Summary: in Selected Works of J.W. Cahn, eds. W.C. Johnson and W.C. Carter (TMS, 1998), pp. 207-9
Introduction to "The Molecular Mechanism of Solidification", by J.W. Cahn,
W.B. Hillig and G.W. Sears.
Michael J. Aziz
Division of Engineering and Applied Sciences
Cambridge, MA 02138
By the mid 1950's, crystal-vapor interfaces were commonly believed to be atomically smooth and
to advance by a stepwise growth mechanism: a monolayer nucleation barrier prevented continuous
local motion of the interface normal to itself; growth was mediated by two-dimensional nucleation
and lateral spreading of new monolayers or by growth spirals emerging from screw dislocations).
Crystal-melt interfaces were commonly believed to be atomically rough and to advance by
continuous local motion of the interface normal to itself without the need for these stepwise growth
In 1960 Cahn published "Theory of Crystal Growth and Interface Motion in Crystalline Materials"
[Cahn 1960], in which he predicted that all interfaces would advance by a stepwise mechanism at
sufficiently low driving force and by a continuous growth mechanism at sufficiently large driving
force. These conclusions were the result of applying to interfaces involving crystalline materials
the Cahn-Hilliard diffuse-interface theory [Cahn 1958], containing a gradient-squared energy cost
associated with any spatially varying order parameter. The two phases were distinguished by a