High temperature measurements of levitated gold nanospheres derived from gold suspensions

We describe a technique for preparing highly charged Au nanospheres that can be collected in a quadrupole ion trap and heated beyond the melting point of Au, using a laser, without discharging. Au nanospheres are first added to solutions of (NH4)(2)CO3 to prepare stable suspensions. Electrospray emission of these suspensions introduces single Au nanospheres into an ion trap in high vacuum, where their charge and mass can be determined from the effect of discrete discharging on their charge to mass ratio, (q/m). After heat treatment to remove residue, q is stable and the nanosphere temperature T can be estimated by mass loss from Au thermal evaporation. Using this technique, we probe the nanosphere melting behavior across the phase transition at T = 1337 K. Finally, we observe that contaminants in the vacuum, probably C, can have a profound effect on the thermal and optical properties of the Au nanospheres near their melting point. (C) 2021 The Authors. Published by Elsevier Ltd.