor) is essential and H₂O (as a base) can accelerate the reaction. In contrast, hot electron (from surface plasmon decay) induction drives the reverse reaction of DMAB to 4ATP, where H₂O (or H₂) acts as the hydrogen source. More interestingly, the cyclic redox between 4ATP and DMAB by SPAC approach has been demonstrated. This SPAC methodology presents a unique platform for studying chemical reactions that are not possible under standard synthetic conditions.

Here we demonstrate, for the first time, the fabrication of Au nanostructures on polyaniline (PANI) membrane surfaces for surface enhanced Raman spectroscopy (SERS) applications, through a direct chemical reduction by PANI. Introduction of acids into the HAuCl(4) solution leads to homogeneous Au structures on the PANI surfaces, which show only sub-ppm detection levels toward the target analyte, 4-mercaptobenzoic acid (4-MBA), because of limited surface area and lack of surface roughness. Thorny Au nanostructures can be obtained through controlled reaction conditions and the addition of a capping agent poly (vinyl pyrrolidone) (PVP) in the HAuCl(4) solution and the temperature kept at 80 °C in an oven. Those thorny Au nanostructures, with higher surface areas and unique geometric feature, show a SERS detection sensitivity of 1 × 10(-9) M (sub-ppb level) toward two different analyte molecules, 4-MBA and Rhodamine B, demonstrating their generality for SERS applications. These highly sensitive SERS-active substrates offer novel robust structures for trace detection of chemical and biological analytes.

We demonstrate that photon antibunching observed for individual nanocrystal quantum dots (NQDs) can be transformed into photon bunching characterized by super-Poissonian statistics when they are coupled to metal nanostructures (MNs). This observation indicates that, while the quantum yield of a biexciton (${Q}_{2\mathrm{X}}$) is lower than that of a single exciton (${Q}_{1\mathrm{X}}$) in freestanding NQDs, ${Q}_{2\mathrm{X}}$ becomes greater than ${Q}_{1\mathrm{X}}$ in NQDs coupled to MNs. This unique phenomenon is attributed to metal-induced quenching with a rate that scales more slowly with exciton multiplicity than the radiative decay rate and dominates over other nonradiative decay channels for both single excitons and biexcitons.

The growth of heteroepitaxially strained semiconductors at the nanoscale enables tailoring of material properties for enhanced device performance. For core/shell nanowires (NWs), theoretical predictions of the coherency limits and the implications they carry remain uncertain without proper identification of the mechanisms by which strains relax. We present here for the Ge/Si core/shell NW system the first experimental measurement of critical shell thickness for strain relaxation in a semiconductor NW heterostructure and the identification of the relaxation mechanisms. Axial and tangential strain relief is initiated by the formation of periodic a/2 ⟨110⟩ perfect dislocations via nucleation and glide on {111} slip-planes. Glide of dislocation segments is directly confirmed by real-time in situ transmission electron microscope observations and by dislocation dynamics simulations. Further shell growth leads to roughening and grain formation which provides additional strain relief. As a consequence of core/shell strain sharing in NWs, a 16 nm radius Ge NW with a 3 nm Si shell is shown to accommodate 3% coherent strain at equilibrium, a factor of 3 increase over the 1 nm equilibrium critical thickness for planar Si/Ge heteroepitaxial growth.

We demonstrate that sub-Poissonian statistics (photon antibunching) of photon emission from individual core-shell quantum dots can be transformed to super-Poissonian statistics (photon bunching) by coupling dots to a rough silver film

A new non-precious metal oxygen reduction catalyst was developed via heat treatment of in situ polymerized polyaniline onto TiO(2) particles in the presence of Fe species. The TiO(2) provides for improved performance relative to a carbon black-based catalyst and, at a high catalyst loading, allows for reducing the performance gap between non-precious-metal catalyst and Pt/C to ca. 20 mV in RDE testing.

We describe a modified bifunctional analogue of polyacrylamide that spontaneously forms self-assembled polymeric thin films on Au surfaces. The film is engineered to specifically bind histidine tagged proteins (6His), while simultaneously remaining inherently resistant to the non-specific adsorption of proteins in solution. The backbone of a polyacrylamide-co-n-acryloxysuccinimide copolymer is functionalized via tandem active ester (NHS) couplings with 3-(methylthio)propylamine (MTP) and nitrilotriacetic acid (NTA). The resulting functionalized polymers form stable and exceptionally hydrophilic thin films that are approximately 2-5 nm thick, a mass coverage that varies with the MTP graft density. These films are characterized using a variety of techniques (X-ray photoelectron spectroscopy (XPS), reflection absorption infrared spectroscopy (RAIRS), ellipsometry, surface plasmon resonance (SPR), and matrix assisted laser desorption ionization (MALDI)) to establish their structure and function. The protein resistance of the films, as demonstrated by their exposure to solutions of bovine serum albumin (BSA), can be modulated by the amount of MTP grafted to the polymer, which in turn, affects their mass coverage. We show that it is possible to specifically capture hexahistidine tagged proteins with low incidences of nonspecific adsorption using these materials, a discrimination quantified using surface plasmon resonance (SPR) at concentrations down to approximately 20 nM. These polymers also bind strongly to the surfaces of Au nanoparticles, stabilizing them against aggregation, providing them with a similar capacity to selectively bind 6His tagged proteins that can then be speciated using MALDI.

We present a new type of surface-enhanced Raman scattering (SERS) substrate that exhibits extremely large and uniform cross-section enhancements over a macroscopic (greater than 25 mm2) area. The substrates are fabricated using a femtosecond laser nanostructuring process, followed by thermal deposition of silver. SERS signals from adsorbed molecules show a spatially uniform enhancement factor of approximately 10(7). Spectroscopic characterization of these substrates suggests their potential for use in few or single-molecule Raman spectroscopy.

Carbon nanotubes (CNTs) have unique properties that make them ideal for applications like constructing medical devices and drug delivery. Human health consequences resulting from exposure to CNTs in a medical setting remain unclear. Thus far, studies aimed at determining the biocompatibility of CNTs have relied on traditional toxicological endpoints such as cell death. Such studies have not led to a definitive answer regarding specific biological effects or health consequences of exposure to sub-toxic doses of CNTs. One potential health consequence of exposure to CNTs is the activation of the innate immune system that could result in chronic inflammation and compromised immunity. In experiments performed to identify biomarkers for MWCNT exposure and to determine if such exposure activates an innate immune response, the levels cytokines/chemokines were determined after MWCNT treatment of mouse macrophage cells (RAW264.7). Increased extracellular levels of a subset of cytokines/chemokines were observed upon MWCNT treatment. This subset of induced cytokines/chemokines represent potential biomarkers for CNT exposure. Furthermore, MWCNT treatment did not lead to the induction of all cytokines/chemokines tested suggesting that exposure to MWCNTs results in the activation of specific pathways of the innate immune system and not general inflammation.

Secondary electron emission is developed as a means to quantify and image protein binding to Au surfaces modified with patterned organic thin-film arrays. Alkane thiols were patterned via microcontact printing on gold, and their effects on the secondary electron (SE) yield of the surface, systematically quantified. We show that a self-assembled monolayer (SAM) of hexadecane thiol significantly increases the SE yield over the native gold surface, a yield that increases as a function of alkane chain length (C8-C16). This effect is linearly correlated with the surface potentials and wetting properties of these SAMs. Surface layers comprised of poly(ethylene glycol) (PEG) grafted polyacrylamide polymers behave differently, affecting the SE yield by attenuation according to the polymer thickness. These results demonstrate the relative contributions of factors related to the adsorbate molecular structures that serve to strongly mediate the SE yield, providing a foundation for exploiting them as a quantitative electron imaging probe. The latter capability is demonstrated using a model microfluidic assay in which a series of proteins was spatially addressed to a SAM-based pixel array. The gray scale contrasts seen with protein adsorption are directly correlated with both protein molecular weight and mass coverage. These methods are used in two model protein assay experiments: (1) the measurement of the concentration dependent adsorption isotherm for a model protein (fibrinogen); and (2) the selective recognition of a biotinylated protein layer by avidin. These results demonstrate a unique approach to imaging protein binding processes on surfaces with both high analytical and spatial sensitivity.

Data related to the pH-dependent photophysics of a class of rhenium complexes containing the hydroxypyridine ligand are presented. Data include ground-state pKa values, emission energies, and lifetimes. The complexes all have ground-state pKa values near 7.0 and exhibit a dramatic change in emission intensity near this pH. The lifetimes of these complexes, however, are constant over this pH range. A model is presented to account for the observed photophysical behavior. The pH-dependent emission properties of these species make them good candidates for luminescence-based pH probes, especially in the environmental and biomedical fields.

A multicomponent luminescent sensor system is described that uses probe species with constant lifetimes to generate an analyte-dependent change in the apparent sensor lifetime. This new sensing scheme not only allows for lifetime-based measurement techniques to be applied to sensors that employ static quenching interactions but also provides the ability to vary the sensitivity of the sensor system with simple changes in instrumental parameters. A model for the multicomponent sensor is presented, followed by data measured using a prototype pH sensor based on the model.

Non-precious metal catalysts (NPMCs) synthesized from earth-abundant elements, nitrogen and carbon, have been identified as potential alternatives to more scarce Pt-based catalysts currently used in the cathode oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs). Nevertheless, understanding the role of each component of state-of-the-art NPMCs remains a significant challenge due to their highly heterogeneous structure. This understanding is necessary for the development of next-generation NPMCs with improved catalytic activity and durability that could ultimately replace Pt-based ORR catalysts. In this work, a bottom-up systematic approach, starting from model graphene-based precursors, has been applied to eliminate the complexity of NPMCs and better understand the role of each component. Graphene and graphene-oxide (GO) thin-films transferred onto glassy carbon electrodes were used as starting materials. Nitrogen heteroatoms were incorporated into the thin-film substrates either by chemical modification in high-temperature ammonia treatments or by direct chemical activation using a unique high-flux energetic nitrogen atom beam technology, which overcomes thermal activation reaction barriers. Identification and speciation of doped nitrogen heteroatoms was performed via XPS. By varying reaction conditions, different nitrogen contents and species were obtained. Chemical-structure-to-activity relationships were then attempted through detailed physical and electrochemical characterization of the synthesis process to provide detailed information about the importance of each component addition for the formation of active and selective NPMCs. Acknowledgment Financial support from the Los Alamos National Laboratory Laboratory-Directed Research and Development (LDRD) Program is gratefully acknowledged.

Rhenium(I) tricarbonyl complexes have been studied as possible luminescence-based pH probes. A dramatic change in luminescence intensity near pH 7 was observed for those species containing the hydroxypyridine ligand. The change in intensity was not accompanied by any significant change in excited state lifetime, indicating a static quenching mechanism. A bimolecular quenching study with phenol and phenolate ions indicates that an intramolecular quenching mechanism is responsible for the observed photophysical changes.

Synthesis of germanium/silicon (Ge/Si) core/shell nanowire heterostructures is typically accompanied by unwanted gold (Au) diffusion on the Ge nanowire sidewalls, resulting in rough surface morphology, undesired whisker growth, and detrimental performance of electronic devices. Here, we advance understanding of this Au diffusion on nanowires, its diameter dependence and its kinetic origin. We devise a growth procedure to form a blocking layer between the Au seed and Ge nanowire sidewalls leading to elimination the Au diffusion for in situ synthesis of high quality Ge/Si core/shell heterostructures.

In this report, we present the systematic preparation of active and durable non-precious metal catalysts (NPMCs) for the oxygen reduction reaction in polymer electrolyte fuel cells (PEFCs) based on the heat treatment of polyaniline/metal/carbon precursors. Variation of the synthesis steps, heat-treatment temperature, metal loading, and the metal type in the synthesis leads to markedly different catalyst activity, speciation, and morphology. Microscopy studies demonstrate notable differences in the carbon structure as a function of these variables. Balancing the need to increase the catalyst’s degree of graphitization through heat treatment versus the excessive loss of surface area that occurs at higher temperatures is a key to preparing an active catalyst. XPS and XAFS spectra are consistent with the presence of Me–Nx structures in both the Co and Fe versions of the catalyst, which are often proposed to be active sites. The average speciation and coordination environment of nitrogen and metal, however, depends greatly on the choice of Co or Fe. Taken together, the data indicate that better control of the metal-catalyzed transformations of the polymer into new graphitized carbon forms in the heat-treatment step will allow for even further improvement of this class of catalysts.

Conducting polymers have been proved to be effective reducing agents in the synthesis of noble metal nanoparticles. We demonstrate here the fabrication of homogeneous Ag nanosheet assemblies on conducting polymer membranes with 5 wt% polyaniline (PANI) substituted by conductive additives like graphite (G) or multi-walled carbon nanotubes (CNTs). The inclusion of conductive additives that act as electrical connectors for the PANI particles changes the surface property and creates a homogeneous nucleation environment, leading to the membrane surface completely covered by the Ag nanosheet structures. The pack density of the nanosheets can be simply tuned by modulating the concentration of AgNO3 aqueous solution. The as-prepared Ag nanosheet assemblies with abundant interstitial sites show strong SERS responses toward the mercaptobenzoic acid (MBA) molecules, with a detection sensitivity down to 5 ppm. A proper acid etching of these Ag nanosheet structures in 0.1 M HNO3 aqueous solution makes the nanoparticles that form the nanosheets much more exposed to the analyte molecules, and an even stronger Raman enhancement can be obtained. We believe the homogeneous Ag nanosheet assemblies supported on conducting polymer membranes can be sensitive and cost-effective SERS substrates in molecule detection.

A gradient of novel silver nanostructures with widely varying sizes and morphologies is fabricated on a single conducting polyaniline-graphite (P-G) membrane with the assistance of an external electric field. It is believed that the formation of such a silver gradient is a synergetic consequence of the generation of a silver ion concentration gradient along with an electrokinetic flow of silver ions in the field-assisted model, which greatly influences the nucleation and growth mechanism of Ag particles on the P-G membrane. The produced silver dendrites, flowers and microspheres, with sharp edges, intersections and bifurcations, all present strong surface enhanced Raman spectroscopy (SERS) responses toward an organic target molecule, mercaptobenzoic acid (MBA). This facile field-assisted synthesis of Ag nanoparticles via chemical reduction presents an alternative approach to nanomaterial fabrication, which can yield a wide range of unique structures with enhanced optical properties that were previously inaccessible by other synthetic routes.

This paper describes a new type of plasmonic sensor fabricated by imprint lithography using a soft, elastomeric mold. Angle-dependent, zero-order transmission experiments demonstrate the sensing potential of this device, which uses a two dimensional plasmonic crystal. Full angle-dependent mapping shows that the sensitivity to surface chemical binding events reaches maxima near regions of the plasmonic Brillouin zone where the dispersion curves of multiple surface plasmon polariton modes converge. This behavior, together with the simple, low cost procedures for building the structures, suggests a potentially important role for these devices in high performance chemical and biological sensing.