The effect of surface roughness on self-assembly tungsten nanoneedles induced by focused Ga+ ion beam bombardment

The effect of surface roughness on the morphological evolution of polycrystalline tungsten during bombardment by focused ion beam has been investigated. The nanoneedles were self-assembled on the mechanically polished tungsten surface with high roughness (Rz = 8.9 nm). In contrast, a specific surface without nanoneedles was formed on the electrochemically polished tungsten surface with low roughness (Rz = 1.4 nm) although all bombardment parameters except for surface roughness were the same. The concave–convex surface morphology significantly influences nanoneedle formation due to its effect on the dynamic competition between the roughening and smoothing process. This discovery shows the importance of original surface roughness in controlling the morphological evolution of tungsten during ion irradiation and suggests a means for fabricating tungsten nanoneedles that might be used in quantum, photon and electron devices.