Factors influencing metal impurity induced ion beam patterning of Si(001)

On Si(001) ion beam pattern formation at angles θ<45 with respect to the surface normal takes only place in the presence of metal impurities. Here we report experiments addressing the factors influencing impurity induced pattern formation using well controlled UHV experiments. Ion erosion is performed through fluences >5 x 1021ions/m2 of 2 keV Kr+ with a differentially pumped fine focus ion source. Co-deposition of metal impurities is performed through co-sputtering and co-evaporation of Fe. With increasing Fe concentration under otherwise identical conditions a smooth unpatterned surface, a dot pattern and finally for the highest Fe concentrations a ripple pattern is observed. Co-sputtering measurements at temperatures below and above room temperature lead to identical pattern sequences. Thus thermal diffusion is irrelevant for ion beam pattern formation on Si(001) at room temperature. Finally, the orientation of ripple patterns appears to be associated with the direction of impinging Fe atoms.