Nanoscale Dynamics During Self-Organized Ion Beam Patterning Of Si. I. Ar+ Bombardment

X-ray photon correlation spectroscopy (XPCS) is used to investigate the fluctuation dynamics during self-organized nanopatterning of silicon by Ar+ bombardment at 65 degrees polar angle. Rich structure is observed in the development of the correlation dynamics as seen in the evolving correlation time tau(q(vertical bar vertical bar)) and fluctuation relaxation exponent n(q(vertical bar vertical bar)). On length scales of the ripple structure, local structure becomes ever more long lived as coarsening progresses. In addition, tau(q(vertical bar vertical bar)) develops a peak on length scales corresponding to the ripple wavelength. As patterning progresses, correlation times become asymmetric between the positive and negative directions, suggesting the possibility of different dynamics on the slopes facing toward and away from the ion beam. Relaxation exponents show evolution from linear dynamics at early times to compressed exponential relaxation at low wave numbers and stretched exponential relaxation at high wave numbers. Compressed exponential behavior is reminiscent of stress relaxation processes observed in glasses.