NOVELTY - Preparing a graphene nano ribbon involves either depositing graphene sheet on at least one surface of substrate, forming plasma mask with nano pattern on the sheet, and forming nano pattern in the sheet by plasma treating stack structure including plasma mask; or plasma treating a graphene sheet including at least one graphene layer to form a graphene pattern. The method further involves forming a carbon mask on the graphene sheet; thermally treating the graphene pattern and the carbon mask to remove the carbon mask and transform the graphene pattern into carbon nano ribbons.    USE - For preparing graphene nano ribbon, used in transparent electrode and in electronic device (claimed). Also used in various display devices, e.g. field emission display (FED), a liquid crystal display (LCD), and an organic light emitting device (OLED); in various electrical devices, e.g. super-capacitor, nano-device, and an energy device; in various energy devices, e.g. lithium battery, solar cell and fuel cell; and in various nano-devices, e.g. field-effect transistor (FET), and memory device, transparent electrode, hydrogen storage device, an optical fiber, sensor and another electrical device.    ADVANTAGE - The method is performed under normal atmospheric conditions and uses a plasma mask including amorphous carbon (e.g. instead of an expensive resist composition), thus the method is an economical method for preparing graphene nano ribbon.    DETAILED DESCRIPTION - Preparing a graphene nano ribbon involves either depositing graphene sheet on at least one surface of a substrate, forming plasma mask with a nano pattern on the graphene sheet, and forming nano pattern in the graphene sheet by plasma treating a stack structure including the plasma mask; or plasma treating a graphene sheet including at least one graphene layer to form a graphene pattern. The method further involves forming a carbon mask on the graphene sheet; thermally treating the graphene pattern and the carbon mask to remove the carbon mask and transform the graphene pattern into carbon nano ribbons, where forming the carbon mask includes irradiating a carbon layer with laser without the presence of a photoresist, and the carbon layer includes amorphous carbon. The step of forming of the plasma mask includes stacking amorphous carbon on the graphene sheet; and forming a nano pattern in the amorphous carbon by irradiating the amorphous carbon with light. The method further involves removing the plasma mask after forming the nano pattern. The graphene sheet includes 1-10 layers of graphene. The light irradiation of the amorphous carbon includes laser light irradiation.    DESCRIPTION OF DRAWING(S) - The figure shows a flow chart of the method of preparing graphene nano ribbon.