A Kinetically Driven Growth Instability in Stressed Solids*
L. J. Gray and Theodore Kaplan (ORNL)
William Barvosa-Carter and Michael J. Aziz
(Harvard)
Stress can have a significant effect on crystal growth. It is well
known that, in equilibrium, a non-hydrostatic stress provides a driving
force which creates a rippling instability of a flat surface.
However, in addition to energetics, growth and morphology of a solid are
also determined by the "non-equilibrium" mobilities of the
interface atoms. Previously, the effect of stress on mobility and
its subsequent effect on growth morphology has been entirely
ignored.
This paper describes a new morphological instability that is driven by
the stress dependence of the mobilities during growth. This
"kinetically driven" interfacial instability was observed when
a non-hydrostatic stress was applied during far-from-equilibrium growth
of crystalline silicon from amorphous silicon. This new effect is
of general relevance to the growth of all non-hydrostatically stressed
solids, and is therefore important in film synthesis, with potentially
significant applications in electronic devices and thin film
coatings.
To prove that it was the kinetic mechanism driving the
observed instability, a computational model for predicting the interface
evolution was developed. The calculations employed a new boundary
integral technique capable of accurately calculating the stress state
along an arbitrary growth front. The growth rate model included the
effect of stress on the energetics and the kinetics, and direct
comparison of experiment and simulations clearly demonstrated that the
kinetic mechanism was dominant. The combined experimental and
computational work therefore establishes the existence of this new
mechanism for morphological instability.
*W. Barvosa-Carter, M. J.
Aziz, L. J. Gray, and T. Kaplan, "A kinetically driven interfacial
instability for nonhydrostatically-stressed solids," Phys. Rev.
Lett. 81 1445 (1998)