Atomic-scale aspects of oriented attachment

Abstract

TiO 2 nanocrystal aggregation mechanisms are quantified using molecular dynamics. In vacuum, TiO 2 nanocrystal aggregation is directed by electrostatics. In water, TiO 2 nanocrystals exhibit oriented attachment. Oriented attachment is facilitated by adsorbed water and surface hydroxyls. a b s t r a c tOriented attachment (OA), or the non-random aggregation of crystallites to form single or twinned crystals, has been observed is a variety of different systems during crystal growth. OA is believed to underlie the growth of anisotropic and potentially useful nanostructures, such as wires and plates, as well as complex hierarchical nanostructures. However, its origins are poorly understood. I review insights into OA that we gained in two sets of molecular-dynamics simulation studies of titanium dioxide (anatase) nanocrystals. In the first set of studies, we focused on the role of intrinsic nanocrystal forces in facilitating nanocrystal alignment and aggregation in vacuum. These studies show that, although nanocrystal aggregation occurs in a predictable way, OA is not a common outcome. In a second set of studies, we used the ReaxFF reactive force field to study anatase nanocrystal aggregation in an aqueous (humid) environment. OA occurs in these studies and is mediated by adsorbed water and surface hydroxyls. The OA mechanisms that we find for anatase may be common to other aqueous metal-oxide systems.

Oriented attachment mechanism of triangular Ag nanoplates: a molecular dynamics study

“…Among these, oriented attachment (OA) has received considerable attention. [6][7][8][9][10][11] OA is the aggregation of two crystallites in a way that produces a single crystal 12 or a crystal with planar defects at the attachment plane. 13 Considering all possible morphologies that could occur when two nanocrystals aggregate, we can envision many random, polycrystalline structures and a vanishingly small subset of aggregates that would exhibit OA.…”

Shape-Dependent Aggregation of Silver Particles by Molecular Dynamics Simulation

“…In 1998, Penn and Banfield [12,13] investigated the growth of titania nanocrystals under hydrothermal conditions through high-resolution transmission electron microscopy (HRTEM) and found that the crystal grew through oriented aggregation or oriented attachment (OA). Afterwards, adequate experimental observations confirmed the validity of the OA mechanism [14,15]. In the OA growth process, nanoparticles (building blocks) with identical crystallographic orientations directly combine together to form larger ones.…”

Atomic imaging of the coherent interface between orientedly-attached Mn3O4 nanoparticles

“…Two relevant theories have been propounded: Ostwald Ripening and "oriented attachment" (OA). The OA theory was proposed just before the dawn of the new millennium [2], after which several efforts [3][4][5][6][7][8][9][10][11] have been made to investigate this newly-born theory in the one and a half decade and a number of works has focused on the underlying physical mechanism of OA [12][13][14][15]. Aggregation and coalescence of nanoparticles is considered to be a wide spread process during crystal growth in biological and natural systems [16][17][18] as well as the synthesis of nano-scale materials [19,20].…”