IR and XPS studies on the surface structure of poled ZnO-TeO2 glasses with second-order nonlinearity

The effect of thermal/electrical poling on the surface structure of 30ZnO . 70TeO(2) glass has been investigated by means of IR reflectance and X-ray photoelectron spectroscopy (XPS), All the poled glasses exhibit a common characteristic that the second-order nonlinearity is induced preferentially in an anode-side surface region. The reflectance from the anode-side glass surface at around 635 cm(-1) assignable to the vibrational mode of the Te-O-ax bond, where ax stands for the axial position of the TeO4 trigonal bipyramid, is smaller in comparison with both as-annealed and cathode-side surfaces. The XPS analysis of the anode-side surface shows a depletion of Zn2+ ions and penetration of Na+ ions from the borosilicate glass which was placed between the sample and the anode during poling, These results suggest that the poling brings about both the breaking of the tellurite glass network and compositional changes at the anode-side surface below which the second-order nonlinearity is preferentially induced.