In situ observation of surface morphology evolution in tungsten under focused Ga+ ion irradiation

The effects of energetic Ga ion bombardment on the surface morphology of mechanically polished polycrystalline tungsten are investigated by focused Ga+ ion beam irradiation with in situ scanning electron microscopy, as well as ex situ atomic force microscopy. The amount of removed material from the tungsten surface increased with increasing of incident ion angle, and also increased with ion energy from 5 to 30 keV while keeping all other bombardment parameters constant. The nanoneedle-shaped morphology formed by self-assembly in the surface of tungsten under off-normal angle bombardment, the larger the incident angle, the easier for the needle formation. In contrast, only a net-like microstructure formed under normal incident angle. Moreover, more Ga+ ion fluence was needed to form pores at normal incident angle comparing to that under 52° incident angle.