We prepare Nd-Bi codoped zeolites by a method consisting of a simple ion-exchange process and subsequent high-temperature annealing. The emission covers the range of 970∼1450 nm, corresponding to the electronic transitions of Nd3+ ions and Bi-related active centers (BiRAC), respectively. The introduction of Bi distinctly broadens the excitation band of Nd3+ in the visible region, and the lifetime of Nd3+ reaches as long as 354 μs. In the zeolite matrix, Bi ions exist as BiRAC and Bi oxide agglomerates. The former one act as a sensitizer of Nd3+ ions, and the latter one act as a blockage to avoid the quenching effect of coordinated water, which enable Nd3+ ions to show efficient near-infrared (NIR) emission even the zeolites contain large amount of coordinated water. The excellent optical and structural properties make these NIR emitting nanoparticles promising in application as laser materials and biological probes.

Molecular dynamics simulations were performed to estimate sequence dependentforce required to stretch single stranded DNA (ssDNA) homo oligonucleotides.Simulations suggest that polyA and polyC oligonucleotides exhibit similarforce profiles and corresponding elongation. Among single stranded DNAstrands polyT is the most flexible and needs the most force to unwind froman equilibrium folded structure. In contrast, polyG had a very smallrecoverable deformation prior to a non-linear stretching. Our resultsindicate that mechanical properties of ssDNA chains are directly related totheir sequence.

Metal-free and Au-catalyzed silicon nanowires (Si-NWs) grown at low temperatures have been analyzed through transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and their crystalline phase studied. All the observed nanowires are crystalline, grow along two different directions, <110> or <112>, and contain high density of planar defects, such as stacking faults (SFs) and twins. The defect size is comparable to the wire diameter for the metal-free process whilst it is much larger than the wire diameter for the Aucatalyzed Si-NWs. In this latter case parallel SFs may re-arrange and transform in a metastable rhombohedral 9R polytype structure whose formation mechanism is discussed.

In this study, we investigated the effects of DNA/Pt-DNA strands as hole collecting layers in polymer heterojunction solar cells based on ITO/PEDOT:PSS/P3HT:PCBM/LiF/Al structure. We demonstrated that by introducing DNA or Pt-DNA layers between the polymer electrode (PEDOT:PSS) and the active layer (P3HT:PCBM), lead to an improvement in the hole collection efficiency and power conversion efficiency and the absorbance spectra of the devices indicate that Pt particles work as surface plasmons and increase the absorbance of the devices.

A method to calculate the multiplet states of lanthanide impurities in solids is presented. This approach is based on a semi-empirical density functional method which includes corrections to account for the correlation and spin-orbit coupling of the 4f electrons. Specific multiplet states of the rare earth are produced by constraining the system. This approach is then used to investigate some of the properties of substitutional europium impurities in gallium nitride, reproducing the relative energy of two multiplets, and discussing a potential excitation mechanism for these centers.

Spectroelectrochemical study on a new absorption band of radical cations of4,4’-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (α-NPD) as anelectron-donor hole-transporting material used in organic electronics isreported in this work. UV-visible spectroscopic and cyclic voltammetricproperties for α-NPD in solution are also examined. We find that the resultsare attributed to quenching process for blue fluorescence from α-NPD byexcess α-NPD+ radical cations accumulated in the emission regionin the organic light-emitting devices related to a relatively large overlapbetween the fluorescence spectrum of α-NPD and the absorption spectrum of α-NPD+ radical cations. The band gap energy for α-NPD iscalculated from the UV-visible spectroscopic data.

The co-doping of hexagonal GaN with Er and O is investigated by means of density functional calculations. Predominantly Er-O defect-pairs characterized by a binding energy around 0.5 eV are formed. Different geometric configurations with various orientations (i.e. axial and basal pairs with C3v or C1h symmetry) are expected with similar formation energies. Independent of the particular configuration, the presence of oxygen does not deeply affect the atomic structure and the electronic charge distribution around the Er centers. The relatively high binding energy suggests that Er-O pairs should survive thermal treatment. An investigation of the binding energy per bond indicates that on the other hand Er-Ox complexes (x=2,3,4) are not likely to be formed (differently from Er-O co-doped Si). Rather, as long as the oxygen fluence does not overtake the Er fluence, different oxygen ions will be bound to different Er-centers.

Gravure contact printing is the highest volume, large area printing technique known. It is ideally suited for the fabrication of large-area polymer light emitting diode (PLED) based lighting, backlights and displays. Here we show how gravure can be used to fabricate the poly (3,4-ethylene dioxythiophene) : poly(styrene sulfonate) hole injection layer and the light emitting polymer emissive layer in a conventional PLED, as well as the cesium carbonate electron injection layer in an inverted PLED. The performance equals or exceeds that of devices where these layers are deposited by conventional spin-coating.

STM studies reveal that irregular non-equilibrium two-dimensional Al islands form during deposition of Al on NiAl(110) at 300 K. These structures reflect the multiple adsorption sites and diffusion paths available for Al adatoms on the binary alloy surface, as well as the details of inhibited edge diffusion and detachment-attachment kinetics of Al adatoms for numerous distinct step edge configurations. We attempt to capture these features by multi-site lattice-gas modeling incorporating DFT energetics for adatoms both at adsorption sites and transition states. This formulation enables description and elucidation of the observed island growth shapes.

We develop a novel patterning technique to create 3D patterns of micro, nanoparticle assembly via evaporative self-assembly based on confinement/release of micro/nano particles assembly based on the coffee-ring effect of evaporating suspension. Based on the presented technique, we demonstrate that the patterns of 3D assembly of various sizes of microparticles (Silica), metal oxide nanoparticles (TiO2, ZnO) and metallic nanoparticles (Ag) can be successfully generated by low-concentrated particle suspension (1.25 wt % ~ 5 wt %) without additional sintering steps and we also show the geometries of the patterns can be finely controlled by adjusting the parameters of the process.

Non-destructive Raman spectroscopy was applied to three kinds of porcelain glaze samples: (i) Guan wares of Song Dynasty; (ii) Imitated Guan wares; (Both (i) and (ii) are from the Palace Museum (Beijing, China) collections); (iii) Porcelain shards are collected from the Xiuneisi kiln site which is one of two excavated Guan ware imperial kilns in Hangzhou, the capital of the Southern Song Dynasty. Raman spectra of the glassy phase network were used to discuss the composition and firing temperature of the glaze. The index of polymerization (Ip) is strongly correlated with the firing temperature and the composition of the glaze. According to the Ip values of the glaze, those Guan wares (i) can be classified into three groups. The provenance of Guan wares (i) was discussed by comparing the Ip values to imitations (ii) and shards(iii). The study of classification and provenance are also supported by the X-ray fluorescence data. The Ip values of several recently prepared glazed samples of known firing temperature were measured to build empirical relationship between the Ip value and the firing temperature. Based on the relationship, the firing temperature of the Guan ware glazes was at 1170-1300°C.

Silver can be used as the back contact and reflector in thin film silicon solar cells. When deposited on textured substrates, silver films often exhibit reduced reflectance due to absorption losses by the excitation of surface plasmon resonances. We show that thermal annealing of the silver back reflector increases its reflectance drastically. The process is performed at low temperature (150°C) to allow the use of plastic sheets such as polyethylene naphthalate and increases the efficiency of single junction amorphous solar cells dramatically. We present the best result obtained on a flexible substrate: a cell with 9.9% initial efficiency and 15.82 mA/cm2 in short circuit current is realized in n-i-p configuration.

A study is presented on the morphology and electric properties of heavily boron-doped nanocrystalline diamond (B:NCD) thin films (≈150snm) grown with two different C/H-ratios (1% and 5%) and a fixed 5000sppm B/C-ratio in gas phase on fused silica substrates. AFM measurements confirm that a higher C/H-ratio leads to smaller grains and more grain boundaries. Electric transport measurements reveal a higher resistivity and a lower mobility as function of the C/H-ratio for all temperatures measured. The resistivity of the 1% sample is almost not temperature dependent while the 5% sample is much more temperature dependent. The electric transport properties of the grain boundaries, more present in the 5% sample, can be responsible for the difference in transport properties of both samples. The active boron concentration, calculated from the electric transport measurements, is remarkably higher for the 5% sample which indicates there is more boron incorporation for higher C/H-ratios. Although both samples are disordered metals, the 1% sample with the least grain boundaries tends more to the behavior of a highly doped single crystalline diamond film, which behaves like a real metal when heavily boron-doped.

Systematic studies have been conducted on the electrical characteristics of poly(3-hexylthiophene)-based organic thin film transistors (OTFTs). The OTFTs have been characterized at low-operating voltages and deductions have been made regarding the current modulation mechanisms involved. Irreproducibility of transfer characteristics in these devices beyond a certain gate voltage, as well as a slow time-dependant component to drain current at certain gate voltages, indicates electrochemical changes occurring in the device during operation. It is hoped that this work can help to improve the understanding of OTFTs of this type and, in turn, their performance in the future.

Using molecular dynamics (MD) simulation, we investigated the mechanical properties of graphene and graphite, which contain cluster-type vacancies. We found that as the vacancy size increases, the tensile strength drastically decreases to at least 56% of that of pristine graphene, whereas Young’s modulus hardly changes. In vacancy-containing graphene, we also found that slip deformation followed by fracture occurs under zigzag tension. In general, tensile strength decreases as the size of cluster-type vacancies increases. However, the tensile strength of graphene with a clustered sextuple vacancy increases as the vacancy disappears because slip deformation proceeds. Furthermore, we found that slip deformation by vacancies in graphite occurs less easily than in graphene.

Our results suggest that the shape of vacancies affects the strengths of graphene and graphite.

The formation of carbon nanostructures using silica nanoparticles from quartz substrates as a catalyst in an aerosol assisted chemical vapor deposition process was examined. The silica particles are reduced to silicon carbide via a carbothermal reduction process. The recyclability of the explored quartz substrates is also presented. The addition of triethyl borate improves the efficiency of the carbothermal reduction process and carbon nanotubes formation. Moreover, the addition of hydrogen during the chemical vapor deposition leads to the helical carbon nanostructures formation.

Hybrid piezoelectric composites were obtained by embedding barium titanate (BTO) nanofibers into a polyvinylidene fluoride (PVDF) matrix. Green BTO fibers were obtained by electrospinning a precursor polymeric solution under an electric field of 1 kV/cm. A network of non-woven ceramic BTO fibers was obtained after calcination of the green fibers. A PVDF solution was deposited over the ceramic fibers by spin-coating and then subjected to a low temperature heat treatment, to evaporate the solvent and promote the crystallization of the polar beta phase of PVDF.

In average, the diameter of the ceramic fibers ranged from 105 to 225 nm, presenting ribbon-like shape in some cases. Crystalline phases of BTO and PVDF were confirmed by X-ray diffraction and infrared spectroscopy, respectively. Polarization hysteresis curves revealed a ferroelectric behavior in all samples.

The most frequently used characterization technique for biaxial texture formation in thin films is x-ray pole figure analysis. However, x-rays interact weakly with matter and can penetrate a few microns deep into the film. The texture obtained by x-rays is therefore an average texture from the entire thickness of the film. As the texture of a film often changes during growth, information on the basic mechanisms that control the final texture is often lost. In contrast electrons interact strongly with matter and they have very limited penetration and escape depths of a few nm. In this paper we will show how we can use our newly developed reflection high energy electron diffraction (RHEED) surface pole figure technique to probe the surface texture evolution of the growth front from the initial stage (nm thick) to the later stage. The RHEED pole figure technique is a surface-sensitive technique that allows us to obtain information on the dynamic behavior of texture evolution of the growth front during film deposition. We shall explain the principle, measurement, and construction of such RHEED surface pole figures. An example of the biaxial texture evolution of CaF2 due to the atomic shadowing effect during oblique angle deposition is described.