Performance of an ionomer blend-nanocomposite as an effective gas barrier material for organic devices

A new, flexible, gas barrier material has been synthesized by exfoliating organically modified nano-clays (MMT) in the blends of Surlyn (PEMA) using a copolymer of vinyl alcohol (EVOH) and demonstrated as a gas barrier material. The materials were characterized by Fourier transform infra red (FTIR) and UV-visible spectroscopy, differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and tensile studies. The oxygen and water-vapor permeabilities of the fabricated films were determined by calcium degradation test and a novel permeability setup based on cavity ring down spectroscopy, respectively. Hierarchical simulations of these materials helped us to understand the effect of intermolecular interactions on diffusivities of oxygen and water molecules in these materials. Schottky structured poly(3-hexylthiophene) based organic devices were encapsulated with the fabricated films and aging studies were carried under accelerated conditions. Based on permeability test results and accelerated aging studies, the fabricated PEMA/EVOH/MMT composites were found to be effective in decreasing the permeabilities for gases by about two orders of magnitude and maintaining the lifetime of organic devices.

Stable and low resistive zinc contacts for SnS based optoelectronic devices

The contact behavior of tin mono sulfide (SnS) nanocrystalline thin films with zinc (Zn) and silver (Ag) contacts was studied. SnS films have been deposited on glass substrates by thermal evaporation technique at a growth temperature of 300 degrees C. The as-grown SnS films composed of vertically aligned nanocrystallites with a preferential orientation along the < 010 > direction. SnS films exhibited excellent chemical stoichiometry and direct optical band gap of 1.96 eV. These films also exhibited excellent Ohmic characteristics and low electrical resistivity with Zn contacts. The observed electrical resistivity of SnS films with Zn contacts is 22 times lower than that of the resistivity with Ag contacts. The interfacing analysis reveals the formation of conductive Zn-S layer between SnS and Zn as interfacial layer. (C) 2014 Elsevier B. V. All rights reserved.

Aminosilane Functionalized Cenosphere in Poly(vinyl butyral) Composite Films: Moisture Resistant Encapsulated Schottky Devices

Functionalized cenosphere in PVB composite films were fabricated by melt processing. The composites show higher tensile strength with lower failure strain with increased filler ratio in the matrix. Fractographic images of the samples and DMA studies indicate brittle failure of the matrix. Moisture permeation and water contact angle studies reveal improved hydrophobicity of the matrix, while the factor of surface roughness increases the wettability at higher filler content. Schottky-structured devices encapsulated with functionalized cenosphere indicate enhanced resistance to moisture and increased life time for the devices.

Modelling of optical transport behavior of organic photovoltaic devices with nano-pillar transparent conducting electrodes

Optical transport behavior of organic photo-voltaic devices with nano-pillar transparent electrodes is investigated in this paper in order to understand possible enhancement of their charge-collection efficiency. Modeling and simulations of optical transport due to this architecture show an interesting regime of length-scale dependent optical characteristics. An electromagnetic wave propagation model is employed with simulation objectives toward understanding the mechanism of optical scattering and waveguide effects due to the nano-pillars and effective transmission through the active layer. Partial filling of gaps between the nano-pillars due to the nano-fabrication process is taken into consideration. Observations made in this paper will facilitate appropriate design rules for nano-pillar electrodes. (C) 2014 AIP Publishing LLC.

High-quality ZnO nanorod based flexible devices for electronic and biological applications

Vertically aligned zinc oxide nanorods (ZnO NRs) were synthesized on kapton flexible sheets using a simple and cost-effective three-step process (electrochemical seeding, annealing under ambient conditions, and chemical solution growth). Scanning electron microscopy studies reveal that ZnO NRs grown on seed-layers, developed by electrochemical deposition at a negative potential of 1.5 V over a duration of 2.5 min and annealed at 200 degrees C for 2 h, consist of uniform morphology and good chemical stoichiometry. Transmission electron microscopy analyses show that the as-grown ZnO NRs have single crystalline hexagonal structure with a preferential growth direction of < 001 >. Highly flexible p-n junction diodes fabricated by using p-type conductive polymer exhibited excellent diode characteristics even under the fold state.

The importance of crystallographic texture in the use of titanium as an orthopedic biomaterial

Crystallographic texture is perceived to play an important role in controlling material properties. However, the influence of texture in modulating the properties of biomedical materials has not been well investigated. In this work, commercially pure titanium (cp-Ti) was processed through six different routes to generate a variety of textures. The effect of texture on mechanical properties, corrosion behavior, cell proliferation and osteogenesis was characterized for potential use in orthopedic applications. The presence of closely packed, low-energy crystallographic planes at the material surface was influenced by the volume fraction of the components in the overall texture, thereby influencing surface energy and corrosion behavior. Texture modulated osteoblast proliferation through variations in surface water wettability. It also affected mineralization by possibly influencing the coherency between the substrate and calcium phosphate deposits. This study demonstrates that crystallographic texture can be an important tool in improving the properties of biomaterials to achieve the enhanced performance of biomedical implants.

Field dependent and disorder-induced nonlinear charge transport in electrochemically doped polypyrrole devices

Electric field activated charge transport is studied in the metal/polymer/metal device structure of electropolymerized polypyrrole down to 10 K with varying carrier density and disorder. Disorder induced nonlinear behaviour is observed in polypyrrole devices grown at room temperature which is correlated to delocalization of states. The slope parameter of currentvoltage characteristics (in log-log scale) increases as the temperature decreases, which indicates the onset of stronger field dependence. The field dependence of mobility becomes dominant as the carrier density decreases. The sharp dip in differential conductance indicates the localization of carriers at low temperatures which reduces the effective number of carriers involved in the transport.

ZnO/ITO core/shell nanostructure electrodes for future prototype solar cell devices

The impact of indium tin oxide (ITO) layers over vertically aligned zinc oxide nanorods (ZnO NRs) has been investigated to consider ITO nanolayers as transparent conducting oxide electrodes (TCOE) for hierarchical heteronanostructure solar cell devices that have ZnO nanostructures as branches. ZnO/ITO core/shell nanostructures were prepared in two- steps using vapor-liquid-solid and evaporation processes, and further the structures were annealed at various temperatures. Transmission electron microscopic studies show that the as-grown ZnO/ITO structures consist of an amorphous ITO shell on single crystalline ZnO cores, whereas the structures annealed above 300 degrees C consist of a single crystalline ITO shell. ITO layer deposited ZnO NRs exhibit a small red-shift in ZnO near-band-edge emission as well as optical band gap. The electrical measurements carried out on single ZnO/ITO core/shell NR under dark and UV light showed excellent thermionic transport properties. From these investigations it is emphasized that ITO nanolayers could be used as TCO electrodes for prototype ZnO based hierarchical solar cell devices.

Nanocomposite Based Organic-Inorganic Cu3BiS3 High Sensitive Hybrid Photonic Devices

We report the synthesis and application Cu3BiS3 nanorods in infrared photodectection. Cu3BiS3 nano rods were characterized structurally, optically and electrically. The detailed IR photodectection properties in terms of photo response were demonstrated with IA lamp and 1064 nm laser illuminations. The rapid photocurrent time constants followed by the slower components, resulting due to the defect states. The photo detecting properties for different concentrations of nanorods blended with the conjugate polymer devices were demonstrated. Further the photocurrent was enhanced to threefold increase from 3.47 x 10(-7) A to 2.37 x 10(-3) A at 1 V for 10 mg nanorods embedded in the polymer device. Responsivity of hybrid device was enhanced from 0.0158 NW to 102 NW. The detailed trap assisted space charge transport properties were studied considering the different regimes. Hence Cu3BiS3 can be a promising candidate in the nano switchable near IA photodetectors.

Sparse Representation Based Acoustic Rangefinders: From Sensor Platforms to Mobile Devices

Acoustic rangerfinders are a promising technology for accurate proximity detection, a critical requirement for many emerging mobile computing applications. While state-of-the-art systems deliver robust ranging performance, the computational intensiveness of their detection mechanism expedites the energy depletion of the associated devices that are typically powered by batteries. The contribution of this article is fourfold. First, it outlines the common factors that are important for ranging. Second, it presents a review of acoustic rangers and identifies their potential problems. Third, it explores the design of an information processing framework based on sparse representation that could potentially address existing challenges, especially for mobile devices. Finally, it presents mu-BeepBeep: a low energy acoustic ranging service for mobile devices, and empirically evaluates its benefits.

Optically transparent polymer devices for in situ assessment of cell electroporation

In order to study cell electroporation in situ, polymer devices have been fabricated from poly-dimethyl siloxane with transparent indium tin oxide parallel plate electrodes in horizontal geometry. This geometry with cells located on a single focal plane at the interface of the bottom electrode allows a longer observation time in both transmitted bright-field and reflected fluorescence microscopy modes. Using propidium iodide (PI) as a marker dye, the number of electroporated cells in a typical culture volume of 10-100 mu l was quantified in situ as a function of applied voltage from 10 to 90 V in a series of 2-ms pulses across 0.5-mm electrode spacing. The electric field at the interface and device current was calculated using a model that takes into account bulk screening of the transient pulse. The voltage dependence of the number of electroporated cells could be explained using a stochastic model for the electroporation kinetics, and the free energy for pore formation was found to be kT at room temperature. With this device, the optimum electroporation conditions can be quickly determined by monitoring the uptake of PI marker dye in situ under the application of millisecond voltage pulses. The electroporation efficiency was also quantified using an ex situ fluorescence-assisted cell sorter, and the morphology of cultured cells was evaluated after the pulsing experiment. Importantly, the efficacy of the developed device was tested independently using two cell lines (C2C12 mouse myoblast cells and yeast cells) as well as in three different electroporation buffers (phosphate buffer saline, electroporation buffer and 10 % glycerol).

Absence of systemic toxicity in mouse model towards BaTiO3 nanoparticulate based eluate treatment

One of the existing issues in implant failure of orthopedic biomaterials is the toxicity induced by the fine particles released during long term use in vivo, leading to acute inflammatory response. In developing a new class of piezobiocomposite to mimic the integrated electrical and mechanical properties of bone, bone-mimicking physical properties as well as in vitro cytocompatibility properties have been achieved with spark plasma sintered hydroxyapatite (HA)-barium titanate (BaTiO3) composites. However, the presence of BaTiO3 remains a concern towards the potential toxicity effect. To address this issue, present work reports the first result to conclusively confirm the non-toxic effect of HA-BaTiO3 piezobiocomposite nanoparticulates, in vivo. Twenty BALB/c mice were intraarticularly injected at their right knee joints with different concentrations of HA-BaTiO3 composite of up to 25 mg/ml. The histopathological examination confirmed the absence of any trace of injected particles or any sign of inflammatory reaction in the vital organs, such as heart, spleen, kidney and liver at 7 days post-exposure period. Rather, the injected nanoparticulates were found to be agglomerated in the vicinity of the knee joint, surrounded by macrophages. Importantly, the absence of any systemic toxicity response in any of the vital organs in the treated mouse model, other than a mild local response at the site of delivery, was recorded. The serum biochemical analyses using proinflammatory cytokines (TNF-alpha and IL-1 beta) also complimented to the non-immunogenic response to injected particulates. Altogether, the absence of any inflammatory/ adverse reaction will open up myriad of opportunities for BaTiO3 based piezoelectric implantable devices in biomedical applications.

Chemical Functionalization of Graphene To Augment Stem Cell Osteogenesis and Inhibit Biofilm Formation on Polymer Composites for Orthopedic Applications

Toward designing the next generation of resorbable biomaterials for orthopedic applications, we studied poly(epsilon-caprolactone) (PCL) composites containing graphene. The role, if any, of the functionalization of graphene on mechanical properties, stem cell response, and biofilm formation was systematically evaluated. PCL composites of graphene oxide (GO), reduced GO (RGO), and amine-functionalized GO (AGO) were prepared at different filler contents (1%, 3%, and 5%). Although the addition of the nanoparticles to PCL markedly increased the storage modulus, this increase was largest for GO followed by AGO and RGO. In vitro cell studies revealed that the AGO and GO particles significantly increased human mesenchymal stem cell proliferation. AGO was most effective in augmenting stem cell osteogenesis leading to mineralization. Bacterial studies revealed that interaction with functionalized GO induced bacterial cell death because of membrane damage, which was further accentuated by amine groups in AGO. As a result, AGO composites were best at inhibiting biofilm formation. The synergistic effect of oxygen containing functional groups and amine groups on AGO imparts the optimal combination of improved modulus, favorable stem cell response, and biofilm inhibition in AGO-reinforced composites desired for orthopedic applications. This work elucidates the importance of chemical functionalization of graphene in polymer composites for biomedical applications.

On the Origin of Steep I-V Nonlinearity in Mixed-Ionic-Electronic-Conduction-Based Access Devices

Numerical modeling is used to explain the origin of the large ON/OFF ratios, ultralow leakage, and high ON-current densities exhibited by back-end-of-the-line-friendly access devices based on copper-containing mixed-ionic-electronic-conduction (MIEC) materials. Hall effect measurements confirm that the electronic current is hole dominated; a commercial semiconductor modeling tool is adapted to model MIEC. Motion of large populations of copper ions and vacancies leads to exponential increases in hole current, with a turn-ON voltage that depends on material bandgap. Device simulations match experimental observations as a function of temperature, electrode aspect ratio, thickness, and device diameter.

Hybrid Elements for Modelling Squeeze Film Effects Coupled with Structural Interactions in Vibratory MEMS Devices

We present a hybrid finite element based methodology to solve the coupled fluid structure problem of squeeze film effects in vibratory MEMS devices, such as gyroscopes, RF switches, and 2D resonators. The aforementioned devices often have a thin plate like structure vibrating normally to a fixed substrate, and are generally not perfectly vacuum packed. This results in a thin air film being trapped between the vibrating plate and the fixed substrate which behaves like a squeeze film offering both stiffness and damping. For accurate modelling of such devices the squeeze film effects must be incorporated. Extensive literature is available on squeeze film modelling, however only a few studies address the coupled fluid elasticity problem. The majority of the studies that account for the plate elasticity coupled with the fluid equation, either use approximate mode shapes for the plate or use iterative solution strategies. In an earlier work we presented a single step coupled methodology using only one type of displacement based element to solve the coupled problem. The displacement based finite element models suffer from locking issues when it comes to modelling very thin structures with the lateral dimensions much larger than the plate thickness as is typical in MEMS devices with squeeze film effects. In this work we present another coupled formulation where we have used hybrid elements to model the structural domain. The numerical results show a huge improvement in convergence and accuracy with coarse hybrid mesh as compared to displacement based formulations. We further compare our numerical results with experimental data from literature and find them to be in good accordance.