Phosphorescent white organic light-emitting devices (WOLEDs) with a multilayer structure were fabricated, and colour stability was studied by manipulating electron transport property of the hole-blocking layer 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBi) and the electron transporting layer 4,7-diphenyl-1,10-phenanthroline (Bphen). With 20 nm thick TPBi and 20 nm Bphen tailoring electron transport, the WOLED yielded a slight Commission Internationale de l’Eclairage coordinates variation of (−0.003, 0.007) in a wide range of bias voltages. Additionally, a peak current efficiency of 32.4 cd/A and a peak external quantum efficiency of 12.7% were also realised. It was found that the enhancement of colour stability was due to optimisation of the electron transport, by adjusting the thicknesses of TPBi and Bphen to improve the charge carrier balance.

We report the charge generation layer (CGL) structure comprising of Li2CO3 doped bathocuproine (BCP:Li2CO3)/MoO3 doped 4,4-N,N-bis [N-1-naphthyl-N-phenyl-amino]biphenyl (NPB:MoO3)/MoO3 doped 4,4′-N,N′-dicarbazole-biphenyl (CBP:MoO3) for tandem organic light emitting diodes (TOLEDs). Compared to the TOLED using the conventional CGL structure of BCP:Li2CO3/20 nm CBP:MoO3, the one using the CGL structure of BCP:Li2CO3/5 nm NPB:MoO3/15 nm CBP:MoO3 showed increased electrical and luminous properties, mostly because the introduction of the higher-conductivity NPB:MoO3 relative to CBP:MoO3 could improve the current conduction in the CGL structure. Whereas, the performance of the CGL structure of BCP:Li2CO3/x nm NPB:MoO3/20- x nm CBP:MoO3 decreased with x increasing, mostly due to the fact that the CBP:MoO3 became depleted of mobile holes upon contacting p-doped NPB: the smaller thickness of CBP:MoO3, the worse conductivity for it. We provide some in-depth insights on designing the high-performance CGLs for TOLEDs.

The influence of precursor medium was investigated on the structural, morphological, optical and electrical properties of spray pyrolysis deposited nanostructured ZnO thin films. Three batches of ZnO thin films were deposited on glass substrates using three different solvents (water, water-ethanol [ratio of 1:1] and ethanol) based precursor solution of zinc nitrate hexahydrate. The substrate temperature was fixed at 523 K. The variation in film thickness from 150 to 875 nm was observed as the effect of changing solvent medium. X-ray diffraction (XRD) data confirmed the formation of polycrystalline ZnO thin films with hexagonal wurtzite crystallite structure and the estimated crystallite size was found to be ranging from 31 to 55 nm. Scanning electron micrographs revealed the formation of water-hyacinth shaped nanostructures when water-ethanol mixture was used as the solvent medium. Interestingly, UV-vis spectrophotometer revealed the formation of ZnO film with twin optical band gap of 3.15 eV and 3.56 eV when ethanol was used as the solvent medium. The modulation of film thickness and grain size by solvent medium has strongly influenced the electrical conductivity of ZnO thin films. The homogenous nano-spherical grains with uniform grain boundaries showed a good response towards 100 ppm of ammonia at room temperature.

The emission of aligned dichroic dyes in a luminescent solar concentrator (LSC) illuminated from one side with collimated light results in a non-isotropic light distribution. We develop a model to describe emission profiles for dichroic dyes aligned at a general tilt angle with respect to a lightguide surface (including planar and homeotropic alignments) for various order parameters. We compare calculations with experimental results, demonstrating the dichroic nature of the dyes can have significant impact on the surface loss of luminescent solar concentrators. Including this dichroic nature is essential in correctly simulating the preferred edge emissions demonstrated experimentally in dyes aligned planarly on the surface of a lightguide.

The effect of electron beam irradiation of stoichiometric hydroxyapatite (Ca10(PO4)6(OH)2, HAP) is investigated using electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) mode equipped with a LaB6 gun. Initial irradiation at 160 A cm−2 dose rate shows no modification of the low loss spectra. No difference of mass loss for Ca, O and P is observed for two different probe diameters: 4 nm (dose rate = 160 A cm−2) and 24 nm (dose rate = 70 A cm−2). Furthermore no formation of CaO is observed for both experimental conditions. It is proposed that the low values of both electron dose rates and doses (from 350 to 2400 C cm−2) avoid mass loss. At the higher dose rate obtained with a field emission gun (FEG), transformations are observed for the lowloss signal as well as for the Ca, P and O signals. These results might be very useful for the future studies of apatite particles at the nanoscale.

The characteristic parameters of initiating defects in HfO2/SiO2 high-reflector film at wavelength of 1064 nm are investigated through the combined application of laser-conditioning process and the multispot damage threshold test. The laser damage tests before and after laser-conditioning are carried out within three different spot diameters. The damage threshold and the density are considered to characterize the initiating defects which are shown to be susceptible to laser damage. These characteristic parameters are obtained through fitting the damage data with the spot size effect. The influence of laser-conditioning effect on the initiating defects is analyzed. The initiating defects are specified by a Gaussian distribution after laser-conditioning. It is discussed the essential roles of the initiating defects to the damage threshold of the film. The investigation on characteristic parameters of initiating defects has potential to be applied in the mechanisms of laser induced damage and laser-conditioning, as well as in the direction the preparation of the films.

We reported material characterization of the nano-structured TiO2 thin films prepared by the sol-gel dip-coating process on glass substrates. The dependence of the structural, morphological and optical properties of the synthesized films on the fabrication parameters such as withdrawal velocity and annealing temperature were investigated by the techniques of X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-visible spectrophotometry. The results indicate that for the TiO2 films annealed at 500 °C there exhibits (1 0 1) XRD peak corresponding to the anatase phase of TiO2. The latter is consistent with the recorded Raman signal observed at 142 cm-1 (Eg mode) and 391 cm-1 (B1g mode), respectively. From the analyses made on the SEM micrographs and AFM images, it was revealed that the morphology and surface roughness of the thin films would depend on the withdrawal speed and the heat treatment temperature. The UV-visible spectroscopy analyses show that all the films were transparent in the visible region with an average transmittance of more than 70%. With an increase on the dip-coating speed from 1 cm/min to 3 cm/min, we observed a spectral red shift of the absorption edge from 3.76 eV to 3.71 eV, indicating a decrease in the bandgap energy (Eg) of the films.

AlInN thin films were synthesized on Si substrates by using stacked elemental layers (SEL) technique. Three stacking sequence Al/InN, Al/InN/Al/InN and Al/InN/Al/InN/Al/InN were prepared on Si (1 0 0) substrates by reactive RF sputtering of In target in Ar-N2 and DC sputtering of Al target in Ar atmosphere at room temperature. Annealing of the deposited stacks was carried out at 400 °C for 6 h in a three zone tube furnace. Structural properties of the annealed films were investigated using X-ray diffraction (XRD) whereas the surface analysis of the films was carried out using field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). XRD results show the formation of wurtzite AlInN thin films which become more obvious with increasing the stacked layers. FESEM analysis reveals drops-like polycrystalline films structure with randomly oriented grains whereas the AFM results show a decrease in the surface roughness with increasing stacking sequence. The formation of more prominent AlInN films with increase of stacking layers is attributed to a uniform interaction among the top and bottom Al and InN multilayers as a result of the annealing.

In the present work, we have studied the effect of impurity position on energy levels, the donor binding energy and third harmonic generation of a pyramid and a cone like quantum dot. For this goal, we have calculated the energy levels, wave functions and binding energy using finite element method for various impurity positions. Our results show that the impurity location plays an important and considerable role in the electronic and optical properties in a pyramid and a cone like quantum dot. We found that the third harmonic generation and binding energy of both quantum dots have a maximum value at a special impurity position. The special impurity location is different for the two quantum dots. Also, we have deduced that the third harmonic generation of a cone like quantum dot is larger than a pyramid quantum dot for same volumes and heights.

Using the first-principles calculations based on the spin-polarized density functional theory (DFT), we investigated the structural, electronic and magnetic properties of Cu-doped single walled ZnO nanotubes (SWZnONTs). Our results show that for a unit cell with 40 Zn and 40 O atoms, substitution of a single Zn atom by a Cu leads from a semiconductor to a ferromagnetic (FM) half-metallic phase transition with 100% spin polarization. In this case the total magnetic moment of super cell is 1.0 μB. To investigate the effects of Cu-codpoed SWZnONTs two different configurations are considered, first we assumed the two Zn atoms replaced by two Cu atoms are close and second they are far from each other. When Cu atoms are at the nearest-neighboring positions, the antiferromagnetism (AFM) phase is stable, while increasing the distance between the two Cu atoms, the ferromagnetism stability increases. In the AFM phase the structures are nonmagnetic semiconductors, but in the FM phase all these systems are half-metallic systems with 100% spin polarization, so it can be used as magnetic nanostructure and future applications in permanent magnetism, magnetic recording, and spintronics.

Hydrogen doping in the bulk of anatase TiO2 was studied by density functional theory approach. Our results show that hydrogen atom prefers the interstitial sites which are closer to the oxygen atoms. Investigation of the electronic structures of different hydrogen doped systems indicates the increment of Fermi energy and bond length, affecting the instability of the system. Hydrogen doping in the anatase TiO2 structure injects electron in the lower region of the conduction band, around the Ti states, leading Ti4+ toward Ti3+, while having no effect on the band gap energy value of TiO2. Therefore, the observed hydrogen induced band gap narrowing in TiO2 samples could be due to the structural disorders generated in the hydrogenation process. The hydrogen storage capacity of approximately 3 H atoms per supercell (Ti32O64) is also obtained, which is promising for renewable energy storage issue.

SnO2-Fe2O3 composite thin films were deposited on quartz substrate at 650 °C by pulsed laser deposition with Fe2O3 content varying between 0 and 50 wt.%. The effect of increasing Fe2O3 content on structural, optical and electrical properties of SnO2-Fe2O3 films were investigated. X-ray diffraction analysis indicates that the nature of deposited composite films can be tune from crystalline to amorphous with increase in the Fe2O3 content. X-ray photoelectron spectroscopy studies confirm the presence of SnO2 and Fe2O3 in the microstructure. Atomic force microscopy studies of the deposited films indicate that RMS roughness vary between 114.4 and 1.48 nm. The average optical transmittance decreases from 92 to 72% with increasing Fe2O3 content of the deposited films. The optical bandgap was decreased from 3.69 to 3.31 eV with increase in Fe2O3 content. The minimum resistivity was observed 3.71 × 10−2 Ω cm for the 30 wt.% Fe2O3 composite film. The low resistivity and high transmittance in the visible region enables these films suitable for optoelectronic applications.

The dynamical processes of a low-energy carbon ion collision with the graphene sheet supported by diamond at three impact positions are studied by using empirical potential molecular dynamics simulations. The energy transformation and the structural evolution have been studied. Five types of processes are observed: adsorption, hybridization, defects formation in diamond, atom emission and transmission. We find that the irradiation damage is closely related to the incident energy and impact position. In our simulations, as the projectile collides at a graphene atom, it transfers most of its energy to the primary knock-on atom, and defects are created in graphene. When the projectile moves perpendicular towards the center of a C-C bond in the graphene sheet, the energy transferred from the projectile to the atoms associated with the bond increases firstly and then decreases with the increasing incident energy, and the graphene sheet remains two-dimensional crystal structure after collision when the incident energy is larger than 360 eV. While the impact location is the center of a hexagonal ring on the graphene sheet, the energy transferred from the projectile to the atoms of the target ring is very small regardless of how large is the incident energy, and the graphene sheet is able to keep perfect crystal structure when the incident energy is larger than 34 eV.

Pb1-xSnxS nanopowder with different Sn concentrations (x = 0.02, 0.05, 0.10, 0.20, 0.50 and 1.00) were synthesized by chemical precipitation route under N2 atmosphere. The samples were characterized by X-ray diffraction(XRD), UV-vis absorption spectra and photoluminescence (PL) spectra. The XRD results show that the samples with 0 ≤ x ≤ 0.2 have cubic (fcc) structure with diameter in the 12.8–24 nm range. The sample with x = 0.5 has orthorhombic structure with a diameter of 9.2 nm. The band gap (or absorption edge) of PbS exhibits a large blue shift when the crystallite size is reduced to nanometer scale, from 0.4 eV in bulk samples to 1.8 eV in nanosize samples, which can be related to large Bohr excitonic radius of PbS nanoparticles. PL emission spectra of Pb1-xSnxS in red region excited at 315 nm, for x = 0 showed three broad peaks located at 776.5 nm, 809 nm and 826 nm which due to the defect densities and for x = 0.02, 0.05, 0.10 there are two relatively strong emission peaks located at 786 nm and 823 nm which can be related to transition from sulfur vacancy level and Sn+2 ion level respectively.

ZnO nanopowders with different 3d transition metal (TM) doping (TM = Mn, Fe, Co, Ni) were synthesized by a new protocol based on slow hydrolyse of zinc acetate dissolved in methanol and supercritical drying in ethyl alcohol. The prepared Zn1−xTMxO (x = 0.25) nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), optical absorption and electron paramagnetic resonance spectroscopy (EPR). The results demonstrated that the TM dopant significantly affects the structural and magnetic properties of the samples. From the XRD spectra, the lattice parameters, average crystallite size and microstrain values were obtained. All ZnTMO nanoparticles show an expansion of the lattice parameters compared those of the bulk samples. Unit cell volume was minimized with Fe doping and increased as the atomic number of the dopant moved away from Fe. The XRD pattern indicates the formation of hexagonal wurtzite phase of ZnO for all the TM dopants. Electron microscopy characterization showed that the size of the Zn1−xTMxO particles is about 25 nm did not change significantly for the different dopants. Optical absorption measurements show that band gap energies of the TM-doped ZnO nanoparticles are around 3.2 eV. The Urbach energy of the ZnTMO nanopowders varies with the TM dopant. From magnetic measurements we observed the presence of room temperature ferromagnetic order in our TM-doped ZnO samples. EPR spectra confirm that TM ions were mainly incorporated as TM2+, occupying the Zn2+ sites in the wurtzite structure of ZnO. Room temperature ferromagnetic order was observed only in Ni- and Co-doped ZnO samples, whereas Mn- and Fe-doped powders showed only antiferromagnetic and paramagnetic interactions, respectively. The correlation between the structural and magnetic properties as a function of the TM dopant is discussed.

We propose a comprehensive description of the strain configuration induced by the lattice mismatch in a core-shell nanowire with circular cross-section, taking into account the crystal anisotropy and the difference in stiffness constants of the two materials. We use an analytical approach which fully exploits the symmetry properties of the system. Explicit formulae are given for nanowires with the wurtzite structure or the zinc-blende structure with the hexagonal/trigonal axis along the nanowire, and the results are compared to available numerical calculations and experimental data on nanowires made of different III–V and II–VI semiconductors. The method is also applied to multishell nanowires, and to core-shell nanowires grown along the 〈0 0 1〉 axis of cubic semiconductors. It can be extended to other orientations and other crystal structures.

In order to improve the utilisation and performance of anode catalysts in direct methanol fuel cells (DMFCs), functionalised multi-walled carbon nanotubes (MWCNTs) are used as a support for palladium (Pd) nanoparticles synthesised by photochemical reduction. MWCNTs are modified by methylene blue (MB) under ultraviolet light (fuv-MWCNTs), and then Pd nanoparticles are assembled on the fuv-MWCNTs to form composites (Pd/fuv-MWCNTs). The method is green, simple and does not destroy the pristine structure of the MWCNTs. The morphology and structure of prepared composites are characterised by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that Pd nanoparticles with face-centred cubic crystal structure are about 3.9 nm in size, and are uniformly dispersed on the surface of fuv-MWCNTs. X-ray photoelectron spectroscopy (XPS) reveals that N-containing and S-containing groups exist in fuv-MWCNTs. These groups might be active sites for assembly of Pd nanoparticles on the surface of fuv-MWCNTs, and can modify the electronic structure of Pd nanoparticles. Electrochemical experiments indicate that the prepared Pd/fuv-MWCNTs catalyst exhibits excellent catalytic performance. The catalytic activity of Pd/fuv-MWCNTs is 1.94 times higher than that of commercial Pd/C for methanol oxidation in alkaline solution. It indicates that UV irradiation can facilitate MB to functionalise MWCNTs, reinforce the modification of the electronic structure of Pd, and enhance the catalytic activity of Pd/fuv-MWCNTs.

Crystallization of Lennard-Jones nanoparticles has been studied by molecular dynamics (MD) simulations. Spherical models with free surface are cooled from the melt to crystalline state. In the cooling process, thermodynamics, structural properties and atomic mechanism of the crystallization are investigated. We found that crystallization in nanoparticles follows the Ostwald’s step rule like that found in the past. Due to free surface contribution, the solidification exhibits non-homogeneous behavior which proceeds in different manners between core and surface: homogeneous crystallization in the core and heterogeneous one in the surface layer of nanoparticles. It is due to the discrepancy between structures of two parts: highly ordered structure dominates in the core region while the surface exhibits defective one with a high fraction of undercoordinated sites. Also, our results are consistent with previous ones about the free surface-induced phenomena.

The geometries, binding energies, electronic structures and magnetic properties of TMCn clusters (TM = Fe, Co, Ni, n = 9–15) have been systematically investigated with the generalized gradient approximation (GGA) based on all-electron density functional theory. Optimization results indicate that TMC9 clusters prefer linear structures with the TM atom at one end, while monocyclic planar structures are predicted to be the most favorable for TMCn (n = 10–15) clusters. The calculated second-order energy differences and fragmentation energies indicate that the magic numbers for stability appear at n = 10, 12, 14 for FeCn, and n = 11 and 14 for CoCn and NiCn, implying that these clusters possess relatively higher stability. Mülliken population analysis shows that charge always transfers from the TM atoms to C atoms. The magnetic moment of TMCn clusters mainly is located mainly on the TM atom. The 3d electrons in the TM atom play a dominant role in the determination of the magnetism of the TM atom.

In this work, optical properties of colloidal silica crystals are investigated theoretically. Numerical calculations are discussed and compared to experimental measurements. The existence of photonic band gap (or stop band) is inferred by analyzing the transmission spectra and dips of low transmission are typically correlated with photonic band gaps. The position of the main dip in simulated spectra matches the pseudo photonic band gap expected by the calculated photonic band gap diagram. Positions of stop band show a strong dependence on the diameter of silica spheres. We note that positions of the main dips deduced from simulated and measured spectra are very near. Good agreement between measured and theoretical results is then reported.