Pulsed laser ablation of Sn and SnO₂ targets: Neutral composition, energetics, and wavelength dependence

We report time-of-flight mass spectrometric studies of neutral gas-phase species generated in 532 and 355 nm laser ablation of Sn and SnO₂ targets at intensities of ≈10⁸ W cm^-2, below the plasma threshold. A wavelength-dependent yield of Sn:Sn_xO_y species is observed for the oxide target, with Sn_xO_x (x = 1-3) the primary products at 532 nm and atomic Sn dominant at 355 nm. Sn and Sn₂ are the primary products of Sn metal ablation, and the relative Sn:Sn₂ yield increases at the shorter wavelength. The speed distributions of neutrals ejected from the oxide target are well represented by unshifted time-transformed Maxwell-Boltzmann (MB) distributions, while those ejected from the metal target exhibit bimodal MB distributions. Typical most-probable speeds are (1-2) × 10⁵ cm s^-1, with peak kinetic energies (KEs) of 1-2 eV. The implications of our results for pulsed laser deposition of SnO_x films will be emphasized.