Adsorption of fluorine on Pt(100)

Abstract

The adsorption of elemental fluorine on a Pt(100)-(5 × 20) surface has been studied by thermal desorption mass spectrometry, LEED and work function measurements. Fluorine atoms are adsorbed with high efficiency via a precursor state. At monolayer coverage on heating a (1 × 1)F structure is formed which is interpreted to consist of fluorine atoms adsorbed on a (1 × 1) substrate. In this stage the work function is increased by Δφ = 0.5 eV. Thermal desorption yields fluorine atoms which are desorbed in a narrow peak with the peak maximum shifting to higher temperatures (925–950 K) as the initial coverage increases. The typical features of the desorption traces seem to be effected by the transformation of the (1 × 1) into the reconstructed (5 × 20) substrate structure occuring during desorption. The low coverage desorption energy is estimated to be 54 kcal mol −1. At high coverage a broad unresolved additional fluorine atom peak emerges at the leading edge of the main peak. Fluorine exposures beyond saturation of the chemisorption layer produce a surface fluoride which is desorbed as PtF 4 in a very sharp peak at 740 K.