Step bunching in potassium dihydrogen phosphate crystal growth: Phenomenology

We have developed a real-time phase-shifting interferometer capable of imaging interfacial morphology with a depth resolution of approximately 25 Angstrom, with a lateral resolution of approximately 0.5 mum across a field of view of 2 x 2 mm(2), and with time resolution of 0.1 s. The method is applied in situ to the (101) face of potassium dihydrogen phosphate crystals growing from an aqueous solution. We image the formation and evolution of solution-flow-induced step bunches and determine their characteristic wavelength to be lambda(c) = 45 mum. This wavelength is within the range predicted by a stability theory on the basis of the balance between the diffusion interaction between steps and capillarity. The value of lambda(c) suggests that step-step interactions are the likely major factor for instability.