XPS studies of pulsed laser induced surface modification of vanadium phosphate glass samples

Vanadium phosphate glass with the nominal chemical composition [(V ₂O ₅) _0.5(P ₂O ₅) _0.5] was irradiated using three different wavelengths (IR, Visible and UV) generated from Nd:YAG laser. The effect of this laser irradiation on the local glass structure as well as on the valence state of V ions was investigated by X-ray photoelectron spectroscopy (XPS). The core level spectra V 2p, O 1s, P 2p and C 1s have been recorded under the same conditions and analyzed. A decrease in the intensity of the V 2p core level peaks was observed indicating a gradual loss of V ions from the surface of the sample with a change of the laser wavelength from UV(355 nm) to IR(1064 nm) region. The O 1s and P 2p core level peaks also showed a significant decrease in intensity for the sample irradiated with 1064 nm laser. Asymmetries found in the O 1s, P 2p, and V 2p core level spectra indicate the presence of primarily P-O-P, P-O-V and V-O-V structural bonds, a spin-orbit splitting of P 2p core level, and more than one valence state of V ions being present. The curve fitting of the V 2p spectra for the unirradiated sample showed that vanadium ions are in V ³, V ⁴ and V ⁵ states while for the irradiated glass samples vanadium ions are mainly in the V ³ and V ⁴ states. The O 1s spectra were all curved fitted with two contributions, one from the presence of oxygen atoms in the P-O-P, P-O-V, V-OV environment (bridging oxygen BO) and the other from oxygen atoms in PO environment (non-bridging oxygen NBO). The ratio of NBO to total oxygen was found to decrease with an increase in incident laser energy.