CO-induced destruction of Cu(100)-(2 x 1)Li studied by HREELS

CO adsorption on Cu(100)-(2 x 1)Li was studied by means of LEED, TPD and HR EELS. The (2 x 1) structure is known as a 'missing-row structure', where on e of every two [001] copper atomic rows is replaced by a Li atomic row. Fro m LEED observations, it was found that the (2 x 1) subspots of Cu(100)-(2 x 1)Li were weakened by the post-adsorption of CO at 120 K and disappeared a fter annealing to 200 K. Without CO, the (2 x 1) structure is stable up to 340 K. Vibrational spectra were obtained for these processes by HREELS. Li/ Cu(100) gave a v(Li-Cu) peak at 290 cm(-1) corresponding to the (2 x 1) str ucture. After CO adsorption at 100 K with the coverage of 0.21 ML, a C-O st retching frequency [v(C-O)] appeared at 2045 cm(-1), and v(Cu-CO) appeared at 340 cm(-1). Upon annealing to 200 K, a new peak appeared at 1200 cm(-1) in correlation with the disappearance of the (2 x 1) order. In the case of CO adsorption on Cu(100)-c(2 x 2)Li with Li atoms located at fourfold hollo w sites and without reconstruction of the Cu substrate, the 1200 cm(-1) pea k was found at 100 K. These results suggest that the formation of the speci es with v(C-O) of 1200 cm(-1) induces destruction of the (2 x 1) order. (C) 1999 Elsevier Science B.V. All rights reserved.