Influence of oxidation on optical diffuse reflectance spectra in nanoscale silicon powder

Received: 5 June 1997/Accepted: 30 July 1997     

Bound state spectra of three-body muonic molecular ions

The results of highly accurate calculations are presented for all twenty-two known bound S(L = 0)-, P(L = 1)-, D(L = 2)- and F(L = 3)-states in the six three-body muonic molecular ions ppμ,pdμ,ptμ,ddμ,dtμ and ttμ. A number of bound state properties of these muonic molecular ions have been determined numerically to high accuracy. The dependence of the total energies of these muonic molecules upon particle masses is considered. We also discuss the current status of muon-catalysis of nuclear fusion reactions.     

Diffuse reflectance spectra of aluminum oxide micropowders,modified powders,and nanopowders and their changes upon electron irradiation

Comparative analysis of the diffuse reflectance spectra (300–2100 nm) and of the integrated absorption factor of coatings based on micropowders, nanopowders, and micropowders modified with Al₂O₃ nanopowders has been performed. In addition, the changes in the spectra resulting from electron irradiation of the powders with energies of 30 keV at a fluence of up to 3∙16 cm^–2 have been analyzed. It has been found that the diffuse reflectance decreases in order of coatings based on micro-powders, nano-powders and modified powders, while radiation resistance increases in order of coatings based on nano-powders, modified and micropowders.     

Photoacoustic and reflectance spectra of zirconium-silicate pigments

Photoacoustic spectra and diffusion reflectance spectra of powdered zirconium-silicate ceramic pigments (Zr_0·97V_0.03Si₄, Zr_0·98Pr_0·02SiO₄ and ZrSiO₄ 0·05 -Fe₂O₃) have been measured and found to be closely correlated. The signal saturation problem connected with both spectral techniques is extensively discussed with respect to a particle size of powdered samples. The photoacoustic technique enables one to establish the bulk optical absorption coefficients of the powdered samples and thermal parameters, knowing the particle size diameters.     

Diffuse reflectance spectroscopy with a self-calibrating fiber optic probe

Calibration of the diffuse reflectance spectrum for instrument response and time-dependent fluctuation as well as interdevice variations is complicated, time consuming, and potentially inaccurate. We describe a novel fiber optic probe with a real-time self-calibration capability that can be used for tissue optical spectroscopy. The probe was tested in a number of liquid phantoms over a relevant range of tissue optical properties. Absorption and scattering coefficients are extracted with an average absolute error and standard deviation of 6.9%+/-7.2% and 3.5%+/-1.5%, respectively.     

Argon L x-ray spectra from collisions of argon ions with various solid state targets

Spectral measurements have been made of Ar-L-shell X-rays produced by Ar ions incident on various solid state targets. Different spectra have been observed for targets with Z < 18 and Z > 18 respectively. The data are discussed within the framework of the electron promotion model of Barat and Lichten.     

Temperature dependence of infrared reflectance spectra of InN

To investigate both the optical and electrical properties of InN, we have measured the infrared reflectance spectra of InN thin films and performed the fitting analyses of the infrared spectra to obtain not only phonon frequencies and the damping factors but also the carrier concentration of InN. In this paper, we extend the aim of those analyses to the electron mobility and demonstrate that the temperature dependence of the electron mobility can be discussed using the infrared reflectance spectra analyses.     

Amplitude-phase reflectance spectra of amorphous silicon-based Bragg structures

Amplitude-phase spectra of light reflection from distributed Bragg reflectors and Fabry-Pérot microcavities based on a-Si: H/a-SiO_x: H thin films have been studied. The frequency dependence of the phase difference between the amplitude p-and s-light reflection coefficients within the photonic band gap is measured. The phase spectrum exhibits predominantly a monotonic, close-to-linear frequency behavior, except for spectral regions near the stop band edges and near the singularities related to the microcavity eigenmodes. The experimental spectra are compared with theoretical calculations based on the transfer matrix method and approximate analytical relations. A method based on analyzing amplitude-phase reflectance spectra is proposed for structural characterization of multilayer microcavity systems.     

Direct ionization of pure TCNQ in the solid state. Evidence from powder infrared absorption spectra.

This is the first presentation of a novel method of producing an efficient and controlled ionization of the TCNQ molecules in pure molecular microcrystals. According to whether the ionization is complete or incomplete, the highly distinct structures of the simple and complex TCNQ salts are respectively reproduced in the infrared spectra.     

Selective inversion in inhomogeneously broadened powder spectra

It is shown how amplitude-modulated radio-frequency pulses optimized for selective inversion of magnetization can be applied to static powder samples with inhomogeneously broadened spectra. Selective one-dimensional methods can in principle provide information similar to two-dimensional exchange spectroscopy, and they are often more efficient for determining the rates of dynamic processes. However, in systems where transverse magnetization is subject to significant homogeneous decay during the rf pulses, selective one-dimensional methods do not necessarily offer the expected advantages over two-dimensional spectroscopy.     

Fast acquisition of reflectance spectra using wide spectral lines

We analyze a recently proposed technique for fast acquisition of the two-dimensional (2D) spatial distribution of reflectance spectra to figure out how much its ability of distinguishing almost similar spectra declines with increase of the spectral line bandwidth of the light source. This analysis was carried out using the experimentally measured reflectance spectra of four metameric samples and simulating the system response to an illumination by spectral lines with variable bandwidth. It was shown that the metameric samples are distinguishable even when the bandwidth of illuminating lines is 20–30 nm. A wider bandwidth allows implementation of simultaneous illumination of an object that leads to a diminution of the acquisition time of 2D-multispectral images due to both faster operation in the parallel mode of Light-emitting diodes (LEDs) switching and higher output power.     

Vibrational spectra of the tetramethylpnikogenonium ions

The tetramethylpnikogenonium ions (CH₃)₄X⁺ (X = N, P, As, Sb) have been studied by infrared and Raman spectroscopy. Additionally, their structures and vibrational frequencies were ab initio calculated at the HF/6-31+G* and for (CH₃)₄Sb⁺ at the HF/6-31+G*/LANL2DZ level of theory. For the tetrahedral cations an assignment of the vibrational frequencies is discussed on the basis of a comparison of calculated and measured frequencies.     

Special frequencies in the optical reflectance spectra of resonant Bragg structures

The optical reflectance spectra of resonant Bragg quantum-well structures are studied theoretically. The existence of two special frequencies in the spectra at which the reflectance depends only weakly on the number of quantum wells in the structure is explained analytically. The effect of nonradiative exciton damping on the reflectance spectra in the vicinity of the special frequencies is analyzed. It is shown that the inclusion of the dielectric contrast leads to the appearance of a third special frequency, at which the contributions to the reflectance due to the dielectric contrast and exciton resonance completely cancel each other.     

Diffuse reflectance spectrum of Co3+-N-acetylacetone-anthralinic acid complex

Diffuse reflectance spectrum of Co³⁺-N-Acetylacetone-anthranilic acid complex is reported between 50.000-10.000 cm^?1. Two absorption peaks have been observed at 34.310 and 20.000 cm^?. They have been assigned to ¹T_2g ? ¹A_1g and ¹T_1g ? ¹A_1g transitions.     

Temperature dependence of aluminum nitride reflectance spectra in vacuum ultraviolet region

Temperature dependence of optical reflectance spectra in vacuum ultraviolet region for aluminum nitride has been measured on high-quality single crystal with synchrotron radiation. The dominant structure due to the interband transition is observed at photon energy around 7.7 eV. With decreasing temperature, the energy position of the dominant structure in the reflectance spectra shifts towards higher energy. The experimental data has been fitted to the Bose-Einstein expression and the obtained parameter related to the strength of the electron-phonon interactions is much smaller than that for the peak at 6.2 eV, suggesting that the higher-lying interband transition energy decreases more slowly with increasing temperature in aluminum nitride (AlN).     

The spectra of helium-like ions in laser-produced plasmas

We calculate intensities of lines arising from the n = 2 and n = 3 levels of highly-charged, helium-like ions in very dense plasmas. We determine the importance of recombination and cascading, and of radiation trapping, on certain line-intensity ratios, and we illustrate the relevance of these calculations to laser-plasma diagnostics. Finally, we outline the pitfalls inherent, at very high densities, in some other techniques commonly used to interpret plasma spectra.