Phase transitions in adsorbed films of barium on W(011)

Phase transitions in barium submonolayers adsorbed on W(011) are studied in a wide range of temperatures and coverages by the LEED technique, including the temperature measurement of the diffraction intensity. The regions of ordered and disordered structures are determined, the result is presented in the form of phase diagram. The temperature dependence of the adfilm Bragg intensity in the low temperature limit (the lowest temperature is 5 K) shows an appreciable slope for all incoherent and almost all coherent structures, except for (3×2). The fact is discussed in terms of the adfilm long- and quasi-long-range order. The disordering of the (3 × 2) lattice near T_c=130 K is the second-order phase transition with the order parameter critical exponent β=0.16. the adfilm is two-phase in the range n=(3.2?3.8)×10¹⁴cm^?2 and singlehase for the rest of the coverages. The effect of the first-order phase transition on the character of the work function change in the two-phase region is discussed.