Reliability of low-energy electron diffraction for studies of surface order-disorder phenomena

It is shown that a determination of critical exponents in surface phase transformations based on a kinematic analysis of LEED peak intensities is subject to errors caused by multiple scattering that are large enough to prevent a clear assignment to a known universality class. The multiple-scattering contribution arises from short-range flucutations and has its maximum value at the transition temperature. The specific-heat exponent of the surface phase can be measured directly from the variation of the integral-order-beam intensity with temperature that is caused by the multiple scattering

Interaction of oxygen with submonolayer beryllium films on Mo(1 1 2)

Interaction of oxygen with the Mo(1 1 2) surface precovered by submonolayer beryllium films with various coverage degrees (θBe < 1) has been investigated by Auger electron spectroscopy, LEED and contact potential difference techniques. We have studied the effect of Be coverage degree on the oxygen adsorption kinetics, atomic structure and electronic properties of the O/Be/Mo(1 1 2) system. Contrary to the case of full-monolayer Be precoverage (θBe = 1), beryllium submonolayers can speed up the initial adsorption kinetics of oxygen by a factor of 10. The high sticking coefficient of oxygen on the Be/Mo(1 1 2) surface at θBe < 1 can be explained by the existence of areas on Mo(1 1 2) that are free of Be and provide fast oxygen adsorption, with O adatoms migrating further to the areas covered with Be (the spillover effect). The creation of beryllium oxide even on limited surface areas substantially decreases the oxygen sticking coefficient. This effect may originate from the surface deformation due to a structural misfit between the Be/O layer and the substrate. The coadsorbed Be/O layers with θBe < 1 modify the work function to values between those specific of the O/Be/Mo(1 1 2) systems with θBe = 0 and 1, which complies with the heterogeneous adlayer model

A vitrifying structure transition in the Dy/Mo(112) adsorption system

Annealing-driven irreversible structural transitions are studied by low-energy electron diffraction in submonolayer Dy films adsorbed on the Mo(112) surface. In a wide coverage range θ>0.07, Dy overlayers deposited at low temperatures (T≈100 K) are ordered and keep their structure upon annealing up to 350–600 K. Near θ=0.68, the overlayers are stable to high-temperature annealing (Ta=1000 K) as well, whereas the denser films are metastable and transform to more stable ordered structures. An unusual annealing effect is found for θ<0.58: the initially ordered metastable phases are replaced by phases having no extended order, which are assumed to be two-dimensional glasses. © 2001 American Institute of Physics

Irreversible structure transitions in Gd monolayers on Mo(112)

68.43.Fg Adsorbate structure, 68.35.Rh Phase transitions and critical phenomena,

Orientational phase transitions in a lithium overlayer on Mo(112)

We study the unusual behavior of the incommensurate lattice formed by Li on the anisotropic trough-like surface of Mo(112). Starting at a coverage of 0.66, we found a continuous transformation of a rectangular into an oblique unit cell. This oblique cell transforms back into a rectangular cell at coverages higher than 0.85. Both transitions are explained by an instability in the shear modulus of the layers at the respective critical coverages. It leads to the development of smectic-like fluctuations and finally to a melting transition. For the oblique phase below melting, long-range correlations along the troughs, but correlations over less than 10 lattice constants normal to the troughs are observed in experiment. The experimental results are in reasonable agreement with the theoretical model proposed