My name is Adam Ahmed, and I am a sixth year Ph.D. student in physics at the Ohio State University.
My passion in Roland’s group is thin film growth. The ability to grow a crystal with single orientation over the entire wafer is extremely exciting!
Our main growth technique is molecular beam epitaxy (MBE). Essentially, we heat elemental materials and evaporate them towards a single crystal substrate by which we perform epitaxy. We can vary several growth parameters (substrate temperature, growth rate, oxygen partial pressure, etc.) to influence the crystal structure and stoichiometry of the films we grow. In my opinion, the most exciting part of thin film growth is reflection high energy electron diffraction (RHEED). In this in-situ technique, electrons are accelerated at the thin film during growth where the electron diffract off the crystal planes. These electrons form a reciprocal space representation at a fluorescent screen imaged with a camera. Using RHEED allows us to monitor thin film growth in real time! We can even record when an atomic layer begins to grow and when a complete layer is finished growing (a.k.a. layer-by-layer growth).
I implement this technique to grow a wide variety of materials in the lab. My thesis work is primarily focused on the materials development, manipulation, and measurement of skyrmions. A skyrmion is a magnetic swirl/deformation/bubble in a ferromagnetic background. The magnetization at the center of the skyrmion is opposite to that of the surrounding ferromagnet. In this project, we want to understand how we can control the size of the skyrmions. Currently, I am growing a particular skyrmion material—FeGe. It has a Curie temperature of 280 K and is the largest Curie temperature for any bulk skyrmion system. By appropriately doping our samples with MBE, we intend to change the fundamental interactions responsible for allowing skyrmions to exist (exchange interaction and Dzyaloshinskii-Moriya interaction).
| Team | Adam Ahmed