Influence of coadsorbed potassium on the electron-stimulated desorption of F sup + , F sup minus , and F sup * from PF sub 3 on Ru(0001)

The electron-stimulated-desorption ion angular distributions (ESDIAD) of positive ions, negative ions, and metastable species from PF{sub 3} and K coadsorbed on a Ru(0001) surface are measured. In the absence of K, only positive- and negative-ion ESDIAD is observed, showing highly anisotropic, off-normal fluorine-ion emission (F{sup +}, F{sup {minus}}) from PF{sub 3}, which demonstrates that PF bonds are inclined away from the surface normal. In the presence of K, ESDIAD patterns of F{sup +}, F{sup {minus}}, and metastable F{sup *} display only normal emission, suggesting a reorientation or chemical reaction which results in fluorine bonding perpendicular to the surface. Thermal desorption spectrometry, Auger electron spectroscopy, and soft-x-ray photoemission (SXPS) are used to determine the surface chemistry as an aid in intepreting the ESDIAD results. The SXPS data show that in the presence of potassium, PF{sub 3} dissociates, possibly forming KF-like species, which suggests that an alkali-metal-induced chemical reaction is reponsible for the changes observed in ESDIAD. The yields of the various desorbed fluorine species vary strongly with potassium coverage; the results for F{sup {minus}} and F{sup *} are interpreted in terms of a charge-transfer model.