High-resolution detection of surface potential in strained MoS₂ by multifrequency electrostatic force microscopy

Detection and mechanistic investigation of out-of-plane surface potential variations induced by strain gradients in two-dimensional materials remain a bottleneck for understanding local electromechanical coupling at the nanoscale. Here, we develop a quantitative multifrequency electrostatic force microscopy (MF-EFM) method which, by establishing a quantitative relationship between the response of the probe in the second mode and the sample surface potential, enables precise measurement of the electrical properties in wrinkled regions of MoS_2 films. We find that the potential distribution in these regions is consistent with estimates based on the flexoelectric effect induced by strain gradients, both being on the order of a few millivolts. This study directly demonstrates the modulation of local electronic properties in transition metal dichalcogenides by strain gradients and confirms the potential of MF-EFM, owing to its superior spatial resolution, for electrical characterization of advanced materials.