1：Experimental Design and Method Selection:

The study involves the use of terahertz spectroscopy to investigate plasmon resonances in graphene with periodic carrier density modulation. The carrier density modulation is achieved by chemical doping from a micro-ribbon array of a self-assembled monolayer (SAM) of organosilane formed between graphene and a SiO2/Si substrate. A global back gate is used to tune the conductivity by shifting the carrier density.

2：Sample Selection and Data Sources:

Homogeneous monolayer graphene grown by chemical vapor deposition was transferred to the patterned substrate. The SAM was patterned in an array of 1.7-μm-wide ribbons spaced by 6.3 μm by photolithography and oxygen plasma etching.

3：7-μm-wide ribbons spaced by 3 μm by photolithography and oxygen plasma etching. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: A polarized Fourier transform infrared (FTIR) spectrometer was used for transmission spectroscopy with the frequency range between 1.3 and 20 THz. The samples were kept in vacuum overnight and then heated at 80 °C for 30 min before every measurement to exclude effects of moisture.

4：3 and 20 THz. The samples were kept in vacuum overnight and then heated at 80 °C for 30 min before every measurement to exclude effects of moisture. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: The two-terminal resistance R of the sample as a function of back gate voltage VG was measured. Extinction spectra for the incident light polarized parallel and perpendicular to the SAM ribbon pattern were obtained.

5：Data Analysis Methods:

The extinction spectra were analyzed using the Drude model and a linear combination of two resonance functions to explain the observed two peaks.