The latest research from Xijiao University: using femtosecond laser pulses to cr

It is reported that a research team of Xi'an Jiaotong University is focusing on a promising nanostructure manufacturing technology: femtosecond laser direct writing (FLDW).

From the latest research of Xijiao: the surface and profile view of a sample shows a nano channel with a length of several microns and a diameter far below 30nm, which means that the aspect ratio is very high (>200).

So far, only the shallow nano channels through lithography technology have been widely and successfully replicated. For most applications, nanochannels made of hard and brittle materials (such as silicon dioxide, diamond and sapphire) have high chemical stability and durability in harsh environments.

Researchers are making efforts in this regard.

A research team of Xi'an Jiaotong University is focusing on a promising nanostructure manufacturing technology: femtosecond laser direct writing (FLDW). In a nutshell, FLDW uses extremely short (10-15 seconds) and high-precision high-energy laser pulses to create the required nanostructures (e.g., nanopores, nanopores, and nanostones). In the latest research published on Advanced Photonics Nexus, the team successfully used FLDW to create a silica nano channel with a diameter of 30 nm, which is smaller than that reported in any previous research, and the aspect ratio exceeds 200. This is attributed to a new laser matter interaction phenomenon discovered in the process.

1.0μJ Single fabrication of nanostructures by femtosecond Bessel beams

In their work, the team used Bessel beams, a laser beam that can maintain its shape when propagating or even focusing on a small point. A single Bessel beam pulse of 515 nm wavelength (obtained from a 1030 nm laser by frequency doubling) is focused at just the right distance from the surface of the silica sample. Some experiments using different laser pulse energies and sample distances have shown very impressive results. At low pulse energy, according to the sample distance, near the silica surface (less than 1 μ m) A 30 nm nano channel or pure crater structure was found. At high pulse energy μ M below) will form a longer cavity and a pit on the surface.

After careful theoretical analysis and simulation, the team realized that the interaction between laser and material that has not been discovered so far is playing a role. The team called it "surface assisted material jet", which generates cavities in the internal "thermal domain" generated by Bessel beam.

Leverage 2.0- μ The nanostructures were fabricated by femtosecond Bessel beam with J pulse energy in a single pass.

Paulina Segovia Olvera, deputy editor in chief of Advanced Photonics Nexus, noted that this work has greatly promoted the progress of knowledge in the field of laser material processing: "This work provides new insights into the basic principles of laser matter interaction. It shows that nano channel structures with a size far below the diffraction limit can be fabricated, which usually sets the lower limit of the characteristic size of nanostructures for traditional laser based manufacturing."

Time evolution of the interaction between femtosecond Bessel beam and silica sample is simulated. Pulse energy applied in simulation is 1 μ J.

In view of this knowledge progress, this study may pave the way for adopting FLDW as a robust, flexible and cost-effective method to manufacture nano channels with submicron accuracy. In turn, this will help promote its applications in other fields, such as genome science, catalysis and sensors.

Source:Y. Lu, L. Kai, et al., “Nanochannels with a 18-nm feature size and ultrahigh aspect ratio on silica through surface assisting material ejection,” Adv. Photon. Nexus 1(2), 026004 (2022), doi 10.1117/1.APN.1.2.026004.