Al69 134 Surface Science 183 (1987) 134-146 North-Holland. Amsterdam SURFACE SEGREGATION IN In-Pb ALLOYS - SOLID AND LIQUID STATES J.A. BARNARD, P. WYNBLATI’, William C. JOHNSON and W.W. MULLINS Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University, Pittsburgh, PA 15213, USA Received 7 September 1986; accepted for publication 25 November 1986 The surface compositions of three alloys (1.42, 3.07 and 5.86 at% Pb) in the In-Pb system have been obtained as a function of temperature in both solid and liquid states using the scanning Auger microprobe (SAM). All data were obtained at temperature, from equilibrated samples, in a region of about fifty degrees on either side of the liquidus temperature. Lead has been found to be the segregating component in all cases. From these measurements, the heat of segregation has been calculated for all alloys in both states. In each alloy the magnitude of the heat of segregation declines significantly on melting although the absolute surface compositions are found to be continuous across the two phase solid-liquid field. These results are interpreted in the light of current segregation theories. Particular attention is paid to the role of elastic effects on solute segregation to free surfaces. Surface Science 183 (1987) 147-160 North-Holland, Amsterdam 147 EQUATION OF MOTION METHOD FOR THE TIME-DEPENDENT NEWNS-ANDERSON MODEL Hideaki KASAI and Ayao OKIJI Department of AppIied Physics, Osaka University, Suita, Osaka 565, Japan Received 1 September 1986; accepted for publication 3 December 1986 The time-dependent Newns-Anderson model including the intra-atomic Coulomb interaction is investigated by means of the Heisenberg equation of motion. It is shown that a hierarchy of equations can be derived for the time-dependent expectation values of charged states for atoms moving near metal surfaces. A truncation procedure is used to reduce these equations to a closed form. A simple case of time-dependence for parameters in the model is examined numerically. Surface Science 183 (1987) 161-179 North-Holland, Amsterdam 161 A PROPOSED ABSORPTION SPECTROSCOPY FOR STUDYING ENERGY LEVELS OF ATOMS IN COLLISION WITH SURFACES R. KAWAI *, K.C. LIU, D.M. NEWNS * Department of Mathematics, Imperial CoIlege, London S W7 282, UK and

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Page 1: Surface segregation in In-Pb alloys -solid and liquid states

Al69

134 Surface Science 183 (1987) 134-146 North-Holland. Amsterdam

SURFACE SEGREGATION IN In-Pb ALLOYS - SOLID AND LIQUID STATES

J.A. BARNARD, P. WYNBLATI’, William C. JOHNSON and W.W. MULLINS

Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University, Pittsburgh, PA 15213, USA

Received 7 September 1986; accepted for publication 25 November 1986

The surface compositions of three alloys (1.42, 3.07 and 5.86 at% Pb) in the In-Pb system have been obtained as a function of temperature in both solid and liquid states using the scanning Auger microprobe (SAM). All data were obtained at temperature, from equilibrated samples, in a region of about fifty degrees on either side of the liquidus temperature. Lead has been found to be the segregating component in all cases. From these measurements, the heat of segregation has been calculated for all alloys in both states. In each alloy the magnitude of the heat of segregation declines significantly on melting although the absolute surface compositions are found to be continuous across the two phase solid-liquid field. These results are interpreted in the light of current segregation theories. Particular attention is paid to the role of elastic effects on solute segregation to free surfaces.

Surface Science 183 (1987) 147-160 North-Holland, Amsterdam

147

EQUATION OF MOTION METHOD FOR THE TIME-DEPENDENT NEWNS-ANDERSON MODEL Hideaki KASAI and Ayao OKIJI

Department of AppIied Physics, Osaka University, Suita, Osaka 565, Japan

Received 1 September 1986; accepted for publication 3 December 1986

The time-dependent Newns-Anderson model including the intra-atomic Coulomb interaction is investigated by means of the Heisenberg equation of motion. It is shown that a hierarchy of equations can be derived for the time-dependent expectation values of charged states for atoms moving near metal surfaces. A truncation procedure is used to reduce these equations to a closed form. A simple case of time-dependence for parameters in the model is examined numerically.

Surface Science 183 (1987) 161-179 North-Holland, Amsterdam

161

A PROPOSED ABSORPTION SPECTROSCOPY FOR STUDYING ENERGY LEVELS OF ATOMS IN COLLISION WITH SURFACES

R. KAWAI *, K.C. LIU, D.M. NEWNS *

Department of Mathematics, Imperial CoIlege, London S W7 282, UK

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