Identification and characterization of SWNT IMJs

SEM (Jeol, JSM-7600F) was utilized to reveal the morphology of SWNTs over a large area. SEM images were taken at 1 kV acceleration voltage. AFM (Asylum Research, Cypher AFM) in tapping mode was as well employed to display SWNT morphology in 2D images. The AFM height profile can provide information of the SWNT diameters. Raman images and spectra of SWNTs were collected with a confocal Raman system (Renishaw, inVia Raman microscope) at room temperature, using three laser lines as the excitation source: 633 nm (HeNe, Renishaw, RL633), 514 nm and 488 nm (Ar⁺, Stellar-Ren, Modu laser, LLC). The spectrometer was equipped with a 100× microscope objective (Leica, NA = 0.85) and an X-Y translation stage. Laser beam was focused on the sample through the microscope objective, providing a 1 μm excitation spot size. The laser power on sample (measured by a power meter) was kept below 0.5 mW to avoid the heating effect. Raman imaging and Raman spectra were taken in the backscattering configuration.