Characterization of atmospheric-pressure spark generated atomic silver and gold clusters by time-of-flight mass spectrometry

The potential of using atmospheric-pressure spark ablation for production of atomic clusters has been shown in the recent past. In this study we used this method to produce atomic clusters in Argon and investigated their chemical composition with an atmospheric pressure interface time-of-flight mass spectrometer (APi-TOF-MS). Both anionic and cationic silver and gold clusters were generated and characterised. The carrier gas was used directly from the gas cylinder without the application of any additional gas purification. As a result, the carrier gas stream contained trace impurities of N₂, O₂, and H₂O, as well as radicals such as O, OH, and H and their ionized forms resulting from the plasma created by the sparks. The experimental results show that different reactivities towards oxygen and water traces can be observed depending on the number of metal atoms in the clusters, their polarity, as well as their compositions; e.g., Au_n⁻ shows less reactive behaviour towards oxygen and hydrogen compared to Ag_n⁻. The results also show that certain cluster types can be generated at large enough quantities by atmospheric-pressure spark ablation, which considering the low installation and operating cost of the technique can pave the way towards its exploitation for numerous technological applications.