Craig Rottman

Step doubling and related transitions on vicinal surfaces

We discuss two types of step‐height doubling transitions on vicinal surfaces. In one type, exemplified by Ge(111)‐[121], a phase transition can occur since the symmetry between alternate terraces is broken at low temperatures. There is evidence in both experiment and in Monte Carlo simulations that this transition can have Ising character. In the second type, exemplified by Si(001)‐[110], one subset of terraces is always favored, so that no symmetry is broken. If an actual phase transition occurs (rather than a smooth crossover), it is expected to be first order, implying a coexistence region in a temperature‐misorientation phase diagram. Finally, the coalescence of steps into steps of height more than two atomic layers is briefly considered.

Phase transitions in grain boundaries with structural multiplicity

In the case of the model only second-order transitions have been found above. However, many other studies have looked at the effects of further-neighbor interactions, and in these cases first-order transitions into the disordered phase are also possible. It would be impossible to rule these out for grain-boundary transitions in general, since further-neighbor interactions are, in general, present. In such cases, it may also be possible to exploit previously published results on the appropriate model to determine the order of the transition as well as the transition temperature T c

Morphological Stability of Semicoherent Solid-Solid Interfaces: a Simple Model

The stability of semicoherent interfaces between two solids with small lattice mismatch is examined. I consider the cases in which the rotation θ between the two solids is both zero and small. The interface orientation, characterized by a single angle φ, is arbitrary. The interfaces are composed of regularly spaced misfit dislocations, steps, and lattice dislocations. For a wide range of φ, many flat interfaces are unstable with respect to breaking up into two interfaces of distinct orientations, one of which contains only one of the two types of dislocations possible.

Theoretical Aspects of Phase Transitions in Internal Interfaces

Phase transitions which are possible in internal interfaces are grouped into several classes. Simple examples of these transitions, corresponding to coherent interphase boundaries and antiphase boundaries, are given for each class. Lattice models may be used to study these transitions. Interfacial phase behavior closely connected with bulk phase transitions is also discussed. Implications for extended faults bounded by partial dislocations are suggested.