Adsorption of thiophene and pyridine on W(1 1 0)

Abstract

The adsorption of thiophene and pyridine on W(1 1 0) at 90 K has been studied with thermal desorption spectroscopy (TDS), Kelvin probe work function measurements, and X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS). Saturation exposure of the tungsten surface to thiophene causes its work function to decrease by 1.18 eV. XPS, UPS and work function measurements indicate that a significant fraction of the adsorbed thiophene is chemisorbed molecularly at 90 K, but this decomposes upon warming from 90 to 200 K. TDS demonstrates multilayer desorption below 180 K and molecular hydrogen desorption from 220 to 650 K. In the case of pyridine, saturation dosing of W(1 1 0) leads to a work function decrease of 1.90 eV. Physisorbed pyridine desorbs at temperatures less than 190 K, and the chemisorbed layer dissociatively desorbs as molecular hydrogen, peaked at 380 K. The UPS spectrum of monolayer pyridine is similar to that of the multilayer, indicating intact (molecular) adsorption at 90 K which does not decompose until temperatures greater than 190 K. C 1s peak area analysis for monolayer pyridine yields a coverage of (4.5 ± 0.5) × 10 14 molecules/cm 2. This high coverage is consistent with adsorption of pyridine with the plane of its ring tilted, presumably bonding to the surface via its nitrogen lone pair electrons.