Electrochemical Impedance Spectroscopy (EIS) and the Parallel Electrical Dielectric Response Analysis (PEDRA) application were used to describe the inner barrier oxide films on irradiated zirconium alloys. This is achieved with minimal surface preparation and without disturbing the outer porous oxide. These two distinguishable inner and outer oxide layers result from a growth-fracture oxidation mechanism. Key to success of the EIS technique in describing the barrier oxide layer are: 1) the model and procedure used to fit EIS spectra, 2) the validation of the fit, and 3) converting circuit parameters (R, C and n) into physical attributes of the barrier oxide.

The barrier oxide is defined as the inner-dense layer adjacent to the metal-oxide interface. The integrity of barrier oxide is thought to effect both oxidation (i.e. access of water to the interface), and hydrogen pickup (i.e. failure hydrogen to escape away from the interface). Using EIS and the PEDRA application, the barrier oxide is described in terms of multiple independent dielectric responses to yield a unique 'micro-macro' picture of the barrier oxide that can be used to explain observed H pickup behavior.

Bone is a natural protein (collagen)-mineral (hydroxyapatite) nanocomposite with hierarchically organized structure. Our previous work has demonstrated orientational differences in stoichiometry of hydroxyapatite resulting from orientationally dependent collagen-mineral interactions in bone. The nature of these interactions has been investigated both through molecular dynamics simulations as well as nanomechanical and infrared spectroscopic experiments. In this study, we report experimental studies on human cortical bone with osteogenesis imperfecta (OI), a disease characterized by fragility of bones and other tissues rich in type I collagen. About 90% of OI cases result from causative variant in one of the two structural genes (COL1A1 or COL1A2) for type I procollagens. OI provides an interesting platform for investigating how alterations of collagen at the molecular level cause changes in structure and mechanics of bone. Fourier transform spectroscopy, electron microscopy (SEM), and nanomechanical experiments describe the structural and molecular differences in bone ultrastructure due to presence of diseases. Photoacoustic-Fourier transform infrared spectroscopy (PA-FTIR) experiments have been conducted to investigate the orientational differences in molecular structure of OI bone, which is also compared with that of healthy human cortical bone. Further, in situ SEM static nanomechanical testing is conducted in the transverse and longitudinal directions in the OI bone. Microstructural defects and abnormities of OI bone were ascertained using scanning electron microscopies. These results provide an insight into molecular basis of deformation and mechanical behavior of healthy human bone and OI bone.

Molybdenum silicides and borosilicides are promising structural materials for advanced power plants. A major challenge, however, is to simultaneously achieve high oxidation resistance and acceptable mechanical properties at high temperatures. For example, molybdenum disilicide (MoSi2) has excellent oxidation resistance and poor mechanical properties, while Mo-rich silicides such as Mo5Si3 (called T1) have much better mechanical properties but poor oxidation resistance. One approach is based on the fabrication of MoSi2−T1 composites that combine high oxidation resistance of MoSi2 and good mechanical properties of T1. Another approach involves the addition of boron to Mo-rich silicides for improving their oxidation resistance through the formation of a borosilicate surface layer. In particular, Mo5SiB2 (called T2) phase and alloys based on this phase are promising materials.

In the present paper, MoSi2−T1 composites and materials based on T2 phase are obtained by mechanically activated self-propagating high-temperature synthesis (MASHS). To obtain denser products, the so-called SHS compaction (quasi-isostatic pressing of hot combustion products) has been employed. Thermal analysis has shown that SHS compaction significantly improves the oxidation resistance. Self-sustained combustion of Mo/Si/B mixtures for the formation of T2 phase becomes possible if the composition is designed for adding a more exothermic reaction of MoB formation. These mixtures exhibit spin combustion. Oxidation resistance of the obtained multi-phase Mo−Si−B materials is independent on the concentration of Mo phase in the products. The “chemical oven” technique has been used to obtain a single Mo5SiB2 phase and an alloy consisting of α-Mo, Mo5SiB2, and Mo3Si phases.

A scanning force microscope for in situ nanofocused X-ray studies (SFINX) has been developed which can be installed on diffractometers at synchrotron beamlines allowing for the combination with various techniques such as coherent X-ray diffraction and fluorescence. The capabilities of this device are demonstrated on Cu nanowires and on Au islands grown on sapphire (0001). The sample topography, crystallinity, and elemental distribution of the same area are investigated by recording simultaneously an AFM image, a scanning X-ray diffraction map, and a fluorescence map. Additionally, the mechanical response of Au islands is studied by in situ indentation tests employing the AFM-tip and recording 2D X-ray diffraction patterns during mechanical loading.

We have investigated surface modification methods for avalanche photodiodes using dielectrics deposited by atomic layer deposition (ALD). Arrays of mesa GaN APDs were fabricated, and ALD Al2O3 was used for sidewall passivation prior to completing the APD array. The use of ALD Al2O3 in this manner was observed to result in a large average improvement in APD dark current when compared with devices using more conventional SiO2 passivation layers produced by chemical vapor deposition. Co-processed metal-oxide-semiconductor (MOS) capacitors fabricated with the same passivation layers show significant improvement in electrical interface quality for devices with ALD Al2O3.

This contribution shows the results of a study carried out in order to determinate the deterioration mechanisms suffered by stucco masks from the important archaeological Mayan site of Edzná, Campeche, México; due to their long exposition to the tropical environment of the zone. Stratigraphic analysis of fragments from the masks containing pigments and surface neoformation products, were analyzed by optical microscopy and scanning electron microscopy coupled to a secondary X-ray emission system. Crystalized salts mineral composition were characterized by X-ray diffraction. Also, during the study, environmental parameter like temperature and relative humidity were monitored in site. Results indicate that stuccos mineral matrix is formed by calcareous materials, covered by films with variable proportions of ferrous materials (red, ochre and yellow colors) and rich carbon content (black color). Compounds were associated to blue and green colors. Al these materials showed a high level of deterioration because of differential forces caused by stucco and deposits of environmental soluble salts during dissolution crystallization cycles caused by humidity differences between stucco and environmental as a consequence of their particular exposure conditions.

A novel allergy biosensor is designed and fabricated by using thin film bulk acoustic resonator (TFBAR) devices with shear mode ZnO piezoelectric thin films. To fabricate TFBAR devices, the off-axis RF magnetron sputtering method for the growth of piezoelectric ZnO piezoelectric thin films is adopted. The influences of the relative distance and sputtering parameters are investigated. In this report, the piezoelectric ZnO thin films with tilting angle are set by controlling the deposition parameters. The properties of the shear mode ZnO thin films are investigated by X-ray diffraction and scanning electron microscopy. The frequency response is measured using an HP8720 network analyzer with a CASCADE probe station. The resonance frequency of the shear mode is 796.75 MHz. The sensitivity of the shear mode is calculated to be 462.5 kHz·cm2/ng.

As an emerging manufacturing technique, nanoimprint lithography (NIL) can fabricate micro and nanoscale features of microfluidic devices at very high accuracy and reliability. In high-temperature TNIL process, a polymer melt such as polymethyl-methacrylate (PMMA) is heated beyond the melting temperature so that it behaves predominantly as a fluid during the imprint process. The process parameters such as pressure, temperature, and material properties play critical roles in the NIL process. In this work, the process of thermal nanoimprint lithography (TNIL) is studied computationally with emphasis on the effect of soft-mold deformation on polymer melt flow and finished result by-way-of fluid-structure interaction (FSI) technology. Process is assumed isothermal at 180 °C. Applications of this modeling technique range from micro- and nano-patterns used in micro-channels for biomedical devices to other applications such as biological/particle sensors or super-hydrophobic surfaces. The simulation result is compared to experimental results, and traits observed in TNIL done with soft mold are supported and explained through numerical results.

In this work the thermal and kinetic analysis of the cooling and solidification of a near eutectic Al-Cu alloy is performed using inverse thermal and solidification kinetics analysis. The Fourier thermal analysis is applied to experimental cooling curves to obtain data on solid fraction evolution and latent heat of solidification. Inverse thermal analysis is applied to calculate the global heat transfer coefficients that allow correct simulation of the cooling of experimental probes. The free growth method is used to obtain the eutectic growth coefficients. All the obtained parameters are feed into a heat transfer-solidification kinetics model to validate the methodology and results generated from this work. It is found a relatively good agreement between experimental and predicted cooling curves which suggest that this methodology could be used to generate useful information needed to simulate eutectic solidification.

Crystalline TiO2 nanoparticles were produced by scalable flame spray pyrolysis of organometallic solutions. A protocol is presented for the optimized functionalization of these particles with fluorescein isothiocyanate (FITC), an important biomedical dye via a lysine linker. The pH, stoichiometry and time for lysine reaction were determined for highest dye loading and minimized degree of polylysine formation. Acidic reaction conditions, low lysine concentration and short reaction times were found to meet this aim. The resulting particles were used for imaging single neurons, showing high fluorescence emission and ability for the particles to diffuse into small neuron structures such as dendrites.

The Center for Functional Nanoscale Materials (CFNM), an NSF Center for Research Excellence in Science and Technology, at Clark Atlanta University has partnered with ACS (American Chemical Society) Project SEED. The ACS project SEED program is recognized nationally as providing hands-on research opportunities to disadvantaged high school students who historically lack exposures to scientific careers. The University is a minority serving institution (MSI) and has an excellent relationship with Atlanta area school systems, which serve the African American community. Students entering their junior and senior years in high school were selected based on their academic performance, an essay and letters of recommendation for participation the Center’s eight week summer nanoscholar Program. Professors served as advisors and/or mentors and graduate students and doctoral fellows served as mentors. The Program included a variety of enrichment activities. All summer nanoscholars had personal research projects that were integral to the research programs of their advisors, and they presented their work in the form of a symposium at the end of the Program. We have completed three summers as an ACS Project SEED site. So far we have had one SEED scholar submit a major manuscript, two were invited to present at ACS National Meetings and one was awarded an eight year Gates-Millennium fellowship. Evaluation of the project strongly suggests that our approach is effective for opening doors for the economically disadvantaged students and tapping the best and the brightest for careers in the sciences and engineering. In the words of one of our young scholars “I realized that research is a continuous learning process. You can never know everything. Even a professor has credentials but they’re still continuing to learn.”

We report crystallization of amorphous silicon (a-Si) thin films and improvement of thin film transistors (TFTs) characteristics using 2.45 GHz microwave heating assisted with carbon powders. Undoped 50-nm-thick a-Si films were formed on quartz substrates and heated by microwave irradiation for 2, 3, and 4 min. Raman scattering spectra revealed that the crystalline volume ratio increased to 0.42 for the 4-min heated sample. The dark and photo electrical conductivities measured by Air mass 1.5 at 100 mW/cm2 were 2.6x10-6 and 5.2x10-6 S/cm in the case of 4-min microwave heating followed by 1.3x106-Pa-H2O vapor heat treatment at 260°C for 3 h. N channel polycrystalline silicon TFTs characteristics were improved by the combination of microwave heating with high-pressure H2O vapor heat treatment. The threshold voltage decreased from 5.3 to 4.2 V and the effective carrier mobility increased from 18 to 25 cm2/Vs.

Water-splitting by using electric power produced by solar cells is promising system to produce hydrogen without fossil fuels. Oxygen evolving catalyst is, however, major problem to prevent using this system widely because precious materials are used in the catalyst. Considering from the photosynthesis II of plants, the compound of Ca-Mn-O is one of the candidates for the oxygen evolving catalyst. In this study, the synthesis condition and the oxygen evolving electrocatalytic activity of CaMn2O4•xH2O are investigated. The overpotential at 0.1 mA/cm2 was 0.28 V when using the electrode of carbon paste and CaMn2O4•H2O with the weight ratio of 3:1.

The aim of this work is to process by equal channel angular pressing (ECAP) a low carbon – triple-alloyed steel containing 0.2% C, 0.5% Cr, 0.6% Ni, 0.2% Mo and 0.8 Mo. The process is performed at room temperature for up to four passes using route Bc with an equivalent strain of ∼0.6 after a single pass. Structure evolution before and after deformation is studied using scanning electron microscopy (SEM) and x-ray diffraction (XRD) and mechanical properties are assessed by microhardness and tensile testing. A significant improvement of the mechanical properties is found with increasing number of ECAP passes. Micro-hardness increases from 216 HV for the initial sample to 302 HV after four passes and tensile strength increases to 1200 MPa compared with 430 MPa prior to ECAP. X-ray diffraction and SEM analysis show changes in the original ferritic-perlitic structure through ferrite grain refinement and the deformation of perlite. This nickel-chromium-molybdenum alloy is used in manufacturing as gear material, and when it is hardened and formed through carburizing or boronizing it can be used to make hard-wearing machine parts. However, the ECAP process has not been used to harden this steel and to change its structure to obtain better mechanical performance.

In this paper we present an innovative on-chip platform suitable for the simultaneous manipulation and detection of the transit of a single magnetic bead. This system is based on the controlled displacement of constrained magnetic domain walls (DWs) that are used to move and sense particles in suspension over the chip. To this scope, the high stray field from the transverse DWs created at the corners of ferromagnetic zig-zag structures is used for particles manipulation, while electrical contacts flanking a single corner are employed to simultaneously monitor the DW passage through that corner, via anisotropic magneto resistance (AMR) measurements. A single DW carrying a magnetic particle is nucleated and manipulated within the zig-zag shaped magnetic conduit, trough the action of external magnetic fields. At the same time, the variation of the voltage drop across a corner flanked by a pair of electrical leads is measured, allowing to detect the transit of the DW thanks to the change of the relative orientation of current and spins at the corner related to the peculiar micromagnetic configuration of the DW (AMR). Work is in progress in order to selectively distinguish the transit of a naked DW from that of a DW bound to a magnetic particle. This work paves the way to the development of a closed-loop microlfuidic platform for on-chip bead manipulation, where single bead can be finely moved and their motion continuously checked, via AMR electrical detection and without need of optical monitoring, in a fully integrated closed-loop system.

The use of organic nonlinear optical (ONLO) materials in electro-optic (EO) modulators requires that the active molecular components (chromophores) be acentrically oriented. The fundamental molecular constituents are in a condensed, glassy phase. Molecular orientation in such systems is typically achieved by applying a DC poling field to the glassy material. We are developing efficient coarse-grained classical Monte Carlo (MC) methods to simulate the order of such systems. The most challenging aspects of these simulations are convergence to an experimentally relevant equilibrium ensemble and verification of simulation accuracy. We use a variety of molecular descriptions and a variety of MC methods to achieve proper order in the shortest number of computational cycles possible. Herein, we illustrate a few examples of the types of calculations and compare with experimental results with representative amorphous organic materials, including electro-optic chromophores.

In this paper, we review our recent work on triplet harvesting (TH) and its application in white organic light-emitting diodes (OLEDs). This includes the configuration of highly efficient single unit two-color and tandem four-color white OLEDs reaching efficacies of more than 30 lm/W at 1000 cd/m², as well as the development of new blue fluorescent emitters. The new compounds are chemically designed to exhibit a high triplet energy to allow TH by a green phosphorescent emitter. In a first step towards white TH OLEDs, we fabricated blue-green TH OLEDs to prove the validity of our concept.