Size-dependent melting modes and behaviors of Ag nanoparticles: a molecular dynamics study

Abstract

The size-dependent melting behaviors and mechanisms of Ag nanoparticles (NPs) with diameters of 3.5-16 nm were investigated by molecular dynamics (MD). Two distinct melting modes, non-premelting and premelting with transition ranges of about 7-8 nm, for Ag NPs were demonstrated via the evolution of distribution and transition of atomic physical states during annealing. The small Ag NPs (3.5-7 nm) melt abruptly without a stable liquid shell before the melting point, which is characterized as non-premelting. A solid-solid crystal transformation is conducted through the migration of adatoms on the surface of Ag NPs with diameters of 3.5-6 nm before the initial melting, which is mainly responsible for slightly increasing the melting point of Ag NPs. On the other hand, surface premelting of Ag NPs with diameters of 8-16 nm propagates from the outer shell to the inner core with initial anisotropy and late isotropy as the temperature increases, and the close-packed facets {111} melt by a side-consumed way which is responsible for facets {111} melting in advance relative to the crystallographic plane {111}. Once a stable liquid shell is formed, its size-independent minimum thickness is obtained, and a three-layer structure of atomic physical states is set up. Lastly, the theory of point defect-pair (vacancy-interstitial) severing as the mechanism of formation and movement of the solid-liquid interface was also confirmed. Our study provides a basic understanding and theoretical guidance for the research, production and application of Ag NPs.

A universal signature in the melting of metallic nanoparticles

“…For reference, Table S1 includes all melting temperatures obtained from both methods. Previous numerical studies 51,71,[73][74][75] have qualitatively discussed the temperature dependence of the PDDF profile. However, the signature of the PDDF-peak at the bulk lattice distance disappearing when the melting occurs was not previously recognised, nor the correlation between the second-nearest-neighbour PDDF cross-entropy with the caloric or heat capacity curves.…”

“…the Lindemann's criterion. [50][51][52] Besides all the studies performed, the quest to identify a universal signature that marks a phase change of nanoparticles and, at the same time, is common to both numerical simulations and experiments is still open and motivates our investigation.…”

Size and shape-dependent melting mechanism of Pd nanoparticles

“…Several models have been developed to predict the nanoparticles sizedependent T mp (Goldstein et al, 1992;Jiang et al, 1999;Safaei, 2010) and H mp (Zhang et al, 2000;Jiang et al, 2002;Attarian Shandiz and Safaei, 2008;Fu et al, 2017). However, developing a universal model requires an extensive effort and each model has to be verified with experimental or simulation data (Liang et al, 2017) which, to our knowledge, is not available for Pd clusters. In addition, these models fail to describe the melting dynamic and size-dependent melting mechanisms.…”

“…In addition, these models fail to describe the melting dynamic and size-dependent melting mechanisms. For instance, quite recently, it has been shown that reshaping of Ag particles depends on the size and a transition from homogeneous to surface melting mechanism occurs by an increase in the particle size (Liang et al, 2017).…”

Droplet‐Based Techniques for Printing of Functional Inks for Flexible Physical Sensors

“…It is well-known that the Ag nanoparticles melting point decreases with increasing surface to volume ratio (size decrease). [62] Liang et al [63] developed a molecular dynamic model to predict the melting behavior of Ag nanoparticles with diameters ranging from 3.5 to 16 nm. Their results demonstrated decrease in melting point with particle size reduction.…”