Changes in surface morphology and vaporization rate upon vaporization of arsenic (111) cleavage surfaces

The initial vaporization of freshly cleaved As(111) surfaces has been studied by a combination of microbalance weight-loss measurements and continuous microinterferometry. Vaporization is accompanied by formation and growth of triangular pits on the originally flat surface. The slopes (5°–9°) and other characteristics of the pits show that they have a terrace–ledge structure and form at dislocations. Pit sides have constant slope indicative of an average, constant terrace width between ledges. Isolated pits grow outwards at a constant rate while mass loss from a freshly cleaved increases quadratically with time. The mass-loss rate attains steady state, independent of the pit density, when the surface is covered by intersecting pits. The slopes of pits formed on surfaces sublimed into a vacuum are greater than those on surfaces vaporized under saturations nearer equilibrium. The pit growth rates and characteristics, as well as the time-dependent mass-loss rates, are quantitatively consistent with a vaporization mechanism in which the vaporization rate is proportional to the total ledge length on the surface. The results imply that formation of As4 vapor species occurs with equal probability, per unit length of ledge, along any ledge segment.