Growth Mechanism of Highly Branched Titanium Dioxide Nanowires via Oriented Attachment

Abstract

Understanding fundamental crystal nucleation and growth mechanisms is critical for producing materials with controlled size and morphological features and uncovering structure–function relationships in these semiconducting oxides. Under hydro-solvothermal conditions, uniform branched and spherulitic TiO2 rutile nanostructures were formed via (101) twins. On the basis of detailed, high-resolution scanning electron microscopy and transmission electron microscopy analyses, we propose a mechanism of branched growth and the (101) twin formation via oriented attachment and subsequent transformation from anatase to rutile.

Crystallization by particle attachment in synthetic, biogenic, and geologic environments

“…This dependence can even invert the sequence of polymorph stability relative to that observed for the bulk phases (58). Thus, primary particles may be a polymorph that is only stable at a small size, while the secondary particles have the structure of the stable bulk form (34,56,57,60). That is, the free-energy barrier to nucleating small particles possessing a form that is metastable in the bulk phase will be lower than the barrier to nucleating particles of the same size possessing the stable bulk form.…”

“…1 and 4). Precursors can include one or more solid amorphous phases (10,12,14,15,18,30,46,64,65), dense liquids or gels (21,49,53), or crystalline nanoparticles (30,57,60,63). Each results in a distinct growth history, but whether or not the final outcomes are also distinct should depend on the extent to which monomer-by-monomer addition competes with the particle-attachment pathways and coarsening or recrystallization processes modify the structure and morphology of the growing crystal.…”

“…In some cases, increasing size can result in decreased internal strain and defect content (82). Finally, in systems for which there is a switch in phase stability with particle size, as discussed above, nanoparticles of one phase may initially form and transform to the bulk phase as they aggregate and grow in size (34,56,57,60). For example ~1-nm ferrihydrite-like primary particles structurally rearrange upon attachment to the surface of magnetite crystals to merge with the magnetite crystal structure (57).…”

Trends in mica–mica adhesion reflect the influence of molecular details on long-range dispersion forces underlying aggregation and coalignment

“…Among the numerous styles of CPA, none has garnered more attention than oriented attachment (OA) by which crystalline nanoparticles assemble into larger single-crystal structures through attachment on coaligned crystal faces (4,5). OA often leads to formation of hierarchical structures, such as highly branched nanowires (6), tetrapods (7), and nanoparticle superlattices (8), endowed with unique properties (9) that are inexorably tied to this nonclassical process of crystallization.…”

“…OA has been inferred for metals (10), semiconductors (11), and insulating oxides (6); it has been directly observed via liquid phase transmission electron microscopy (LP-TEM) (5), and the evolution of particle distributions during OA has been captured with cryogenic TEM (12). OA is highly dependent on solution conditions, including pH, ionic strength, and temperature, and is marked by two important stages.…”