Spectral Energies Research Articles

Polarized surface differential reflectivity and oxygen chemisorption on InP(110) surfaces

We present surface differential reflectivity (SDR) results on the polarization dependence of optical transitions and on the oxidation of InP(110) surfaces in the energy range between 2.0 and 4.0 eV. The surface dielectric function has been derived for the light electric vector along [110] and [001] directions. The data show two anisotropic peaks at 2.6 eV (excited with the light electric vector along the [110] direction) and 3.5 eV (excited with the light electric vector along the [001] direction) and an almost isotropic behaviour for the peak at 3.1 eV. Absorption kinetics is analyzed by following the reflectivity variation between 1 × 102 and 2 × 106 langmuirs of molecular oxygen at three selected spectral energies. Several well-defined steps of the oxidation process are clearly resolved and discussed in terms of disappearance of intrinsic surface states, creation of acceptor and donor defect states, and growth of In2O3.

Polarized surface differential reflectivity and oxygen chemisorption on InP(110) surfaces

Abstract We present surface differential reflectivity (SDR) results on the polarization dependence of optical transitions and on the oxidation of InP(110) surfaces in the energy range between 2.0 and 4.0 eV. The surface dielectric function has been derived for the light electric vector along [110] and [001] directions. The data show two anisotropic peaks at 2.6 eV (excited with the light electric vector along the [110] direction) and 3.5 eV (excited with the light electric vector along the [001] direction) and an almost isotropic behaviour for the peak at 3.1 eV. Absorption kinetics is analyzed by following the reflectivity variation between 1 × 10 2 and 2 × 10 6 langmuirs of molecular oxygen at three selected spectral energies. Several well-defined steps of the oxidation process are clearly resolved and discussed in terms of disappearance of intrinsic surface states, creation of acceptor and donor defect states, and growth of In 2 O 3 .

Clean and oxygen covered InP(110) surfaces differential reflectivity

We present surface differential reflectivity results on the polarization dependence of optical transitions and on the oxidation of InP(110) surfaces in the energy range between 2.0 and 4.0 eV. The surface dielectric function has been computed for light electric vector along [110] and [001] directions. Three well defined optical peaks have been detected at the following energies: 2.6 eV (light electric vector along [110] direction), 3.1 eV (unpolarized), and 3.5 eV (light electric vector along [001] direction). Absorption kinetics is analyzed by following the reflectivity variation between 1×102 and 2×106 L of molecular oxygen at three selected spectral energies. Several well defined steps of the oxidation process are clearly resolved and discussed in terms of disappearance of intrinsic surface states, creation of acceptor and donor defect states, growth of In2O3.

Oxygen chemisorption on cleaved InP(110) surfaces studied with surface differential reflectivity.

We present surface-differential-reflectivity results on the oxidation of InP(110) surfaces in the energy range between 2.0 and 4.0 eV. Absorption kinetics is analyzed by following the reflectivity variation between 1\ifmmode\times\else\texttimes\fi{}${10}^{2}$ and 2\ifmmode\times\else\texttimes\fi{}${10}^{6}$ langmuirs of molecular oxygen at three selected spectral energies. Several well-defined steps of the oxidation process are clearly resolved and discussed in terms of the disappearance of intrinsic surface states, the creation of acceptor and donor defect states, and the growth of ${\mathrm{In}}_{2}$${\mathrm{O}}_{3}$.

Optical absorption of Cu implanted silica

The extinction coefficient (EC) per ion was measured over the spectral range from 1.8 to 6.2 eV for a series of Cu ion implanted silica substrates. The substrates were implanted with nominal doses ranging from 0.3 to 12.0 × 106 ions/cm2 at substrate temperatures of 100, 296 and 673 K. The EC was observed to increase for both increasing dose and substrate temperature. The absorption in the spectral region < 5.0 eV is attributed to the formation of spherical and oblate spheroidal colloids. At spectral energies > 5.0 eV, the absorption is attributed to radiation damage effects.

Evaluation of P- and S-wave sources for shallow seismic reflection

The theoretical attractiveness of utilising both P- and S-reflection information is offset in the shallow environment by the practical difficulty of isolating high resolution reflections from other non-reflection energy. Source design is a critical component in a range of mandatory acquisition and processing optimisations. Four near-surface P-wave sources (high explosive, shotgun, weight drop, and hammer) have been evaluated in terms of their suitability for shallow reflection at a test site in the Ipswich Basin, southeast Queensland. Cross power spectral analyses of trace segments in the reflection window provide an estimate of the ‘coherent bandwidth’ of the different sources. Although the high explosive has superior signal levels, consideration of spectral symmetry, autocorrelation shape, and logistic aspects indicates that the shotgun source is a viable alternative. A pneumatic powered S-wave generator has been constructed and tested. Integrated spectral energies have been used to monitor piston velocity limitations and hence define optimum operating parameters. The pneumatic source is more controllable and of higher energy than a sledgehammer-powered equivalent.

Oscillatory activity of single units in a somatosensory cortex of an awake monkey and their possible role in texture analysis.

Neuronal activity was extracellularly recorded in the cortex of an awake monkey (Macaca fascicularis). Single units displaying oscillatory firing patterns were found in the upper bank of the lateral sulcus in a region where most of the neurons responded to somatosensory stimuli. The spectral energies of the oscillating activity were distributed in a trimodal fashion--0-15, 15-50, and 80-250 Hz--with the most common frequencies around 30 Hz. The oscillatory activity was not affected by anesthesia, but it was often reduced by tactile stimulation or self-initiated movements. Analysis of the spike trains suggests that the majority of oscillatory activity was intrinsically generated by the neurons. A neural model of texture analysis is offered based on a corticothalamic phase-locked loop. The newly identified oscillators play a key role in this model. The relevance of the model to physiological, anatomical, and psychophysical data, as well as testable predictions, are discussed.

Impact of Various Processes on the Transient Evolution of Spectral Kinetic Energies

Geopotential height fields for nine winters (1967/68–1975/76) and summers on three levels (300, 500, 1000 mb), provided by the German Weather Service, are used to compute daily budgets of kinetic energy (Km) for single zonal wavenumbers m within a quasi-geostrophic framework. The energetics are averaged over the depth of the troposphere and the latitudinal belt 40°N ≤ ϕ ≤ 85°N. Inadequate field resolution by data, and inevitable model approximations justify regressive corrections of the energy conversion estimates, leading to upper-bound estimates of the fraction of kinetic energy variance explained by different conversions (hindcast skills). The results are (i) Persistence is most important for the evolution of Km for m ≤ 4; the skill ranges from 76% to 59% (in winter). The importance is less for m ⩾ 5, according to the skills ranging from 51% to 43% (in winter). (ii) For 1 ≤ m ≤ 4 the sum of energy conversions explains approximately 35%–45% of the variance of Km, left unexplained by persistence in winter. In this wave range the leading process is the nonlinear interaction with waves m ≤ 5, whereas conversions between Kz and Km as well as lateral boundary fluxes are of the least importance. The evolution of Km for m = 2,…,4 is unexpectedly well correlated to the conversion between available potential energies C(AzAm) which appears to be a good substitute for C(AmKm), which is proportional to the vertical sensible heatflux. (iii) For waves with 5 ≤ m ≤ 8 the sum of conversions explains 30%–50% of the variance of Km, left unexplained by persistence in winter. The baroclinic conversion C(AmKm) contributes the largest skill; however, C(AzAm) is a better indicator of baroclinic activity even in this wave range. The next largest impact on Km stems from nonlinear wave- wave interactions involving at least one other short wave with m = 6,…,12. The influence of C(KzKm) is insignificant in the wave range 5 ≤ m ≤ 8. (iv) The total skill of our model (including persistency) ranges from 65% (synoptic scales) to 85% (ultralong waves) in winter. (v) In summer, the amount of variance of Km, explained by different conversions, is generally lower than in winters, whereas the overall scale-dependent skill patterns are essentially preserved.

Thermal and quantal fluctuations in deformed nuclei

The quantal RPA corrections to the nuclear partition function are studied for hamiltonians with a quadrupole-quadrupole interaction. In the path-integral formulation, the RPA corrections are obtained as small amplitude fluctuations around the static paths. For a realistic hamiltonian, the quantal corrections are found to effect the level density mainly by lowering the spectral energies.

Relation between macroseismic intensity and instrumental parameters of strong motions ? A statistical approach

One hundred and twenty-eight strong ground motion CALTECH (Earthquakes in the U.S.A., 1940–1971) records of five Californian earthquakes, recorded at ground level and in basements, for which the modified Mercalli macroseismic intensities are known, were statistically processed to calculate 165 wave parameters. Correlation of the peak values of particle acceleration, velocity and displacement, energy, impulse and root-mean-square amplitude of the vibrations, durations of vibrations for certain levels of the peak amplitude, and spectral energies of 10 frequency windows with macroseismic intensity are discussed from the viewpoint of classification of ground-motion records.

One-dimensional multiple scattering model for low-energy electron diffraction in the normal geometry

A one-dimensional multiple scattering model for low energy electron diffraction in the normal geometry is proposed. This model reduces to the regular or a modified kinematic approximation in the weak scattering limit. The one-dimensional multiple scattering model is applied to Xe(111), Ni(001) and Cu(001). The results with Xe(111) are very encouraging in that the calculated LEED spectral peak energies and intensities agree well with experiment. The Ni(001) and Cu(001) results are also encouraging. Although only half the peaks present in the experimental data are present in the Ni(001) and Cu(001) calculated spectra, those peaks present in the calculated spectra are in agreement with the experimental spectra. The authors hypothesize that these missing peaks can be explained by the alternating filled and vacant site structure of (001) planes in face centered cubic crystals.

Large exchange interactions in the electron gas of GaAs quantum wells.

Inelastic-light-scattering measurements show that exchange Coulomb interactions in the two-dimensional electron gas of GaAs microstructures are more important than previously anticipated. Small-wave-vector spectra from modulation-doped quantum wells exhibit unexpected single-particle intersubband transitions in addition to collective spin-density and charge-density modes. From the measured spectral energies the direct and exchange intersubband Coulomb interactions are determined and found to be of comparable strengths.

Heavy-residue spectra in the interaction of 85A MeV 12C with 197Au

We have measured the heavy-residue differential range distributions in the interaction of 85 MeV/nucleon 12C with 197Au. The range distributions were converted to energy spectra using known range-energy relationships. The mean residue energies range from 15 keV/nucleon ( A = 189) to 314 keV/nucleon ( A = 131). Longitudinal momenta of the heavy residues have been deduced. The mean spectral energies and the shapes of the residue spectra are shown to be in agreement with the predictions of the VUU model.

Implementation of principal components spectral analysis of speech in a wearable tactile aid

One common configuration of a vibrotactile sensory aid for the hearing impaired is the vocoder scheme employing a bank of bandpass filters that model human audition. These systems result in 16 or more spectral energy outputs, each of which drives a vibrator. Although successful in laboratory and classroom settings, the large number of vibrators required makes the implementation of wearable versions difficult. By performing a principal components analysis of the filter bank outputs, the spectral information can be recorded in as few as four parameters. A compact principal components analysis system has been implemented using digital signal‐processing techniques. The system consists of a 1/3‐oct bandpass filter bank, high‐speed energy detectors for each filter, logarithmic scaling of spectral energies, and a principal component calculator, all in software running on a commercial DSP microchip. In this paper, the principal components system is compared to the traditional vocoder method, as well as to the pitch and formant extraction schemes.

Transform-ratio ternary phase-amplitude filter formulation for improved correlation discrimination

A method of formulating ternary-valued (-1,0,1) correlation filters based on the ratio of spectral energies of target and nontarget patterns is proposed, and performance of such filters is investigated by computer simulations of correlation. The results confirm the intuitive expectation that such filters can enhance signalto- clutter and discrimination performance for target recognition in the presence of large amounts of input noise. These filters may be viewed as an extension of binary phase-only filters and similarly are motivated by the prospect of near-term real-time implementation.

Donor binding energies determined from temperature dependence of photoluminescence spectra in undoped and aluminum-doped beta SiC films

Measurements of the temperature dependence of N-Al donor-acceptor pair photoluminescence spectra in cubic SiC films demonstrate that the thermal activation energy for the nitrogen donors is equivalent to the 54 meV binding energy for nitrogen determined from the spectral energies of the sharp-line close pair spectra. It follows that the 15–20 meV donor which dominates the electrical properties of n-type films is not isolated, substitutional nitrogen. Spatial variations observed in the intensity of a new 2.368 eV luminescence band demonstrate that the radiative recombination centers are inhomogeneously distributed in the films.

Field emission current fluctuations from clean tungsten field emitters in the built-up state

Field emission flicker noise spectral density functions of the (012), (113) and (111) tungsten region were measured in the built-up state of the emitter. Their dependence on temperature is analysed in terms of the spectral density and knee frequency activation energies. By comparison with FIM single tungsten adatom migration energies and build-up activation energies of the polyhedral tip and by discussion of the shape of the spectra some conclusions are drawn as to the mechanism of the flicker noise. From the given data favourable operating conditions of TF cathodes can be derived according to the requirements on bandwidth and signal-to-noise ratio.

An investigation of methods for the on-line estimation of tool wear

The paper examines the use of the measurements of spindle motor power for the estimation of wear and the detection of the end of effective tool life for a vertical milling machine. The measurements are analysed using spectral analysis and the effectiveness of using moving averages, running-means and cumulative sum of the power spectrum values to estimate wear is evaluated. For a specific machine tool (Beaver NC5), workpiece material (stainless steel) and under a particular set of cutting conditions it is shown that (a) there is a strong correlation between the cumulative sum of the power spectral energies and the total flank wear, and (b) the residuals obtained from computing a least squares linear fit to the plot of cumulative sums of the power spectral energies against cutting time clearly indicates when the tool is entering the region of high wear.

A comparative study of spectral energies and oscillator strengths of PrCl 3 organic complexes

Both the UV-visible and NIR absorption spectra of PrCl 3 in methyl, ethyl, isopropyl, butyl and amyl alcohols have been measured. The evaluation of various Spectroscopic parameters in understanding the energy level structures and intensities of the observed bands has been carried out. The environmental effects on the spectral features and lifetimes of the fluorescent levels have been studied and the results thus obtained are presented.

Electron-hole recombination spectra and kinetics in PbTe/PbEuTeSe multiquantum wells

We have investigated basic optical properties of PbTe/PbEuTeSe multiple quantum wells in samples of two different well thicknesses ( L z = 92 Å and 51 Å) from measurements of photoluminescence over a range of temperatures and magnetic fields. Spectral energies yield tentative assignments for values of the band offsets. Hot electron effects are pronounced in the L z = 92 Å sample and show that the electron-LO phonon interaction is substantially reduced in comparison with bulk PbTe. The energies of the lowest Landau levels have been measured in several samples from shifts in luminescence energies in external fields. Finally, measurements of excess electron-hole recombination rates by time-resolved techniques show lifetimes less than 10 ns in these quantum wells.