Surface-adsorbate-induced fluorescence-type Raman background of Pb(Zr _0.4Ti _0.6)O ₃ nanotubes

We report the effects of adsorbates on the Raman spectra of Pb(Zr _0.4Ti _0.6)O ₃ nanotubes (PZT-NTs). PZT-NTs with adsorbates were prepared by exposing PZT-NTs to air for 1 day. We found that the presence of surface adsorbates can cause an intense and broad Raman background that hinders the observation of the Raman vibrational modes of the PZT-NTs. This background can be suppressed by adjusting the Raman excitation wavelength from 514.5 nm to 414.6 nm. It can also be removed by post-annealing the PZT-NTs at 500 °C, but it returns readily after re-exposure to air. X-ray photoelectron and Fourier transform infrared spectroscopies show that hydroxyl and carbonate groups are adsorbed onto the surfaces of the PZT-NTs during exposure to air. Moreover, dispersive Raman spectra reveal that the background is a tail of a very broad band from 1000 to 4000 cm ^-1, which corresponds to hydroxyl groups. These results suggest that the main contribution to the Raman background of the PZT-NTs is that of surface hydroxyl groups rather than carbonate groups.