A simple method for large scale synthesis of highly monodisperse gold nanoparticles atroom temperature and their electron relaxation properties

Abstract

Here we demonstrate a simple method for large scale preparation ofmonodisperse gold nanoparticles by simple mixing of chloroauricacid (HAuCl4) with oleylamine (OA) at room temperature. The as-prepared gold nanoparticles havehigh monodispersity with an average diameter of 13 nm and can self-organize intotwo-dimensional (2D) hexagonal close-packed arrays. The size of the gold nanoparticles canbe experimentally controlled. The capping agent, oleylamine, can be easily replaced withother capping agents such as thiol groups for further functionalization. The electronrelaxation dynamics of these gold nanoparticles in toluene was studied by femtosecondpump–probe measurements, in comparison with the citrate-stabilized gold nanoparticles inwater. The phonon–phonon relaxation time of gold nanoparticles in toluene is slower thanthat of citrate-capped gold nanoparticles in water, due to the lower thermal conductivity oftoluene than water. The electron–phonon relaxation of the gold nanoparticlesin toluene was found to display weaker pump energy dependence, compared tothat of citrate-capped gold nanoparticles in water. The different electron–phononrelaxation dynamics is ascribed to the extra vibrational states provided by gold-NH2, which serves as an extra nonradiative relaxation pathway for the e–ph relaxation inoleylamine-capped gold nanoparticles in toluene.