Nontechnical Abstract Tremendous progress has been made on discovering various new materials with enhanced functionalities. The technological applications of functional materials, however, demand extreme control of composition and imperfections of functional materials. The control of defects, especially point defects is crucial for the performance of semiconductor devices, which are building blocks of all modern electronics such as computers, cell phones, etc. Yet it is notoriously difficult to directly probe and exam individual point defects in functional materials. Scanning tunneling microscope (STM) is one of the few tools that allow scientists to directly probe atomic scale phenomena, including point defects and responses of local electronic properties. This project investigates the impacts of point defects, either intentionally or unintentionally introduced to bulk materials during synthesis, on novel electronic materials called layered chalcogenides. Using STM to visualize interesting electronic phenomena at nanometer scale, the principle investigator aims to obtain fundamental understandings of the driving mechanisms and the control of point defects in these functional materials. Education and training of graduate and undergraduate students is seamlessly integrated to the research activities, which enable them to learn fundamental material science, to master advanced microscopic techniques, and more importantly, to learn independent thinking. This project also integrates education and training of under-representative undergraduate students through various programs such as Aresty Research Center research program and Research Experiences for Undergraduates program at Rutgers, and of high school students through the Partner in Science program of Liberty Science Center. Technical AbstractLayered chalcogenides have been the active playground for various correlated phenomena in condensed matter physics, ranging from charge density wave and superconductivity. Incorporating heavy elements in layered chalcogenides introduces additional twists of strong spin-orbital coupling or dimerization, leading to emergent phenomena such as topological insulators and dimerization induced stripe modulations. This project addresses the impact of point defects (either intrinsic or extrinsic) on these fascinating phenomena to gain fundamental understanding of their driving mechanisms. Topological insulators are new quantum states of matter where insulating bulk states are surrounded by conducting surface states because of nontrivial topology of electronic wave functions. Native defects in topological insulators are known to induce substantial bulk conduction, which is detrimental for the observation and technological applications of exotic phenomena related to topological surface states. The influence of chemical inhomogeneity is crucial for fundamental understanding of 'topological phase transitions' induced by chemical doping. The goal of this project is to identify and to control native and/or extrinsic point defects in layered chalcogenide topological insulators such as Bi2Se3 and Sb2Te3. In addition, this project aims to achieve a comprehensive understanding of the mechanism of emergent multiple stripe modulations in the heavy di-chalcogenide IrTe2 which is closely related to devil's staircase phenomena due to competing interactions. Atomic-scale defects, electronic modulations and nanoscale inhomogeneity in these materials are visualized and examined using state-of-the-art scanning tunneling microscopy and spectroscopy. These research efforts are complimented by bulk probes, first-principle calculations and theoretical modeling via domestic and international collaborations.
|Effective start/end date||6/15/15 → 5/31/18|
- National Science Foundation (National Science Foundation (NSF))