CAREER: Development of 2d Materials with High Optical Sensitivity and Efficient Charge Transport Through Local Chemical Modification
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Materials only a single atom thick, known as two-dimensional (2D) materials, possess optical and electronic properties that rival many traditional materials. Two key properties of these 2D materials - ability to absorb light and the ability to move charge - are often competing physical properties, where enhancement of one diminishes the other. This research activity seeks to develop 2D materials with both high optical absorptivity and high electrical conductivity through nanometer-scale control of local surface chemistry. The project investigates new chemical routes to functionalize 2D materials, and how optically active regions interact with electronically active regions on the surface of a single 2D sheet. Such functionality is critical for a wide range of applications, including photodetectors, solar photovoltaics, and chemical sensors. The project activities provide training to graduate and undergraduate students in the research areas of electrochemistry, surface science, chemical spectroscopy, and nanoscale transport phenomena. Additionally, the research supports interactive laboratory activities for underrepresented and economically disadvantaged secondary school students, as well development of open source book chapters through the Open Textbook Library Initiative and the OAKTrust Digital Repository.This research project explores new chemical pathways and techniques to improve both optical sensitivity and response time on atomically thin sheets of graphene, molybdenum disulfide, and telluride containing chalcogenides. Chemically altering the surface of 2D materials to interact strongly with electromagnetic radiation without disrupting charge transport within the material is currently a significant challenge. Here, chemical functionalization of 2D materials with optically active organic dyes and quantum dots is explored via multi-step electrochemical oxidation and reduction reactions utilizing diazonium salts to create 2D materials possessing strong interaction with visible and infrared light. Further, optical lithography and tip-based nanolithography provide routes to integrate optically active regions with regions of high electrical conductivity, such that charge states optically excited in one region can efficiently couple to adjacent regions. The synthesis efforts are complimented by a wide range of optical and electronic measurement techniques, including nanoscale infrared microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, and fluorescence microscopy in concert with back-gated transistor measurements to investigate the effect of local chemical composition on charge excitation and transport. The fundamental knowledge gained in this study can be applied to impart unique optical, thermal, and mechanical properties to a wide range of 2D materials without sacrificing charge transport performance.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.