Low-energy secondary electrons

For low-LET radiations, nearly 30% of dose is deposited by low-energy secondary electrons [115],... 

Ultimately, resolution in electron beam lithography is set by the range over which the primary electrons interact with the resist. That is by the distance over which the low energy secondary electrons are created (the resist is exposed mainly by secondaries) and by the range of the secondaries in the resist. For thin resists, and thin substrates (thin compared with the primary electron penetration) this resolution limit has been measured to be about 12 nm (43). 

In principle, electron beams should be able to produce structures with dimensions as small as the beam diameter in a STEM (0.5 nm), but before this can be done techniques must be found which are sensitive to the high energy primary electrons, rather than the low energy secondaries electrons. This is... 

Primary electron energy dissociative electron capture results from low-energy secondary electrons released from a metal surface. 

The first process involves electron ionization to form radical M-1"1 molecular ions. This process has been observed primarily for nonpolar molecules. The proposed mechanisms are charge-exchange transitions between sputtered ions and the neutral organic molecules or electron attachment of low-energy secondary electrons to neutral molecules. The fragmentation reactions of the M ions usually follow the dissociation pathways for odd-electron gas-phase ions. 

Scanning Electron Microscopy (SEM) [21], Topographical images in a SEM are formed from back-scattered primary or low-energy secondary electrons. The best resolution is about 2-5 nm but many routine studies are satisfied with a lower value and exploit the... 

Tang H, Walker TG, Hopster H et al (1993) Anomalous behavior in the spin polarization of low-energy secondary electrons from Gd(0001). Phys Rev B 47 5047... 

The most traditional secondary electron detector is the Everhart Thomley detector (Fig. 7.10). The low energy secondary electrons are easily attracted and deflected by the field produced by the collector (polarised grid at a voltage of+200V). This potential is sufficient to curve the trajectories of these electrons and guarantee a significant collection angle. The detector receives electrons even from object points not visible to it. 

This technique is used to study the surface or near-surface characteristics of specimens, and is one of the most versatile and widely used instruments in science. In this technique, a beam of electrons from a thermionic emission type tungsten filament is accelerated to 20-40 KeV, demagnified and reduced in diameter to 2-10nm on point of contact with a sample. The fine beam is scanned across the sample and a detector counts the number of low-energy secondary electrons or the radiation given off from each point on the surface (McHardy and Bimie, 1987 Newbury et al., 1987 Goodhew and Humphreys, 1988). Electron emission from a... 

The majority of the electrons emitted under EUV irradiation have low energies, <10 eV. The inset in this figure shows a peak at 80 eV in electron emission, which is probably due to photoelectrons emitted directly from the discrete absorption of EUV photons. The large peak in the secondary elec tron spectrum is due to the low energy secondary electrons, which are created by the photoelectrons that did not escape the surface immediately, in a process as described above. 

Depth sensitivity depends on the analysis mode and energy range used. SEM with low energy secondary electrons can result in a surface sensitivity of 20 A, whilst EDX reveals information about the top few microns of the sample. Depth sensitivity for back-scattered electrons is greatly dependent upon the electron beam energy and the elemental composition of the sample but is generally hundreds of nanometers. 

The major problem encountered in APS is the signal-to-noise ratio. In the SXAPS, broad-band noise is present due to Bremsstrahlung photons, and this increases steadily with the primary electron energy [45]. In AEAPS, the yield of low energy secondary electrons k not a simple... 

But allowance for the second-order process gives rise to one more (low-energy) secondary electron, an intermediate-state electron, whose scattering by the local atomic structure must be taken into account. As in the case of the final electron, we restrict our consideration to single scattering by neighboring atoms. 

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