Nanostructured surfaces

Incoherent structures in lithium submonolayer films on tungsten and molybdenum (112) faces
Zayika S.O.1, Loburets A.T.1, Fedorus A.G.2
1Yuri Kondratyuk Poltava Polytechnic National University.
Pershotravnevyj Ave, 24, Poltava-36004, Ukraine. 
E-mail: zaikasvetlana@gmail.com
2 Institute of Physics of the NAS of Ukraine. 
Prospect Nauki, 46, Kyiv-03039, Ukraine. 

In two-dimensional submonolayer metal-on-metal adsorbed films, different structures can form even at low coverages. This is possible because of values of electronegativities of adatoms and adsorbent will be significantly different [1]. Initially, a structure of the films is consistent with a periodic potential of the surface. As the coverage degree θ increases, such a consistency begins to be lost. Reasons are a lateral interaction of adatoms and their size. A vivid example of such films is lithium adsorbed on anisotropic grooved (112) faces of tungsten and molybdenum [2]. Maximum coverage, at which the structures remain consistent with the substrate, is half of the monolayer with a structure p(1×2). Applying a mathematical model of surface diffusion created by us in a homogeneous film, we found that a formation of a coherent structure p(1 × 2) leads to a very sharp decrease of a diffusion coefficient if there are no defects in such a film. The film becomes incoherent in the range of coverages 0.5 < θ < 1. Rectangular at θ = 0.5 elementary cell becomes oblique-angled one due to a displacement of rows of adatoms. This is accompanied by loss of a distant order, i.e. a hexatic phase is formed. In real systems, a similar phenomenon was observed by authors [3] in a range of coverages 0.66 < θ < 0.85 by measuring the intensity of LEED profiles. In contrast to modern research, a transformation of the structure in the two-dimensional crystalline phase was studied. 

1.	Naumovets A.G. Two-dimensional phase transitions in alkali-metal adlayers // The Chemical Physics of Solid Surfaces. – 1994. – 7. – P. 163-213.
2.	Gupalo M.S., Medvedev V.K., Palyukh B.M., and Smereka T.P. Adsorption of lithium on the (112) face of molybdenum crystal // Sov. Phys. Sol. State. – 1979. – 21. – P. 568-573.
3.	Fedorus А.G., Lyuksyutov I. F., Kolthoff D., Koval V., Naumovets A. G., and Pfnur H. Еurophysics letters // Europhys. Lett. – 1999. – 48 (4). – P. 442-448.