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). Modulation of incident He ion energy with a span on the order of 50 eV and below the sputtering threshold at a frequency of 13.56 MHz results in nano-tendril bundles (NTBs) and free-standing W whiskers on the surface at 1020 K. The NTBs are distributed intra-granularly with coverage of less than 10% while reaching up to 30 microns normal to the surface for He ion fluence of 5.8 x 10^25 m^-2 and a flux density of 1.0 x 10^22 m^-2 s^-1. Analysis of the NTB interior and sub-surface structure is provided through focused ion beam cross section.