Co-Doped ZnS Clusters and Nanostructures Produced by Pulsed Laser Ablation

In this work, we synthesize Co-doped ZnS nanocrystals by pulsed laser ablation and deposition and investigate the composition and dynamics of the plasma produced in the ablation by time-of-flight mass spectrometry. The first experimental observation of Co-substituted ZnS clusters in the ablation plasma is reported; three series of cationic bimetallic clusters Zn_{<i>n</i>–<i>m</i>}Co<i>_m</i>S_<i>n</i>⁺, Zn_{<i>n</i>–<i>m</i>}Co_<i>m</i>S_<i>n</i>+1⁺, and Zn_{<i>n</i>–<i>m</i>}Co_<i>m</i>S_<i>n</i>–1⁺ are identified upon 1064 nm laser ablation of targets of Co (2%) in ZnS. Neutral clusters produced in the ablation are also observed by F₂ laser (λ = 157 nm) postionization. Deposits are collected at the same laser ablation wavelength and fluence at which the above bimetallic clusters are observed in the plasma. Analysis by high-resolution transmission electron microscopy and energy-dispersive X-ray spectrometry obtains that the deposits are composed of Zn_0.96Co_0.04S nanocrystals with local structure showing epitaxial growth between the zinc blende and wurtzite politypes. The deposits show paramagnetic behavior, but no magnetic ordering is observed. The results constitute a first step to help to elucidate the participation of cluster assembly processes in the synthesis of Co-doped ZnS nanomaterials by pulsed laser ablation and deposition