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

这项德美两国合作项目的重点是利用表面声波光谱技术研究二维过渡金属二卤化物的电输运性质。这种方法是非接触的，并且在没有任何由电接触引起的扰动的情况下提供了对传输特性调制的洞察，而电接触是替代方法至关重要的。该方法利用叉指换能器产生和记录的表面声波，这些换能器与被调查的胶片相距几毫米。本项目中研究的薄膜是使用完全可扩展的方法--化学气相沉积--在技术成熟和新兴的用于混合器件架构的功能基板上生长的。光激发被用来改变薄膜的输运性质，其衍射极限空间分辨率可与目前的光致发光和拉曼光谱相媲美。这使得对过渡金属二卤化物薄膜输运性质的空间变化有了新的认识。德美研究小组探索了过渡金属二卤化物合金的组成梯度、晶界、横向界面和其他材料扰动对局部电导率的影响。它旨在揭示这些材料在技术上极其重要的射频领域(100 MHz至3 GHz)的基本电输运特性，这些异质结构是下一代先进的过渡金属二卤化物异质结，从单片到衬底规模的连续薄膜。重点将放在大面积薄膜的实际应用上。它们将作为声表面波解调相机的有源探测介质。一种成分分级的薄膜将这种装置推向分光计。这两种设备都与现有的表面声波技术完全兼容，并可以通过RF-ID标签无线通信进行接口和寻址。该项目结合了奥格斯堡大学在声光和声电光谱学以及使用表面声波控制光学活性纳米系统方面的专业知识，以及加州大学河滨分校提供的制备技术。这项研究有望加深对含缺陷、异质结或其他局域变化的过渡金属二卤化物薄膜中载流子输运的理解。所获得的知识是设计将这种薄膜的异质结作为功能元件的新型器件的基础。

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.