A262

Surface Science 118 (1982) 585-596

North-Holland Publishing Company

585

FACE’ITING, STEPS AND RECONSTRUCTION ON GaAs (001)

L. D;iWERITZ

Zentrulinstitut fiir Elektronenphvsik der Akudemie der Wissenschuften der DDR, Mohrenstrusse

40/41, DDR-1080 Berlin, DDR

Received 18 August 1981; accepted for publication 17 February 1982

Assuming that facets develop on a microscopic scale during MBE growth of macroscopically flat GaAs (001) surfaces, models were made for the different structures found for surfaces prepared

under UHV conditions as reported in the literature. The deduced surface structures are discussed

in connection with data available from experimental work on the composition and structure of the

reconstructed surface.

Surface Science 118 (1982) 597-612

North-Holland Publishing Company

EFFECTIVE SYMMETRY OF A LA’ITICE OF MOLECULES ADSORBED ON A SUBSTRATE LATTICE Henry NICHOLS and Robert M. HEXTER

Department of Chemistry Vnioersify of Mmnesota, Minneapolis, Minnesota, USA

Received 22 December 1981

597

A procedure for determining the group describing the symmetry of the system adsorbate-plus-

substrate, is presented for systems in which both the adsorbate and substrate have two-dimensional

lattices. Site group operations for the combined adsorbate-plus-substrate lattice are shown to be

those operations which may be simultaneously applied to both adsorbate and substrate lattices. In

the low barrier to rotation limit for adsorbed molecules, a new combined lattice is required to

describe the system adsorbate-plus-substrate. The symmetry operations of the factor group

appropriate for adsorbed molecules experiencing low barriers to rotation can be derived from the

point group of the free molecule, the site group in the high barrier to rotation limit, and the factor

group of the combined lattice in the high barrier to rotation limit. Examples are given to illustrate

the procedures.

Surface Science 118 (1982) 613-622 613 North-Holland Publishing Company

SURFACE STATES AT THE METAL-ELECTROLYTE INTERFACE

W. BOECK and D.M. KOLB *

Fritz-Haber-institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-1000 Berlin 33, Fed. Rep. of

Germany

Received 18 December 1981

Normal incidence electroreflectance spectra of Ag and Au single crystal electrodes in aqueous

electrolytes reveal pronounced structural features, which can be assigned to optical transitions

involving empty surface states. The transition energies show a marked dependence on the electrode

potential as predicted by the calculation of Ho, Harmon and Liu. It is demonstrated that

electroreflectance of metal electrodes in the double layer charging region is a sensitive tool for studying metallic surface states.