ZnMgTe(Cladding)/ZnTe(Core)/ZnMgTe(Cladding) thin film waveguide had been grown by molecular beam epitaxy (MBE) and presented a great potential to be a high performance Electro-optical (EO) modulator. For a low propagation loss ZnMgTe/ZnTe waveguide, thick cladding layer with high Mg composition (Mg %) is needed. However, the in-plane lattice mismatch of the fabricated device with high Mg % and thick cladding layer was large. It might cause the cladding/core interface roughness and asperities due to the misfit dislocation, and degrade the device performance. Because EO property of waveguide device is primarily influence by the structure thickness, the device efficiency improvement in this study was only considered to reduce the defects asperities that would cause propagation loss without decreasing the Mg % or the total thickness of the cladding layers. Therefore, we introduced a low Mg % layer between the cladding and the core layer to circumvent the effect of large lattice mismatch. The in-plane lattice mismatch of the devices was monitored using reciprocal space mapping, and surface morphologies were also observed using atom force microscope. The two-step index ZnMgTe/ZnTe waveguide had shown to have lower degree of relaxation compared to that of single-step index waveguide device with close Mg % and cladding layer thickness. Therefore, the crystal degradation of the two-step-index waveguide caused by lattice mismatch was successfully suppressed by introduction extra low Mg % layers. The morphologies of the two kinds of waveguide structures have similar surface asperities, which indicated the extra inserted layers did not produce additional large scale asperities at the interfaces that would increase the propagation loss.

The enhancement of photovoltaic efficiency by incorporation of down-shifting phosphor materials in optically active and inactive regions of solar modules is presented. Thin film photovoltaic modules suffer from various optical losses, including front glass reflectance, thermalization loss of absorbed high energy photons, window layer absorption, and the loss of photons to scribe regions. There have been various efforts to improve the performance of solar modules by application of down-shifting (DS), down-converting, and up-converting materials systems. Here we show results towards the development of a low-cost phosphor film system tuned to the solar spectrum and specifically designed for CdTe thin film modules.

While the growth of pits in passive metals exposed to chloride solutions is well understood, the processes associated with the initiation and propagation of stable pits, versus pits that form and apparently re-passivate, are still a matter of conjecture. A major challenge in studying pit initiation using electron microscopy has been alteration of the structure and chemistry of the hydrated corrosion films upon transfer to the vacuum environment of the microscope. A recently developed technique uses a microfluidic liquid cell to maintain the aqueous environment in contact with the sample. This work uses such cells to directly observe pits initiating, and growing before reaching stability, in aluminum thin films under potentiostatic polarization in situ in the electron microscope. Polarization curves developed in the cell show good agreement with those observed under conventional electrochemical experimental conditions. We observed current transients representative of metastable pitting and were able to relate crystalline features found in situ with topographic features using atomic force microscopy (AFM). An accumulation of aluminum surrounding an initiated pit, combined with depth profiling using Auger electron spectroscopy suggests that aluminum metal is deposited during the pit initiation process, and may serve to reduce lateral dissolution of the aluminum film. Work is currently underway to determine if this observation is unique to the geometry of the microfluidics cell or if is a general result that occurs at the very beginning of pit initiation.

This study investigates the use of shape memory polymers (SMPs) as a substrate for a self-coiling cochlear implant electrode array and investigates the self-coiling ability of a sham probe micromachined atop such a substrate. Through the use of a self-coiling cochlear implant, the capability to avoid contact with the tissue of the cochlear duct is investigated via the insertion of a dummy device into a model cochlea heated to an ambient 34 °C. Finally, a prototype straightening and insertion tool is developed for automated retraction and locking of the coiled shape into a bar geometry. Preliminary demonstration of the deployment of self-coiling cochlear implants is shown and paves the way for future studies focused on using histological analysis of the cochlear wall tissue to compare the degree of trauma resulting from linear cochlear implant arrays versus the self-coiling, non-contact probes demonstrated herein.

The disposal of materials at the end of their lifecycle, especially for complex manufactured products, presents challenges in terms of both protecting the environment and human health. In particular, used automobiles are disposed of by removal of various component parts, followed by shredding. In this study, air particulates were collected over several days by DRUM impactor downwind of an automobile shredding plant, size separated, and analyzed by scanning and transmission electron microscopy (SEM and TEM), and energy-dispersive x-ray spectroscopy (EDXS), in order to determine their particle size distribution and corresponding chemical composition. Results for larger particles, ranging in size from 2.5 to 10.0 μm, showed mainly diatoms and salts, from the plant’s ocean side location, and aluminosilicates, consistent with geological sources. As particle size decreased from 10 μm to 0.09 μm, particle loading decreased, and composition shifted to mainly oxygen and sulfur, indicative of sulfates, which along with nickel and vanadium that were detected, could be attributed to emissions from nearby shipping traffic. Iron was found to be present, including in spherical particles that were ∼ 2 μm in diameter, indicating they originated from a high temperature process. Spherical iron particles also were found to correlate with plant operations, making them a useful “tracer” material for plant emissions. Lead, cerium, barium, chromium and zinc were also detected and their possible correlation to plant feedstocks is discussed. The implications of these results for the environment, particularly soil and water deposition, and for human health as a result of inhalation, are discussed.

Sodium carbonate is currently being considered as a wash-out reagent for the removal of the settled solids in the unagitated Highly Active Liquor (HAL) storage tanks at Sellafield. As the settled solids are expected to comprise mainly zirconium molybdate (ZM), this will result in a challenging feed to the Waste Vitrification Plant (WVP) containing high concentrations of both molybdenum and sodium.

In previous studies, it was shown that at high wash-out waste loadings, i.e. 10 – 12 wt% MoO3 incorporation, there was very little tolerance in ‘Ca/Zn’ base glass for extra sodium before the formation of significant separated sodium molybdate salt phase. However, higher amounts of sodium can be accommodated in borosilicate glasses if the wash-out waste loading is reduced. Further studies have now been carried out to investigate the vitrification of more representative calcined waste feeds. Both pure zirconium molybdate (ZM) and blended ZM-reprocessing waste calcines were produced from the appropriate liquor feeds. The maximum waste incorporations of these two calcines in ‘Ca/Zn’ base glass have been determined, along with a complete product quality assessment. This assessment included measuring the bulk density, degree of crystallinity, heat treatment, durability (Soxhlet and PCT), glass transition temperature, and viscosity.

Ytterbium disilicate is of interest as a potential environmental barrier coating for aerospace applications, notably for use in next generation jet turbine engines. In such applications, the transport of oxygen and water vapor through these coatings to the ceramic substrate is undesirable if high temperature oxidation is to be avoided. In an effort to understand the diffusion process in these materials, we have performed kinetic Monte Carlo simulations of vacancy-mediated and interstitial oxygen diffusion in Ytterbium disilicate. Oxygen vacancy and interstitial site energies, vacancy and interstitial formation energies, and migration barrier energies were computed using Density Functional Theory. We have found that, in the case of vacancy-mediated diffusion, many potential diffusion paths involve large barrier energies, but some paths have barrier energies smaller than one electron volt. However, computed vacancy formation energies suggest that the intrinsic vacancy concentration is small. In the case of interstitial diffusion, migration barrier energies are typically around one electron volt, but the interstitial defect formation energies are positive, with the result that the disilicate is unlikely to exhibit experience significant oxygen permeability except at very high temperature.

The thermal and electrical properties of organic semiconductor are playing critical roles in the device applications especially on the devices with large area. Although the effect may be minor in a single device like field effect transistors, the unwanted waste heat would cause much more severe problems in large-scale devices as the power density will go up significantly. The waste heat would lead to performance degradation or even failure of the devices, and thus a more detailed study on the thermal conductivity and carrier mobility of the organic thin film would be beneficial to predict the limits of the device or design a thermally stable device. Here we explore the thermal annealing effect on the thermal and electrical properties of the small molecule organic semiconductor, dinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene (DNTT). After the post deposition thermal annealing, the grain size of the film increases and in-plane crystallinity improves while cross-plane crystallinity keeps relatively constant. We demonstrated the cross-plane thermal conductivity is independent of the thermal annealing temperature and high annealing temperature will reduce the space-charge-limited current (SCLC) mobility. When the annealing temperature increase from 24 °C to 140 °C, the field effect mobility shows a gradual increase while the threshold voltage shifts from positive to negative. The different dependence of the SCLC mobility and field effect mobility on the annealing temperature suggest the improvement of the film crystallinity after thermal annealing is not the only dominating effect. Our investigation provides the constructive information to tune the thermal and electrical properties of organic semiconductors.

It is widely received that resistive switching in electrode (EL)/metal oxide (MO)/EL cell is caused by formation and rupture of a conductive filament (CF) consisting of oxygen vacancies, VO’s. However, driving forces that migrate VO’s are not elucidated yet. Considering an experimental fact that good data endurance more than 106 cycles is often observed, an isotropic driving force that gathers oxygen vacancies and form a CF for set switching is required instead of an electric field drift that is widely received as the driving force of set switching.

In this paper, we reexamined driving forces and succeeded in reproducing pulse response data for wide rise time, t rise, range by simulating VO migration assuming Fick and Soret diffusion, without including the electric-field drift. Therefore, it was suggested that controlling T distribution considering the waveforms of write/erase pulses and the thermodynamic parameters of ELs as well as MO is crucial for the optimization of switching speed of ReRAM.

All inorganic quantum dot light emitting devices with solution processedtransport layers are investigated. The device consists of an anode, a holetransport layer, a quantum dot emissive layer, an electron transport layer and acathode. Indium tin oxide coated glass slides are used as substrates with theindium tin oxide acting as the transparent anode electrode. The transport layersare both inorganic, which are relatively insensitive to moisture and otherenvironmental factors as compared to their organic counterparts. Nickel oxideacts as the hole transport layer, while zinc oxide nanocrystals act as theelectron transport layer. The nickel oxide hole transport layer is formed byannealing a spin coated layer of nickel hydroxide sol-gel. On top of the holetransport layer, CdSe/ZnS quantum dots synthesized by hot injection method isspin coated. Finally, zinc oxide nanocrystals, dispersed in methanol, are spincoated over the quantum dot emissive layer as the electron transport layer. Thematerial characterization of different layers is performed by using absorbance,Raman scattering, XRD, and photoluminescence measurements. The completed deviceperformance is evaluated by measuring the IV characteristics,electroluminescence and quantum efficiency measurements. The device turn on isaround 4V with a maximum current density of ∼200 mA/cm2 at9 V.

Shape-memory hydrogels (SMHs) are potential candidate materials for biomedical applications as they can mimic the elastic properties of soft tissue and exhibit shape transformations at body temperature. Here we explored, whether architectured SMHs can be designed by incorporating oligo(ε-caprolactone) (OCL, ${\overline M _n}$ = 4500 g·mol-1, Tm = 54 °C) side chains as switching segment into hydrophilic polymer networks based on N-vinylpyrrolidone as backbone forming component and oligo(ethylene glycol)divinylether (OEGDVE, ${\overline M _n}$ = 250 g·mol-1) as crosslinker. By utilizing NaCl and NaHCO3 as porogene during thermal crosslinking architectured hydrogels having pore diameters between 30 and 500 µm and wall thicknesses ranging from 10 to 190 µm in the swollen state were synthesized. According to the porous microstructure, a macroscopic form stability was obtained when the polymer networks were swollen until equilibrium in water. Material properties were investigated as function of the OCL content, which was varied between 20 and 40 wt%. In compression experiments the architectured hydrogels exhibited strain fixity and strain recovery ratios above 80%. These architectured SMHs might enable biomaterial applications as smart implants with the recovery of bulky structures from compact shapes.

The paper presents the research results of formation peculiarities of barrier electrically insulated coatings based on titanium oxide (TiO2) under conditions of AC-DC electrochemical anodizing. It is shown that overlapping of AC component (at the frequency of 100 kHz – 10 MHz) leads to formation of coatings 1.2-1.4 times thicker. Dependences of the coating thickness on frequency under various ratios of the AC-component amplitude to the DC-component of anodizing voltage have been obtained.

We investigated the fabrication of convex diamond-like carbon (DLC) based microgears in room-temperature curing nanoimprint lithography (RTC-NIL) using the ladder-type hydrogen silsesquioxane (HSQ), as an application for the medical micro electro mechanical system (MEMS). The HSQ which is an inorganic polymer of sol-gel system turns into a gel when exposed to air and has the siloxane bond. Therefore, the HSQ was used as RT-imprinting material, and also used as an oxide mask material in electron cyclotron resonance (ECR) oxygen (O2) ion shower etching. We fabricated the polydimethylsiloxane (PDMS) mold with concave microgear patterns which has 40, 50 and 60 μm-tip diameter and 300 nm-depth. We carried out the RTC-NIL process using the PDMS mold under the following optimum conditions of 0.10 MPa-imprinting pressure and 1.0 min-imprinting time. We found that the residual layer of imprinted HSQ microgear patterns was removed with ECR trifluoromethane (CHF3) ion shower under the following conditions of 300 eV-ion energy and 2.0 min-etching time, and then microgears of the HSQ on the DLC film were etched with ECR O2 ion shower under the following conditions of 400 eV-ion energy and 10 min-etching time. As a result, the convex DLC based microgears which have 40, 50 and 60 μm-tip diameter and 400 nm-height were fabricated with high accuracy in the new fabrication process of RTC-NIL.