This paper describes light trapping in superstrate-type amorphous Si solar cells incorporated with Ag nanostructures (nanodisks) fabricated by a transfer-printing approach. The changes in external quantum efficiency (EQE) and current-voltage characteristics were investigated by changing the position and size (thickness) of the Ag nanodisks in the cells fabricated on flat superstrates. It was confirmed that the optimized Ag nanodisk-configuration led to the enhanced EQE (20%) in the 600-800 nm wavelength range, and the enhanced EQE led to the improved overall conversion efficiency (7.5%) compared to the cell without Ag nanodisks (7.2%). However, the integration of the optimized Ag nanodisk-configuration with the cells fabricated on textured superstrates did not result in the enhanced EQE and conversion efficiency, suggesting further optical designs are necessary to exploit both texture- and plasmon-mediated light trapping effects.

Elongated micro- and nanostructures of Sn doped or Sn and Cr co-doped monoclinic gallium oxide have been grown by a thermal method. The presence of Sn during growth has been shown to strongly influence the morphology of the resulting structures, including Sn doped branched wires, whips, and needles. Subsequent co-doping with Cr is achieved through thermal diffusion for photonic purposes. The formation mechanism of the branched structures has been studied by transmission electron microscopy (TEM). Epitaxial growth has been demonstrated in some cases, revealed by a very high quality interface between the central rod and the branches of the structures, while in other cases, formation of extended defects such as twins has been observed in the interface region. Cathodoluminescence (CL) measurements show a Sn-related complex band in the Sn-doped structures. In the Sn−Cr co-doped samples, the characteristic, very intense Cr3+ red luminescence emission quenches the bands observed in the Sn doped samples. Branched, Sn−Cr co-doped structures were studied with microphotoluminescence imaging and spectroscopy, and waveguiding behavior was observed along the trunks and branches of these structures.

Cu2ZnSnSe4 thin films were prepared by using the synthesized Cu2ZnSnSe4 ingot and Na2Se powder at various Na2Se/Cu2ZnSnSe4 mole ratio as evaporation materials for selenization process. From EPMA analysis, the composition was approximately constant even if the Na2Se/Cu2ZnSnSe4 mole ratio increased. X-ray diffraction studies revealed that the thin films had a kesterite Cu2ZnSnSe4 structure and the foreign phases disappeared with increasing the Na2Se/Cu2ZnSnSe4 mole ratio. The Na2Se addition enhanced to grow thin films having a close-packed structure and columnar grains. The values of Voc and Isc in Cu2ZnSnSe4 thin film solar cells increased with increasing the Na2Se/Cu2ZnSnSe4 mole ratio.

Two methods for the fabrication of flexible and stretchable photonic crystal slabs are demonstrated and compared. In both cases a periodically nanostructured polydimethylsiloxane (PDMS) membrane is used as substrate. The first method is based on oblique-angle vapor deposition of SiO as a high refractive index material onto the nanostructured membrane. The deposition is made at an angle of 45° to the surface. The grooves of the nanostructure are aligned such that shading effects cause an inhomogeneous layer thickness distribution on the surface. This supports controlled, periodic cracking of the high index layer upon stretching. In the second approach ZnO nanoparticles are spin-coated on the nanostructured PDMS membrane. Here, the membrane can be stretched and serves as a photonic crystal slab without the need of any further treatment. For both types of flexible photonic crystal slabs a shift of the guided mode resonances to longer wavelengths is observed upon stretching. For a 20% strain perpendicular to the grating grooves a resonance shift of more than 50 nm is obtained.

Here, we propose novel mesoporous Au-loaded TiO2 nanoparticle assemblies (Au-MTA) as highly effective catalysts for the reduction of nitroaromatic compounds into the corresponding aryl amine products. The obtained materials possess a continuous network of interconnected gold and anatase TiO2 (ca. 9 nm in size) nanoparticles with controllable gold particle size (i.e. ranging from ∼3.2 to ∼9.4 nm) and exhibit large and accessible pore surface area (ca. 100–160 m2/g), as evidenced by SAXS, XRD, TEM and N2 physisorption measurements. Interestingly, the Au-MTA mesophases have exhibited remarkable activity and selectivity for the reduction of nitro into amine groups using NaBH4 as reducing agent. Indeed, the Au loading and particle size have a key effect on hydrogenation reactions, affecting significantly the yield and product composition.

Most recently, magnetic ceramic nanoparticles have attracted considerable scientific interest from the basic research point of view and for their prospective use in chemical sensing, catalysis and electrochemical applications. In this paper we report the successful synthesis of xSnO2-(1-x)α-Fe2O3 system by hydrothermal synthesis and that of xZrO2-(1-x)α-Fe2O3 system by mechanochemical activation. The two nanoparticle systems were analyzed side-by-side using X-ray diffraction (XRD) and Mössbauer spectroscopy. The latter technique was used in its complexity, including the determination of the recoilless fraction using our dual absorber method. This was correlated with the onset of new phases in the systems of interest.

Thin films of pure aluminum doped ZnO and with addition of nitrogen, oxygen and hydrogen have been prepared by magnetron sputtering. The spectral absorption coefficient close to the band gap energy has been determined by spectrophotometry and analyzed regarding band tailing and creation of defect bands. We found, that an improvement of Raman crystallinity under O2- rich growth conditions is not accompanied by a suppression of band tailing as expected. An additional absorption feature evolves for layers grown in N2 containing atmosphere. Doping with hydrogen attenuates sub-band gap absorption.

In our previous studies [1-3], four kinds of stacking faults in 4H-SiC bulk crystal have been distinguished based on their contrast behavior differences in synchrotron white beam x-ray topography images. These faults are Shockley faults, Frank faults, Shockley plus c/2 Frank faults, and Shockley plus c/4 Frank faults. Our proposed formation mechanisms for these stacking faults involve the overgrowth of the surface outcrop associated with threading screw dislocations (TSDs) or threading mixed dislocations (TMDs) with Burgers vector of c+a by macrosteps and the consequent deflection of TSDs or TMDs onto the basal plane. Previous synchrotron x-ray topography observations were made in offcut basal wafers using transmission geometry. In this paper, further evidence is reported to confirm the proposed stacking fault formation mechanism. Observations are made in axially cut slices with surface plane {11-20}. Several kinds of stacking faults are recognized and their contrast behavior agrees with the four kinds previously reported. Direct observation is obtained of a Shockley plus c/4 Frank stacking fault nucleating from a TMD deflected onto the basal plane. The contrast from stacking faults on the basal plane in the axial slices is enhanced by recording images after rotating the crystal about the active -1010 reflection vector enabling a broader projection of the basal plane.

The solubility of molybdenum in borosilicate glasses is low. The UK National Nuclear Laboratory has developed a new glass formulation containing calcium and zinc for the vitrification of high molybdenum containing waste arising from the Post Operational Clean Out of the Highly Active Storage Tanks at Sellafield that will decrease the number of product containers required, reducing both production and disposal costs. The new formulation increases the quantity of molybdenum that can be vitrified through the formation of a durable CaMoO4 phase once the solubility limit of molybdenum in the glass has been exceeded. Extensive laboratory trials confirmed the potential to increase the Mo loading significantly. Recently full scale testing has been performed on the Vitrification Test Rig using highly active liquor simulants to determine the maximum MoO3 loading that can be achieved. This paper explores the full scale testing and product quality of the glass manufactured during this study.

Nanocrystalline Silicon-Germanium (Si,Ge) is a potentially useful material for photovoltaic devices and photo-detectors. Its bandgap can be controlled across the entire bandgap region from that of Si to that of Ge by changing the alloy composition during growth. In this work, we study the fabrication and electronic properties of nanocrystalline devices grown using PECVD techniques. We discovered that upon adding Ge to Si during growth, the intrinsic layer changes from n-type to p-type. We can change it back to n-type by using ppm levels of phosphorus, and make reasonable quality devices when phosphine gas was added to the deposition mix. We also measured the defect density spectrum using capacitance frequency techniques, and find that defect density decreases systematically as more phosphine is added to the gas phase. We also find that the ratio of Germanium to Silicon in the solid phase is higher than the ratio in the gas phase.

Literature data of the Mn-Si system is analyzed and discordances are pointed out. First principles calculations are performed to clarify the enthalpies of formation of the intermetallic phases. Especially the enthalpies of formation of the various possible structures of the MnSix are discussed. On the basis of these new data, a thermodynamic description of the Gibbs energy of the phases is performed using the Calphad method. The system Ge-Mn is also assessed using the Calphad method for the first time.

The mixing enthalpy in the D88 solid solution is calculated between Mn5Ge3 and Mn5Si3 by DFT calculations.

Finally a thermodynamic description of the ternary system is suggested. Especially the solubility of germanium in MnSix is modeled.

Because of the aesthetics, handy and low cost features, acrylic resin is the main material in denture fabrication last 40 years. The purpose of this study is to improve mechanical properties of acrylic based dental composites used in dentistry by applying nanofiber approaches. Polymethylmethacrylate (PMMA) is commonly used as a base acrylic denture material with benefits of rapid and easy handling but sometime this material can be fractured or cracked in clinical use because of the strength issues that is frequently used in restorative dentistry in recent years. A wide variety of fillers that are used to produce PMMA composites draw the attention in literature. Using PMMA composite resins with electrospun polyvinylalcohol (PVA) nanofiber fillers is our first novelty. Also the producing and using aligned electrospun fibers as a filler is our second novelty of this practice. PVA was selected as composite filler because of biocompatibility and preparing easily also has non-toxic solvent. Electrospinning system is manufactured that allows manipulation of electric field used in the application of alignment in lab scale. Various auxillary electrode systems are used for different patterns of alignment with the manufactured device and electrode systems produce fibers in different range of diameter. Scanning electron microscopy (SEM) is used for physical characterization and determined the range of fiber diameters. After the optimization of concentration step non-woven and aligned fibers are also analyzed. Non-woven fiber has no unique pattern because of the nature of electrospinning but aligned fibers has crossed lines. These produced fibers structured as layer-by-layer form with different features are used in producing PMMA dental composites with different volume ratios. In the last part of the research, PMMA dental composites are produced with aligned and formless fibers that are characterized with three-point bending test. The maximum flexural strength figure shows that fiber load by weight %0.25 and above improves the maximum. The change of flexural strength, elastic modulus values and toughness are obtained and compared with formless and aligned PVA nanofiber included composite specimens. As a result, mechanical properties of PMMA dental composites are improved with using PVA nanofibers as a filler also with the usage of aligned fibers instead of the formless ones the effects of improvement gets better with maximum values as 5.1 MPa (flexural strength), 0.8 GPa (elastic modulus), 170kJ/m3 (toughness).

Dimagnesium silicide (Mg2Si) is an eco-friendly material useful for thermoelectric generation using waste heat of temperature range of 600 to 900 K. To improve the thermoelectric performance of the Mg2Si compound, we made the Al-added compounds under magnesium-rich condition (with 67.0 at% of Mg) using a liquid-solid phase reaction and using a pulse discharge sintering. The thermoelectric performance of each sample containing Al of 0 to 2.0 at% was measured during 50 h air exposure with temperature difference. The temperature difference was given by contacting the hot side of a sample with a hot plate kept at 773 K and by contacting the cold side with a heat sink with cooling fan. The electrical resistivity of the Al-free sample increased with air exposure time by internal oxidation. All the Al-added samples kept the low resistivity during the air exposure test. We confirmed the resistance to deterioration in thermoelectric performance of the Al-added samples during air exposure with temperature difference.

Resistively switching devices have attracted great attention for potential use in future nonvolatile information storage. Among various oxide materials that show resistive switching (RS) behavior, SrTiO3 (STO) is regarded as a model material to study the effect of valence changes accompanying RS in the oxide [1]. In this class of materials, the RS effect is attributed to rely on the migration of oxygen vacancies and an associated valence change in the cation sublattice. To achieve a switchable state, an initial electroforming step is typically required, which is believed to create conductive regions in the insulating material [2]. Under high electrical stress, an oxygen-deficient region, often referred to as the virtual cathode (VC), is formed [3]. The RS occurs across a very short distance between the VC and the anode, allowing for very short switching times. As the electroforming step greatly impacts the device performance and switching variability, its understanding is essential for device optimization. Electroforming is affected by multiple parameters, e.g. voltage, current, temperature, dopant and defect concentrations, ambient gas atmosphere and time. Distinguishing the influence of the particular parameters is a desirable aim and challenging task. Electrocoloration of Fe-doped STO single crystals has proven a valuable means to visualize valence changes of the Fe ions and is thus suitable to study the formation of the VC. Therefore, we performed electrocoloration experiments and used high resolution transmission light optical microscopy to make the redoxprocesses during electroforming visible. The influence of process driving parameters on the evolution of the VC region is studied. The evolution of the VC is interpreted by drift-diffusion simulation of the time evolution of the oxygen vacancy distribution.

The Diels-Alder (DA) pericyclic chemistry is one of the most powerful reactions in synthetic chemistry. We have recently shown that the unique zero-band-gap electronic structure of graphene at the Dirac point facilitates the band-gap-dependent DA reaction of graphene, although graphene is the thermochemical reference for carbon. We have shown that in the DA reactions, graphene can function either as a diene or a dienophile (dual nature). Such DA functionalization of graphene when applied to graphene-FET devices allows balanced functionalization (creation of a pair of new sp3 centers or divacancies) at both A and B graphene sublattices, allowing the fabrication of high mobility DA-functionalized single-layer graphene devices (DA-SLG) with acceptable on/off ratio. The chemistry is thermally reversible via retro-DA chemistry, thus allowing reversible engineering of graphene devices.

Thin-film absorber layers for photovoltaics have attracted much attention for their potential for low cost per unit power generation, due both to reduced material consumption and to higher tolerance for defects such as grain boundaries. Cu2ZnGeSe4 (CZGSe) comprises one such material system which has a near-optimal direct band gap of 1.6 eV for absorption of the solar spectrum, and is made primarily from earth-abundant elements.

CZGSe metallic precursor films were sputtered from Cu, Zn, and Ge onto Mo-coated soda lime glass substrates. These were then selenized in a two-zone close-space sublimation furnace using elemental Se as the source, with temperatures in the range of 400 to 500 C, and at a variety of background pressures. Films approximately 1-1.5 µm thick were obtained with the expected stannite crystal structure.

Next, Cu2ZnSnSe4 (CZTSe), which has a direct band gap of 1.0 eV, was prepared in a similar manner and combined with CZGSe as either compositionally homogeneous or layered absorbers. The compositional uniformity of selenide absorbers made by selenizing compositionally homogeneous Cu-Zn-Ge-Sn precursor layers was determined and the band gap as a function of composition was investigated in order to demonstrate that the band gap is tuneable for a range of compositions. For layered Cu-Zn-Ge/Cu-Zn-Sn precursor films, the composition profile was measured before and after selenization to assess the stability of the layered structure, and its applicability for forming a band-gap-graded device for improved current collection.

We report the growth of ZnO horizontal (NRs) on p-Si substrate at low temperature without any assisting mechanism. The NRs were grown at 90°C on a ZnO film previously deposited using metal-organic chemical vapor deposition. The horizontal nanowires have diameters in the range of 200 – 500nm and lengths between 1 – 7 µm, depending upon the duration of the growth and the ratio of the precursors. The density of the NRs was controlled by varying the concentration of zinc nitrate (Zn(NO3)2) while keeping hexamethylenetetramine (HMTA) constant. Density of horizontal NRs increased with lower zinc nitrate concentration (from 11.35 to 3.29 mMol) for a growth duration of 18hrs. Increased zinc nitrate concentration of 3.29mMol resulted in an asymmetric growth along the vertical axis due to oxygen termination giving rise to slower growth rates.

Optical properties of ZnO-CdTe electrochemically prepared on a core-shell nanostructure (NS) were studied. Numerical simulations based on effective medium approximation give higher absorption than ZnO-CdS samples and a sensitive dependence on CdTe content. The absorption edges for deep black samples found by transmittance (T(λ)) and diffuse reflectance (R diff (λ)) measurements were at 1.33eV and 1.55eV, respectively. A split-off band edge was also found by R diff (λ) at ∼2.5eV. The red shift observed in T(λ), previously observed in ZnO-CdS, and may confirm the enhancement of sub-bandgap absorption due to the NS nature of samples.

Ensuring microstructural stability under technical relevant conditions is a determining criterion for the development of innovative high-temperature materials. In this work, the influ-ence of C and Si on the microstructural stability during creep exposure was investigated for a β-solidifying γ-TiAl based alloy with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in at.%), named TNM. With a two-step heat treatment a microstructure consisting of fine lamellar α2/γ-colonies, surrounded by βo-phase and areas of discontinuous precipitation, starting from the boundaries of the lamellar colonies, was adjusted. Creep tests were carried out to examine the potential of C and Si to prevent microstructural instability during creep and hence improving the creep properties. At 815 °C the discontinuous precipitation process of the TNM alloy continues during ensuing creep testing leading to a reduced creep resistance. In comparison, the minimum creep rate of the TNM-0.3C-0.3Si alloy was significantly decreased caused by the lower βo-phase content and average lamellar spacing within the α2/γ-colonies, the precipitation of p-Ti3AlC carbides and the retarded kinetics of discontinuous precipitation.

The structures and electronic properties of graphene with defects consisting of one to six atomic vacancies are investigated using first-principles calculation. All of the geometrically possible initial structures of a movacancy or a multivacancy in graphene are equilibrated. The formation energies and electronic band structures for the equilibrated defective structures are calculated. It is suggested non-zero bandgaps may be induced in graphene by introducing some types of monovacancy or multivacancy although further checks regarding supercell size are necessary to ensure the present results.