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The electrical conductivity and optical properties of graphene oxide are determined by and can be tuned through its degree of reduction, while residual oxygen-containing groups serve as active sites for functionalization and chemical sensing. Reduction is typically achieved via chemical or thermal methods. Laser reduction, by contrast, is a single-step, localized process that requires neither masks nor chemical agents [1].
In this study, a local reduction of graphene oxide films was performed by laser engraver with emission wavelength of 355 nm. For obtaining the initial graphene oxide films, a graphene oxide solution (Merck) was deposited onto quartz substrates via drop-casting and dried at 100°C for 1.5 hours. Several samples were obtained for further investigations, by annealing the as deposited GO films with different regimes of operation of the laser engraver, such as at a frequency of the pulses, a pulse width, and a scanning speed. The obtained samples were characterized by Raman spectroscopy and by four-probe conductivity measurements. On selected samples the thickness of the films was determined by Atomic Force Microscopy. Based on the analysis performed, the following optimal processing parameters were determined: 100 laser passes at a frequency of 130 kHz, and a scanning speed of 2000 mm/s. Under these conditions, the electrical characteristics were measured, revealing a resistance for the reduced graphene oxide (rGO) ranging from 4 kΩ/sq to 5.4 kΩ/sq. The results demonstrate that laser photoreduction of graphene oxide enables the control of surface resistance. Raman spectroscopy was employed to investigate the structural changes in graphene oxide resulting from laser photoreduction. This technique allows for the assessment of the carbon structure's state, the degree of structural ordering, and the presence of defects within the graphene matrix. Particular attention was focused on the characteristic D and G bands, located at approximately 1350 cm⁻¹ and 1580 cm⁻¹, respectively. Additionally, the 2D band (~2700 cm⁻¹) was observed and analyzed; its intensity increases noticeably following laser annealing, indicating transformation of a significant part of graphene oxide into graphene.
The results obtained confirm the high potential of laser-induced reduction for the localized formation of electrically conductive thin-film structures and the creation of functional elements for electronic and chemical sensing systems.
The work was supported by the National Research Foundation of Ukraine, project # 2023.05/0022.
[1] V. Dzhagan, Y. Azhniuk, O. Dubikovskyi and D.R.T. Zahn. Advances in laser-based lithography and processing of semiconductors and insulators. J. Phys.: Condensed Matter 38 (25), 253001.
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