Adsorption of H 2, N 2, NH 3 and PF 3 on ultra-thin Fe films on W(100)

Abstract

The morphologies of ultra-thin Fe films (0.1 to 10 monolayer) on W(100) and the chemisorption properties of H 2, N 2, NH 3 and PF 3on these films have been investigated by Auger electron spectroscopy (AES), temperature programmed desorption (TPD) and low energy electron diffraction (LEED). For ⩽ 1 ML coverage dosed at T < 200 K, Fe forms an epitaxial overlayer on W(100) and annealing to 1100 K does not change the AES, LEED and chemisorption properties. Above 1 ML, Fe grows layer-by-layer at 200 K. However, annealing to 1100 K results in the formation of three-dimensional Fe islands over the first monolayer and alters the AES, LEED, and chemisorption properties. Generally, the overlayers with ⩽ 2 ML Fe coverage do not behave like a superposition of pure Fe and W but have unique properties. On monolayer Fe films there is an increase in both the adsorption bond strength and the sticking probability of N 2 compared to bulk Fe. For H 2, there is a high temperature TPD state attributed to absorption of H at the metal-metal interface between Fe and W.