Center for Functional Nanomaterials Seminar

In this talk I will present my experience using low-energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) techniques to study ultra-thin sheets of crystalline materials. I will talk about Si nanomembranes - nanometer-thick sheets of single crystal Si which were either free-standing or supported by different kinds of materials developed in University of Wisonsin – Madison. Strain was applied in different ways to change the electronic band structure of Si to improve the mobilities of electrons and holes. LEEM and PEEM were very nice tools that help check that the nanomembranes were without dislocations and Ge nano-stressors can be used with Si nano-ribbons to create a periodic modulation in the electronic structure for thermoelectric applications. The nanomembranes could also be thinned down to create the quantum confinement effect. For the second part, I will present the works that have been done at the PEEM end-station at the Thai synchrotron where I currently work as a beamline scientist. The works are in collaboration with many researchers who are interested in 2D materials such as graphene, h-Bn, MoS2, WSe2, HfSe2 and a few other less-known materials like MXenes, borophene and 2D metal-organic crystals. A few selected LEEM/PEEM experiments and results on these materials will be presented in this talk. I will focus on three topics: variation of electronic structure of epitaxial graphene by F4-TCNQ doping, the surface passivation capability of graphene, and the study of how B segregation affects h-BN formation. I will also briefly introduce my in-house developed programs that run in Igor Pro which helps our users analyze their experimental results.