Silver films grown on a rhenium(0001) surface: a combined TDS, XPS, and Delta Phi study

The energetics and kinetics of Ag thin film growth on Re(0001) were studied by means of temperature-programmed thermal desorption spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS), and work function change (Delta Phi ) measurements. The formation of three individual Ag layers shows up in TDS as three distinct desorption maxima beta(1)-beta(3) appearing between 950 and 1010 K (beta(3)), between 900 and 960 K (beta(2)). and between 870 and 970 K (beta(1)). Except in the very low coverage (Theta) range, in which th e desorption is a first-order process, the Ag desorption follows zero-order kinetics. For the first two layers, activation energy of desorption (E-des *) is strongly Theta dependent: within the first layer, E-des* increases al most linearly with Theta from approximate to 250 kJ mol(-1) at Theta = 0.05 to about 290 kJ mol(-1), reflecting attractive Ag-Ag interactions. From Th eta = 0.5 to 0.9, E-des* rises by only some 10 kJ mol(-1). A similar (but m uch less pronounced) Theta dependence appears for the second monolayer. A d etailed shape analysis of the submonolayer TD spectra reveals a phase equil ibrium between Ag condensed in islands and individual, mobile Ag atoms (2D gas phase). in XPS, the absence of any energy shift of the Ag and Re core l evels underlines the weakness of chemical Ag-Re interactions. Two Ag layers lower the work function of the Re(0001) surface by about 750 meV, with a s hallow minimum near the second monolayer. We discuss our data in conjunctio n with previous STM and LEED results for the same system and compare this s ystem with other Ag-on-metal systems. (C) 1998 Elsevier Science B.V. All ri ghts reserved.