X-ray Photon Correlation Spectroscopy Studies of Ion Beam Nanopatterning Kinetics and Dynamics

Solid surfaces can be ultra-smoothened or patterned on the nanoscale by irradiating with a broad beam of energetic ions. Different nano-patterns can be achieved by varying target-ion combination, the energy of ions, ions’ incident angle or the temperature of the solid target. There are several theories that seek to explain nanopatterning processes, but a definitive fundamental understanding has not been reached. In this study, the surface sensitive X-ray technique of Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) is used to do real-time investigations of nano-pattern formation on Silicon and Germanium due to Ar⁺ and Kr⁺ bombardment. The coherent X-ray beam that is utilized in these GISAXS experiments enables us to study not only the kinetics, but also the fluctuations around the average kinetics, i.e. the dynamics of the nanopatterning process. The X-ray Photon Correlation Spectroscopy (XPCS) two-time correlation function shows a novel behavior in the early stage, with memory stretching back to the beginning of the bombardment. During the late stage, the stationary intensity auto-correlations are computed to determine the correlation times as a function of length-scale.