Figure 8. Curved-edge vaterite platelets form by tilting of vaterite nanohexagons.

SEM images without added amino acid (control) showing hexagonal symmetric vaterite at low (a) and high magnification (b,c) with straight-edge growth of platelets (white dashed lines), with matched and aligned subunit nanostructured growth (light grey hexagons), rather than the rounded/curved-edge platelet growth seen in the presence of chiral acidic amino acids. (d–g) Low- and high-magnification SEM images of chiral toroid platelets showing tilting (by approximately −4° or +4°) of nanoparticle (nanohexagon) growth induced by selective chiral amino-acid adsorption. This chirality-inducing effect causes rounded/curved platelet edge growth having either a counterclockwise direction for L-Asp (green arrows) or a clockwise direction for D-Asp (yellow arrows). (h) High-resolution TEM image showing a counterclockwise (long green arrow) growing platelet edge formed in the presence of L-Asp with visible nanohexagons and their internal lattice structure. For consequential ‘daughter' hexagon 2, its (100) plane (blue line) is tilted by approximately −4° (in the counterclockwise direction, short green arrow) relative to the same plane (purple line) in the ‘mother' hexagon 1. Another adjacent hexagon 3 in the field also shows the −4° tilt (red line). This slight offset between the (100) planes of the hexagons is also confirmed by nanobeam electron diffraction in TEM (inset) from the white dashed-circle region. Scale bars, 4 μm (a), 300 nm (b,c,e,g), 2 μm (d,f) and 5 nm (h).