Observing the Layer-Number-Dependent Local Dielectric Response of WSe₂ by Electrostatic Force Microscopy

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Tungsten diselenide (WSe2) is a 2D van der Waals semiconductor with tunable electronic properties.
• Understanding the dielectric response of WSe2 is crucial for its application in electronic devices.
• Layer-dependent properties of 2D materials significantly impact their performance.

Purpose of the Study:

• To investigate the layer-number-dependent dielectric response of WSe2.
• To correlate dielectric properties with charge carrier concentration and mobility.
• To explore the potential for controlling dielectric properties in 2D materials.

Main Methods:

• Utilized electrostatic force microscopy (EFM) to measure the phase shift (Φ).
• Applied the plane capacitor model to analyze capacitive coupling between the EFM tip and WSe2.
• Calculated the second derivative of capacitance (C'') to quantify dielectric response.
• Constructed spatially resolved C'' maps for local dielectric analysis.

Main Results:

• The dielectric response of WSe2 exhibits a clear dependence on the number of layers.
• C'' values increase with layer number in few-layer WSe2 and saturate to bulk values.
• Dielectric constant increases with layer number, approaching the bulk value.
• Spatially resolved C'' maps reveal local variations in dielectric behavior.

Conclusions:

• The dielectric constant of WSe2 is layer-number-dependent, offering a pathway for property tuning.
• The observed dielectric behavior is linked to charge carrier concentration and mobility.
• This research provides insights for optimizing electronic devices using controllable dielectric properties of 2D materials.