Laser-stepwise-induced graphene enables tunable electromagnetic shielding with remarkably low sheet resistance
image: Schematic illustration showing the difference between focused and defocused laser irradiation and the design of the LSIG method for reducing sheet resistance in laser-induced graphene.
Credit: Nano Research, Tsinghua University Press
Graphene has been studied for more than a decade as one of the most notable two-dimensional materials, owing to its combination of electrical conductivity, mechanical strength, and thermal stability. These properties make it a candidate for applications ranging from flexible electronics and communication systems to energy storage and stealth technologies. Yet, the path from laboratory-scale synthesis to practical integration into devices has remained challenging. A central difficulty lies in producing large-area graphene films that are both defect-free and highly conductive, without resorting to costly or complex processing routes. Conventional fabrication methods, including chemical vapor deposition, liquid-phase exfoliation, and epitaxial growth, face persistent issues related to scalability, cost, or reproducibility. These constraints have limited the wider adoption of graphene in commercial and defense-related technologies.
Laser-induced graphene (LIG), first reported in 2014, was introduced as a more accessible alternative. This technique enables the direct writing of porous graphene films from polymer substrates, such as polyimide, under ambient conditions and without the need for catalysts. LIG is attractive because it allows mask-free patterning, scalability, and relatively low cost, and it has been applied in areas such as sensors, supercapacitors, and energy harvesters. However, the ultrafast kinetics of the laser ablation process often lead to an amorphous, defect-rich carbon structure. As a result, LIG tends to exhibit relatively high sheet resistance and limited crystalline ordering, restricting its use in applications that demand both high conductivity and structural stability, such as electromagnetic shielding and advanced electronic devices.
To address this limitation, a research team from Wuhan University of Technology developed an approach termed laser-stepwise-induced graphene (LSIG). The key feature of LSIG is a two-step laser sequence applied directly to polyimide precursors. In the first stage, a focused laser pulse drives the conversion of polyimide molecules into graphene, penetrating vertically into the substrate. This step enables effective graphitization but also leaves behind a density of defects. In the second stage, a defocused laser pulse is applied, which reduces the local energy density and allows time for defect healing and crystalline domain growth. Raman spectroscopy confirmed the structural changes: the ID/IG ratio decreased from 0.94 to 0.81, and the 2D band narrowed, both indicators of enhanced crystallinity. Importantly, this dual-laser strategy lowered the sheet resistance from 25.3 Ω sq-1 to 15.0 Ω sq-1, a reduction achieved without chemical post-treatments or high-temperature annealing.
Pengfei Chen, the first author of the study, explained that this method combines simplicity, scalability, and efficiency: “By designing a two-stage laser sequence, we can directly write high-quality graphene films that are both conductive and structurally robust. This makes it more straightforward to integrate graphene into practical devices.” To illustrate the method’s potential, the team fabricated a flexible frequency-selective surface (FSS) consisting of a patterned array of graphene square loops. The LSIG FSS demonstrated effective electromagnetic manipulation, with an enhanced bandwidth of 4.92 GHz and a transmission coefficient of 0.057 at resonance. Such performance shows the role of reduced sheet resistance in enabling higher-efficiency electromagnetic shielding.
Beyond electromagnetic applications, the LSIG films also showed infrared stealth performance. Infrared imaging experiments indicated that the LSIG surface attenuated thermal emission from heated objects placed behind it, making the shielded region less distinguishable from the background. This property suggests potential for camouflage and the protection of electronic systems from both electromagnetic interference and infrared detection. In addition, the films exhibited stable performance under different conditions: after 72 hours of exposure to water, salt solutions, acid, and elevated temperatures, the sheet resistance showed little change. Mechanical tests further demonstrated that LSIG films could withstand repeated tensile strain without loss of conductivity, indicating robustness in practical use.
In summary, LSIG provides a route to improve the electrical and structural characteristics of LIG while preserving the advantages of mask-free, ambient-condition processing. With its combination of lower sheet resistance, chemical and mechanical stability, flexibility, and multifunctionality, LSIG can support applications in flexible electronics, electromagnetic compatibility, stealth materials, and communication technologies. The researchers plan to continue optimizing the LSIG process and to explore its utility in sensors, energy storage devices, and other systems, suggesting that this approach may help accelerate the wider use of graphene across multiple application areas.
About Nano Research
Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.