ADSORPTION OF CHLORINE ON RU(001) AND CODESORPTION WITH LITHIUM

Chlorine adsorption on the clean Ru(001) surface and its codesorption with lithium have been studied. TPD, AES and LEED investigations sugge st that chlorine adsorbs at 400 K via a precursor state and forms a ch emisorbed overlayer. An initial sticking probability of close to unity was derived from the chlorine uptake at different Cl-2 dosages. LEED investigations showed that already at low coverage (theta=0.08), a Cl- (root 3x root 3)R30 degrees structure is formed which saturates at the ta=1/3. If the coverage exceeds 1/3, more complex LEED patterns appear , which are most probably due to a compressed chlorine overlayer. Chlo rine desorbs exclusively as atomic Cl. No ruthenium desorption yield h as been detected in TPD experiments, suggesting that no etching of the substrate took place. The codesorption of chlorine and lithium was st udied after having dosed chlorine and then lithium in small quantities (resulting theta(Cl), theta(Li)less than or equal to 0.4) and various relative abundances. Chlorine and lithium codesorb al temperatures be tween 600 and 800 K, significantly below the temperature where chlorin e or lithium desorb alone from Ru(001). The fragmentation pattern of t he codesorption peak was constant at all coverages. Ion fragments of L iCl monomers and dimers were detected. We conclude that LiCl is formed on the surface, and desorbs in monomeric and multimeric form between 600 and 800 K. (C) 1997 Elsevier Science BV.