Subsurface miscibility of metal overlayers with V, Nb and Ta substrates

[摘要] The high solubility and diffusivity of oxygen in Nb, Ta and V are responsible for the difficulty in the preparation of a clean, well-ordered (100) surfaces of these early transition metals. The deposition and subsequent annealing of a metal overlayer on Nb(100) are a convenient route for the preparation of flat surfaces with the Nb lattice constant and a metallic character. Such well-ordered, stable, inert and easily reproducible Nb(100)-like surfaces can be produced due to the suppression of oxygen surface segregation by a suitable layer blocking sub-surface oxygen diffusion. For example, a Nb(100)-like surface can be obtained by annealing thin Au or Pd films deposited on Nb(100), since this results in a Au-Nb or Pd-Nb alloy situated just below the surface which preserves the structure of the Nb-lattice and effectively suppresses the oxygen segregation toward the surface. In contrast, Ag and Cu layers do not show this property as these metals do not form a bulk alloy with Nb. The presence or absence of bulk alloying and its relation to surface oxygen contamination is a general phenomena observed for many metallic layers deposited on V, Nb and Ta substrates. A discussion of results reported in the literature is given for these adsorbate systems. (c) 2005 Elsevier B.V. All rights reserved.

[发布日期] 2005-04-10

[关键词] subsurface alloying;surface contamination;epitaxial growth