What is the fine-grained topic of the following text: Xiaodong Zhou, Alexander Kerelsky, Mirza M. Elahi, Dennis Wang, K. M. Masum Habib, Redwan N. Sajjad, Pratik Agnihotri, Ji Ung Lee, Avik W. Ghosh, Frances M. Ross, and Abhay N. Pasupathy, ACS Nano , 13 (2) :2558 (2019). Only return the topic.
The text does not provide sufficient information to determine a fine-grained topic.