Date: Tuesday, February 18, 2014
Time: 11:00 am
Speaker: Dr. Frank Q. Zhu, HGST
Title: Controlled Nucleation Growth of Granular Thin Films by Templating Effect and Self-Assembly
Location: 67-3111 Chemla Room
Control of thin film grain size in the range of 5~15nm as well as grain size uniformity is a challenging yet crucial task for modern high performance thin film devices. There is no existing lithography technique that can readily accomplish this task at wafer scale. I will present an approach of using self-assembled monolayer of nanoparticles as the template to purposefully locate nucleation sites for growth of granular films. Oxide nanoparticles, with long chain polystyrene ligands, are dispersed in solvent and then spun coated on the substrate. A monolayer of nanoparticles is formed with an appropriate process, resulting in a narrow distribution of particle center-to-center distance of 8~15%, which is significantly narrower than the 20~23% commonly seen in randomly distributed system. To illustrate the templating effect, we deposited a very thin layer of Ru (with a few supporting underlayers) on nanoparticle monolayer, we observed that the Ru nucleation sites were not dispersed randomly but precisely located above the nanoparticles. This registry is apparent in energy-filtered TEM in which the locations of the nanoparticle (black) and Ru (white) are superimposed (Fig1(a)). Granular thin films with columnar microstructures have been successfully grown using this approach (Fig1b). TEM confirms that the registry of columnar islands to the nanoparticles is preserved during full film growth. This approach could be applied to manufacture a wide range of high quality thin films with superior mechanical, optical, electrical or magnetic properties.