Figure 3.

Single-particle analysis of the ring-like pore structures. About 30 dispersed hexagonally ring-like particles were boxed and averaged to give a reference. Then 1,077 particles in the lattice packing form were extracted automatically by a cross-correlation method and screened manually for final processing. Shift alignment to the reference is first performed without angular rotation alignment. The particles were then masked with a circle to exclude the boundary elements and rotationally aligned by free alignment followed with the hierarchical classification. The variances among the particles are so small that only the global average maps were calculated (1). The global average map of all of the particles with only shift alignment but without rotational alignment were also calculated (2). The difference between the rotationally aligned and unaligned average images is so small that the final projection map was calculated only from the global average map without rotational alignment (3). The resolution of the averages were determined to be 3.2 nm by different phase residual method (32). The image box length represents 11.7 nm.