Size-dependent emission of negative ions from gold nanoparticles bombarded with C60 and Au400

This study reports on the secondary ion (SI) emission from individual Au nanoparticles (AuNPs) with secondary ion mass spectrometry (SIMS) operating in event-by-event bombardment/detection mode. This methodology allows one to obtain quantitatively the effective yields of SI emission from individual nano-objects. The analyses of gold cluster emission from a series of AuNPs of different sizes (2, 5, 10, 15, 20, 50 nm in diameter) were conducted with two massive projectiles, 50 keV C602+ and 520 keV Au4004+. The results indicate that the emission of Au2− and Au3− varies as a function of particle size. Due to different mechanisms of energy transfer and energy densities deposited into the NPs, the optimum sizes for maximum Au2− and Au3− emission are: 20 nm for 520 keV Au4004+ and 10 nm for 50 keV C602+. Moreover, the abundance of Au2− and Au3− is also affected by the nature of the projectile. In the case of Au400 impacts, the enhanced SI emission of larger clusters is observed not only from 15 and 20 nm but also from 10 nm AuNPs. The observation of the size- and projectile-dependent SI emission points out the necessity of accurate data interpretation when dealing with nanoscale objects.