Size and shape of Au nanoparticles formed in ionic liquids by electron beam irradiation.

Au nano-particles were synthesized via a reductive reaction in ionic liquid solution containing Au(3+) ions using a low-energy electron irradiation technique. In this study, we focused on how the electron beam conditions (acceleration energy, beam current and irradiation time) and the kinds of ionic liquid affected the size and shape of the prepared Au particles. The sizes of the primary particles increased with higher acceleration energy of the electron beam, whereas they did not depend so much on the beam current. Although the amount of secondary particles increased with longer irradiation time, the sizes of the primary particles remained constant. The anion of the ionic liquid strongly affected the size and shape of the primary particles, which was due to the different local structure of the ionic liquid around the Au particles. When the thickness of the ionic liquid layer was smaller than the penetration length of the electron beam, the formation of secondary particles was suppressed. The present results gave an important knowledge for controlling the size and shape of the metal particles, which is important for application of various catalyst or devices.