Atomic force microscope

The spectral, morphological, and electrical characteristics of SWNTs before and after being functionalized by MPs were investigated by atomic force microscopy (AFM), Raman, UV-Vis spectrometry, current-voltage (I-V), and field-effect transistor (FET) measurement. AFM images were obtained using an atomic force microscope (Veeco Innova, Santa Barbara, CA, USA). Raman spectra were measured with a Nicolet Almega XR Dispersive microscope with 532-nm laser excitation. The UV spectrum was acquired by a Beckman DU640 UV/Vis spectrophotometer (Beckman Coulter, Inc. USA). Electrical measurements were made using a semiconductor parameter analyzer (Keithley 2636, USA).
For FET measurements, the Si substrate was covered with gold film, which served as the base, and charged with a linear voltage ranging from −60 V to +20 V. The two gold electrodes etched on the SiO₂ surface acted as the drain and source, to which a constant voltage (0.1 V) was applied. A dielectric layer of 100-nm thick SiO₂ was used to separate the base from the source-drain.

Scanning electron microscopy (SEM) images were recorded by an S-4800 field emission scanning electron microscope (Hitachi, Japan). Transmission electron microscopy (TEM) images were obtained on a JEM-1400 transmission electron microscope (JEOL, Japan). Atomic force microscopy (AFM) images were obtained on an atomic force microscope (Veeco, USA). Static water contact angles were measured using an OCA50 system (Dataphysics, Germany). Circular dichroism (CD) spectra were collected on the Chirascan spectropolarimeter. Isothermal titration calorimetry (ITC) was performed using a Nano calorimeter (Waters, TA Instruments, USA). FT-IR spectra were obtained from a Fourier transform infrared spectrometer (Nicolet IS10, Thermo Fisher). Zeta potential was detected on Malvern Zetasizer Nano-ZS90 (ZEN3590, UK). The UV−Vis absorption spectra were recorded on a Thermo Scientific NanoDrop 2000/2000C spectrophotometer. Fluorescence spectra were recorded on a HORIBA Scientific Fluoromax-4 spectrofluorometer.

TEM images and TEM-EDS images were obtained using a JEOL JEM-1010 and JEM-2100F, respectively. AFM images were obtained using a Veeco atomic force microscope. Raman spectroscopy measurements were carried out on a Dongwoo DM500i Raman spectrometer using green (514.5 nm) laser excitation. BET surface area and BJH pore size distributions were measured by using a Micromeritics Tristar 3000. XPS was carried out using a Kratos AXIS-HSi. Elemental analysis was performed using a Thermo Scientific Flash 2000 analyzer at NCIRF (National Center for Inter-university Research Facilities, Seoul National University, Korea).