RUI:Unraveling the Influence of Free Carriers, Phonons and Band Electrons from the Dielectric Function of van der Waals Solids

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Non-technical AbstractThe focus of this project is to investigate a new class of materials called 2D van der Walls solids which have interesting properties that can be exploited for making novel electronic and optical devices. A technique known as spectroscopic ellipsometry with a uniquely wide light energy range is used to study the characteristics of a variety of the 2D van der Walls solids. Knowledge gained from this study could advance the development of various devices, such as light emitting diodes, transistors, photovoltaic devices, and lasers. The research work is performed by undergraduate students in a liberal-arts setting, who receive training in materials characterization, preparing them for graduate studies and careers in science and technology. To enhance educational goals, several experimental activities are incorporated into current courses in the curriculum. Additionally, to foster a wider interest in the sciences, several outreach activities for high school students are conducted. Technical AbstractBy combining spectroscopic ellipsometry and reflectivity measurements to cover a wide-spectral range (i.e. 1 meV to 6 eV), this project explores the dielectric function and the complex conductivity of 2D van der Walls materials, particularly transition metal dichalcogenides (TMDCs). Having access to a high spectral range enables the study of the contributions of free carriers, phonons and band electrons (and excitons) of TMDCs. Specifically, the following issues are addressed: (i) the excitonic effects of band transitions; (ii) evolution of transitions with the number of layers; (iii) the mechanism that governs the carrier relaxation time; (iv) the influence of dopants on the transport properties; (v) the significance of electron-phonon coupling on TMDCs; and (vi) quantifying the circular dichroism in TMDCs and explaining their differences. The research work is performed by undergraduate students in a liberal-arts setting. Several experimental activities are injected into current courses such as Condensed Matter Physics, Optics and Advanced Lab. The undergraduate students receive training in materials characterization, optics, and cryogenics, preparing them for graduate studies or careers in STEM-based fields. Additionally, several outreach activities for high school students are conducted in order to foster a wider interest in the sciences.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.