Energy shift and broadening of the spectra of electrons backscattered elastically from solid surfaces

Abstract

In the present work our experimental results on the energy shifts and energy widths (full width of half-maximum) of the quasi-elastic peaks (1-5 keV) obtained using a high-energy-resolution electron spectrometer and different (C, Si, Ni and Au) surfaces are compared with those calculated by assuming single elastic scattering on free atoms having a Maxwell-Boltzmann thermal velocity distribution. There is a good agreement in the case of the energy shifts as well as for the energy broadenings obtained using higher atomic number polycrystalline samples (Ni, Au). In the case of Si, however, the measured energy broadening is systematically larger by 15-20% than the calculated broadening for the whole primary beam energy range. Compared with the calculated values, considerably larger broadenings (by 30-60%, depending on the primary beam energy) were observed for carbonic samples. The contribution of the multiple elastic scattering to the yield of the electrons backscattered elastically, and the effect of the multiple scattering on the energy shifts and Doppler broadenings, have been determined using Monte Carlo simulations. Our results show that multiple scattering causes only small changes in energy shifts and energy broadenings of elastic peaks in the case of the samples and primary electron energy region studied.

The Potential of Materials Analysis by Electron Rutherford Backscattering as Illustrated by a Case Study of Mouse Bones and Related Compounds

“…It is based on the fact that energetic~multiple keV! electrons scattered over large angles transfer a significant amount of momentum to the scattering nucleus~Vos, 2001; Varga et al, 2001Varga et al, , 2006!. As a consequence, the nucleus acquires kinetic energy, and the energy of the electron is reduced by this amount.…”

Influence of Recoil Effect and Surface Excitations on the Inelastic Mean Free Paths of Electrons in Polymers

“…The classical approach for explaining and describing the recoil effect was given by Börsch et al [11]. The quasi-elastic scattering of electron of given kinetic energy, E, on atom characterized by atomic number, Z, results in a shift of the energy of the elastic peak position, ∆E (energy loss) [12], and energy broadening of the elastic peak [13,14]. This energy loss, ∆E, is proportional to the incident energy, E, the mass of the electron, m, and sin 2 (θ 0 /2) (where θ 0 is the electron scattering angle), and inversely proportional to the atomic mass of the scattering atom, M [11].…”

“…the Doppler broadening due to thermal motion of the scattering atoms is proportional to sin(θ 0 /2)(Em/M ) 1/2 and temperature, T 1/2 , as well as the thermal vibration energy of the lattice atoms [11,13,14]. The validity of the Börsch et al formula was verified experimentally [11][12][13][14]. A study of the recoil shift in Cu, Ag, and Au using 250-3000 eV electrons has been published by Laser and Seah [12].…”

“…For the multicomponent compounds, different recoil energy losses and energy broadenings for the constituent atoms, especially those with very different atomic numbers Z, modify the shape of the elastic peak [13]. The total cross-section for electron elastic scattering on atom varies approximately as the square of the atomic number, Z, and the effect of multiple scattering by different atoms cannot be neglected [14]. These effects can be important for experimental determining of the IMFPs using the EPES method, especially when polymers of high hydrogen content and samples containing elements of varying atomic number range are investigated.…”

“…The Monte Carlo (MC) algorithm used for simulating electron transport in a solid neglects recoil effect [11][12][13][14] and surface excitations [15][16][17][18][19][20][21][22][23]. The IMFPs for polythiophenes measured by EPES using a high resolution analyser have already been published [10].…”