MRI: Development of an Ultrafast Photoluminescence and Transient Absorption Microscope in Ultrahigh Vacuum for Studying Electronic Properties of 2-Dimensional Materials

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The ability to control the growth and doping of semiconductors such as silicon enabled the development of electronic materials that revolutionized modern society in the digital age. Two-dimensional materials such as transition metal dichalcogenides are a new class of electronic materials that have the potential to open new technological advances on a similar scale. Major advances in the growth of two-dimensional materials have occurred in recent years. However, there remains a fundamental need to develop doping and processing chemistries that enable the control of the electronic properties of two-dimensional materials. The instrument developed in this project combines an ultrafast photoluminescence and transient absorption microscope, to characterize the electronic properties of two-dimensional materials, with an ultrahigh vacuum system that controls doping chemistries. It significantly expands the research infrastructure for users of the NSF Materials Innovation Platform focused on two-dimensional materials by enabling correlative measurements at the same locations in the samples using multiple characterization methods. The instrument serves a user-base of researchers both at Pennsylvania State University and in the broader national two-dimensional materials community. Graduate students and post-doctoral scholars using the instrument gain important professional development experience by facilitating workshops and associated training modules that are offered and advertised through the Materials Research Institute at Pennsylvania State University and the Center for Atomically Thin Multifunctional Coatings, which is an Industry-University Cooperative Research Center. The development of the ultrafast photoluminescence and transient absorption microscope in an ultrahigh vacuum system opens the ability to probe both emissive and non-emissive states with ultrafast time resolution in an imaging platform. It also enables the control of the sample environment and doping chemistry for characterization of the electronic and transport properties of two-dimensional materials. These capabilities are critical because two-dimensional materials are single- or few layer-structures with electronic properties that are strongly influenced by surface interactions. Furthermore, many of the electronic states involved in charge transfer and transport in two-dimensional materials are weakly- or non-emissive with diffusion properties and lifetimes that depend sensitively on the epitaxial alignment and growth of the materials. The ultrafast microscopy capability of the instrument combined with an ultrahigh vacuum sample transfer system and attached preparation chamber enables the dynamics and transport of excitons and charge carriers to be spatially and temporally resolved and correlated with their growth and doping chemistries. The electronic and transport properties of the same regions of the samples can be investigated using scanned probe and electron microscopy measurements and photoemission studies for complete characterization and development of design rules that will guide the development of two-dimensional materials and devices.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.