The energetics of the W(001) surface reconstruction phase transition

A654 375

Surface Science 178 (1986) 375-381 North-Holland, Amsterdam

MODEL CALCULATIONS FOR THE TUNNELING CURRENT FROM A TUNGSTEN TIP TO A FLAT AND STEPPED NICKEL (100) SURFACE G. DOYEN

and D. DRAKOVA

*

Institut ftir Physikalische Chemie, Universittit Miinchen, Theresienstrasse 37. D-8000 Munich, Fed. Rep. of German-v Received

18 March

1986: accepted

for publication

16 June 1986

The tungsten tip is represented by a tungsten atom chemisorbed on a flat W(110) surface. The chemisorption calculation is based on a mode1 Hamiltonian which has been tested for many adsorption systems. The chemisorption calculation yields the wavefunctions needed for evaluating the tunnel current. The 6s and 6p components of the tip wavefunction are assumed to contribute to the tunneling process. The wavefunctions for the flat and stepped nickel surface are obtained by using the embedded cluster technique developed recently. The contours of constant tunneling current are quite similar to the charge density contours.

Surface

382

DYNAMICS

AND MELTING

J.F. VAN DEB VEEN

Science 178 (1986) 382-395 North-Holland, Amsterdam

OF SURFACES

and J.W.M.

FRENKEN

FOM-Institute for Atomic and Moleculur Physics, Kruislaan 407, IO98 SJ Amsterdam, The Netherlandr Received

1 April 1986; accepted

for publication

2 June 1986

Melting has long been suspected to be a surface-initiated process. Recently the first direct experimental observation of a melting point depression was made on the surface of a lead crystal. The experimental findings are in agreement both with modem theories on the role of surfaces in first-order phase transitions in solids and with computer simulations on model crystals close to melting. After a brief review of early predictions of surface melting and of macroscopic observations related to this phenomenon, the recent experiments and theories are discussed.

Surface

396

THE ENERGETICS OF THE W(O01) SURFACE PHASE TRANSITION L.D. ROELOFS *

Science 178 (1986) 396-405 North-Holland, Amsterdam

RECONSTRUCTION

Institut fir Physikalische Chemie, Universitiit Miinchen, Sophienstrasse II, D-8000 Munich 2, Fed. Rep. of Germany Received

11 March

1986; accepted

for publication

30 April 1986

A parameterized mode1 for the surface reconstruction phase transition of clean W(OO1) is discussed and studied by means of a Monte Carlo simulation. We find that existing first-principles calculations give insufficient reconstruction energy/surface atom to explain persistence of order up to experimentally measured transition temperatures. We also discuss the interplay between various contributions to the total energy over a wide temperature range, and show that substantial variation of system properties occurs between T = 0 and near but below the transition.