Sabbatical Locquet: Thin film coatings and layer transfer techniques for crystalline oxide mirrors.
The research activities to be performed during the sabbatical are related to the development of crystalline oxide coatings for gravitational wave detector mirror bodies consisting of either Silicon or Sapphire. One of the key challenges in this field is the Quantum vibration (Brownian motion) noise of the mirror coatings that has become a limiting factor in the overall performance of the GW detector. The focus of the effort is on exploring epitaxial single crystalline – in contrast to the state of the art amorphous – oxide compounds coatings. These should have superior mechanical and thermal properties compared to their amorphous equivalents.
There are two objectives of the sabbatical leave. – related to the development of such crystalline coatings for mirror bodies – that will be addressed in this project. The first issue is the need to insert a good crystalline oxide buffer layer on top of Silicon. At this moment, the best material that can fulfil this requirement is strontium titanate (SrTiO3), although it still remains a tedious and complicated process. So, the first research objective is to explore if and how such buffer layers can be used for the crystalline mirror coatings envisioned The second objective is related to the concept of layer transfer. While the crystalline oxides can be grown on top of a standard 200- or 300-mm Silicon or Sapphire substrate wafer, this is not compatible with putting a coating on a massive (40 kg) mirror body. Therefore, after the coating is deposited, it needs to be removed from the substrate wafer and transferred to the mirror body where it must be tightly bonded. At this moment, there is no knowledge about layer transfer of crystalline oxides at KULeuven. Hence, the second research topic is to learn how our crystalline oxide coatings can be transferred to state-of-the-art mirror bodies.