Instabilities and coarsening of stressed crystal surfaces in aqueous solution

Strong pattern formation occurs on polished miscut surfaces of sodium chlorate (NaClO3) single crystals that are uniaxially stressed perpendicular to the step edge direction and placed in a saturated aqueous solution. The wavelength lambda of the stress-induced surface instability increased continuously in experiments up to 9 days after placed in the solution. There were three successive regimes of coarsening: (i) one-dimensional step bunching with lambda approximately t(1/4) until an undulation transition was reached, (ii) a two-dimensional coarsening mechanism with lambda approximately t(1/2), and a gradual transition to (iii) Ostwald ripening-like coarsening with lambda approximately t(1/3). The coarsening of the surface patterns towards a stable, flat surface implies the spontaneous formation of a stress-free skin on the surface of the stressed solid.