A436

Surface Science 101 (1980) 173-179 @ North-Holland Publishing Company

THE METAL-ELECTROLYTE BOUNDARY STUDIED WITH IN SITU PHOTOEMISSION

D.E. GRIDER and T.E. FURTAK Ames Laboratory-USDOE and Department of Physics, Iowa State University, Ames, Iowa S&II 1, USA

Received 18 October 1979

The boundary between copper (111) and OSM HzS04 was investigated using interfacial

photoemission spectroscopy. Exploiting knowledge of electron momentum restrictions a feature

in the ratio of p-polarized to s-polarized photoelectron yield was correlated with the onset of

transitions to Bloch-like final states within the metal at 4.1 eV. This provided some energy

specification in the electron energy integrated yield data. We have used our understanding of

this process to monitor the quality of the interface using both clean and adsorbate (thiourea,

Br-) covered Cu surfaces. The major effect of adsorption is attributed to a loss of conservation of electron momentum parallel to the surface during the emission process.

Surface Science 101 (1980) 180-188

0 North-Holland Publishing Company

SURFACE BARRIER HEIGHTS AND CHANGES INDUCED BY FERROCENE GROUP ADDITION ON Ge AND Si SURFACES CLEAVED IN ELECTROLYTES S. HINCKLEY and D. HANEMAN School of Physics, The University of New South Wales, P.O. Box 1, Kensington, Australia 2033

Received 15 October 1979; accepted for publication 28 December 1979

Ge and Si single crystals were cleaved inside electrolytes of ferrocene in tetrabutyl

ammonium perchlorate and ethanol, and the stable surface barrier heights measured from

photocurrent-potential plots. When hydroxymethylferrocene (HMF) was added, the Ge barrier

height reduced from 0.19 to O.l4eV, but Si was unchanged at 0.68 eV. The results are

interpreted as due to inability of HMF to dislodge ferrocene from the Si surfaces, but ability to

replace it on Ge surfaces; the packing density of the molecules is concluded to be lower than for

ferrocene.

Surface Science 101 (1980) 189-193

@ North-Holland Publishing Company

APPLICATION OF THE GENERALIZED MEAN SPHERICAL APPROXIMATION TO THE ELECTRIC DOUBLE LAYER

Douglas HENDERSON IBM Research Laboratory, San Jose, California 9-5193, USA

and

A437

Lesser BLUM * Department of Physics, University of Puerto Rico, Rio Piedras, Puerto Rico 00931

Received 27 September 1979

Analytic expressions can be obtained for the density and charge profiles from a pair of

integral equations which include the effects, missing in the Poisson-Boltzmann approximation,

of ionic cores. If the parameters in the expressions are adjusted to agree with theoretical

conditions on the profiles and their derivatives at contact, results, comparable to those of more

elaborate approximations, are obtained.

Surface Science 101 (1980) 194-204

@ North-Holland Publishing Company

ELLIPSO-REFLECTOMETRY AT NICKEL IN SULPHURIC ACID SOLUTIONS

K.E. HEUSLER and T. OHTSUKA l

Abteilung Korrosion, Technische Univcrsiriif Clausthal. D-.73% Clausthal-Zelletfeld,, Federal Republic of Germany

Received 27 September 1979; accepted for publication 14 December 1979

A method was established to derive the optical properties of a substrate and of a thin film

on its surface by measuring the intensities at three directions of polarization after reflection of

incident monochromatic. linearly1 polarized light and at different angles of incidence. Results

concerning the optical properties, of the film were compared to those obtained from a second

method in which the reflectivity; changes at different angles of incidence with incident light

polarized in parallel and perpendicular to the plane of incidence were measured. Measurements

were performed with nickel in acjd sulphate solutions at different pH values. At A = 500 nm. the

optical constants of nickel were determined and the dependences of optical constants and

thicknesses for steady state films evaluated as functions of electrode potential and pH value.

The state of oxidation increases continuously as the potential becomes more positive. The state

of hydration grows as the potential becomes more positive and the pH value becomes larger. At

negative potentials. the kinetics of activation is characterized by a fast reduction and hydration

of the non-stoichiometric oxide formed at positive potentials, followed by a slow potential-

independent dissolution of the resulting nickel(U) hydroxide. The spectrum of the optical

constants in the region 1.4 G hv G 4.8 eV for a steady-state film is characteristic of a partly hydrated semiconducting nickel oxide. Optical properties of the film derived from the first

method are independent of the angle of incidence within the experimental accuracy. There is a

small systematic difference between the mean values from the first method and the values from

the second method. The systematic difference is close to the mean scatter of the measurements

at different angles of incidence using the first method. Thus. there is no indication of an optical anisotropy of the film.