Temperature dependent interactions of C2N2 with Ni(110):: high resolution electron spectroscopy

We present a comprehensive study of the interactions of C2N2 with Ni(110) over the temperature range 90-800 K with high resolution X-ray photon spectroscopy, using synchrotron radiation, and high resolution electron energy loss spectroscopy. At room temperature C2N2 dissociates to give a c(2 x 2)-CN structure, which at low coverages consists of a single in-groove CN species. At high coverages a second CN species is observed, the proportion of which increases upon heating. Additional CN species can be formed by heating a multilayer - formed by dosing at 90 K - to room temperature, where a disordered monolayer results. At least four different adsorption species are indicated for these extra, on-ridge, CN species, which undergo thermal decomposition at ca 450 K. By contrast the in-groove CN is stable to ca 650 K, after which the C dissolves into the bulk, with the N desorbing at 800 K. C2N2 undergoes partial dissociation at 90 K, with some competition between C2N2 and CN for the in-groove sites. Different multilayer growth modes are indicated for C2N2 adsorption on clean Ni(110) and the saturated c(2 x 2)-CN at 90 K. The C2N2 monolayer, produced by warming a multilayer to ca 120 K, is shown to be a combination of in-groove CN and a tilted across-groove C2N2 species. It is this latter species which dissociates to give the multiple disordered CN species at room temperature. (C) 1998 Elsevier Science B.V. All rights reserved.