Abstract
The kinetic and thermodynamic properties of adsorption and desorption of Sb onto a Si(111) surface are analyzed by mass spectrometry and ab initio calculations. Two domains of temperature are evidenced. At there is an irreversible adsorption involving a subtle competition between sticking, adsorption, then dissociation of tetramers associated to a partial reflection of molecules on the Sb-covered surface. At , molecules are dissociated close to the surface leading to a simple reversible adsorption/desorption of Sb monomers. In this temperature range, adsorption/desorption isotherms can be recorded for various temperatures, which reveal a surprising behavior since quasi-Langmuir isotherms appear to be the consequence of a two-dimensional (2D) phase transition. More precisely, as shown by ab initio calculations, during the submonolayer adsorption process, the adsorption site evolves (as a function of coverage) from ternary towards on-top position and the character of the Sb-Sb effective interactions changes from repulsive towards attractive. The 2D phase transition close to ML seems to be associated to characteristic signatures in many other experiments. Then for high enough supersaturations, it is possible to overpass ML by the formation of dimers, first partially located on top sites which repel one another, up to a second phase transition around ML in which dimers leave the on top sites and stand up to occupy almost vertically the hollow ones for building the second Sb layer. Lastly surfactant effect is quantified.
3 More- Received 29 August 2007
DOI:https://doi.org/10.1103/PhysRevB.77.085402
©2008 American Physical Society