Eco-Friendly Synthesis of Wrinkle-Free Ultra-Flat Multi-Layer Graphene by Femtosecond Laser Irradiation of Graphite under Ambient Conditions

Here, we report a single-step, high-yield technique for producing planar sheets of wrinkle-free multi-layer graphene (MLG) under ambient conditions by ablation of graphite powder dispersed in ethanol using a femtosecond laser. The parameters for the synthesis of MLG have been optimized and established. The number of layers and quality of MLG produced at several laser fluences (39.4 J/cm 2 , 98.72 J/cm 2 , 197.45 J/cm 2 , 296.16 J/cm 2 ) was established based on detailed characterization using field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) with selected area electron diffraction (SAED), atomic force microscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). Wrinkle-free, ultra-flat crystalline MLG sheets with 2-12 layers were produced in each case with an average lateral dimension of ∼1--3 μm. The associated oxy- functional groups were characterized and quantified using FTIR and XPS. The highest percentage of sp 2 C atoms and C/O ratio for MLG was achieved at the lowest laser fluence. The higher the laser fluence higher the defects produced in the MLG sheets. The technique produces zero chemical waste, has a very high yield of ∼ 95%, and is promising for bulk-scale production of MLG.