The effect of grain boundary (GB) and matrix precipitates on high temperature strength was investigated in Fe3Al base alloys containing Cr, Mo and C. Tensile tests were conducted at 600°C for three types of microstructures consisting of: (I) film-like κ phase precipitates covering GBs and fine M2C particles in the matrix, (II) only fine M2C particles in the matrix and (III) no second-phase particles in the matrix. It was found that κ films on GBs are more than twice as effective as finely dispersed M2C particles for improving the proof stress.

In this study, we report the luminescence quenching by radical cations ofaromatic diamines used as a hole transport layer (HTL) in organicelectroluminescent (EL) devices. The EL characteristics of green organic ELdevices with an electron transport layer (ETL) as an emitter i.e. ITO/TPD HTL/Alq3 ETL/Al is studied. Here, ITO, TPD, and Alq3 are abbreviations for indium-tin-oxide,N,N’-diphenyl-N,N’-bis(3-methylphenyl)-1,1’-biphenyl-4,4’-diamine, and tris(8-hydroxyquinoline) aluminum, respectively. UV-visible absorption andelectrochemical data indicate the formation of radical cations in thin filmand solution of TPD after chemical oxidation. We find that the EL luminanceincreases less than linearly with an increase in current for the EL devicesstudied in this study. The luminance loss in the devices is attributed toquenching of singlet excited states by large excess radical cations of TPDare accumulated in the emission zone due to large overlap between aflourescence spectrum of Alq3 and an absorption spectrum ofradical cations of TPD.

In this work the release of atomic hydrogen from SiNx:H films is investigated. Thermal treatment as well as UV-illumination induces the formation of H2, increasing the tensile stress in the film. N-rich SiNx:H films release hydrogen only by UV-illumination, indicating involvement of charge trapping. Ab initio calculations show a possible reaction path for the release and diffusion of protons that also explain the diffusion of hydrogen into Si substrates.

Multiwall Carbon Nanotubes (MWCNTs) form a nematic liquid crystalline (LC) phase in their lyotropic form, enabling their mixing and coupling of their director to that of nematic LCs. An important aspect of this LC/MWCNT interaction, for applications other than display technology, is looking at the ways the MWCNTs affect the physical properties of the LCs. We study the effect of MWCNTs on the nematic to crystal (N-C) phase transition of 4-cyano-4-npentylbiphenyl (5CB). Our Differential Scanning Calorimetry (DSC) results show a dramatic increase in N-C phase transition temperature of 14°C for only 0.1% and of 20°C for 1% MWCNT, due to the crystal nucleation activity of the nanotubes. Using Polarized Microscopy we observe a change in the crystalline order of 5CB from spherulitic at 0% MWCNTs to a multidomain in presence of MWCNTs. The new crystals resemble those formed by a smectic LC 4- Decyloxybenzoic acid. This is in line with predictions from simulations, that the MWCNTs form smectic order in nematic 5CB at their interface. MWCNTs induced modifications of the crystal phase of 5CB promise to create controlled novel crystal forms for the purposes of optical transmission and other applications.

This talk reviews work on the optical properties of Eu-doped GaN at the Semiconductor Spectroscopy laboratory of the University of Strathclyde. The principal experimental technique used has been lamp-based Photoluminescence/Excitation (PL/E) spectroscopy on samples produced mainly by high-energy ion implantation and annealing, either at low or high pressures of nitrogen, as described by Lorenz et al. [1]. These have been supplemented by samples doped in-situ either by Molecular Beam Epitaxy or Metallorganic Vapour Phase Epitaxy. Magneto-optic experiments on GaN:Eu were carried out in collaboration with the University of Bath.

From the material point of view, the extracellular matrix (ECM) of bone is anatural nanocomposite consisting of an organic matrix (mainly collagen) andinorganic nanofillers (bone apatite) which are inserted in a parallel wayinto the collagen fibrils. For human bone tissue repair or regeneration,nanocomposites consisting of a biodegradable polymer matrix and nano-sizedfillers such as bioactive ceramics or glasses, which mimic the hierarchicalstructure of bone, are considered a promising strategy. Combining livingcells with biodegradable materials and/or bioactive component(s), theconcept of tissue engineering first elucidated in the early 1990srepresented a paradigm shift from tissue grafting, with autografts being thegold standard, or even completely from prosthesis implantation. Inscaffold-based tissue engineering, scaffolds play an important role fortissue regeneration. Currently, acellular scaffolds with or withoutbiomolecules such as growth factors are considered as an effective strategyfor certain tissue repair due to their relatively low costs and easierprocess to gain surgeons’ acceptance and regulatory approval. In the currentstudy, integrating an advanced manufacturing technique, nanocompositematerial and controlled delivery of growth factor to form multifunctionaltissue engineering scaffolds was investigated. Three-dimensional,osteoconductive and totally biodegradable calcium phosphate(Ca-P)/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocompositescaffolds with customized architecture, controlled porosity andinterconnecting pores were designed and fabricated using selective lasersintering (SLS). The surface of nanocomposite scaffolds was modified withgelatin and then heparin, which facilitated the incorporation of a growthfactor, recombinant human bone morphogenetic protein-2 (rhBMP-2).Experimental results demonstrated the effectiveness of this strategy inguiding the osteogenic differentiation of mesenchymal stem cells. Togetherwith osteoconductive nanocomposite material and controlled growth factordelivery, the use of SLS technique to form complex scaffolds provides apromising route towards individualized bone tissue regeneration.

Catalysts in which Pt and Cu are immobilized on support particles of γ-Fe2O3 were synthesized by the radiolytic process and were evaluated for CO oxidation in a gas flow mixture (1% CO, 0.5% O2, 67.2% H2 and N2 balance) by measuring the CO concentration in the outlet gas. The Pt/Cu atomic ratios of the as-synthesized catalysts were determined to be 100:0, 90:10, 78:22, 50:50, 21:79, and 11:89, and the total metal loadings determined by chemical analyses were 10 wt%. Material characterization was performed using X-ray diffraction, X-ray absorption near edge structure, and transmission electron microscopy, and it was indicated that the composite catalysts consist of Pt-Cu bimetallic grains immobilized on the support at higher Pt-loading, while CuO with poor crystallinity is also observed at lower Pt-loading. The catalytic activity decreased as the Pt-loading was decreased to 50 at%, and also with increasing temperature. However, as the Pt-loading was further decreased, the activity contrariwise increased, and increased with increasing temperature up to 100 °C. The sample containing only 11 at% Pt exhibited the highest activity at 100 °C, which is higher than that of the commercial catalyst measured for comparison, and given at a lower temperature than that for the commercial catalyst. This enhanced activity, despite the low Pt-loading, could be attributed to oxygen supply via CuO from the O2-poor atmosphere to PtCu bimetallic grains trapping CO molecules. This new material is promising for use as a catalyst to purify hydrogen gas fed to a polymer electrolyte fuel cell.

The bonding between two dissimilar materials has been a problem, partiularly in coating metals with non-metallic protective layer. In this work, it is demonstrated that a strong bonding between ceramics/metal can be achieved by mixing the atoms at the interface by ion-beam. Specifically, SiC coating on Hastelloy X was studied for a high temperature corrosion protection. Auger elemental mapping across the interface shows a far broader mixed region than the region expected by SRIM calculation, which is thought to be due to the thermal spike liquid state diffusion. The results showed that, although the thermal expansion coefficient of Hastelloy X is about three times higher than that of SiC, the film did not peel-off at above 900 o C confirming excellent adhesion. Instead, the SiC film was cracked along the grain boundary of the substrate above 700 o C. At above 900 o C, the film was crystallized forming islands on the substrate so that a considerable part of the substrate surface could be exposed to the corrosive environment. To cover the exposed area, it is suggested that the coating/IBM process should be repeated multiply.

Polymer/oxide nano hybrid multilayer permeation barriers are emerging as a promising solution to the stringent barrier requirement of flexible electronics. Yet the mechanical failure of the multilayer permeation barriers could be fatal to their barrier performance. We study two co-evolving failure mechanisms of the multilayer permeation barriers under tension, namely, the cracking of the inorganic oxide layer and the delamination along the oxide-organic interface, using computational modeling. An effective driving force for the oxide layer cracking is determined, which decreases as the oxide-organic interfacial adhesion increases.

Elastic properties, thermal expansion and deformation behavior of Cr5Si3 with the D8m structure were investigated using single crystals. From the values of Cauchy pressures as well as the ratio of the polycrystalline bulk modulus (B) to shear moduls (G) estimated from single-crystal elastic constants (c ij), deformation behavior of Cr5Si3 is expected to be relatively brittle compared to Mo5Si3 with the same crystal structure. However, plastic deformation of Cr5Si3 is confirmed above 900 ~ 1100 °C depending on the loading axis orientations.

The focus of this present work is concerned with a novel and facile method for obtaining colored Ag nanoparticle films using a sulfide as a coloring agent. The Ag nanoparticle films change their colors depending on the dipping time in a solution of a sulfide and the dipping time is at most on the second time scale. The color of the films, initially sliver (shiny white), changes to shiny yellow, red, and blue. Our scanning electron microscopy studies indicate that the color of the Ag nanoparticle films depend on the particle size of the Ag nanoparticle films.

Light trapping is one of the key challenges for the next generation of thin film solar cells. In this work, we have identified the distinct light trapping effects for short and long wavelength solar spectrum ranges, by investigating lighting trapping structures on both sides of Si thin film solar cells. The sub-wavelength moth-eye-like photonic front surface and multi-layer grating photonic crystal reflector on the bottom surface are studied in detail via the Finite Difference Time Domain method for its solar energy absorption characteristics. Our study reveals the drastic difference in the light trapping effects within the solar spectrum wavelength. This work may provide guidance for efficiency enhancement of next generation thin film photovoltaic cells.

We demonstrate a dual-mode sensing platform based on porous silicon (PSi)substrates coated with colloidal gold (Au) nanoparticles (NPs). This Au-PSicomposite structure supports both molecular fingerprinting via surfaceenhanced Raman scattering (SERS) and quantification of molecular binding viareflectance measurements. Reflectance shifts of 7-10 nm in the infraredregion were observed in the case of adsorbing benzenethiol or antioxidantglutathione molecules on the surface of Au NPs. Subsequent SERS measurementsshowed unique identification for both molecules and provided a < 1 μM and< 1 mM detection resolution for benzenethiol and glutathione,respectively.

Nanosized titanium dioxide photocatalysts with anatase structure or mixture of anatase and rutile phases have been synthesized. Homogeneous precipitation of aqueous solutions containing TiOSO4 and ammonia and following treatment with H2O2 was used to prepare porous yellowish (Ti-Per) gel. The gel was lyophilized for 48h and (Ti-Per)LYO-powder was obtained. Single phase anatase TiO2 samples were prepared by heating of the (Ti-Per)LYO powder. The lamella-like particle morphology of TiO2 samples determined by SEM were stable in air up to 950°C.The structure evolution during heating of the starting (Ti-Per)LYO powder was studied by DTA and XRD analyses in overall temperature range of phase transformation. The morphology and microstucture characteristics were also obtained by HRTEM and BET methods. The photocatalytic activity of the sample titania TI-LYO/950 heated to 950ºC in air contained 78.4% anatase and 21.6% rutile was higher than standard Degussa P25. Titania sample TI-LYO/950 reveals the highest catalytic activity during the photocatalyzed degradation course of 4-chlorophenol in aqueous suspension under UV-irradiation.

The site preference of ternary additions in GCP (geometrically close-packed) Ni3X-type compounds with D0a structure was determined from the direction of the single-phase region of the D0a phase in the reported ternary phase diagrams. The thermodynamic model based on the Bragg-Williams approximation, which is based on the change in heat of formation of the host compound by a small addition of ternary solute, was applied to predict the site preference of ternary additions. The heat of formation used in the thermodynamic calculation was derived from Miedema’s formula. Good agreement was obtained between the thermodynamic model and the result of the literature search.

The University of Florida (UF) have recently collaborated with Raith Inc. to modify Raith’s ion beam lithography, nanofabrication and engineering (ionLiNE) station that utilizes only Ga ions, into a multi-ion beam system (MionLiNE) by adding the capabilities to use liquid metal alloy sources (LMAIS) to access a variety of ions and an EXB filter for mass separation. The MionLiNE modifications discussed below provide a wide range of spatial and temporal precision that can be used to investigate ion solid interactions under extended boundary conditions, as well as for ion lithography and nanofabrication. Here we demonstrate the ion beam lithographic capabilities of the MionLiNE for fabricating patterned arrays of Au and Si nanocrystals, with nanoscale dimensions, in SiO2 substrates, by direct implantation; and show that the same directwrite/maskless-implantation features can be used for in situ fabrication of nanoelectronic devices. Additionally, the spatial and temporal capabilities of the MionLiNE are used to explore the effects of dose rate on the long-standing surface morphological transformation that occurs in ion bombarded Ge.

We present theoretical calculations for electron plasmon spectra at wurtzite Aluminum Gallium Nitride/ Silicon Carbide heterojunctions. Spontaneous and piezoelectric polarizations in wurtzite semiconductors give rise to polarization discontinuities at interfaces and to bound interface sheet charges. These charges are of the order of 1013 electrons per cm2 and give rise to two dimensional electron or hole gases near heterojunctions. Electron-electron interactions in the two-dimensional electron gases give rise to collective plasmon excitations. We calculate the dielectric function in these electron gases under the well-known and widely studied random phase approximation. Our calculations are relevant to the determination of the plasmon spectra at wurtzite Aluminum Gallium Nitride / Silicon Carbide heterojunctions and are of potential interest for determining the limits of mobility in two-dimensional electron gases. They are also of interest for terahertz electronics applications.