Direct discrimination between semiconducting and metallic single-walled carbon nanotubes with high spatial resolution by SEM

Single-walled carbon nanotube (SWCNT) films with a high density exhibit broad functionality and great potential in nanodevices, as SWCNTs can be either metallic or semiconducting in behavior. The films greatly benefit from characterization technologies that can efficiently identify and group SWCNTs based on metallic or semiconducting natures with high spatial resolution. Here, we developed a facile imaging technique using scanning electron microscopy (SEM) to discriminate between semiconducting and metallic SWCNTs based on black and white colors. The average width of the single-SWCNT image was reduced to ~9 nm, ~1/5 of previous imaging results. These achievements were attributed to reduced surface charging on the SiO₂/Si substrate under enhanced accelerating voltages. With this identification technique, a CNT transistor with an on/off ratio of > 10⁵ was fabricated by identifying and etching out the white metallic SWCNTs. This improved SEM imaging technique can be widely applied in evaluating the selective growth and sorting of SWCNTs.