Context: 2D materials like graphene, transition material dichalcogenides (TMDs) and MXenes form a versatile body of materials with various electronic tendencies ranging from metallic, semi-conducting, and insulating to various topologically active electronic states. The different flavors of 2D materials can then be arranged on top of each other to form heterostructures exhibiting new properties often called emergent properties. Patterning of 2D materials defining nano/microscopic shapes from these materials to engineer their electronics to form devices. Femtosecond patterning demonstated in a work is a clean process which minimizes impurities on the patterns.

TL;DR: The article presents a novel method for ultrafast and resist-free nanopatterning of two-dimensional (2D) materials using femtosecond laser irradiation. This technique enables the creation of precise nanostructures in materials such as platinum diselenide, molybdenum disulfide, and graphene without the need for traditional resist materials. The process utilizes a two-photon 3D printer in an oil immersion configuration, enhancing resolution and minimizing contamination. The resulting patterns have significant implications for improving the performance of electronic, photonic, and sensing devices, showcasing the potential of 2D materials in advanced applications.

The structured patterned by two-photon direct writing of various 2D materials emonstrate the versatility of the patterning technique and its potential applications in various fields and can be classified into three categories as follows.

1. Nanohole Arrays: These were created in the 2D materials and are useful for applications in optical sensing, plasmonics, and electrochemistry.
2. Line Patterns: These lines were used to outline the boundaries of active areas in functional devices.
3. Cleared Rectangular Areas: This involved removing the 2D material surrounding specific structures to ensure electrical insulation between different portions of the 2D material.

In the X-ray photoelectron spectroscopy (XPS) studies conducted in the research, the comparison between irradiated and non-irradiated 2D materials showed no significant evidence of material degradation due to the laser patterning process. The XPS characterization focused on specific core orbitals of interest, such as molybdenum (Mo) and sulfur (S) for MoS₂, and platinum (Pt) and selenium (Se) for PtSe₂.

The analysis involved high-resolution scans of these elements, and the results indicated that the surrounding (remaining) 2D material did not exhibit substantial changes in chemical composition or bonding states as a result of the laser exposure. This suggests that the patterning process effectively preserves the integrity of the non-irradiated areas of the 2D materials, maintaining their properties for potential applications.

The electrical characterization of the patterned films revealed that the resistance of the patterned channels was higher than that of the pristine (continuous) channels. Specifically, the devices displayed a linear resistive behavior, and the resistance for the patterned channels was approximately double that of the continuous channels. This increase in resistance is attributed to the reduction of the effective width of the conductive paths due to the nanohole patterning, which effectively constricts the flow of current.

Despite this increase in resistance, the study found no significant change in film conductivity due to edge effects or material degradation, indicating that the patterning process did not adversely affect the overall electrical performance of the 2D materials

Reference:

Ultrafast and Resist-Free Nanopatterning of 2D Materials by Femtosecond Laser Irradiation