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

Abstract

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 H2 (∼ 10−) — 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 H2 leads to the formation of sorbed hydrogen and is accompanied by valence charge transfer from Nd to H. The kinetics of H2 desorption from alloy films and Nd overlayers are markedly different: this feature provides a sensitive test for the overlayer → alloy transformation.