Search

After made black by a reactive ion etching process and SiNx deposition, unprecedentedly, the efficiency of ultrathin solar microcell was improved from 8% to 11.5% and short circuit current increased by 65.7%.

Energy storage is an increasingly critical component of modern technology, with applications that include energy infrastructure, transportation systems, and portable electronics. Improvements to lithium-ion battery energy/power density through the adoption of silicon anodes promising both gravimetric and volumetric capacities that far exceed traditional carbon-based anodes has been limited by similar to 300% strains and poor coulombic efficiency during charge and discharge ((dis)charge) cycling which result in short operational lifetimes. We examine encapsulated micropore-modified silicon anodes that define lithium mass-transfer dynamics to constrain strain evolution and improve capacity retention during (dis)charge cycling. Fully integrated cells incorporating this silicon anode and a commercial grade LiCoO2 cathode maintain their capacity for 110 cycles with >99% average coulombic efficiency from cycles 5 to 100. Anodes with thicknesses up to 50 mu m resulted in area-normalized capacities of up to 12.7 mAhcm(-2). When the silicon anode microstructure pitch is varied, a direct relationship is found to exist between the rate capability and volumetric capacity of the anode. Helium-ion Microscopy, Secondary Ion Mass Spectrometry, and Scanning Electron Microscopy, used as ex-situ characterization methods for the evolution of the electrode's structure on cycling, reveal significant changes in nanoscale morphology that otherwise retain the essential laminate micropore motif of the initial Si anode. (C) 2013 The Electrochemical Society. All rights reserved.

The reactions of bis(hexafluoroacetylacetonato)palladium(II), Pd(hfac) 2, on copper have been studied. Whereas multilayers of Pd(hfac)2 desorb molecularly from copper surfaces between 200 and 270 K, submonolayer coverages of Pd(hfac)2 react in a multistep sequence. At temperatures below 120 K, Pd(hfac)2 transfers its hfac ligands to the copper surface and the metal center is reduced to Pd 0 . The hfac groups adopt a variety of molecular orientations on the surface at 120 K but undergo an apparent ordering transition near 300 K that re-orients the hfac groups to an upright geometry (perpendicular to the surface plane). At low coverages on clean surfaces, further annealing results in the decomposition of the surface-bound hfac ligands to give adsorbed Pd atoms and COCF3, CF3, and fluoride species. These intermediates ultimately yield a partial monolayer of Pd atoms, a carbon (possibly graphitic) deposit, and a variety of organic products that desorb between 500 and 650 K; the desorbing flux after ionization consists of CF3COF, COCF3 ,C F 3, and CO fragments. The activation parameters for the decomposition of hfac groups on copper foils have been determined to be A ) 1.3 10 13 s -1 and Ea ) 36.8 kcal mol -1 . When Pd(hfac)2 is dosed onto copper surfaces bearing submonolayer coverages of carbon, a new reaction channel is evident: some of the hfac ligands abstract copper atoms from the surface and generate Cu(hfac)2, which desorbs when the surface is heated. The palladium atoms remain behind and diffuse into the bulk of the Cu crystal. This redox transmetalation reaction (Pd II (hfac)2 + Cu 0 f Pd 0 + Cu II (hfac)2) is the same one that is responsible for the ability of Pd(hfac)2 to effect the chemical vapor deposition of palladium selectively on copper at higher pressures. This redox transmetalation reaction is the first example of the simultaneous etching of copper and deposition of palladium.

We describe a non-lithographic monolayer based patterning process for depositing copper thin film microstructures by chemical vapor deposition (CVD). The technique combines the microcontact printin...

The atomic structures of several distinct adlayers of Cd underpotentially deposited onto a Au(111) surface in sulfuric acid electrolyte were revealed by in situ scanning tunneling microscopy (STM). Three ordered adlattices were observed, all of which have a long-range linear morphology rotated by 30° from the substrate's lattice directions. Complete geometric descriptions and proposed structures are presented for each. A purely electrostatic model is insufficient to explain the banded morphology which is observed; therefore, other structure-forming interactions, including lattice strain, are discussed as possible contributors.

A set of supported bimetallic catalysts, designated [Re7Ir−N], [Re7Ir−P], [Re5IrRe2−N], and [Re5IrRe2−P], has been prepared from two structural isomers (1 and 2) of the cluster compound [Z]2[Re7IrC(CO)23] (Z+ = NEt4+, N(PPh3)2+) by deposition onto high surface area alumina (≤1% Re) and activation in H2 at 773 K. The specific activities of the catalysts for ethane hydrogenolysis at 500 K vary significantly (3−63 mmol of CH4/mol of Re7Ir per s) and depend on both the metal framework structure and the counterion present in the precursor. Interpretation of EXAFS data (from both Re and Ir L3-edges) has enabled the development of specific models for the catalyst particle nanostructures that correlate with the catalytic activities. The more active catalysts ([Re7Ir−N] and [Re5IrRe2−N]) are modeled by a hemisphere of close-packed (hcp) metal atoms (average diameter 1 nm) with Ir at the core. On the other hand, the less active catalysts ([Re7Ir−P] and [Re5IrRe2−P]) are better described as two-dimensional layer str...

The reaction pathways and kinetics for the selective deposition of palladium on copper from the metal−organic precursor Pd(hfac)2 have been established by means of reactive molecular beam−surface scattering where a flux of Pd(hfac)2 (ranging from 1013 to 1014 molecules cm-2 s-1) impinges continuously on the copper surface. The surface selectivity of the deposition process is a consequence of a “redox transmetalation” reaction, which is best described by the stoichiometric equation Pd(hfac)2 + Cu → Pd + Cu(hfac)2. On polycrystalline copper foils, the production and subsequent desorption of Cu(hfac)2 from the surface occurs with unit efficiency at temperatures between 400 and 600 K. At temperatures above 600 K, the yield of Cu(hfac)2 decreases and eventually falls to zero at 800 K as the thermolytic decomposition of the hfac ligands on the surface becomes kinetically competitive. We have devised a steady-state kinetic model of the adsorption of Pd(hfac)2, desorption of Cu(hfac)2, and thermolytic decompositi...

The synthesis, characterization, chemical vapor deposition, and mechanistic investigation of the thermal decomposition in aromatic solvents of cis-bis(η2,η1-pent-4-en-1-yl)platinum (1) are described. Complex 1 has a unique chelated structure, giving rise to enhanced volatility, and has proved useful for the chemical vapor deposition of thin platinum films under mild conditions. Films deposited on a glass slide in a hot walled glass tube at 175 °C have an elemental composition of 82% Pt and 18% C. Kinetic, deuterium labeling, and chemical trapping experiments indicate that the decomposition of 1 in aromatic solvents proceeds by reversible β-hydride elimination followed by reversible dissociation of 1,4-pentadiene to give a 3-coordinate platinum hydride intermediate (9). Reductive elimination of 1-pentene from 9 deposits metallic platinum. The rate of decomposition exhibits a significant β-deuterium isotope effect of kH/kD = 3.8 ± 0.3. Added olefins are rapidly isomerized during the decomposition of 1; trap...

Free-standing micro- and nanoscale objects of single crystal silicon can be fabricated from silicon-on-insulator wafers by lithographic patterning of resist, etching of the exposed top silicon, and removing the underlying SiO2 to lift-off the remaining silicon. A large collection of such objects constitutes a type of material that can be deposited and patterned, by dry transfer printing or solution casting, onto plastic substrates to yield mechanically flexible thin film transistors that have excellent electrical properties. Effective mobilities of devices built with this material, which we refer to as microstructured silicon (μs-Si), are demonstrated to be as high as 180cm2∕Vs on plastic substrates. This form of “top down” microtechnology might represent an attractive route to high performance flexible electronic systems.

The ability to control the orientation, morphology, and electrophysiological characteristics of neurons in culture allows the construction of neural circuits with defined physiological properties. Using microfluidic protein deposition onto chemically modified glass, we achieve the controlled growth of Aplysia neurons on geometrical patterns of poly-L-lysine and collagen IV, surrounded by nonadhesive regions of bovine albumin. We investigate the parameters essential for forming functional neuronal networks, the morphology, biochemistry, and electrophysiology under engineered cell culture conditions. We demonstrate that not only the orientation of neurite extension but also the number of primary neurites originating from the cell soma, their length, and branching pattern depend on the spatial constraints presented by the size and shape of the adhesion region on the patterned substrate. In addition, the physicochemical properties of the support layer influence the electrical activity of the cultured neurons. Substrate-dependent changes in the amplitude and in the dynamic parameters of the action potential cause decreased spike broadening in patterned neurons, which reflects changes in the number or functioning of active membrane ion channels. In contrast to morphology and electrophysiology, the neuropeptide content, as determined by mass spectrometry of individual patterned neurons, is not affected by the growth on patterned surfaces. Our results suggest that the morphological and electrophysiological parameters of neurons can be predictably altered/engineered by modulation of the chemical, physical, and topographical features of culture substrates. We also demonstrate that a full suite of techniques is required for functional characterization of neurons on engineered substrates.

Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) are popular and powerful techniques used to characterize heterogeneous catalysts. Rapid developments in electron microscopy – especially aberration correctors and in situ methods – permit remarkable capabilities for visualizing both morphologies and atomic and electronic structures. The purpose of this review is to summarize the significant developments and achievements in this field with particular emphasis on the characterization of catalysts. We also highlight the potential and limitations of the various methods, describe the need for synergistic and complementary tools when characterizing heterogeneous catalysts, and conclude with an outlook that also envisions future needs in the field.

This communication describes a technique used to pattern oxide thin layers using microcontact printing ({mu}CP) and sol-gel deposition. The technique involves {mu}CP of self-assembled monolayers (SAM`s) of alkylsiloxane on various substrates (SiO{sub 2}/Si, sapphire, ITO, and glass), followed by deposition of oxide thin layers from sol-gel precursors. Delamination of oxide layers from SAM-derivatized regions allows selective deposition of crystalline dielectric oxide layers on underivatized regions. To demonstrate the viability of this technique for integrated microelectronics and optics applications, patterned (Pb,La)TiO{sub 3} (PLT) and LiNbO{sub 3} layers were deposited on sapphire, silicon, and indium tin oxide (ITO) substrates. Use of lattice-matched substrates allows lithography-free deposition of patterned heteroepitaxial oxide layers. Strip waveguides of heteroepitaxial LiNbO{sub 3} with 4 {mu}m lateral dimensions were fabricated on sapphire. Dielectric measurements for patterned PLT thin layers on ITO are also reported. {copyright} {ital 1995} {ital Materials} {ital Research} {ital Society}.

This paper outlines a general synthetic route to alkanethiols useful in forming self-assembled monolayers (SAMs) starting from amines, RNH 2 , and converting them, via α-chloroamides RNHCOCH 2 Cl, to thiols having the structure RNHCOCH 2 SH. The wettabilities (estimated from contact angles of water and hexadecane) and the thicknesses (as measured by ellipsometry and X-ray photoelectron spectroscopy, XPS) of SAMs having an amide moiety β to Au/thiolate were similar to those of SAMs of alkanethiols with similar backbone length on gold. The internal amide group present in SAMs prepared from CF 3 CH 2 -NHCOCH 2 SH increases their stability against desorption or exchange with hexadecanethiol in ethanol relative to SAMs from CF 3 (CH 2 ) 3 SH. The desorption of SAMs from CF 3 (CH 2 ) 3 SH was first order in the alkanethiolate and had a half-life of ∼2 h at 10 -9 Torr ; SAMs from CF 3 CH 2 NHCOCH 2 SH, by contrast, showed no loss after 48 h at ∼ 10 9 Torr. The rate of exchange of a SAM from CF 3 CH 2 NHCOCH 2 SH with hexadecanethiol in ethanol was 10 2 -10 3 times slower than the SAMs from CH 3 (CH 2 ) 3 SH or from CF 3 (CH 2 ) 3 -SH. The susceptibility of a SAM prepared from a short-chain alkanethiol (e.g., CH 3 (CH 2 ) 3 SH or CF 3 -CH 2 NHCOCH 2 SH) to damage by UV was 10 times greater than that observed for a SAM prepared from hexadecanethiol (as measured by XPS). UV damage of SAMs derived from CF 3 CH 2 NHCOCH 2 SH, followed by protection ofthe UV-damaged SAM by replacement with hexadecanethiol and etching, gave gold patterns with minimum feature sizes of 5 μm ; these sizes were limited by the lithographic procedure used and do not reflect the true edge resolution of this photolithographic method.

The melting of ordered monolayers of n-hexane, n-octane, and n-decane adsorbed on Pt(111) has been studied by reflection-absorption infrared spectroscopy (RAIRS). Each alkane forms an overlayer at low temperatures (

Two kinds of amorphous carbon (a-C) thin film samples were synthesized, one by magnetron sputtering, the other by filtered cathodic arc deposition. X-ray photoelectron spectroscopy (XPS) showed that the C 1s envelope for each sample was primarily a convolution of three peaks which are assignable to sp2 hybridized carbon, sp3 hybridized carbon (shifted from the sp2 peak by ∼ 1 eV) and an sp2 satellite peak, possibly due to π-π ∗ transition. The satellite typically comprised just under 14% of the total sp2 signal and was shifted from the main sp2 peak by ∼ 2 eV. The relative amounts of each bonding type were determined by comparing the integrated areas of the sp2 and sp3 peaks. Auger electron spectroscopy (AES) was also performed on these samples, along with highly ordered pyrolytic graphite (100% sp2) and natural diamond (100% sp3) for comparison purposes. The binding energy width D between the highest maximum and lowest minimum values of the first derivative C (KLL) spectra were obtained and a linear relationship between D and the amount of sp3 bonding assumed. When comparing sp3 values obtained by AES and deconvoluted XPS spectra an error range within ±1.5% was found, making XPS a satisfactory method for obtaining hybridization information. It was noted that Ar+ ion bombardment has a substantial effect on the surface sp2/sp3 ratio, as observed by XPS. These results are related to other studies of ion bombardment of graphite and diamond.

We report a detailed study using reflection absorption infrared (RAIR), temperature-programmed reaction (TPR), Auger electron (AES) spectroscopies, and low-energy electron diffraction (LEED) of the interaction and thermolytic reactions ofdisilane on a Cu(111) surface. Disilane adsorbs dissociatively on Cu(111) at temperatures as low as 90 K. At low coverages Si-Si and Si-H bond scissions yield two adsorbed fragments which are identified as being the SiH fragment and adsorbed H atoms, respectively. Low fluxes of disilane (≤ 5 x 10 12 molecules/s) favor the formation of these dissociative adsorption products. Using higher fluxes, the exposures lead to the concomittant formation of SiH 2 and SiH 3 moieties. The yields of these later species depend very sensitively on both the absolute and relative surface coverages of Si and H. The decomposition processes of adsorbed SiH 3 and SiH 2 are characterized strongly by coverage dependent kinetics. The SiH 3 species is stable over a limited temperature range (T 250 K), leaving behind surface bound Si. The recombinative desorption of dihydrogen occurs at ∼300 K. This bimolecular process competes with another associative reaction which leads to the formation and desorption of silane (T ∼ 230 K) from the surface. The amount of Si deposited on the surface depends sensitively on the surface temperature and the magnitude of the disilane exposure. A high coverage silicide surface phase is readily formed above the dihydrogen desorption temperature. This thin film is characterized by an ordered (√3 x √3)R30° overlayer structure which is thermally stable over a wide range of temperatures. At higher temperatures, where atomic mobilities are higher, the growth of multilayer intermetallic thin films can be effected.

The structure and reactivity of norbornadiene (NBD) adsorbed on Pt(111) has been studied by several physical techniques. At 130 K, NBD is bound to the surface in an unusual way: through only one C-C double bond and through an agostic interaction involving one of the C-H bonds of the bridging CH{sub 2} group. The latter interaction is characterized by an intense, broad band centered at 2670 cm{sup -1} (fwhm nearly equals 50 cm{sup -1}) in the RAIR spectra. The data strongly suggest that the other C-C double bond of NBD does not interact with the surface. This unusual binding mode, which may be adopted because steric factors favor it over the alternative {eta}{sup 2}:{eta}{sup 2} geometry, persists to 220-260 K, whereupon the agostic C-H bond is cleaved to give a norbornadienyl intermediate that is stable to 400-450 K. In this latter temperature range the norbornadienyl intermediate decomposes, probably via a retro cyclization reaction, to give benzene and dihydrogen (which desorb) and a fractional monolayer of carbon (which remains on the surface). Comparisons of the low-frequency C-H stretching mode seen for NBD with those seen for other adsorbed hydrocarbons suggest that the line width of these modes is largely due tomore » inhomogeneous broadening, not to dispersion or lifetime effects. 49 refs., 6 figs., 4 tabs.« less

© 2016 IOP Publishing Ltd. For decades, progress in the field of optical (including solar) energy conversion was dominated by advances in the conventional concentrating optics and materials design. In recent years, however, conceptual and technological breakthroughs in the fields of nanophotonics and plasmonics combined with a better understanding of the thermodynamics of the photon energy-conversion processes reshaped the landscape of energy-conversion schemes and devices. Nanostructured devices and materials that make use of size quantization effects to manipulate photon density of states offer a way to overcome the conventional light absorption limits. Novel optical spectrum splitting and photon-recycling schemes reduce the entropy production in the optical energy-conversion platforms and boost their efficiencies. Optical design concepts are rapidly expanding into the infrared energy band, offering new approaches to harvest waste heat, to reduce the thermal emission losses, and to achieve noncontact radiative cooling of solar cells as well as of optical and electronic circuitries. Light-matter interaction enabled by nanophotonics and plasmonics underlie the performance of the third- and fourth-generation energy-conversion devices, including up- and down-conversion of photon energy, near-field radiative energy transfer, and hot electron generation and harvesting. Finally, the increased market penetration of alternative solar energy-conversion technologies amplifies the role of cost-driven and environmental considerations. This roadmap on optical energy conversion provides a snapshot of the state of the art in optical energy conversion, remaining challenges, and most promising approaches to address these challenges. Leading experts authored 19 focused short sections of the roadmap where they share their vision on a specific aspect of this burgeoning research field. The roadmap opens up with a tutorial section, which introduces major concepts and terminology. It is our hope that the roadmap will serve as an important resource for the scientific community, new generations of researchers, funding agencies, industry experts, and investors.

Solid state electrolytes (SE) are believed to be the ultimate solution for the current electrode dissolution (and other stability) problems encountered in Li-ion batteries. The safety enhancements that would be engendered by a viable technology based on non-flammable solid-phase electrolyte materials cannot be overstated and would have transformational impacts. Some of the currently developed bulk type solid state Li ion conductors exhibit comparable Li ionic conductivity as liquid electrolyte. However, poor interface contact remains to be a critical issue when assemble solid electrolyte into a useful all solid state battery. Assembly of bulk solid electrolyte into a battery usually requires deformation of interfaces between electrolyte and two electrodes high pressures to achieve good interface contact. This process is hard to handle and less reproducible. In order to avoid the high pressure press and achieve better reproducibility a liquid electrolyte based buffer Li-ion transport layer was applied at interfaces to bridge these interfaces. Results show that the cell impedance reduced by up to two orders of magnitude with the interface buffer layer.

Departments of Materials Science and Engineering and Chemistry, Uniuersity of lllinois,Urbana-Champaign, (Irbana, Illinois 61801Receiued September 79, 1994eLong-chain alkanehydroxamic acids adsorb on the native oxides of metals and formed oriented self-assembled monolayers (SAMs). This study examined SAMs of hydroxamic acids on the native oxides ofcopper, silver, titanium, aluminum, zirconium, and iron. These SAMs were characterized usingwettability,X-ray photoelectron spectroscopy (XPS), and polarized infrared external reflectance spectroscopy (PIERS).Alkanehydroxamic acids give better monolayers than the corresponding alkanecarboxylic acids on certainbasic metal oxides (especially copper(Il) oxide). On the native oxide of copper (which has an isoelectricpoint greater than the pK" of the hydroxamic acid), the ligand is bound to the surface predominantly asthe hydroxamate. The strength of the interaction between copper oxide and the hydroxamate allowsincorporation of polar tail groups into the monolayer. On acidic or neutral metal oxides (e.g., TiO2), thepredominant species bound to the surface is the hydroxamic acid. Alkanehvdroxamic acids on titaniumdioxide bind relatively weakly but. nonetheless. form SAlts that are more stable than those from carboxylicacids (although not as stable as those from alkanephosphonic acids r.

We demonstrate a method for combining sputtered TiO2 deposition with liquid phase dip-coating of a quantum dot (QD) layer that enables precise depth placement of QD emitters within a high-index dielectric film, using a photonic crystal (PC) slab resonator to demonstrate enhanced emission from the QDs when they are located at a specific depth within the film. The depth of the QDs within the PC is found to modulate the resonant wavelength of the PC as well as the emission enhancement efficiency, as the semiconducting material embedded within the dielectric changes its spatial overlap with the resonant mode.

The reactivity of two bicyclic alkenes, bicyclo(2.2.2)octene (BOE) and norbomene (NBE), has been studied on Pt(ll1) in both the absence and the presence of co-adsorbed hydrogen. The inability of these alkenes to rearrange to alkylidyne species on the surface considerably alters their reaction chemistry. At 130 K, the alkenes are bound molecularly to the surface via two interactions: (1) a z or di-a interaction with a C=C double bond, and (2) an apparent agostic interaction with a C-H bond. The geometries of these bicyclic alkenes strongly suggest that they are interacting with three mutually-adjacent surface Pt atoms, but it is not clear from the data whether the alkene group bridges between two Pt atoms and the agostic interaction involves one Pt atom or vice versa. Several reactions ensue upon thermolysis. At -250 K, the agostic C-H bond is cleaved and a surface-bound alkyl intermediate is formed. The resulting surface-bound hydrogen atoms do not immediately desorb, but some of them transfer to unreacted BOE and NBE molecules to form the alkanes bicyclo(2.2.2)octane (BOA) and norbomane (NBA), respectively. The rate-detennining step for this self-hydrogenation reaction is the dehydrogenation of BOE or NBE; these processes appear to follow first-order rate laws with activation energies of -16 kcdmol. If the FT( 11 1) surface is first treated with hydrogen and then dosed with the bicyclic alkene, alkane is formed at lower temperatures (as low as 190 K) and in significantly greater amounts. In the presence of co-adsorbed Dz, BOE and NBE are hydrogenated to a distribution of alkane isotopomers with up to four deuterium atoms per molecule; these observations suggest that the surface-bound alkyl intermediates can a-eliminate and reversibly form alkylidenes. Surface carbon atoms, when present at sufficiently high coverages, inhibit the hydrogenation and self-hydrogenation of these bicyclic alkenes due to the reduced ability of the carbonaceous Pt( 11 1) surface to activate H-H or C-H bonds. At higher temperatures (470-520 K), both BOE and NBE eventually decompose to give benzene (part of which desorbs) and surface C,H, fragments. The latter decompose by -620 K to give a partial carbonaceous overlayer and HZ gas.

The chemical vapor deposition (CVD) of copper from (hexafluoroacetylacetonate)(vinyltrimethylsilane)-copper(I) [Cu[sup I](hfac)(vtms)] and the thermal evaporation of copper on pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyimide have been studied with a variety of techniques including reflection absorption infrared spectroscopy (RAIRS), ellipsometry, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Our studies reveal that the nucleation and growth of Cu by CVD occurs by the preferential reaction of surface carbonyl groups, (C=O)[sub a], of PMDA-ODA with the CVD reagent. Preferential trapping of thermally deposited metal atoms also has been seen, although the nucleation processes appear to be less chemically specific than is seen in CVD growth on this substrate. Carbonyl groups at the surface of the polyimide react with the precursor molecules at 300 K, although the reactive sticking probabilities appear to be low ([much lt]10[sup [minus]3]). The facility of nucleation on the polyimide surface depends on both the number and orientation of the carbony groups on the polymer surface which, in turn, depends sensitively on the thickness of the film. The nucleation of Cu growth from Cu[sup I](hfac)(vtms) is found to proceed from surface reactions mediated by these surface groups. 63 refs., 19 figs., 2 tabs.

Transfer printing represents a set of techniques for deterministic assembly of micro-and nanomaterials into spatially organized, functional arrangements with two and three-dimensional layouts. Such processes provide versatile routes not only to test structures and vehicles for scientific studies but also to high-performance, heterogeneously integrated functional systems, including those in flexible electronics, three-dimensional and/or curvilinear optoelectronics, and bio-integrated sensing and therapeutic devices. This article summarizes recent advances in a variety of transfer printing techniques, ranging from the mechanics and materials aspects that govern their operation to engineering features of their use in systems with varying levels of complexity. A concluding section presents perspectives on opportunities for basic and applied research, and on emerging use of these methods in high throughput, industrial-scale manufacturing.

Monte Carlo ray tracing modeling is used for design optimization of luminescent solar concentrator for micro solar cell arrays. Key parameter is identified as luminophore self-absorption. For DCM dye the optimum dimension is at the scale of millimeters.

We describe here nanoimprinted plasmonic crystals composed of highly uniform subwavelength metal nanohole and nanopost arrays and their application in surface-enhanced sensing and imaging. Soft nanoimprint lithography is a versatile, cost-effective method to precisely replicate these structures with well-characterized optical properties. These plasmonic crystals support multiple surface plasmon modes controlled by the design rules of the nanostructures, allowing us to optimize the devices for operation in a particular wavelength range. We have demonstrated the ability to spectroscopically measure bulk refractive index changes and mechanical deformation of hydrogels resulting from pH changes, thin film imaging with sensitivities down to submonolayer levels using a common optical microscope, and Raman signal enhancement using a single common device framework. These plasmonic crystals have the potential to overcome many of the technological limitations that have limited the widespread application and integration of surface-enhanced analytical techniques.

The adsorption and subsequent reactions of the C[sub g] cyclic hydrocarbons cyclooctane (COA), cyclooctene (COE), 1,3-cyclooctadiene (1,3-COD), 1,5-cyclooctadiene (1,5-COD), and cyclooctatetraene (COT) have been studied on a platinum(111) single crystal surface. On clean Pt(111), the majority of the adsorbed COA desorbs molecularly, whereas all of the unsaturated hydrocarbons are dehydrogenated to COT and then converted to benzene. In several cases, intermediates in the dehydrogenation pathway can be identified spectroscopically; for example, COE is dehydrogenated to COT via the diene 1,3-COD. In all cases, whether added directly to the surface or formed via dehydrogenation reactions, COT is bound to the surface initially in a tub-shaped [eta]+4 fashion and is converted to a planar [eta]+3 structure at higher temperatures. The conversion of COT to benzene follows thereafter. Co-adsorption experiments with COT and COT-d[sub 8] indicate that the majority of the benzene is formed via an intramolecular rearrangement and not by complete fragmentation of COT to acetylene followed by cyclotrimerization. We propose that, at 475 K, COT undergoes ring contraction to form bicyclo[4.2.0]-octa-1,3,5-triene (BOT). The BOT is then transformed via a retro[2 +2]cyclization to benzene, which desorbs, and acetylene, which is dehydrogenated first to surface ethynyls and then to a surface carbon overlayer.more » 72 refs., 14 figs., 3 tabs.« less

Research in electronic nanomaterials, historically dominated by studies of nanocrystals/fullerenes and nanowires/nanotubes, now incorporates a growing focus on sheets with nanoscale thicknesses, referred to as nanomembranes. Such materials have practical appeal because their two-dimensional geometries facilitate integration into devices, with realistic pathways to manufacturing. Recent advances in synthesis provide access to nanomembranes with extraordinary properties in a variety of configurations, some of which exploit quantum and other size-dependent effects. This progress, together with emerging methods for deterministic assembly, leads to compelling opportunities for research, from basic studies of two-dimensional physics to the development of applications of heterogeneous electronics.

We describe here soft nanofabrication methods using spin-on glass (SOG) materials for the fabrication of both bulk materials and replica masters. The precision of soft nanofabrication using SOG is tested using features on size scales ranging from 0.6 nm to 1.0 μm. The performance of the embossed optics is tested quantitatively via replica patterning of new classes of plasmonic crystals formed by soft nanoimprinting of SOG. These crystals are found to offer significant improvements over previously reported plasmonic crystals fabricated using embossed polymeric substrate materials in several ways. The SOG structures are shown to be particularly robust, being stable in organic solvent environments and at high temperatures (∼450 °C), thus extending the capacities and scope of plasmonic crystal applications to sensing in these environments. They also provide a stable, and particularly high-performance, platform for surface-enhanced Raman scattering. We further illustrate that SOG embossed nanostructures can serve as regenerable masters for the fabrication of plasmonic crystals. Perhaps most significantly, we show how the design rules of plasmonic crystals replicated from a single master can be tuned during the embossing steps of the fabrication process to provide useful modifications of their optical responses. We illustrate how the strongest feature in the transmission spectrum of a plasmonic crystal formed using a single SOG master can be shifted precisely in a SOG replica between 700 and 900 nm for an exemplary design of a full 3D plasmonic crystal by careful manipulation of the process parameters used to fabricate the optical device.

Three-dimensional (3D) microperiodic scaffolds of poly(2-hydroxyethyl methacrylate) (pHEMA) have been fabricated by direct-write assembly of a photopolymerizable hydrogel ink. The ink is initially composed of physically entangled pHEMA chains dissolved in a solution of HEMA monomer, comonomer, photoinitiator and water. Upon printing 3D scaffolds of varying architecture, the ink filaments are exposed to UV light, where they are transformed into an interpenetrating hydrogel network of chemically cross-linked and physically entangled pHEMA chains. These 3D microperiodic scaffolds are rendered growth compliant for primary rat hippocampal neurons by absorption of polylysine. Neuronal cells thrive on these scaffolds, forming differentiated, intricately branched networks. Confocal laser scanning microscopy reveals that both cell distribution and extent of neuronal process alignment depend upon scaffold architecture. This work provides an important step forward in the creation of suitable platforms for in vitro study of sensitive cell types.

A method for fabricating chemical gradients on planar and nonplanar substrates using grayscale lithography is reported. Compliant grayscale amplitude masks are fabricated using a vacuum-assisted microfluidic filling protocol that employs dilutions of a carbon-black-containing polydimethylsiloxane emulsion (bPDMS) within traditional clear PDMS (cPDMS) to create planar, fully self-supporting mask elements. The mask is then placed over a surface functionalized with a hydrophobic coumarin-based photocleavable monolayer, which exposes a polar group upon irradiation. The mask serves to modulate the intensity of incident UV light, thereby controlling the density of molecules cleaved. The resulting molecular-level grayscale patterns are characterized by condensation microscopy and imaging mode time-of-flight secondary-ion mass spectrometry (ToF-SIMS). Due to the inherent flexibility of this technique, the photofuse as well as the gradient patterns can be designed for a wide range of applications; in this paper two proof-of-concept demonstrations are shown. The first utilizes the ability to control the resulting contact angle of the surface for the fabrication of a passive pressure-sensitive microfluidic gating system. The second is a model surface modification process that utilizes the functional groups deprotected during the photocleavage to pattern the deposition of moieties with complementary chemistry. The spatial layout, resolution, and concentration of these covalently linked molecules follow the gradient pattern created by the grayscale mask during exposure. The programmable chemical gradient fabrication scheme presented in this work allows explicit engineering of both surface properties that dictate nonspecific interactions (surface energy, charge, etc.) and functional chemistry necessary for covalent bonding.

Ziegler-type hydrogenation catalysts are important for industrial processes, namely, the large-scale selective hydrogenation of styrenic block copolymers. Ziegler-type hydrogenation catalysts are composed of a group 8-10 transition metal precatalyst plus an alkylaluminum cocatalyst (and they are not the same as Ziegler-Natta polymerization catalysts). However, for ∼50 years two unsettled issues central to Ziegler-type hydrogenation catalysis are the nature of the metal species present after catalyst synthesis, and whether the species primarily responsible for catalytic hydrogenation activity are homogeneous (e.g., monometallic complexes) or heterogeneous (e.g., Ziegler nanoclusters defined as metal nanoclusters made from combination of Ziegler-type hydrogenation catalyst precursors). A critical review of the existing literature (Alley et al. J. Mol. Catal. A: Chem. 2010, 315, 1-27) and a recently published study using an Ir model system (Alley et al. Inorg. Chem. 2010, 49, 8131-8147) help to guide the present investigation of Ziegler-type hydrogenation catalysts made from the industrially favored precursors Co(neodecanoate)(2) or Ni(2-ethylhexanoate)(2), plus AlEt(3). The approach and methods used herein parallel those used in the study of the Ir model system. Specifically, a combination of Z-contrast scanning transmission electron microscopy (STEM), matrix assisted laser desorption ionization mass spectrometry (MALDI MS), and X-ray absorption fine structure (XAFS) spectroscopy are used to characterize the transition metal species both before and after hydrogenation. Kinetic studies including Hg(0) poisoning experiments are utilized to test which species are the most active catalysts. The main findings are that, both before and after catalytic cyclohexene hydrogenation, the species present comprise a broad distribution of metal cluster sizes from subnanometer to nanometer scale particles, with estimated mean cluster diameters of about 1 nm for both Co and Ni. The XAFS results also imply that the catalyst solutions are a mixture of the metal clusters described above, plus unreduced metal ions. The kinetics-based Hg(0) poisoning evidence suggests that Co and Ni Ziegler nanoclusters (i.e., M(≥4)) are the most active Ziegler-type hydrogenation catalysts in these industrial systems. Overall, the novelty and primary conclusions of this study are as follows: (i) this study examines Co- and Ni-based catalysts made from the actual industrial precursor materials, catalysts that are notoriously problematic regarding their characterization; (ii) the Z-contrast STEM results reported herein represent, to our knowledge, the best microscopic analysis of the industrial Co and Ni Ziegler-type hydrogenation catalysts; (iii) this study is the first explicit application of an established method, using multiple analytical methods and kinetics-based studies, for distinguishing homogeneous from heterogeneous catalysis in these Ziegler-type systems; and (iv) this study parallels the successful study of an Ir model Ziegler catalyst system, thereby benefiting from a comparison to those previously unavailable findings, although the greater M-M bond energy, and tendency to agglomerate, of Ir versus Ni or Co are important differences to be noted. Overall, the main result of this work is that it provides the leading hypothesis going forward to try to refute in future work, namely, that sub, M(≥4) to larger, M(n) Ziegler nanoclusters are the dominant, industrial, Co- and Ni- plus AlR(3) catalysts in Ziegler-type hydrogenation systems.

Current technology development in light emitting diodes has enabled high efficiency operation, low energy consumption and lifetimes, thereby creating new possibilities in conventional display and lighting industry. Recent work is also creating more unusual uses in biomedicine and in sensing applications, where conformal contact over curvilinear surfaces is required. Here, ultrathin device geometries and optimized mechanical designs, including neutral mechanical plane layouts and serpentine interconnects, provide indicators and lighting modules with arbitrary shapes capable of integrated on nearly any type of substrates. Biomedical devices such as light emitting suture threads, and glove-mounted optical proximity sensors demonstrate the versatility of this strategy and create great new opportunities.

Unconventional methods to exploit monocrystalline silicon and other established materials in photovoltaic (PV) systems can create new engineering opportunities, device capabilities and cost structures. Here we show a type of composite luminescent concentrator PV system that embeds large scale, interconnected arrays of microscale silicon solar cells in thin matrix layers doped with luminophores. Photons that strike cells directly generate power in the usual manner; those incident on the matrix launch wavelength-downconverted photons that reflect and waveguide into the sides and bottom surfaces of the cells to increase further their power output, by more than 300% in examples reported here. Unlike conventional luminescent photovoltaics, this unusual design can be implemented in ultrathin, mechanically bendable formats. Detailed studies of design considerations and fabrication aspects for such devices, using both experimental and computational approaches, provide quantitative descriptions of the underlying materials science and optics.

The ARO Nano Engineered Energetic Materials (NEEM) MURI program has been exploring new methodologies for developing energetic material formulations with control of all constituents over a wide range of length scales from 1 nm to 1 mm and larger and employing the latest techniques in molecular self-assembly and supramolecular chemistry for synthesizing and assembling NEEMs. The synthetic efforts have been guided by theoretical calculations and dynamic performance testing methodologies that also operate on all length scales. This final report provides a summary of the accomplishments. In particular, new methods to generate metal nanoclusters were developed that are stabilized against environmental degradation while preserving their high energy content. Rapid expansion supercritical solution processes were developed and applied to synthesize nanosized particulate oxidizers and energetic oxidizer shell/fuel core composites. Surface science and experimental chemistry methods were applied to study the structures and energy releasing reaction pathways of NEEMs. Unique diagnostic capabilities were developed and applied to study the fundamental mechanisms that underlie NEEM dynamic performance. Combustion mechanisms of various NEEMs, including nanothermites and nanoparticulate fuel/liquid oxidizer systems, were experimentally analyzed. The reactive and thermal characteristics of NEEMs were studied using large (billion atoms) multiscale simulations that couple quantum-mechanical calculations to molecular dynamics calculations. In particular, the stability, structure and energetics of metallic nanoparticles with a special focus on the relationships between particle size, shape and excess surface free energy were studied. A unified theory of ignition and combustion of aluminum particles for a wide range of sizes, from nano to meso scales was established.

The activation and decomposition of silane on Cu(111) have been studied using Fourier transform infrared (FTIR), Auger electron (AES), and temperature-programmed reaction (TPRS) spectroscopies, as well as low-energy electron diffraction (LEED). Silane dissociatively chemisorbs on Cu(111) at 90 K. Cleavage of the Si-H bond yields two structurally distinct adsorbed silyl fragments. Infrared spectroscopy identifies the predominant intermediates formed under these conditions as being adsorbed SiH[sub 2] and SiH species. The relative and absolute concentrations of these intermediates depend sensitively on the surface coverage of both Si and H, which themselves depend upon the silane exposure. SiH[sub 2] is stable over a wide range of coverage up to 180 K, where it then undergoes Si-H bond cleavage to form surface bound SiH. At higher temperatures, bond scission in the Si-H moiety results in the formation of adsorbed silicon atoms and the desorption of dihydrogen in a peak centered at [approximately]330 K. Auger electron spectra show that the amount of silicon deposited on the Cu(111) surface in this way is approximately one-third of the amount deposited on a stable Cu[sub 3]Si surface. This latter surface is readily formed by carrying out the silane exposure at temperatures above 300 K. 39 refs., 15more » figs., 1 tab.« less

Low‐energy electron diffraction and reflection‐absorption infrared spectroscopy were used to study the monolayers formed by the adsorption of n‐alkane thiols [HS(CH2)mCH3] on both (111) and (100) single‐crystal gold substrates. Samples were prepared by dosing either from solution (m=15, 17, 18, and 21) or in ultrahigh vacuum (m=0–9). On Au(111), ordered surface structures are obtained which can be indexed as (n√3×√3)R30°, where n varies from 1 to 6. On Au(100), the adsorption of short chain thiols leads to the formation of a c(2×2) overlayer while the longer chain homologs show additional diffraction spot splittings. It is also found that chain length influences both the character of the diffraction seen and perturbs the reactive sticking probability of molecules dosed in UHV. Infrared studies reveal that the polymethylene chains of the monolayers formed on Au(100) are comprised of nearly all‐trans conformations and are less canted than the comparable structures formed on Au(111). A simple model is propos...

The activation and decomposition of silane on Cu(111) have been studied using Fourier transform infrared (FTIR), Auger electron (AES), and temperature-programmed reaction (TPRS) spectroscopies, as well as low-energy electron diffraction (LEED). Silane dissociatively chemisorbs on Cu(111) at 90 K. Cleavage of the Si-H bond yields two structurally distinct adsorbed silyl fragments. Infrared spectroscopy identifies the predominant intermediates formed under these conditions as being adsorbed SiH[sub 2] and SiH species. The relative and absolute concentrations of these intermediates depend sensitively on the surface coverage of both Si and H, which themselves depend upon the silane exposure. SiH[sub 2] is stable over a wide range of coverage up to 180 K, where it then undergoes Si-H bond cleavage to form surface bound SiH. At higher temperatures, bond scission in the Si-H moiety results in the formation of adsorbed silicon atoms and the desorption of dihydrogen in a peak centered at [approximately]330 K. Auger electron spectra show that the amount of silicon deposited on the Cu(111) surface in this way is approximately one-third of the amount deposited on a stable Cu[sub 3]Si surface. This latter surface is readily formed by carrying out the silane exposure at temperatures above 300 K. 39 refs., 15more » figs., 1 tab.« less

Ziegler-type hydrogenation catalysts, those made from a group 8-10 transition metal precatalyst and an AlR(3) cocatalyst, are often used for large scale industrial polymer hydrogenation; note that Ziegler-type hydrogenation catalysts are not the same as Ziegler-Natta polymerization catalysts. A review of prior studies of Ziegler-type hydrogenation catalysts (Alley et al. J. Mol. Catal. A: Chem. 2010, 315, 1-27) reveals that a approximately 50 year old problem is identifying the metal species present before, during, and after Ziegler-type hydrogenation catalysis, and which species are the kinetically best, fastest catalysts--that is, which species are the true hydrogenation catalysts. Also of significant interest is whether what we have termed "Ziegler nanoclusters" are present and what their relative catalytic activity is. Reported herein is the characterization of an Ir Ziegler-type hydrogenation catalyst, a valuable model (vide infra) for the Co-based industrial Ziegler-type hydrogenation catalyst, made from the crystallographically characterized [(1,5-COD)Ir(mu-O(2)C(8)H(15))](2) precatalyst plus AlEt(3). Characterization of this Ir model system is accomplished before and after catalysis using a battery of physical methods including Z-contrast scanning transmission electron microscopy (STEM), high resolution (HR)TEM, and X-ray absorption fine structure (XAFS) spectroscopy. Kinetic studies plus Hg(0) poisoning experiments are then employed to probe which species are the fastest catalysts. The main findings herein are that (i) a combination of the catalyst precursors [(1,5-COD)Ir(mu-O(2)C(8)H(15))](2) and AlEt(3) gives catalytically active solutions containing a broad distribution of Ir(n) species ranging from monometallic Ir complexes to nanometer scale, noncrystalline Ir(n) nanoclusters (up to Ir(approximately 100) by Z-contrast STEM) with the estimated mean Ir species being 0.5-0.7 nm, Ir(approximately 4-15) clusters considering the similar, but not identical results from the different analytical methods; furthermore, (ii) the mean Ir(n) species are practically the same regardless of the Al/Ir ratio employed, suggesting that the observed changes in catalytic activity at different Al/Ir ratios are primarily the result of changes in the form or function of the Al-derived component (and not due to significant AlEt(3)-induced changes in initial Ir(n) nuclearity). However (iii), during hydrogenation, a shift in the population of Ir species toward roughly 1.0-1.6 nm, fcc Ir(0)(approximately 40-150), Ziegler nanoclusters occurs with, significantly, (iv) a concomitant increase in catalytic activity. Importantly, and although catalysis by discrete subnanometer Ir species is not ruled out by this study, (v) the increases in activity with increased nanocluster size, plus Hg(0) poisoning studies, provide the best evidence to date that the approximately 1.0-1.6 nm, fcc Ir(0)(approximately 40-150), heterogeneous Ziegler nanoclusters are the fastest catalysts in this industrially related catalytic hydrogenation system (and in the simplest, Ockham's Razor interpretation of the data). In addition, (vi) Ziegler nanoclusters are confirmed to be an unusual, hydrocarbon-soluble, highly coordinatively unsaturated, Lewis-acid containing, and highly catalytically active type of nanocluster for use in other catalytic applications and other areas.

The atomic structures of several distinct adlayers of Cd underpotentially deposited onto a Au(111) surface in sulfuric acid electrolyte were revealed by in situ scanning tunneling microscopy (STM). Three ordered adlattices were observed, all of which have a long-range linear morphology rotated by 30° from the substrate's lattice directions. Complete geometric descriptions and proposed structures are presented for each. A purely electrostatic model is insufficient to explain the banded morphology which is observed; therefore, other structure-forming interactions, including lattice strain, are discussed as possible contributors.

The authors have investigated the growth, morphology, and phase evolution of Pt-Si intermetallic thin films using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). These materials were formed through an inverted CVD deposition process that involves the exposure of a Pt(100) crystal to silane (SiH{sup 4}) followed by flash annealing treatments. Structural studies performed as a function of the annealing temperature reveal a complicated phase behavior that involves the sequential formation of four atomically ordered phases with multilevel character. The nature of this process is analyzed to obtain information about the primary structure-determining interactions responsible for the phase transformations seen in this system. This report describes the structure-determining influences seen on the Pt(100) surface and provide a comparison with earlier results obtained on Pt(111) and Ni surfaces. The substrate effects are marked and the differences between the results obtained on Pt(100) and Pt(111) are discussed in detail. A model is presented that relates the structure of the phases obtained on the Pt(100) surface to known bulk Pt silicide phases. Of particular interest is the finding that inverted CVD via the thermolytic decomposition of SiH{sub 4} on the Pt(100) substrate yields, upon suitable thermal treatment, amore » ({radical} 17 x {radical} 17)R14.0{degree} overlayer structure exhibiting two chiral surface domains. This multilayer structure is well described by a termination of the bulk Pt-Si intermetallic phase that is isomorphic with the well-known Ni{sub 12}P{sub 5} structure.« less

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.