Analysis of ion-bombarded and laser-irradiated surfaces of ZnS and Zn via two-photon high-resolution laser-induced fluorescence spectroscopy

Abstract

Doppler-shifted two-photon laser-induced fluorescence spectroscopy (LFS) has been used to measure the velocity distributions of Zn atoms ejected by Ar+ ion bombardment from both a Zn surface and a ZnS single crystal. Doppler-shifted spectroscopy in combination with time of flight(TOF), has also been employed to investigate Zn atoms ejected from a ZnS single crystal under irradiation by 308-nm photons (XeCl excimer laser). The absolute Zn sputtering yields from ion-bombarded and laser-irradiated ZnS samples were determined by comparison with LFS measurements of Zn atoms sputtered from pure Zn targets by Ar+ ions since the absolute sputtering yield is known. For the Zn target the velocity distributions of the ion-induced sputtered Zn atoms were in good agreement with the Sigmund–Thompson distribution based on the known binding energy of 1.35 eV. On the other hand, the velocity distribution of Zn atoms ion sputtered from ZnS showed some deviation from the Sigmund–Thompson distribution and had a lower binding energy, ∼0.9 eV. The velocity distributions of the laser-ablated Zn atoms from ZnS were Maxwell–Boltzmann in nature with characteristic temperatures increasing from 2000 to 9000 K at fluences of 20 and 80 mJ/cm2, respectively. The absolute sputtering yield (Y) of Zn sputtered from ZnS was found to be Y≂8 atoms/ion for ion sputtering and Y≂10−6 atoms/photon at a laser fluence of 30 mJ/cm2 for laser ablation. High-resolution Doppler-shift techniques have been combined with TOF techniques. This promising combination permits unambiguous detection of prompt and delayed emission of ablated atoms, as well as the observation of possible molecular or cluster fragmentation. The results obtained indicate that no delayed emission is occurring and suggest the possibility of molecule or cluster emission from ZnS.