An increase in molecular weight of the polymer generally impedes solubility in common solvents and may influence the polymer optoelectronic properties as well. Indeed, higher molecular weights are expected to increase charge carrier mobilities and therefore give rise to better photovoltaic performances of bulk heterojunction solar cells. In this work, we use copolymers based on 2,1,3-benzothiadiazole, thiophene and thieno[3,2-b]thiophene units of various fractions differing in molecular weights almost by a factor of 4 with a fullerene based acceptor material Indene-C60 Bisadduct (IC[60]BA) to elaborate bulk heterojunction solar cells. We investigate the influence of post-deposition annealing temperatures and polymer:fullerene ratios on the final cell performances. We use IC[60]BA as an acceptor to enhance the open circuit voltage due to its high lying LUMO level [1]. Additionally, charge carrier mobilities were probed using bottom contact organic field-effect transistors. As expected, higher molecular weights (as long as homogeneity was maintained) resulted in an increase of the hole field-effect mobility (up to 7x10-3 cm2V-1s-1). Consequently, the power conversion efficiencies of bulk heterojunction solar cells could be improved by increasing the copolymer molecular weight. A power conversion efficiency of 2.4% with an open circuit voltage of 0.82V was reached in a standard device configuration with aluminum as a cathode after post-deposition thermal annealing.

It is known that methanol and ethylene form distinct one-dimensional patterns along the dimer row on the Ge(100)-2 × 1 surface. A unified explanation for the pattern formation is attempted in this study through theoretical methods. Kinetic parameters of the precursor-mediated adsorption of the two molecules are calculated using density functional theory methods. The potential energy surface along the reaction channel was found to vary according to nearest-neighbor occupation. Monte Carlo simulations were performed with calculated kinetic coefficients and assumptions of a one-dimensional lattice with nearest neighbor interactions. The simulation results effectively reproduce the coverage-dependent evolution of longer-range adsorption patterns.

To apply thin ZnO film to photoacoustic tomography sensors, we investigated methods to improve its piezoelectricity with high optical transmittance. ZnO film was deposited by RF magnetron sputtering on a quartz substrate with various changes of the following conditions: RF sputtering power, Ar gas pressure, and substrate temperature (TSUB). The preliminary optimization of sputtering conditions is to form the ZnO film with good c-axis crystalline alignment. The results of X-ray diffraction measurement and cross-sectional observations indicated that the high-TSUB condition was preferable. This was because the desorption of Zn due to high-TSUB during the deposition process induced the formation of excellent columnar grains normal to the substrate. To enhance the piezoresponse, the substitution of Zn with different crystal-radius atoms was investigated, the aim being to increase the electrically neutral dipole moment by the partial displacement of the Zn-O bond. The transition metal V, with the potential to have the various configurations and coordination numbers, was selected as the dopant. As a result, it was confirmed that the diffraction peak from the (002) plane shifted to low angles with small degradation of the diffraction intensities.

VO2films were deposited on sapphire, ITO glass and 200 nm thick silicon nitride membranes by Pulsed Laser Deposition (PLD). The electrical and optical properties have been investigated. Joule heating devices fabricated on silicon nitride membranes switches from semiconductor phase to metal phase by applying a constant voltage across two metal contacts. Compared to the devices fabricated on the normal substrates, such as sapphire, silicon or glasses, the switching speed of the devices on membrane is an order of magnitude faster. Decreasing the area and thickness of VO2 on top of thinner membranes allows kHz bandwidth to be achieved.

Although uranium oxides have played essential roles in many nuclear reactions, it is imperative to pursue alternative solutions to reuse the spent fuels due to paramount safety and economic concern. Spent nuclear oxide fuels include uranium dioxide (UO2), triuranium octoxide (U3O8) and uranium trioxide (UO3). In this work, first principles calculations based on density functional theory (DFT) were carried out on MUO2, MU3O8 and MUO3 (M= Li, Na and K) to explore their possibilities to serve as grid-storage-based cathode materials. In particular, the result of the optimal structures, average open circuit voltages (OCV) and mechanic stabilities during charge and discharge processes are presented. These results are also compared to available experimental data.

Progress in tailoring the size, shape and positioning of Quantum Dots on the substrate is crucial for their potential applications in new optoelectronic devices for nano-photonics as well as in quantum information and computation. Using Molecular Beam Epitaxy in pulsed deposition mode we demonstrate that the nucleation of InAs Quantum Dots can be selectively guided on the GaAs(001) surface by a suitable choice of the kinetic parameters for the growth of both the GaAs buffer layer and the InAs Quantum Dots. By developing a two-species rate-equation kinetic model we show that the positioning of the Quantum Dots on only one side of mounds of the GaAs buffer can be traced back to the very small As flux gradient between the two mound slopes $\left( {\Delta F_A /F_A\approx 1 - 5\% } \right)$ caused by the proper tilting of the incoming As flux. Such gradient originates, at the relatively high growth-temperature, a net cation flow from one slope of the mound to the other that is responsible for the selective growth.

The effects of the pulsed green laser annealing at ambient nitrogen for two different heights-CNWs grown on silicon substrate were investigated on the crystallinity and morphology using Raman spectroscopy, SEM, TEM and XPS. For the 1μm height-CNWs, the peak intensity of D-band spectra decreased as the laser energy density increased up to 1.3Jcm-2, ID/IG ratio decreased from 2.5 to 0.7. The crystallinity of CNWs was improved by the laser irradiation. For the 1μm height-CNWs irradiated above 1.5Jcm-2, the height of CNWs decreased gradually as the laser energy density increased, it was clarified that the surfaces of CNWs were vaporized by the laser irradiation. For the 20μm height-CNWs, the peak intensity of D band spectra also decreased until the laser energy density increased up to 0.8Jcm-2, ID/IG ratio decreased from 1.6 to 0.5. From the TEM observation of CNWs irradiated at 0.8 Jcm-2, it was confirmed that the laser irradiation changed CNWs to be highly oriented crystal structure. However above 0.8Jcm-2, the crystallinity was deteriorated due to the vaporization of CNWs as the same as the 1μm height-CNWs. The pulsed green laser annealing is effective to improve the crystallinity of CNWs on optimal laser energy density for both height-CNWs, the higher laser energy densities vaporized the CNWs and changed the morphology and crystallinity of CNWs.

We present two distinct methods to nanostructure the surface of amorphous silicon to produce unique, nanoscale surface features. One method is a dry etch process that employs a modified Bosch1 process on an advanced silicon etcher to produce needle-like features of amorphous silicon. Likewise, we also investigated metal-assisted wet chemical etching2 as an alternative method to nanostructure the amorphous silicon to produce porous-like features. The resulting surface topography leads to an optically black appearance over patterned or large areas. This is a result of the interspacing between each needle and pore that leads to a high optical absorption. Thus, we designate it as black amorphous silicon (b-a-Si). We have deposited and formed regions of b-a-Si on variety of insulating films and metal electrodes, including chrome and titanium. In this study, we characterize the electrical and optical properties of as-deposited amorphous silicon and nanostructured amorphous silicon.

Scanning Tunneling Microscope (STM) was used to examine the morphologies of selfassembled InGaAs quantum dots (QDs). In order to induce the self-assembly, unlike the conventional Stranski-Krastanov (S-K) growth method, spatial thermal modulations in nanoscale were created in-situ on strained-but-flat InGaAs surfaces in a Molecular Beam Epitaxy (MBE) growth reactor by applying interferential irradiations of laser pulses (IILP). As-irradiated surfaces were examined using an attached ultra-high vacuum (UHV) STM. STM images indicate that the irradiation of 7 nano second laser pulse induces self-assembly of QDs. The average size of laser-induced QDs is smaller while their density is larger than that of QDs formed by annealing strained but flat epilayers conventionally. Furthermore, the dot density is modulated sinusoidally with a periodicity commensurate with that of the interference, which suggests that the placement of QDs can be controlled on the scale of the optical wavelength used. QD volume analysis suggests that dots grow faster laterally than vertically so that dots become flattened as they get larger.

Composite PVA/ZnO-nanorods fibers, synthesized through co-axial flux extrusion exhibit higher anisotropic photonic properties, both in absorption and emission, as a result of the collective alignment of the ZnO nanorods along the main axis of the PVA fiber. This photonic anisotropy is triggered by a synergistic interaction between the PVA matrix, stretched above Tg, and cooled down under strain. Compared with non-elongated fibers that present an isotropic emission, composite fibers previously submitted to a tensile stress absorb selectively UV emission when the polarized laser beam is parallel to the main axis of the fiber. In addition, their photoluminescence is also anisotropic, with a waveguide behavior along the fiber’s main axis.

In order to elucidate a link between density and structure of liquid Si-M (M=Fe, Ni, and Ge) alloys, synchrotron x-ray diffraction experiments have been conducted with the use of a conical nozzle levitation technique. Liquid structure factors of the Si-Fe and the Si-Ni alloys indicate a correlation of medium range ordering with the increase of the Si content. Although the total molar volume expands with the increase of the Si content in these alloys, the concentration dependence of the average interatomic distance shows a minimum around 70 at.% Si content. On the other hand, the Si-Ge alloys shows tendency of concentration dependence as ideal mixture in both total molar volume and the average interatomic distance. These results were discussed taking into account the formation of anisotropic bonds between 3d transition metal and Si atoms, which may induce a spatial expansion in the microscopic scale.

Nanodiamond holds great interest in a variety of optical applications, the properties being correlated with surface modification, and the presence of both impurities and defects (contained either on their surface or within the crystal structure). Undecyl-nanodiamond produced by attachment of 1-undecene onto the nanodiamond surface could be a good candidate as a luminescent marker in the future; therefore, understanding of its optical properties is essential. In this work, the optical properties of the acid-purified nanodiamond and undecyl-nanodiamond were characterised using surface enhanced Raman spectroscopy (SERS) and photoluminescence spectroscopy. The results demonstrate that the characteristic diamond Raman signal at 1330 cm-1 was still observed after chemical surface modification, while the signal at ∼1600 cm-1 (attributed to graphite bands) disappeared after the modification. Broad photoluminescence emission is detected in the range 1.5-2.5 eV (500-800 nm), as typically found for isolated nanodiamond; these emission bands became narrower with attachment of 1-undecene as compared to the sample without surface functionalisation. The observed emission could be related to structural disorder on the nanodiamond surface. The temperature dependence of the intensity, peak position and band widths of each sample has been characterised.

Neutral, hydrophilic, polymer-based architectures are widely investigated for a wide range of biomedical applications from drug-conjugates to delivery systems and scaffolds for regenerative therapies. In most cases, it is crucial that biomaterials provide a blank, inert background in order to hinder unspecific cell-material interactions so that protein mediated biological events leading to foreign body reactions are prevented. Hydrophilic polyglycerol-based polymer network films are a recently developed class of amorphous macroscopic materials, which offer great versatility in design and control of resultant properties. In this study, protein adsorption on polyglycerol-based polymer network films is investigated by using Micro BCA protein assay for three types of proteins having critical roles in the human body, and various copolymer networks with differing sidechains and crosslink densities.

We have examined segregation behavior of various alloying elements at lamellar interfaces of C40-NbSi2/C11b-MoSi2 duplex silicide by a phase-field simulation, which takes into account not only bulk chemical free energy but also segregation energy evaluated by the first principles calculation to reflect interaction between solutes and interface. The simulation suggests that segregation behaviors greatly depend on additive elements. In the case of Cr-addition, the C40-phase becomes enriched with Nb and Cr, while the C11b-phase becomes enriched with Mo, which agrees with the equilibrium phase diagram. Slight segregation of Cr atoms is observed at the interface, whereas Nb and Mo concentrations monotonically change across the diffuse interface between C11b and C40 phases. Significant segregations of Zr and Hf are formed at static interfaces, which are attributed to the chemical interaction between solute atoms and the static interface.

We have developed our original DFT (density-functional theory) calculation code “RSDFT” using real-space schemes. The code is FFT-free, leading to high-performance computing in massively-parallel supercomputers. The code allows us to deal with systems including huge numbers of atoms from first-principles. We have applied our schemes to clarify atomic and electronic structures of two relevant nano-scale systems: twisted bilayer graphene and silicene on Ag substrate.

We have prepared 2% Al doped ZnO (AZO) thin films on SrTiO3 and Al2O3 substrates by Pulsed Laser Deposition (PLD) technique at various deposition temperatures (Tdep = 300 °C – 600 °C). Transport and thermoelectric properties of AZO thin films were studied in low temperature range (300 K - 600 K). AZO/STO films present superior performance respect to AZO/Al2O3 films deposited at the same temperature, except for films deposited at 400 °C. Best film is the fully c-axis oriented AZO/STO deposited at 300 °C, with electrical conductivity 310 S/cm, Seebeck coefficient -65 μV/K and power factor 0.13 × 10-3 Wm-1K-2 at 300 K. Its performance increases with temperature. For instance, power factor is enhanced up to × 10-3 Wm-1K-2 at 600 K, surpassing the best AZO film previously reported in literature.

Wire array solar cells benefit from enhanced coupling of light into the active area of the device, significantly decreased collection lengths due to radial charge separation and collection, and easier access to grain boundaries for passivation which may enable future deposition on non-wafer substrates. We report on an analysis of the junction operation of wire array based GaAs solar cells through temperature and light intensity dependent current-voltage analysis and compare these data to matched planar devices. We see evidence of non-ideal recombination pathways indicated by activation energies for generation-recombination that are significantly less than the band gap of GaAs. We observe voltage shifts in the wire array devices at low temperature and high light intensity that we posit can be explained by electron accumulation in the window layers of the devices.

The effect of oxygen vacancy (VO) on the electronic and magnetic properties of ZnCoO was studied with first principle methods based on density functional theory (DFT). Calculations were performed, on a periodic 3×3×3 wurtzite supercell of ZnO which consists of 108 atoms with two Co ions substituted for two Zn atoms, using the generalized gradient approximation with Hubbard U correction method (GGA+U). We have studied the interatomic exchange interaction with and without VO for different configurations with different magnetic atom lattice arrangements. The total energies, electronic structures and magnetic moments were calculated for each configuration.