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The van der Waals-London dispersion (vdW-Ld) spectra are calculated for the [9,3,m] metallic and [6,5,s] semiconducting single wall carbon nanotubes (SWCNTs), graphite, and graphene (a single carbon sheet of the graphite structure) using uniaxial optical properties determined from ab initio band structure calculations. The [9,3,m], exhibiting metallic optical properties in the axial direction versus semiconducting optical properties in the radial direction, highlights the strong anisotropic nature of metallic SWCNTs. Availability of both efficient ab initio local density band structure codes and sufficient computational power has allowed us to calculate the imaginary parts of the frequency dependent dielectric spectra, which are then easily converted to the required vdW-Ld spectra for Hamaker coefficient calculations. The resulting Hamaker coefficients, calculated from the Lifshitz quantum electrodynamic theory, show that neither graphite nor graphene are accurate model materials for estimating the Hamaker coefficients of SWCNTs. Additionally, Hamaker coefficients were calculated between pure radial-radial, radial-axial, and axial-axial components of both SWCNTs. Analysis of these coefficients reveals that the vdW-Ld interactions will depend on both chirality and the particular orientation between neighboring SWCNTs. The minimization of energy, with respect to orientation, predicts that vdW-Ld alignment forces will arise as a result of the anisotropic optical properties of SWCNTs. [ABSTRACT FROM AUTHOR]

Working at the macroscopic continuum level, we investigate effective van der Waals interactions between two layers within a multilayer assembly. By comparing the pair interactions between two layers with effective pair interactions within an assembly we assess the significant consequences of nonadditivity of van der Waals interactions. This allows us to evaluate the best numerical estimate to date for the Hamaker coefficient of van der Waals interactions in lipid-water multilamellar systems. [ABSTRACT FROM AUTHOR]

Valence electron-energy loss spectroscopy (VEELS) in a dedicated scanning transmission electron microscope, vacuum ultraviolet spectroscopy and spectroscopic ellipsometry, and ab initio band structure calculations in the local density approximation have been used to determine the optical properties and the electronic structure of SrTiO[sub 3]. Assignments of the interband transitions in the electronic structure of bulk SrTiO[sub 3] have been determined quantitatively by comparison of VEELS spectra with vacuum ultraviolet spectra and with the ab initio calculated densities of states. The experimentally determined indirect band gap energy is 3.25 eV, while the direct band gap energy is 3.75 eV. The conduction bands in SrTiO[sub 3] correspond to the bands composed of mainly Ti 3d t[sub 2g] and e[sub g] states, followed at higher energies by the bands of Sr 4d t[sub 2g] and e[sub g] states, and free electron like states dominating at energies above 15 eV. The upper valence band (UVB) contains 18 electrons in dominantly O 2p states, hybridized with Ti and Sr states, and has a bandwidth of 5 eV. The interband transitions from the UVB to the Ti 3d bands and to the Sr 4d bands give rise to the transitions spanning from the indirect band gap energy of 3.25 eV up to 15 eV. The lower valence band contains 12 electrons in Sr 4p and O 2s states which are separated by 2 eV, while having a bandwidth of 5 eV. The interband transitions from the Sr 4p to the Ti 3d and Sr 4d bands give rise to transition energies spanning from 15 to 24 eV. Interband transitions from the O 2s band to the conduction bands appear at 26 eV. A very narrow band at -33 eV below the top of the valence band is composed of Sr 4s and Ti 3p states and contains eight electrons. [ABSTRACT FROM AUTHOR]

When film coatings are made of pigment particles embedded in a transparent resin, the optical characteristics of the resulting film are determined not only by the bulk optical properties of the constituent materials, but also by the spatial distribution of the light scattered from small particles. If the particles are separated by distances comparable to their diameter, as is the case for high particle concentrations or agglomerated systems, the near-field interactions between the radiation fields of the particles can strongly influence the resulting far-field intensity distribution. In this work we have used full-field finite-element solutions of Maxwell's equations to calculate the near- and far-field scattering patterns for single 500 nm quinacridone spheres and for pairs of particles. We find that the scattered intensity forms a forward-directed plume that extends far beyond the particle surface, especially at short wavelengths and where the absorption is large. This results in near-field interactions between pairs of particles that can either increase or decrease the scattering (both the total scattering and the fraction of the scattered light that is directed into the backward hemisphere), depending on the orientation of the particle pair relative to the direction of the incident light. In some cases, particularly if the particles are aligned along the incident direction, the two spheres can produce a far-field scattering distribution that is approximately that of a single, larger (sometimes much larger) sphere. If the particles are aligned perpendicular to the incident direction, the strength of the scattering per particle volume is roughly the same as for a single particle, but the scattering is more forward directed. These interaction effects occur even though the surface-to-surface separation of the particles is larger than the distance for which a single particle shows significant scattered intensity. These near-field and far-field phenomena are... [ABSTRACT FROM AUTHOR]

In the optical analysis of collections of particles embedded in a matrix, the ultimate goal is to predict the optical properties of the final film, given the optical characteristics of the materials of which it is made, the particle size, and the fraction of the volume occupied by the particles. The first task in the pursuit of this goal is to make connections between the optical properties of the bulk materials of which the particles and medium are made and the spatial distribution of the scattered intensity from the individual particles. The second is to relate the calculated far-field scattering and absorption cross sections for a single particle to the measured optical characteristics of real films. Here we accomplish these tasks for a regime that is rarely considered in the literature but is quite important in applications. This regime is characterized by three conditions: (a) the extinction coefficient of the particle is significant; (b) the particle size is comparable to the wavelength in the medium; and (c) the optical density of the films is large enough that multiple scattering is significant, and yet direct transmission of collimated radiation through the film is not negligible. We have measured the visible diffuse reflectance and transmission of films of quinacridone particles in a transparent resin at various particle volume concentrations, and used the Kubelka-Munk formalism as a parametrization method to extract scattering and absorption parameters for this strongly absorbing, multiple-scattering system in the resonant regime. We have modeled the scattering parameter S[sup *] as a convolution of the angular distribution of the scattering from a single particle (derived from Mie theory) and a multiple-scattering function that characterizes the effects of the concentration and arrangement of the particles in the film. We find that the multiple-scattering function has an angular distribution that is strongly peaked in the backscattering directi... [ABSTRACT FROM AUTHOR]

Presents a photoelectron spectroscopy study of the interaction of copper with Al[sub2]O[sub3] and AIN model systems processed under ultrahigh vacuum conditions and compares the intrinsic electronic interactions between the two cases. Evolution of the electronic structure and bonding of copper to AIN; Indication of the binding energy shift and line shape change of the aluminum core levels.

Presents a study which measured the hamaker constants and dispersion forces interactions of materials of increasing interest and the advent of atomic force microscopy. Integration of the interaction force; Approach in surface formulation; Development of a parametric model for a probe.

Presents a study which reported the room-temperature optical absorption over a large dynamic range for single-crystal undoped yttrium aluminum garnet (YAG). Presentation of the absorption results; Experimental procedures; Additional growth parameters for YAG I-III.

Reports on the room-temperature optical absorption in undoped aluminum compound. Previous research on undoped aluminum compound; Details on the experiments; Discussion on the results of the study.

This scattering of light by small particles embedded in a continuous transparent medium is influenced not only by the bulk optical properties of the particles and the medium but also by the size, shape, and spatial arrangement of the particles--that is, by the microstructure. If the particles are close together, as in agglomerated coatings or stereolithographic suspensions, interactions between the radiation fields of adjacent particles can lead to variations in the magnitude and spatial arrangement of the scattered light in the near and the far field, which can affect the color and hiding power of a coating, the cure depth and homogeneity in stereolithography, and the threshold intensity for stimulated emission in random lasers. Our calculations of the near- and the far-field scattering distribution for 200-nm Ti[O.sub.2] spheres in pairs of various orientations and in an ordered array of five particles show that, depending on the orientation of the particles with respect to the incident light, these interactions can either increase or decrease the scattering efficiency, the isotropy of the scattering, and the magnitude of the electric field strength within the matrix and the particles. In the mid-visible range, two particles in line increase the backscattering fraction by 28% and the scattering strength by 38% over that of a single particle, whereas if the particles are in the diagonal configuration the backscattering fraction and scattering strength are actually reduced by addition of the second particle. At shorter or longer wavelengths the backscattering fraction is reduced regardless of the location of the second particle, by as much as 60% when five particles are arranged in the zigzag configuration. These results are surprising in that it is generally assumed that multiple scattering enhances backscattering. Simple models of multiple scattering or scattering of two particles as a single, larger particle are inadequate to explain these results.

The surface plasmon resonance of Ag nanoparticles (NPs) and SiO2 coating had been extensively employed to improve the photoluminescence (PL) intensity of nanomaterials. In the article, the LaPO4:Eu3+ inverse opal photonic crystals were fabricated via combining a self-assembly process with a sol-gel method. The SiO2 shells were formed on the skeleton surface of LaPO4:Eu3+ inverse opals and the Ag NPs were added into the voids of LaPO4:Eu3+ inverse opals with the SiO2 shells. The influence of the SiO2 shells and Ag NPs on the PL of the LaPO4:Eu3+ inverse opals were investigated. About sevenfold luminescence enhancement of LaPO4:Eu3+ inverse opals was obtained by the coordination action of surface plasmon absorption effects of Ag nanoparticle and silica-coating effects. The luminescence enhancement mechanisms of LaPO4:Eu3+ inverse opals were discussed. [ABSTRACT FROM AUTHOR]

Ce3+-doped Gd3Fe5O12 (Ce:GIG) film has a good application prospect in the field of integrated optical device. In this article, Ce:GIG and Ce,Ga:GIG films were deposited onto the quartz glass substrate by using radio-frequency magnetron sputtering technology. The crystal phase, surface morphology, magnetization, and magnetic circular dichroism properties of films were characterized by using the X-ray powder diffraction, atomic force microscopy, vibrating sample magnetometer, and circular dichroism spectrometer. The results show that as-prepared Ce,Ga:GIG films has a good quality and show an excellent magneto-optical performance, and the doping of Ga3+ ion and the annealing process have significant effect on the magnetism and magneto-optical performances. It is expected that Ce,Ga:GIG film with a moderate Ga3+-doping content is a better candidate than Ce:GIG and Ce:YIG films for the next generation of integrated optical isolator and other magneto-optical equipment. [ABSTRACT FROM AUTHOR]