Paper SS-TuP19
Coverage and Temperature Dependence of LEED Streak Intensity on Li adsorbed on Cu(001) Surface at Lower Coverage

Tuesday, October 16, 2007, 6:00 pm, Room 4C

Arced shape streaks, which connect four fold spots are observed in LEED experiment, in Li adsorbed system on Cu (001) surface, where the four fold spots correspond to c(2x2) structure of adsorbed Li atoms. The streaks originate from second neighbor pair (d=2a) of Li atoms in the c(2x2) structure sites. Especially, there are two types of adatoms in terms (y-)component of wave number of the streak (k_y = π /a). Both types of the sub-lattices give an anti-phase relation on the streak. If Li atoms are fully occupied on the c(2x2) sites at a coverage 0.5, the intensity is vanished. While, if the coverage is less than 0.5, a deviation of the number of atoms in the two types of sub-lattices gives a certain intensity of the streak; it becomes strongest at coverage 0.25 (H.Mitani et al. J.Phys.Soc.Jpn. 2005). In this paper, using Monte Carlo simulation, we obtain arrangements of Li atoms on adsorption sites on Cu (001) surface, as a lattice gas model, in a range of coverage (0-0.5), and a certain temperature width. By Fourier transforming of the arrangement of the atoms, we obtain almost square type streaks, which correspond to the arced shape steaks in the experiment. The reason of change from the line streaks in the square to the arced one, as shown in the experiment has already been clarified (H.Mitani et al. J.Phys. Cond.Matt. 2006). It is not a matter in the present paper. We also obtain coverage and temperature dependence of an intensity of the streak and also the four fold spots. Especially the coverage dependence of the intensity, reproduces a result of experiment; it increase along the coverage (0-0.25), and decrease in coverage (0.25-0.5). We also obtain the coverage-dependence of the intensity of the four fold spots. In terms of temperature-dependence, there is no result in experiment now. We obtain that the intensity of the streaks, broadly speaking, increases as temperature. Especially at coverage 0.5, it shows as Shottkey type behavior. On the other hand, the intensity of the four fold spots, shows second order transition, which has a certain phase transition point.