Microtopography of surfaces eroded by ion-bombardment

The Stewart-Thompson Theory applied to the Glow Discharge

“…[4], it is also evident when comparing picture 3a On closer inspection of an inclusion (Fig. 4 a) suspected of causing the formation of cones, it was found that the inclusion consists of a core and some kind of coating.…”

“…The theory predicts that after the formation of a small surface step, induced by a foreign particle such as an inclusion, the dependence of the sputter ratio on the angle of incidence causes the formation of cones. The sputter ratio increases when the angle between the incident ion and the normal of the bombarded surface is increased and decreases again after passing a maximum of an angle, typically 70-80°, referred to as the angle for optimum sputtering [4], This theory applies, according to Stewart and Thompson, when samples of pure crystals (metals) are bombarded by 5 -8keV argon ions.…”

“…Therefore, a sputtering mechanism different from the one where high energy particles (IMMA: 20 keV; Ref. [4]: 5-8 keV) penetrate deeply into the lattice (IMMA: ^ 12 nm; Ref. [4]: nm) must also be considered.…”

“…[4]: 5-8 keV) penetrate deeply into the lattice (IMMA: ^ 12 nm; Ref. [4]: nm) must also be considered. High energy particles cause a cascade of collisions in the direction of the lattice whereby the momentum transferred is spread over a wide angle and will finally have a component which points outwards from the lattice, transferring enough energy to a surface atom to be released.…”

“…The formation of these particularities on the sputtered sample surface has been related to the dependence of the sputtering ratio on the angle of incidence [4] and resulted in the theory of Stewart and Thompson. This theory has been confirmed by several authors [5,6].…”