Kinetic energy and mass distribution of ablated species formed during pulsed laser deposition

Abstract

Pulsed laser deposition is a rapidly developing thin film growth technique. It is suited to the deposition of a large variety of solid materials. As with related growth techniques the quality of the deposited film is highly dependent on the physical properties of the evaporated species. The physical nature and composition of the ablation plume is still neither well understood nor quantified. The study reported here has been performed using a modified cylindrical mirror analyser (CMA) coupled with a quadrupole mass spectrometer (QMS) to analyse the energy and mass of the ionic component of the laser ablation plasma generated by 4ns duration frequency doubled Nd: YAG laser (λ=532nm) radiation impinging upon Fe and YBa 2Cu 3O 7-δ targets. The effects of laser fluences were investigated. Importantly, we have found that the high particle fluxes produced can interfere with the operation of the CMA detection system. Low particle densities induced by normal ablation conditions, however, allow accurate measurement of both energy and mass spectra. Comparison of these data with ion emission spectra obtained using a Faraday cup arrangement gives important information on the angular distribution of the species ejected from the target. The energy distributions of the singly and multiply ionised species are reported for various laser fluences. Close to the oblation threshold for both target materials the only detectable ions were singly ionised with energies in the 0–50eV range. For increased laser fluences higher energy distributions were observed (0–300eV) and the quantity of the multiple ionised species increases.