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.