Optical trapping and optical force positioning of two-dimensional materials.

Area of Science:

• Materials Science
• Nanotechnology
• Optics

Background:

• Two-dimensional (2D) materials are synthesized and characterized using various methods.
• Liquid phase exfoliation (LPE) is a scalable technique for producing mono- and few-layer 2D materials.
• Contactless manipulation and characterization of individual nanosheets are crucial for advanced applications.

Purpose of the Study:

• To utilize optical forces for high-resolution structural characterization and precise mechanical positioning of 2D nanosheets.
• To investigate the trapping behavior of different 2D materials (hexagonal boron nitride, molybdenum disulfide, tungsten disulfide) in optical tweezers.
• To demonstrate the application of optical forces for substrate patterning and selective nanosheet deposition.

Main Methods:

• Optical tweezers were employed to trap and manipulate nanosheets of hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide obtained via LPE.
• Analysis of thermal fluctuations in trapped hexagonal boron nitride nanosheets was used to measure optical forces and flake size.
• T-matrix light scattering calculations were performed to compare with experimental optical trapping constants.
• Substrate patterning was achieved by selective deposition of 2D nanosheets using optical forces.

Main Results:

• Weakly absorbing hexagonal boron nitride nanosheets were successfully trapped in optical tweezers.
• Optical forces and mean flake size were directly measured from thermal fluctuations of trapped hexagonal boron nitride.
• A quadratic size scaling of optical trapping constants was observed for small hexagonal boron nitride flakes, consistent with bidimensional systems.
• Strongly absorbing molybdenum disulfide and tungsten disulfide nanosheets were not stably trapped due to radiation pressure dominance.
• Optical forces enabled rapid (minutes) and surface-independent patterning of substrates with 2D nanosheets.

Conclusions:

• Optical forces are effective for characterizing and manipulating weakly absorbing 2D materials like hexagonal boron nitride.
• Radiation pressure limits stable optical trapping of strongly absorbing 2D materials such as molybdenum disulfide and tungsten disulfide.
• Optical force-mediated patterning offers a promising method for fabricating devices and improving techniques like inkjet printing with 2D materials.