The researchers used lasers to induce single-layer graphene nanomachings

Graphene was discovered in 2004 and revolutionized every field of science. It has significant properties such as high electron mobility, mechanical strength and thermal conductivity. A lot of time and effort has been put into exploring its potential as a next-generation semiconductor material, leading to the development of graphene-based transistors, transparent electrodes and sensors.

But to put these devices to practical use, it is crucial to have efficient processing techniques that can build graphene films at the micron and nanoscale. Nano-lithography and focused ion beam methods are commonly used for micro/nano scale material processing and device manufacturing. However, these pose long-term challenges for laboratory researchers due to the large equipment required, long manufacturing times and complex operations.

Back in January, researchers at Northeastern University created a technique for micro/nano-fabrication of thin silicon nitride devices in the thickness range of 5 to 50 nanometers. The method uses femtosecond lasers, which emit extremely short, fast pulses of light. It proved to be able to handle thin materials quickly and easily without a vacuum environment.

By applying this method to graphene's ultra-thin atomic layers, the team has now managed to drill multiple holes without damaging the graphene film. Details of their breakthrough are reported in the May 16, 2023, issue of Nano Letters.

"By properly controlling the input energy and laser emission times, we were able to perform precise machining and create holes ranging in diameter from 70 nanometers (much smaller than the laser wavelength of 520 nanometers) to more than 1 mm," says Yuuki Uesugi, assistant professor at Northeastern University's Multidisciplinary Institute for Advanced Materials and co-author of the paper.

Using a high-powered electron microscope, Uesugi and his colleagues carefully examined areas that had been irradiated with low-energy laser pulses. These areas had not formed holes, and Uesugi and his colleagues found that contaminants had also been removed from the graphene. A closer look revealed nanopores less than 10 nanometers in diameter and atomic-level defects, where graphene's crystal structure was missing several carbon atoms.

Depending on the application, atomic defects in graphene can be both harmful and beneficial. While defects sometimes degrade certain attributes, they also introduce new functionality or enhance specific features.

"The observed trend that the density of nanopore and defect increases in proportion to the energy and number of lasers emitted led us to conclude that nanopore and defect formation can be controlled by using femtosecond laser irradiation," Uesugi added. "By forming nanoporous and atomic-scale defects in graphene, it is possible to control not only electrical conductivity but also quantum-scale characteristics such as spin and valley. In addition, the removal of contaminants by femtosecond laser irradiation discovered in this study could develop a new method for nondestructive clean cleaning of high purity graphene."

Going forward, the team aims to build a clean technology that uses lasers and conduct detailed research on how atomic defect formation can be carried out. Further breakthroughs will have a major impact on fields ranging from quantum material research to biosensor development.

Source: Laser Net