Periodic Ripple Patterns Research Articles

Nonlinear amplitude evolution during spontaneous patterning of ion-bombarded Si(001)

The time evolution of the amplitude of periodic nanoscale ripple patterns formed on Ar+ sputtered Si(001) surfaces was examined using a recently developed in situ spectroscopic technique. At sufficiently long times, we find that the amplitude does not continue to grow exponentially as predicted by the standard Bradley–Harper sputter rippling model. In accounting for this discrepancy, we rule out effects related to the concentration of mobile species, high surface curvature, surface energy anisotropy, and ion-surface interactions. We observe that for all wavelengths the amplitude ceases to grow when the width of the topmost terrace of the ripples is reduced to approximately 25 nm. This observation suggests that a short circuit relaxation mechanism limits amplitude growth. A strategy for influencing the ultimate ripple amplitude is discussed.

Various phase transitions and changes in surface morphology of crystalline silicon induced by 4–260-ps pulses of 1-μm radiation

We report the first pulse width study of the various morphological changes and bulk phase transitions of single crystal silicon irradiated by 1-μm pulses of 4–260-ps duration. In particular, we find that amorphous silicon is formed from the melt contrary to published expectations, but only for pulse widths less than 10 ps. We also find that the single shot melting threshold is pulse width dependent. Additionally, we observe the growth of multishot damage and of periodic ripple patterns with pulses as short as 4 ps.

Laser-induced periodic surface structure. II. Experiments on Ge, Si, Al, and brass

We report the results of a detailed investigation into the properties of the periodic damage structure that can be produced on nominally smooth surfaces of solids when they are irradiated with a single beam of intense laser radiation. The study is primarily concerned with extracting information from the Fourier transform of the damage structure as observed via the Fraunhofer diffraction pattern produced by reflecting a cw laser beam from the surface. In particular, the patterns produced in Ge, Si, Al, and brass by pulsed 1.06- and 0.53-\ensuremath{\mu}m radiation are compared as a function of the angle of incidence and polarization of the beam. We find that all materials contain similar and much more intricate detailed structure than has been previously appreciated. Whereas periodic ripple patterns oriented perpendicular to the polarization at near-normal incidence are commonly reported, the diffraction patterns reveal that in fact there exists a continuous distribution of periodic structure oriented at all angles with respect to the polarization. At near-normal incidence there are two dominant sets of "fringes" running perpendicular to the polarization, while for a $p$-polarized beam incident at >35\ifmmode^\circ\else\textdegree\fi{} there exist three dominant periodic structures; two which run perpendicular to the polarization and one which is oriented parallel to it. For $s$-polarized light incident at angles >35\ifmmode^\circ\else\textdegree\fi{} there are two dominant patterns which form a cross-hatched pattern with axes oriented at 45\ifmmode^\circ\else\textdegree\fi{} to the plane of incidence. A study of the evolution of the patterns on a shot-to-shot basis indicates that both the initial and laser-induced surface roughness play important roles in the evolution of the damage. We conclude with a comparison of our experimental results with those predicted by the theory developed in the preceding paper. Excellent agreement is found.