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 Z(n-m)Co(m)S(n)(+), Znn-mComSn+1+, and Znn-mComSn-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 F-2 laser (lambda = 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 Zn0.96Co0.04S 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.