WETTING AND ADHESION IN METAL-SILICON CARBIDE
SYSTEMS: THE EFFECT OF SURFACE POLARITY OF SiC
C. Rado, S. Kalogeropoulou and N. Eustathopoulos
Laboratoire de Thermodynamique et Physico-Chimie Me ´tallurgiques, UA 29 CNRS, ENSEEG, BP
75, 38402 Saint Martin d’He `res Cedex, France
(Received June 21, 1999)
(Accepted October 1, 1999)
Keywords: Surfaces and interfaces; Liquid metals; Carbides; Adhesion
Introduction
Crystallographic polarity is an important feature of surfaces of both hexagonal () and cubic () SiC.
The structure of -SiC perpendicular to the 0001 axis (a similar description holds for the (111)
surface of -SiC) consists of hexagonal double layers, each sub-layer being occupied by only one type
of atom, Si or C. Consequently in the same crystal two polar surfaces of different chemical nature exist:
the ideal (0001) and (0001
) polar faces which are terminated with a layer of Si and C atoms
respectively. (0001)-Si and (0001
)-C surfaces have different oxidation rates [1], and electronic prop-
erties [2], different nucleation rates when grown from the vapour phase [3] and different behaviour in
chemical etching. The last difference is often employed to distinguish the polar faces [4]. Given the
major benefits of SiC as a semiconductor compound, numerous experimental [4 –7] and theoretical
[2,8,9] studies over the past fifteen years have been devoted to the atomic and electronic structure of
SiC polar faces. In this study, the wetting of the two polar faces of -SiC by non reactive metallic melts
(molten Si and two metal-silicon alloys) is investigated by the sessile drop technique in order to measure
the contact angle of a liquid drop on a flat substrate. The results are used to discuss the nature of
predominant alloy/SiC interfacial interactions. The energy of these interactions is quantified by the
work of adhesion W
a
of the liquid on the substrate evaluated by the following equation:
W
a
=
SV
+
LV
-
SL
=
LV
1 + cos (1)
In this equation
ij
denotes the characteristic surface energies of the solid (S) –liquid (L) –vapour (V)
system. Knowing
LV
,W
a
can be evaluated from equation (1) as well as another fundamental quantity,
the work of immersion W
i
defined by the equation:
W
i
=
SL
-
SV
= -
LV
cos (2)
Experimental Procedure
The experimental apparatus used for the sessile drop experiments consists of an alumina tube heated
externally by a silicon carbide resistor. The tube is connected to a gas supply and to a vacuum system
consisting of a rotary vane and an oil diffusion pump, each being equipped with a liquid nitrogen trap.
Experiments are carried out either under a dynamic high vacuum or in a static atmosphere of helium.
Scripta mater. 42 (2000) 203–208
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