Taking Account of the Nonstationarity in Analyzing the Optically Stimulated Electron Emission of Irradiated Dielectrics

Abstract

The distortions of the optically stimulated electron emission (OSEE) spectra resulting from the exponential decay in the recording time have been analyzed. It has been shown that taking account of the emission current nonstationary in analyzing the emission spectra permits obtaining isochronal temperature dependences of intensity for selective OSEE bands. The procedure for calculating the quantum yield of the OSEE and the activation barriers of thermal ionization of the excited states of defects is described. Analysis of the photoemission kinetics permits estimating the concentration of active OSEE centers with unknown parameters (optical transition oscillator strength, quantum yield). For diamagnetic oxygen-deficient centers in glassy SiO 2 , the photoemission kinetics has been calculated and the thermal ionization barrier of the photoexcited singlet state and the quantum yield of the OSEE have been determined.Introduction. In our previous work [1], it has been shown that the photoemission properties of the surface of irradiated dielectrics can be interpreted in the stationary approximation. In most cases, such an approach proves to be totally justified and sufficient for estimating a number of characteristics of point defects and the photoemission properties of the surface layer of investigated dielectric materials. At the same time, it should be noted that the stationary approach does not explicitly take into account the distortions of the experimental OSEEs arising during their recording due to the nonstationarity of the emission process [2]. And the question of the qualitative aspect of the degree of distortion of the spectra as well as of the applicability limits of the above approximation in studying the nature of the centers and the laws and mechanisms of OSEE is still open [3][4][5][6]. It may be expected that the most appreciable effect on the results of the OSEE spectra analysis will be produced by the emission nonstationarity in the case of measurements under nonisothermal conditions, where the decay rate of the emission centers varies over a wide range [2].The main aim of the present paper is to develop a method for OSEE spectra processing with allowance for the nonstationarity of the emission kinetics. In so doing, we additionally aim at revealing new information capabilities of nonstationary OSEE spectroscopy as applied to the analysis of the physical parameters of point defects.Photoemission Decay Model. Investigations of the kinetic mechanisms of the relaxation processes of excited states [7] show that they are described, as a rule, by the hyperbolic or the exponential law. When the mechanism of OSEE incorporates the stage of intracenter optical excitation of the defect, then the emission decay obeys the laws of monomolecular kinetics similarly to the processes of radioactive decay [7]. In this case, release of an electron from each local center occurs independently of the state of the other centers and is only determined by the probability of its decay. Therefore, the decay rate of emission cent...

Macroscopic Behavior and Microscopic Factors of Electron Emission from Chained Nanocarbon Coatings

“…The ASED electron spectrometer ( Figure 1, Ekaterinburg, Russia) made it possible to measure the electron emission spectral response in the temperature interval of 20-400 • C. Contrary to stationary external photoelectron emission and internal photoinjection currents over interface barriers, the OSEE is a nonstationary photoelectron emission from localized surface-near electronic states into vacuum [9]. The spectra obtained in our experiments were normalized against the source light flux.…”