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Fabrication of ultrathin films of dielectric (with particular reference to materials with high dielectric constants) materials has significance in many advanced technological applications including hard protective coatings, sensors, and next generation logic devices. Current state-of-the-art in microelectronics for fabricating these thin films is a combination of atomic layer deposition and photolithography. As feature size decreases and aspect ratios increase, conformality of the films becomes paramount. Here, we show a polymer brush template assisted deposition of highly conformal, ultrathin (sub 5 nm) high-κ dielectric metal oxide films (hafnium oxide and zirconium oxide) on topographically patterned silicon nitride substrates. This technique, using hydroxyl terminated poly-4-vinyl pyridine (P4VP-OH) as the polymer brush, allows for conformal deposition with uniform thickness along the trenches and sidewalls of the substrate. Metal salts are infiltrated into the grafted monolayer polymer brush films via solution deposition. Tailoring specific polymer interfacial chemistries for ion infiltration combined with subsequent oxygen plasma treatment enabled the fabrication of high-quality sub 5 nm metal oxide films.

Conductive metal-organic frameworks are opening new perspectives for the use of these porous materials for applications traditionally limited to more classical inorganic materials, such as their integration into electronic devices. This has enabled the development of chemiresistive sensors capable of transducing the presence of specific guests into an electrical response with good selectivity and sensitivity. By combining experimental data with computational modelling, a possible origin for the underlying mechanism of this phenomenon in ultrathin films (ca. 30 nm) of Cu-CAT-1 is described. ispartof: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION vol:57 issue:46 pages:15086-15090 ispartof: location:Germany status: published

Hydrogen-related technologies are rapidly developing, driven by the necessity of efficient and high-density energy storage. This poses new challenges to the detection of dangerous gases, in particular the realization of cheap, sensitive, and fast hydrogen sensors. Several materials are being studied for this application, but most present critical bottlenecks, such as high operational temperature, low sensitivity, slow response time, and/or complex fabrication procedures. Here, we demonstrate that WO3 in the form of single-crystal, ultrathin films with a Pt catalyst allows high-performance sensing of H2 gas at room temperature. Thanks to the high electrical resistance in the pristine state, this material is able to detect hydrogen concentrations down to 1 ppm near room temperature. Moreover, the high surface-to-volume ratio of WO3 ultrathin films determines fast sensor response and recovery, with characteristic times as low as 1 s when the concentration exceeds 100 ppm. By modeling the hydrogen (de)intercalation dynamics with a kinetic model, we extract the energy barriers of the relevant processes and relate the doping mechanism to the formation of oxygen vacancies. Our results reveal the potential of single-crystal WO3 ultrathin films toward the development of sub-ppm hydrogen detectors working at room temperature.

The presence of interfaces and geometrical confinement can have a strong influence on the structure and morphology of thin films of semicrystalline polymers. Using surface-sensitive grazing incidence wide angle X-ray scattering and atomic force microscopy to investigate the vertical structure of thin films of poly(3-hexylthiophene) crystallized from the melt, we show that highly oriented crystallites are induced at the air/polymer interface and not as sometimes assumed at the interface to the substrate. These crystallites are oriented with their crystallographic a-axis perpendicular to the plane of the film. While the corresponding orientation dominates in thinner films, for sufficiently thick films (>60 nm) a layer containing unoriented crystals is present below the surface layer. Due to the anisotropic charge transport properties, the observed effects are expected to be of special relevance for potential applications of semiconductor polymers in the field of organic photovoltaics for which vertical transport in thicker films plays an important role.

Herein, we elucidate the impact of tubular confinement on the structure and relaxation behavior of poly(vinylidene difluoride) (PVDF) and how these affect the para-/ferroelectric behavior of this polymer. We use PVDF nanotubes that were solidified in anodic aluminum oxide (AAO) templates. Dielectric spectroscopy measurements evidence a bimodal relaxation process for PVDF nanotubes: besides the bulk-like α-relaxation, we detect a notably slower relaxation that is associated with the PVDF regions of restricted dynamics at the interface with the AAO pore. Strikingly, both the bulk-like and the interfacial relaxation tend to become temperature independent as the temperature increases, a behavior that has been observed before in inorganic relaxor ferroelectrics. In line with this, we observe that the real part of the dielectric permittivity of the PVDF nanotubes exhibits a broad maximum when plotted against the temperature, which is, again, a typical feature of relaxor ferroelectrics. As such, we propose that, in nanotubular PVDF, ferroelectric-like nanodomains are formed in the amorphous phase regions adjacent to the AAO interface. These ferroelectric nanodomains may result from an anisotropic chain conformation and a preferred orientation of local dipoles due to selective H-bond formation between the PVDF macromolecues and the AAO walls. Such relaxor-ferroelectric-like behavior has not been observed for nonirradiated PVDF homopolymer; our findings thus may enable in the future alternative applications for this bulk commodity plastic, e.g., for the production of electrocaloric devices for solid-state refrigeration which benefit from a relaxor-ferroelectric-like response., J.M. acknowledges support from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant, agreement No. 654682. A.A. and A.I. acknowledge financial support from the Spanish Ministry Ministerio de Economia y Competitividad (MINECO) (code: MAT2015-63704-P (MINECO/FEDER, UE)) and the Eusko Jaurlaritza (Basque Government) (code: IT-654-13). A.C. would like to acknowledge the financial support of the EPSRC (EP/M014142/1). A.N., T.A.E., and C.M. acknowledge financial support from MINECO (codes: MAT2014-59187-R, MAT2015-66443-C02-1-R, and MAT2014-53437-C2-1P, respectively). N.S. is in addition grateful for support from a European Research Council ERC Starting Independent Research Fellowship under the grant agreement No. 279587.

International audience; Germanene is a single layer allotrope of Ge, with a honeycomb structure similar to graphene. This report concerns the electrochemical formation of germanene in a pH 4.5 solution. The studies were performed using in situ Electrochemical Scanning Tunneling Microscopy (EC-STM), voltammetry, coulometry, surface X-ray diffraction (SXRD) and Raman spectroscopy to study germanene electrodeposition on Au(111) terraces. The deposition of Ge is kinetically slow and stops after 2-3 monolayers. EC-STM revealed a honeycomb (HC) structure with a rhombic unit cell, 0.44 +/- 0.02 nm on a side, very close to that predicted for germanene in the literature. Ideally the HC structure is a continuous sheet, with six Ge atoms around each hole. However, only small domains, surrounded by defects, of this structure were observed in this study. The small coherence length and multiple rotations domains made direct observation with surface X-ray diffraction difficult. Raman spectroscopy was used to investigate the multi-layer Ge deposits. A peak near 290 cm(-1), predicted to correspond to germanene, was observed on one particular area of the sample, while the rest resembled amorphous germanium. Electrochemical studies of germanene showed limited stability when exposed to oxygen.

WOS: 000506316400038, In this study, Au/n-Si/p-CZTS/Ag solar cells have been produced by using PLD technique. Ultrathin CZTS films have been grown on n-Si wafer in different thicknesses depending on number of laser pulses. These ultrathin CZTS films were analysed by XRD, AFM and UV-vis spectra. J-V characteristics of Au/n-Si/p-CZTS/Ag solar cells have been determined based on thickness of ultrathin CZTS films under AM 1.5 solar radiation of 80 mW/cm(2). Short circuit current density (mA/cm(2)), fill factor, open circuit voltage (V) and power conversion efficiency (%) of ultrathin CZTS film solar cells have been determined for device produced in this work. The photovoltaic (PV) characteristics of ultrathin CZTS film solar cells has been discussed in detail in this present article and, as a result, the ideal ultrathin CZTS film solar cell structure having the highest efficiency has been determined and concluded., Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [1649B031503748]; Selcuk University, Scientific Research Projects Coordination (BAP)UnitSelcuk University [18401178, 18401124, 15201070], Authors kindly would like to thank, The Scientific and Technological Research Council of Turkey (TUBITAK) for financial support via Grant No. 1649B031503748,; -Selcuk University, High Technology Research and Application Center for supplying with Infrastructure and; -Selcuk University, Scientific Research Projects Coordination (BAP)Unit for grands via projects with references of 18401178, 18401124 and 15201070.

The electrical transport mechanism of non-percolated copper ultrathin films was studied. For this purpose, resistance behavior was measured during sample growth, aging in vacuum and oxidation in air, and contrasted with a model based on tunnel current and on film’s morphology. In addition, the electrical characterization of chromium and gold ultrathin films was performed and compared with that obtained for copper. All films were grown on muscovite mica through thermal evaporation under high vacuum conditions. Electrical characterization throughout films’ growth, aging and oxidation was performed in situ and in real time. Finally, to address the transport mechanism of non-percolated oxidized copper films, samples were put into a cryostat in which electrical resistance was measured changing the temperature between 35 and 300 K. It was found that the three materials present an almost constant resistance decay during growth. This resistance decrease was studied for copper films by fitting a tunnel transport model which considered islands’ distance as a function of film thickness, indicating a resistance reduction given by coalescing islands. During aging, the resistance of copper and gold ultrathin films increases without reaching a saturation value after 30 min, with a behavior independent of the material or the initial resistance. The theoretical model applied to copper film resistance explains the increment by further formation of 3D structures, mainly conducted by atom diffusion on the substrate. Finally, a change in the resistance behavior is observed during the oxidation of copper ultrathin films, electrical transport is mediated by two mechanisms a semi-conductor type, resembling that of oxidized chromium layers, and a tunnel conduction type, observed in gold films. The first mechanism dominates when temperature is above 200 K, while tunneling is the main process for temperatures below 150 K.

Ultrathin transition metal oxide films exhibit unique physical and chemical properties not observed for the corresponding bulk oxides. These properties, originating mainly from the limited thickness and the interaction with the support, make those films similar to other supported 2D materials with bulk counterparts, such as transition metal dichalcogenides. Ultrathin iron oxide (FeO) films, for example, were shown to exhibit unique electronic, catalytic and magnetic properties that depend on the type of the used support. Ag(111) has always been considered a promising substrate for FeO growth, as it has the same surface symmetry, only ~5% lattice mismatch, is considered to be weakly-interacting and relatively resistant to oxidation. The reports on the growth and structure of ultrathin FeO films on Ag(111) are scarce and often contradictory to each other. We attempted to shed more light on this system by growing the films using different preparation procedures and studying their structure using scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). We observed the formation of a previously unreported Moir&eacute, superstructure with 45 &Aring, periodicity, as well as other reconstructed and reconstruction-free surface species. The experimental results obtained by us and other groups indicate that the structure of FeO films on this particular support critically depends on the films&rsquo, preparation conditions. We also performed density functional theory (DFT) calculations on the structure and properties of a conceptual reconstruction-free FeO film on Ag(111). The results indicate that such a film, if successfully grown, should exhibit tunable thickness-dependent properties, being substrate-influenced in the monolayer regime and free-standing-FeO-like when in the bilayer form.

Iron oxide films epitaxially grown on close-packed metal single crystal substrates exhibit nearly-perfect structural order, high catalytic activity (FeO) and room-temperature magnetism (Fe3O4). However, the morphology of the films, especially in the ultrathin regime, can be significantly influenced by the crystalline structure of the used support. This work reports an ultra-high vacuum (UHV) low energy electron/synchrotron light-based X-ray photoemission electron microscopy (LEEM/XPEEM) and electron diffraction (&micro, LEED) study of the growth of FeO and Fe3O4 on two closed-packed metal single crystal surfaces: Pt(111) and Ru(0001). The results reveal the influence of the mutual orientation of adjacent substrate terraces on the morphology of iron oxide films epitaxially grown on top of them. On fcc Pt(111), which has the same mutual orientation of adjacent monoatomic terraces, FeO(111) grows with the same in-plane orientation on all substrate terraces. For Fe3O4(111), one or two orientations are observed depending on the growth conditions. On hcp Ru(0001), the adjacent terraces of which are &lsquo, rotated&rsquo, by 180&deg, with respect to each other, the in-plane orientation of initial FeO(111) and Fe3O4(111) crystallites is determined by the orientation of the substrate terrace on which they nucleated. The adaptation of three-fold symmetric iron oxides to three-fold symmetric substrate terraces leads to natural structuring of iron oxide films, i.e., the formation of patch-like magnetite layers on Pt(111) and stripe-like FeO and Fe3O4 structures on Ru(0001).

This research explores fundamental, structural differences of ultrathin films, prepared with three distinct deposition methods using 2,2,6,6-tetramethyl-piperidin-1-oxyl radical oxidized cellulose nanofibres (TEMPO-CNFs) derived from never dried bleached birch pulp. There is standard characterization by atomic force microscopy (morphology, roughness) and ellipsometry (thickness) and important structural data is gained by exposing the films to water vapor and monitoring the vapor uptake with quartz crystal microbalance (QCM). Significant distinctions were found from QCM data that could be linked to the structure of the films, originating from the three deposition methods: adsorption, spin coating and electrophoretic deposition. Moreover, the results shown here have potential implications for various types of films that comprise of amphiphilic nanomaterials that have a distinct response to moisture or aqueous based solutions.

International audience; Thin films of a molecular spin crossover iron(II) complex featuring a photochromic diarylethene-based ligand have been grown by sublimation in ultra-high vacuum on an Au(111) single crystal, and investigated by X-ray and UV photoelectron spectroscopies. Temperature-dependent studies demonstrate that the thermally induced spin crossover behaviour is preserved in thin films. The photochromic ligand deliberately integrated into the complex allows photoswitching of the spin states of this iron(II) complex at room temperature, and this photomagnetic effect is still observed in 5 nm thick sublimated films. Thus, this work opens new horizons and pushes bistable spin crossover systems closer to prospective applications in molecular electronics and molecular spintronics devices functioning at room temperature.

Simultaneously synthesizing and structuring atomically thick or ultrathin 2D non-precious metal nanocrystal may offer a new class of materials to replace the state-of-art noble-metal electrocatalysts; however, the synthetic strategy is the bottleneck which should be urgently solved. Here we report the synthesis of an ultrathin nickel nanosheet array (Ni-NSA) through in situ topotactic reduction from Ni(OH)2 array precursors. The Ni nanosheets showed a single-crystalline lamellar structure with only ten atomic layers in thickness and an exposed (111) facet. Combined with a superaerophobic (low bubble adhesive) arrayed structure the Ni-NSAs exhibited a dramatic enhancement on both activity and stability towards the hydrazine-oxidation reaction (HzOR) relative to platinum. Furthermore, the partial oxidization of Ni-NSAs in ambient atmosphere resulted in effective water-splitting electrocatalysts for the hydrogen-evolution reaction (HER).

This work demonstrates the fabrication of molecular hybrid films comprising gold nanoparticles (AuNPs) incorporated in covalently assembled, substituted polythiophene (poly(3-(2-bromoethoxy)ethoxymethylthiophene-2,5-diyl (PBrEEMT))) films by different surface chemistry routes. AuNPs are incorporated in the immobilized polythiophene matrix due to its affinity for amine and sulfur. The amount of AuNPs present depends on the nature of the incorporation, the extent of film coverage and interaction of thiophene and amine groups. PBrEEMT films functionalized with amine rich polyallylamine immobilize greater numbers of AuNPs due to more extensive gold–amine interactions. Covalent binding between AuNP and PBrEEMT films was accomplished by using pre-functionalised AuNPs (4-aminothiophenol functionalized AuNPs). Atomic force microscopy, field emission scanning electron microscopy and X-ray photoelectron spectroscopy were used to study the morphology and chemical constituents of assembled films. These approaches will pave the way for developing facile methods for nanoparticle incorporation and will also facilitate direct interaction of nanoparticles with the conducting polymer matrix and enhance the electrical properties of the films. Refereed/Peer-reviewed

We characterize the surface passivation properties of ultrathin titanium oxide (TiO x ) films deposited by atomic layer deposition (ALD) on crystalline silicon by means of carrier lifetime measurements. We compare different silicon surface treatments prior to TiO x deposition, such as native silicon oxide (SiO y ), chemically grown SiO y and thermally grown SiO y . The best passivation quality is achieved with a native SiO y grown over 4 months and a TiO x layer thickness of 5 nm, resulting in an effective lifetime of 1.2 ms on 1.3 Ωcm p-type float-zone silicon. The measured maximum lifetime corresponds to an implied open-circuit voltage ( iV oc ) of 710 mV. For thinner TiO x layers the passivation quality is reduced, however, samples passivated with only 2 nm of TiO x still show a lifetime of 612 μs and an iV oc of 694 mV. The contact resistivity of the TiO x including the SiO y interlayer between the silicon wafer and the TiO x is below 0.8 Ωcm 2 . The combination of excellent surface passivation and low contact resistivity has the potential for silicon solar cells with efficiencies exceeding 26%.

A multiplexed, microfluidic platform to detect reactive metabolites is described, and its performance is illustrated for compounds metabolized by oxidative and bioconjugation enzymes in multi-enzyme pathways to mimic natural human drug metabolism. The device features four 8-electrode screen printed carbon arrays coated with thin films of DNA, a ruthenium-polyvinylpyridine (RuPVP) catalyst, and multiple enzyme sources including human liver microsomes (HLM), cytochrome P450 (cyt P450) 1B1 supersomes, microsomal epoxide hydrolase (EH), human S9 liver fractions (Hs9) and N-acetyltransferase (NAT). Arrays are arranged in parallel to facilitate multiple compound screening, enabling up to 32 enzyme reactions and measurements in 20–30 min. In the first step of the assay, metabolic reactions are achieved under constant flow of oxygenated reactant solutions by electrode driven natural catalytic cycles of cyt P450s and cofactor-supported bioconjugation enzymes. Reactive metabolites formed in the enzyme reactions can react with DNA. Relative DNA damage is measuring in the second assay step using square wave voltammetry (SWV) with RuPVP as catalyst. Studies were done on chemicals known to require metabolic activation to induce genotoxicity, and results reproduced known features of metabolite DNA-reactivity for the test compounds. Metabolism of benzo[a]pyrene (B[a]P) by cyt P450s and epoxide hydrolase showed an enhanced relative DNA damage rate for DNA damage compared to cyt P450s alone. DNA damage rates for arylamines by pathways featuring both oxidative and conjugative enzymes at pH 7.4 gave better correlation with rodent genotoxicity metric TD50. Results illustrate the broad utility of the reactive metabolite screening device.

Exposure to chemical pollutants and pharmaceuticals may cause health issues caused by metabolite-related toxicity. This paper reports a new microfluidic electrochemical sensor array with the ability to simultaneously detect common types of DNA damage including oxidation and nucleobase adduct formation. Sensors in the 8-electrode screen-printed carbon array were coated with thin films of metallopolymers osmium or ruthenium bipyridyl-poly( vinylpyridine) chloride (OsPVP, RuPVP) along with DNA and metabolic enzymes by layer-by-layer electrostatic assembly. After a reaction step in which test chemicals and other necessary reagents flow over the array, OsPVP selectively detects oxidized guanines on the DNA strands, and RuPVP detects DNA adduction by metabolites on nucleobases. We demonstrate array performance for test chemicals including 17 beta-estradiol (E-2), its metabolites 4-hydroxyestradiol (4-OHE2), 2-hydroxyestradiol (2-OHE2), catechol, 2-nitrosotoluene (2-NO-T), 4-(methylnitrosamino)-1-(3-pyridyl)1-butanone (NNK), and 2-acetylaminofluorene (2-AAF). Results revealed DNA-adduct and oxidation damage in a single run to provide a metabolic-genotoxic chemistry screen. The array measures damage directly in unhydrolyzed DNA, and is less expensive, faster, and simpler than conventional methods to detect DNA damage. The detection limit for oxidation is 672 8-oxodG per 10(6) bases. Each sensor requires only 22 ng of DNA, so the mass detection limit is 15 pg (similar to 10 pmol) 8-oxodG.

This article reviews recent progress from our laboratory in electrochemiluminescence (ECL) arrays designed for screening toxicity-related chemistry of chemical and drug candidates. Cytochrome P450s and metabolic bioconjugation enzymes convert lipophilic chemicals in our bodies by oxidation and bioconjugation that can lead to toxic metabolites. DNA can be used as an easily measurable toxicity-related endpoint, targeting DNA oxidation and addcut formation with metabolites. ECL using guanosines in the DNA strands as co-reactants have been used in high throughput arrays utilizing DNA-enzyme films fabricated layer-by-layer. This review describes approaches developed to provide new high throughput ECL arrays to aid in toxicity assessment for drug and chemical product development.

A new top-down approach to generate stable nanoscale films via catalyst induced cross-linking (CIC) is demonstrated. Polymers with various compositions and bearing pendent norbornene groups (defined as macrocross-linkers) are initially spin-coated onto substrates to form nanometre-thick films; when the films are brought into contact with a catalyst solution, ring-opening metathesis polymerization (ROMP)-mediated cross-linking efficiently occurs to lock the film into place. CIC provides a new paradigm for the fabrication of stable nanoscale films and provides an alternative to traditional methods that use external stimuli (e.g., heat or light) to trigger film cross-linking. The process requires short cross-linking times (

Using high resolution and ambient pressure X-ray photoelectron spectroscopy we show that the catalytically active FeO $$_{2}$$ trilayer films grown on Pt(111) are very active for water dissociation, in contrast to inert FeO(111) bilayer films. The FeO $$_{2}$$ trilayer is so active for water dissociation that it becomes hydroxylated upon formation, regardless of the applied preparation method. FeO $$_{2}$$ trilayers were grown by oxidation of FeO(111) bilayer films either with molecular oxygen in the mbar regime, or by NO $$_2$$ and atomic oxygen exposures, respectively, in the ultrahigh vacuum regime. Because it was impossible to prepare clean FeO $$_{2}$$ without any hydroxyls we propose that catalytically highly active FeO $$_{2}$$ trilayer films are generally hydroxylated. In addition, we provide spectroscopic fingerprints both for Pt(111)-supported FeO(111) and FeO $$_2$$ films that can serve as reference for future in situ studies.

A mononuclear Fe(ii) complex involving a tetrathiafulvalene-based ligand exhibits thermal spin-crossover (around 143 K) with pronounced hysteresis behaviour (48 K). The chromophoric and π-extended ligand allows Near-Infrared (NIR) sensitization for the light-induced excited spin-state trapping (LIESST) with T(LIESST) = 90 K.

Optically selective low-emissive (low-E) filters, constituted of different ultrathin layers and suitable to an effective employment in glazing technology for low energy consumption buildings have been designed and fabricated on glass by means of sputtering technique. Sputtering process parameters, layers sequence of the stacked structure and thicknesses of the layers have been selected by means of a semi-empirical approach. Once defined optical requirements of high visible transmittance and low emissivity (< 5%), proper materials have been selected as metals and ceramics to create the optical filter. In particular, silver as highly IR reflecting metal and aluminium nitride as transparent insulating material, have been alternated in a very simple and highly effective coating formulation. However, preliminary optical simulation of optimized low-E coating did not take into account critical technological aspects such as the difficulty in producing high metallic quality ultrathin Ag layers and the undesired photo-emissive metal-nitrogen complexes formation at the Ag/AlN interfaces. The goal of obtaining Ag ultrathin compact layers has been reached with the aid of a proper aluminium nitride as adaptive layer. At the same time the chemical reactivity at the metal/ceramic interface (with consequent photo-emissive defects formation) has been prevented working in transition regime during AlN reactive sputtering process. In conclusion, a very simple low cost sputtering process is proposed for fabricating highly effective low-E coatings on large area glasses.

This paper presents an overview of the recent work on ultrathin polymer blend films containing cellulose. Three systems prepared via trimethylsilyl cellulose derivative, which is subsequently hydrolyzed to cellulose, are presented: polystyrene/ cellulose, poly(methyl methacrylate)/cellulose and polystyrene-block-polyethylene-oxide/cellulose. Diverse textures emerge within the films depending on the interactions between the polymers and their interactions with the substrate as well as on different solubilities of the polymers. Furthermore, an ultrathin film containing a cellulose/xylan blend is presented. This film was deposited directly from a common solvent (dimethylacetamide/lithium chloride) and it did not exhibit distinct morphological patterns comparable to the blends with synthetic polymers.

International audience; Morphology of polymer electrolytes membranes (PEM), e.g., Nafion, inside PEM fuel cell catalyst layers has a significant impact on the electrochemical activity and transport phenomena that determine cell performance. In those regions, Nafion can be found as an ultrathin film, coating the catalyst and the catalyst support surfaces. The impact of the hydrophilic/hydrophobic character of these surfaces on the structural formation of the films has not been sufficiently explored yet. Here, we report an extensive molecular dynamics simulation investigation of the substrate effects on the ionomer ultrathin film morphology at different hydration levels. We use a mean-field-like model that we introduced in previous publications for the interaction of the hydrated Nafion ionomer with a substrate, characterized by a tunable degree of hydrophilicity. We show that the affinity of the substrate with water plays a crucial role in the molecular rearrangement of the ionomer film, resulting in completely different morphologies. Detailed structural description in different regions of the film shows evidence of strongly heterogeneous behavior. A qualitative discussion of the implications of our observations on the PEMFC catalyst layer performance is finally proposed.

Ultra-thin films with low surface roughness that support surface plasmon-polaritons in the infra-red and visible ranges are needed in order to improve the performance of devices based on the manipulation of plasmon propagation. Increasing amount of efforts is made in order not only to improve the quality of the deposited layers but also to diminish their thickness and to find new materials that could be used in this field. In this review, we consider various thin films used in the field of plasmonics and metamaterials in the visible and IR range. We focus our presentation on technological issues of their deposition and reported characterization of film plasmonic performance.

Thin and ultrathin crystalline polymer films are of funda mental scientific as well as practical interest concerning their structures and properties. 6] For the preparation of ultrathin ( 0.1 mm) films the polymer is applied to the substrate in a non ordered state, usually as a dilute solution in an organic solvent. To overcome the intra and intermolecular interac tions responsible for crystalline order in the solid polymer, and render it soluble, high temperatures are often required. Crystalline order only forms on the substrate during solvent removal or cooling. As a different approach to ultrathin films of crystalline polymers we report on their preparation at room temperature from aqueous dispersions of prefabricated polymer nanocrystals functioning as building blocks (Scheme 1). The very small particle size, in combination with the basic phenomenon that the amorphous regions are located at the surface exclusively in polymer single crystals, results in an efficient interaction between particles in films.

Oxidative stress in humans causes damage to biomolecules by generating reactive oxygen species (ROS). DNA can be oxidatively damaged by ROS, which may lead to carcinogenesis. Here we report a microfluidic electrochemical array designed to rapidly detect oxidation in intact DNA in replicate measurements. Sensor arrays were fabricated by wet-chemistry patterning of gold compact discs. The eight-sensor array is incorporated into a 60 mu L microfluidic channel connected to a pump and sample valve. The array features 7 nm thick osmium bipyridyl poly(vinylpyridine) chloride [Os(bpy)(2)(PVP)(10)Cl](+) films assembled layer-by-layer with polyions onto the gold sensors. 8-Hydroxy-7,8-hydro-2'-deoxyguanosine (8-oxodG) is selectively oxidized by [Os(bpy)(2)(PVP)(10)Cl](+) in intact ds-DNA to provide catalytic square wave voltammograms (SWV). The device is easy-to-use, fast, inexpensive, reusable, and can detect one 8-oxodG per 6600 nucleobases. The mass detection limit is 150-fold lower than a previously reported dip-and-read voltammetric sensor for oxidized DNA. Fast assays (

We investigate the use of laccase enzymes to couple short nonpolar chains containing aromatic groups onto flax fibers and nanofibrillated cellulose (NFC) with different lignin contents. Trametes villosa , Pycnoporus cinnabarinus , and Myceliophthora thermophila were used to facilitate surface coupling and to produce materials with different levels of hydrophobicity. Heat treatment of fiber webs after lacccase-mediated coupling markedly increased the resistance to water absorption. The highest hydrophobization levels of flax fibers was achieved by coupling dodecyl 3,4,5-trihydroxybenzoate (HB-C12), which yielded water contact angles (WCAs) of 80-96 degrees and water absorption times (drop tests) of ca. 73 min. The results from apparent aromatic content and FTIR analyses confirmed the laccase-mediated coupling of HB-C12 onto the cellulose fibers. Ultrathin films of NFC were also used as substrates for enzyme-mediated hydrophobization with HB-C12. In these cases, WCAs in the range of 87-104 degrees were achieved, depending on the conditions. Quartz crystal microgravimetry (QCM) was used to study the dynamics and the extent of the coupling process onto cellulose. The results help to better understand the mechanisms involved in laccase-mediated hydrophobization and provide a proof of a biotechnological platform for the development of value-added fiber products.

Sequential growth in solution is a powerful tool to control the growth of coordination networks on surfaces. We used this approach to prepare nanolayers of the bistable copper-molybdenum cyanide-bridged network. The nanolayers were grown on functionalized silicon and on bare platinum surfaces. The use of platinum dots organized on silicon oxide led to the growth of isolated and organized coordination objects. The bistable properties, characteristic of the bulk, have been evidenced for the nanolayers using infrared spectroscopy.

The structure of polymer electrolyte membranes, e.g., Nafion, inside fuel cell catalyst layers has significant impact on the electrochemical activity and transport phenomena that determine cell performance. In those regions, Nafion can be found as an ultrathin film, coating the catalyst and the catalyst support surfaces. The impact of the hydrophilic/hydrophobic character of these surfaces on the structural formation of the films and, in turn, on transport properties has not been sufficiently explored yet. Here, we report classical molecular dynamics simulations of hydrated Nafion thin films in contact with unstructured supports, characterized by their global wetting properties only. We have investigated structure and transport in different regions of the film and found evidence of strongly heterogeneous behavior. We speculate about the implications of our work on experimental and technological activity. © 2013 American Chemical Society.

Liver microsomes provide a representative source of enzymes for metabolic toxicity studies that can provide good comparability with in vivo bioassays [1]. Human liver microsomes (HLM) are liver cell membrane fractions containing cytochrome P450s (cyt P450), a superfamily of enzymes responsible for the major fraction of human oxidative metabolism. HLMs contain a collection of cyt P450s accompanied by redox partner cyt P450 reductase (CPR), and activation of oxidative metabolic reactions requires only an electron donor such as NADPH. The proposed pathway involves initial donation of an electron from NADPH via CPR to the cyt P450 followed by dioxygen binding to the heme iron [2–4]. A second electron transfer from CPR leads to the active ferryloxy radical cation of cyt P450 that transfers oxygen to substrates. Cyt P450s in thin films have enormous potential in selective biosynthesis and biosensors. Thin-film voltammetry of a number of cyt P450s has been studied [5–9]. Three general pathways to activate cyt P450s on electrodes have been elaborated: (a) direct electron transfer to pure cyt P450FeIII in films in aerobic solutions results in catalytic reduction of oxygen to hydrogen peroxide (H2O2), which transfers oxygen to the heme iron [5]; (b) fusion proteins with an electron acceptor protein linked to a cyt P450 feature electron flow from electrode, to electron acceptor protein, to the cyt P450 [7]; and (c) microsomal CPR/cyt P450 films where electrons flow from electrode to CPR to the cyt P450 as in the natural catalytic pathway [8]. All these approaches substitute the electrode for NADPH as an electron donor. We have reported successful electrochemical activation of cyt P450 via CPR in films that combined CPR microsomes with excess cyt P450 1A2 and 2E1 [8, 10], as well as in films of rat liver microsomes [11, 12]. Such a pathway may also occur in genetically enriched cyt P450 1A2 and cyt P450 3A4 supersomes [13] in polyion films on electrodes. However, it has not yet been confirmed that cyt P450s in HLMs can be electrochemically activated in the same fashion. In this communication, we report successful electrochemical activation of the natural catalytic pathway of cyt P450s in films of HLM and polyions on pyrolytic graphite (PG) electrodes. Cyt P450 1B1 supersomes (cyt P450 1B1), which contain cyt P450 1B1 and CPR, and CPR microsomes which contains only CPR as a negative control were also used in this study. We demonstrate direct conversion of a substrate using thin films of the HLM to generate reactive metabolites from 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which are shown to react with DNA in a toxicity screening assay. Quartz crystal microbalance (QCM) studies [14] confirmed stable, reproducible formation of the films containing enzymes and polyions on PG electrodes used in this work (Table 1). Cyclic voltammograms (CVs) of (PDDA/HLM)3 and (PDDA/cyt P450 1B1)3 showed the characteristics of non-ideal quasireversible protein film voltammetry [15]. Reduction–oxidation peak pairs had midpoint potentials (E°) −0.50 V vs. saturated calomel reference electrode (SCE) for HLM and −0.51 V for cyt P450 1B1 and CPR microsomes. Peak current was linear vs. scan rate up to 1000 mV s−1, reduction peak currents shifted negative with increasing scan rate, and oxidation-reduction peak current ratios were ~1. Table 1 Characteristics of films of polyions and enzyme sources from QCM results. For FeIII heme protein films in solutions containing CO, protein FeII-CO complexes form upon reduction that result in 35–50 mV positive shift of midpoint potentials due to the follow-up chemical reaction of the protein FeII form with CO [8, 10, 16]. CV peaks of CPR microsome, HLM or cyt P450 1B1 supersome films did not shift with CO in solution (Figure 1). This lack of midpoint potential shifts for CPR microsomes, HLM and cyt P450 1B1 films suggests that CV peaks originated not from cyt P450s but from CPR [8, 11, 13, 17]. CPR contains FAD and FMN cofactors, and CPR voltammetry has been interpreted previously [11, 13, 17]. Further, midpoint potentials near −0.5 V vs. SCE are characteristic of CPR and not cyt P450s, which have CV midpoint potentials in similar films of about −0.30 to −0.35 V vs. SCE [6, 8]. Fig. 1 Background subtracted cyclic voltammograms of the films on PG electrodes at 1 Vs−1 in 50 mM phosphate buffer pH 7.4+0.1 M NaCl: (A) (PDDA/HLM)3, (B) (PDDA/CPR microsomes)3, (C) (PDDA/cyt P450 1B1 supersomes)3. Curve labels: (a) buffer saturated ... Catalytic reduction of H2O2 can be observed by voltammetrically in films of iron heme proteins including cyt P450s. [11, 13, 15]. However, films of HLM or CPR microsomes did not show catalytic behavior in 2 mM H2O2 (see Figure S1). In contrast, films of positive control heme protein myoglobin (Mb) gave a large peak for catalytic reduction of H2O2 (Figure S1). These findings further confirm that the redox peaks of HLM and CPR microsomes (Figure 1, Scheme 1) originate from CPR and not cyt P450s. Species responsible for the CV peaks of HLM films did not catalytically reduce H2O2, nor did peaks shift under the influence of CO. All these results suggest peak assignment to CPR, which does not catalytically reduce H2O2 or react with CO in its reduced form [11, 13, 17]. Scheme 1 Electrochemical processes occurring in the microsomal films. To demonstrate that electrons injected into CPR can be used to activate the cyt P450 enzymes in the HLM film, we used a microfluidic electrochemical toxicity screening device reported previously using rat liver enzymes [12]. This device is designed to produce and detect reactive metabolites formed by cyt P450 enzymes by monitoring their reactions with DNA in DNA/RuPVP ([Ru(bpy)2(PVP)10](ClO4); bpy=2,2-bipyridyl; PVP=poly(4-vinylpyridine))/enzyme films. Electrolysis was done at a potential negative of the film’s reduction peak (−0.7 V vs. SCE, see Figure 1) to deliver electrons to CPR and activate the natural cyt P450 catalytic cycle. The enzyme reactions were done using constant flow of oxygenated 50 µM 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). After the enzyme reaction, square wave voltammetry (SWV) detects DNA damage caused by reactive metabolites. Cyt P450-catalyzed NNK metabolism involves the formation of an N-methyl hydroxylated metabolite, which reacts with DNA to produce a covalently attached guanine adduct [18]. The difference SWV peak at ~1.1 V vs. SCE originates from oxidation of RuII sites in the polymer to RuIII, which catalytically oxidizes guanines in the DNA. If DNA forms covalent adducts with the metabolites, the double stranded structure is disrupted and RuIII sites gain better access to guanines. This results in larger catalytic oxidation rates and larger peak currents in SWV [19, 20]. The ratio of the SWV difference peak current after the enzyme reaction (Ip,f) to that of controls with no enzyme reaction (Ip,i)) is the measured quantity indicative of DNA damage [5, 12]. Increase in SWV peak current densities were observed with time of enzyme reaction in the HLM/DNA film indicating reactive metabolites of NNK form and damage DNA (Figure 2 a). Figure 2 b suggests progressive DNA damage by metabolites of NNK until saturation is reached. In contrast, CPR microsomes did not show an increase in SWV ratio, indicating no metabolism of NNK due to the lack of cyt P450s. Fig. 2 SWV detection of DNA damage caused by reactive metabolites of 50 µM NNK in anaerobic pH 7.4 phosphate buffer in a microfluidic metabolic toxicity screening assay: (a) Background-subtracted averaged (n=8) difference SWV peak current densities for ... Results from microfluidic genotoxicity screening arrays indicate that electrochemical activation via CPR causes the electrons to be subsequently transferred to cyt P450 enzymes to convert the NNK substrate to reactive metabolites that react with DNA (Figure 2). The turnover rate of NNK oxidation by HLM is 176±22 ({µg protein−1} s−1 mM−1 for 50 mM NNK under these conditions. Reactive metabolites were formed from HLM, but not from CPR microsomes that lack cyt P450s. This result indicates further that the natural catalytic cycle of cyt P450 can be submitted by electrochemical activation in the HLM films. The pathway involves reduction of the cyt P450 to the FeII form, then subsequent reactions with oxygen and a second electron from CPR to yield the active oxidant, ferryloxy cyt P450 [4, 8]. In summary, voltammograms and metabolite generation presented above strongly suggest that electrons are transferred from electrode to CPR to cyt P450s in HLM films. Results document the successful electrode-driven activation of HLM in the sensing arrays used here. This approach was concurrently used to validate a new, higher throughput microfluidic array for genotoxicity screening combining HLMs with representative metabolic bioconjugation enzymes [21].

Monitoring the impact of annealing on the dynamic glass transition of nanometres-thick polymer layers provides new insights into the mechanisms behind the tremendous changes in the performance of macromolecular materials in close proximity to an interface. Here we present results revealing a correlation between deviations from bulk behaviour, manifesting in changes to the glass transition temperature, the reduction of dielectric strength and the growth of an irreversibly adsorbed layer (Guiselin brushes). The non-universal behaviour of polymers under confinement could be explained in terms of a dimensionless number given by the ratio between the timescale of adsorption and the annealing time. In particular, in the case of slow adsorption kinetics, such as for polystyrene on aluminium, deviations from bulk behaviour correspond to metastable states with an extremely long lifetime. ispartof: Nature communications vol:2 issue:1 status: published

We measure surface recombination velocities (SRVs) below 10 cm/s on low-resistivity (1.4 Ωcm) p-type crystalline silicon wafers passivated with plasma-assisted and thermal atomic layer deposited (ALD) aluminium oxide (Al2O3) films. Ultrathin Al2O3 films (< 5 nm) are particularly relevant for the implementation into solar cells, as the deposition rate of the ALD process is very low compared to e.g. plasma-enhanced chemical vapor deposition (PECVD). Hence, we examine the passivation quality of a stack consisting of an ultrathin Al2O 3 passivation layer deposited by ALD and a SiNx capping layer deposited by PECVD. Our experiments show a substantial improvement of the thermal stability during firing at 810°C for the Al2O 3/SiNx stacks compared to a single Al2O 3 layer. We report on a 'regeneration effect' observed for Al 2O3 single layers after firing, where the degraded passivation is significantly improved after annealing at 400°C and also by illumination at room temperature using a halogen lamp. Nevertheless, for Al 2O3/SiNx stacks we measure SRVs < 15 cm/s after firing, whereas for Al2O3 single layers the regenerated SRVs are in the range of 10-30 cm/s. Al2O 3/SiNx stacks are hence ideally suited for the implementation into industrial-type silicon solar cells, although 'regenerated' Al2O3 single layers should result in a comparable cell performance. State of Lower Saxony German Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU)/0325050

The cold crystallization process in poly(ethylene terephthalate) (PET) spin-coated ultrathin films was studied by infrared spectroscopy. The conformational change associated to the formation of crystal phase during annealing at 107 °C was measured in real time, by monitoring both intensity and frequency shift of trans and gauche conformer bands of the PET glycol segment. Enhancement of crystallization kinetics was observed in thin films deposited on amorphous silicon, with respect to a 20 μm thick free standing film used as reference, where the fastest kinetics was observed for the thinnest (35 nm) film. Experimental findings were interpreted in terms of scarce interaction between PET films and silicon substrate, which does not provide slowing down of crystallization kinetics as observed on different substrates. This results in a dominant effect of the polymer/air interface, where faster kinetics is observed, as also confirmed by atomic force microscopy imaging, particularly on the thinnest film. Additionally, Avrami and Avramov analyses evidence a decrease of both the Avrami exponent, related to growth dimensionality, and induction time, related to delay of nucleation start, when decreasing film thickness. Therefore, the reported results enrich the description of confinement and substrate interaction effects on the cold crystallization process taking place in PET ultrathin films.

Zirconia ultrathin films were deposited by aqueous chemical solution deposition, using citratoperoxo-Zr(IV) precursors with different citric acid content. The precursor synthesis, thermal decomposition and crystallization of oxide powders were studied. This showed an effect of the citric acid content in every stage. The precursors were applied for the deposition of uniform, ultrathin films (

We explored the structural limits of unconventional electron-beam lithography by directly writing with an electron beam into ultrathin SiO2 films. The obtained structures were analyzed by tunneling microscopy. The Auger excitation process (Knotek-Feibelman mechanism) necessary for electron-stimulated oxygen desorption allows generation of ultrasmall structures. The subsequent processing step combines thermal desorption of the remaining monoxide and simultaneous etching promoted by thermally activated silicon atoms, which turns out to be a strongly anisotropic process close to step edges. Applying this combination of processes to a regularly stepped Si(557) sample, linewidths close to the resolution of the electron microscope of 5 nm were obtained. © 2008 American Institute of Physics.

In this letter, we have studied transient photoinduced absorption in as-grown nanocrystallinc silicon films with thickness varied from 5 to 30 nm. Effects of quantum confinement (QC) in z-direction and grain boundary distortions alter the carrier dynamics of these films considerably. Based on the determination of critical points in the first Brillouin zone of the band structure of materials, we have time-resolved the relaxation times of surface-related states and indirect valleys. When decreasing the film thickness down to the QC limit (∼ 10 nm) new ultrafast relaxation mechanisms start to play a dominant role in carrier dynamics due to the topological disordering of these ultrathin films. These relaxation mechanisms seem to be related with the traping/ de-traping of the excited carriers prior to recombination. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. 2 1 19 21 Cited By :4

We perform molecular dynamics Simulations to study the dielectric relaxation of a head-spring model for a polymer melt in the bulk and in Supported films. By assigning dipole moments parallel and perpendicular to the backbone of all chains ill the completed simulation trajectories, we calculate the dielectric spectra of so-called type-A polymers which exhibit relaxation processes due to the local motion of chain segments ("segmental mode") and due to fluctuations of the end-to-end vector ("normal mode"). We investigate the dependence of both processes on film thickness and chain length and for the segmental mode also oil temperature T. We find that the relaxation of both modes is enhanced in the films relative to the bulk. For the segmental mode this difference between film and bulk dynamics increases oil cooling toward the glass transition. By a layer-resolved analysis of the segmental relaxation, we show that the acceleration of the average film dynamics is a consequence of a smooth gradient in relaxation, originating from both interfaces where the segmental dipoles relax much faster than in the bulk. Additionally. near the interfaces the segmental relaxation is more strongly stretched than in the center of the film where bulk behavior prevails. As the average film dynamics comprises contributions from all layers, the dielectric spectra of the films are broader than in the bulk at the same T. Finally. starting from the layer-resolved analysis which associates a dielectric function and so a capacitance with each layer. we suggest to think of a film as being a system of capacitors. The capacitors are arranged ill series, if the electric (E) field is perpendicular to the plane of the film (the usual experimental Situation), and in parallel. if the field is parallel to the plane. Because of these different arrangements of the capacitors, the resulting dielectric spectra depend on the direction of the E-field. For instance, we find that, although the segmental relaxation ill each layer is taken to be the same for both field directions. the average dielectric spectra differ because the layer-dependent dielectric strength and file limiting high-frequency permittivity enter into the average dielectric response in different ways for the E-field being perpendicular or parallel to the film plane. ispartof: Macromolecules vol:41 issue:20 pages:7729-7743 status: published

The unexpected glide of dislocations on a plane parallel to the film/substrate interface in ultrathin copper films, which has been called parallel glide (Balk et al 2003 Acta Metall. 51 447), is described using an analytical model. The phenomenon is observed as a problem involving inlet/outlet flow from different positions of a grain boundary into the grain channel. In this sense, parallel glide is presented as the flow of dislocations with an internal stress source/sink distribution.

The growth and the crystalline and electronic structure of Ni deposited on single crystalline Cu(111) were studied by scanning tunnelling microscopy (STM), grazing incidence X-ray diffraction (GIXD) and angle-resolved photoemission spectroscopy (ARPES). In the early stages of growth monoatomic-high flat Ni islands, partially covered by Cu migrating from the surface, are observed. Starting from a pseudomorphic epitaxial relationship the in-plane lattice parameter progressively relaxes with increasing coverage. For a 20 monolayer (ML) thick deposit the in-plane lattice parameter is still found halfway between the bulk Ni and Cu lattice parameters. ARPES data also rule out the layer-by-layer growth and provide the values of the Ni exchange splitting. (c) 2006 Elsevier B.V. All rights reserved.

Kinetic and equilibrium aspects of three different poly(ethylene oxide) alkylethers (C12E5, C12E7, C14E7) near a flat cellulose surface are studied. The equilibrium adsorption isotherms look very similar for these surfactants, each showing three different regions with increasing surfactant concentration. At low surfactant content both the headgroup and the tail contribute to the adsorption. At higher surface concentrations, lateral attraction becomes prominent and leads to the formation of aggregates on the surface. The general shape of the isotherms and the magnitude of the adsorption resemble mostly those for hydrophilic surfaces, but both the ethylene oxide and the aliphatic segments determine affinity for the surface. The adsorption and desorption kinetics are strongly dependent on surfactant composition. At bulk concentrations below the CMC, the initial adsorption rate is attachment-controlled. Above the CMC, the micellar diffusion coefficient and the micellar dissociation rate play a crucial role. For the most hydrophilic surfactant, C12E7, both parameters are relatively large. In this case, the initial adsorption rate increases with increasing surfactant concentration, also above the CMC. For C12E5 and C14E7 there is no micellar contribution to the initial adsorption rate. The initial desorption kinetics are governed by monomer detachment from the surface aggregates. The desorption rate constants scale with the CMC, indicating an analogy between the surface aggregates and those formed in solution.

Characterisation of ultrathin Prussian Blue films has been performed using in situ electrochemical surface plasmon resonance technique. Prussian Blue films have been prepared by potentiostatic method on a gold-coated glass surface plasmon resonance sensor. The electrochemical reduction of Prussian Blue to Prussian White and oxidation to Berlin Green are accompanied by a change of the refractive index; the system shows repeating voltammetric responses over subsequent potential cycles. The surface plasmon resonance signal is capable of evidencing minute electrochemically induced changes in the inorganic film coating the electrode.