Advances in nanostructure fabrication: Laser direct writing on Au nanofilm

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A research team led by Xuesong Mei and Jianlei Cui from Xi'an Jiaotong University has made significant progress in the field of nanotechnology. They have successfully achieved the direct writing of nanostructures on Au nano-film using a nanosecond-laser-irradiated cantilevered scanning near-field optical microscopy (SNOM) probe tip.

The fabrication of nanostructures beyond the diffraction limit has been a substantial challenge in nanotechnology. Conventional optical lithography is hindered by the diffraction limit, and electron beam lithography is not applicable to metal nanofilms. Scanning probe lithography (SPL) offers a solution for nanofabrication, but each type of SPL has its unique application conditions.

In the study, the researchers used a laser direct-writing system consisting of a nanosecond laser, optical elements, and an atomic force microscope (AFM). The laser was focused on the tip aperture of the SNOM probe, which was used to directly write subwavelength nanostructures on the Au nanofilm without the need for a mask or vacuum atmosphere.

The findings are published in the journal Engineering.

The team obtained a minimum linewidth of 83.6 nm and a repeatable linewidth of approximately 167.8 ± 6.6 nm on the Au nano-film. They also investigated the factors influencing the feature widths of the nanostructure, such as the single-pulse energy (EL) and polarization (α).

Theoretical calculations revealed that the elliptical heat distribution under the SNOM tip generated different linewidths when the tip scanned vertically and horizontally.

Elemental analysis by energy dispersive spectrometer (EDS) indicated that the mechanism of this method was the melting of the Au nanofilm instead of oxidation. The locally excited surface plasmon polaritons (SPPs) generate a high-temperature spot underneath the tip, providing a nanosized energy source for high-resolution nanofabrication.

This technology is considered convenient and economical for nanostructure fabrication and has the potential to be applied in nanolithography on multiple materials and even in nanowelding.

More information: Xuewen Wang et al, Direct Writing Nanostructures on Au Nano-Film by Laser Irradiating Cantilevered Scanning Near-Field Optical Microscope Tip, Engineering (2024). DOI: 10.1016/j.eng.2024.07.014

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