Analysis of Transient Plasmas for Pulsed Laser Deposition using Spatiotemporally Resolving Laser-Induced Fluorescence Spectroscopy

Abstract

The goal of the work presented in this thesis is to realize a spectroscopic spatiotemporal mapping of selected species in laser-induced plasmas used in pulsed laser deposition (PLD), for a better understanding of the internal plasma dynamics and chemistry. We are especially interested in the influence of external parameters on the plasma dynamics and chemistry, such as the fluence of the ablation laser and the composition of the background gas and its pressure, as this can be the key to an improved understanding and control of stoichiometric film growth. We have chosen a combination of laser-induced fluorescence (LIF) and absorption spectroscopy (AS). LIF enables the detection of plasma constituents even in dark plasmas, i.e., also when the plasma plume has cooled down and no longer spontaneously fluoresces. AS provides a means to calibrate the relative density distribution maps obtained from LIF measurements for obtaining absolute density distributions. The combination of spectroscopic (also called chemical) in-situ spatiotemporal mapping of individual plasma constituents with a detailed analysis of the grown films has enabled an unparalleled insight in the influence of the external PLD parameters on the plasma propagation, chemical evolution and material deposition. In this thesis we present the results of three materials we have investigated, LaAlO3, SrTiO3 and YBiO3, of which we have spatiotemporally mapped the ground state populations of several plasma species. From these three materials it can already be seen that spatiotemporally resolved LIF is a highly valuable analytic approach for analyzing and understanding intricate details and features in PLD growth processes. Even when only mapping a select number of plasma constituents of a deposition material, much additional insight can be obtained. Having applied LIF in various different material systems has clearly shown that there are no universal plasma and growth dynamics. Instead, each material system, due to its individual chemical and physical properties, provides its own dynamics in the plasma, both at the substrate and at the target. This observed wide span in variety promises that there is much more to discover and understand through LIF and possibly also other types of spectroscopy.