Laser-induced failure modes in plasmonic thin films

Abstract

In order for the areal density of magnetic hard-drives to continue increasing, it is necessary to improve upon current recording technologies. The proposed next-generation magnetic recording process, heat-assisted magnetic recording (HAMR), will potentially allow for areal densities of 4 Tb/in2 or more, but its implementation is limited by thermal failure of the nanoscale Au plasmonic focusing element that is integral to the recording process. Any attempts at improving the thermal stability of the Au element can only be considered successful if the plasmonic performance of the Au is not negatively affected. In this thesis, the laser-induced degradation mechanisms on Au thin films are studied, and different stabilization methods are presented. The main source of thermal degradation in the Au was found to be caused by solid-state dewetting. Other degradation mechanisms observed included grain growth and crystalline texturing. The time dynamics of solid-state dewetting were measured using a customized microscope set-up, which allowed for a quantitative comparison between stabilization methods. The stabilization methods studied in this thesis were adhesion layers, alloying and capping layers. While no improvement was observed in the thermal stability of the Au upon alloying, the use of adhesion and capping layers resulted in significant increases in resistance against dewetting, with sub-nanometer adhesion/capping layers resulting in the greatest increase. In Chapter 1, a brief introduction to the current state of magnetic recording is given, and the motivations behind the work in this thesis are presented. In Chapter 2, the theoretical background behind the main concepts within this thesis are described, including solid-state dewetting, laser-induced heating, and plasmonics. In Chapter 3, the main experimental techniques used within the thesis are described. In Chapter 4, the effects of CW-laser annealing on an Au thin film are discussed, showing the changes in film quality caused by solid-state dewetting, grain growth and crystalline texturing. In Chapter 5, the effect of an adhesion layer on increasing the resistance of the film against solid-state dewetting is discussed, and the optimal thickness for a metallic adhesion layer is found. In Chapter 6, the optical and thermal properties of an AuCu alloy are investigated. In Chapter 7, the effect of dielectric capping layers on the solid-state dewetting characteristics of an Au film is shown, and the optimal adhesion layer/capping layer combination is stated. Finally, Chapter 8 states the final conclusions that can be taken from the work presented, and gives suggestions for future work are given.