Electrical and Thermal Conductivities of Gold and Silver Nanoparticles in Solutions and Films and Electrical Field Enhanced Surface-Enhanced Raman Scattering (SERS)

摘要

Electrical and thermal conductivities of metal nanoparticles and their aggregates are important for many device applications involving nanomaterials. In this work, the electrical conductivity of gold nanoparticle aggregates has been measured and found to be a useful probe of the surface chemistry of the nanoparticles. It has been observed that the conductivity of the gold nanoparticle aggregates in solution increases with light illumination or thermal heating and recovers completely to the initial value upon removal of the light or heat. The amount of change in conductivity depends on the amount of heat or light. The conductivity change is tentatively attributed to ion dissociation from the nanoparticle surface due to heating or light illumination. Meanwhile, the thermal conductivity of dried silver nanoparticles (30-60 nm) has been measured and found to be around 2 W/m·K. This is consistent with previous prediction of significantly reduced thermal conductivity of Ag nanoparticles/aggregates. In addition, external DC electrical field enhanced surface-enhanced Raman scattering (SERS) was also observed with the excitation laser light focused in between the electrodes instead of on the electrodes. Various potential were applied and an enhancement factor of 5 has been achieved. Possible explanations for this enhancement are provided.