Microwave Near-Field Imaging of Two-Dimensional Semiconductors
Samuel Berweger, Joel C. Weber, Jimmy J. Li, Jesus M. Velazquez, Adam Pieterick, Norman A. Sanford, Albert V. Davydov, Thomas M. Wallis, Pavel Kabos
Optimizing new generations of 2D devices based on van der Waals materials will require techniques capable of measuring variations in electronic properties in situ and with nanometer spatial resolution. We perform scanning microwave microscopy (SMM) imaging of single-layers of MoS2 and n-and p-doped WSE2. By controlling the sample charge carrier concentration through the tip bias, we are able to reversibly control and optimize the SMM contrast to image variations in electronic structure and the localized effect of surface contaminants. By further performing tip bias dependent spectroscopy together with finite element modeling, we are able to semi-quantitatively determine the local dominant charge carrier species and dopant concentration. These results underscore the capability of SMM for the study of 2D materials of image, identify, and study, electronic defects.