| Abstract
| - We aim at insight into the unsteady kinetics and the formation of spatiotemporal patterns of steps during thecrystal growth in systems, in which the growth rate is controlled by the rate of supply of material. For this,we apply phase-shifting interferometry to the crystallization of the protein ferritin. We find that the locallymeasured growth rate, step density and step velocity fluctuate by up to 80−100% of their average values.The fluctuations are due to passage of step bunches generated at the facet edges due to unsteady surfacenucleation. The fluctuation amplitudes decrease with higher supersaturation and larger crystal size, as wellas with increasing distance from the step sources, even while the average value of local slope, a destabilizingfactor, increases. Since size and supersaturation are parameters affecting the solute supply field, we concludethat fluctuations are rooted in the coupling of the interfacial processes of growth to the bulk transport in thesolution. To understand the counterintuitive suppression of the instability, we analyzed the step velocitydependence on local slope and found only a very weak interaction between the steps, likely due to competitionfor supply from the solution. Accordingly, the step bunches propagate with the same velocity as elementarysteps. We conclude that in transport-controlled systems with noninteracting or weakly interacting steps thestable growth mode is that via equidistant step trains, and randomly arising step bunches decay. Stronger stepinteractions may reverse this conclusion, or slow the rate, at which step bunches decay and stability is reached.
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