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

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This bi-national German-US project is focused on studying the electrical transport properties of two-dimensional (2D) transition metal dichalcogenides by applying surface acoustic wave spectroscopy. This method is contactless and provides insight into the transport properties modulations in absence of any perturbation caused by electrical contacts crucially 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. The films studied in this project are grown using a fully scalable approach, chemical vapor deposition, on technologically mature and emerging functional substrates for hybrid device architectures. 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 German-US research team explores the impact of composition gradients in alloys of transition metal dichalcogenides, grain boundaries, lateral interfaces, and other material perturbations on the local conductivity. It aims to unravel the fundamental electrical transport properties of these in the technologically extremely important radio frequency domain (100 MHz up to 3 GHz) of next-generation advanced transition metal dichalcogenide heterostructures, from single flakes to substrate-scale continuous films. Emphasis will be set on the practical application of large-area films. These will be applied as the active detection medium of a surface acoustic wave-interrogated camera. A composition-graded film advances this device towards a spectrometer. Both devices are fully compatible with existing surface acoustic wave technology and can be interfaced and addressed via RF-ID tagged wireless communication. The project combines the expertise on acousto-optic and acousto-electric spectroscopy and control of optically active nanosystems using surface acoustic waves at Universität Augsburg and preparative techniques available at the University of California, Riverside. 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.