Influence of the scattering potential model on low energy electron diffraction from Cu(001)−c(2 × 2)-Pb

Abstract

A dynamical LEED intensity analysis is reported for Cu(001)-c(2 × 2)-Pb. The adsorbate layer distance from the substrate is determined as 2.29 A, and the topmost interlayer spacing for the substrate is the same as in bulk Cu, in contrast to a contraction for clean Cu(001). This structural result is, within the accuracy reached, insensitive to changes in the assumed scattering potential models. The r-factors suggest a weak preference for an energy-dependent exchange correlation and a moderate one for adding a localized adsorption part inside the muffin-tin spheres. The sensitivity of spectra and r-factors to chal~ges in the assumed isotropic Debye temperature for Pb suggests that vibrational anisotropy should be taken into account in order to improve the accuracy of the analysis. Calculated spin polarization spectra are very sensitive to the exchange approximation, the localized absorption and the Debye temperature. Together with experimental data, they should be useful in particular for determining the vibrational anisotropy.

Leed analysis of a dense lead monolayer on copper (100)

“…A detailed analysis of the influence of the potential model performed for the c(2 x 2) structure showed very little influence on the structural parameters [15] and we expect the same to be the case for the (5fi x fi)R45" superstructure. For clean copper an energy-dependent real part of the inner potential was derived [15] and proved to be in good accordance with comparable measurements [16,17] and theory [18]. The energy dependence of the real part of the inner potential used in the intensity analysis was V,,(E) = -3.9 -57.8( E + 12.0) , 'I* eV where the correction due to the work function of the tungsten cathode is not included.…”

“…This value corresponds well to 0.42 A, which would result for equidistant atoms in antiphase arrangement. The layer spacing amounts to 2.32(5) A, which is equivalent to the 2.29(4) A, obtained for the c(2 x 2) structure [15]. The spacing between the topmost two copper layers is 1.82(3) A, slightly larger than the topmost layer spacing of the contracted clean (100) surface of copper [lO,ll], but comparable to the (100) layer distance in bulk copper (1.807 A) and to the topmost copper spacing which was found underneath the c(2 x 2) lead structure [15].…”

“…During increasing coverage these beams gain a maximum of intensity, followed by a diminution, until a well expressed c(2 X 2) structure is depicted by intense half-order beams. The LEED analysis confirmed that this structure is formed by lead atoms in the fourfold hollow sites at a lead-copper spacing which is about 4% closer than the sum of both metallic radii [10,15]. With further increasing coverage the half-order beams become rapidly diffuse and split into satellites which later on move to the beam positions of the c(5& X fi)R45" superstructure.…”

“…Biberian and Huber preferred the antiphase hollow site model [9], following Huber and Oudar, who had suggested corresponding "high symmetry models" for a number of comparable systems 1231. The top site antiphase model, which is composed of domains of top site c(2 x 2) structure, can be ruled out here, since the hollow sites were confirmed unequivocally for the c(2 X 2) structure [10,15]. Thus the pseudo-hexagonal top site model gains more probability, since it places two of three lead atoms close to the hollow sites, so that in total three of the four models from above had to be considered in the calculations.…”

Surface morphology changes during Pb deposition on Cu(100): evidence for surface alloyed Cu(100)–c(2×2) Pb

“…Previous investigations by low energy electron diffraction (LEED) [1][2][3][4][5][6][7][8][9][10], He atom scattering [11][12][13], scanning tunneling microscopy (STM) [14,15] and Rutherford backscattering [16] have established that Pb grows on CU(1OO) in a prototypical StranskiKrastanov mode with three well-defined ordered structures at submonolayer coverages.…”