A48

complications and simplifications in the related techniques of LEED and surface EXAFS. It is concluded that single scattering calculations do provide a realistic basis for structural determina- tions with PhD, but the scattering process has an enhanced degree of localisation which can be attributed to correlated thermal vibrations and elastic scattering damping. Some account of these effects must be included in the calculations to get the best agreement with experiment, but this can be achieved simply and can even lead to shorter computational times. Some comparisons with analysis using Fourier transform methods are made.

Surface Science 166 (1986) 391-402 391 North-Holland, Amsterdam

AN ELECTRON ENERGY LOSS STUDY OF THE EPITAXIAL G R O W T H OF IRON ON Cu(100)

Y.C. LEE, H. MIN and P.A. M O N T A N O

Physics Department, West Virginia Unieersitv, Morgantown, West Virginia 26506-6023, USA

Received 30 July 1985: accepted for publication 17 September 1985

Iron was deposited under ultrahigh vacuum conditions on a clean Cu(100) surface followed by observation of the LEED patterns and EELS measurements. The LEED patterns showed a (1 × 1) structure with iron deposition indicative of epitaxial growth. Considerable changes in electron energy loss structures were observed with iron coverage. For low Fe coverages ( < 2 ML) the electron energy loss peaks of Cu(100) are distinguishable although there may be diminution in intensities and /o r increase in peak widths. For higher Fe coverages, new loss features were observed. They can be associated with the fcc y-Fe film. For a thick layer of Fe on Cu(100), the spectrum is very similar to that observed for bcc a-Fe.

Surface Science 166 (1986) 403-418 403 North-Holland, Amsterdam

SPUTI'ERING OF M U L T I C O M P O N E N T MATERIALS: THE D I F F U S I O N LIMIT

Antonino OLIVA *, Roger KELLY and Giovanni FALCONE *

IBM Thomas J Watson Research Center. Yorktown tteights. New York 10598, USA

Received 23 April 1985; accepted for publication 26 August 1985

Bombardment of systems such as binary alloys normally results in the preferential sputtering of one component combined with a subsurface depletion of the same component. Driving forces for preferential loss include mass differences, chemical binding differences, and Gibhsian or similar segregation. We are here concerned with the simpler profiles which are set up in the absence of segregation. This problem has most commonly been reduced to one of conventional diffusion, governed by relocation and surface recession but not conserving lattice sites. More recently, a ballistic treatment was introduced which in its most complete form allowed for relocation, surface recession, and conservation of lattice sites. We show that the ballistic treatment can be re-ex- pressed in a diffusion limit such that conservation of lattice sites is retained and that. moreover, a closed-form steady-state solution exists. It is further shown that the diffusion limit satisfactorily defines the various diffusion coefficients, the steady-state surface compositions, the sputtering yields, and the overall profile shape.