A DFT and Monte Carlo study of lateral interactions in Be layers on W(112)

Results of performed DFT calculations show that Be atoms adsorb in the furrows of the W(112) surface up to the 1.33 ML coverage, thus smoothing the surface. As the coverage increases, the smoothing results in a linear increase of the work function, which is attributed to a geometric effect. It is found that the dominant lateral interaction between Be adatoms on W(112) is the attraction in the direction along the furrows, which precludes the formation of linear atomic chains aligned normal to the furrows, pertinent to other alkaline earth adsorbates on the W(112) and Mo(112) surfaces. The absence of an electrostatic part of the lateral interaction allows for a compression of Be rows up to 14% with respect to the nearest-neighbor distance in Be crystal. The formation of the second Be layer partly restores the surface corrugation and leads to a significant decrease of the work function. For sufficiently high annealing temperatures (~ 700 K), Be adatoms, due to revealed lateral attraction, condensate into islands of a dense structure. This result explains the dramatic dependence of the work function on the annealing temperature, reported in the experiment [E. Chrzanowski and E. Bauer, Surf. Sci. 173 (1986) 106].