Probing Local Structural and Chemical Properties of Atomically Thin Two-Dimensional Materials by Optical Scanning Tunneling Microscopy

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NON-TECHNICAL SUMMARYThe development of new technological applications requires new materials with appropriate properties. Two-dimensional (2D) materials attract tremendous interest because they have a broad range of material properties for creating complex artificial structures with novel functionalities unavailable in natural bulk materials. By harnessing their unique properties, 2D materials can be used for many applications, such as flexible electronics, miniaturized devices, and providing electricity for wearable electronics. In this project, funded by the Solid State and Materials Chemistry Program of the Division of Materials Research, Prof. Nan Jiang and his research group at the University of Illinois, Chicago, will focus on the synthesis of boron monolayer (borophene) related 2D materials, which have unique structural and physical properties. The project encompasses the development of complex borophene-based structures and the measurement of their local properties with an unprecedented spatial resolution. Such advanced understanding is essential for fine-tuning the properties of 2D structures for electronics, photonics, sensing, and energy-harvesting applications. This project will recruit and train undergraduate and graduate students from underrepresented groups and will be integrated into a broad set of outreach efforts, including programs and demonstrations in elementary schools. TECHNICAL SUMMARYThis project, supported by the Solid State and Materials Chemistry Program of the Division of Materials Research, develops a new approach to precisely control and fundamentally understand the interplay among lattice, defects, and the electronic structure of novel 2D materials, such as borophene. The studies involve the direct observation of vibrational modes of borophene-based structures using a state-of-the-art technique that combines scanning tunneling microscopy (STM) with tip-enhanced Raman spectroscopy (TERS). This method facilitates the imaging and characterization of local vibrational and electron-phonon coupling properties of nano- and atomic-scale heterogeneity with approximately 5-Angstrom spatial resolution and 5-wavenumber spectroscopic resolution. In addition to detecting topographical and electronic properties, the STM-TERS approach elucidates localized interfacial features, including strain, defects, and doping at the atomic-thickness limit. Building on these groundbreaking technological advances, the project investigates the chemical modification of borophene via oxygen, defines the hybridization of borophene with organic molecules, and constructs borophene-related 2D van der Waals heterostructures. Collectively, these studies provide unprecedented insights into the relationship between charge and lattice at the atomic-thickness limit.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.