On the mechanism of laser bleaching of aerosol synthesized single walled carbon nanotubes on the polymer substrate

Results of study of continuous 632.8 nm helium-neon laser with semitransparent single-walled carbon nanotubes (SWNTs) films interaction are presented. SWNTs films were produced by aerosol technique based on high-temperature ferrocene vapor decomposition in a gas flow of carbon monoxide. The SWNTs contained capsulated iron nanoparticles. The films were deposited on membrane filters and then transferred to a polymer (polyethylene terephthalate) substrate. It is experimentally shown that the films are irreversibly bleached under the focused 7.5 kW/cm$^2$ laser beam. The bleaching is accompanied with a decrease of the optical density at visible wavelength range. Using Raman spectroscopy it is demonstrated that bleaching of the film occurs without destruction of the carbon nanotubes. It is found out that the radial breathing mode (RBM) (the peaks with Raman shift below 350 cm$^{-1}$, characterizing the SWNTs with different diameters) of bleached film is more pronounced. Some of the RBM peaks of bleached films are shifted to the smaller Raman shifts ($\approx 1$ cm$^{-1}$) in comparison to that of initial film. At the same time G-mode after bleaching is shifted to the higher Raman shifts ($\approx 1$ cm$^{-1}$) in comparison to that before bleaching. The X-ray electron spectroscopy study results showed that decreasing of the film optical density results from the oxidation of the encapsulated in SWNTs iron nanoparticles with the products of polymer substrate decomposition that arise from its heating.
The study results can be applied for increasing the SWNTs films transparency, that are used as electro conductive films with high transparency at the visible spectral region. The results obtained can be also used for laser image recording (see figure).