CAREER:Two-Dimensional Materials with Addressable Surfaces

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Non-Technical Summary:Two-dimensional (2D) materials are crystalline materials which are only a single layer or a few layers of atoms thick. Such materials have recently received widespread attention for the development of novel technologies in nano(opto)electronics, catalysis, sensing, and energy production. This NSF CAREER project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, integrates research and educational activities centered on the design and synthesis of a new family of 2D materials, and advances the understanding of the relation between their surface functionalization and physical properties. Realizing the great transformative promises of 2D materials hinges on the development of effective methods to control the surface chemistry and thereby change the intrinsic physical properties and materials chemistry of the thin layers. This remains a major challenge for most known 2D materials. They are chemically non-reactive. To overcome this hurdle, the project develops a series of cluster-based metal chalcogenide 2D materials. The surfaces of the individual clusters can be modified more easily while leaving the internal structure of the inorganic layer intact. The overall goal is to develop chemical strategies to change the outside of these 2D materials by attaching different molecules, and then study how these modifications alter the optical and electronic properties of the layers. This project advances the scientific understanding and potential technological applications of 2D materials by providing a path towards creating multifunctional 2D materials with tunable physical, chemical and surface properties. Such 2D materials have never been synthesized and their novel cluster-based structures produces unique physical properties. The research effort is integrated with educational and outreach activities aimed at increasing the participation of historically underrepresented groups in STEM, and strengthening the scientific workforce. A coordinated effort spans high school and middle school outreach, interdisciplinary research training for undergraduate and graduate scientists, and curriculum development.Technical Summary:This NSF CAREER project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, integrates research and educational activities centered on the design and synthesis of a new family of 2D materials, and furthers the understanding of the relation between their surface functionalization and physical properties. The proposed materials are composed of covalently-linked metal chalcogenide clusters capped by substitutionally labile halogen atoms. These 2D materials are exfoliated from bulk layered van der Waals cluster solids, Re6Se8Cl2 and Mo6S3Br6. The research tests the hypothesis that the optical and electronic properties of these 2D materials are strongly influenced by the nature of the ligands on the surface. The PI and his students develop substitution reactions to functionalize the surface of the 2D materials with a series of ligands with programmed characteristics (charge, ligand field strength, dipole), and measure the resulting optical properties and surface electronic states, before and after functionalization. The materials are integrated into model electrical devices to probe the effect of ligand substitution on the electronic properties. A critical factor for the development of the field of 2D materials is the ability to control their properties. In this context, the development of surface functionalization strategies is of great scientific and technological interest as a path towards creating multifunctional 2D materials with tunable physical, chemical and surface properties. Current methods are severely limited because they yield very low surface coverage, they generate a vast number of defects and/or they rely on weak non-covalent interactions. This research overcomes these hurdles and enable the covalent functionalization of 2D materials with high coverage rates while preserving the internal structure of the inorganic framework.The educational component of this NSF CAREER project aims to inspire students (middle school, high school, undergraduate, and graduate) to pursue careers in STEM, as well as broaden the participation of historically underrepresented groups in STEM and enhance the undergraduate chemistry curriculum. The focus on recruiting students form historically underrepresented groups prevails in four approaches: (1) Outreach activities to middle-school and high-school students from Central Harlem and the Bronx in New York City; (2) Recruit undergraduate students to work in the PI's laboratory for early research experiences; (3) Recruit and mentor graduate students in multidisciplinary research combining chemistry and materials science; (4) Integrate the research into the Chemistry undergraduate curriculum.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.