By pumping AlGaN/GaN HEMTs with below band-gap light we observe changes in drain current that correspond to the trapping and detrapping of carriers within the band-gap. These changes in drain current are indicators of trap density, since the energy from a specific wavelength of light pumps traps whose activation energies are less than or equal to that of the light source.

AlGaN/GaN HEMTs on SiC with dual submicron gates with widths of 125nm, 140nm, or 170nm, are DC-stressed under three different conditions along a load line: VGS=0, VDS=5 (on-state), VGS=-2, VDS=9.2 and, VGS=-6, VDS=25 (off-state). The stress tests are interrupted at 20% degradation and the optically pumped comparisons to the baseline are measured.

This paper describes the optical pumping technique and results from experiments of AlGaN/GaN HEMTs under the three DC stress biases along a load line.

Polymer and carbon nanotubes (CNTs) nanocomposites exhibit many properties that are not present in either the pure polymer or CNTs. The polymer crystallization kinetics and crystal forms are greatly changed by dispersion of CNTs nanotubes. In addition to various thermophysical properties, CNTs are metallic or semiconductive and highly anisotropic while the polymer hosts are typically excellent insulators and isotropic. In this work, measurements of the electrical conductivity, σ, of thin-film nanocomposites of isotactic polypropylene (iPP) and CNTs as a function of CNT concentration (0, 1, 2, and 5% by weight of CNT) and melt-shearing induced anisotropy in σ between parallel and perpendicular to the shearing axis is presented and compared them with analogous data for their thermal transport properties. The iPP host is itself one of the most widely used polymers, has liquid crystalline phases, and it is expected that iPP/CNT nanocomposites will be widely used in many polymer applications, some of which are for flexible electrodes, medical and electronics packaging and chemical sensors. The effect of melt-shearing is expected to induce anisotropy in the various properties of the iPP/CNT thin film that should be particularly apparent in the electrical conductivity of the polymer films, higher in the direction of the alignment and lower in the direction perpendicular to it. With increasing CNT content, the average conductivity 〈σ〉 increases slightly from 0 to 2% CNT then dramatically increases by eight orders of magnitude for 5%. The shear induced property of anisotropy, δσs = (σ‖ − σ┴) / 〈σ〉, overall increases with CNT content, revealing a large spike for the 1% sample, indicating the possibility of enhanced δσs due to optimized orienting procedures.

Escherichia coli, like other gram-negative bacteria, is protected from the surrounding harsh environment by a cell wall consisting of the peptidoglycan and outer membrane. Whereas the cytoplasmic membrane is the selective barrier, the cell wall provides mechanical strength for the cell. As bacteria navigate various environments, osmotic pressure can change dramatically due to changes in local solute concentration. The peptidoglycan together with the cellular proteins mitigates the osmotic stress that would otherwise cause lysis. The mechanical properties of E. coli cells and its individual layers have been largely indeterminable until the recent development of probe-based measurement tools. Since their invention, scientists have reported significant data measuring elasticity, modulus, and stiffness using atomic force microscopy (AFM). Fundamentally, in order to determine these mechanical properties through probe-based techniques, the contact area and load should be well defined. The load can be precisely calculated through the AFM cantilever spring constant. However, the silicon tip contact area can only be estimated, potentially leading to compounding uncertainties. Therefore, we developed a methodology to determine nanomechanical properties of E. coli using a nanoindenter.

Physical properties of porous membranes made of biocompatible and biodegradable polymers have been studied. The membranes are intended to be used as scaffolds for the regeneration of soft and hard tissues. Polylactides, polycaprolactone and some of their derivates are biocompatible as well as biodegradable materials, and are used for the preparation of nanofibers and nanoporous membranes. These membranes also have comparative advantages as cellular scaffolds for tissue engineering since they can be prepared to mimic the morphology of the extra cellular matrix.

Chemical, physical, and biological properties of microfibers and scaffolds of polylactic acid (PLLA), as well as PLLA modified with hydroxyapatite nanoparticles and collagen (Col) are reported in this paper. The microfibers and the scaffolds were prepared by electrospinning. Morphology, diameter and porosity of the scaffold were determined by scanning electron microscopy and an image analyzer program. The microfibers are semicrystalline showing a shell of crystalline nanofibrils. The diameter of the fibers varied between 100 and 800 nm and the porous area of the membrane is between 60 and 80%. The mechanical properties of the microfibers and scaffolds were evaluated by microtensile tests and their behavior was simulated by using an original multiscale asymptotic homogenization model. Cultures of mesenchymal stem cells were used to evaluate their biological activity. Cell adhesion was observed in the modified PLLA scaffolds with grafted hydroxyapatite.

This work presents the development of three-terminal photodiodes which have their origin in bipolar pinipip-diode-structures [1,2]. The idea is to develop an unipolar diode and to contact a buried p-layer by an interior TCO-anode (transparent conductive oxide) instead of nip-stacking. The simulation of the optical material properties shows promising results. At first, both parts of the diode-structure were produced separately. The manufactured bottom (Cr/nip/TCO) and top (TCO/pip/TCO) parts were measured optically and electrically. These measurements are required to simulate the SR of the total-diode. Finally, a Cr/nip-a-Si:H/TCO/pip-a-Si:H/TCO multi-layer stack was deposited. The measured SR of the integrated diode validates the simulated data. The SR maximum shift amounts to 100nm, from 540nm by contacting the interior anode, to 640nm at the top anode. Furthermore, the curves are clearly split and do not enclose each other. The presented approach, with additional bandgap engineering, promises good prospects to improve color separation compared to currently existing detectors and should lead to a tunable multi-spectral photodiodes for high quality color recognition. Such a diode can be used in photonic devices, e.g. for safety and security applications.

In situ x-ray absorption spectroscopy (XAS) measurements were made on Fe3O4 nanoparticles in supercritical aqueous fluids to 500 °C in order to study their reactivity with Co2+ aqua ions and to investigate the structural properties of the reacted nanoparticles. The analyses of the x-ray absorption near edge structure (XANES) of XAS indicate that reactivity of Fe3O4 nanoparticles with Co2+ ions is minimal to 200 °C but becomes significant in the 250–500 °C temperature range. XANES and angular momentum projected density of states (l-DOS) calculations were carried out using the FEFF8.2 code and analyses were made using multi-peak fitting to determine the origin of the features exhibited in the spectra.

We propose a new nonvolatile resistance device having a metal/Al2O3/3C-SiC/n-Si/metal metal-insulator-semiconductor (MIS) structure. It is explained that the electron trapping states are generated in the Al2O3/3C-SiC interface region of the 3C-SiC layer due to partial oxidation of the 3C-SiC near the interface, and that the on and off states of the device are caused by trapping and detrapping of electrons in the defect states through the Al2O3 layer. The electron capture in the defect states causes high electric-field in the oxide layer which results in high-rate electron tunneling through the oxide layer and lowering the device resistance. We have previously reported the similar memory behavior with a metal/SiO2/SiOx /3C-SiC/n-Si/metal MIS structure, however the new memory exhibits more enhanced endurance characteristics than those of the previous memory, where the trapped electrons are injected and ejected through the 3C-SiC layer.

Tungsten oxide (WO3) films were prepared by using magnetron sputtering. Substrate temperature and sputtering pressure were adjusted to vary the microstructure. The films were found to contain nanoclusters; while their size L, and porosity θ and surface roughness zRMS of the film can be varied. After adding a palladium coating on the film surface, the hydrogen (H2) sensing properties of the films, including sensitivity of detection, response time and recovery time were measured. Their dependences on L, θ and zRMS were analyzed and interpreted. The information achieved is useful for improving H2 sensor technology.

ZnO nanorods were grown homogenously and vertically on ITO using electrochemical techniques. The physical properties of the nanorods were characterized using SEM and optical absorption. The electrical conductivity, deduced using STM at different tip heights, and was found to be 20 Ω-cm with a carrier concentration of 3x1015 cm-3.The results show that electrochemically grown ZnO nanorods have electrical properties suitable for use in electronic devices such as solar cells and transistors. A-Si:H p-i-n solar cells were then deposited after the fabrication on the ZnO on ITO-coated substrates. The results show that the textured solar cell performance was 30% higher than the planar solar cell.

Biomineralized composite materials found in nature have a compromise of good mechanical properties and relatively small embodied energies in the process of their formation. The Alternate Soaking Process (ASP) is a laboratory technique that has only recently been applied to replicating composite biomineralization. The nexus of the ASP – heterogeneous nucleation – makes it ideal for replicating biominerals where the mineral is templated onto an organic substrate, such as occurs in avian eggshell. Here we demonstrate the deposition of a calcium carbonate gelatin composite on either glass cover slips or demineralized eggshell membranes using an automated ASP. SEM images and FTIR spectra of the resulting mineral show that by altering the amount of gelatin in the growth solutions the final organic component can be controlled accurately in the range of 1-10%, similar to that of natural eggshell. This study shows for the first time the co-precipitation of a CaCO3 – gelatin composite by an ASP and that the organic fraction of this mineral can be tuned to mimic that of natural biomineralized composites.

An approach to control the tensile stress and Q factor of thin Si film beams in MEMS resonators was investigated. Metal-induced lateral crystallization (MILC) using Ni nanoparticles that were synthesized within a cage-shaped protein, apoferritin, was applied to a thin morphous Si film for making a MEMS resonator with thin film beams. The MILC produced a thin polycrystalline Si (poly-Si) film with large crystallized domain (50-60 μm) with nearly the same crystalline orientation, whereas the poly-Si film obtained by conventional annealing (without MILC) consisted of small grains (less than 1 μm) with random orientation. The MEMS resonator with a beam made of poly-Si film by MILC was fabricated. The large domain size and the improved crystallinity increased the tensile stress, and resulted in 20% increase in Q factor in the resonant characteristics.

Yttrium aluminosilicate (YAS) glasses have been proposed as host matrices for the immobilization of radioactive elements. In addition, yttrium has been used to simulate actinides [1]. It is well known that these glasses are resistant to water corrosion and exhibit high Tg and good mechanical properties [2]. As shown in [3], on heating, yttrium disilicate and mullite / sillimanite crystals grow from the pre-existing nucleation sites on the surface, until each glass particle volume is fully crystallized (volume-homogeneous nucleation was not observed), decreasing the glassy surface available for sintering by viscous flow. Sintering takes place simultaneously, by viscous flow but competes with surface crystallization; thus, if thermal treatment is not carefully designed a vitroceramic is obtained. In this paper we study the isothermal sintering kinetics of a YAS glass-powder-size distribution and non-isothermal sintering kinetics at 1, 3, 5, 10 and 15 K/min of two YAS glass-powder-size distributions. From the experimental evidence obtained, and crystallization data from [3], we design a sintering procedure in order to achieve a high-density glass monolith with submicrometric crystalline phases.

Nanodiamond powder (ND) has become one of the most promising and well-studied nanomaterials applied in various fields of science, technology and medicine. Recent achievements in the development of advanced ND applications present new demands to ND quality: purity, homogeneity of primary particle dimensions and surface area chemistry. ND produced by state-of-the-art technology of detonation synthesis doesn’t meet requirements for biomedical and optical applications. Therefore, alternative methods of ND synthesis from pure carbon raw materials enabling to control the process are of especial importance.

The novel technology for ND laser synthesis has been developed by Ray Techniques Ltd. The method is based on high-intensive laser radiation treatment of the specially prepared target containing non-diamond carbon soot and hydrocarbons, placed in a liquid media. As a result, carbon atoms collect to form a cubic diamond crystalline lattice. To reach that, the appropriate parameters of the laser radiation, special composition of the target and the liquid media, as well as the treatment procedures were determined. The “winning” combination of these factors enables to obtain pure nanodiamonds (RayND). In contrast to the existing technology, the RT method is highly controllable, environment-friendly and efficient.

RayND obtained under different conditions were studied and compared with detonation ND currently available at the market. It is proved that the higher level of purity and homogeneity of RayND constitutes significant advantages for most ND applications. Using RayND opens new frontiers in biomedicine (drug- and gene-delivery and bio-imaging agents), electronic industry (abrasives for wafer polishing, heat-conductive electrical-insulating compounds, CVD coatings, emitters, etc) and optics (displays, protective transparent films, laser lenses, optical windows and filters).

To realize applications based on nanowires, the development of methods that allow the organization of nanostructures into integrated arrangements is crucial. While many different methods exist, the direct synthesis of complex nanowire structures is one of the most suitable approaches to efficiently connect numerous nanostructures to the macroscopic world. The fabrication of various 3D nanowire assemblies including arrays, networks, and hierarchical structures by combining specifically designed template materials with electrochemical deposition is demonstrated. The ion track template method is extended to create more complex structures by changing template production and electrodeposition parameters. In contrast to current synthesis routes, it is possible to independently control many of the parameters defining both (i) characteristics of individual nanowires (including dimensions and composition) and (ii) the arrangement of the nanoscale building blocks into nanowire assemblies determined by nanowire orientation and integration level. Results that highlight the benefits arising from the design of advanced 3D nanowire architectures are presented.

We present experimental and theoretical Raman spectra of natural graphite mineral of Sonora, Mexico. In this work, we take the advantage of the utility of the RAMAN spectroscopy as a technique to determine the crystallinity and structure of graphite mineral. The RAMAN spectroscopy provides information that can be used to determine the degree of graphitization, which in turn can be used to know the metamorphic degree of the host rock. The resulting RAMAN spectra of graphite were divided in first and second order regions, in the first region (1100-1800cm-1) the E2g vibration mode with D6h crystal symmetry occurs at 1580cm-1 (G band) that indicates poorly organized graphite, additional bands appears in the first order region at 1350 cm-1 (D band) called the defect band, and another at 1620 cm-1 (D* band). The second-order region (2200-3400cm-1) shows several bands at ~2400 ~2700 ~2900 ~3300cm-1, all of them attributed to electron-phonon interactions or combination scattering. The density functional theory calculations were applied to determine the vibrational properties and the stacking layers of graphite.

A computational model of amorphous SiCOH materials is described that will facilitate studies of SiCOH behavior under different thermal and mechanical stresses. This involved developing an atomic-scale model of an SiCOH thin film, which exhibited structural, mechanical and electrical properties in agreement with experimental studies. We developed a unique process for computationally creating the structure of SiCOH films. We created an algorithm for introducing and estimating porosity in the system, which provides detailed information about the system’s pore size distribution on multiple length scales. We used Density Functional Theory (DFT) to develop a simple correlation that calculates the dielectric constant of a large SiCOH structure based only on its atomic composition and volume. Finally, we confirmed the mechanical properties of the model using established Molecular Dynamics techniques. We verified that essential electronic and mechanical properties of the model structure reproduce experimental data for a representative SiCOH material within acceptable accuracy. We find the mechanical properties are significantly weakened by the presence of pendant carbon groups.

During the lifetime of a nuclear facility, radioactive material may become deposited onto process and structural material surfaces. Due to their high corrosion resistance, steels comprise the largest class of metal-based materials encountered on nuclear sites. A greater understanding of the mechanisms of how contaminant radionuclides interact with and attach to process steels in nuclear plant environments is required in order to enable informed decisions to be made about the design and effective application of decontamination techniques, reducing secondary wastes.

There is limited literature relating to radionuclide sorption mechanisms on steels. Key studies have found that sorbed contamination is almost entirely located in the outermost oxide layers formed at steel surfaces. Thus, a molecular level investigation of contaminant uptake during induced oxide formation would be beneficial in developing steel decontamination strategies.

Stainless steel 316L is commonly employed in the nuclear industry in process streams and pipework. Thus, we describe work carried out on electrochemically accelerated oxide growth on 316L and SS2343 (a 316L analog) in nitric acid media and its characterisation using combined voltammetric and microgravimetric measurements. These allow identification of active, passive, high voltage passive, transpassive and secondary passivation regimes in the associated current voltage curves. EQCM on SS2343 coated quartz crystal piezoelectrodes, combined with potentiodynamic polarisation data have allowed us to determine that fastest net growth of surface oxide occurs in the low voltage passive regime. Further, we have directly measured the growth of that layer by using in situ microgravimetry for the first time. We will be shortly using the methods described above and radionuclide surrogates for the study of contaminant uptake during oxide formation and uptake onto preformed oxide layers. XPS will be used to determine layer composition and mode of contaminant uptake.