Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

Figure 35 High-resolution TEM (along [100] TiO 2 anatase) of a crystal segmentformed by oriented attachment of at least four particles (numbered 1–4). Arrowheadsand lines (0.48 nm apart) show edge dislocations. (From Ref. 97; reprintedwith permission.)thick and are separated by van der Waals gaps. Solution-phase growth at lowtemperature (f200jC) generates nanocrystal platelets (5–20 nm) that selfassemble,or ‘‘self-attach,’’ to form large micron-scale sheets. The underlyingpsuedographitic layered structure supports growth of nanocrystals in theform of 2D platelets. The van der Waals surfaces of the nanocrystal ab plane(the large-area plane in the platelets) are low-energy, coordinatively saturated‘‘faces,’’ whereas the edges of the nanocrystallites are characterized by higherenergyunsaturated sites. Therefore, it is at the edges that the nanoplateletslikely attach, generating the larger sheets. Electron-diffraction patternscollected perpendicular to the large-area sheet surfaces and over large areas(collection radii c 150 nm) demonstrate not only that the crystallographic caxes are indeed perpendicular to the sheet surfaces but that the sheets diffractcoherently, as single crystals would (Fig. 36). Therefore, assembly andCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.