Differential phase-shifting interferometry for in situ surface characterization during solution growth of crystals

We have developed a phase-shifting interferometer for high-resolution in situ imaging of the interfacial morphology during the growth of fast-growing crystals from solution. We demonstrate that the evolution of the surface morphology can be captured as the height distribution over surface areas as large as 2×2 mm2 with a depth resolution of 3 nm and a lateral resolution down to 0.5 μm with a frequency of 10–12 surface images per second. We describe the five image phase-shifting algorithm and subsequent processing, which quantify the surface morphology and yield the height differences between surface features. We illustrate the application of the technique to the (101) face of potassium di-hydrogen phosphate crystals. We visualize and monitor the formation of step bunches on the surface of this crystal during growth.