Video-microscopy-based study of molecular crystal growth modes

Control over molecular crystal growth modes requires control over growth rates. Improvements in crystal size, morphology and defects due to improved control over growth rates have been reported using a modification of the standard constant current method of electrocrystallization. This modified method seeks to maintain a constant current density at the crystal surface, using a theoretical approximation of the actual time-dependence of the crystal surface area. In this paper, we present direct experimental observations of the time dependence of the crystal surface area (and the location and rate of new growth) for single crystals of (BEDT-TTF) 2Cu(SCN)2. Contrary to theory, we find that growth at crystal faces normal to the high conductivity plane does not occur uniformly but instead occurs primarily along electric field lines. Our results illustrate the need for in-situ measurements to control the current density at the crystal surface. The change in the effective surface area for oxidation due to the anisotropic conductivity of molecular crystals is also discussed.