Discrete polarization absorption property of carbon nanotubes studied by using scanning near-field optical microscope

By using scanning near-field optical microscopy (SNOM), we have observed the polarization phenomena of carbon nanotubes (CNTs), which were synthesized by pyrolysis of a metal phthalocyanine method. Using SNOM, an area of about 100 nm in the thin part of the honeycomblike aligned CNT can be investigated, where the CNTs are nearly parallel or cross aligned with only a few layers. Transmission intensity of the light absorption with constant height scan identified the thickness of the nanotube layers. By changing the linear polarization of the incident light, the dependence of transmission versus polarization angle was recorded. The observed different polarization cannot be explained by using the model of optical absorption of continuum medium. We have proposed a model of discrete polarization absorption, which can be used to identify the number of layers of CNTs and their relative orientations. The combination of SNOM technique and our model can be used for optical polarization of carbon nanotubes of discrete medium.