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

Nano structure formations on Au surfaces by Ar gas cluster ion beams (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. However, ripples were formed on Au surfaces at incident angle of 60° without sample rotation. By irradiations of GCIB at incident angle of 60° with sample rotation, cone like structures with 50 nm in diameters were fabricated. However, the surface roughness suddenly decreased above 60°. Even though the surface roughness was the same, ripple structures were formed parallel to the incoming GCIB directions at 85° without sample rotation. The incident angle (θ) dependence on the sputtering depth decreased following cosθ dependence. Very efficient surface smoothing without removing materials were realized with oblique incidence of GCIB.