Reaction of ethylenediamine with ultra-thin titanium oxides on Cu(100) modified by sodium oxide

The interaction of sodium oxide with ultra-thin TiO2 prepared on Cu(1 0 0) surface has been studied by using X-ray photoelectron spectroscopy, X-ray induced Auger electron spectroscopy and low energy electron diffraction. Three types of sodium ions were formed on the surface in succession with increase in the sodium oxide coverage after heating the surface at 623 K in O2 (1 × 10-5 Pa) for 10 min. The sodium oxide located on top of the TiO2 surface up to the coverage of ∼0.6 LE. The subsequent addition of the sodium oxide resulted in the penetration of sodium ions into the TiO2 lattice by breaking the Ti-O-Ti bonds. The extra sodium oxide was then accumulated on the surface to form bulk-like Na2O oxide. The change in the reactivity of the titanium oxide modified with the sodium oxides was investigated by adsorbing ethylenediamine molecule. The penetrated sodium oxide depressed the adsorption of molecular ethylenediamine on the surface at a room temperature. However the adsorption was activated by heating at 523 K to give strongly bonded ethylenediamine while the molecularly adsorbed ethylenediamine was largely desorbed at 523 K on the TiO2 surface not modified with the sodium oxide. The promotion of the ethylenediamine adsorption was discussed by the change of the labile Ti-O(Na) bonds in the sodium oxide-penetrated titanium oxide into the Ti-N bonds during the adsorption of ethylenediamine at the elevated temperature. © 2002 Elsevier Science B.V. All rights reserved.