[en] A simple analytical model has been used to determine the effects of backscattered electrons on the analysis area in scanning Auger microscopy. For normally incident electrons, the radius r_a of the analysis area is calculated corresponding to detection of 80, 90, and 95% of the total Auger-electron signal as a function of two sample parameters, the backscattering factor R and the Gaussian parameter σ_b describing the radial distribution of the backscattered electrons. For a reasonable range of these parameters, r_a depends linearly on σ_b and to a lesser extent on R. Values of r_a can also be appreciably larger, by more than a factor of 100, than the widths of the incident beam in modern instruments, and need to be considered in quantitative analyses of particles and inclusions. Monte-Carlo calculations are needed for more realistic evaluations of the analysis area and to determine this area for non-normal incidence of the electron beam

No abstract available

[en] The report summarizes technical activities and accomplishments of the NIST Surface Science Division during Fiscal Year 1990. Overviews are presented of the Division and of its three constituent groups: Surface Dynamical Processes, Thin Films and Interfaces, and Surface Spectroscopies and Standards. These overviews are followed by reports of selected technical accomplishments during the year. A summary is given of Division outputs and interactions that includes lists of publications, talks, committee assignments, seminars (including both Division seminars and Interface Science seminars arranged through the Division), conferences organized, and a standard reference material certified. Finally, lists are given of Division staff and of guest scientists who have worked in the Division during the past year

No abstract available

[en] An important measure of the opacity of a solid with respect to monoenergetic electrons in a solid is the effective attenuation length (EAL). However, there is much controversy in the literature concerning the definition of this parameter. It has been shown recently that different quantitative applications of electron spectroscopies require EALs resulting from different expressions. In the present report, these expressions for typical applications of X-ray photoelectron spectroscopy and Auger electron spectroscopy are briefly reviewed. The EALs needed for determination of overlayer thicknesses and for measurement of surface composition are compared for the same experimental configuration. These comparisons are made for selected photoelectron lines for which we expect strong electron elastic-scattering effects (Cu2s and Cu2p_3/2 in Cu and Au4s and Au4f_7/2 in Au). Substantial differences between EALs for these lines were found for the two applications. Synchrotron radiation can be used for experimental determination of the EAL values. These values can facilitate evaluation of the reliability of theoretical models used in calculations of EALs

[en] We describe two NIST databases that can be used to characterize thin films from Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) measurements. First, the NIST Electron Effective-Attenuation-Length Database provides values of effective attenuation lengths (EALs) for user-specified materials and measurement conditions. The EALs differ from the corresponding inelastic mean free paths on account of elastic-scattering of the signal electrons. The database supplies 'practical' EALs that can be used to determine overlayer-film thicknesses. Practical EALs are plotted as a function of film thickness, and an average value is shown for a user-selected thickness. The average practical EAL can be utilized as the 'lambda parameter' to obtain film thicknesses from simple equations in which the effects of elastic-scattering are neglected. A single average practical EAL can generally be employed for a useful range of film thicknesses and for electron emission angles of up to about 60 deg. . For larger emission angles, the practical EAL should be found for the particular conditions. Second, we describe a new NIST database for the Simulation of Electron Spectra for Surface Analysis (SESSA) to be released in 2004. This database provides data for many parameters needed in quantitative AES and XPS (e.g., excitation cross-sections, electron-scattering cross-sections, lineshapes, fluorescence yields, and backscattering factors). Relevant data for a user-specified experiment are automatically retrieved by a small expert system. In addition, Auger electron and photoelectron spectra can be simulated for layered samples. The simulated spectra, for layer compositions and thicknesses specified by the user, can be compared with measured spectra. The layer compositions and thicknesses can then be adjusted to find maximum consistency between simulated and measured spectra, and thus, provide more detailed characterizations of multilayer thin-film materials. SESSA can also provide practical EALs, and we compare values provided by the NIST EAL database and SESSA for hafnium dioxide. Differences of up to 10% were found for film thicknesses less than 20 A due to the use of different physical models in each database

[en] A survey is given of the available cross-section data for ionization of inner-shell electrons by incident electrons in the range of interest for electron-probe microanalysis and for Auger-electron spectroscopy of solid surfaces. Owing to the paucity of data, the bulk of the discussion is limited to K-shell and L-shell ionization of light atoms. Calculated, semiempirical, and experimental cross-section data have been intercompared graphically and through fits to the linearized Bethe equation for inner-shell ionization (the Fano plot). Almost all of the data could be satisfactorily fitted over the range 4 approx.greater than or equal to U/sub nl/approx.greater than or equal to 30, where U/sub n/=E₀/E/sub nl/, E₀ is the incident electron energy, and E/sub nl/ is the binding energy of electrons in the nl shell. From these fits, values could be obtained of the ''effective'' Bethe parameters b/sub nl/ and c/sub nl/. Values of the parameter b/sub nl/ have also been derived from photoabsorption data and were found to be generally consistent with the ionization data if account was taken of the distribution of differential oscillator strength with respect to excitation energy and the consequent expected variation of b/sub nl/ with incident electron energy. The derived ''effective'' Bethe parameters should not therefore be used outside the range of each fit

[en] Differential cross sections (DCSs) for elastic scattering of electrons by neutral atoms are extensively used in studies of electron transport in solids and liquids. A new NIST database has recently been released with DCSs calculated from a relativistic Dirac partial-wave analysis in which the potentials were obtained from Dirac-Hartree-Fock electron densities computed self-consistently for free atoms. We have compared calculated DCSs with measured DCSs for argon for electron energies between 50 eV and 3 keV, and found good agreement for electron energies above about 1 keV but with increasing deviations as the energy is reduced. These deviations are due to the neglect of absorption and polarizability effects in the calculations. Nevertheless, DCSs for neutral atoms have been successfully used in simulations of elastic backscattering of electrons by solid surfaces with energies down to 300 eV as well as for many other applications. It is suggested that this success might be due at least partially to the smaller absorption correction for the DCSs in solids on account of the smaller total inelastic scattering cross sections than for the corresponding free atoms

[en] The imaging properties and energy aberrations of a commercial double-pass cylindrical-mirror analyzer have been characterized using an extension of the method recently reported by Seah and Mathieu. The electron beam from the coaxial electron gun was rastered across a test surface and the intensity of either elastically scattered electrons or of electrons at other selected energies was stored in a computer as a function of beam position on the specimen and other experimental parameters. The intensity data were later plotted to provide an ''image'' of the detected intensity. Images of this type are presented for electron energies of 100, 500, and 1000 eV and for the application of small offset voltages (typically between -1 and +5 V) between the analyzer and the gun cathode with the instrument operated in conditions appropriate for XPS or AES. Small offset voltages (<1.5 V) lead to significant changes in image shapes while larger offset voltages (> or approx. =5 V) lead to image shapes similar to those for the elastic peak but with 20%--40% increased widths. Deflection of the incident beam by up to 2 mm from the axis caused variations of up to +-0.15 eV in the measured positions of the elastic peak. Our observations can be interpreted qualitatively in terms of the known relationship between detected signal and combinations of position of electron emission from the specimen, angle of emission, and electron energy. The images obtained with elastically and inelastically scattered electrons provide a convenient and quantitative means of assessing instrument performance and of defining the specimen area being analyzed for the particular combination of instrument operating conditions and the energy width of AES or XPS features from the specimen

[en] Large final-state effects have been observed in the 3p, 3s, and 2p electron energy-loss spectra of vanadium as the incident-electron energy was reduced from 1500 eV to about 50 eV above the core threshold. Changes in the line shapes for the onset of 2p₃2/ excitation and changes in measured threshold energies for 2p₃2/, 3s, and 3p excitation show the significance of the transition from sudden to adiabatic excitation. Strong excitations due to exchange effects are also observed in the 3p spectra at low incident energies