# Imaging the Quantum Capacitance of Strained MoS2 Monolayers by Electrostatic Force Microscopy

## TL;DR

This study uses RF-assisted electrostatic force microscopy to visualize the quantum capacitance of strained MoS2 monolayers, distinguishing intrinsic properties from defect contributions at nanoscale resolution.

## Contribution

It introduces a non-invasive, finite-frequency capacitance imaging method to analyze quantum capacitance in strained 2D materials, separating defect effects from intrinsic properties.

## Key findings

- Visualized quantum capacitance of strained MoS2 monolayers.
- Demonstrated frequency-dependent separation of defect and intrinsic capacitance.
- Provided nanoscale insights into electron compressibility in quantum materials.

## Abstract

We implemented radio frequency-assisted electrostatic force microscopy (RF-EFM) to investigate the electric field response of biaxially strained molybdenum disulfide (MoS2) monolayers (MLs) in the form of mesoscopic bubbles, produced via hydrogen (H)-ion irradiation of the bulk crystal. MoS2 ML, a semiconducting transition metal dichalcogenide, has recently attracted significant attention due to its promising optoelectronic properties, further tunable by strain. Here, we take advantage of the RF excitation to distinguish the intrinsic quantum capacitance of the strained ML from that due to atomic scale defects, presumably sulfur vacancies or H-passivated sulfur vacancies. In fact, at frequencies fRF larger than the inverse defect trapping time, the defect contribution to the total capacitance and to transport is negligible. Using RF-EFM at fRF = 300 MHz, we visualize simultaneously the bubble topography and its quantum capacitance. Our finite-frequency capacitance imaging technique is non-invasive and nanoscale, and can contribute to the investigation of time and spatial-dependent phenomena, such as the electron compressibility in quantum materials, which are difficult to measure by other methods.