Crystallographic reorientation and nanoparticle coalescence

Abstract

Complementary experimental and theoretical results on the coalescence of nanoparticles demonstrate the importance of the crystallographic orientation on the coalescence process. In situ hot-stage transmission electron microscopy studies on self-supporting films consisting of indium tin oxide nanoparticles clearly show rotations of neighboring particles preceding their coalescence. Both rotation and coalescence are observed well below half the melting temperature. The coalescence of two adjacent nanoparticles is simulated by means of a combination of the kinetic Monte Carlo method for atomic diffusion with an integration of the equations of motion for the rigid body degrees of freedom of the two particles. This allows analyzing the reorientation of the two crystal lattices prior to the merging process. Thus, nanoparticle coalescence has theoretically as well as experimentally been shown to be a two-step process: first a reorientation of adjacent nanoparticles, and second their complete or incomplete coalescence depending on the matching of the crystallographic orientations.

Estudo da sinterização de nanopartículas por microscopia eletrônica de transmissão in situ

“…5, o nanocristal (NC 01) de coordenação 3 se reorienta em relação ao seu par de coordenação 5, o que pode ser explicado pelo maior grau de liberdade das partículas de menor coordenação para ao rearranjo. Embora a força motriz para esse processo de reorientação ainda seja discutida em vários estudos, simulações mostram que a diminuição da energia livre de superfície seja a mais provável, juntamente à valências não satisfeitas ("dangling bonds") dos átomos da superfície das partículas [22,23].…”

In situ transmission electron microscopy and scanning transmission electron microscopy studies of sintering of Ag and Pt nanoparticles

“…Previous in situ TEM experiments [12][13][14][15][16][17][18][19][20][21][22][23][24] used a miniature furnace with a heating coil to indirectly heat the sample, while temperature was measured with an attached thermocouple. Indirect heating results in substantial thermal drift, making it difficult to perform these experiments at high magnifications.…”

Nanoparticle heterocoalescence induced by deposition

“…The degree of epitaxy of the two clusters has been investigated as a function of this separation, and of the type of material. The effect of the temperature as activation of grain-boundary movement to get the complete epitaxy has been also analyzed in the projectile cluster.Nanoparticle coalescence has theoretically as well as experimentally been shown to be a twostep process: first a reorientation of adjacent nanoparticles, and second a complete or incomplete adhesion depending on the matching of the crystallographic orientations [16]. This work is mainly focused on the first process, since the appearance, movement, and disappearance of grains after the collision has been described.…”

“…Nanoparticle coalescence has theoretically as well as experimentally been shown to be a twostep process: first a reorientation of adjacent nanoparticles, and second a complete or incomplete adhesion depending on the matching of the crystallographic orientations [16]. This work is mainly focused on the first process, since the appearance, movement, and disappearance of grains after the collision has been described.…”

“…Therefore, atomistic models describing coalescence must account for changing crystallographic mismatch. Many groups have performed crystallite rotation techniques in order to investigate the reorientation during sintering for metals [10][11][12][13][14] and oxide particles [15,16]. For metals, the mechanism of reorientation may then include the formation or migration of grain-boundary dislocations.…”