S.N. Ermolov

Neutralization of He ions scattered from Ca surface

The neutralization of He ions scattered from a Ca surface, as well as Al and Cu surfaces as references, is discussed on the basis of the incident energy dependence of low energy ion scattering (LEIS) spectra. The neutralization probability obtained for Ca is much higher than that expected on the basis of the Auger mechanism, indicating that the collision-induced (CI) process is dominant for the neutralization. The markedly large background component in the LEIS spectrum for Ca, corresponding to the re-ionization at the surface of He ions scattered and neutralized in the bulk, is consistent with the high probability of a CI process.

Growth and characterization of monocrystalline tungsten substrates

High-purity tungsten single crystals of different crystallographic orientations were prepared by electron beam floating zone melting as well as by a strain-annealing technique. The substructure of these substrates was examined by SEM, optical microscopy and X-ray diffraction methods. Samples were prepared with different crystallographic planes and with substructures free from small-angle boundaries. The samples had excellent structure parameters, as deduced from the full-width at half-maximum of the rocking curves which was less than 0.1° for the substrates prepared by strain annealing. The substrates were subsequently cleaned in UHV using a newly designed compact electron beam gun for heating to 2500°C. The surface cleaning procedures were studied using AES, LEIS and LEED. Clean and well-ordered surfaces were obtained.