Nano structure formation by gas cluster ion beam irradiations at oblique incidence

ABSTRACTNano structure formations on Au surfaces by 20 keV Ar gas cluster ion beam (GCIB) irradiation at an oblique incidence were studied. When the incident angle was close to 0° from the surface normal of Au targets, the Au surface was smoothed due to the lateral sputtering effects and there were no structure formations on the surfaces. However, ripples were formed on Au surfaces at incident angle of 60° without sample rotation. When the Au samples were irradiated with Ar-GCIB at 60° with sample rotation, cone like structures with 50nm in diameters were fabricated and the surface roughness had a maximum value. However, the surface roughness suddenly decreased over incident angle of 60°. Even though the surface roughness was the same in the cases with and without sample rotations at 85° incidence, ripple structures were formed parallel to the incoming GCIB directions when there was no rotation. The incident angle dependence of the sputtering depth decreased following cosθ dependence. Very efficient surface smoothing without removing materials were realized with oblique incidence.