New collective trampoline mechanism of accelerated ion-plasma sputtering

Abstract

Results of the newly found anomalous accelerated plasma ion sputtering of solid-state targets are presented. The rate of sputtered particles comprises from one to several tens of atoms per one impinging ion, ion energies being in the range of tens to five hundreds electron volts. The anomalous sputtering is realized for ion current density in the plasma flow being not less than 10 mA cm −2 and threshold specific power of the ion flow from 0.7 to 2 W cm −2 depending on the target material. The qualitative explanation proposed dubbed 'collective trampoline accelerated sputtering'. The collective nature of this sputtering regime differs from the conventional pair collision cascade one. The trampoline sputtering leads to the intense texturing of the materials with submicron characteristic structure sizes. The new sputtering method could be applied (i) in the technology of plasma ion deposition of the functional coatings to replace the widespread magnetron sputtering sources of lower productivity; (ii) in the photovoltaics to solve the problem of the so-called 'black' multi-crystalline silicon in order to reduce the light reflectance coefficient; (iii) in the production of silicon composite anodes for lithium ion batteries to enhance their lifetimes regarding charge/discharge cycles, for which the final positive result is largely determined by the surface structure of the silicon wafer for photovoltaics and the surface structure of the anode current collector for lithium-ion batteries.

Nanosized Structure Formation by Trampoline Ion-Plasma Sputtering

“…We surmise that the ejection of the material during trampoline sputtering is due to the emission of not only individual atoms, but also the nanoscale clusters. This assumption supported by high trampoline sputtering coefficients [4], which are two orders of magnitude higher than the coefficients of a classical cascade sputtering [3]. Experiments on the formation of coatings during trampoline sputtering of targets from various materials confirm this assumption.…”

“…The trampoline sputtering demonstrates a threshold character and occurs when the ion current density on the j  sample exceeds about 10 mA/cm 2 , and the ion energy E i exceeds about 70-100 eV [4]. Nanoscale structures were formed more efficiently near the threshold values of the ion-plasma flow parameters.…”

“…The surface, severely distorted by the trampoline sputtering, remembers its modified state. This phenomenon makes the trampoline sputtering even more promising from the technological point of view in addition to its advantageously high productivity in target sputtering [4].…”

“…The experiments were performed on the equipment [4], in which the ion-plasma flow with a density of up to 50 mA/cm 2 and with energy of up to 30 eV is created by a helicon source. If a negative potential up to 700 eV was applied to the sample holder, it is possible to increase the energy of ions that bombard the sample with practically unchanged plasma parameters in the region of plasma flow genera-tion.…”

“…In this paper, the authors studied the texturing effects for the surfaces of metals, insulators, and semiconductors when exposed to collective trampoline ion-plasma sputtering found by us recently [4]. In particular, the trampoline sputtering leads to the formation of the surface structure on the target with two characteristic scales: nanoscale patterns (from several to tens of nanometres) and submicron structures (from hundreds to thousands of nanometres).…”