Regular and irregular growth and dissolution of (101) ADP faces under low supersaturations
Abstract A technique has been developed to automatically measure normal growth rates as low as 3 × 10 -9 cm/s and higher, the tangential growth rates and hillock slopes. The method was applied to the (101) ADP growth in the kinetic regime at various supersaturations 0.05% σ ⋍ 8.5 × 10 −7 erg/cm (corresponding to the surface energy of 16 erg/cm 2 ), and the step kinetic coefficient (i.e. the rate of incorporation at the steps), ⋍ 0.3 cm/s. The rates of growth (incorporation) and dissolution at steps were found to be nearly equal, whereas the dissolution rates at dislocations exceed the growth rates by up to 3 times. This effect is considered as evidence of a stress field around a dislocation. At supersaturations σ ∗ = 0.25% and pH =3.6, the growth stopped completely. At 0.25% σ σ > 0.35%, regular growth were observed. Increase in pH results in a shift of these supersaturation ranges to lower values. After an exposure at σ ∗ , the not-growing face became poisoned: when, after the exposure, the supersaturation is raised to a value σ > σ ∗ , the face still does not grow for several minutes. If this new value σ > σ ∗ is high enough, the growth sta immediately. This phenomenon is attributed to the formation of stoppers previnting propagation of steps (Cabrera-Vermilyea mechanism). The minimal supersaturation above which the growth starts is a direct function of the exposure duration and allowed us to estimate the surface density of stoppers and their adsorption isotherm.