Probing Fundamental Magneto-Electronic Properties of Two-Dimensional Metal Halides

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Nontechnical Summary:Researchers have recently learned how to produce atomically thin materials that are referred to as two-dimensional (2D) materials since they are extended in two dimensions (i.e., length and width) but are confined in the third dimension (i.e., depth) at the atomic scale. Due to a range of superlative properties and new physics in the atomically thin limit, 2D materials have attracted significant interest for fundamental studies and prototype device development. Thus far, chemically inert 2D materials have been the most widely studied since they can be processed in ambient conditions with minimal further precautions. However, the family of 2D materials has hundreds of additional members, which have been underexplored due to their high chemical reactivities that introduce challenges in preparing and handling samples for electronic testing. To address this knowledge gap, this project develops encapsulation and related sample preparation protocols to enable characterization of the fundamental properties of chemically reactive 2D materials. Of particular interest are the 2D metal halides since they are theoretically predicted to possess unique combinations of electronic and magnetic properties that are relevant to next-generation computing and quantum technologies. These research results are widely disseminated to diverse audiences through a series of education and outreach activities including Illuminate, which assists and enables low-income, first-generation, and/or underrepresented minority students to attend and complete college, and Science with Seniors, which organizes visits to retirement homes for interactive science presentations and demonstrations.Technical Summary:Among the most chemically reactive two-dimensional (2D) materials are the layered van der Waals transition metal halides. Due to their high chemical reactivity, experimental studies of bulk metal halides are rare and have traditionally required an inert environment and/or vacuum equipment. However, theoretical models have predicted many layered metal halides to be mechanically exfoliatable due to low cleavage energies and large in-plane bond strength, suggesting that they could be explored in the 2D limit if suitable passivation and processing conditions were identified. This project develops atomic layer deposition encapsulation layers that allow 2D metal halides to be handled, processed, and tested in ambient conditions. Preceding atomic layer deposition, the 2D metal halides are passivated with organic buffer layers that minimize charge trapping and scattering, thus allowing intrinsic properties to be probed. The interplay among the electronic, magnetic, and optical properties of 2D metal halides is characterized as a function of temperature using lateral field-effect transistors, vertical heterostructures, and Hall bar electrode arrays. By elucidating fundamental charge transport phenomena such as the quantized anomalous Hall effect, this work provides guidance to emerging efforts to incorporate 2D metal halides into advanced magneto-electronic applications including spintronic devices, quantum technologies, and non-volatile memory.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.