This paper reports improved optical characteristics of InGaN-based light-emitting-diode (LED) grown on Si(111) substrate by the insertion of an Al0.06Ga0.94N/GaN strained-layer-superlattices (SLS) cladding layer after AlN/GaN multilayer (ML) growth, under the multi-quantum-well (MQW) active layer. The insertion of underlying Al0.06Ga0.94N/GaN SLS cladding layer has shown to improve epitaxial layer quality in x-ray diffraction (XRD) analysis, reduce wavelength peak fluctuations in photoluminescence (PL) surface mapping, and improve optical and electrical characteristics of the LED sample. A 34% increase of light intensity at 50 mA current injection and a narrower wavelength peak have been achieved by the insertion of Al0.06Ga0.94N/GaN SLS cladding layer. LED with underlying Al0.06Ga0.94N/GaN also shows superior current-voltage (I-V) characteristics with operation voltage of 3.2 V at 20 mA and series resistance of 16 Ω.

Since 2006, French research on spent fuel has focused on the main issues related to transport and extended in-pool storage of spent fuel assembly. Studies on creep behaviour of irradiated cladding have resulted in a new creep model which is valid over a wide domain of temperature, internal pressure and time. Under nominal conditions, no evolution of the spent fuel rod is expected during in-pool storage. In case of defective fuel rods in the storage pool, the consequences of fuel alteration on the initial defect of the cladding depend on the matrix alteration rate and nature of the secondary phases formed. Considering the optional scenario of direct disposal, the long-term behaviour of the spent fuel is investigated focusing on helium consequences before water contact on the one hand and on the influence of repository conditions on matrix alteration on the other hand. The aim of the on-going studies is to improve the safety margins initially introduced in the radionuclide source term models.

Residual stresses in sputtered ZnO films on Si are investigated and discussed. By means of X-ray diffraction, we show that as-deposited ZnO films encapsulated or not by Si3N4 protective coatings are highly compressively stressed. Moreover, a transition of stress is observed as a function of the post-deposition annealing temperature. After a heat treatment at 800°C, ZnO films are tensily stressed while ZnO films encapsulated by Si3N4 are stress-free. With the aid of in-situ X-ray diffraction, we argue that this thermally-activated stress relaxation can be attributed to a variation of the chemical composition of the ZnO films.

The mixture of polyaniline (PANi) and PANi grafted multi-walled carbon nanotube (PANi-g-MWNT) was prepared by two step reaction sequences. MWNT was first functionalized with 4-aminobenzoic acid via “direct” Firedel-Crafts acylation in polyphosphoric acid (PPA)/phosphorous pentoxide (P2O5) medium to afford aminobenzoyl-functionalized MWNT (AF-MWNT). Then, aniline was polymerized via in-situ static interfacial polymerization in H2O/CH2Cl2 in the presence of AF-MWNT in organic phase to yield the mixture of PANi and PANi-g-MWNT. The mixture was characterized with a various analytical techniques such as Fourier transform infrared spectroscopy (FT-IR), wide angle x-ray diffraction (WAXD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammogram (CV). Even after dedoping, the mixture displayed semimetallic conductivity (4.9 S/cm). The capacitance of the mixture was also greatly enhanced and its capacitance decay with respect to cycle times was significantly reduced.

We present advanced light trapping concepts for thin film silicon solar cells. When an amorphous and a microcrystalline absorber layers are combined into a micromorph tandem cell, light trapping becomes a challenge because it should combine the spectral region from 600 to 750 nm for the amorphous top cell and from 800 to 1100 for the microcrystalline bottom cell. Because light trapping is typically achieved by growing on textured substrates, the effect of interface textures on the material and electric properties has to be taken into account, and importantly, how the surface textures evolve with the thickness of the overgrowing layers. We present different scenarios for the n-i-p configuration on flexible polymer substrates and p-i-n cells on glass substrate, and we present our latest stabilized efficiencies of 9.8% and 11.1%, respectively.

Fusion of metallic nanoparticles at both surfaces of silica colloids and nanoporous bulk materials has been utilized as an effective method to integrate inorganic and organic components into nanocomposite materials. When performed on substrates that have been modified with hydrophobic functional groups, aminosilica colloids doped with metallic nanoparticles through the ethylenediamine functional groups adhere to the substrates and self-assemble into nanocomposite film with its thickness to be the function of the time. On the contrary, without metal-bound functional groups, fusion of metallic nanoparticles can be induced at the interface of nanoporous silica when polymer is utilized as the mobile phase for metal nanoparticles inside of silica. Formation, mobilization, and fusion of metallic nanoparticles within the polymer phase can be simultaneously induced at 160 ˚C, during which reactions alter the physical appearance of the materials from transparent to silver metallic color. These two methods can combine with soft-lithography method to create functional structures that exhibit enhanced electrochemical property.

To determine the optimum baking temperatures for nanopowder introduction, the variation of reflective spectrum of baked zinc oxide powders, which are used as pigments for thermal control coatings of spacecraft, has been investigated over the wavelength range of 0.225–2.5 μm after being baked at temperatures between 400 °C and 850 °C. It has been established that baking temperatures over 750 °C result in a reduction of spectral reflectance in the visible light spectrum region. This is due to the formation of absorption bands of intrinsic point defects and thus increasing the spectral reflectance in the near-infrared region. The optimum temperature is 650 °C at which the bleaching effect was observed long after heat treatment. Moreover, an increase in the reflection coefficient occurs in the regions of 380–450 nm and 1100–2500 nm in this case.

Nitrogen and tellurium co-doped ZnO (ZnO:[N+Te]) films have been grown on (0001) ZnO substrate by plasma-assisted molecular beam epitaxy. The electron concentration of tellurium doped ZnO (ZnO:Te) gradually increases, compared that of undoped ZnO (u-ZnO). On the other hand, conductivity of ZnO:[N+Te] changes from n-type to p-type characteristic with a hole concentration of 4×1016 cm-3. However, nitrogen doped ZnO film (ZnO:N) still remain as n-type conductivity with a electron concentration of 2.5×1017 cm-3. Secondary ion mass spectroscopy reveals that nitrogen concentration ([N]) of ZnO:[N+Te] film (2×1021 cm-3) is relatively higher than that of ZnO:N film (3×1020 cm-3). 10 K photoluminescence spectra shows that considerable improvement of emission properties of ZnO:[N+Te] with an emergence of narrow acceptor bound exciton (A°X, 3.359 eV) and donor-acceptor pair (DAP, 3.217 eV), compared with those of u-ZnO. Consequently, high quality p-type ZnO with high N concentration is realized by using Te and N co-doping technique due to reduction of Madelung energy.

The degradation of carbon supported Pt catalyst used in polymer electrolyte membrane fuel cells is a significant durability problem affected by the agglomeration and detachment of Pt particles from carbon support. The bond between Pt and carbon must be significantly strengthened in order to prevent performance loss. In this work, first principles calculations were carried out in an attempt to understand the role that metallic adatoms play in the enhancement of the Pt/carbon interface adhesion. Metallic adatoms including all first row transition metals as well as Li, Al, Zr, Nb, and Au were inserted into a Pt(111)/graphene interface. The work of separation required to break the interface between Pt-adatom or carbon-adatom bond was then calculated for each configuration, revealing that the carbon-adatom bond was weaker than the Pt-adatom bond, making it easier to break the interface from the carbon-adatom bond side. While Sc, Ti, Zr, and Nb displayed strong binding to both Pt and graphene surfaces, at the Pt/graphene interface, the bond with graphene was weakened. The strength of the Pt-adatom bond was proportional to the amount of charge transferred from the adatom to the graphene. Co, Ni and V were the most promising metals for strengthening the Pt/graphene interface. These metals donated charges that were distributed evenly between carbon and Pt and formed strong covalent bonds with carbon and moderate bonding to Pt.

A variety of junction capacitance-based characterization methods were used to investigate alloys of Ag into Cu(In1-xGax)Se2 photovoltaic solar cells over a broad range of compositions. Alloys show encouraging trends of increasing VOC with increasing Ag content, opening the possibility of wide-gap cells for use in tandem device applications. Drive level capacitance profiling (DLCP) has shown very low free carrier concentrations for all Ag-alloyed devices, in some cases less than 1014 cm−3, which is roughly an order of magnitude lower than that of CIGS devices. Transient photocapacitance spectroscopy has revealed very steep Urbach edges, with energies between 10 meV and 20 meV, in the Ag-alloyed samples. This is in general lower than the Urbach edges measured for standard CIGS samples and suggests a significantly lower degree of structural disorder.

This study examines the kinetics of the martensitic phase transformation in a representative Ni-Mn-Sn Heusler alloy. Here, we present data on isothermal and continuous cooling/warming transformations in both bulk polycrystalline and individual small particle samples. We demonstrate that while the martensite to austenite transformation proceeds very rapidly (faster than the time-scale of our observations), the austenite to martensite transformation has a significant isothermal component. A similar asymmetry is also noted in transformation behavior of individual martensite plates. We conclude that the observed time dependence is due primarily to nucleation-limited kinetics.

Effects of H2O partial pressure on ZnO crystal growth by chemical vapor transport (CVT) have been investigated. The use of H2O causes the increase in growth rate of ZnO, indicating that H2O acts as a dominant oxygen source in ZnO growth by CVT. The use of H2O also improves structural, electrical, and optical properties of the CVT-grown ZnO crystals. A sharp X-ray rocking curve for the ZnO (0002) reflection was obtained, and the full width at half maximum value was 38 arcsec. Strong near band edge emission was observed in photoluminescence spectra at room temperature. Both carrier concentration and Hall mobility increased with partial pressure of H2O. The dependence of the carrier concentration on temperature indicates that there exist two donors in the CVT-grown ZnO crystals. The estimated ionization energy for the shallow donor was 35±5 meV and that for the deep donor was 115±5 meV.

Simplicity of construction and operation are advantages of iTMC (ionic transition metal complex) OLEDs compared with multi-layer OLED devices. Unfortunately, lifetimes do not compare favorably with the best multi-layer devices. We have previously shown for Ru(bpy)3(PF6)2 based iTMC OLEDs that electrical drive produces emission-quenching dimers of the active species. We report evidence here that a chemical process may also be implicated in degradation of devices based on Ir(ppy)2(dtb-bpy)PF6 albeit by a very different mechanism. It appears that degradation of operating devices made with this Ir-based complex is related to current-induced heating of the organic layer, resulting in loss of the dtb-bpy ligand. (The dtb-bpy ligand is labile compared with the cyclometallated ppy ligands.) Morphological changes observed in electrically driven Ir(ppy)2(dtb-bpy)PF6 OLEDs provide evidence of substantial heating during device operation. Evidence from UV-vis spectra in the presence of an electric field as well as MALDI-TOF mass spectra of the OLED materials before and after electrical drive add support for this model of the degradation process.

The Sellafield Waste Vitrification Plant (WVP) immobilises highly active liquid waste (HAL) arising from the reprocessing of spent nuclear fuel in the UK. In order to optimise WVP operations a full scale working replica of a WVP processing line, the Vitrification Test Rig (VTR), was constructed to processes non-active HAL simulants. Recently the VTR has been used to determine an operational envelope for the vitrification of HAL from Magnox reprocessing at a waste oxide incorporation rate in glass of up to 35wt% (compared to a “standard” incorporation rate of 25wt%). This paper discusses the differences in operating conditions necessary to achieve acceptable waste throughput at the increased incorporation rate. The chemical durability of the resulting vitrified product is also discussed, along with the formation of secondary phases, and a comparison is drawn between 35wt% incorporation glasses and products made at the standard 25wt% incorporation.

In this paper we report on kinetics studies of the growth rates of a hydride phase during the metal-hydride phase transformation of Mg films doped with transition metals (=Ti, Fe). Infrared emission imaging of wedge-shaped thin films during hydrogen loading reveals different effects of Ti and Fe additives on Mg hydride growth rates. Compared to hydrogenation of pure Mg, Ti addition (atomic fraction 1.6 % and 2.3 %) does not increase the Mg hydride growth rate. However, this doping results in the formation of a thicker hydride layer residing on top of the films. The hydrogenation rate is increased by an order of magnitude for addition of atomic fraction 3.1 % of Fe and the thickness of Mg hydride layer is more than twice that of the hydride layer during hydrogenation of pure Mg. Results obtained here can be used to guide powder design for hydrogen storage applications.

Permalloy particles were fabricated by pulsed excimer laser ablation in distilled water and Tween 80 aqueous solution with the same laser parameters. Nearly spherical particles and irregular and porous fragments were obtained in water due to rapid condensation and growth of the laser ablated clusters. The products obtained in Tween 80 aqueous solution contained well-shaped spheres but some were laser sintered together via laser-particle interactions. Holes or pits were observed on the surface of some particles, which we consider were caused by laser induced bubbles in the liquid. Our results demonstrate the rich environment ablation in liquids can be for novel particle formation.

Bioglass 45S is a promising bone implant material with superior biocompatibility. Past research showed that adhesion of bone cells to titanium is strongly affected by its surface architecture. However, little is known about the role of surface topology of glass on its use as an implant. Thus, we systematically investigated the effect of surface roughness (Ra ∼ 0.01 – 1.2 μm) on cell adhesion and proliferation on 45S Bioglass in vitro. MG63 osteosarcoma and MC3T3 osteoblast precursor cells were seeded on the glass samples, and incubated for up to 6 days. The attachment, morphology and proliferation of cells were investigated using fluorescence microscopy. Our results show that cell attachment (as indicated by cell spreading and number of focal adhesion sites), and proliferation rate decrease with increasing roughness of bioactive glass surface. These findings provide important insight for improving surface characteristics of bioactive glass bone implants.

An increasingly important application of thin film hydrogenated amorphous silicon (α-Si:H) is in infrared detection for microbolometer thermal imaging arrays. Such arrays consist of thin α-Si:H films that are integrated into a floating thermally isolated membrane structure. Among the α-Si:H material properties affecting the design and performance of microbolometers is the microstructure. In this work, Raman spectroscopy is used to study changes in the microstructure of protocrystalline p-type α-Si:H films grown by PECVD as substrate temperature, dopant concentration, and hydrogen dilution are varied. The films exhibit the four Raman spectral peaks corresponding to the TO, LO, LA, and TA modes. It is found that the TO Raman peak becomes increasingly well defined (decreasing line width and increasing intensity), and shifts towards the crystalline TO energy as substrate temperature is increased, H dilution of the reactants is increased, or as dopant concentration is decreased.

We performed an ab initio characterization of ferro- and nonmagnetic Ni2CoGa and Ni2CoZn compounds with respect to their potential application as new ferromagnetic shape memory alloys. The calculation of structural energy differences and mixing energies in the commonX2YZ Heusler structure and the inverse (XY)XZ structure revealed, that both alloys are stable in the tetragonal distorted Heusler structure with a c/a ratio of 1.38 and show ferromagnetic ordering. The Curie temperatures are of the order of ≃ 250 K. Exchanging Ga with Zn improves the magnetic properties of the alloy without qualitative modification of the structural energy landscape, but at the expense of a reduced mixing energy.

Multilayer microcantilevers present in micro-/nano- electromechanical system (MEMS/NEMS) applications serving passive and active structural roles. The application and commercialization of MEMS devices suffer from reliability problems. Appropriate nanocoatings, such as atomic layer deposition (ALD), have been demonstrated to be promising solutions for these reliability problems in MEMS devices. However, the micro/nano- mechanics within and/or between the microcantilevers and nanocoatings are not fully understood, especially when temperature, time, microstructural evolution and material nonlinearities play significant roles in thermomechanical response. The overall goal of this work is to suppress and understand the inelastic deformation and microstructural evolution in multilayer microcantilevers with nanocoatings. Moreover, to better understand the stress relief and Al2O3 suppression mechanism, scanning electron microscopy (SEM) was employed to explore the microstructural evolution.