Femtosecond Laser Irradiation: The Future of 2D Material Nanopatterning

6 mins read

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.

Nanopatterning of Two-Dimensional Materials. This research introduces an advanced technique for nanopatterning 2D materials using asophisticated two-photon 3D printing system. The process involves:
Material Preparation: The 2D material is either directly grown or carefully transferred onto the surface of a thin glass coverslip.
Laser Writing Setup: A high-precision 63× objective (Numerical Aperture = 1.4) is employed, with immersion oil applied to the reverse side of the coverslip for optimal focusing.
Patterning Process: The 2D material undergoes precise patterning through controlled laser exposure.
Material Versatility: The study demonstrates successful patterning on three distinct 2D materials: a) Platinum diselenide (PtSe2) b) Molybdenum disulfide (MoS2) c) Graphene
Nanohole Array Creation: The lower portion of the figure showcases intricate nanohole arrays created in each material, with progressively decreasing hole-to-hole distances.
Scale Reference: To provide perspective on the nanoscale nature of this work, scale bars are included: – PtSe2: 1 μm – MoS2: 500 nm – Graphene: 300 nm
This cutting-edge technique opens up new possibilities for precise manipulation of 2D materials at the nanoscale, potentially revolutionizing their application in various fields of nanotechnology.

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 comparison of patterned using two-photon direct writing and unpatterned 2D materials is compared in this figure, panels (a)-(e) describes procedure and structure of patterned materials. The actual comparison of electrical properties are seen in figure f for three different 2D materials.

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

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