Book chapter 5
## Introduction to Surface and Thin Film Processes

John A. Venables

*Cambridge University Press (2000)*

### Supplementary notes by John A. Venables

© *Arizona Board of Regents for Arizona State University
and John A. Venables*

## Section 5.1: Introduction: growth modes and nucleation barriers

In section 5.1.3 a point of confusion (in the orginal 2000 printing) has been noted by some students about the
relation between a) the statement on page 146 starting "When we deposit material A on B,
we get layer growth if γ_{A} < γ_{B} + γ*, where
γ* is the interface energy, and vice versa for island growth",
and b) the illustrations of figure 5.3(a) and (b) on page 147. This addendum discusses
this confusion in more detail so that you can become *really* confused...
It seems to be "common sense" that the equation should have the γ* on the the other side,
since by depositing A on B, we are replacing the (free) energy γ_{B} by
γ_{A}. If we take into account the interface energy γ*, thinking of it
as a positive but small energy, then indeed we should have γ_{A} + γ* <
γ_{B}; the free energy must go down to be consistent with layer growth.
This statement occurs in our review article (Venables *et al.* 1984) on
page 405 in equation 1.3, correctly, and the equation has been corrected in the text of 2006 printing.
These statements are traceable directly to the review by Kern *et al.* (1979), where they discuss
this topic in much more detail, considering several sub-cases and possible mechanisms. You may however
note in passing that figure 1 in our review was garbled,
with inconsistencies between the text, figure captions and the figure.

Figure 5.3 derives from my more recent review (Venables 1994, figure 1) where I was wishing
to compare compactly both the layer and the SK growth mode in what is here figure 5.3(a).
The point here is that layer growth is definitely favored if γ_{A} < γ_{B}.
However if the interface energy builds up as the layers are deposited, then at some stage a
switch to islands can occur; this is the SK mode. But figure 5.3(b) illustrates the growth
of islands of *B on A*, not A on B. So in this case the equation on page 146 describes
island growth of B on A: γ_{B} + γ* > γ_{A}; the interest in
considering A on B, and then B on A, arises from the role of these two different interfaces in multilayers.

Just to prove that this topic has a jinx on it, there was also an error in the 1994 review
text description of what is here figure 5.3(a). But the bottom line is that the statement on
page 146 of the original printing was incorrect for describing layer growth of A on B; it should be
γ_{A} + γ* < γ_{B}, and has been corrected in the 2006 printing.
Thanks especially to Dr John R. Abelson
and his students at UIUC for pointing out this error, and for veryifying this "clarification".

New references for section 5.1

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*Latest version 21st January 2013, ex 4th March 2001.*