Ultrafast Laser Ablation and Deposition of Wide Band Gap Semiconductors

Isolated nanoparticles of the wide band gap II−VI semiconductors CdS and ZnS were produced by ultrafast pulsed laser deposition using pulses of ≈300 fs at two wavelengths of 527 and 263 nm. Upon repetitive target irradiation, the isolated nanoparticles assemble to form a nanostructured film whose structural and chemical properties are compared to those of the targets. UV ablation at 263 nm yields nanoparticles of 5 nm average diameter in the case of CdS. At this wavelength the crystalline phase and stoichiometry of the films markedly differ from those of the target. At 527 nm the average size of the nanoparticles is larger, about 13 nm, but the deposits keep the structural and chemical characteristics of the target. For ZnS the size of the nanoparticles is larger than for CdS although their properties also resemble those of the target when they are produced upon irradiation in the visible. The results obtained allow discussion of the interplay between the light absorption step, the plume dynamics, and the film growth and their impact on the structure and nanometer morphology of the deposited material, while at the same time they exemplify the possibility of their control through the choice of the wavelength of the femtosecond pulses.