Crystal structure dependence of the elastic constants of gold nanorods

Time- resolved spectroscopy has been used to examine the elastic properties of single crystal gold nanorods with a [ 100] growth direction. These rods were produce by seed- mediated growth in the presence of silver ions, using both chemical and photochemical reduction. Analysis of the experimental data yields a value of Young's modulus for the nanorods of E-NR = 31 +/- 1 GPa. This is approximately 26% smaller than the value for bulk gold of E-[100] = 42 GPa. The reduction in the size of Young's modulus is consistent with our previous studies of penta- twinned, [ 110] growth direction nanorods, where we found E-NR = 64 +/- 2 GPa compared to E-[110] = 81 GPa for bulk gold. The fact that both the single crystal and the penta- twinned nanorods show a similar reduction in E compared to the bulk values ( 20% - 30%) shows that this effect does not arise from the presence of twin planes in the nanorods. Our data show a weak correlation between the measured values of E-NR for the [ 100] nanorods and the surface- to- volume ratio of the rods. The larger value of Young's modulus at small size is possibly due to defect elimination. These results underscore the importance of growth direction in determining the elastic properties of nanorods and nanowires.