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Vapor-phase infiltration (VPI) is an emerging organic-inorganic materials hybridization technique derived from atomic layer deposition (ALD) wherein gaseous organometallic precursors and co-reactants diffuse into starting organic templates in a sequential and cyclic manner and become hybridized with the organic matrix. The resulting hybrids feature uniquely enhanced materials properties, including but not limited to mechanical, chemical, dielectric, optical, and electrical properties, which are controllable by the type and amount of infiltrated inorganic species. When combined with polymer templates with either dimensional confinement (e.g., lithographically defined polymer patterns) or intrinsic spatial chemical contrast (e.g., self-assembled block copolymer (BCP) thin films), the technique also yields a site-specific infiltration, analogous to area-selective ALD, creating a spatially localized hybridization. Furthermore, the organic matrix of such infiltrated hybrids can be selectively removed by plasma ashing and thermal annealing to generate inorganic nanostructures that inherit the morphology of starting polymer templates, providing an alternative inorganic nanopatterning methodology. In this talk, I will showcase how these features of VPI can be utilized for the applications in microelectronics, including: (a) arbitrary patterning ultrahigh aspect-ratio metal oxide nanostructures; (b) generation of metal-oxide-based nanowire and nanomesh structures for conductometric sensing; and (c) VPI-derived metal-oxide-infiltrated hybrid photoresists for extreme ultraviolet (EUV) lithography.

A novel atomic layer method for encapsulating individual micro- and nano-particles with thin (sub-10-nm) dielectric films is presented. This method leverages the diffusion of vapor-phase precursors through an underlying inert polymer film to achieve growth of a metal oxide film on all sides of the particle simultaneously; even on the side that is in contact with the substrate. Crucially, the deposition is performed on stationary particles and does not require an agitation mechanism or a special reaction chamber. Here, conformal coatings of alumina are shown to improve stability in aqueous environments for two optically-relevant particles: compound semiconductor laser microparticles and lead halide perovskite nanocrystals.

We have developed an organic-inorganic hybrid resist platform featuring versatile ex-situ control of its performance by incorporating inorganic elements using vapor-phase infiltration (VPI) into standard organic resists. With poly(methyl methacrylate) (PMMA)-AlOx hybrid as a model composition we unveiled controllability of the critical exposure dose, contrast (as high as ~30), and etch resistance; estimated Si etch selectivity over ~300, demonstrating high aspect ratio ~17 with ~30 nm resolution Si fin-structures. Building upon the demonstration of PMMA-AlOx hybrid resist, we expanded our material portfolio to a high sensitivity resist and other inorganic moieties. We present preliminary results obtained from the extreme ultraviolet (EUV) lithography dose tests conducted on corresponding infiltrated hybrids and optimization of infiltration with the help of transmission electron microscopy (TEM).

Mixed matrix materials (MMMs) hold great potential for membrane gas separations by merging nanofillers with unique nanostructures and polymers with excellent processability. In situ growth of the nanofillers is adapted to mitigate interfacial incompatibility to avoid the selectivity loss. Surprisingly, functional polymers have not been exploited to co-grow the nanofillers for membrane applications. Herein, in situ synergistic growth of crystalline zeolite imidazole framework-8 (ZIF-8) in polybenzimidazole (PBI), creating highly porous structures with high gas permeability, is demonstrated. More importantly, PBI contains benzimidazole groups (similar to the precursor for ZIF-8, i.e., 2-methylimidazole) and induces the formation of amorphous ZIFs, enhancing interfacial compatibility and creating highly size-discriminating bottlenecks. For instance, the formation of 15 mass% ZIF-8 in PBI improves H

Recently, ultrathin metal-oxide thin film transistors (TFTs) have shown very high on-off ratio and ultra-sharp subthreshold swing, making them promising candidates for applications beyond conventional large-area electronics. While the on-off operation in typical TFTs results primarily from the modulation of charge carrier density by gate voltage, the high on-off ratio in ultrathin oxide TFTs can be associated with a large carrier mobility modulation, whose origin remains unknown. We investigate 3.5 nm-thick TiOx-based ultrathin TFTs exhibiting on-off ratio of ~106, predominantly driven by ~6-decade gate-induced mobility modulation. The power law behavior of the mobility features two regimes, with a very high exponent at low gate voltages, unprecedented for oxide TFTs. We find that this phenomenon is well explained by the presence of high-density tail states near the conduction band edge, which supports carrier transport via variable range hopping. The observed two-exponent regimes reflect the bi-exponential distribution of the density of band-tail states. This improved understanding would be significant in fabricating high-performance ultrathin oxide devices. The origin of large mobility modulation in ultrathin oxide transistors, promising for their high on-off ratio, remains mostly unknown. Here, a 106 gate-induced mobility modulation in 3.5 nm-thick TiOx transistors is explained by a high density of tail states, mediating variable range hopping of carriers.

Energy transfer (ET) from nanocrystals (NCs) has shown potential to enhance the optoelectronic performance of ultrathin semiconductor devices such as ultrathin Si solar cells, but the experimental identification of optimal device geometries for maximizing the performance enhancement is highly challenging due to a large parameter space. Here, we have demonstrated a general theoretical framework combining transfer matrix method (TMM) simulations and energy transfer (ET) calculations to reveal critical device design guidelines for developing an efficient, NC-based ET sensitization of ultrathin Si solar cells, which are otherwise infeasible to identify experimentally. The results uncover that the ET-driven NC sensitization is highly effective in enhancing the short circuit current (JSC) in sub-100 nm-thick Si layers, where, for example, the ET contribution can account for over 60% of the maximum achievable JSC in 10 nm-thick ultrathin Si. The study also reveals the limitation of the ET approach, which becomes ineffective for Si active layers thicker than 5 μm, being dominated by conventional optical coupling. The demonstrated simulation approach not only enables the development of efficient ultrathin Si solar cells but also should be applicable to precisely assessing and analyzing diverse experimental device geometries and configurations for developing new efficient ET-based ultrathin semiconductor optoelectronic devices.

The spontaneous formation of well-organized three-dimensional (3D) nanostructures from self-assembled block copolymers (BCPs) holds promise for nanofabrication and lithography. The addition of a th...

We demonstrate a simple ex-situ inorganic infiltration route for transforming standard organic resists into high-performance positive tone hybrid resist platform. A model thin film PMMA-AlOx hybrid resist system has been synthesized by hybridization of PMMA with AlOx and investigated for electron beam lithography. The approach possesses full controllability of the resist performance in terms of critical does, patterning contrast reaching up to 30 and etch resistance for plasma-based pattern transfer processes. The high selectivity Si etching capability demonstrated using a low-temperature cryo-Si etch process, based on the controlled infiltration outperforms commercial resists and typical hard mask material thermal SiO2, with estimated achievable selectivity in excess of ~300. Si nanostructures down to ~30 nm with aspect ratio up to ~17 are also transferred into the Si substrate. Easy implementation and adaptability for different inorganic infiltrations, this platform is well capable of potentially delivering the resist performance and throughput necessary for EUV lithography.

We here report the self-organization process of poly(styrene-b-ethylene/butadiene-b-styrene) (SEBS) triblock copolymer chains physically adsorbed on a non-neutral surface. Spin-cast SEBS thin films were prepared on silicon (Si) substrates and then annealed at a high temperature far above the bulk glass transition temperatures of the two constituent blocks. To reveal the buried interfacial structure, we utilized solvent rinsing processes and a suite of surface-sensitive techniques including ellipsometry, X-ray reflectivity, atomic force microscopy, and grazing incidence small angle X-ray scattering. We revealed that the SEBS chains form two different chain structures on the substrate simultaneously: (i) “flattened chains” with the average height of 2.5 nm but without forming microdomain structures; (ii) “loosely adsorbed chains” with the average height of 11.0 nm and the formation of perpendicularly oriented cylindrical microdomains to the substrate surface. In addition, the kinetics to form the perpendicular-oriented cylinder was sluggish (∼200 h) and proceeded via multistep processes toward the equilibrium state. We also found that the lateral microdomain structures were distorted, and the characteristic lengths of the microdomains were slightly different from the bulk even after reaching “quasiequilibrium” state within the observed time window. Furthermore, we highlight the vital role of the adsorbed chains in the self-assembling process of the entire SEBS thin film: a long-range perturbation associated with the adsorbed chains propagates into the film interior, overwhelming the free surface effect associated with surface segregation of the lower surface tension of polystyrene blocks.

ipso-Arylative ring-opening polymerization of 2-bromo-8-aryl-8H-indeno[2,1-b]thiophen-8-ol monomers proceeds to Mn up to 9 kg mol-1 with conversion of the monomer diarylcarbinol groups to pendent conjugated aroylphenyl side chains (2-benzoylphenyl or 2-(4-hexylbenzoyl)phenyl), which influence the optical and electronic properties of the resulting polythiophenes. Poly(3-(2-(4-hexylbenzoyl)phenyl)thiophene) was found to have lower frontier orbital energy levels (HOMO/LUMO=-5.9/-4.0 eV) than poly(3-hexylthiophene) owing to the electron-withdrawing ability of the aryl ketone side chains. The electron mobility (ca. 2×10-3 cm2 V-1 s-1 ) for poly(3-(2-(4-hexylbenzoyl)phenyl)thiophene) was found to be significantly higher than the hole mobility (ca. 8×10-6 cm2 V-1 s-1 ), which suggests such polymers are candidates for n-type organic semiconductors. Density functional theory calculations suggest that backbone distortion resulting from side-chain steric interactions could be a key factor influencing charge mobilities.

Polymer–inorganic hybrid nanocomposites exhibit enhanced material properties, combining the advantages of both their organic and inorganic subcomponents. Extensive research is being carried out to functionalize polymers towards various improved physicochemical characteristics such as electrical, optical, and mechanical properties for various applications. Vapor-phase material infiltration is an emerging hybridization route, derived from atomic layer deposition, which facilitates uniform incorporation of inorganic entities into a polymer matrix, leading to novel applications in fields such as microelectronics, energy storage, smart coatings, and smart fabrics. In this article, recent advances in employing vapor-phase material infiltration as a hybridization and nanopatterning technique for various application avenues are reviewed.

Oxygen and water vapor sensing properties are investigated in metal-oxide-hybrid polymer nanocomposite thin films generated by infiltration synthesis, which incorporates molecular ZnO into the matrix of SU-8 polymer, a common negative-tone photoresist. The hybrid thin films display 20-fold higher gravimetric responses to oxygen and water vapor than those of control ZnO thin films in the dark. An additional 50-500% enhanced responses are detected under UV irradiation. The overall enhanced gravimetric response in the hybrid film is attributed to the ZnO molecules distributed in the polymer matrix, whereas the UV enhancement is explained by the light-induced, reversible generation of hydrophilic fluoroantimonic acid from triarylsulfonium hexafluoroantimonate photoacids, which leads to the increased surface potential and adsorption energies for oxygen and water. A gravimetric sensor based on a series of ZnO-infiltrated SU-8 films under UV excitation enables 96% accurate classification of water and oxygen environment with sub 10 mTorr detection limits. The results demonstrate UV-induced fully reversible surface hydrophilicity of ZnO/SU-8 hybrid nanocomposites.

Solution-processable organic semiconductors have potentials as visible photoelectrochemical (PEC) water splitting photoelectrodes due to their tunable small band gap and electronic energy levels, but they are typically limited by poor stability and photocatalytic activity. Here, we demonstrate the direct visible PEC water oxidation on solution-processed organic semiconductor thin films with improved stability and performance by ultrathin metal oxide passivation layers. N-type fullerene-derivative thin films passivated by sub-2 nm ZnO via atomic layer deposition enabled the visible PEC water oxidation at wavelengths longer than 600 nm in harsh alkaline electrolyte environments with up to 30 μA/cm2 photocurrents at the thermodynamic water-oxidation equilibrium potential and the photoanode half-lifetime extended to ∼1000 s. The systematic investigation reveals the enhanced water oxidation catalytic activity afforded by ZnO passivation and the charge tunneling governing the hole transfer through passivation l...

Despite successful applications of solution-processed organic–inorganic hybrid perovskites (OIHPs) such as archetypical methylammonium lead iodide (MAPI) in high-performance optoelectronic devices including solar cells and light emitting diodes, their application in field-effect transistors (FETs) remains relatively limited due to the unresolved issues caused by ion migration in OIHPs, such as screening of gate electric fields, lowered device on-off ratios and field-effect mobility, and large hysteresis in the FET transfer characteristics. Here, we report improved performances of the MAPI-based FET via a polymer-additive-based grain boundary (GB) passivation approach that suppresses the ion migration. Polycaprolactone (PCL) was incorporated into the MAPI FET as a GB-passivation additive as confirmed by scanning electron and atomic force microscopies. Unlike the typical n-type behavior and large transfer hysteresis in the starting, pristine MAPI FETs, the GB passivation by PCL led to a drastically reduced hysteresis in FET transfer characteristics, while hinting at an ambipolar transport and slight improvement in mobility, indicating a reduced ion migration in the PCL-incorporated MAPI FET. The effect of PCL GB passivation in suppressing ion migration was directly confirmed by the measured, increased activation energy for ion migration in the PCL-incorporated MAPI. The results not only represent the first report of the polymer-additive-based mitigation of the ion migration in the MAPI FET but also suggest potential utilities of the approach for enabling high-performance OIHP FETs and electronic devices in general.

Patterning materials efficiently at the smallest length scales is a longstanding challenge in nanotechnology. Electron-beam lithography (EBL) is the primary method for patterning arbitrary features, but EBL has not reliably provided sub-4 nm patterns. The few competing techniques that have achieved this resolution are orders of magnitude slower than EBL. In this work, we employed an aberration-corrected scanning transmission electron microscope for lithography to achieve unprecedented resolution. Here we show aberration-corrected EBL at the one nanometer length scale using poly(methyl methacrylate) (PMMA) and have produced both the smallest isolated feature in any conventional resist (1.7 ± 0.5 nm) and the highest density patterns in PMMA (10.7 nm pitch for negative-tone and 17.5 nm pitch for positive-tone PMMA). We also demonstrate pattern transfer from the resist to semiconductor and metallic materials at the sub-5 nm scale. These results indicate that polymer-based nanofabrication can achieve feature sizes comparable to the Kuhn length of PMMA and ten times smaller than its radius of gyration. Use of aberration-corrected EBL will increase the resolution, speed, and complexity in nanomaterial fabrication.

Nanodiamonds hosting colour centres are a promising material platform for various quantum technologies. The fabrication of non-aggregated and uniformly-sized nanodiamonds with systematic integration of single quantum emitters has so far been lacking. Here, we present a top-down fabrication method to produce 30.0$\pm$5.4 nm uniformly-sized single-crystal nanodiamonds by block copolymer self-assembled nanomask patterning together with directional and isotropic reactive ion etching. We show detected emission from bright single nitrogen vacancy centres hosted in the fabricated nanodiamonds. The lithographically precise patterning of large areas of diamond by self-assembled masks and their release into uniformly sized nanodiamonds open up new possibilities for quantum information processing and sensing., Comment: 15 pages, 2 figures

In this paper, we investigate the polarization retention of Hf0.5Zr0.5O2 (HZO)-based metal–ferroelectric–insulator–Si (MFIS) capacitors with scaling of the ferroelectric (FE) layer thickness from 5 nm to 20 nm. The capacitors have a constant interface layer capacitance of ∼24 μF/cm2, developed due to the integration of HZO on a degenerated Si as a bottom conducting electrode. It is observed that 20 nm HZO films show a small change (∼5%) in FE polarization (PFE) between short (10 μs) and long (6 s) retention time, while 5-nm-thick films exhibit a large difference (∼90%). The dependence of PFE retention loss on the FE thickness can be understood by the presence of a built-in electric field in the FE layer, generated due to charge continuity between the FE and the interface layers in the ground state without any external bias. A direct experimental observation also confirms that a residual voltage is developed at the node between the metal–ferroelectric–metal and metal–oxide–semiconductor capacitors connected in series, in the ground state with zero external bias. It is expected that a proper understanding of the built-in field developed in the FE layer in an MFIS stack is crucial for FE memory retention characteristics.

The change in the interplanar spacing (d-spacing) including the ferroelectric orthorhombic (O) phase in the low-temperature fabricated HfxZr1−xO2 (HZO) films was studied using synchrotron grazing-incidence wide-angle x-ray scattering analysis. The 10-nm-thick HZO films were fabricated by thermal and plasma-enhanced atomic layer deposition (TH- and PE-ALD) methods using H2O gas and O2 plasma as oxidants, respectively, and a post-metallization annealing (PMA) was performed at 300–400 °C. The d-spacing of the mixture of (111)-, (101)-, and (111)-planes of O, tetragonal (T), and cubic (C) phases, respectively, for the TH- and PE-ALD HZO films increased up to 2.99 Å with an increase in PMA temperature, while the d-spacing estimated by conventional x-ray diffraction was 2.92 Å regardless of the PMA temperature. The remanent polarization (2Pr = Pr+ − Pr−) of the HZO films increased as the PMA temperature increased. It is clear that the 2Pr value satisfied a linear relationship as a function of the d-spacing of O(111)/T(101)/C(111) phases. Furthermore, the wake-up effect was found to depend on the ferroelectric O phase formation. The wake-up effect was significantly reduced in both the TH- and PE-ALD HZO films after the PMA at 400 °C due to the increase in the ferroelectric O phase formation. The leakage current density (J)–electric field properties of the PE-ALD HZO film with the lowest d-spacing were divided into three steps, such as low, middle, and large J values, in the wake-up (103 cycles), pristine (100 cycle), and fatigue (107 cycles) states, respectively. Therefore, an analysis of the ferroelectric O phase is very important for understanding the ferroelectricity including endurance.

We report the effects of compressed CO, molecules as a novel plasticization agent for poly(3-hexylthiophene) (P3HT)-conjugated polymer thin films. In situ neutron reflectivity experiments demonstrated the excess sorption of CO, molecules in the P3HT thin films (about 40 nm in thickness) at low pressure (P = 8.2 MPa) under the isothermal condition of T = 36 degrees C, which is far below the polymer bulk melting point. The results proved that these CO2, molecules accelerated the crystallization process of the polymer on the basis of ex situ grazing incidence X-ray diffraction measurements after drying the films-via rapid depressurization to atmospheric pressure: both the out-of-plane lamellar ordering of the backbone chains and the intraplane pi-pi stacking of the side chains were significantly improved, when compared with those in the control P3HT films subjected to conventional thermal annealing (at T = 170 degrees C). Electrical measurements elucidated that the CO2-annealed P3HT thin films exhibited enhanced charge carrier mobility along with decreased background charge carrier concentration and trap density compared with those in the thermally annealed counterpart. This is attributed to the CO2-induced increase in polymer chain mobility that can drive the detrapping of molecular oxygen and healing of conformational defects in the polymer thin film. Given the universality of the excess sorption of CO2 regardless of the type of polymers, the present findings suggest that CO2 annealing near the critical point can be useful as a robust processing strategy for improving the structural and electrical characteristics of other semiconducting conjugated polymers and related systems such as polymer:fullerene bulk heterojunction films.

Infiltration synthesis is a process technique derived from atomic layer deposition (ALD), where polymeric templates, such as those lithographically patterned and self-assembled, are infiltrated by vapor-phase inorganic precursors to form novel organic-inorganic hybrids with enhanced materials properties. These hybrids can be further transformed by selectively removing the organic matrix to finally form metal oxide nanostructures with morphology and positional registry as dictated and designed by the starting polymer templates. In this talk, I will highlight a few examples of our recent efforts to generate functional inorganic nanostructures by using infiltration synthesis including, patterning arbitrary metal oxide nanostructures with sub-40 nm linewidth and over 15 aspect ratio, structural characteristics extremely difficult to achieve by conventional microfabrication techniques; fully CMOS compatible, wafer-scale synthesis and integration of in-plane aligned ZnO nanowire array phototransistors; and three-dimensional (3D) ZnO nanomesh structures derived from self-assembled block copolymer (BCP) templates with layer-number-dependent percolative electrical conductance.

Atomically thin two-dimensional (2D) semiconductors boast numerous intriguing enhanced material properties for various potential electronic device applications. For optoelectronic devices, such as photodetectors and photovoltaics, an efficient light harvesting is highly demanded, and the relatively low absolute optical absorption of 2D semiconductors can, therefore, limit associated device performances, including photodetector responsivity and solar cell power conversion efficiency. Recently, the sensitization by quantum dots (QDs) has shown promises for improving the optical absorption in 2D semiconductors. In this talk, I will highlight our recent efforts towards utilizing QD sensitization for improving the photo-response of 2D semiconductor field-effect transistor (FET) photodetectors. The first example demonstrates a 500% enhancement in photocurrent response by the application of energy transfer from CdSe/ZnS core/shell QDs in 2D SnS2, a model 2D system with indirect band gap nature. Also detailed is the case of 2D MoS2, where we show that the light-intensity-dependent photo-response characterized by scanning photocurrent microscopy (SPCM) can distinguish two fundamental modes of interfacial interaction between QDs and 2D materials, namely energy and charge transfers, which are extremely difficult to distinguish under typically optical interrogation methods. I will try to discuss the potential implication of these two modes towards the optoelectronic application of QD-2D hybrid materials.

This paper describes the design and construction of a compact, “user-friendly” polarization-modulation infrared reflection absorption spectroscopy (PM-IRRAS) instrument at the Center for Functional Nanomaterials (CFN) of Brookhaven National Laboratory, which allows studying surfaces at pressures ranging from ultra-high vacuum to 100 Torr. Surface infrared spectroscopy is ideally suited for studying these processes as the vibrational frequencies of the IR chromophores are sensitive to the nature of the bonding environment on the surface. Relying on the surface selection rules, by modulating the polarization of incident light, it is possible to separate the contributions from the isotropic gas or solution phase, from the surface bound species. A spectral frequency range between 1000 cm−1 and 4000 cm−1 can be acquired. While typical spectra with a good signal to noise ratio can be obtained at elevated pressures of gases in ∼2 min at 4 cm−1 resolution, we have also acquired higher resolution spectra at 0.25 c...

Modulus of resilience, the measure of a material’s ability to store and release elastic strain energy, is critical for realizing advanced mechanical actuation technologies in micro/nanoelectromechanical systems. In general, engineering the modulus of resilience is difficult because it requires asymmetrically increasing yield strength and Young’s modulus against their mutual scaling behavior. This task becomes further challenging if it needs to be carried out at the nanometer scale. Here, we demonstrate organic–inorganic hybrid composite nanopillars with one of the highest modulus of resilience per density by utilizing vapor-phase aluminum oxide infiltration in lithographically patterned negative photoresist SU-8. In situ nanomechanical measurements reveal a metal-like high yield strength (∼500 MPa) with an unusually low, foam-like Young’s modulus (∼7 GPa), a unique pairing that yields ultrahigh modulus of resilience, reaching up to ∼24 MJ/m3 as well as exceptional modulus of resilience per density of ∼13....

We report that the addition of a non-photoactive tertiary polymer phase in the binary bulk heterojunction (BHJ) polymer solar cell leads to a self-assembled columnar nanostructure, enhancing the charge mobilities and photovoltaic efficiency with surprisingly increased optimal active blend thicknesses over 300 nm, 3–4 times larger than that of the binary counterpart. Using the prototypical poly(3-hexylthiophene) (P3HT):fullerene blend as a model BHJ system, we discover that the inert poly(methyl methacrylate) (PMMA) added in the binary BHJ blend self-assembles into vertical columns, which not only template the phase segregation of electron acceptor fullerenes but also induce the out-of-plane rotation of the edge-on-orientated crystalline P3HT phase. Using complementary interrogation methods including neutron reflectivity, X-ray scattering, atomic force microscopy, transmission electron microscopy, and molecular dynamics simulations, we show that the enhanced charge transport originates from the more randomized molecular stacking of the P3HT phase and the spontaneous segregation of fullerenes at the P3HT/PMMA interface, driven by the high surface tension between the two polymeric components. The results demonstrate a potential method for increasing the thicknesses of high-performance polymer BHJ solar cells with improved photovoltaic efficiency, alleviating the burden of stringently controlling the ultrathin blend thickness during the roll-to-roll-type large-area manufacturing environment.

In this work, we have used synchrotron-based grazing incidence X-ray scattering to measure the molecular orientation and morphology of nanostructured thin films of blended poly(3-hexylthiophene)/[6,6]-phenyl C61-butyric acid methyl ester blends patterned with nanoimprint lithography. Imprinting the blend films at 150 °C results in significant polymer chain orientational anisotropy, in contrast to patterning the film at only 100 °C. The temperature-dependent evolution of the X-ray scattering data reveals that the imprint-induced polymer reorientation remains at high temperatures even after the patterned topographic features vanish upon melting. Photovoltaic devices fabricated from the blend films imprinted at 150 °C exhibit a ∼21% improvement in power conversion efficiency compared to those imprinted at 100 °C, consistent with a polymer chain configuration better suited to charge carrier collection.

Inverted polymer:fullerene bulk heterojunction solar cells employing a conjugated polyelectrolyte electron transfer layer display light soaking effects as the oxygen adsorbed on indium tin oxide (ITO) during an ambient air device processing induces interface charge trap states in the conjugated polyelectrolyte layer and reduces its interface dipole. The light soaking populates the trap states with photoexcited electrons and reinstates the electric dipole, leading to a recovery of efficient charge extraction and normal illuminated current–voltage characteristics consequently. The identified effect of adsorbed oxygen not only enables a remedy of the light soaking issue of the inverted solar cells via hydrogen plasma treatment of ITO but also suggests the importance of properly handling adsorbed oxygen species on ITO for achieving high performance organic devices based on ITO substrates in general.

We report a general strategy for fine-tuning the bandgap of donor-acceptor-donor based organic molecules by modulating the electron-donating ability of the donor moiety by changing the benzochalcogenophene donor groups from benzothiophenes to benzoselenophenes to benzotellurophenes. These molecules show red-shifts in absorption and external quantum efficiency maxima from sulfur to selenium to tellurium. In bulk heterojunction solar cell devices, the benzoselenophene derivative shows a power conversion efficiency as high as 5.8% with PC61BM as the electron acceptor.

Cobalt oxide (Co3O4), a low-cost transitional metal oxide, has been widely studied for catalytic total oxidation of CO and hydrocarbons. However, much less attention has been paid to the poisoning effect due to alkali metals in such oxidation catalysts despite the ease of access to such poisons in both mobile and stationary combustion sources. In this study, the alkali metals such as Na, K and Li were readily deposited onto a Co3O4 catalyst to study their poisoning effect on CO and propane oxidation. 1% doping onto Co3O4 was found to increase the light-off temperature by 50 °C in CO oxidation and over 160 °C in propane oxidation. It is also noted that alkali metals exhibited a ‘locking-effect’ on oxygen of Co3O4, leading to poor oxygen mobility of alkali metal doped catalysts. During the reaction, alkali metals can significantly promote the adsorption of CO2 to form robust surface carbonate species even at high temperature, another reason for the poisoning effect of alkali metals on Co3O4 nanocatalysts for catalytic oxidation.

Zinc oxide nanowire photoanodes are chemically stabilized by conformal growth of an ultrathin shell of titania through atomic layer deposition, permitting their stable operation for water splitting in a strongly alkaline solution. Because of the passivation of zinc oxide surface charge traps by titania coating, core/shell nanowire arrays supply a photocurrent density of 0.5 mA/cm2 under simulated AM1.5G sunlight at the thermodynamic oxygen evolving potential, demonstrating 25% higher photoelectrochemical water splitting activity compared to as-grown zinc oxide wires. By thermally annealing the zinc oxide wire arrays prior to surface passivation, we further increase the photocurrent density to 0.7 mA/cm2—the highest reported value for doped or undoped zinc oxide photoanodes studied under similar simulated sunlight. Photoexcitations at energies above the zinc oxide band gap are converted with efficiency greater than 80%. Photoluminescence measurements of the best-performing nanowire arrays are consistent wi...

We incorporated a thin but structurally dense TiO2 layer prepared by atomic layer deposition (ALD) as an efficient hole blocking layer in the TiO2 nanofiber based solid-state dye sensitized solar cell (ss-DSSC). The nanofiber ss-DSSCs having ALD TiO2 layers displayed increased open circuit voltage, short circuit current density, and power conversion efficiency compared to control devices with blocking layers prepared by spin-coating liquid TiO2 precursor. We attribute the improved photovoltaic device performance to the structural integrity of ALD-coated TiO2 layer and consequently enhanced hole blocking effect that results in reduced dark leakage current and increased charge carrier lifetime.

We report the effects of compressed CO

Noble metal nanoparticles are extensively used for sensitizing metal oxide chemical sensors through the catalytic spillover mechanism. However, due to earth-scarcity and high cost of noble metals, finding replacements presents a great economic benefit. Besides, high temperature and harsh environment sensor applications demand material stability under conditions approaching thermal and chemical stability limits of noble metals. In this study, we employed thermally stable perovskite-type La(0.8)Sr(0.2)FeO3 (LSFO) nanoparticle surface decoration on Ga2O3 nanorod array gas sensors and discovered an order of magnitude enhanced sensitivity to carbon monoxide at 500 °C. The LSFO nanoparticle catalysts was of comparable performance to that achieved by Pt nanoparticles, with a much lower weight loading than Pt. Detailed electron microscopy and X-ray photoelectron spectroscopy studies suggested the LSFO nanoparticle sensitization effect is attributed to a spillover-like effect associated with the gas-LSFO-Ga2O3 triple-interfaces that spread the negatively charged surface oxygen ions from LSFO nanoparticles surfaces over to β-Ga2O3 nanorod surfaces with faster surface CO oxidation reactions.

We report chemical modification of self-assembled block copolymer thin films by ultraviolet light that enhances the block-selective affinity of organometallic precursors otherwise lacking preference for either copolymer block. Sequential precursor loading and reaction facilitate formation of zinc oxide, titanium dioxide, and aluminum oxide nanostructures within the polystyrene domains of both lamellar- and cylindrical-phase modified polystyrene-block-poly(methyl methacrylate) thin film templates. Near-edge X-ray absorption fine structure measurements and Fourier transform infrared spectroscopy show that photo-oxidation by ultraviolet light creates Lewis basic groups within polystyrene, resulting in an increased Lewis base-acid interaction with the organometallic precursors. The approach provides a method for generating both aluminum oxide patterns and their corresponding inverses using the same block copolymer template.

In this report, we demonstrate a straightforward two-terminal-device-based electrical measurement and analysis scheme that can simultaneously determine the bulk free charge carrier concentration and out-of-plane charge mobility in organic semiconductors by understanding the transition behavior of device current–voltage characteristics from ohmic to space charge limited conduction. As a model system, we characterize the properties of a semicrystalline poly(3-hexylthiophene) (P3HT) conjugated polymer film in which free carrier concentration is systematically controlled by adjusting oxygen doping level. The observed dependence of out-of-plane charge mobility on the carrier concentration is analyzed in the context of percolative variable range hopping conduction, and we identify the rate-limiting charge hopping process in P3HT and correlate it with the role of disordered polymer regions in mediating the charge transport between neighboring crystalline polymer lamellar domains.

PEDOT:PSS thin films are successfully patterned using water-vapor-assisted nanoimprinting, a process compatible with organic electronic devices. The imprinted patterns are characterized via grazing-incident small-angle X-ray scattering and scanning electron microscopy. Superior pattern transfer quality of water-vapor assisted nanoimprinting over conventional thermal nanoimprinting is demonstrated.

High photovoltaic device performance is demonstrated in ambient-air-processed bulk heterojunction solar cells having an active blend layer of organic poly(3-hexylthiophene) (P3HT): [6,6]-phenyl-C{sub 61}-butyric acid methyl ester (PCBM), with power conversion efficiencies as high as 4.1%, which is comparable to state-of-the-art bulk heterojunction devices fabricated in air-free environments. High-resolution transmission electron microscopy is combined with detailed analysis of electronic carrier transport in order to quantitatively understand the effects of oxygen exposure and different thermal treatments on electronic conduction through the highly nanostructured active blend network. Improvement in photovoltaic device performance by suitable post-fabrication thermal processing results from the reduced oxygen charge trap density in the active blend layer and is consistent with a corresponding slight increase in thickness of an {approx}4 nm aluminum oxide hole-blocking layer present at the electron-collecting contact interface.

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. Conventionally reserved for the fabrication of metal thin films, thermal evaporation deposits bismuth into an array of vertical single crystalline nanowires over a flat thin film of vanadium held at RT, which is freshly deposited by magnetron sputtering or thermal evaporation. By controlling the temperature of the growth substrate the length and width of the nanowires can be tuned over a wide range. Responsible for this novel technique is a previously unknown nanowire growth mechanism that roots in the mild porosity of the vanadium thin film. Infiltrated into the vanadium pores, the bismuth domains (~ 1 nm) carry excessive surface energy that suppresses their melting point and continuously expels them out of the vanadium matrix to form nanowires. This discovery demonstrates the feasibility of scalable vapor phase synthesis of high purity nanomaterials without using any catalysts.