[[abstract]]We report the degradation effects on optical properties of NaxCoO2 (x = 0.68 and 0.75, thickness 100 nm, 280 nm, and 500 nm) thin films. Our primary techniques are Raman-scattering and ellipsometric spectroscopy. Previous Raman-scattering spectra of NaxCoO2 single crystals (x = 0.68 and 0.75) show two significant Raman-active phonons at about 465 cm-1 and 580 cm-1 [22, 33, 49, 56, 61].Our fresh x = 0.75 thin film with thickness 280 nm and 500 nm exhibit similar results. Interestingly, other fresh NaxCoO2 thin films (x = 0.68, thickness 100 nm, 280 nm, and 500 nm；x = 075, thickness 100 nm) demonstrate additional phonon mode at about 445 cm-1, corresponding to sodium ion’s E2g (Na) vibrations. Notably, this phonon peak gradually diminishes with time in that sensitively gauges the Na ion’s order-disorder effects. Moreover, we observe lots of black dots with dimesion 40 ?m on the surface of fresh x = 0.68 thin film. Raman-scattering spectra indicate dramatic Na ion’s diffusion occurs toward the center area. Finally, optical conductivity obtain from the ellipsometric measurements in both x = 0.68 and 0.75 thin films displays complicated varations with time, suggesting degradation effects also induce changes in the electronic structure of CoO2 layer.
To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.