Surface-adsorbate-induced fluorescence-type Raman background of Pb(Zr0.4Ti0.6)O3 nanotubes

We report the effects of adsorbates on the Raman spectra of Pb(Zr0.4Ti0.6)O3 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.

► Pb(Zr,Ti)O3 nanotubes with adsorbates were prepared by exposing nanotubes to air for 1 day.
► An abnormally intense and broad Raman background was observed from the Pb(Zr,Ti)O3 with adsorbates. 
► The Raman background could be removed by post-annealing nanotubes at 500 °C, but it readily returns after re-exposure to air.
► The occurrence of the Raman background could be attributed to the presence of hydroxyl groups on the surfaces and the very high ratio of surface area to volume of the nanotubes.