GaN-based dilute magnetic semiconductors (DMS) have recently been investigated for use in spintronic devices. In particular, Gd-doped GaN has shown very promising room temperature ferromagnetic behavior and potential for use in spintronics applications. III-Nitride materials have recently had their thermoelectric properties investigated; however this work has not been extended to Nitride-based DMS. Understanding the spin-calorimetric characteristics of GaN-based DMS is important to the successful development of low-power spintronic devices. In this paper the Seebeck and spin-Seebeck effect in MOCVD grown Gd-doped GaN (Gd: GaN) are investigated.

The goal of this work is to understand the role of nano-confinement in designing an inexpensive and user friendly ‘point- of- care’ (POC) protein biosensor. We used printed circuit board based gold chips and integrated them with nanoporous alumina membranes in generating high density arrays of nano scale confined spaces. We initially tested the role of a nanomembrane in achieving signal enhancement through size based confinement of proteins. As a later part of the experiment, we studied the role of pore size on achieving signal enhancement by using membranes of two different pore sizes of 100 and 200 nm. It is critical that ultralow detection of biomolecules be achieved as they have significant impact in designing diagnostics platforms for early disease diagnosis. Commercially available nano-porous membranes made out of anodized alumina were evaluated for their role in nano-confinement and enhancing sensitivity of detection. In this biosensor configuration sandwich assay, an electrical double layer is formed between a test protein (C-reactive protein) and the gold surface underneath the porous membrane. Using electrical impedance spectroscopy, the capacitance/impedance changes in the electrical double layer, was analyzed which translated to identifying the sensitivity and the linear dose response of the sensor for two specific conditions (a) with nano confinement and (b) for varying size of confined spaces

The distribution of carbon in Ti–45Al–5Nb–0.5C was studied using small-angle neutron scattering (SANS). In an earlier study, carbon had been found to form small perovskite precipitates in a γ-TiAl alloy without Nb, which significantly increase the strength of the material. In the Nb-containing alloy, however, no strengthening precipitates were observed, but most of the C was found to be homogeneously distributed. Atom probe investigations revealed only few C-enriched regions. The present SANS investigation was carried out to confirm the presence and size distribution of these C-enriched regions in the material. The SANS results show that a small volume fraction of such C-enriched regions is present, while the large number of small precipitates found in the alloy without Nb is indeed missing in the Nb-containing alloy.

Methods for extracting or harvesting energy from the surrounding battlefield environment are of great importance to the United States Army. Scavenging energy from local environments reduces the required energy and weight transported to the theater. Micro- and nano-scale metal-insulator-metal (MIM) tunnel diodes are being developed to provide half-wave rectification as part of a “rectenna” energy harvesting system, which includes a radiation-collecting antenna, a rectifying MIM tunnel diode, and a storage capacitor. In this work, high-frequency MIM tunnel diodes for power rectification were designed, fabricated and characterized. Planar Pt/TiO2/Ti stacks are being fabricated to create a diode with highly asymmetric I-V characteristics that has a very low threshold voltage. The metals were chosen for their high work function difference, and the insulator was chosen for its barrier height, its compatibility with Ti, and its availability. The energy band diagram and the I-V characteristics were modeled to determine the feasibility of the Pt/TiO2/Ti material system for use as a rectifier diode in a rectenna system. Metals and insulator thin films were deposited onto silicon dioxide/silicon substrates. Pillars with lateral dimensions ranging from 20 μm x 20 μm up to 100 μm x 100 μm were fabricated. The dielectric thickness of the MIM diode was varied from 5 nm up to 50 nm to determine the optimal thickness for quantum tunneling. I-V measurements were taken using an electrical characterization system to confirm a non-linear, asymmetric response on a survey of devices fabricated with varying areas. Preliminary results exhibit asymmetric I-V characteristics with threshold voltages of less than 700 mV.

A nondeterministic multiple scale approach based on numerical solution of the Monte-Carlo master equation coupled with a standard finite-element formulation of material mechanics is presented. The approach is illustrated in application to the long-term evolutionary processes of self-diffusion, precipitation and crack/void healing in nanocrystalline fcc and bcc solids. Effect of static and dynamic loading patterns on the crack healing rates are investigated. The approach is widely applicable to the modeling and characterization of advanced functional materials with evolutionary internal structure, as well as emerging behavior in materials systems.

Synthesis of InSb nanowires using chemical vapor deposition (CVD) is technically challenging due to the tuning of III-V vapor pressures. Growth parameters such as the choice of the metal catalyst, growth temperature and vapor pressure of constituents affect the morphology and stoichiometry of InSb nanowires. By controlling the growth temperature, it was possible to grow either stoichiometric InSb nanowires or In nanowires that contained no Sb within detectable limits. We present a simple model to show that the occurrence of native point defects in InSb is influenced by the growth kinetics and by the thermodynamics of defect formation. Results from this model are in good agreement with our experimental findings of the evidence of point defects in these nanowires.

The Phase-field method is recognized as the method of choice for space-resolved microstructure simulation. In theoretic phase-field approaches, the underlying diffuse interface representation is discussed in the sharp interface limit. Applied phase-field models, however, have to cope with interfaces of finite size. Numerical solution based on finite differences naturally implies a discretization error. This error may result in significant deviations from the analytical sharp-interface solution, especially in cases of interface-controlled growth. Benchmark simula-tions revealed a direct correlation between the accuracy of the finite-difference solution and the number of numerical cells used to resolve the finite-sized interface width. This poses a problem, because high numbers of interface cells are unfavorable for numerical performance. To enable efficient high-accuracy computations, a new Finite Phase-Field approach is proposed, which closely links phase-field modeling and numerical discretization. The approach is based on a parabolic potential function, corresponding to phase-field solutions with a sinusoidal interface pro-file. Consideration of this profile during numerical differentiation allows an exact quantification of the bias evoked by grid spacing and interface width, which then a priori can be compensated.

The crystal structure of thermoelectric rhenium silicide with an ordered arrangement of vacancies is investigated by utilizing spherical aberration (Cs) corrected scanning transmission electron microscopy (STEM) combined with synchrotron X-ray diffraction and conventional transmission electron microscopy. By STEM Cs corrected imaging, we can clearly observe Si vacancies in rhenium silicide, which is impossible without Cs correction. In addition, significantly reduced contrast levels are noted in STEM images for particular Si sites near vacancies. From the STEM image simulation, the reduced contrast levels are concluded to be due to anomalously large local thermal vibration of these Si atoms. The crystal structure of rhenium silicide can be successfully refined by the synchrotron X-ray diffraction starting with the deduced structure model from the STEM images and the occurrence of large local thermal vibration can be qualitatively confirmed. Furthermore, we confirm the validity of the refined crystal structure of rhenium silicide by comparing experimental images with simulated image generating with the refined crystal structure parameters.

In this work, the low index faces of lanthanum zirconate (La2Zr2O7, LZ) are studied at the level of density-functional theory, representing the first theoretical attempt to characterize the surfaces of a pyrochlore oxide. All possible surface terminations formed by cleaving a perfect crystal are considered, as well as selected defective surfaces. After deriving the expression for the free energy of an LZ surface, surface free energies are computed. The most stable surface terminations are identified, their geometric and electronic structures discussed, and a motivation provided for calculating ratios of certain surface free energies more accurately for comparison to experimental results that will be obtained.

ZnO:Al films with a thickness of about 880nm were deposited by magnetron sputtering. The glass substrate was not heated neither before during nor after the deposition. Subsequently the deposited layers were treated by flash lamp annealing (FLA) at 1.3 ms. Using this method, the resistivity of the ZnO:Al films was decreased by a factor of two, down to 1.0 x 10-3 Ωcm. These results are in good agreement with results reported from rapid thermal processing or furnace annealing treatments. Despite the very short annealing time of only 1.3 ms not only the resistivity but also the transmittance in the UV and the blue range were considerably improved.

Silicon carbide (SiC) has received increasing attention on the integration of microelectro-mechanical system (MEMS) due to its excellent mechanical and chemical stability at elevated temperatures. However, the deposition process of SiC thin films tends to induce relative large residual stress. In this work, the relative low stress material silicon oxide was added into SiC by RF magnetron co-sputtering to form silicon oxycarbide (SiOC) composite films. The composition of the films was characterized by Energy dispersive X-ray (EDX) analysis. The Young’s modulus and hardness of the films were measured by nanoindentation technique. The influence of oxygen/carbon ratio and rapid thermal annealing (RTA) temperature on the residual stress of the composite films was investigated by film-substrate curvature measurement using the Stoney’s equation. By choosing the appropriate composition and post processing, a film with relative low residual stress could be obtained.

Recently, Elias et al. (Science 323, 610 (2009).) reported the experimental realization of the formation of graphane from hydrogenation of graphene membranes under cold plasma exposure. In graphane, the carbon-carbon bonds are in sp 3 configuration, as opposed to the sp 2 hybridization of graphene, and the C–H bonds exhibit an alternating pattern (up and down with relation to the plane defined by the carbon atoms). In this work we have investigated, using reactive molecular dynamics simulations, the role of H frustration (breaking the H atoms up and down alternating pattern) in graphane-like structures. Our results show that a significant percentage of uncorrelated H frustrated domains are formed in the early stages of the hydrogenation process, leading to membrane shrinkage and extensive membrane corrugations. This might explain the significant broad distribution of values of lattice parameter experimentally observed. For comparison purposes we have also analyzed fluorinated graphane-like structures. Our results show that similarly to H, F atoms also create significant uncorrelated frustrated domains on graphene membranes.

Metal-catalyzed graphitization from vapor phase sources of carbon is now an established technique for producing few-layer graphene, a candidate material of interest for post-silicon electronics. Here we describe two alternative metal-catalyzed graphene formation processes utilizing solid phase sources of carbon. In the first, carbon is introduced as part of a cosputtered Ni-C alloy; in the second, carbon is introduced as one of the layers in an amorphous carbon (a-C)/Ni bilayer stack. We examine the quality and characteristics of the resulting graphene as a function of starting film thicknesses, Ni-C alloy composition or a-C deposition method (physical or chemical vapor deposition), and annealing conditions. We then discuss some of the competing processes playing a role in graphitic carbon formation and review recent evidence showing that the graphitic carbon in the a-C/Ni system initially forms by a metal-induced crystallization mechanism (analogous to what is seen with Al-induced crystallization of amorphous Si) rather than by the dissolution-upon-heating/precipitation-upon-cooling mechanism seen when graphene is grown by metal-catalyzed chemical vapor deposition methods.

This article examines, from the energy viewpoint, a new lightweight, slim, high energy efficient, light-transmitting envelope system, providing for seamless, free-form designs for use in architectural projects. The research was based on envelope components already existing on the market, especially components implemented with granular silica aerogel insulation, as this is the most effective translucent thermal insulation there is today. The tests run on these materials revealed that there is not one that has all the features required of the new envelope model, although some do have properties that could be exploited to generate this envelope, namely, the vacuum chamber of vacuum insulated panels (VIP), the monolithic aerogel used as insulation in some prototypes, and reinforced polyester barriers. By combining these three design components — the high-performance thermal insulation of the vacuum chamber combined with monolithic silica aerogel insulation, the free-form design potential provided by materials like reinforced polyester and epoxy resins—, we have been able to define and test a new, variable geometry, energy-saving envelope system.

In recent years, microfluidic devices have emerged as a platform in which to culture tissue for various applications such as drug discovery, toxicity testing, and fundamental investigations of cell-cell interactions. We examine the transport phenomena associated with gradients of soluble factors and oxygen in a microfluidic device for co-culture. This work focuses on emulating conditions known to be important in sustaining a viable culture of cells. Critical parameters include the flow and the resulting shear stresses, the transport of various soluble factors throughout the flow media, and the mechanical arrangement of the cells in the device. Using analytical models derived from first principles, we investigate interactions between flow conditions and transport in a microfluidic device. A particular device of interest is a bilayer configuration in which critical solutes such as oxygen are delivered through the media into one channel, transported across a nanoporous membrane, and consumed by cells cultured in another. The ability to control the flow conditions in this membrane bilayer device to achieve sufficient oxygenation without shear damage is shown to be superior to the case present in a single channel system. Using the results of these analyses, a set of criteria that characterize the geometric and transport properties of a robust microfluidic device are provided.

Three synthesis techniques have been explored as routes to produce copper oxide for use in resistive memory devices (RMDs). The major results and their impact on device current-voltage characteristics are summarized. The majority of the devices fabricated from thermally oxidized copper exhibited a diode-like behavior independent of the top electrode. When these devices were etched to form mesa structures, bipolar switching was observed with set voltages <2.5 V, reset voltages <(-1) V and ROFF/RON ∼103-104. Bipolar switching behavior was also observed for devices fabricated from copper oxide synthesized by RT plasma oxidation (ROFF/RON up to 108). Voiding at the copper-copper oxide interface occurred in films produced by thermal and plasma oxidation performed at ≥200°C. The copper oxide synthesized by reactive sputtering had large areas of open volume in the microstructure; this resulted in short circuited devices because of electrical contact between the bottom and top electrodes. The results for fabricating copper oxide into ≤100 nm features are also discussed.