UNIVERSITY PARK, Pa. — Pairing elements such as sulfur, selenium or tellurium with metals produces compounds whose atomic interactions give them unusual and useful electrical, optical and magnetic behavior. These materials, called chalcogenides, are the focus of Qihua “David” Zhang’s work as a postdoctoral researcher in the Two-Dimensional Crystal Consortium (2DCC) at Penn State in the laboratory of Stephanie Law, Wilson Family Fellow and associate professor of materials science and engineering. Zhang recently earned the 2025 American Vacuum Society’s Thin Film Division Distinguished Technologist Award for his contributions to growing these materials with extreme purity and precision.
In the following Q&A, Zhang offered a window into a fast-moving field that he said could transform future devices, and also reflected on the role of the 2DCC, a U.S. National Science Foundation Materials Innovation Platform and national user facility, in shaping his research and what he hopes to help enable in the years ahead.
Q: Why are chalcogenide materials considered a promising for developing next-generation electronics?
Zhang: Some of today’s most promising ultra-thin two-dimensional materials, as well as newer three-dimensional materials like tin telluride and manganese telluride, all fall into the family of chalcogenide materials. Each type of chalcogenide can have its own unique electrical, optical and magnetic properties, but many of these traits are still not fully understood because earlier studies were limited by materials that weren’t made purely or precisely enough. My goal is to grow these materials with extremely high quality and tight control over their composition/stoichiometry so we can finally uncover what they are truly capable of.
Q: How do you create extremely pure, precise thin films of chalcogenide materials?
Zhang: Molecular beam epitaxy (MBE) is a material synthesis technique that takes place in an ultra-high vacuum environment and uses high purity elemental sources. The almost perfect vacuum virtually eliminates contaminants such as carbon, oxygen and hydrogen, which act as defects that degrade performance of the fabricated devices. As a result, MBE-grown films routinely achieve pristine crystalline quality and chemical purity that are unmatched by most other methods. MBE also enables layer-by-layer growth control with extreme precision, which allows us to track the composition, thickness, phase and more of the material. Combining all these features allow us to “tune" the material at an atomic-layer accuracy, which is critical for the fabrication of high-performance devices and uncovering novel quantum phenomena.
Q: How has the 2DCC impacted your research?
Zhang: The decision to join the Penn State's 2DCC as a postdoc was a very rewarding move for my career. We have many talented scientists all trying to work towards one goal — to advance the research and development of 2D materials. The people here are professional, patient and collaborative. I am especially thankful to my adviser, Professor Stephanie Law, for bringing me on this journey and teaching me so much — not just knowledge, but to always think critically and deeply, and to turn bold ideas into real discoveries. Although my research background was not in 2D materials, she has always been patient and encouraging, which helped me a lot in getting familiar with this field. Moreover, I’ve had many opportunities to collaborate with external users, who often brought new ideas on new 2D material and/or novel 2D heterostructures to us; and we as 2DCC provide the synthesis, characterization and theory study to fulfill their ideas. Through these experiences, I have gained so much knowledge such as new characterization techniques, generating new research ideas and finding the right collaborators.
Q: What do you hope your research will enable in the future?
Zhang: My research goal has always been focusing on synthesizing pristine thin films — with high structural and crystal quality and smooth surface — as I believe they will unlock exceptional performance when they are fabricated into devices. Moreover, many of these behaviors depend strongly on the elements it is made from, the precise ratio of those elements and how uniformly the atoms of those elements are arranged in a single, well-defined crystal structure. So, synthesizing pristine materials will be key to uncovering these properties I would like to realize these thin films with the structural and magnetic order that are high enough that we can uncover and evaluate these unique material properties.