Surface Acoustic Spectroscopy Offers Novel, Broadband, and Spatially-Resolved Insight into Transition Metal Dichalcogenides Films

University Of California-Riverside, Riverside CA

Investigators

Abstract

Non-technical Description: When an earthquake hits it shakes the buildings: energy is transferred from the ground to the buildings and - if the buildings are not designed appropriately - they cannot get rid of that energy and become damaged or collapsed. This research project uses a similar approach to study a particular class of novel semiconducting materials called transition metal dichalcogenides. Usually, these materials are only a single atomic layer thick and they hold tremendous opportunity for next generation electronic devices, because they can serve in a transistor at a thinness unattainable by silicon while at the same time allowing for optical communication. This method uses sound waves within surfaces - waves much akin to those that shake the ground during earthquakes - to rock the semiconductor thin layers and to study how the charge carriers in them dissipate the energy. The approach provides unique knowledge about the dynamic properties of charge carriers and how free they are to move around so that they can sustain fast electronic applications. The great advantage of this technique is that it does not require fabrication of electrical contacts or attaching wires to the material under investigation. Because the material is so thin, the metal of the wires can have a huge impact on the results of measurements using more conventional techniques. This research explores novel strategies for the integration of these materials into electronic devices. The University of California at Riverside is a Hispanic serving institution with every third student being Hispanic and every other student being the first in the family to attend college. This research project is conducted by a Hispanic graduate student and offers undergraduate research opportunity to UC Riverside's diverse student body. Technical Description: This research is focused on studying the transport properties of two-dimensional (2D) transition metal dichalcogenides by applying surface acoustic wave spectroscopy. The method is contactless and provides insight into the transport properties modulations in absence of any perturbation caused by electrical contacts needed for alternative methods. The approach utilizes surface acoustic waves generated and recorded by means of interdigital transducers that are spaced millimeters away from the films under investigation. Optical excitation is used to modify the transport properties of the films at diffraction-limited spatial resolution rivaling that of current photoluminescence and Raman maps. This allows new insight into the spatial variation of transport properties in transition metal dichalcogenide films. The research team explores the impact of grain boundaries, lateral and vertical interfaces, and other material perturbations on the local conductivity. The project is interdisciplinary, combining the preparative techniques available at the University of California, Riverside, with the expertise of an international collaborator from University of Augsburg, Germany. The research is expected to enhance the understanding of carrier transport in transition metal dichalcogenide films with defects, heterojunctions or other local variations. The acquired knowledge is a foundation for design of novel devices that incorporate heterojunctions of such films as functional elements.