New imaging modes for analyzing suspended ultra-thin membranes by double-tip scanning probe microscopy

Area of Science:

• Surface and Nanoscience
• Materials Science
• Experimental Physics

Background:

• Scanning probe microscopy (SPM) is crucial for surface and nanoscience, but imaging flexible membranes is challenging due to tip-induced deformations.
• Existing SPM techniques struggle to accurately interpret measurements on suspended, flexible materials because tip-sample interactions cause significant morphological changes.
• Controlling these tip-induced modifications offers potential for exploring novel physical properties and functionalities of membranes.

Purpose of the Study:

• To develop and demonstrate new scanning probe microscopy (SPM) measurement techniques for suspended, flexible membranes.
• To enable simultaneous probing of both sides of a membrane using two SPM instruments (AFM and STM).
• To overcome the limitations of traditional SPM on flexible materials by controlling tip-sample interactions.

Main Methods:

• Utilized two SPM instruments (atomic force microscopy, AFM, and scanning tunneling microscopy, STM) positioned on opposite sides of a suspended 2D material membrane.
• Developed new imaging modes by holding one probe stationary while scanning the other, recording signals from the stationary probe.
• Introduced electrical cross-talk imaging (ECT) for electrical measurements and mechanical cross-talk imaging (MCT) to disentangle mechanical influences.

Main Results:

• Demonstrated electrical cross-talk imaging (ECT) to measure membrane deformation around an AFM tip indentation and perform electrical measurements across the membrane.
• Showcased mechanical cross-talk imaging (MCT) to separate tip-induced membrane deformation topography from tip-sample forces.
• Confirmed that simultaneous probing of both surfaces of ultra-thin membranes provides novel insights into electronic properties.

Conclusions:

• Simultaneous dual-sided SPM is a powerful approach for studying flexible membranes, particularly suspended 2D materials.
• New imaging modes (ECT and MCT) allow for unprecedented control and characterization of tip-sample interactions and material properties.
• This methodology opens new avenues for understanding the electronic and mechanical behavior of advanced materials.