Thermal stability of gold nanorods for high-temperature plasmonic sensing

There are many potential sensing applications for Au nanorods due to a tunable localized surface plasmon resonance (LSPR) frequency that changes with aspect ratio. However, their application at high temperatures is limited due to a shape change that can take place well below the melting point of bulk Au, driven by a reduction in surface energy. A method of stabilizing Au nanorods is provided here by encapsulating them with a 15 nm capping layer of yttria stabilized zirconia (YSZ). After annealing rods with nominal dimensions of 100 × 44 nm to a temperature of 600 C, small reductions in length were observed, but the rods remained stable for all subsequent sensing tests at 500 C, which amounted to 80 h. It was shown with a separate sample that the rod geometry can be preserved even up to 800 C over a 12 h annealing period, although a significant shortening of the rod length occurred, leaving a void space in the YSZ. The sensing response of both the transverse and the longitudinal LSPR peaks was monitored for H₂, CO, and NO₂ exposures in an air background at 500 C. In all cases, the longitudinal LSPR peak shows a larger shift upon gas exposure than does the transverse peak.