X-ray photon correlation spectroscopy (XPCS) is used to investigate the fluctuation dynamics during self-organized nanopatterning of silicon by ${\mathrm{Ar}}^{+}$ bombardment at ${65}^{\circ }$ polar angle. Rich structure is observed in the development of the correlation dynamics as seen in the evolving correlation time $\tau \left(q_{\left|\right|}\right)$ and fluctuation relaxation exponent $n\left(q_{\left|\right|}\right)$. On length scales of the ripple structure, local structure becomes ever more long lived as coarsening progresses. In addition, $\tau \left(q_{\left|\right|}\right)$ 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.

• Received 24 July 2020
• Revised 3 January 2021
• Accepted 4 May 2021

DOI:https://doi.org/10.1103/PhysRevB.103.195423