On the temperature stability of gold nanorods: comparison between thermal and ultrafast laser-induced heating.

The response of gold nanorods to both thermal and ultrafast laser-induced heating has been examined. The thermal heating experiments show structural changes that occur on timescales ranging from hours to days. At the highest temperature examined (250 degrees C) the nanorods are transformed into spheres within an hour. On the other hand, no structural changes are observed in the laser-induced heating experiments up to temperatures of 700 +/- 50 degrees C. This is attributed to thermal diffusion in the laser experiments. Measurements of the period of the extensional mode of the nanorods using time-resolved spectroscopy show a significant softening at high pump laser powers. However, the decrease in the period is less than expected from bulk Young's modulus vs. temperature data.