Controlling nanometer-scale crystal growth on a model biomaterial with a scanning force microscope

We investigate the consequences of exposing an inorganic single-crystal surface to mechanical stimulation with an atomic force microscope tip in the presence of a supersaturated solution. We show that on the {010} cleavage surfaces of brushite (CaHPO₄·2H₂O) layer-by-layer growth at step edges can be induced and controlled with the tip. The growth rates are highly sensitive to the crystallographic orientation of the steps. Experimental evidence is presented that supports a mechanism involving tip-enhanced mass transport of ions to nucleation sites.