At any given time, you’re likely either using or benefitting from a modern electronic device and when that device doesn’t work correctly, it can result in big inconveniences. Penn State’s Danielle Reifsnyder Hickey, assistant research professor of materials science and engineering, is studying defects in 2D materials, research that will enable future electronics to be more powerful, efficient and defect-free. Here’s what she had to say about her work, as well as the benefits of building her career in Happy Valley.
HappyValley Industry: What is your research topic and why is it important on a global scale?
Reifsnyder Hickey: I am studying the defects in an emerging class of semiconductors called two-dimensional (2D) materials. Semiconductors are the backbone of modern electronic devices, such as computers, televisions and smart phones. As a result, we rely on them for many of our everyday activities, including communication, transportation, energy, entertainment and healthcare. How semiconductors function is directly related to the presence and distribution of defect structures in crystals. Thus, it is important to identify and understand these imperfections, learn how the defects are distributed throughout a material and understand how they can affect device performance. Recently, we have discovered new types of defects in the 2D material tungsten disulfide (WS2), and just as importantly, we have correlated the atomic structures with large-area features in WS2 films, which helps us improve the understanding of how WS2 films grow.
HappyValley Industry: How do you envision your research impacting/changing your industry?
Reifsnyder Hickey: Miniscule, atomic-scale defect structures can control the overall performance of materials in devices, and our work has shown that even high-quality WS2 monolayer films can have unexpected defects. Because we have also demonstrated how these small features are organized across length scales (i.e., from the atomic to multi-micrometer), we have been able to understand how they can form during the film growth. This leads to a better understanding of how 2D materials grow and how to harness the unique properties of defect properties or else eliminate them to achieve perfect single crystals. This understanding will improve the scientific community’s ability to grow 2D materials, and subsequently, it will make electronics more powerful.
"In order to create new technologies that improve our lives, it is critical to discover new materials and to find ways to make them of high enough quality to integrate into efficient electronics."
HappyValley Industry: What inspired you to follow this line of research?
Reifsnyder Hickey: In order to create new technologies that improve our lives, it is critical to discover new materials and to find ways to make them of high enough quality to integrate into efficient electronics. One key is to understand in detail how the atoms are arranged in a material because this will control the behavior of the material. Aberration-corrected transmission electron microscopes make it possible to peer into materials to see atomic structures and their subtle distortions. This work is an example of what electron microscopy can uniquely achieve to answer important questions facing the field of 2D material growth.
HappyValley Industry: Why did you choose to conduct this research at Penn State specifically?
Reifsnyder Hickey: Penn State has a very strong research community and is home to a National Science Foundation-sponsored Materials Innovation Platform (NSF-MIP) user facility called the Two-Dimensional Crystal Consortium (2DCC). The 2DCC brings together a substantial number of research labs that have diverse interests related to 2D materials. The work highlighted here demonstrates the type of success the 2DCC enables: through the close collaboration of research groups with complementary specialties (i.e., growing 2D materials, performing atomic-resolution study of their crystal features and defects, and simulating their structures and properties), it is possible to make discoveries and drive insights into this exciting new class of materials.
"Penn State dedicates considerable effort and resources to promoting impactful research."
HappyValley Industry: Would you encourage other researchers to make their home in Happy Valley, and why?
Reifsnyder Hickey: Happy Valley has a lot to offer, both in terms of scientific research and quality of life. Penn State dedicates considerable effort and resources to promoting impactful research. As a result, there is a large and active research community, in which it is possible to connect with researchers with a huge range of expertise. Additionally, the town and surroundings of State College provide a family-friendly atmosphere with many opportunities to engage with nature.
HappyValley Industry: Is there anything else that you would like to add?
Reifsnyder Hickey: Many thanks to the following excellent Penn State collaborators: Prof. Nasim Alem, Prof. Adri van Duin, Prof. Joan Redwing, Prof. Vin Crespi, Nadire Nayir, Mikhail Chubarov, Tanushree Choudhury, Saiphaneendra Bachu, Leixin Miao, Yuanxi Wang, and Chenhao Qian.
Citation: D. Reifsnyder Hickey et al. “Illuminating Invisible Grain Boundaries in Coalesced Single-Orientation WS2 Monolayer Films.” Nano Lett. (2021) 21, 15, 6487-6495.