Coalescence of gold nanoparticles around the end of a carbon nanotube: A molecular-dynamics study

Coalescence of gold nanoparticles (Au NPs) around the end of a multi-walled carbon nanotube (MWCNT) and their interaction with the CNT at elevated temperatures may often be important processes during the fabrication of CNT-metal composite (e.g., through laser sintering). However, an atomic-scale fundamental study of such processes through molecular dynamics (MD) simulations has been rarely reported to the authors' best knowledge. Such a study has been reported in this paper. First, MD-predicted NP melting points are compared with experiment-deduced results from the literature to at least partially test the modeling approach. Then the coalescence of 3-nm Au NPs around the end of a MWCNT and their interactions with the CNT are studied through MD simulations. The simulated period includes a 100-ps heating period (at the end of which the system is raised to a certain heating temperature) followed by another 500-ps period. Studies have been performed under different CNT diameters, and for different heating temperatures. Several interesting phenomena have been found under the studied conditions, such as: (i) a CNT with a sufficiently large diameter can draw some Au atoms into the tube, even though the heating temperature (600 K) is well below the melting point of the Au NPs. Such an interesting capillary effect of CNT below the metal NPs' melting point has been rarely reported before to the authors' best knowledge; (ii) Under a heating temperature of 800 K, at the end of the simulated period, lattice structures can still be observed in the merged Au nanocluster if no CNT is nearby; however, the Au atoms become mostly disordered if the NP coalescence takes place near the end of a CNT; and (iii) if significant entrance of Au atoms into the CNT occurs, the arrangement of most Au atoms inside the CNT also follows a multi-layer tube pattern.