How does a gold nanorod melt?

Structural transformation of gold nanorods are investigated by high-resolut ion transmission electron microscopy after they have been exposed to low-en ergy femtosecond and nanosecond laser pulses in colloidal solution. The pul se energies were below the gold nanorod melting threshold, but allowed earl y stage shape transformation processes, It is found that while the as-prepa red nanorods are defect-free, laser-irradiation induces point and line defe cts. The defects are dominated by (multiple) twins and stacking faults (pla nar defects), which are the precursor that drives the nanorods to convert t heir {110} facets into the more stable {100} and {111} facets and hence min imize their surface energy. These observations suggest that short-laser pul sed photothermal melting begins with the creation of defects inside the nan orods followed by surface reconstruction and diffusion, in contrast with th e thermal melting of the rods or the bulk material, where the melting start s at the surface.