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Plasmonic crystals fabricated with precisely controlled arrays of subwavelength metal nanostructures provide a promising platform for sensing and imaging of surface binding events with micrometer spatial resolution over large areas. Soft nanoimprint lithography provides a robust, cost-effective method for producing highly uniform plasmonic crystals of this type with predictable optical properties. The tunable multimode plasmonic resonances of these crystals and their ability for integration into lab-on-a-chip microfluidic systems can both be harnessed to achieve exceptionally high analytical sensitivities down to submonolayer levels using even a common optical microscope, circumventing numerous technical limitations of more conventional surface plasmon resonance techniques. In this article, we highlight some recent advances in this field with an emphasis on the fabrication and characterization of these integrated devices and their demonstrated applications.

Interest in the properties of thin-film organic materials, especially regard­ ing organized monoand multilayer assemblies, has grown enormously in recent years. The impetus for this renaissance-the relevance of such structures and materials to biological interfaces and membranes, corrosion protection, electrochemistry, wetting, adhesion, and microelectronic cir­ cuit fabrication, for example-has been discussed extensively (1,2). Such materials are clearly contributing significantly to our more general under­ standing of the physics and chemistry of complex surfaces and interfaces. In this article, we provide a general overview of areas in which this has been persuasively demonstrated and, in so doing, suggest the intellectual issues that drive current research in this field. Until recently, there were no generally applicable methods to construct well-ordered, organic surface phases by using any rational synthetic scheme. Metal, semiconductor, and oxide surfaces can be easily prepared by orienting, cutting (or cleaving), and polishing single-crystal substrates followed by cleaning in ultrahigh vacuum (URV) (i.e. by ion bom

We have characterized and correlated the structure and wetting properties of self-assembled monolayers (SAMs) on gold derived from two different mixtures of n-alkanethiols (C12SH and CI3SH; Cr2SH and C22SH); in each of these SAMs, one thiol had a perdeuterated alkyl chain and one a perprotonated chain to allow the two alkanethiols to be distinguished in the SAM by polarized infrared external reflectance spectroscopy (PIERS). The hydrocarbon parts of the SAMs consist of well-defined regions exhibiting structural characteristics reminiscent of those formed in crystalline and liquidlike states. In each SAM, both the shorter alkanethiolate and the section of the longer alkanethiolate closest to the gold contain very low densities of gauche conformations (and presumably are ordered) over all compositions of the SAM. The terminal portion of the longer alkanethiolate-that which extends beyond the terminus of the shorter alkanethiolate-is disordered. The density of gauche conformers present in this mmponent decreases as its concentration in the SAM is increased. The advancing and receding contact angles (0" and d,, respectively) of water and hexadecane (HD) respond differently to the disordered region: for hexadecane, 0.(HD) and d,(HD) reach minima when the interface is present in the disordered, liquidlike state; for water, d"(H2O) and 0,(H2O) appear insensitive to the presentr of this disorder. The IR spectra of these mixed SAMs are consistent with previous inferences from wetting that the components of the SAMs, as prepared here (adsorption of 1 mM thiol from ethanolic solutions over 24-48 h at -25 oC), do not phase segregate into macroscopic islands. The larger interpretation which follows from the data, however, is that this result reflects a structural architecture derived from a kinetically controlled growth process. Under suitable conditions, phase segregation is important as might be expected from consideration of elementary thermodynamics. The importance of kinetic and thermodynamic factors in the structural characteristics of multicomponent SAMs is discussed.

The adsorption of water on methyl and carboxylic acid terminated monolayers of n-alkanethiols adsorbed on gold substrates was studied using reflection-absorption infrared spectroscopy. Despite the differences in substrate polarity, the adsorption of multilayer quantitie of water at temperature 130 K) leads to the formation of polycrystalline ice. The transformation of the adsorbed overlayers from the amorphous to the polycrystalline state was followed using temperature-programmed infrared spectroscopy

We describe a data analysis method for extended x-ray absorption fine structure spectroscopy suitable for use with compounds of diverse form that contain overlapping absorption edges. This method employs direct concurrent analysis of the data—demonstrated here for cases involving two interfering metal edges—and does not utilize subtractive or data filtering strategies that have been previously used to address this challenge. Its generality and precision are demonstrated in analyses made on two model nanoscale samples: 1 a Ir-Pt nanoparticle system supported on -Al2O3 and 2 a hybrid system of Pt nanowires on which Au nanoparticles have been nucleated and grown at the nanowire tips, stacking faults, and twinning boundaries. The results obtained demonstrate the unique compositional and structural qualities of these two systems as well as the broader utility of the new x-ray absorption spectroscopy based protocol used to characterize them.

The surfaces of boron nanoparticles 10-150 nm in diameter, prepared by gas phase pyrolysis of decaborane vapour at 1 atm and 700-900 degrees C, can be halogenated by treatment with Br2 or XeF2; the surface halogenation somewhat increases the onset temperature for the oxidation of the particles under O2.

We describe the results of a study at atomic resolution of the structures exhibited by polymer-capped monometallic and bimetallic Pt and Pd nanoclusters--models for nanoscale material electrocatalysts--as carried out using an aberration-corrected scanning transmission electron microscope (STEM). The coupling of sub-nanometer resolution with Z-contrast measurements provides unprecedented insights into the atomic structures and relative elemental speciation of Pt and Pd within these clusters. The work further defines the nature of deeply quenched states that prevent facile conversions of core-shell motifs to equilibrium alloys and the nature of nonidealities such as twinning (icosahedral cores) and atomic segregation that these structures can embed. The nature of the facet structure present in these model systems is revealed by theory directed modeling in which experimental intensity profiles obtained in Z-contrast measurements at atomic resolution are compared to simulated intensity profiles using theoretically predicted cluster geometries. These comparisons show close correspondences between experiment and model and highlight striking structural complexities in these systems that are compositionally sensitive and subject to amplification by subsequent cluster growth processes. The work demonstrates an empowering competency in nanomaterials research for STEM measurements carried out using aberration corrected microscopes, approaches that hold considerable promise for characterizing the structure of these and other important catalytic materials systems at the atomic scale.

We recently reported a strategy, in which modules consist of large-scale arrays of small, interconnected ultrathin (i.e. 1–20 µm) Si microcells (μ-cells) formed by anisotropic etching of bulk wafers and integrated with a soft printing technique. Here we report three new advances in this type of printed, μ-cell technology. First, we show that μ-cells formed with low purity, solar grade wafers (Dow Corning ® 101 SOG Si metal), can achieve efficiencies much higher than those possible with corresponding bulk cells formed with the same material. Second, we demonstrate high voltage mini-modules that incorporate these μ-cells and lead to high voltage outputs. Finally, we demonstrate the fabrication of mechanically stretchable solar cell modules which are non-coplanar (i.e. arch shaped). The results show that these materials and designs yield a stretchable layout that can undergo strains of up to 30 % without failure.

The cell-microenvironment interaction is critical for cells to perceive environmental cues and co-ordinate signaling cascades to regulate physiological functions. Herein, a soft-lithography technique, micropattern via micromolding in capillaries (MIMIC), is explored to create cell-adhesive micropatterns on glass coverslips. Genetically encoded Src and RhoA fluorescence resonance energy transfer (FRET) biosensors are used to monitor the Src and RhoA activities in nonpatterned cells (stochastically migrating cells, SMCs) and those constrained to grow on micropatterned surfaces (restrictedly migrating cells, RMCs). The results reveal that epidermal growth factor (EGF) induces a decrease of RhoA and an increase of Src activities with biphasic time courses in RMCs. In contrast, the time courses of such activities in SMCs upon EGF stimulation are relatively monophasic. The inhibition of Src activity, actin network, or myosin machinery abolishes the biphasic RhoA response upon EGF stimulation in RMCs. The results indicate that this microenvironment effect on the biphasic RhoA activation in RMCs is mediated by Src and actomyosin machinery. Through the integration of FRET and micropatterning technologies, it is demonstrated that the microenvironment impacts significantly on cell shapes and subsequently the spatiotemporal signaling network of RhoA and Src in living cells. The results help to advance mechanistic understanding of how cells perceive and interpret microenvironments to co-ordinate intracellular molecular signals and ultimately physiological responses.

The structural dynamics-cluster size and adsorbate-dependent thermal behaviors of the metal-metal (M-M) bond distances and interatomic order-of Pt nanoclusters supported on a gamma-Al(2)O(3) are described. Data from scanning transmission electron microscopy (STEM) and X-ray absorption spectroscopy (XAS) studies reveal that these materials possess a dramatically nonbulklike nature. Under an inert atmosphere small, subnanometer Pt/gamma-Al(2)O(3) clusters exhibit marked relaxations of the M-M bond distances, negative thermal expansion (NTE) with an average linear thermal expansion coefficient alpha = (-2.4 +/- 0.4) x 10(-5) K(-1), large static disorder and dynamical bond (interatomic) disorder that is poorly modeled within the constraints of classical theory. The data further demonstrate a significant temperature-dependence to the electronic structure of the Pt clusters, thereby suggesting the necessity of an active model to describe the cluster/support interactions mediating the cluster's dynamical structure. The quantitative dependences of these nonbulklike behaviors on cluster size (0.9 to 2.9 nm), ambient atmosphere (He, 4% H(2) in He or 20% O(2) in He) and support identity (gamma-Al(2)O(3) or carbon black) are systematically investigated. We show that the nonbulk structural, electronic and dynamical perturbations are most dramatically evidenced for the smallest clusters. The adsorption of hydrogen on the clusters leads to an increase of the Pt-Pt bondlengths (due to a lifting of the surface relaxation) and significant attenuation of the disorder present in the system. Oxidation of these same clusters has the opposite effect, leading to an increase in Pt-Pt bond strain and subsequent enhancement in nonbulklike thermal properties. The structural and electronic properties of Pt nanoclusters supported on carbon black contrast markedly with those of the Pt/gamma-Al(2)O(3) samples in that neither NTE nor comparable levels of atomic disorder are observed. The Pt/C nanoclusters do exhibit, however, both size- and adsorbate-induced trends in bond strain that are similar to those of their Pt/gamma-Al(2)O(3) analogues. Taken together, the data highlight the significant role that electronic effects--specifically charge exchange due to both metal-support and metal-adsorbate interactions--play in mediating the structural dynamics of supported nanoscale metal clusters that are broadly used as heterogeneous catalysts.

Flexible, stretchable, and spanning microelectrodes that carry signals from one circuit element to another are needed for many emerging forms of electronic and optoelectronic devices. We have patterned silver microelectrodes by omnidirectional printing of concentrated nanoparticle inks in both uniform and high–aspect ratio motifs with minimum widths of approximately 2 micrometers onto semiconductor, plastic, and glass substrates. The patterned microelectrodes can withstand repeated bending and stretching to large levels of strain with minimal degradation of their electrical properties. With this approach, wire bonding to fragile three-dimensional devices and spanning interconnects for solar cell and light-emitting diode arrays are demonstrated.

We explore textural cues as a mechanism for controlling neuronal process outgrowth in primary cultures of mammalian neurons. The work uses a form of decal transfer lithography to generate arrays of PDMS posts of various dimensions and spacings on glass substrates that are rendered growth-compliant by subsequent treatment with a protein activator. Hippocampal neurons plated on these substrates are used to determine how the posts direct process growth by acting as attachment points or guidance cues. Textural features varying over a large range, even as large as 100 microm in diameter, dramatically affect process growth. Indeed, two growth regimes are observed; at the smaller feature sizes considered, process branching strongly aligns (at right angles) along the post mesh, while neuronal outgrowth on the larger feature sizes elicits process wrapping. The latter behavior most strongly manifests in neurons plated initially at approximately 100 cells/mm(2), where the cells were able to form networks, while for isolated neurons, the cells exhibit poorer viability and development. Bag cell neurons from Aplysia californica also display regular growth patterns, but in this case are guided by contact avoidance of the posts, a behavior qualitatively different than that of the hippocampal neurons.

The amounts of copolymers of various molecular weight and composition adsorbed on oxidized silicon and mica are measured. A dimensionless surface density σ* is found to be a unique function of a copolymer block size asymmetry radio. Within this correlation, two regimes of behavior are found. For copolymers of moderate asymmetry, the surface density σ is influenced more strongly by the molecular weight of the adsorbing PVP block. These results agree well with a model by Marques et al. For copolymers with large PS blocks (high asymmetry), the surface density is determined primarily by the molecular weight of the PS block

We have observed an etching reaction on the Al/Si(111) surface (θAl≥1) induced by the chemisorption of atomic hydrogen at low temperature (T=250–400 K). The major silicon containing product detected by temperature programmed desorption (TPD) is silane (SiH4). An approximate sixfold increase in silane production is observed in the presence of aluminum, with a decrease in the TPD peak temperature from 645 K on Si(111) to 335 K on Al/Si(111). A kinetic model is presented to explain this catalyzed etching reaction.

Triethylamine alane (TEAA) decomposes on an Al(111) single crystal surface at temperatures above ∼310 K to yield pure aluminum thin films, liberating hydrogen and triethylamine into the gas phase. Aluminum deposition is epitaxial and clean (no carbon or nitrogen containing species are observed by Auger electron spectroscopy). The film growth rate is limited by the rate of the recombinative desorption of hydrogen from the surface. These results are compared to similar data from experiments on the surface-mediated thermal decomposition of trimethylamine alane.

Surface metallacycles are formed on aluminum single-crystal substrates when dihaloalkanes of the general structure RCHX(CH 2 ) n CH 2 X (R=Me, H; n=1, 2; X=Br, I) are dissociatively adsorbed in ultrahigh vacuum. All members of this class thermally decompose to evolve hydrocarbon products between 450 and 550 K. The energetics of the reaction pathways are similar to those reported in the preceding paper for β-carbon-hydrogen bond activation on Al surfaces. The C 3 metallacycles derived from 1,3-dihalopropanes yield propylene, while the C 4 species derived from the corresponding 1,4-dihalobutanes yield predominantly butadiene. The metallacycle derived from 1,3-dibromobutane partitions selectively along the olefin yielding reaction channel. A unified mechanism consistent with isotopic labeling experiments and surface vibrational spectroscopy studies is presented along with a discussion of the nature and structure of the intermediates involved

The themal decomposition of alkyl iodides adsorbed on Al(100) and Al(111) surfaces has been studied by using temperature-programmed desorption, integrated desorption mass spectrometry, and high-resolution electron energy loss spectroscopy. We find that alkyl iodides with three or more carbons adsorb dissociatively on aluminum at temperatures ≥130 K. The adsorbed alkyl ligands generated by C-I bond scission are stable on the surface up to ∼450 K and are not significantly affected by the presence of the coadsorbed halogen atom. The dominant mechanism for thermal decomposition of the alkyl fragment is β-hydride elimination, and the kinetics of this surface reaction are similar to those for β-hydride elimination by aluminum alkyls in both the gas phase and solution

Patterned polymer films were grown on SiO2/Si surfaces by a process starting with microcontact printing (μCP) of octadecyltrichlorosilane (OTS), formation of a monolayer derived from norbornenyl trichlorosilane (Nbn–SiCl3) in areas not protected by OTS, activation of the surfaces derived from Nbn–SiCl3 with a ruthenium catalyst, and surface-initiated ring-opening metathesis polymerization of derivatives of norbornene by the catalytically active ruthenium species. These patterned polymer films were successfully used as reactive ion etching resists. The combination of μCP and surface-initiated polymerization makes possible molecular-level control of polymer composition and thickness in both lateral and vertical directions: the smallest patterned lateral features were 2 μm lines; this width was determined by the features of the stamp used in μCP and is not the intrinsic limit of the method. The thickness of the polymer film was, typically, 5–100 nm and could be controlled by monomer concentration and reaction time.

The nature of local atomic and electronic structure at the nanoscale is of both fundamental and technological importance. For example, supported metal nanoclusters exhibit a number of unusual phenomena including large structural disorder and bond-length contraction with increasing temperature. We investigate this behavior for a prototypical ten atom Pt cluster supported on $\ensuremath{\gamma}$ alumina using temperature-dependent, real-time simulations based on density functional theory/molecular-dynamics and x-ray spectroscopy theory. The simulations reveal a complex dynamical structure on multiple-time scales including librational motion of the center of mass and fluctuating bonding characteristics, which explain many of the unusual properties.

The distinguishing feature of our collaborative program of study is the focus it brings to emergent phenomena originating from the unique structural/electronic environments found in nanoscale materials. We exploit and develop frontier methods of atomic-scale materials characterization based on electron microscopy (Yang) and synchrotron X-ray absorption spectroscopy (Frenkel) that are in turn coupled innately with advanced first principles theory and methods of computational modeling (Johnson). In the past year we have made significant experimental advances that have led to important new understandings of the structural dynamics of what are unquestionably the most important classes of heterogeneous catalysts—the materials used to both produce and mitigate the consequences of the use of liquid hydrocarbon fuels.

The high natural abundance of silicon, together with its excellent reliability and good efficiency in solar cells, suggest its continued use in production of solar energy, on massive scales, for the foreseeable future. Although organics, nanocrystals, nanowires and other new materials hold significant promise, many opportunities continue to exist for research into unconventional means of exploiting silicon in advanced photovoltaic systems. Here, we describe modules that use large-scale arrays of silicon solar microcells created from bulk wafers and integrated in diverse spatial layouts on foreign substrates by transfer printing. The resulting devices can offer useful features, including high degrees of mechanical flexibility, user-definable transparency and ultrathin-form-factor microconcentrator designs. Detailed studies of the processes for creating and manipulating such microcells, together with theoretical and experimental investigations of the electrical, mechanical and optical characteristics of several types of module that incorporate them, illuminate the key aspects.

The mechanism and kinetics of the thermal decomposition of trimethylamine alane (TMAA) on aluminum and silicon single crystal surfaces in ultrahigh vacuum are reported. The products obtained are elementally pure aluminum thin films and gas phase hydrogen and trimethylamine. On single crystal aluminum substrates, epitaxial growth is observed. On Si(111), polycrystalline growth is noted although LEED studies suggest that the initial growth is heavily (111) textured. The reactive sticking probability on aluminum surfaces in the temperature range 80–280 K is low and we present evidence for the importance of TMAA decomposition at defects. At higher temperatures ( t ≳ 320 K.) the reactive sticking probabilities are high and steady-state film growth is observed. Under these growth conditions, the rate of deposition is described by a single first-order rate law. The decomposition of TMAA on clean silicon and oxidized aluminum is kinetically complex and more highly activated than the steady-state growth process.

The influences of temperature on the infrared spectra of a docosylthiol (C22) monolayer on a gold substrate are reported. The data suggest that this adsorbate exhibits a complex phase state at 300 K in which gauche conformations concentrated at the chain termina figure prominently. The detailed temperature dependence of the spectral band intensities is found to be very similar in many regards to that of bulk hydrocarbon crystals. At low temperature, band splittings are observed which suggest the lowest energy structure for this adsorbate is one containing two chains per unit cell. A simple lattice argument, consistent with steric models and low‐energy electron diffraction data, is presented to explain these observations.

Self-assembled monolayers of a series of terminally substituted alkyl thiols and disulfides chemisorbed on an Au(111) single-crystal surface were used as substrates for subsequent temperature-programmed desorption (TPD) studies. The monolayers studied were derived from adsorbates of the general structure HS(CH 2 ) 15 X or (S(CH 2 ) 15 X 1 ) (where X=CH 3 , CO 2 CH 3 , CH 2 OH, CO 2 H, and CONH 2 ). The adsorption of n-hexane, methanol, and water on these materials as well as on the clean Au(111) surface was examined. The data reveal complex behavior for the adsorption of secondary overlayers on these dense molecular solids especially in those substrate-adsorbate pairings capable of forming interlayer hydrogen bonds. It is also found that certain correlations can be made between the TPD data, a microscopic measurement, and the macroscopic wetting properties as defined by contact angle data

Monolayers of a series of terminally substituted alkyl thiols, X(CH 2 ) 15 SH (X=CH 3 , CH 2 OH, CO 2 H, CO 2 CH 3 , and CONH 2 ), have been prepared by adsorption from solution onto evaporated gold substrates. The structures habe been characterized by infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ellipsometry, and temperature-programmed desorption (TPD). The IR data shows the monolayer films to be densely packed, crystalline-like structures with all-trans conformation alkyl chains exhibiting average tilt angles of the chain axis in a range of 28-40° from the surface normal and an approximate 55° twist of the chain axis away from a configuration with the CCC plane perpendicular to the surface plane

The influences of temperature on the structure of hexadecanethiol (C 16 ) and heptadecanethiol (C 17 ) monolayers adsorbed on gold substrates are reported. Infrared Spectroscopy and molecular dynamics simulations show that defects in these layers (i.e. gauche conformations) are concentrated at the chain termini and decrease with decreasing surface temperature. Adsorption band intensity oscillations as a function of chain length show that the chain terminating group is highly oriented. Band splittings observed at low temperature establish that there must be at least two chains per unit cell. The temperature dependence of the spectral band intensities of the polymethylene chains is very similar to that found in bulk hydrocarbon crystals.

Transfer printing by kinetically switchable adhesion to an elastomeric stamp shows promise as a powerful micromanufacturing method to pickup microstructures and microdevices from the donor substrate and to print them to the receiving substrate. This can be viewed as the competing fracture of two interfaces. This paper examines the mechanics of competing fracture in a model transfer printing system composed of three laminates: an elastic substrate, an elastic thin film, and a viscoelastic member (stamp). As the system is peeled apart, either the interface between the substrate and thin film fails or the interface between the thin film and the stamp fails. The speed-dependent nature of the film/stamp interface leads to the prediction of a critical separation velocity above which separation occurs between the film and the substrate (i.e., pickup) and below which separation occurs between the film and the stamp (i.e., printing). Experiments verify this prediction using films of gold adhered to glass, and the theoretical treatment extends to consider the competing fracture as it applies to discrete micro-objects. Temperature plays an important role in kinetically controlled transfer printing with its influences, making it advantageous to pickup printable objects at the reduced temperatures and to print them at the elevated ones.

This work describes an integrated microfluidic (mu-fl) device that can be used to effect separations that discriminate single-nucleotide polymorphisms (SNP) based on kinetic differences in the lability of perfectly matched (PM) and mismatched (MM) DNA duplexes during alkaline dehybridization. For this purpose a 21-base single-stranded DNA (ssDNA) probe sequence was immobilized on agarose-coated magnetic beads, that in turn can be localized within the channels of a poly(dimethylsiloxane) microfluidic device using an embedded magnetic separator. The PM and MM ssDNA targets were hybridized with the probe to form a mixture of PM and MM DNA duplexes using standard protocols, and the hydroxide ions necessary for mediating the dehybridization were generated electrochemically in situ by performing the oxygen reduction reaction (ORR) using O2 that passively permeates the device at a Pt working electrode (Pt-WE) embedded within the microfluidic channel system. The alkaline DNA dehybridization process was followed using fluorescence microscopy. The results of this study show that the two duplexes exhibit different kinetics of dehybridization, rate profiles that can be manipulated as a function of both the amount of the hydroxide ions generated and the mass-transfer characteristics of their transport within the device. This system is shown to function as a durable platform for effecting hybridization/dehybridization cycles using a nonthermal, electrochemical actuation mechanism, one that may enable new designs for lab-on-a-chip devices used in DNA analysis.

Microfluidic devices are well suited for manipulating and measuring mass limited samples. Here we adapt a microfluidic device containing functionalized surfaces to chemically stimulate a small number of neurons (down to a single neuron), collect the release of neuropeptides, and characterize them using mass spectrometry. As only a small fraction of the peptides present in a neuron are released with physiologically relevant stimulations, the amount of material available for measurement is small, thereby requiring minimal sample loss and high-sensitivity detection. Although a number of detection schemes are used with microfluidic devices, mass spectrometric detection is used here because of its high information content, allowing the characterization of the released peptide complement. Rather than using an on-line approach, off-line analysis is used; after collection of the peptides onto a surface, mass spectrometric imaging interrogates that surface to determine the peptides released from the cell. The overall utility of this scheme is demonstrated using several device formats with measurement of neuropeptides released from Aplysia californica bag cell neurons.

The integration of synthetic, experimental and theoretical tools into a self‐consistent data analysis methodology allowed us to develop unique new levels of detail in nanoparticle characterization. We describe our methods using an example of Au13 monolayer‐protected clusters (MPCs), synthesized by ligand exchange methods. The combination of atom counting methods of scanning transmission electron microscopy and Au L3‐edge EXAFS allowed us to characterize these clusters as icosahedral, with surface strain reduced from 5% (as in ideal, regular icosahedra) to 3%, due to the interaction with ligands. Charge transfer from Au to the thiol and phosphine ligands was evidenced by S and P K‐edge XANES. A comparison of total energies of bare clusters of different geometries was performed by equivalent crystal theory calculations.

Nano-catalysts, Au nano-particles on TiO2 (anatase), were studied by means of quantitative scanning transmission electron microcopy (Q-STEM) and high-resolution transmission electron microcopy (HRTEM). All the Au nano-catalysts were produced from an Au13 precursor, Au13[PPh3]4[S(CH2)11CH3]4, TiO2 supports, with three treatments: (1) thermal heating in the air at 400°C for 2 hours, (2) exposure to ozone (O3) at room temperature, and (3) exposure to atomic oxygen (AO, or O) with a AO dose of 7.3 ×1018 atom/cm2 at room temperature. Both reactive oxygen species O3 and AO produced significantly small sizes of Au particles as compared to those from the heating treatment in the air (2.7 ± 0.6 nm, 324 b 264 atoms). Ozone produced the smallest (1.2 ± 0.5 nm, 40 ± 49 atoms), whereas AO produced smaller (2.1 ± 0.7 nm, 72 ± 98 atoms), with a broad size distribution and a variety of shapes. HRTEM studies on the AO treated Au/TiO2 samples found that there could exist relationship between the particles size and their shapes which also affected by the interaction with TiO2 supports. The support effect of TiO2 to the shapes of Au particles was also studied.

Tailored optical output, such as color purity and efficient optical intensity, are critical considerations for displays, particularly in mobile applications. To this end, we demonstrate a replica molded photonic crystal structure with embedded quantum dots. Electrohydrodynamic jet printing is used to control the position of the quantum dots within the device structure. This results in significantly less waste of the quantum dot material than application through drop-casting or spin coating. In addition, the targeted placement of the quantum dots minimizes any emission outside of the resonant enhancement field, which enables an 8× output enhancement and highly polarized emission from the photonic crystal structure.

We compare the electrochemistry of Mg deposition and stripping from three Mg-battery electrolytes: EtMgBr, Mg(AlCl2EtBu)2, and MgCl2-AlCl3. These electrolytes represent three generations of progress in Mg-battery development, and include a simple Grignard reagent, an organohaloaluminate, and an all inorganic system, respectively. Our electrochemical measurements coupled with surface and bulk analytical techniques elucidate the requirements for reversible Mg deposition and definitively establish that voltammetric cycling of the electrolyte significantly alters their composition and performance. In the cases of EtMgBr and Mg(AlCl2EtBu)2, electrochemical quartz crystal microbalance measurements demonstrate that mass is gained and lost from the electrode with relatively high efficiency. However, the charge passed during stripping is consistently less than that passed during deposition, resulting in chronoamperometric charge efficiencies between 80-100% for EtMgBr and 50-70% for Mg(AlCl2EtBu)2. SEM-EDS analysis of electrode surfaces demonstrates irreversible Mg deposition and stripping. GC-MS and NMR analysis of electrolytes reveal decomposition of the solvent-electrolyte system. For the all inorganic system containing MgCl2-AlCl3 in THF, elemental analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy (SEM-EDS) results demonstrate that irreversible Mg and Al deposits form during early cycles. Electrospray ionization-mass spectrometry (ESI-MS) data show that inhibitory oligomers develop in THF-based solutions. These oligomers form via the well-established mechanism of a cationic ring-opening polymerization of THF during the initial synthesis of the MgCl2-AlCl3 electrolyte and under resting conditions. In contrast, solutions containing MgCl2-AlCl3 in 1,2-dimethoxyethane (DME), an acyclic solvent, do not evolve as dramatically at open circuit potential. From these results, we propose a mechanism describing how the conditioning process of MgCl2-AlCl3 in THF improves its performance by both tuning the Mg:Al stoichiometry and eliminating oligomers. We also explore the role that other solvents and metal chlorides play in the properties of inorganic Mg-battery electrolytes.

The power efficiency, spectral characteristics, and output directionality of light emitting diodes (LEDs) used for lighting and video display may be tailored by integrating nanostructures that interact with photon emitters. In this work, we demonstrate an approach in which visible-wavelength-emitting quantum dots (QDs) are integrated within a polymer-based photonic crystal (PC) and excited by an ultraviolet-emitting LED. The PC design incorporates two interleaved regions, each with distinct periods in orthogonal directions. The structure enables simultaneous resonant coupling of ultraviolet excitation photons to the QDs and visible QD emission at two different wavelengths to efficiently extract photons normal to the PC surface. The combined excitation and extraction enhancements result in a 5.8X increase in the QD output intensity. Further, we demonstrate multiple QD-doped PCs combined on a single surface to optimally couple with distinct populations of QDs, offering a means for blending color output and directionality of multiple wavelengths. Devices are fabricated upon flexible plastic surfaces by a manufacturable replica molding approach.

This work was supported by the DARPA-funded AFRL-managed Macroelectronics Program and used the Center for Microanalysis of Materials and the Laser and Spectroscopy Facility of the Frederick Seitz Materials Research Laboratory, supported by the Department of Energy (DEFG02-96ER45439). K.L. thanks Prof. Jae Min Myoung in the Department of Materials Science and Engineering at Yonsei University for valuable information related to the processing of GaN thin films.

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.

We describe a novel soft-lithographic technique possessing broad utility for the fabrication of large area, nanoscale ( approximately 100 nm) multilayer resist structures on electronic material substrates. This additive patterning method transfers ultrathin poly(dimethylsiloxane) (PDMS) decals to an underlying SiO(2)-capped organic planarazation layer. The PDMS patterns serve as a latent image through which high-quality multilayer resist structures can be developed using reactive ion-beam etching.

A composite image is shown that highlights examples of device architectures that either incorporate or exploit polymer-embedded metallic microstructures. In work reported by Nuzzo and co-workers on p. 557, new applications of soft lithography, in conjunction with advanced forms of multilayer metallization, are used to construct these exceptionally durable structures. They are suitable for use in non-planar lithographic patterning, and as device components finding applications ranging from microelectronics to Lab-on-a-Chip analytical systems. This article describes the fabrication of durable metallic patterns that are embedded in poly(dimethylsiloxane) (PDMS) and demonstrates their use in several representative applications. The method involves the transfer and subsequent embedding of micrometer-scale gold (and other thin-film material) patterns into PDMS via adhesion chemistries mediated by silane coupling agents. We demonstrate the process as a suitable method for patterning stable functional metallization structures on PDMS, ones with limiting feature sizes less than 5 μm, and their subsequent utilization as structures suitable for use in applications ranging from soft-lithographic patterning, non-planar electronics, and microfluidic (lab-on-a-chip, LOC) analytical systems. We demonstrate specifically that metal patterns embedded in both planar and spherically curved PDMS substrates can be used as compliant contact photomasks for conventional photolithographic processes. The non-planar photomask fabricated with this technique has the same surface shape as the substrate, and thus facilitates the registration of structures in multilevel devices. This quality was specifically tested in a model demonstration in which an array of one hundred metal oxide semiconductor field-effect transistor (MOSFET) devices was fabricated on a spherically curved Si single-crystalline lens. The most significant opportunities for the processes reported here, however, appear to reside in applications in analytical chemistry that exploit devices fabricated using the methods of soft lithography. Toward this end, we demonstrate durably bonded metal patterns on PDMS that are appropriate for use in microfluidic, microanalytical, and microelectromechanical systems. We describe a multilayer metal-electrode fabrication scheme (multilaminate metal–insulator–metal (MIM) structures that substantially enhance performance and stability) and use it to enable the construction of PDMS LOC devices using electrochemical detection. A polymer-based microelectrochemical analytical system, one incorporating an electrode array for cyclic voltammetry and a microfluidic system for the electrophoretic separation of dopamine and catechol with amperometric detection, is demonstrated.

Visible-near-IR luminescence spectra of gold MPCs that are similar, irrespective of the number of core atoms (all

Our direct density function-based simulations of Ru-, Pt- and mixed Ru-Pt clusters on carbon-based supports reveal that substrates can mediate the PtRu5 particles [1]. Oblate structure of PtRu5 on C has been found [2]. Nevertheless, the cluster-substrate interface interactions are still unknown. In this work, we present the applications of combinations of quantitative z-contrast imaging and high resolution electron microscopy in investigating the effect of different substrates and ligand shells on metal particles. Specifically, we developed a relatively new and powerful method to determine numbers of atoms in a nanoparticle as well as three-dimensional structures of particles including size and shape of particles on the substrates by very high angle (~96mrad) annular dark-field (HAADF) imaging [2-4] techniques. Recently, we successfully synthesize icosahedra Au13 clusters with mixed ligands and cuboctahedral Au13 cores with thiol ligands, which have been shown by TEM to be of sub-nanometer size (0.84nm) and highly monodisperse narrow distribution. X-ray absorption and UV-visible spectra indicate many differences between icosahedra and cuboctahedral Au13 cores. Particles with different ligands show different emissions and higher quantum efficiency has been found in Au11 (PPH3) SC12)2C12. We plan to deposit those ligands-protected gold clusters onto different substrates, such as, TiO2 and graphite, etc. Aforementioned analysis procedure will be performed for those particles on the substrates and results will be correlated with that of our simulations and activity properties. This approach will lead to an understanding of the cluster-substrates relationship for consideration in real applications.

We describe the fabrication and performance of an integrated microelectrochemical reactor—a design possessing utility for multiple applications that include electrochemical sensing, the generation and manipulation of in-channel microfluidic pH gradients, and fluid actuation and flow. The device architecture is based on a three-electrode electrochemical cell design that incorporates a Pt interdigitated array (IDA) working (WE), a Pt counter (CE), and Ag pseudo-reference (RE) electrodes within a microfluidic network in which the WE is fully immersed in a liquid electrolyte confined in the channels. The microchannels are made from a conventional poly(dimethylsiloxane) (PDMS) elastomer, which serves also as a thin gas-permeable membrane through which gaseous reactants in the external ambient environment are supplied to the working electrode by diffusion. Due to the high permeability of oxygen through PDMS, the microfluidic cell supports significantly (>order of magnitude) higher current densities in the oxygen reduction reaction (ORR) than those measured in conventional (quiescent) electrochemical cells for the same electrode areas. We demonstrate in this work that, when operated at constant potential under mass transport control, the device can be utilized as a membrane-covered oxygen sensor, the response of which can be tuned by varying the thickness of the PDMS membrane. Depending on the experimental conditions under which the electrochemical ORR is performed, the data establish that the device can be operated as both a programmable pH gradient generator and a microfluidic pump.