LEED intensity

Heinz K and Muller K 1982 LEED intensities—experimental progress and new possibilities of... 

In Fig. 9 we show the evolution of the experimental (left panels) and calculated (right panels) LEED intensities during desorption for initial coverages 1/3, 1/2, and 2/3ML but for a smaller heating rate (IKs ) than in Fig. 8(a). Also shown are the corresponding experimental and... 

FIG. 9 (a-c) Experimental LEED intensities for (1 x 3) (solid line) and (1x2) (long-short dashed) structures and corresponding TPD rates (dotted lines) as a function of desorption temperature for approximate initial coverages 1 /3, 1 /2, 2/3 ML. Arbitrary units, (d-f) Theoretical LEED intensities, calculated with Eq. (40), and theoretical TPD rates for these initial coverages. Heating rate 1 K/s. (Reprinted from Ref. 39 with permission from Elsevier Science.)... 

RELATIVISTIC CALCULATIONS OF PHOTOEMISSION-AND LEED-INTENSITIES FOR ORDERED AND DISORDERED ALLOYS APPLICATION TO CusPt and Cu Pta... 

Heinz K, Starke U, Vanhove MA, Somoijai GA. 1992. The angular-dependence of diffuse LEED intensities and its structural information-content. Siuf Sci 261 57 -63. 

A series of LEED intensity studies, together with ion-scattering spectroscopy, established that a missing row structure was the correct model for the (1 x 2) phase,14 with some small subsurface relaxation and reconstruction.10... 

LEED intensities also depend on the lattice vibrations at the surface of the crystal. A high Debye temperature of the surface results in intense LEED spots. In fact, measurement of spot intensities as a function of primary electron energy provides a way to determine the surface Debye temperature [20]. 

Fig. 13. (a) Experimental phase diagram for H adsorbed on Pd(lOO). Crosses denote the points where the LEED intensities have dropped to one-half of their low-temperature values. Dashed curve is a theoretic phase diagram obtained from ° for R, = - 1/2. (b) LEED intensities plotted versus... 

Fig. IS. Phase diagram of the H/Fe(110) system, as detenniiied from LEED intensities. Fuli dots represent experimentally determined data points shaded areas correspond to incommensurate or antiphase domain regions. A possible interpretation for the ordered (2 x 1) and (3 x 1) phases is indicated in Fig. 16, assuming that the adsorption sites form a centered rectangular lattice as shown in Fig. lb. (From Imbihl et...

Fig. 24. Contour plot of the structure factor (the kinematic LEED intensity) of a x y/i monolayer in a triangular lattice gas with nearest-neighbor repulsion, at a temperature k TIi = 0.355 (about 5% above T ) and a chemical potential // = 1.5 (0c = 0.336 at the transition temperature.) Contour increments are in a (common) logarithmic scale separated by 0.1, starting with 3.2 at the outermost contour. Center of the surface Brillouin zon is to the left k, and k the radial and azimuthal components of kH, are in units of nlXla, a being the lattice spacing. Data are based on averages over 2x10 Monte Carlo steps per site. (From Bartelt et...

The top layer of a (111) surface actually has sixfold symmetry, but the rotational symmetry of the top layers together is threefold. Since the near surface region can influence where gases adsorb on the surface and the LEED intensities exhibit threefold rotational symmetry at normal incidence, the (111) surface will be considered to have threefold rotational symmetry. Although most of the adsorption studies have been carried out on fee and bcc crystals, there have been several studies reported on hep crystals. For hep metals the basal or (0001) plane is the surface most frequently studied by LEED investigations and it is the most densely packed plane having threefold rotational symmetry. 

Adsorption in many different adsorption sites simultaneously is expected for overlayers with an incommensurate lattice (cf. Sect. III). This has been confirmed by LEED intensity analyses for the case of an incommensurate overlayer of Xe on Ag(l 11), where both the substrate and the overlayer consist of hexagonally close-packed layers (with unrelated unit cells) parallel to the surface. 

However, given the uncertainty in the experimental determinations and the necessary assumption that the best LEED pattern corresponds to complete occupation of all available sites, the unambiguous assignment of a coverage to the 2 x 2 structure can only be done with a LEED intensity calculation. Order-disorder transitions at elevated temperatures have been reported for the 2 x 2 structures formed on Ru(001) (148) as well as on Rh(l 11) (146). In the latter case this process is irreversible. 

It is quite probable that the patterns that order only at elevated temperatures are due to a mixed layer of oxygen and the metal in question. Ducros and Merrill (134) have suggested that the complex patterns observed on Pt(U0) can be attributed to an epitaxial layer of Pt02 with the (100) plane of the oxide parallel to the Pt(110) surface. Conrad et al. (130) explained the LEED patterns obtained by exposure of Pd( 111) to NO at elevated temperatures by a PdO epitaxial layer with the PdO (100) surface parallel to the substrate. Many of the other patterns observed cannot be explained by simple models and, at the present state of development, LEED intensity calculations are not able to deal with such complicated unit cells so that the... 

Fig. 22. LEED intensity profiles for Pt(110) in a C0/02 mixture showing continuous splitting due to formation of facets. (From Ref. 39.)...

Fig. 26. LEED intensity distributions over a 4 x 7-mm2 Pt(IOO) sample from spots characterizing the CO c2 x 2 structure (left) and the hex structure (right) during kinetic oscillations, illustrating the propagation of waves of structural transformations across the surface. (From Ref. JO.)...

LEED, AES 46 Segregation of S to 6 = 0.3 lowers Ni LEED intensity. No additional spots due to sulfur. Interpreted as random sulfur... 

Fig. 3. Location of adsorbed atomic sulfur on the (110), (100), and (111) planes of Ni determined from LEED intensity measurements. Solid circles represent sulfur atoms open circles, nickel atoms. Dimensions are given in angstroms (Ref. 6) a denotes top view, b side view.

Fig. 5. The adsorption geometry of ethylidyne on Pt(lll) as determined by LEED intensity analysis.

Experimental and theoretical results support the fact that the CO molecules are adsorbed on the densely packed surfaces of Pt, Pd, Rh, and Ir with the C-O axis normal to the surface and with the carbon atom directed to the surface. Experimental evidence is derived from angular resolved UPS, ESDIAD, ion scattering, low-energy electron diffraction (LEED) intensity analysis, and EELS. 

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