A8

B. SUNDQVIST, P. HkANSSON, A. HEDIN, M. SALEHPOUR and G. SAVE

Tandem Accelerator L.uboratoryy. Box 533, S-751 21, Sweden

Received 4 March 1986; accepted for publication 11 August 1986

It is shown that deviations of the dependence of sputtering yield on the incident angle, 0, from

the standard (cos 0))’ dependence can be indicative of a depth dependence in the net energy

deposition in the surface region. Information about the sputter ejection mechanism is shown to be

obtained only secondarily. We give expressions that allow one to relate the measured dependence

of the yields on angle of incidence to the dependence of energy deposition on depth. This is used

to analyze results for condensed gas sputtering and heavy ion desorption of organic molecular

ions. This analysis indicates that the spatial distribution of excitations produced by the secondary

electrons is important in determining these yields. This is also confirmed by observed differences

in the yields for transmission and back-sputtering which is a closely related effect.

Surface Science 179 (1987) 199-208

North-Holland, Amsterdam

199

SHADOWING AND FOCUSING EFFECTS IN THE ANGULAR DISTRIBUTIONS OF LOW-ENERGY RARE-GAS IONS SCAITERED FROM SOLID SURFACES

R. SOUDA, M. AONO *, C. OSHIMA, S. OTANI and Y. ISHIZAWA

Natlonul Instrtute for Research m Inorganic Materrals, I-1 Namikl, Sakura, Nlihan, Ibarakl 305,

Japan

Received 4 July 1986; accepted for publication 1 August 1986

Low-energy rare-gas ion scattering spectroscopy (ISS) has been improved by the use of neutral

beams as projectiles, which we call neutral beam incident ion scattering spectroscopy (NBISS).

Features of the two techniques (NBISS and ISS) have been discussed on the basis of electron

exchange between projectiles and solid surfaces. The shadowing and focusing effects are clearly

observed in the NBISS results, while these effects are sometimes suppressed in the ISS results. It is

found that the occurrence of the ionization of neutralized rare-gas atoms is necessary for the

appearance of these effects. On the basis of such inspections, the guidelines for applying NBISS

and ISS to surface structure analysis are given.

Surface Science 179 (1987) 209-218

North-Holland, Amsterdam 209

SURFACE STRUCTURAL TRANSITIONS DURING TIN SEGREGATION TO THE SURFACE OF A (100) IRON CRYSTAL

Y.X. ZHOU, R. HSIAO, C.J. McMAHON, Jr.

Department of Materials Science and Engineering, University of Pennsylvania,

Philadelphra, PA 19104, USA

and

A9

E.W. PLUMMER

Department of Physics, University of Pennsylvania, Philadelphia, PA 19104, USA

Received 27 May 1986; accepted for publication 11 August 1986

A study of the segregation of Sn to the (100) surface of an Fe-l.25 at’% Sn crystal has been carried out by means of AES, LEED, and UPS using synchrotron radiation. The room tempera-

ture LEED patterns transformed gradually with increasing Sn coverage from p(1 X 1) for the clean

surface to c(2 x 2) at a half-monolayer, then to p(1 X 1) at one monolayer, and finally to p(2 X 2) at

the maximum observed coverage of 1.2 monolayers. The latter was the ultimate, presumably

equilibrium, coverage achieved at 500°C; above that temperature the equilibrium coverage

decreased linearly up to 650°C above which evaporation occurred. The final LEED pattern

transition was accompanied by a rapid increase in the Sn4d binding energy toward the value

associated with pure Sn and also a broadening of the Sn4d 5,2 peak. At the ultimate maximum

coverage of 1.2 monolayers the LEED pattern transformed gradually and reversibly from p(2 x 2)

to ~(2x2) upon heating above about 300°C. A further gradual and reversible transformation to

p(1 x 1) occurred upon heating above about 570°C and was presumably associated with the

reduction in equilibrium coverage above 500°C. These results differ in several respects from a

contemporaneous study of a similar alloy, and they raise interesting questions about the nature of

the equilibrium surface in this intriguing alloy system.

Surface Science 179 (1987) 219-229

North-Holland, Amsterdam

EPITAXIAL GROWTH OF fee Fe ON Cu(100)

M. ONELLION, M.A. THOMPSON, J.L. ERSKINE

Department of Physics, University of Texas, Austin, TX 78712, USA

C.B. DUKE and A. PATON

Xerox Webster Research Center, Webster, NY 14627, USA

219

Layer-by-layer epittial growth of Fe on Cu(100) is reported. The epitaxy is characterized

using Auger electron spectroscopy and low energy electron diffraction intensity analysis. Good

quality epittial Fe films having thicknesses ranging from one to four monolayers are stabilized

by the Cu(100) substrate. The overlayer structure is shown to be nearly identical to a continuation

of the fee lattice of the substrate.