System 1000

The graphene sheet was functionalized by plasma treatment, employing a 50 kHz radio frequency plasma source at 50 W using a plasma generator (CUTE, Femto Science Co. Ltd., Hwaseong-Si, Korea). The plasma treatment was carried out at 28 °C (gas pressure fixed at 1 × 10⁻² Torr) on the graphene gate channel in an O₂ gas environment to oxidize for 10 s or in a C₃F₈ gas environment to fluorinate for 20 min. The O₂ and C₃F₈ gas flow rates were maintained at 20 and 10 sccm, respectively. Thereafter, the fluorinated graphene gate channel was exposed to air at 28 °C and left to stabilize for 72 h.
A spatially resolved X-ray photoelectron spectroscope (XPS; Thermo Fisher, Waltham, MA, USA) was used for determining the surface composition and bonding state of the functionalized graphene sheets with a monochromatic Al Kα (1486.6 eV) X-ray source. The beam diameter was set to 400 μm, and survey scans using a resolution of 10 scans were performed on the graphene that was transferred onto the SiO₂/Si substrate. The properties of the functionalized graphene were characterized by Raman spectroscopy (Renishaw, system1000, Gloucestershire, UK) using an argon-ion laser at an excitation wavelength of 514 nm and a spot size of 1 μm. All Raman measurements were performed at room temperature.

The microscopy studies were carried out using field emission scanning electron microscopy (FE-SEM) (Tescan MAIA 3 LM) and transmission electron microscopy (TEM) (Jeol JEM-2100), and the crystal structures were analyzed using an X-ray diffractometer (XRD) (SmartLab) with Cu–Kα radiation (λ = 1.5406 Å). Thermogravimetric analysis was performed using an Auto-TGA Q500 instrument (TA Instruments). Raman analysis was performed using System 1000 (Renishaw). The Brunauer–Emmett–Teller (BET) specific surface area and pore size distribution were measured by nitrogen adsorption and desorption experiments at −196 °C using an accelerated surface area and porosity analyzer (ASAP 2420, Micromeritics).