Soft-x-ray-induced secondary-electron emission from semiconductors and insulators: Models and measurements

Abstract

Secondary-electron energy distribution curves (EDC's) and the total secondary-electron yields relative to such for gold have been measured for seven semiconductors for which electron-electron scattering losses within the emitter were considered dominant and for nine insulators (alkali halides) for which electronphonon scattering losses were expected to be dominant in the transport process. The secondary-electron spectra were excited by Al-Ka (1487 eV) photons and were measured from evaporated dielectric films (of about 0.3 p, thickness) on conducting substrates with an electrostatic hemispherical analyzer of about 0.03-eV resolution. Some of the dielectric photoemitters have appreciably narrower energy distributions and higher yields than has gold; CuI and CsI have EDC widths at half-maximum of about one-third of that for gold, and yield values of 11 and 30 times greater. The FWHM and secondary-electron yield for gold were measured to be about 4 eV and 0.50 electrons per normally incident photon, respectively. The shapes of the EDC's were found to be essentially unchanged for photon excitation in the 0.1 -10-keV region. Strong structural features appear only in the alkali halide EDC's, and it is proposed that these are mainly the result of single-electron promotion of secondaries from the valence band by plasmon deexcitation. A relatively simple model for x-ray photoemission has been developed which assumes that direct excitation of secondaries by photoelectron and Auger-electron "primaries" is the dominant excitation mechanism, and accounts for both electron-electron and'electron-phonon scattering in the transport process. Free-electron conduction-band descriptions are assumed. The theoretical and experimental curves are in satisfactory agreement.

Secondary Electron Cascade Dynamics in KI and CsI

“…Still missing in our approach is a proper treatment of the low-energy regime, where phonon scattering becomes significant for the energy loss of the SEs. 20,22,26 Since our main objective is to compare the characteristics of the electron cascades generated in KI and CsI, we have, for the sake of simplicity, not included the treatment of holes. The average electron-hole pair creation energy is given by the ratio between the energy deposited in the system and the total number of SEs generated.…”

“…[18][19][20] Kane 21 presented a first derivation for the rate of inelastic scattering of electrons by considering the production of electronhole pairs in silicon. Henke et al 22 performed further investigations for semiconductors and insulators as compared to gold, both theoretically and experimentally, with respect to the electrons' total yield and their distribution in energy. In their model they accounted for both electron and phonon scattering, but worked under a free-electron band description and thus did not fully treat the bound nature of the collective excitations.…”

A modified and calibrated drift-diffusion-reaction model for time-domain analysis of charging phenomena in electron-beam irradiated insulators

“…[8][9][10][11] These and more recent [12][13][14][15][16][17][18] studies have not yet been able to provide a complete and coherent account of all observed phenomena. This could be due to the prevailing emphasis on static (stationary) models [19][20][21] rather than time-domain analysis. Studying the dynamics of charging in time domain is especially important in the analysis of response times in particle detectors 2 and in designing novel scanning strategies for SEM.…”

X-ray calibration facility for plasma diagnostics of the MégaJoule laser

“…Figure 2 shows results of x-ray calibrations of the LIL XSC#5 equipped successively with hard (5000 Å lexan/260 Å Al/ 2400 Å CsI) and soft x-ray photocathodes (1000 Å lexan/260 Å Al/ 2400 Å CsI). Measurements are compared to a modified transmission Henke's model [2][3][4] and are in a relatively good agreement. Relative uncertainties achieved thanks to our transposition system and collimation system calibration range henceforth from 7 to 9% k=2 (squared plots on figure 3).…”

“…The same calibrated visible CCD is used to record visible emission coming from the phosphor screen. Figure 4 shows an example of yield calibration for these 13004-p. 3 cameras. Experimental data are compared to both CEA-DIF's work and one XFC model we developed which simulates the behaviour of MCP and phosphor screen in the calibration experimental conditions.…”