Distribution Of Backscattered Electrons Research Articles

Effects of backscattering on the resolution of scanning Auger Microscopy

We have previously shown that the combination of a UHV SEM with a field emmission gun and a CMA for Auger detection is a valuable tool for surface microanalysis /1,2 3/, and we have demonstrated 30nm resolution using conventional N'(E) detection /4/. Although Auger images can be produced in some circumstances with the resolution of the beam diameter, the size of the analysis volume is influenced by backscattered electrons, and this resolution limit has not previously been experimentally determined. In the present preliminary experiments we have observed Auger line scans across abrupt chemical boundaries as a function of incidence angle, ø, and beam energy, Ep. These intensity profiles show reasonable agreement with Monte Carlo calculations /5, 6, 7, 8/ of the spatial distribution of backscattered electrons. For near-normal incidence, most of the Auger current will be emitted from within the primary beam area.A polycrystalline tungsten surface was flashed clean by electron bombardment heating and 2-5pm diam

Inactivation of catalase monolayers by irradiation with 100 keV electrons.

A catalase monolayer adsorbed on a layer of arachidic acid deposited on a solid support was irradiated with 100 keV electrons simulating the conditions of electron microscopic imaging. Effective doses were calculated taking into account the angular and energy distribution of backscattered electrons. Enzymatic inactivation was chosen as the criterion for damage and was monitored by a rapid and quantifiable but nevertheless sensitive assay. Dose-response curves revealed that inactivation is a one-hit-multiple-target phenomenon, which is consistent with biochemical evidence for a cooperative function of subunits. The experimentally determined target size coincides fairly well with both calculated cross sections for inelastic interactions based on the atomic composition of catalase and with calculated cross sections for ionizing events based on the chemical bonds involved. This legitimates both types of calculations even for complex biomolecules.

Spatial distribution of backscattered electrons in the scanning electron microscope and electron microprobe

Monte Carlo calculations have been applied to the electron scattering theory in scanning electron microscopy. These calculations are based on a single-scattering model in which the screened Rutherford expression for single-scattering cross section and the continuous energy-loss equation of Bethe are used. The surface distribution of backscattered electrons is obtained for Al and Au targets at 20 keV, with 0° and 45° incidence. From these results the exit areas of the backscattered electrons are discussed and compared with experiment. The penetration depths of the backscattered electrons are given at 0° incidence. Everhart's model for backscattering was modified, taking into account the calculated results. The proportion of the singly backscattered electrons to the total backscattered electrons was estimated by the modified model. The result shows that about half of the total backscattered electrons are caused by large-angle single-scattering events. This is consistent with the previous results of Cosslett and Thomas.

135. The dependence of the angular distribution of backscattered electrons on the atomic number of the target: F Tesar and L Eckertova, Czech J Phys, B23 (8), 1973, 867–870 ( in Czech)

135. The dependence of the angular distribution of backscattered electrons on the atomic number of the target: F Tesar and L Eckertova, Czech J Phys, B23 (8), 1973, 867–870 ( in Czech)

Monte Carlo calculations of magnetic contrast from cubic materials in the scanning electron microscope

Monte Carlo calculations confirm that contrast observed in the scanning electron microscope from magnetic domains in materials of cubic anisotropy is due to the alteration of electron trajectories within the specimen. Results are presented for the effects of electron accelerating potential, specimen tilt, and rotation. The contrast arises mainly from the high-energy portion of the back-scattered electron distribution.

The dependence of the angular distribution of backscattered electrons on the atomic number of the target

The dependence of the angular distribution of backscattered electrons on the atomic number of the target

Electron back-scattering patterns—A new technique for obtaining crystallographic information in the scanning electron microscope

Abstract It is shown that the angular distribution of back-scattered electrons can be observed in a scanning electron microscope, and that the patterns observed can be used to obtain crystallographic information about the specimen. The patterns are termed electron back-scattering patterns (E.B.S.P.). The use of these patterns as a crystallographic techniques is shown to have several significant advantages over two other techniques currently in use in scanning electron microscopes.

Influence of Backscattered Electrons on the Resolution of Transmission Secondary Electron Emitters

The total number, energy, and angular distribution of backscattered electrons at 200-4000 V incident energy have been measured for clean (111)B GaAs surfaces. From the electron reflection data the modulalation transfer functions for transmission secondary electron emitters are calculated.

Measurement of the spectral and angular distributions of back-scattered electrons

Measurement of the spectral and angular distributions of back-scattered electrons

Deconvolution Techniques in Auger Electron Spectroscopy

The use of Auger electron spectroscopy (AES) as a tool for the study of band structure or Auger processes in solid has been limited by the lack of resolution resulting from the excitation and measurement methods used in AES. In addition to these instrument broadening effects, it is found that discrete, inelastic interactions of Auger electrons in solid can contribute a structured, low-energy tail which extends several times the main bandwidth. By using the energy-loss and resolution information contained in the nearly elastically backscattered electron distribution in a deconvolution technique, it was found that the effects of instrument broadening and inelastic interactions in the observed Auger electron energy distribution could be significantly reduced, thus yielding higher resolution Auger spectra. Deconvolved spectra were obtained from In and CdS as well as from oxygen adsorbed on several substrates.

Absorption of Electron Kinetic Energy by Inorganic Phosphors

The fraction of the incident energy not absorbed by a phosphor has been determined by measuring the rediffusion coefficient and the energy distribution of backscattered electrons. Measurements for single crystals and powder samples have shown that a large fraction of the electrons scattered back from powder samples have undergone multiple backscattering, resulting in a reduction in the rediffusion coefficient. New estimates of the maximum attainable cathodoluminescence efficiency of ZnS:Ag have been made.

Prediction of X-Ray Production and Electron Scattering in Electron-Probe Analysis Using a Transport Equation

The solution of a Boltzmann equation for electron transport is discussed with emphasis on its application to x-ray production and electron scattering in electron-probe microanalysis. Particular attention is given to the assumptions involved in associating an energy, a cross section for scattering, and a cross section for ionization with each position along the electron path. The Spencer-Fano theory of electron stopping power is applied. The treatment of electron scattering of Brown and Ogilvie is refined using (1) a single scattering equation for short path lengths, (2) a transport equation for intermediate path lengths, and (3) a diffusion equation for long path lengths. The predictions of this Transport Equation Program are compared with experimental data for (1) the energy distribution of backscattered electrons, (2) the depth distribution of x-ray production, and (3) x-ray intensity ratio as a function of alloy composition. The x-ray intensity ratios are corrected for fluorescence due to the continuum, and it is indicated that this correction may be significant.

Backscattering of Electrons from 3.2 to 14 MeV

Monoenergetic electrons of energies from 3.2 to 14 MeV provided by a linear accelerator have impinged normally on thick solid targets. Backscattered electrons have been detected by an ionization chamber, the multiplication factor of which was calibrated with a Faraday chamber as a function of average energy per backscattered electron. Angular distributions of backscattered electrons measured for a total of seven targets, effectively semi-infinite and ranging in atomic numbers from 4 to 92, show a trend similar to Dressel's result. However, the backscattering coefficients obtained are lower than his values and are consistent with those reported by other previous authors. Variations of angular distribution and backscattering coefficient with target thickness also have been investigated for Cu, Ag, and Au targets at an incident energy of 6.1 MeV. Some of the angular distributions observed were compared with results of a simple calculation proposed by the author, and an interpretation has been given that the relative contribution of sidescattering compared with that of diffusion increases with increasing energy in the region considered. Backscattering coefficients for the thinnest targets of lower atomic numbers level off toward a nonzero intercept similar to Cohen and Koral's lower-energy result. This tendency is considered to be caused by the contribution of energetic secondary electrons. The backscattering coefficient $\ensuremath{\eta}({E}_{0}, Z, \ensuremath{\infty})$ of electrons incident on the semi-infinite target of atomic number $Z$ with kinetic energy ${E}_{0}$ above 1 MeV is expressed by an empirical equation $\ensuremath{\eta}({E}_{0}, Z, \ensuremath{\infty})=1.28\mathrm{exp}[\ensuremath{-}11.9{Z}^{\ensuremath{-}0.65}(1+0.103{Z}^{0.37}{{E}_{0}}^{0.65})]$ (${E}_{0}$ in MeV), appreciable deviations from experimental data occurring only for $Z\ensuremath{\le}6$ and $\frac{Z}{{E}_{0}}\ensuremath{\lesssim}2$ Me${\mathrm{V}}^{\ensuremath{-}1}$.

The loss of X-ray intensity due to backscattering of electrons in microanalyser targets

The loss of X-ray intensity caused by the rediffusion of electrons in microanalyser targets has been determined from published experimental data on the energy distribution of backscattered electrons and from a simple relationship between the electron energy and the X-ray intensity. The calculation involves a numerical integration which has been performed on a computer. The data obtained can be used directly to make corrections in quantitative microanalysis.

Backscattering of Kilovolt Electrons from Solids

The total number and energy distribution of backscattered electrons at 0.2-4 kev incident energy ($V$) have been measured for six elements using electrostatic retarding potential techniques. For atomic number $Z\ensuremath{\lesssim}30$, backscattering was found to be essentially independent of $V$ and almost linearly dependent on $Z$. For $Z\ensuremath{\gtrsim}30$, backscattering decreases with decreasing $V$ below 2-3 kev to values less than those for elements of $Z\ensuremath{\simeq}30$, and it no longer is a simple function of $Z$. The ratio of the mean energy of the backscattered electrons to that of the primaries is found to be close to one-half for $Z=6$ and to increase only slightly for the heavier elements. These results are shown to indicate a dominant role of inelastic processes in the scattering of intermediate energy electrons, in contrast to scattering at very high energies, where elastic interactions control the phenomenon.