Mössbauer effect in the oxide surface layer on iron microcrystals and an interpretation of the spectrum

A413 graphite adsorbent and both atom (A-) and bond (B-) models for the graphite sites are included. The first continuum term in the Fourier expanded potential only differs by a constant factor for these two models, and for isotropic and anisotropic graphite polarizabilities. The second (periodic) Fourier term on the other hand behaves quite differently for the two models. As noted by other workers, graphite anisotropy would increase barrier heights to isotropic adsorbates when the total potential is considered. This is also found to be the case for the anisotropic adsorbate molecules considered here. In addition there are substantial differences between barrier functions predicted by the A- and B-models which show strong orientation dependence for non-spherical adsorbates.

Surface Science 146 (1984) 501-510 North-Holland. Amsterdam MOSSBAUER

EFFECT

MICROCRYSTALS lchiro TAMURA

AND

IN

501 THE

OXIDE

SURFACE

AN INTERPRETATION

and Mitsuhiko

LAYER

OF THE

ON

IRON

SPECTRUM

HAYASHI

Physics Department, Toyama Medical and Pharmaceutical Universi(v, Tovama 930-01, Japan Received 16 April 1984; accepted for publication 13 June 1984 Iron microcrystals with a slowly oxidized surface have been studied by the MOssbauer technique. The spectrum of the oxide surface layer is a hyperfine split pattern at low temperatures and changes into a single very broad absorption band at the room temperature. The temperature change of the spectrum can be explained by the model in which an asymmetrical uniaxial anisotropy is assumed for each of the oxide crystallites constituting the surface layer. The anisotropy results from the combination of a symmetrical uniaxial anisotropy of the crystallite and a smaller unidirectional anisotropy due to the interaction with the contiguous metallic core.

Surface Science 146 (1984) 511-526 North-Holland, Amsterdam THIN

FILM

QUANTUM

511

SIZE

EFFECTS

I!. T h e e f f e c t o f d e f e c t s t r u c t u r e at t h e f i l m / s u b s t r a t e B.T. JONKER

* and Robert

interface

L. P A R K

Uni~,ersi(v of Ma(vland, Department of P/0'sics and Astronomy, College ParM Ma(vland 20742, USA Received 20 January 1984: accepted for publication 2 July 1984 We have investigated the effect of atomic impurities and structural defects at the film/substrate interface on the q u a n t u m size oscillations observed in retarding potential measurements of the sample current versus normally incident electron energy for thin epitaxial (111) Cu and Ag films on W{ll0). The q u a n t u m size oscillations are sensitive to the structural order of the film/substrate interface itself and are capable of providing a relative indication of interface structural perfection. The q u a n t u m size effect (QSE) amplitude is significantly reduced for small a m o u n t s of carbon at the C u / W interface, while oxygen on the substrate surface severely inhibits epitaxial growth. Using the W(I10) LEED (00) beam width as an index of substrate surface roughness produced by mild ion bombat:dment prior to film deposition, we find that the QSE amplitude decreases linearly by 70% for monatomic step atom densities ranging from 1% to 3% at the C u / W interface. The QSE measurements further indicate that annealing does not measurably hnprove the structure of the C u / W interface via a reduction in open-volume defect density before islanding of the film occurs.