High Electronic Excitation Research Articles

Jahn-Teller effect on silicon surface under laser irradiation

The reconstruction of dangling bonds on a silicon surface under powerful laser irradiation has been investigated by EPR technique. This phenomenon is suggested to be due to the Jahn-Teller effect stimulated by high electron excitation of a semiconductor.

Jahn-Teller effect on silicon surface under laser irradiation

The reconstruction of dangling bonds on a silicon surface under powerful laser irradiation has been investigated by EPR technique. This phenomenon is suggested to be due to the Jahn-Teller effect stimulated by high electron excitation of a semiconductor.

Neutral particle emission from zinc oxide surface induced by high-density electronic excitation

Abstract Emission of neutral zinc and oxygen atoms and oxygen molecules emitted from zinc oxide surface by laser irradiation have been measured. It is found that the emission intensity starts to increase when the laser intensity exceeds a certain threshold value, indicating that the particle emission is a high density electronic excitation effect. The energy spectrum of emitted particles is found not to follow the Maxwellian distribution.

Quantitative Auger electron spectroscopy and X-ray fluorescence analysis of CoSm alloy thin films deposited by co-evaporation

High energy electron excitation (up to 50 keV) of Auger spectra with high signal-to-background ratios and a low and flat background slope was used to analyse CoSm alloy thin films. The experiments were performed in an ultrahigh vacuum high energy electron diffraction chamber with in situ co-evaporation of the components onto molybdenum substrates at room temperature and at 550°C. The intensity distributions of the secondary electrons were analysed with a cylindrical mirror analyser and detected via a phosphor-multiplier combination using counting techniques and a multichannel analyser for recording. The analysis of overlapping Auger peaks in the alloy spectra was accomplished by computer-aided subtraction of normalized spectra of the single components. The Auger electron spectroscopy (AES) results were compared with quantitative X-ray fluorescence analysis (XFA) of the films. For deposition of the components at constant rates and the substrate at room temperature, the Auger and X-ray compositions agreed fairly well. However, for deposition at substrate temperatures higher than 500°C, the samarium concentrations were substantially lower than that in the vapour beam, but a relative enrichment of samarium near the film surface was found by comparison of the AES and XFA results. The concentration profile of the films is discussed in terms of an initially low samarium condensation coefficient which increases with the codeposition of cobalt and with time.

Rate of Carbon Contamination on Al Targets in a High Vacuum Electron Excitation X-Ray Tube

The rates of carbon contamination on Al targets caused by electron bombardments in two vacuum systems, one evacuated by a diffusion pump (∼5×10-6 mmHg) and the other by an ion pump (∼5×10-7 mmHg), have been obtained by detecting C K-emission spectra with a grazing incidence concave grating spectrograph. Simultaneously Al L-emission spectra were photographed. Intensity estimates for C K-emission were photographically made in reference to the intensity of graphite C K-emission using a characteristic curve of photographic plates. The rates of carbon contamination are about 1.1×10-5% per sec in the vacuum system of the ion pump and about 6.0×10-4% per sec in the vacuum system of the diffusion pump (oil: Santo Vac 5), expressed as fractions of the intensity of graphite C K-emission. The decrease of Al L-emission intensity was not detected in the ion pump system, but was observed remarkably in the diffusion pump system.

Recent Advances in Studies of Molecular Transition Probabilities

The development of high power electron excitation applied in the High Frequency Deflection technique has enabled time resolved precision spectroscopy to be performed with a resolving power as high as 1:105. This is typically a two orders of magnitude higher resolution than what is commonly achieved using other approaches and this has created new possibilities of studying hitherto unknown properties of fundamental molecules. Thus a great number of time resolved studies of individual rotational levels including resolved spin-orbit and Λ components show that radiationless destructions of molecules are much more common in nature than earlier believed implying a violation of the Born Oppenheimer approximation which demands new theoretical treatments of molecular structure. Among important applications of the radiationless processes should be mentioned determinations of dissociation energies with superior accuracy and molecular formation rates. An extensive programme for theoretical studies of the obtained results is in progress in collaboration with the quantum chemistry groups in Århus and Uppsala. This programme also includes precision estimates of oscillator strengths with applications to molecular abundance estimates and to laser physics.

Carrier diffusion degradation of modulation transfer function in charge coupled imagers

Expressions for the modulation transfer function due to minority carrier diffusion in charge coupled imagers are calculated, following the approach used by Crowell and Labuda. Both front and rear optical illumination of the charge coupled imager are considered; for the rear illumination case interference effects are included. The modulation transfer function for high energy electron excitation is also considered. In all cases, the expressions for the modulation transfer function have been evaluated using typical charge coupled imager parameters. The quantum efficiency predicted by the minority carrier diffusion model is also briefly discussed.

Autoionizing transitions in N2and H2produced by electron impact

Studies have been made of autoionizing transitions in N2 with excitation by low energy electron impact. Electron ejection is observed from states of the neutral molecule in the continuum region 16-19 eV giving levels of the x 2 Sigma g+ state of N2+. Measurements are made of autoionizing states which had previously been detected using photon and high energy electron excitation. In addition new levels are observed which appear to be favoured by low energy electron excitation.

Induced Absorption in the Presence of High Electronic Excitation

Experimental evidence is presented for the existence of an absorption continuum in CdS which is probably caused by the high density of electron-hole pairs and free excitons. The magnitude of this absorption is largest near the absorption edge and tails off toward lower energies. The presence of this continuum causes a change of the line shape of the ${A}_{1}$ exciton absorption.

Spectra of flames supported by free atoms

The spectra of the ‘atomic flames’ of organic compounds with the products of discharges through oxygen, hydrogen and water vapour have been examined. Hydrocarbons give bright flames with water products but not, contrary to previous reports, with dry atomic hydrogen. Carbon tetrachloride and other organic halides and also carbon disulphide do give bright flames with hydrogen. The rotational intensity distribution in the OH band in most atomic flames corresponds to a very high temperature, around 8000° K; it is high for methyl alcohol with water products, but only around 2500° K for methyl alcohol with atomic oxygen. The flame of acetylene with products from heavy water, D 2 O, gives mainly OD and CD rather than OH and CH bands. The mechanism of formation and excitation of CH and OH in flames is discussed. When iron carbonyl is introduced into atomic flames very high electronic excitation of iron atoms is observed, as in the reaction zones of ordinary premixed flames; this high excitation is also observed for the flame of carbon tetrachloride with atomic hydrogen.

Spectroscopic studies of low-pressure flames - V. Evidence for abnormally high electronic excitation

Spectrum-line reversal measurements, using lines of Fe, Pb, Na and Tl, have been made for the reaction zones of many flames. For most organic flames the reversal temperatures exceed theoretical maximum temperatures, the values rising very high for lines in the ultra-violet. Lines of Fe requiring up to at least 173 kcal./mole For their excitation are emitted from the reaction zones, but not from the interconal gases. Various hydrocarbons (CH 4 , C 2 H 4 , C 2 H 6 , C 2 H 2 , C 2 H 8 ), methyl alcohol, cyanogen and ammonia burning in premixed flames with oxygen, air or nitrous oxide all show this abnormally high electronic excitation, but flames of H 2 , CO, CS 2 and formaldehyde do not. The hydrogen/nitrous oxide flame does show some abnormal excitation, but of a different character. Diffusion flames at atmospheric pressure do not show the effect. Processes by which electronic excitation may occur are examined, and the cause of the abnormal excitation is discussed. The spectrum-line reversal method of measuring flame temperatures is criticized.