Chemically Functionalized van der Waals Opto-Spintronic Quantum Materials

Nontechnical Description: Exponentially growing data coupled with energy-intensive artificial intelligence necessitate next-generation technologies for information storage, processing, and communication. Quantum materials that couple charge transport, optical and magnetic properties hold promise for achieving this goal. Among the options for promising quantum materials, two-dimensional (2D) materials and specifically magnetically ordered van der Waals (vdW) semiconductors – layered materials composed of ultra thin sheets of atoms – provide a rich platform for studying electronic, optical, and magnetic properties. Despite the vast promise of vdW magnetic semiconductors, significant issues must be overcome before their full potential can be realized. For instance, the majority of vdW magnetic semiconductors show useful properties only at temperatures well below room temperature, which limits their use in practical applications. In addition, many vdW magnetic semiconductors suffer from processing challenges arising from chemical instability at ambient conditions. Furthermore, effective strategies are lacking for controlling useful impurities and chemical compositions. This project will address these challenges by leveraging useful chemical properties and high surface-to-volume ratios of vdW magnetic semiconductors to controllably modify their optical and magnetic properties. The research results will be widely disseminated through a series of education and outreach activities including a program called Illuminate, which assists students with attending and completing college, and Science with Seniors, which organizes visits to retirement homes for interactive science presentations and demonstrations. Technical Description: Two-dimensional (2D) materials have attracted significant interest for fundamental studies and prototype device development, especially chemically inert 2D materials (e.g., graphene, hexagonal boron nitride, and transition metal dichalcogenides), since they can be processed at ambient conditions with minimal further precautions. However, the family of 2D materials includes hundreds of additional members, particularly van der Waals magnetic semiconductors (e.g., 2D metal halides), which have been underexplored due to their high chemical reactivities that introduce challenges in preparing and handling samples for electronic testing. Rather than trying to suppress this high chemical reactivity, this project will develop chemical functionalization strategies for vdW magnetic semiconductors that will enable tailoring of their opto-spintronic phenomena in the atomically thin limit, thus accelerating progress towards applications in non-volatile memory, neuromorphic computing, opto-magnonics, and quantum spintronic transduction. The goals of this project include (1) controlling p-type and n-type doping of vdW magnetic semiconductors via utilizing electron-withdrawing and electron-donating surface chemical adlayers, respectively; (2) realizing unprecedented chemical compositions and Janus structures in atomically thin magnetic semiconductors via surface-specific anion exchange chemistry; (3) tuning interlayer coupling in vdW magnetic semiconductors via electrochemical and megasonication intercalation of chemical species in the vdW interlayer space; (4) chemically inducing magnetism in nonmagnetic vdW semiconductors by exploiting theoretically predicted Stoner magnetic instabilities at high hole concentrations. 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. NSF Award ID: 2515335 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Mark Hersam | Institution: Northwestern University at Chicago, EVANSTON, IL | Award Amount: $510,000 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2515335 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2515335.html