Experiments on carbon accumulation on gold nanoparticles heated with a laser while levitated in an ion trap in high vacuum

We discuss preliminary results of experiments on the interaction of carbon with gold nanoparticles levitated in an ion trap at a vacuum pressure ~10^-7 Torr. In recent experiments, we have observed that when a nanoparticle of diameter approximately 200 nm undergoes repeated heating cycles via 532 nm laser illumination in high vacuum, its rate of evaporative mass loss declines across dozens of heating cycles. Since this effect is reversible when particles are heated in O₂ (P~10^-6 Torr) ambient, we hypothesize that the evaporation is inhibited by accumulation of carbon on the nanoparticle from residual sources in the vacuum chamber. Other researchers have found evidence that carbon accumulation on gold nanoparticles is enhanced by laser illumination at plasmon resonant frequencies[1]. To investigate this phenomenon, we heat levitated nanoparticles in the presence of a controlled source of carbon in the form of CO gas. In this talk, we will discuss the results of these tests and consider the implications for thermodynamic measurements on levitated nanoparticles that rely on accurate measurement of the rate of evaporative mass loss.

[1] Hung et al., Nano Lett. 8, p.3278-3282 (2008).