Ventilator associated pneumonia (VAP) is a serious and costly clinical problem. Specifically, receiving mechanical ventilation over 24 hours increases the risk of VAP and is associated with high morbidity, mortality and medical costs. Cost effective endotracheal tubes (ETTs) that are resistant to bacterial infection would help to prevent this problem. The objective of this study was to determine differences in bacterial growth on nanomodified and unmodified ETTs under dynamic airway conditions. A bench top model based upon the general design of Hartmann et al. (1999) was constructed to test of the effectiveness of nanomodified ETTs under the airflow conditions present in the airway. Twenty-four hour studies performed in a dynamic flow chamber showed a marked difference in the biofilm formation on different areas of unmodified tubes. Areas where tubes were curved, such as at the entrance to the mouth and the connection between the oropharynx and the larynx, seemed to collect the largest amount of biofilm.

The biofilm formation on ETTs in the airflow system after 24 hours showed a large difference depending upon where tubes were oriented within the apparatus. This illustrates the importance of dynamic flow on biofilm formation in pediatric ETTs. It is of particular interest that increased biofilm density on both unmodified and nanomodified tubes appeared to occur at curves in the tube where changes in flow pattern occurred. This emphasizes the need for more accurate models of airflow within pediatric ETTs, suggesting that not only does flow affect pressure gradients along the tube, but in fact, determines the composition of the film itself. More testing is needed to determine the effects of biofilm formation on the efficiency of ETT under airflow, however this study provides significant evidence for nanomodification alone (without the use of antibiotics) to decrease bacteria function.

The antimicrobial properties of polymer materials are used in a verity of applications. Silver nanoparticles are commonly applied to polyurethane foams to obtain antifungal properties. For this study a series of nanocomposites (PU–Ag) from a urethane-type polymer (PU) were reinforced with various amounts of silver nanoparticles having an average size of 20 nm. The surface morphology and antifungal capacity of the nanocomposites were evaluated. As a result, a different surface morphology from PU was found in PU–Ag nanocomposites. The latter nanocomposite showed enhanced thermal and mechanical properties, when compared with the PU without silver nanoaprticles. The nanocomposite also exhibited good antifungal properties that can be used in a variety of applications.

Electrical energy storage plays a key role in mobile electronic devices, stationary power systems, and hybrid electrical vehicles. High energy density capacitors based on dielectric polymers are a focus of increasing research effort motivated by the possibility to realize compact and flexible energy storage devices, taking advantage of light weight and facile processability of organic materials. In addition, dielectric polymers enjoy inherent advantages of self-healing mechanism and high breakdown strength, leading to capacitors with great reliability and high energy density. It is the focus of this group to develop a multilayered ferroelectric PVDF system for improved energy storage efficiency. These systems are fabricated using enabling technology in co-extrusion which allows more cost effective and large area device production as opposed to more conventional layer-by-layer techniques. Many efforts have been made by the team to fabricate these micro- and nano-layered systems resulting in much improved device performance. A three-time improvement of capacitive electrical energy density has been demonstrated. The focus of this research is to understand the physics of why these multilayered systems perform better than a single layer by developing a characterization technique using both confocal second harmonic generation (SHG) and electric field induced second harmonic (EFISH) laser spectroscopy. Our results have shown that SHG is a very sensitive, non-destructive and versatile technique that can be used to study the ferroelectric and structural properties of layered systems. When combined with EFISH this technique allows the interrogation of structural and dielectric properties within the individual layers and at the interfaces between the layers. Further, the proposed techniques can be readily employed in-situ which can provide information in real time during sample processing with static and time-resolved spectroscopic measurements.

In this contribution, we show that the dominant electroluminescent emission of hydrogenated amorphous silicon (a-Si:H) thin-film solar cells follows a diode law, whose radiative ideality factor n r is larger than one. This is in contrast to crystalline silicon and Cu(In, Ga)Se2 solar cells for which n r equals one. As a consequence, the existing quantitative analysis for the extraction of the local junction voltage V j(r ) from luminescence images fails for a-Si:H solar cells. We expand the existing analysis method, and include the radiative ideality factor n r into the model. With this modification, we are able to determine the local junction voltage V j(r ) for a-Si:H solar cells and modules. We investigated the local junction voltage V j(r ) and the radiative ideality factor n r for both initial and stabilized a-Si:H solar modules. Furthermore, we show that the apparent radiative ideality factor is affected by the spectral sensitivity of the used camera system.

Roughly a decade ago an outstanding thermoelectric figure of merit ZT of 2.4 was reported for nanostructured Bi2Te3/Sb2Te3-based thin film superlattice (SL) structures. The published results strongly fueled and renewed the interest in the development of efficient novel nanostructured thermoelectric materials. This review article shall give an overview over the most recent theoretical and experimental advances on Bi2Te3/Sb2Te3 SLs and related superlattice systems. The presented theoretical models are subdivided into electronic and phononic aspects. The experimental results are summarized with regard to the method used. A more detailed elaboration on structural and transport properties is given in the subsequent sections.

A novel structure for Organic Thin-Film Transistor (OTFT) is here presented. The devices are fabricated using a one-mask, photolithographic self-alignment technique which can be performed with standard photoresists and without further chemical treatments. This technique, combined with a novel technology for the realization of low voltage OTFTs, allows a dramatic reduction of the parasitic capacitances thus leading to a remarkable cut-off frequency. In this paper, the main electrical parameters of low voltage, self-aligned devices are reported, and a complete frequency characterization of the devices is given. These characteristics make the reported approach suitable for the development of basic circuitries for frequency applications.

Papers in the Appendix were published in electronic format as Volume 1534

Bio-silica nanostructures from diatoms (called frustules) featuring plasmonic gold nanoparticles (NPs) are elaborated using two methods based on plasma sputtering of gold. The first investigated method uses a thermal treatment to induce the thermal dewetting of a plasma sputtered gold layer on the diatom frustules. The second method first consists of coating the frustules with polyethylene glycol before sputtering gold on these frustules. For both methods, the amount of gold appears to be a key parameter regarding the final obtained layer, which can either be nanostructured by cavities or consist in individual gold NPs. For an amount of sputtered gold equivalent to form a 5 nm thick layer, both methods allow obtaining diatom frustules covered by gold NPs with a size around 20 nm and a narrow size distribution. The UV-visible characterization of the diatom frustules featuring gold NPs highlights a plasmon extinction band in agreement with individual gold NPs with a size below 25 nm.

Alkyl-terminated SixG1-x nanocrystals are prepared at room temperature by co-reduction of Si and Ge precursors by hydride reducing agents within inverse micelles. Compositional control of the alloy silicon-germanium NCs (ca. 3.6 nm) is achieved by varying the relative amounts of each precursor used in the synthesis. Transmission electron microscopy imaging confirmed that the NCs are highly crystalline with a narrow size distribution; optical spectroscopy shows strong quantum confinement effects, with moderate absorption in the UV spectral range, and a strong blue emission with a marked dependency on excitation wavelength.

Metallic nanostructures can exhibit different optical properties compared to bulk materials mainly depending on their shape, size, and separation. We present the results of an optical modeling study on ordered arrays of aluminum (Al) nanorods with a hexagonal periodic geometry placed on an Al thin film. We used a finite-difference time-domain (FDTD) method to solve the Maxwell's equations and predict the reflectance of the nanorod arrays. The thickness of the base Al film was set to 100 nm, and diameter, height and nanorod center-to-center periodicity were varied. Incident light in the FDTD simulations was an EM-circular polarized plane wave and reflectance profiles were calculated in the wavelength range 200-1800 nm. In addition, we calculated spatial electric field intensity distributions around the nanorods for wavelengths 300, 500, and 700 nm. Our results show that average reflectance of Al nanorods can drop down to as low as ∼50%, which is significantly lower than the ∼90% reflectance of conventional flat Al film at similar wavelengths. In addition to the overall decrease in reflectance, Al nanorod arrays manifest multiple resonant modes (higher-order modes) indicated by several dips in their reflectance spectrums (i.e. multiple attenuation peaks in their absorption profiles). Positions of these dips in the reflectance spectrum and spatial EM field distribution vary with nanorod height and diameter. Multiple reflectance peaks are explained by cavity resonator effects. Spatial EM field distribution profiles indicate enhanced light trapping among the nanorods, which can be useful especially in optoelectronic and solar cell applications.

We investigated the valence band structure of PbSe by a combined study of the optical and transport properties of p-type Pb1-xNaxSe, with Na concentrations ranging from 0 – 4%, yielding carrier densities in a wide range of 1018 – 1020 cm−3. Room temperature infrared reflectivity studies showed that the susceptibility (or conductivity) effective mass m* increases from ∼ 0.06m o to ∼ 0.5m o on increasing Na content from 0.08% to 3%. The Seebeck coefficient scales with doping in the whole temperature range, yielding lower values for higher Na contents, while the Hall coefficient increases on heating from room temperature showing a peak close to 650 K. The room temperature Pisarenko plot is well described by the simple parabolic band model up to ∼ 1·1020 cm−3. In order to describe the behaviour in the whole concentration range, the application of the two band model, i.e. light hole and heavy hole, was used giving density of states effective masses 0.28m o and 2.5m o for the two bands respectively.

Concentration- and layer-dependent percolation thresholds can be determined for carbon nanotube (CNT) films deposited from aqueous dispersions on paper substrates at both the surface of the deposited film (in-plane) and through the thickness of the paper (thru-plane) using impedance spectroscopy. By analyzing the impedance spectra as a function of the number of layers (solution concentration is constant) or the solution concentration (number of layers is constant), the electrical properties and percolation thresholds for CNT-paper composites can be determined. In-plane measurements show that percolation occurs at 4 layers when 1 mg/mL solution concentration is used. In the thru-plane direction, the films are already percolated at 1 mg/mL concentration, which is confirmed by varying the concentration of the solution used to deposit 1 layer films. A second percolation event happens between 8 and 12 layers due to an increased number of interconnections of CNTs within the paper substrate. The lowest sheet resistance achieved was 100 Ω/□.

Implantable electronic biomedical devices are used clinically to diagnose and treat an increasing number of medical conditions. Such devices typically employ hermetic packages that often incorporate electrical feedthroughs made with conventional ceramic-to-metal bonding technologies. This sealing technology is well established and provides robust hermetic seals, but is limited in both the number and spacing of electrical leads. Emerging devices for interfacing with the human nervous system, however, will require a large number of external electrical leads implemented in a miniaturized packaging configuration. Commercially available feedthrough technologies are currently incapable of providing external electrical contacts with spacings as small as 200 to 400 microns, and thus are neither compatible with integrated circuit I/O (input/output) pad spacings nor with miniature implantable packages. We report the development of a hermetic high-density feedthrough (HDF) technology that allows for conductive path densities as high as 1,000 per cm2, and that is capable of supporting neural interface devices. The fabrication process utilizes multilayer high temperature co-fired ceramic (HTCC) technology in conjunction with platinum leads. Before co-firing, green alumina substrates are interleaved with linear, parallel Pt trace arrays in either wire or thin foils to form the electrical feedthroughs. Layered stacks of spatially isolated traces are first compacted into a composite, and then fired to achieve densification. After firing, the densified multilayered composite compacts are sliced perpendicular to the Pt traces and lapped to produce multiple feedthrough arrays with a high density of leads (conductors). Both hermeticity and biocompatibility of such implantable feedthroughs are important, as both moisture and positive mobile ion contamination from the saline environment of the human body can lead to compromised performance or catastrophic failure. HDFs fabricated using this process with 100 conductors and lead-to-lead spacings as low as 400 microns have been helium leak tested repeatedly and found to exceed industry-accepted standards with helium leak rates in the range of 10–11 mbar-l/s. The spacing of the current prototype matches industry standard neural interface technology, and can be scaled to higher densities with lead-to-lead spacings as small as 200 microns. The reported HDF process has several distinct advantages over prior approaches, including the provision of a large number of conductive feedthrough leads suitable for flip-chip bonding with sub-mm lead-to-lead spacings (pitch), and the incorporation of materials (alumina and platinum) that are already used in medical implants. The implementation of such an HDF technology allows for significant package miniaturization, allowing greater flexibility in surgical placement as well as less invasive procedures for implantable electronic biomedical devices.

Titanium dioxide nanoparticles were synthesized by solvothermal treatment in the presence of oleic acid and oleylamine. As Ti(IV) reactant, crystals of [Ti8O12 (H2O)24]Cl8, HCl, 7H2O were preferred because their hydrolysis and condensation can be controlled in ethanol/water solution. The organic surfactants allowed the control of the shape and they can be removed by an acid treatment of the particles. The TiO2 nanoparticles can then be re-dispersed in an ethanol-based charging solution. A fixed applied voltage promotes the electrophoretic deposition of the nanoparticles (<15 nm in size) into pores of anodized aluminium oxide (AAO) template.

Highly transparent composite electrodes made of multilayers of In- and Ga-doped ZnO and Cu (IGZO/Cu/IGZO) thin films (30/3-9/30 nm thick) are deposited onto flexible substrates at room temperature and by using radio frequency magnetron sputtering. The effect of Cu thickness on the electrical and optical properties of the multilayer stack has been studied in accordance with the Cu morphology. The optical and electrical properties of the multilayers are studied with the UV–Vis spectrophotometry, Hall measurement and four point probe analyses. Results are compared with those from a single IGZO layered thin film. The average optical transmittance and sheet resistance both decreases with increase of copper thickness and has been optimized at 6 nm Cu middle layer thickness. The Haacke figure of merit (FOM) has been calculated to evaluate the performance of the films. The highest FOM achieved is 6 x 10-3 Ω-1 for a Cu thickness of 6 nm with a sheet resistance of 12.2 Ω/sq and an average transmittance of 86%. The multilayered thin films are annealed upto 150 °C in vacuum, forming gas and O2 environments and the optical and electrical properties are studied and compared against the as-deposited samples. Thus IGZO/Cu/IGZO multilayer is a promising flexible electrode material for the next-generation flexible optoelectronics.

We have studied a procedure to determine Tight-Binding (TB) parameters automatically, by which the band structure of the crystalline solid can be reproduced so as to be good agreement with that of first-principles molecular dynamics calculation. According to this procedure, we determine TB parameter sets for silicon and diamond accurately, and a fairly good set for their compound SiC.

We studied the transport properties of the Fe/MgO/Fe and Fe/Ag/MgO/Ag/Fe magnetic tunnel junctions (MTJs) with 13-layer MgO barrier under bias voltage based on first-principles calculations. Our results showed that two features determine the TMR value decreases with bias of Fe/MgO/Fe MTJ: (1) interfacial states lying at 1.06 eV in spin down channel (2) the energy level of the spin down Δ1 band of the Fe electrode. Our results showed that an inserted Ag mono-layer at Fe/MgO interface can remarkably improve the TMR effect at a high bias voltage.

The effect on film quality of the dielectric constant εb of the bath solution used for electrophoretic deposition of CdSe quantum dots (QDs) was investigated. Various combinations of solvents yielding different εb were tested, with the best films produced by a bath consisting of hexanes and acetone. Two different types of film were observed, depending on the volume fraction of acetone in the bath: thin, but strongly adhered films for εb < 12 and thick but loose films for εb > 12. This behavior is explained in terms of the rate at which QDs arrive at the surface of the electrode, which depends on the electrophoretic mobility of the QDs and therefore also the dielectric constant of the bath.

Here we discuss two alternative approaches for building flexible batteries for applications in smart textiles. The first approach uses well-studied inorganic electrochemistry (Al-NaOCl galvanic cell) and innovative packaging in order to produce batteries in a slender and flexible fiber form that can be further weaved directly into the textiles. During fabrication process the battery electrodes are co-drawn within a microstructured polymer fiber, which is later filled with liquid electrolyte. The second approach describes Li-ion chemistry within solid polymer electrolytes that are used to build a fully solid and soft rechargeable battery that can be furthermore stitched onto a textile, or integrated as stripes during weaving process.

Ba0.8Sr0.2TiO3/ZrO2 heterostructured thin films with different individual layer ZrO2 thicknesses are deposited on Pt/Ti/SiO2/Si substrates by a sol-gel process. The current versus voltage (I-V) measurements of the above multilayered thin films in metal-insulator-metal (MIM) device structures are taken in the temperature range of 310 to 410K. The electrical conduction mechanisms contributing to the leakage current at different field regions have been studied in this work. Various models are used to know the different conduction mechanisms responsible for the leakage current in these devices. It is observed that Poole-Frenkel mechanism is the dominant conduction process in the high field region with deep electron trap energy levels (φ t ) whereas space charge limited current (SCLC) mechanism is contributing to the leakage current in the medium field region with shallow electron trap levels (E t ). Also, it is seen that Ohmic conduction process is the dominant mechanism in the low field region having activation energy (E a ) for the electrons. The estimated trap level energy varies from 0.2 to 1.31 eV for deep level traps and from 0.08 to 0.18 eV for shallow level traps whereas the activation energy for electrons in ohmic conduction process varies from 0.05 to 0.17 eV with the increase of ZrO2 sub layer thickness. An energy band diagram is given to explain the dominance of the various leakage mechanisms in different field regions for these heterostructured thin films.