Computational screening is becoming increasingly useful in the search for new materials. We are interested in the design of new semiconductors to be used for light harvesting in a photoelectrochemical cell. In the present paper, we study the double perovskite structures obtained by combining 46 stable cubic perovskites which was found to have a finite bandgap in a previous screening-study.1 The four-metal double perovskite space is too large to be investigated completely. For this reason we propose a method for combining different metals to obtain a desired bandgap. We derive some bandgap design rules on how to combine two cubic perovskites to generate a new combination with a larger or smaller bandgap compared with the constituent structures. Those rules are based on the type of orbitals involved in the conduction bands and on the size of the two cubic bandgaps. We also see that a change in the volume has an effect on the size of the bandgap. In addition, we suggest some new candidate materials that can be used as photocatalysts in one- and two-photon water splitting devices.

Layered dielectric films comprising of Diamond like Carbon (DLC) and Amorphous Fluorocarbon (a:C-F) were generated using three different stack configurations for ultra low dielectric constant (ULK) applications. These include a DLC – a:C-F – DLC sandwich, a:C-F – DLC topcoat only and an annealed a:C-F – DLC topcoat only film stack. These films were subsequently evaluated for thickness, dielectric constant, contact angle, surface roughness and chemical structure using IR analysis. Thermal stability was analyzed after annealing in Argon ambient at 400°C for 1 hour. Deposition conditions were optimized for film thickness, roughness, dielectric constant and contact angle using Minitab by tuning process pressure, substrate temperature and FRR. The modified Gaseous Electronics Conference (mGEC) reference cell was used to deposit DLC films using CH4 and Argon as precursors. Structural properties of the deposited thin film were studied using laser excitation of 633 nm in a Jobin Yvon Labram high-resolution micro-Raman spectrometer. Multiple points on each sample were analyzed in terms of the disordered carbon (D-peak) and graphitic carbon (G-peak). The thin film of DLC was subsequently annealed in Ar ambient for 1 hr at 400°C and analyzed. Commercially available graphing software was utilized to deconvolute peaks and the ratio of their intensities as well as the shift in their positions were determined to characterize the as-deposited and annealed film. The film was further characterized using AFM, FTIR, XRD, goniometry and electrical testing. Average film roughness as measured by AFM was less than 1 nm, the k-value was 2.5 and the contact angle with water was 42°. A:C-F films were separately deposited using CF4 and Si2H6 (5% by volume in He) as precursors in a UNAXIS PECVD system. Films deposited using substrate temperatures between 120°C – 200°C, chamber pressure of 300 and 500 mTorr and power of 100 W were independently evaluated in terms of their electrical, physical, structural and optical properties prior to layering with DLC films. After process optimization, seven unique process conditions generated promising layered films with k-values between 1.69 and 1.95. Of these, only one film exhibited very low shrinkage rates acceptable for semiconductor device processing.

We present results of theoretical studies of transition metal dopants in GaAs, based on microscopic tight-binding model and ab-initio calculations. We focus in particular on how the vicinity of surface affects the properties of the hole-acceptor state, its magnetic anisotropy and its magnetic coupling to the magnetic dopant. In agreement with STM experiments, Mn substitutional dopants on the (110) GaAs surface give rise to a deep acceptor state, whose wavefunction is localized around the Mn center. We discuss a refinement of the theory that introduces explicitly the d-levels for the TM dopant. The explicit inclusion of d-levels is particularly important for addressing recent STM experiments on substitutional Fe in GaAs. In the second part of the paper we discuss an analogous investigation of single dopants in Bi2Se3 three-dimensional topological insulators, focusing in particular on how substitutional impurities positioned on the surface affect the electronic structure in the gap. We present explicit results for BiSe antisite defects and compare with STM experiments.

We have investigated the passivation of low lifetime non-polished Czochralski (CZ) mono-crystalline silicon (c-Si) wafers by hydrogenated amorphous silicon (a-Si:H), deposited by plasma enhanced chemical vapor deposition (PECVD) technique. The dependence of the effective lifetime (τeff) on the deposition parameters including hydrogen gas flow, power and temperature has been studied. Minority carrier lifetime was measured as deposited and also after an annealing step in both quasi-steady-state (QSS) and transient mode of photoconductance decay. By comparison between τeff measured in each of the aforementioned modes, two distinguishable behaviors could be observed. Moreover, to get further insight into the surface passivation mechanism, we have modeled the recombination at a-Si:H/c-Si interface based on the amphoteric nature of dangling bonds. The results of our modeling show that the discrepancy observed between QSS and transient mode is due to the high recombination rate that exists in the bulk of defective CZ wafer and also partly related to the different thicknesses monitored in each mode. So, by comparison between the injection level dependency of τeff measured in QSS and transient modes, we introduce a valuable technique for the evaluation of c-Si bulk lifetime.

High Performance Computing (HPC) Wales was launched in 2010 as a five year joint venture between Wales’ six Universities, working in partnership with a variety of academic and industrial stakeholders and funded by the EU, UK and Welsh Governments. The aim of HPC Wales is to deliver a pan-Wales HPC infrastructure: primarily to assist with economic regeneration in the Principality of Wales (which has a population of approximately 3.6 million) through the up-skilling of individuals and by promoting uptake of HPC in Welsh businesses, but also open to collaborations from outside Wales. It is the first national service of its kind in Europe.

In order to encourage the uptake of HPC into small and medium sized enterprises (of up to 250 staff) in Wales, and for HPC Wales itself to become a sustainable business, the development of a strong skills base is vital. Successful delivery will be marked by the successful upskilling of individuals via accredited training programmes, and through outreach and engagement activities. Recognising that a significant amount of upskilling is required, further work is being undertaken by HPC Wales to develop workflows which can help to simplify the HPC job submission process for the end user. This will make it possible for businesses to achieve results without their needing to acquire a high level of specialist HPC skills in the short term.

At a mid-point in this ambitious venture, this paper examines the strategies being developed by HPC Wales which will help to ensure propagation throughout the educational chain so that the requisite skills and workflows are in place which will benefit the next-generation workforce. Through this, HPC Wales hopes to assist in the overall advancement of scientific discovery which will, in turn, help Welsh businesses to become more competitive in the global marketplace.

Effect of oxygen to nickel molar ratio (O2/Ni) on the crystallinity of atmospheric pressure metal organic chemical vapor deposition (APMOCVD) grown NiO at 500°C is reported. X-ray diffraction (XRD) analysis including grazing incident angle θ of 0.6°, θ-2θ, ɸ and rocking curve scan are employed for crystallographic characterization. Furthermore, surface roughness is studied by atomic force microscopy (AFM). No evidence of diffraction peaks in X-ray grazing incident angle measurement confirms that all the grown NiO films are well oriented along a certain direction. θ-2θ scan results further indicate that the samples are highly oriented only along [111] direction on (0001) sapphire substrates. The analysis of full width at half maximum (FWHM) of rocking curve scan of (111) plane shows that higher O2/Ni ratio results in better crystallinity. The best crystallinity is achieved with FWHM as low as 0.106° at (111) rocking curve scan corresponding to 82.57nm grain size. AFM measurement shows that NiO films grown with higher O2/Ni ratio have smoother surface morphology.

Glasses in the Al2O3-B2O3-Fe2O3-Na2O-SiO2 system were produced at a temperature of 1150 °C, poured onto a metal plate and annealed. The nature of the structural units and their bonding in the structure were studied by infrared and Raman spectroscopic techniques. The structural network of all the glasses studied is built from major [SiO4] tetrahedra with 2-3 non-bridging oxygens (NBO). Incorporation of Fe2O3 offers a destructive effect in the glass network.

Development of Al-stabilized Li7La3Zr2O12 (LLZO) fast Li ion conducting thin films was attempted by chemical solution deposition (CSD) method with the nominal composition of Li5.95Al0.35La3Zr2O12. The films were crystallized at 600°C on Pt-coated Si substrates in almost single phase without a preferred orientation to any crystallographic axis. Subsequent thermal annealing at 760°C improved packing of LLZO grains with the film thickness of 1.1μm. AC impedance measurements were conducted both with Li reversible and Au blocking microelectrodes deposited on the films annealed at 760°C. Total Li ion conductivity σtotal comprised of bulk and grain boundary contribution was studied. The temperature dependence of σtotal was described with single thermal activation process and σtotal∼2x10-5 S/cm and activation energy of Ea=0.58eV were estimated. These values may be attributed to tetragonal modification of LLZO crystal.

Pore sealing has become a critical issue for the implementation of porous low-k dielectrics and for realizing acceptable reliability performance of the interconnect. This study focuses on fabrication of ultra-thin, conformal and plasma resistant pore seal layer and on understanding parameters playing a role in sealing the surfaces of porous low-k films. It was found that 2.5 nm-thick pore seal layer shows a perfect toluene seal property for the porous low-k film whose pore radius is 1.48 nm. The pore seal layer still show a good toluene seal property after irradiation of He plasma at 250°C for 10 sec. The increments of dielectric constant by applying the pore seal layer and by the He plasma irradiation for 10 sec are 0.04 and 0.03, respectively. Interestingly, all of toluene seal property, refractive index of the bottom part of the film and dielectric constant started to deteriorate after irradiation of He plasma for 20 sec. It was suggested that when toluene seal property degrades, plasma would start diffusing into pores and both refractive index of the bottom part of the film and k value start to increase.

Multifunctional polymer-based biomaterials, which combine degradability and shapememory capability, are promising candidate materials for biomedical implants. An example is a degradable multiblock copolymer (PDC), composed of poly(p-dioxanone) (PPDO) as hard and poly(ε-caprolactone) (PCL) as switching segments. PDC exhibits a unique linear mass loss during hydrolytic degradation, which can be tailored by the PPDO to PCL weight ratio, as well as an excellent thermally induced dual-shape effect. PDC can be synthesized by co-condensation of two oligomeric macrodiols (PCL-diol and PPDO-diol) using aliphatic diisocyanates as coupling agent. Here, we investigated whether different morphologies could be obtained for PDCs synthesized from identical oligomeric macrodiols (PCL-diol with M n = 2000 g·mol-1 and PPDO-diol with M n = 5300-5500 g·mol-1) with 2, 2(4), 4-trimethyl-hexamethylene diisocyanate (TMDI) and 1, 6-hexamethylene diisocyanate (HDI), respectively. More specifically, atomic force microscopy (AFM) was utilized for an investigation of the surface morphologies in solution casted PDC thin films in the temperature range from 20 °C to 60 °C. The results obtained in differential scanning calorimetry (DSC) and AFM demonstrated that different morphologies were obtained when TMDI (PDC-TMDI) or HDI (PDC-HDI) were used as linker. PCL related crystals in PDC-HDI were more heterogeneous and less ordered than those in PDCTMDI, while HDI resulted in a larger degree of crystallinity than TMDI. This research provides some new suggestions for choosing a suitable coupling agent to tailor the required morphologies and properties of SMPs with crystallizable switching segments.

We have developed a method of a stepwise construction of a gel consisting of (i) astral-shaped actin filaments with their plus end connected on photo-responsive polymer beads and (ii) bipolar myosin filaments as linkers in order to mimic sarcomeric structure, the basic unit of a muscle. In the method, firstly, 4 μm diam. beads were prepared from an acrylate polymer containing azobenzene moiety by a good-solvent evaporation technique. Next, gelsolin, which servers and remains bound to the plus end of an actin filament, was adsorbed and then immobilized on the bead surface by exposure to light from blue light-emitting diodes, and then fluorescent actin filaments were mixed with the beads. Formation of star-like, astral actin filaments on the beads were observed in fluorescent microscopy. Finally, the beads with actin filaments were mixed with myosin mini filaments with ca. 1 μm in length. Dozens of the beads were observed to be assembled into a gel form in optical microscopy. After adding adenosine triphosphate to the gel solution, the gel was slowly contract up to 60% comparing with its original volume, suggesting that linker myosin filaments moved on the actin filaments toward the plus end on the beads.

We report on the study of single devices of phase-change (Ge2Sb2Te5) memory cells in line cell type devices. Devices were investigated employing an x-ray nanobeam of only about 150 nm diameter, which could be fully contained within the spatial extent of the active area within a single device cell. XANES spectra showing the device in the amorphous and crystalline state have been successfully collected after switching the device in situ at the synchrotron. By monitoring the fluorescence response of the sample constituent materials at a constant photon energy (corresponding to the Ge K-edge absorption edge) as a function of x-ray beam position on the sample 2D maps have been produced.

This work clearly demonstrates that the X Ray Reflectometry technique (XRR), extensively used to assess the quality of microelectronic devices can be a useful tool to study the first stages of ion beam mixing. This technique allows measuring the evolution of the Si concentration profile in irradiated Cr/Si layers. From the analysis of the XRR profiles, it clearly appears that the Si profile cannot be described by a simple error function.

Multi-junction III-V solar cells are based on a triple-junction design that employs a 1eV bottom junction grown on the GaAs substrate with a GaAs middle junction and a lattice-matched InGaP top junction. There are two possible approaches implementing the triple-junction design. The first approach is to utilize lattice-matched dilute nitride materials such as InGaAsN(Sb) and the second approach is to utilize lattice-mismatched InGaAs employing a metamorphic buffer layer (MBL). Both approaches have a potential to achieve high performance triple-junction solar cells. A record efficiency of 43.5% was achieved from multi-junction solar cells using the first approach [1] and the solar cells using the second approach yielded an efficiency of 41.1% [2]. We studied carrier dynamics and defects in bulk 1eV InGaAsNSb materials and InGaAs layers with MBL grown by MOVPE for multi-junction solar cells.

Papers in the Appendix were published in electronic format as Volume 1534

We have studied the LME phenomenon for the Cu/Hg couple, from an experimental and a computational point of view. We compared the LME behavior of standard oxygen free high conductivity (OFHC) copper with Grain Boundary Engineered (GBE) copper (containing a high fraction of special Σ3 GBs). Experimentally, we find that special Σ3 GBs in copper are less prone than general GB to LME by liquid mercury. In parallel, we have investigated the difference in LME induced fracture between the symmetric Σ3(111)[110]70.5° tilt GB and the symmetric Σ5(210)[100]36.87° tilt GB by ab-initio calculations. The Hg segregation trend has been evaluated for these 2 GBs. Ab-initio tensile tests on the Σ3(111) GB with and without segregated Hg atoms have been performed. Finally solid/liquid interfaces have been modeled using ab-initio molecular dynamics (AIMD) in order to calculate solid-liquid surface energies (γSL). Using a Griffith approach, we have evaluated the energy difference γGB - 2 γSL. The LME mechanism in Cu/Hg is discussed.

The high resolution X ray diffraction (HR-XRD) diagrams have been studied in the GaAs /InxGa1-xAs /In0.15Ga0.85As/GaAs quantum wells with embedded InAs quantum dots (QDs) in dependence on the composition of the capping InxGa1-xAs layers. The parameter x in capping InxGa1-xAs layers varied from the range 0.10-0.25. These technological changes have been accompanied by the variation non-monotonously of InAs QD emission. Numerical simulation of HR-XRD results has shown that the level of elastic strains and the composition of quantum layers vary none monotonously in studied QD structures. Simultaneously it was revealed that the process of Ga/In inter diffusion at the InxGa1-xAs/InAs QD interface are characterized by the dependence non monotonous versus parameter x in capping InxGa1-xAs layers. The physical reasons of the mentioned optical and structural effects in studied structures have been discussed.

High temperature (>550°C) applications of silver based porous composites have been limited due to relatively low melting temperature (962°C) of Ag. Incorporation of oxide particles was demonstrated as an effective approach for stabilization of the porous Ag microstructures. This study aims developing an understanding based on the relationships between the properties of the incorporated YSZ (yttria-stabilized zirconia), the developed porous microstructures and the electrochemical response of their electrodes. Minimum degradation was observed with the composite microstructure based on comparable Ag and YSZ particle sizes. The results demonstrated that YSZ incorporation into Ag matrix can increase the stable application temperature to 800°C.

Metal films on polymer substrates are commonly used in flexible electronic devices and as gas barrier coatings. One way to evaluate the fracture and adhesion properties of such film systems is the fragmentation test. In the fragmentation test a film-substrate system is strained in tension under an optical microscope or inside a scanning electron microscope to observe the cracking and delamination events in situ. The technique works very well for brittle metal and ceramic films. However, when ductile films are strained they deform plastically before cracks and buckles appear. Therefore, a tensile straining device was developed to fit under an AFM for in situ observation of ductile metal films on polymer substrates. With the new in situ device the first occurrence of plastic deformation in the form of localized thinning of the film and channel cracks are visible. These features can only be detected through a height difference in the AFM images and not with optical or scanning electron micrographs. A comparison to brittle Cr films on polymer substrates was performed.

A facile and cost-effective fabrication approach of active strain sensor based on individual ZnO micro/nanowire was demonstrated. By connecting a ZnO micro/nanowire along polar growth direction with two Ag electrodes on flexible polystyrene (PS) substrate, the fabricated strain sensor was obtained as a typical M-S-M structure. The I-V characteristic of the device was highly sensitive to the strain caused by the obvious change of Schottky barrier height (SBH). Furthermore, both of the symmetric and asymmetric changes of the SBH at the source and drain were observed during device testing process. The respective contribution of piezoresistance effect and the piezoelectric effect to the change of SBHs were also systematically investigated.