Sorption, chemisorption and desorption of hydrogen by neodymium overlayers and Nd/Cu ultra thin alloy films on Cu(100)

Abstract

The various modes of hydrogen uptake exhibited by Nd overlayers and Nd/Cu ultra thin alloy films on Cu(100) have been investigated by LEED, UPS, XPS and thermal desorption measurements. Ultra thin Nd overlayers exhibit very low sticking probabilities for H 2 (~10 −4) — far lower than the values characteristic of thick Nd films. This behaviour is associated with the unusual surface structure adopted by the rare earth when present as a very thin film. Codeposition of Nd and H 2 leads to the formation of sorbed hydrogen and is accompanied by valence charge transfer from Nd to H. The kinetics of H 2 desorption from alloy films and Nd overlayers are markedly different: this feature provides a sensitive test for the overlayer → alloy transformation.