Large scale molecular-dynamics simulations of plane shock loading in SiC are performed to reveal the interplay between shock-induced compaction, structural phase transformation (SPT) and plastic deformation. The shock profile is calculated for a wide range of particle velocity from 0.1 km/s to 6.0 km/s. Single crystalline models indicate no induced plasticity or SPT for shock loading below 2.0 km/s. For intermediate particle velocity, between 2.0 km/s and 4.5 km/s the generated shock wave splits into an elastic precursor and a zinc blende to rocksalt structural transformation wave. That is induced by the increase in shock pressure to over 90 GPa and results in a steep increase of density from 3.21 g/cm3 to ∼4.65 g/cm3. For particle velocity greater than 4.5 km/s a single overdriven transformation shock wave is generated. These simulation results provide an atomistic view of the dynamic effects of shock impact on single crystal high-strength ceramics.

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

Access to cutting-edge technologies in materials science and engineering within K-12 education is a great struggle in developing countries. In this work, a problem-based, hands on set of seven modules for integrating Holographically-formed Polymer Dispersed Liquid Crystal (H-PDLC) Bragg Grating thin films into the Kenyan secondary physics, chemistry and mathematics curriculum is proposed. Through funding provided by the National Science Foundation, a pilot study of the integration of these modules, using the National Academy of Engineering’s (NAE) Grand Challenges for Engineering as a contextual vessel, is carried out. The efficacy of these curriculum-integrated modules in communicating real world materials science and engineering challenges is examined using qualitative and quantitative means. A method for expanding the use of this experience with other graduate students is proposed.

The well-known high irradiation resistance of fluorite-structured oxides is examined on the nanoscale by focused electron beam irradiation of ceria nanoparticles. It is found that ceria is amongst the nanomaterials most resistant to electron beam perforation with mainly swelling and amorphisation damage observed, along with grain reorientation effects. A comparison to reference nano-materials, shows that cubic zirconia behaves similarly resistant but that ultra-fine holes can be drilled, unlike for ceria, while SiC on the other hand can be perforated easily. Ablation of carbon films around electron beam impact zones is found accelerated in ceria, as compared to SiC, and discussed as a potential catalytic effect.

Molecular spintronics devices (MSDs) are capable of harnessing the controllable transport and magnetic properties of molecular device elements and are highly promising candidates for revolutionizing computer logic and memory. A MSD is typically produced by placing magnetic molecule(s) between the two ferromagnetic electrodes. Recent experimental studies show that the molecules produced unprecedented strong exchange couplings between the two ferromagnets, leading to intriguing magnetic and transport properties in a MSD. Future development of MSDs will critically depend on obtaining an in-depth understanding of the molecule induced exchange coupling and its impact on MSD’s switchability and temperature stability. However, the large size of MSD systems and unsuitable device designs are the two biggest hurdles in theoretical and experimental studies of magnetic attributes produced by molecules in a MSD. This research theoretically studies the MSD by performing Monte Carlo Simulation (MCS) studies, which have the capacity to tackle large systems- such as MSD based on magnetic tunnel junction (MTJ) test bed. The MTJ based MSD has the distinctive advantage that MTJ test bed can be subjected to experimental magnetic characterizations before and after transforming it into a MSD by bridging the molecules of interest between the two metal electrodes of a MTJ. Hence the result of our MCS can be verified experimentally.

Electropolishing of p-type silicon has been investigated over a wide range of HF concentrations (0.01-11 wt. %) by potentiodynamic polarization. Oxide dissolution rates were determined from the plateau current densities observed in the electropolishing region during the reverse sweeps; i.e. where the growth and dissolution rates of the anodic oxide film are believed to be equal. Based on the shape of the CV curves the oxide dissolution process was treated as a corrosion process controlled by the dissolution of a salt film, that is its rate controlled by removal of dissolved products away from the surface rather than reactants to the surface as previously proposed. Although a contribution from HF from bulk to surface cannot be completely ruled out, because the removal of the initial dissolution product can be by either mass transport or further chemical reaction with HF species in solution this mechanism is capable of explaining the dependence of the dissolution rate on HF concentration for the whole range investigated.

We report a simple synthesis technique to attached poly(N-isopropylacrylamide) on magnetic nanoparticles. Fe3O4 magnetic nanoparticles were prepared using co-precipitation method. Nearly monodisperse nanoparticles were separated by terminating surface of Fe3O4 with dopamine followed by careful centrifugation and decantation. NHS/EDC coupling chemistry was employed to attached the carboxylic acid terminated poly(N-isopropylacrylamide) to amine end of dopamine on surface of the magnetic particles. Analysis of the polymer brush layers was conducted using UV-Vis spectroscopy, ATR−FTIR, and Transmission electron microscopy techniques. The magnetic property was investigated using direct current superconducting quantum interference device (DC-SQUID) method.

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/□.