Synergistic Role of Electron and Photon Dose in Stepwise Laser-Induced Complete Deoxygenation of Graphene Oxide Revealed by In-situ TEM
Laser-induced reduction of graphene oxide (GO) represents a highly promising route to graphene synthesis, offering spatially localized processing, elimination of hazardous chemical reagents, and compatibility with ambient conditions. Here, we introduce a stepwise laser reduction strategy employing a 532 nm pulsed laser, monitored in real-time by in situ dynamic transmission electron microscopy (DTEM). By systematically varying the pulse sequence and the cumulative photon and electron dose, complete deoxygenation of GO is achieved while preserving film integrity. Core-loss EELS confirms full removal of oxygen functional groups and restoration of the sp$^2$ graphitic network, evidenced by a ${\pi}^*-{\sigma}^*$ energy separation of 7.0 eV, in close agreement with graphite (7.1 eV). Crucially, the cumulative electron dose is identified as an active parameter governing the reduction mechanism: electron beam exposure accounts for approximately 5 at. % of the initial oxygen removal and synergistically lowers the energy barrier for subsequent laser-driven deoxygenation, while excessive electron exposure compromises film integrity through crack formation. The optimal configuration achieves complete deoxygenation at a cumulative photon dose of 2.5 x 10$^3$ mJ/cm$^2$ with superior in-plane crystallographic order and minimal beam-induced thinning. This work establishes a versatile multi-parameter strategy for controlled scalable graphene synthesis via combined electron beam and laser irradiation.