RUI: Electronic Properties of Finite Molecular Layer Transition Metal Dichalcogenides

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Non-Technical: The goal of this project is to better understand the electronic and optical properties of thin sheets of materials with thickness in the range of a few atomic layers. These properties have practical applications in solar cells, light emitting diodes (LEDs), and a wide variety of sensors. A multidisciplinary approach is used to obtain a more complete picture necessary to use these materials in these applications. This research involves undergraduate students trained on a wide variety of techniques that involve electronics, optics and chemistry. Such an environment results in well-rounded students ready for careers in either industry or academia. The University of Northern Iowa provides an excellent opportunity for this project to have a positive impact on elementary, middle, and high school students from diverse backgrounds throughout Iowa and surrounding states. Regular contact with high school science teachers allows faculty research activities and student opportunities to be showcased directly. Such efforts encourage students to explore careers in STEM (science, technology, engineering, and mathematics) fields. Technical: The goal of this project is to develop a more thorough understanding of the electronic and optical properties of a wide variety of finite layer dichalcogenide molecular sheets. Ultrasonic agitation is used to break apart these layered crystals from the bulk into thin nano-sheets. Those sheets with the smallest number of layers are separated using a centrifuge and studied using scanning tunneling microscopy, optical spectroscopy, and ballistic electron emission microscopy. Scanning tunneling microscopy measurements serve to study topological features as well as surface electrical properties on the atomic scale. This includes the zero resistance characteristics associated with charge density waves in two-dimensional dichalcogenides sheets. Raman and photoluminescence complement the electrical measurements made using the localized probe of the scanning tunneling microscope, providing global information on electronic band structure and vibrational properties. Transport measurements are achieved by injecting electrons into these structures using ballistic electron emission microscopy, allowing characterization of electron scattering as a function of temperature and energy. Together, these combined data will enable a more complete understanding of reduced dimensionality on the electronic properties in a wide variety of material systems. More importantly, broadening the research focus of this field to a more diverse array of layered materials will enhance our understanding of the fundamental physics in two-dimensional systems. Modifications of current theories to encompass a wider variety of layered materials leads to more robust theoretical models, essential to device design.