Subsurface imaging of two-dimensional materials at the nanoscale

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• Scanning probe microscopy (SPM) excels at nanoscale surface imaging but lacks depth penetration.
• Subsurface imaging with SPM is limited to cases where features affect surface properties.
• Nanotechnology applications often require understanding buried interfaces and subsurface structures.

Purpose of the Study:

• To investigate the capability of Ultrasonic Force Microscopy (UFM) for subsurface imaging of 2D materials.
• To demonstrate UFM's ability to detect defects and variations in mechanical properties non-destructively.
• To explore UFM's potential for analyzing buried interfaces in nanostructured 2D materials.

Main Methods:

• Utilized Ultrasonic Force Microscopy (UFM), a variant of atomic force microscopy.
• Applied UFM to analyze flakes of graphite and molybdenum disulfide on polymeric substrates.
• Measured dynamic stiffness of the tip-sample elastic contact to probe near-surface elastic fields.

Main Results:

• UFM successfully distinguished between supported and suspended areas of 2D materials.
• Localized defects such as buckling and delamination in multilayered 2D materials.
• Detected variations in local indentation and elastic modulus caused by subsurface features and stress.

Conclusions:

• UFM offers a non-destructive method for probing subsurface characteristics of 2D materials.
• The technique is sensitive to mechanical variations, enabling defect detection.
• UFM shows significant promise for studying buried interfaces in nanostructured 2D materials and devices.