It was in Bristol in the period 1947 to 1949 that he started working on intercrystalline boundaries, together with
Charles Frank. Eventually their research led them to study
epitaxy, and in 1949 they presented the fruits of their research in a series of scientific papers. The result was the
Frank–Van der Merwe crystal growth model which carries both their names. From 1953 to 1964 he served as senior lecturer and Associate Professor in the physics department at the
University of Pretoria. He completed his MSc in Mathematics from the University of Pretoria in 1956. During this period he again worked with a colleague from Bristol,
Frank Nabarro who was then head of Physics at the
University of the Witwatersrand, South Africa. In 1961 he took a sabbatical to the
University of Virginia which led to a refinement of his initial model of thickening two-dimensional interfaces in 1963. The theory of
epitaxy was a major focus of his career and he published many seminal papers, which resulted in him becoming known as the "Father of Epitaxy". With the advance of the semiconductor industry from the 1960s onward, epitaxy became extremely important as it depends on the growth of perfect single crystals for the manufacturing of transistors and IC circuits. An essential role in understanding how to grow such perfect crystals was provided by his theory. Van der Merwe's model of atomic forces paved the way for successful modelling of important physical phenomena in solids at the atomic scale. He personally regarded his solution to a
differential equation in his PhD thesis as one of his biggest achievements. This was basically a
soliton differential equation with an ingenious solution, the first ever analytical solution to a soliton problem. Solitons in solid state and other branches of physics became important for advanced applications in communication technology. In 1965, he was invited by an ex-CSIR colleague, Ernst Marais, to the
University of Port Elizabeth where he was appointed head of the applied mathematics department. During this period Van der Merwe was invited to present plenary talks at many international conferences, during which he made enduring friendships with several surface scientists including
Ernst G. Bauer of the
Clausthal University of Technology,
Germany and Ralf Vanselow of the
University of Wisconsin,
Milwaukee. In 1969 he moved to
UNISA where he became Professor of applied mathematics. In 1970 he spent a seven-month sabbatical at the University of Virginia where he collaborated with William A. Jesser. Almost 30 years later, in 1999 he co-authored a paper with Jesser. In 1972, he accepted the position of head of the physics department at the University of Pretoria. From this point on he regularly collaborated with Gary Shiflet of the University of Virginia. Almost 20 years later, Shiflet and Van der Merwe co-authored papers on interphase boundaries. After his mandatory retirement at age 65, he became
Professor Extraordinarius at UNISA from 1990 to 2003, and
Honorary Professor in the Department of Physics at University of Pretoria from 2004 to 2016. In 1981 and 1989 he was Visiting Professor at the
Clausthal University of Technology, Germany, and Visiting Researcher to
Kodak Research Labs in
Rochester, New York, in 1981. == Awards and honours ==