Nano-spherical tip-based smoothing with minimal damage for 2D van der Waals heterostructures

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science
• Optoelectronics

Background:

• Two-dimensional (2D) materials and heterostructures possess unique properties crucial for advanced materials science and optoelectronics.
• Fabrication and transfer processes introduce impurities, degrading the intrinsic quality of 2D materials.
• Current atomic force microscopy (AFM) probe contact modes offer in situ cleaning but pyramidal probes risk surface damage.

Purpose of the Study:

• To introduce and evaluate a nano-spherical probe contact mode for minimum-damage cleaning of residual and polymer contamination on 2D materials.
• To compare the cleaning efficacy and impact on material properties of nano-spherical probes against traditional pyramidal probes.

Main Methods:

• Utilized atomic force microscopy (AFM) in contact mode with both nano-spherical and pyramidal probes for cleaning MoS₂/hBN substrates.
• Performed comparative analyses of material morphology and photoluminescence (PL) properties before and after cleaning.
• Employed Kelvin probe force microscopy (KPFM) and scanning electron microscopy (SEM) to assess surface potential uniformity and morphology.

Main Results:

• Nano-spherical probes effectively removed bubbles and reduced PL FWHM by 30% (from 0.115 eV to 0.08 eV), indicating improved material quality.
• Pyramidal probes showed limited cleaning efficacy, especially on larger bubbles, resulting in less uniform PL mapping data.
• Nano-spherical probes maintained surface integrity and potential uniformity (KPFM, SEM), unlike pyramidal probes which caused damage at higher forces.

Conclusions:

• Nano-spherical probes provide a significantly more effective and lower-damage cleaning method for 2D materials compared to pyramidal probes.
• This technique minimizes contamination and preserves the intrinsic properties of 2D materials, crucial for their application in optoelectronics.
• The nano-spherical probe method represents a promising advancement for high-quality fabrication and application of 2D materials.