Abstract
Metal oxide shell layers are promising candidates to improve the performance of metal nanoparticles (NPs) in various applications. However, despite a significant amount of experimental work on metal@metal oxide (M@MO) NPs, computational modeling is scarce, particularly on the sintering mechanism, which plays a crucial role in both the synthesis and performance of NPs. Here, we present atomic diffusion and sintering dynamics of M@MO NPs investigated using molecular dynamics based on the ReaxFF potentials. The coalescence process of the metal NPs with amorphous oxide shell is mainly facilitated by the relatively mobile surface atoms and grain-boundary-like diffusion, and thus, it is similar to reported mechanisms for crystalline nanoparticles. Intriguingly, atomic trajectory tracing reveals that surface diffusion is highly localized, contrary to the common understanding of freely moving high-mobility surface atoms. These atomic descriptions provide valuable insights for designing functional NPs with oxide layers and establishing more accurate accounts of the sintering mechanism.
Highlights
We investigated the sintering mechanism of metal@metal oxide core@shell NPs using reactive molecular dynamics
The mean square displacement (MSD) and atomic trajectory tracing reveal that the main sintering mechanisms are surface diffusion and grain-boundarylike diffusion
The sintering mechanism of metal@metal oxide NPs with crystalline cores with amorphous shells is similar to that of crystalline NPs, while the coalescenceinduced crystallization at the boundary often observed between metal NPs is not seen in our study
Summary
Metal@metal oxide (M@MO) core@shell nanoparticles (NPs) gather immense research interest as their properties can be tailored for various applications, such as sensing,[1,2] photocatalysis,[3,4] and dye-sensitized solar cells.[5,6] Oxide shells on metal cores are used to suppress sintering between catalytic NPs.[7,8] In a broad range of applications, sintering (or coalescence) of NPs is a common phenomenon that can be advantageous[9,10] or undesired.[11,12] Molecular dynamics (MD)simulations have been extensively employed in studying sintering of metals,[13−17] metal oxides,[18−23] and bimetallic core@shell NPs.[24,25] no MD studies of the sintering mechanisms of M@MO core@shell NPs have been reported to date.It is generally agreed that the dominating sintering mechanisms are surface diffusion and grain boundary diffusion in crystalline materials[26−28] and viscous flow in amorphous clusters.[29−31] the sintering mechanism of M@MO. Metal@metal oxide (M@MO) core@shell nanoparticles (NPs) gather immense research interest as their properties can be tailored for various applications, such as sensing,[1,2] photocatalysis,[3,4] and dye-sensitized solar cells.[5,6] Oxide shells on metal cores are used to suppress sintering between catalytic NPs.[7,8] In a broad range of applications, sintering (or coalescence) of NPs is a common phenomenon that can be advantageous[9,10] or undesired.[11,12] Molecular dynamics (MD). Simulations have been extensively employed in studying sintering of metals,[13−17] metal oxides,[18−23] and bimetallic core@shell NPs.[24,25] no MD studies of the sintering mechanisms of M@MO core@shell NPs have been reported to date.
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