Isolated nano-tendril bundles on tungsten surfaces exposed to radiofrequency helium plasma

The DIONISOS experiment is used to study the impact of RF helium (He) plasma on the surface morphology of tungsten (W) at a frequency of 13.56 MHz. Helium ion energy distributions with a span of 7075 eV, while still below the sputtering threshold result in nano-tendril bundles (NTBs) and free-standing W whiskers on surfaces at 1020 K. The NTBs are distributed intragranularly with coverage of less than 10% while reaching up to 30 mu m normal to the surface for He ion fluence of 7.6 x 10(25) m(-2) and flux density of 10(22) m(-2) s(-1). Analysis of the NTB interior and sub-surface structure is provided through focused ion beam cross section. (C) 2017 The Authors. Published by Elsevier Ltd.