TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The method comprises: (a) taking a copper foil, which is high-purity oxygen-free copper foil of purity 99.999% as a substrate, processing the surface of the copper substrate by mechanical polishing and electrochemical polishing until the surface roughness is less than 5 nm; (b) ultrasonically cleaning the copper foil for 10 minutes with acetone, ultrasonically cleaning with 25% of hydrochloric acid for 10 minutes, and washing the copper foil with deionized water; (c) increasing the temperature of the cleaned substrate to 1035 degrees C in the presence of argon and hydrogen gas atmosphere, where the flow ratio of argon to hydrogen is 3:1, annealing at 900-1000 degrees C for 30-90 minutes to grow copper crystal particles without fault on the surface, and releasing surface stress of the copper substrate, where the pressure of the mixed gas of argon and hydrogen is 400-1000 Pa and the purity is about 99.999%; (d) decreasing the temperature of argon and hydrogen to 400-700 degrees C for 20-40 minutes, independently heating the polystyrene solid carbon source at 180-280 degrees C, maintaining the temperature for 20- 40 minutes, reacting polystyrene solid carbon source (10-150 mg) with substrate to grow large area graphene with controllable number of layers on the substrate, stopping the heating process and decreasing the temperature to room temperature, where the pressure of mixed gas of hydrogen and argon is 400-1000 Pa, and purity is about 99.999%; (e) spinning a layer of poly(methyl methacrylate) (PMMA)/anisole solvent on the surface of graphene/copper foil, where the ratio of PMMA/anisole is 1:9, drying for 5 minutes in a vacuum drying chamber at 150 degrees C, and removing liquid organic solvent; (f) rusting the copper foil in ammonium sulfate solution (0.1 mol/l) to remove copper, reacting for 5 hours, washing with deionized water for 3-5 times, and removing copper ion in the solution; and (g) transferring PMMA/ graphene onto the target substrate after removing copper foil, soaking in acetone for 3 hours to dissolve and remove PMMA, slowly removing residual acetone by alcohol, and annealing to process residual PMMA of the substrate/graphene. The step (a) is performed for 15 minutes at 800 revolutions/minute, mixing 85% phosphoric acid solution and polyethylene glycol in a volume ratio of 3:1, taking mixed solution as an electrochemical polishing liquid, performing electrochemical polishing for 1800 seconds under the voltage of 1-2 V. The electrochemical polishing adopts electrochemical working station as a power supply and utilizes silver/silver chloride as a reference electrode, placing the copper sheet to be polished on the positive electrode, and copper sheet is used as a negative electrode. PMMA is coated by a coating machine for 45 minutes at 3000 rpm until the thickness is 200-400 nm in the step (e). The annealing process in the step (g) is performed at 300-450 degrees C for 40-90 minutes by hydrogen and argon flows of 100 and 300 standard cubic centimeter per minute (sccm).