We present the propagation properties of Dirac-electrons in multilayered Period-Doubling (MPDGS) and Silver-Mean (MSMGS) graphene structures. The multilayered graphene structures are built arranging breaking and non-breaking symmetry substrates such as SiC and SiO2 following a given quasirregular substitution rule locating on them a graphene sheet. We have implemented the Transfer Matrix technique to calculate the transmittance of these multilayered graphene structures. This technique allows us to analyze readily the main differences of the transmission properties between MPDGS and MSMGS.

Graphene, a two-dimensional carbon allotrope, has raised great interests as a material candidate for future electronics due to its superb carrier transport and unique physics. The demand for future-generation large-scale carbon-based electronics motivates assembly of large-area graphene and selection of ideal substrate material that best preserves the transport property of graphene. In this work, CVD-assembled large-area graphene on thin multilayer hexagonal boron nitride (h-BN) is employed to demonstrate the basic building block of digital circuit - inverter prototype made of two graphene-channel field-effect transistors (GFETs). The doping in the CVD-grown graphene, probed via electrical measurements, is implemented through non-uniform local surface chemistry. The full transfer response of the graphene logic inverter is demonstrated in the localized P/N doping region.

This work covers the design of stimuli-responsive membranes and their ever-expanding range of use. Stimuli-responsive membranes that change their physicochemical properties in response to changes in their environment were synthesized for biomedical application. Responsive cotton-g-[2-(dimethylamino) ethyl methacrylate] membranes were obtained using γ-rays by mutual irradiation (direct method). The effect of absorbed dose, dose rate, and monomer concentration on the grafting yield was determined. The grafted samples were verified by the FTIR-ATR, 1H and 13C HRMAS NMR and 13C CPMAS NMR spectroscopies; thermal properties were analyzed by TGA and DSC and the stimuli-responsive behavior was studied by DSC.

We studied the early stages of polymerization of CO under pressure. We performed DFT simulations of 128 and 432 atom models. Structures of random networks found at zero temperature were used for equilibration at 100 K by employing first principles MD. We found that the polymerization begins at 7 - 8 GPa and slightly depends on the size of the model. It turned out that there are several metastable phases of the extended CO solid, corresponding to different compression pressures from 7 - 8 GPa to 15-18 GPa with different numbers of CO fragments, not connected to the random network. We also found that the transition to the phases is irreversible which results in hysteresis loops. Random network structures obtained, say, under 18 GPa could exist at 3 GPa, whereas compression to 3 GPa results in the delta phase of CO crystal, with intact CO fragments and minor distortion of the cubic phase. To analyze the random structure fragments we calculated normal modes and IR intensities using the dipole approximation. Contributions from the main motifs of the random network are identified and compared with experimental IR measurements.

Modeling of free radical polymerizations of the liquid-crystalline monomer 6-[4-(4-heptyloxyphenylazo)phenoxy]hexylacrylate using the PREDICI software package is reported. The model accounts for all elemental reactions that were identified to be important for radical polymerizations of acrylate-type monomers. On the basis of butyl acrylate kinetic data a remarkable agreement between number average molar masses from modelling (M n,sim) and from experiments (M n,exp) is observed: M n,sim = 17800 g·mol−1 and M n,exp = 17400 g·mol−1. Similarly, dispersity values of 1.8 and 1.6 were determined via modelling and experiments, respectively. It is shown that the assumption of butyl acrylate kinetics provides a reasonable approximation even for acrylate-based monomers having mesogenic substituents.

Current energy demands and future energy needs are a growing industry which at present attracts a large amount of research and investment of which nuclear energy is an integral part. Eight new nuclear stations are proposed to be developed in the UK over the next ten years to meet this demand. In order for nuclear energy to sustain growth and development, nuclear decommissioning of first and second generation power stations needs to be addressed in the U.K. and worldwide. Presently the UK has 36 graphite moderated reactors as a result of the UK military and civil programs, which over the next twenty years will close. This will result in ∼99’000 tonnes of irradiated graphite waste for which no current national decommissioning strategy exists. The main issues associated with this waste are the large volume and activation products associated. By far the greatest inventory is from 3H and 14C. An EU Euroatom FP7 Program; CARBOWASTE was established in 2008 with the aim of developing treatment and disposal options for graphite.

This research is based within CARBOWASTE, the main objectives are to understand the mechanisms involved in the production, location and removal of radioisotopes from nuclear graphite. Computed X-ray Tomography (CT) will be used in order to quantify the initial porosity in conjunction with thermal treatment (ex situ) in order to eventually identify the location of 14C within the matrix of irradiated graphite, through the preferential chemically controlled oxidation of graphite. Unirradiated Pile Grade A graphite samples have been laser and manually marked in order align the samples prior to and post thermal treatment to determine the degree of porosity changes and weight loss under a range of thermal oxidation parameters.

In this work, we present a method able to fabricate thin GaN nanomembranes fit for device applications. Starting from commercial GaN on sapphire substrates, MBE was used to deposit a sacrificial layer, which comprises of a superlattice of InN/InGaN, after which thin a GaN film of hundreds of nanometers thickness was grown on top. Pulsed laser irridiation with photon energy of 2.3eV gives rise to the controlled decomposition of the sacrificial intermediate layer, which can be followed by easy separation of the top GaN membrane from the substrate. This process can be used to manufacture GaN membranes with low defect density and a wider range of thickness. We demonstrated that large area, free-standing GaN membranes, with a thickness from 200nm and up, could be made using this method, and the high crystal quality of the lift-off GaN layers is well preserved in this process.

Intermediate layers between silicon and borosilicate glass are investigated for compatibility with a diode laser crystallization technique for fabrication of thin-film polycrystalline silicon solar cells. SiCx, SiNx and SiOx layers or multilayer stacks of these materials have allowed silicon films of 10μm thickness to be successfully crystallized by diode laser irradiation without dewetting, with each option offering different advantages. SiCx allows the most robust crystallization process, while SiOx is the best barrier to contamination and the most stable layer. SiNx offers the best anti-reflection coating for superstrate configured solar cells. Presently, best device performance is achieved with a SiOxintermediate layer with cells achieving up to ∼540 mV open-circuit voltage.

In this paper, a simple process to fabricate free of disorder nanostructures, large area, flat and mechanically robust free-standing TiO2 nanotube (TNT) membranes was developed. Self-organized TNTs with ultrahigh aspect ratio (∼2000) were fabricated via anodization of Ti foil in fluorine containing ethylene glycol. Then by controlling the evaporation rate of rinsing solvent on the as-anodized TNT films in atmosphere, large area TNT membranes were self-detached uniformly from the metallic Ti substrate during the drying process. These free-standing membranes may exhibit many potential applications for optoelectronic devices.

To assist the precision and stability of wavelength at 1550 nm and 1300 nm in planar optical waveguides, hybrid semiconductor-metal corrugated gratings with nanometer period are integrated into silicon-based optical interconnects. This work utilizes multi-parametric optical waveguide models to compute the mode-coupling coefficients in the silicon photonic devices. For such a semiconductor-metal hybrid structure, a proper photonic technique needs to be utilized to solve this computational complexity. The optical method and the photonic method are used to compute coupling coefficients. Both methods have close numerical values shown in figures. Numerical results demonstrate how the normalized corrugation amplitudes of metal gratings can affect the coupling coefficients. Further physical interpretation and discussion can support and explain the above results. The modeling results can help engineers decide the values of parameters used in the design and fabrication of optical waveguides.

A crucial step in Dye Solar Cell (DSC) fabrication is the sintering of the TiO2 layer which needs to guarantee good electromechanical bonding between nanoparticles whilst maintaining sufficiently large porosity to yield performing devices. The standard procedure for TiO2 sintering requires firing in an oven at ∼ 500°C. An alternative procedure consists in utilizing laser scanning processing which has the advantageous potential of being noncontact, local, low cost, rapid, selective, automated and scalable. We analyzed and optimised a laser process for the sintering of the TiO2 layers in dye solar cells analyzing temperature profiles, throughput and the embodied energy. The development of electronic and photovoltaic devices on plastic substrates is of considerable interest due to the advantages they bring in terms of flexibility and easy processing for lightweight, low-cost large-area applications. An alternative sintering procedure compatible with flexible substrates and large area processing consists in utilizing a UV lamp. We subjected TiO2 pastes deposited on conductive transparent substrates to UV irradiation. Fully plastic devices fabricated through this method showed efficiencies of 4%.

In order to find an efficient method to etch nano-carbon materials by hydrogenation in a controlled manner, we have studied hydrogen-atom adsorption on various deformed nanotubes using computer simulations based on the density-functional theory. The nanotube with an atomic lack is compared to a deformed tube with the Stone-Wales defect and a twisted tube wall. Similar to the known experimental etching condition for graphene, an atomic lack is effective to accumulate hydrogen atoms around the defect. Compared to the flat graphene, however, nanotube walls with curvature allow on-top adsorption of a hydrogen atom and selectivity in the hydrogenated site becomes worse. To achieve a controlled etching process, usage of a tungsten tip which realizes focused hydrogenation is proposed for natotubes and curved graphene.

The fracture behavior of polypropylene (PP) and its composites was studied as a function of concentration of multiwall carbon nanotubes (MWCNT) and modified montmorillonite (m-MMT). SAXS and WAXS (Small/Wide Angle X-ray Scattering) techniques were used to monitor the morphological changes (i.e. nanocomposite structure and crystalline morphology) caused by various nanoparticle concentrations and polymer uniaxial stretching deformation. The effect of nanoparticle nature was also investigated. The mechanical analysis shows a great effect of nanoclay concentration on the PP deformation, while uniaxial stretching of the PP/MWCNT nanocomposites was less affected by carbon nanotubes concentration. The SAXS and WAXS analysis of stretched samples indicated that the pure polypropylene and nanocomposites with low nanoparticles concentrations (1 wt/wt%) developed a fracture governed by shear yielding mechanism, while PP nanocomposites with higher concentrations of carbon nanotubes and nanoclay showed a crazing and microcraking fracture mechanism. On the other hand, different chemical nature of MWCNT and m-MMT did not affect the fracture mechanism of polypropylene at low nanoparticles concentrations.

Polymer nanocomposites (PNC) are complex material systems in which the dominant length scales converge. Our approach to understanding nanocomposite tradespace uses Materials Quantitative Structure-Property Relationships (MQSPRs) to relate molecular structures to the polar and dispersive components of corresponding surface tensions. If the polar and dispersive components of surface tensions in the nanofiller and polymer could be determined a priori, then the propensity to aggregate and the change in polymer mobility near the particle could be predicted. Derived energetic parameters such as work of adhesion, work of spreading and the equilibrium wetting angle may then used as input to continuum mechanics approaches that have been shown able to predict the thermomechanical response of nanocomposites and that have been validated by experiment. The informatics approach developed in this work thus enables future in silico nanocomposite design by enabling virtual experiments to be performed on proposed nanocomposite compositions prior to fabrication and testing.

Carbon nanotubes (CNTs), nanofibers (CNFs) and graphene are promising components for the next generation high performance structural and multi-functional composite materials. One of the largest obstacles to create strong, electrically or thermally conductive CNT/CNF composites is the difficulty of getting a good dispersion of the carbon nanomaterials in a matrix. Typically, time-consuming steps of the carbon nanomaterial purification, ultrasound sonication and functionalization are required. We utilized a new approach to grow CNTs/CNFs directly on the surface of matrix, matrix precursor or filler particles. As the precursor matrix and fillers we utilized cement (clinker), copper powder, fly ash particles, soil and sand. Carbon nanomaterials were successfully grown on these materials without additional catalyst. Investigations of the physical properties of the composite materials based on these carbon modified particles revealed enhancement in the mechanical and electrical properties.

Pyrochlores based on the general composition CaLnZrNbO7 (where Ln = La, Nd, Sm, Gd and Ho) have been prepared, and irradiated through the crystalline-amorphous transition, with 1 MeV Kr ions at the IVEM-TANDEM user facility. The obtained critical temperatures show a decrease from La to Gd (∼680 K to ∼230 K), with Ho being resistant to amorphisation at 50K. The results suggest that the amorphisation cross section for these materials is directly related to the Ln component.

The kinetic arrest of martensitic transformation (MT) has been observed in as-solidified Ni52.2Mn34.3In13.5 melt spun ribbons. The main characteristics of this unusual field-induced magneto-structural phenomenon have been determined through a dc magnetization study. The sample studied was fabricated by rapid solidification using the melt spinning technique at a high quenching rate of 48 ms-1. At room temperature, it is a single phase austenite (AST) with the bcc B2-type crystal structure and Curie temperature of T C A =285 K. With decreasing temperature, the austenite phase transforms into the martensite phase (MST) with T C M ≈185 K at a starting martensitic transition temperature of M S =275 K. A moderate but progressive kinetic arrest of the AST to MST transformation has been observed for magnetic field values above H=10 kOe and was studied up to H max = 90 kOe. The metastable character of the non-equilibrium field-cooled state is revealed by the decreasing behavior of the saturation magnetization under a large magnetic field of 50 kOe after temperature cycling from 10 K to 150 K. The total magnetization difference Δσ between the zero field-cooling and field-cooling pathways of the temperature dependence of magnetization shows irreversible and reversible components and the former decreases with decreasing temperature.

A combined experimental and simulation approach into the impacts of electron irradiation on carbon nanotube morphology was conducted. Single-walled nanotubes (SWCNTs) were irradiated using a JEOL Transmission Electron Microscope (TEM) using a range of accelerating voltages varying from 90keV to 200keV and temperatures between 300K and 800K with different exposure periods (order of minutes). The effects of irradiation were observed and characterised using electron microscopy and Raman spectroscopy. Specimens were observed prior to, during and following irradiation to discern any changes that occurred in SWCNTs as a result of irradiation. Raman spectroscopy was used to characterise the different allotropes of carbon present in irradiated and non-irradiated samples of SWCNTs. Experimental conditions were mimicked using molecular dynamics simulation. SWCNTs were irradiated under conditions equivalent to experimental electron beam intensity and specimen temperature using AIREBO [1,2] and Primary Knock-on (PKA) approximation [3]. The preliminary results indicate that electron beam intensity and temperature affect the type and frequency of modification to CNT structure.

We use spectroscopic imaging to investigate the enhancement of infra-red to visible upconversion in rare-earth doped nano-particles (NaYF4:Yb:Er) supported on nano-fabricated plasmonic substrates consisting of square lattices of Au nano-pillars fabricated by electron beam lithography and designed to support a surface plasmon polariton at frequencies which are nearresonant with the rare-earth ion (Yb3+) absorption. We observe a systematic enhancement in the efficiency of upconversion associated with the interaction of the co-doped nano-particles with the plasmonic substrate. Spectrally-resolved imaging provides a massively parallel means of assessing the range of achievable enhancement and its relation to the specific configuration of the substrate / upconverting nano-particle system. Spectrally-resolved reflectivity of the plasmonic substrates confirms the role of the surface plasmon polariton in the upconversion enhancement. Experimental results are compared to Finite Difference Time Domain simulations of the frequency-dependent reflectivity of these metallic nanostructures.