LEED crystallographic studies for the chemisorption of oxygen on the (100) surface of copper

1988 ◽  
Vol 66 (8) ◽  
pp. 2054-2062 ◽  
Author(s):  
H. C. Zeng ◽  
R. A. McFarlane ◽  
R. N. S. Sodhi ◽  
K. A. R. Mitchell
Keyword(s):  
Antiphase Domain ◽  
Structural Features ◽  
Copper Surface ◽  
Surface Structures ◽  
Photoelectron Diffraction ◽  
Low Energy Electron Diffraction ◽  
Domain Boundaries ◽  
Low Energy Electron ◽  
Structural Analogy ◽  
O Phase

Intensity analyses with low-energy electron diffraction (LEED) are reported for surface structures obtained by adsorbing submonolayer amounts of oxygen on the (100) surface of copper. It is found for chemisorption on the four-coordinate hollow sites that the correspondence between experimental and calculated intensity-versus-energy curves, for 10 diffracted beams, is slightly better for coplanar adsorption than for adsorption about 0.75 Å above the surface (the latter model is essentially as proposed previously by both SEXAFS and photoelectron diffraction). Nevertheless, in neither of these contrasting situations is the agreement sufficient to conclude that the structural analysis is complete. Evidence is presented that nearly coplanar chemisorption, in combination with a missing row model, can accommodate a number of structural features for this system, including the existence of the (2√2 × √2)45°−O phase, beam splittings resulting from antiphase domain boundaries, and the structural analogy noted in other studies between the (2√2 × √2)45°−O phase and the stepped nature of the (410) copper surface which can form by faceting in oxygen. Considerations of O–Cu surface bond lengths, guided by those in bulk Cu2O, suggest that additional lateral relaxations are likely in the topmost copper layer. This study provides no support for the O chemisorption occurring in tetrahedral-type sites.

Growth of Epitaxial Co Layers on Sb-Passivated GaAs(110) Substrates

1998 ◽  
Vol 05 (01) ◽  
pp. 279-283 ◽  
Author(s):  
C. M. Teodorescu ◽  
J. Chrost ◽  
H. Ascolani ◽  
J. Avila ◽  
F. Soria ◽  
...  
Keyword(s):  
Polar Angle ◽  
Low Energy ◽  
Photoelectron Diffraction ◽  
Low Energy Electron Diffraction ◽  
Low Energy Electron ◽  
A Minor ◽  
Bcc Phase ◽  
Crystallographic Axes

The role of Sb in the formation of the Co/GaAs(110) interfaces has been investigated by angular photoelectron diffraction (PD), synchrotron-radiation (SR) core-level photoemission and low-energy electron diffraction. We find that Co forms a metastable bcc phase on GaAs(110), with its principal crystallographic axes parallel to the substrate. From polar-angle-scanned PD, we determine an outward expansion of up to 14% of the lattice constant perpendicular to the surface, for epitaxial Co films grown on nontreated substrates. By Sb passivation of the GaAs(110) surface prior to the Co deposition, the epitaxial quality of the metallic overlayer is improved. The resulting Co phase is found to grow in a perfect bcc (110) orientation with a minor disruption of the substrate underneath and a reduced intralayer spacing outward expansion of less than 1%.

THE CASE FOR ORDER-N METHODS IN LEED THEORY

1997 ◽  
Vol 04 (05) ◽  
pp. 901-905
Author(s):  
J. B. PENDRY
Keyword(s):  
Electron Diffraction ◽  
Point Source ◽  
Surface Structure ◽  
Time Evolution ◽  
Low Energy ◽  
Surface Structures ◽  
New Approach ◽  
Low Energy Electron Diffraction ◽  
Low Energy Electron ◽  
Moderate Complexity

Low energy electron diffraction experiments have superb sensitivity to surface structure, but rely on sophisticated theory for their interpretation. Advances in computer power, and developments in the theory itself, enable us to handle surface structures of moderate complexity. For future advances we must look to a completely new approach and the case is made for order-N methods which follow the time evolution of a point source of electrons to generate all beams for all angles of incidence and all energies in one shot.

scholarly journals SURFACE STRUCTURES OF α-Fe2O3(0001) PHASES DETERMINED BY LEED CRYSTALLOGRAPHY

2001 ◽  
Vol 08 (06) ◽  
pp. 661-683 ◽  
Author(s):  
GUIDO KETTELER ◽  
WERNER WEISS ◽  
WOLFGANG RANKE
Keyword(s):  
Scanning Tunneling Spectroscopy ◽  
Surface Structures ◽  
Scanning Tunneling ◽  
Ion Scattering ◽  
Low Energy Electron Diffraction ◽  
Partial Pressures ◽  
Ion Scattering Spectroscopy ◽  
Oxide Substrate ◽  
Low Energy Electron ◽  
R Factors

We present a dynamical tensor low energy electron diffraction (LEED) study of α- Fe 2 O 3(0001) surface structures that form in an oxygen pressure range from 10-5 to 1 mbar. Epitaxial α- Fe 2 O 3(0001) films were prepared on Pt(111) in defined oxygen partial pressures at temperatures of around 1100 K. In 1 mbar O 2 strongly relaxed oxygen-terminated surface structures are formed, while in 10-5 mbar O 2 three different surface structures yield rather good Pendry R factors. Further experimental evidence from scanning tunneling spectroscopy (STM) and ion scattering spectroscopy (ISS), in combination with a critical review of the literature, is only consistent with a hydroxyl termination forming in 10-5 mbar O 2. The stabilization of both structures is discussed on the basis of electrostatic arguments considering the boundary conditions at the oxide–gas as well as the oxide–substrate interface (autocompensation). For oxygen pressures between 10-4 and 10-1 mbar O 2, the two domains coexist as analyzed using a new, modified version of the symmetrized automated tensor LEED program package. The system investigated in this study turns out to be very complex and the LEED analysis alone is not capable of identifying the involved surface structures unambiguously. Only in combination with results from other surface-sensitive methods was it possible to deduce models for the most likely surface structures.

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