Abstract
Almost all {111} surfaces of natural diamond crystals show trigons: triangular etch pits centred on dislocations. The step patterns that arise when two trigons meet allow us to propose an analytical expression for the velocity of steps during etching as a function of their orientation. This step velocity function has a deep global minimum for 〈110〉 steps on a surface inclined towards {110} and a local minimum for 〈110〉 steps on a surface inclined towards {100}. Continuum simulations, based on the kinematic wave theory, of the evolution of step patterns using the step velocity function are able to reproduce quite satisfactorily intricate step patterns formed by multiple interacting trigons. This means that the assumption, implicit in the simulation, that bulk and surface diffusion are not rate limiting during etching is valid. Occasionally, growth hillocks are observed on a {111} surface of a natural diamond. The step patterns on these surfaces show that the step velocity function governing growth does not have the local minimum for 〈110〉 steps on a surface inclined towards {100}. This confirms that the occasionally observed growth patterns and the usually observed etching patterns are formed under fundamentally different conditions.
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