Showing papers on "Photon energy published in 1980"

Observation of the Auger Resonant Raman Effect

Abstract: Monochromatized synchrotron radiation near the photoionization threshold was used to produce the (2p/sub 3/2/) vacancy state in atomic Xe. Deexcitation of the state through L/sub 3/-M/sub 4/M/sub 5/(/sup 1/G/sub 4/) Auger-electron emission was measured. The 5d spectator-electron Auger satellite was observed. The satellite energy exhibits linear dispersion. The observed width of the /sup 1/G diagram line decreases by approx. 40% when the exciting photon energy reaches the vicinity of the Xe L/sub 3/ binding energy. This radiationless process can thus be construed as the Auger analog of the x-ray resonant Raman effect. The /sup 1/G diagram line is shifted by -+3 eV due to post-collision interaction; this shift varies with excitation energy.

Experimental determination of the phase differences of continuum wavefunctions describing the photoionisation process of xenon atoms. I. Measurements of the spin polarisations of photoelectrons and their comparison with theoretical results

Abstract: The photoionisation of xenon is completely described by the knowledge of either three or five parameters, corresponding respectively to the 2P1/2 and 2P3/2 states of the ion, and their dependence on photon energy. In the photon energy range from 12 to 41 eV two of these have been experimentally determined from measurements of the spin polarisation of photoelectrons emitted by unpolarised and circularly polarised VUV radiation. After a description of the apparatus used the measured results are presented and compared with different theoretical results.

Photodetachment spectroscopy of C2− autodetaching resonances

Abstract: The cross section for photodetachment of C2− is investigated in the photon energy range 14 000–20 000 cm−1 (1.75–2.5 eV). Sharp resonances due to autodetachment are observed at photon energies corresponding to transitions between high vibrational levels of the C2− X 2Σg+ state and high vibrational levels of the C2− B 2Σu+ states. The resonances are narrower than 6 GHz, and those arising from the v=5 level of the B state are about 1/10 as strong as those arising from the v=6 and higher levels. In addition, the signal from the allowed direct photodetachment of C2− X state, which would produce a smooth background cross section, is not observed, indicating that it is less than the 103 peak to background contrast ratio. A rotational analysis of the nine bands of the C2− B–X transition observed in this study, coupled with previous measurements provides a new, more precise set of spectroscopic constants for these states. These constants are then used to generate RKR potential curves for the B and X states of C2−...

Calculated absorption, emission, and gain in In0.72Ga0.28As0.6P0.4

Abstract: The absorption, emission, and gain spectra of In0.72Ga0.28As0.6P0.4 (λg =1.3 μm), which lattice matches InP, is calculated using a Gaussian fit to Halperin‐Lax band tails and Stern’s matrix element. The calculation is done both for p‐ and n‐type material at various impurity concentrations. The spectral width of emission increases both with increasing doping and impurity concentration. All results are for 297 K. The gain‐versus‐excitation rate is given by the equation g (cm−1)=0.057 (Jnom −2400), where Jnom is the nominal current density in the active layer expressed in A/cm2 μm. Also, the photon energy at maximum gain increases with increasing excitation rate.

Photon Energy Dependence of Radiation Effects in MOS Structures

Abstract: MOS capacitors with oxide thicknesses of 750A, 3500A and 6000A were irradiated using a Co60 source and a Cu target x-ray tube At low fields across the oxides (?1MV/cm), shifts in the flatband voltages observed with Co60 were twice those measured with the Cu tube at the same oxide dose At higher fields (>1MV/cm) the differences disappear The observations are interpreted to be due to differences in the electron-hole recombination dynamics for the two radiation energies Additionally, it was observed that the Si-SiO2 interface states trap holes with an efficiency that decreases as the square root of the electric field across the oxide

Use of the multiple‐scattering method for calculating the asymmetry parameter in the angle‐resolved photoelectron spectroscopy of N2, CO, CO2, COS, and CS2

Abstract: Calculations based on the multiple‐scattering method have been performed for the asymmetry parameter (β) as a function of photon energy (from the ionization threshold to 2 Ry above threshold) for the gaseous molecules: N2, CO, CO2, COS, and CS2. For the diatomic molecules N2 and CO we have investigated the use of an overlapping spheres transition state model. The calculations were critically compared with experimental data in the literature. In addition, we have carried out angle‐resolved photoelectron spectroscopy on the five molecules using a polarized source of He(i) radiation. Although the calculations show in general good predictive capability, there are also several instances where these calculations seem inadequate and suggestions are made for future work.

Valence-band structure of TiC and TiN

Abstract: The valence-band structure of single crystals of titanium carbide (TiC) and titanium nitride (TiN) have been studied with angle-integrated photoelectron spectroscopy using ${\mathrm{He}}_{\mathrm{I}}$, ${\mathrm{He}}_{\mathrm{II}}$, and synchrotron radiation for excitation. The results are compared with the partial densities of states derived from an augmented-plane-wave band-structure calculation. Peak positions and widths agree fairly well, but the observed intensity modulations with photon energy cannot be interpreted by such a comparison.

The photoconduction threshold in anthracene single crystals

Abstract: We report the excitation spectrum for intrinsic photoconductivity measured with unpolarized light incident on the 001 face of an anthracene single crystal. Over the photon energy range 3.75 to 4.4 eV, the room temperature (near 295 K) quantum yield of free carriers rises by a factor of 103. The activation energy for free carrier production rises steeply between 3.87 and 4.06 eV and then levels off. These results are compared with recent work by Lyons and Milne and some discrepancies are noted.

Radiation signatures from a locally energized flaring loop

Abstract: The radiation signatures from a locally energized solar flare loop based on the physical properties of the energy release mechanisms were consistent with hard X-ray, microwave, and EUV observations for plausible source parameters. It was found that a suprathermal tail of high energy electrons is produced by the primary energy release, and that the number of energetic charged particles ejected into the interplanetary medium in the model is consistent with observations. The radiation signature model predicts that the intrinsic polarization of the hard X-ray burst should increase over the photon energy range of 20 to 100 keV.

Optical absorption of SiH0.16 films near the optical GAP

Abstract: We have made detailed measurements of the optical transmission and reflection in the photon energy range of 0.5 to 5.0 eV on SiH0.16 films deposited by discharge decomposition of SiH4 on quartz substrates held at 240°C. Above 2.0 eV, the spectral dependence of ϵ2 is in excellent agreement with a model derived for parabolic bands in a disordered material. The range of coherence is about 20A very close to other materials (a-Si, a-Ge, As2Se3). The extrapolated value of the band gap (Eg) is 1.8 eV. Below 1.8 eV we have utilized photoconductivity and optical absorption and have observed an exponential dependence in α to 1.5 eV with an activation energy of 0.06 eV. From 1.5 eV to 1.2 eV absorption occurs to a photoconducting state with a maximum at 1.3 eV.

Surface Raman scattering of the light in antiferromagnetic chromium

Abstract: Raman scattering of light from the plane surface of antiferromagnetic chromium is discussed in terms of conventional second-order time-dependent perturbation theory. The scattering efficiency as a function of frequency and temperature is calculated from the scattering of light by one-electron, one-hole, and electron-hole pair excitations. It is shown that the unphysical divergence of the scattering cross section for the photon energy transfer equal to twice the antiferromagnetic energy gap found by Kwok, Woo, and Jha is removed by taking properly into account the statistical coherence factors.

The angular distribution of photoelectrons from N2, O2, and C0 as a function of photon energy

Abstract: Radiation from the 25 GeV electron synchrotron at the Bonn Physikalisch Institut has been used to measure the spatial distributions of photoelectrons from the molecules N2 and O2 Values of the asymmetry parameter beta of various ionic states have been determined over a photon energy range of 16 to 25 eV using a Seya monochromator to produce plane polarised radiation to a bandwidth of 500 mV Good agreement with He I and Ne I resonance line measurements by other workers is observed and a comparison with theoretical studies is given Additional measurements on N2 and C0 which complement the published date of Marr et al (1979 , 1980) using the Synchrotron Radiation Facility at the Daresbury Laboratory are provided in tabular form

Optically active interface states in MOS structures

Abstract: The results of studies of the interface states in clean n -type MOS capacitors by the low-temperature photocapacitance technique are reported. Energy distribution of the interface states density and photoionization cross-section are determined from the analysis of the photocapacitance kinetic. It is shown that the energy distribution of the interface state density can be described by the Gaussian distribution with maximum at about 0.7 eV below the conduction band edge and standard deviation of about 0.1 eV. The photoionization cross-section of these states can be described by the Lucovsky relationship. The maximum of the photoionization cross-section vs photon energy was equal to about 5 × 10 −20 /( E c − E ss ) cm 2 for a given energy of the interface states E ss . From the comparison of the photocapacitance and quasi-static C-V measurements the existence of two types of interface states is suggested: “optically active states” with density decreasing towards the band edges, and “optically inactive states” with density increasing towards the band edges. No photocapacitance associated with “optically inactive states” was observed.

Angular distribution in the photoelectron spectrum of the ground and first excited vibrational bands of the X 2Σg+ state in N2+ measured as a function of photon energy

Abstract: Angle‐resolved photoelectron spectra were taken of the first ionization state of N2 as a function of photon energy using a monochromatized beam of polarized photons from the Wisconsin Synchrotron Radiation Center. From these results the angular parameters for the first two vibrational states were determined over a range of photon energies from 17.7 to 31.0 eV. In energy ranges where resonance absorption, accompanied by autoionization, is expected to occur, β for the first excited vibrational level (v1) was frequently characterized by near zero values. In energy regions free of discrete autoionization v1 was found to have a value of β considerably larger (∼0.4 to 0.8 units) than that for the ground vibrational level (v0). This result is shown to be in accordance with recent calculations by Dehmer et al., based on the effect of vibrational motion on β in the vicinity of a shape resonance.

Photoconductivity in single crystal polydiacetylene-toluene sulphonate

Abstract: The photoconduction spectrum of the bis(p-toluene sulphonate) ester of 2,4-hexadiyne-1,6-diol (PDA-TS) is reported in the photon energy range 0.62-3.1 eV for conduction along the polymer chain direction. A dominant feature of the spectrum is a steep photoconductive edge at 0.8 eV. This is an agreement with the existence of a localised impurity or defect electron energy level 0.8 eV below the conduction band, if electrons are the majority carriers. Electric field dependence of the photocurrent, examined in the range approximately 15-104 V cm-1, is interpreted on a model which indicates that for current flow parallel and perpendicular to the carbon backbone of the polymer chain, these crystals are model systems for the one- and three-dimensional versions of Onsager's theory (1934) of geminate recombination of bound electron-hole pairs respectively. Also reported are the results of optical transmission measurements on PDA-TS in the photon energy range 0.62-1.84 eV.

Photoelectron diffraction effects in core-level photoemission from Na and Te atoms adsorbed on Ni(001)

Abstract: The diffraction of photoelectrons emitted from the $\mathrm{Na} 2p$ and $\mathrm{Te} 4d$ core levels has been investigated both experimentally and theoretically for these atoms adsorbed in various configurations on an Ni(001) surface The experiments were performed in the photon energy range $\ensuremath{\hbar}\ensuremath{\omega}=70\ensuremath{-}115$ eV and the various modes of observing the photoelectron diffraction effects are described Emphasis is on the azimuthal diffraction patterns which are shown to be sensitive to photoelectron kinetic energy, polar angle of emission, and adsorbate species It is found that these patterns can be matched quite well by theoretical calculations using a multiple-scattering formalism and parameters taken from previous low-energy electron diffraction studies In the case of Na, no adjustment is required to these parameters In the case of Te, a match is obtained only after a rigid shift of the energy scale by 8 eV The sensitivity of the calculated diffractions patterns to the input parameters is reported, and it is suggested that the measurements could form the basis of a surface structural technique with a ${d}_{\ensuremath{\perp}}$ spacing sensitivity of \ensuremath{\sim}01 \AA{}

Strangeness exchange in the photoproduction of K + Λ(1520) between 2.8 and 4.8 GeV

Abstract: A tagged photon beam (2.8

Photodestruction of ions containing sulfur dioxide

Abstract: Photodestruction cross sections have been measured for six ions containing SO2 over the photon energy range 1.55–3.5 eV using a drift tube mass spectrometer and rare gas ion and dye lasers. The cross section for SO2− increases smoothly with photon energy from (0.9 to 2.4) ×10−18 cm2. The photodestruction spectra of SO2 (SO2)− and O2 (SO2)+ consist of broad, structureless bands. These bands are attributed to direct dissociation through repulsive excited states. Cross section for O2 (SO2)−, NO2 (SO2)−, and NO3 (SO2)− are measurably different from zero only at the upper end of the photon energy range.

Theory of Atomic Processes in Strong Resonant Electromagnetic Fields

Abstract: Publisher Summary The objective of this chapter is to describe some recent work on the interaction of atomic systems with intense, near-resonant, and narrow-band laser fields. There are concerns with multiphoton processes but multiphoton processes may be divided for convenience into two types. (1) Those in which there is net absorption (or emission) of two or more photons by the atom, such as multiphoton ionization or two-photon absorption. (2) Those in which there are repeated emissions and absorptions of photons by the atom but in which, at the end of the interaction period, the energy of the atom is unchanged or has changed by only single photon energy. An example is resonance fluorescence where the energy initially residing in the laser field is redistributed by many absorptions and subsequent emissions of photons although, at the end of the interaction period, the atomic energy is unchanged. This chapter concentrates on the resonance fluorescence and the optical Autler–Townes effect. Related phenomena such as Raman scattering in intense fields are also discussed in the chapter.

The measurement of effective photon energy and “linearity” in computerized tomography

Abstract: Two liquid systems have been developed for the measurement of effective photon energy (Eeff) and "linearity" in computerized tomography (CT). A group of sixteen "keV liquids" enables an Eeff to be rapidly determined, by comparing the CT numbers of the specially formulated organic liquid mixtures with similar data for water. The "linearity" of the CT scanner, relating CT nubers to linear attenuation coefficients, may be investigated using 14 selected organic "linearity liquids". Details of these systems, together with some typical results, are presented.

Efficiency of quantum-utilizing solar energy converters in the presence of recombination losses

Abstract: The presence of nonradiative losses limits the optimal absorbance of a solar energy converter. When nonradiative losses exceed radiative losses, the optimal absorbance at ν of a flat‐plate device is approximately (hν−E0)/2.3 kT, where E0 is the threshold photon energy. For a given output potential, the optimal threshold E0 increases approximately as kT ln κ, where κ is the ratio of nonradiative to radiative decay rates within the absorbing material. The maximum efficiency of a terrestrial flat‐plate device (AM 1.5, 28 °C) falls from 0.334 when κ=0, to 0.316 when κ=1, to 0.257 when κ=1000. Curves are displayed showing the dependence of efficiency on the potential of the process driven, the threshold photon energy, and the relative rate of nonradiative decay.

Saturation of intervalence-band transitions in p-type semiconductors

Abstract: We present a theory of the saturation of heavy-hole to light-hole band absorption in $p$-type semiconductors with the diamond or zinc-blende crystal structure by high-intensity light with a wavelength near 10 \ensuremath{\mu}m. The absorption coefficient is found to decrease with intensity in a manner closely approximated by an inhomogeneously broadened two-level model. For temperatures and hole concentrations where hole-phonon scattering dominates hole-impurity and hole-hole scattering, the saturation intensity is independent of the hole concentration. We calculate the saturation intensity as a function of excitation wavelength and temperature for $p\ensuremath{-}\mathrm{Ge}$ and $p\ensuremath{-}\mathrm{GaAs}$. We find that the saturation intensity increases with photon energy and with temperature. The calculated results are compared with the available experimental data and good agreement is found.

Photoionization of helium above the n = 2 photoionization threshold

Abstract: 2014 Using the technique of electron spectrometry and the synchrotron radiation of the storage ring ACO, the photoionization of helium has been investigated between 69 and 150 eV. The probability to leave the residual ion in the n = 2 excited state has been measured as a function of photon energy. The absolute partial photoionization cross section for this process has been determined and found to be in good agreement with recent Multiconfigurational Many-Body Calculations. Tome 41 No 16 15 AOUT 1980 LE JOURNAL DE PHYSIQUE-LETTRES J. Physique LETTRES 41 (1980) L-373 L-37~ 15 AOUT 1980,