THE SEQUENTIAL ADSORPTION OF NOBLE-METAL AND ALKALI-METAL LAYERS ON RU(001) - A COMBINED MQS AND TDS STUDY

The deposition of Ag or Cu layers on K or Li monolayers on Ru(001) was studied to investigate the effect of underlying alkali layers on noble metal properties. The surface electronic structure was probed using metastable quenching spectroscopy (MQS). CO was also used as a chemical probe of the surface properties, using MQS and thermal desorption spectroscopy (TDS). It was found that large amounts (approximately 8 ML, referenced to clean Ru) of Ag or Cu are needed to cover a K monolayer at 88 K, showing that K is displaced from Ru and rapidly diffuses into the noble metal during deposition. Li behaves quite differently; 1 ML of Ag on 1 ML Li/Ru is found to nearly eliminate the Li MQ peak at 88 K. Annealing Ag-covered Li and K monolayers on Ru causes diffusion of the alkali metal atoms to the Ag surface. For coadsorbed K and Cu monolayers on Ru, MQS detects no significant difference in the electronic structure of surfaces prepared by dosing K on Cu versus Cu on K. However, a substantial difference between these surfaces is observed with both MQS and TDS by using CO as a surface probe. Four different K-CO codesorption states as well as a low-temperature CO desorption feature are observed from the Cu/Ru system.