Piet Bennema (1932-2016) is one of the founders of crystal growth science in The Netherlands. As a PhD student at the Delft University of Technology, he performed accurate growth rate experiments that proved that the spiral growth mechanism from the Burton-Cabrera-Frank theory (which was rather new at that time) was also valid during growth from solution. He received his PhD in 1965 under the supervision of W.G. Burgers and van H.G. van Bueren. After a period as a post-doc at the University of Groningen and as an assistant professor in Chapel Hill (North Carolina, U.S.A.), he became Reader at Delft University of Technology in 1969. There he continued his crystal growth experiments, and, together with the theoretical physicist G.H. Gilmer, he performed the first computer simulations of crystal growth processes. This and subsequent computer studies had a tremendous impact on the theoretical research of crystal growth in his own lab and elsewhere.
After eight years at Delft University of Technology, Piet was appointed as a full Professor at the University of Nijmegen in 1976 where he would stay for the rest of his long career. There he deepened the theoretical concepts of crystal growth, together with the theoretician J. van der Eerden. This led to a better insight into the concepts of bond strength, supersaturation, step energy, two-dimensional nucleation, kinetic roughening and spiral growth in crystallization. In cooperation with I. Sunagawa and K. Tsukamoto (Tokohu University, Sendai, Japan) and W. van Enckevort, he became familiar with the ex-situ and in-situ observation of crystal surfaces using advanced optical microscopy and AFM. This work supported his theoretical concepts, which were not obvious at all at that time. He also remained fascinated by the Hartman-Perdok theory; he further developed this approach for deducing crystal morphology from crystal structure to the more modern Connected Net theory. Together with H. Knops (University of Nijmegen) he integrated this theory with modern statistical mechanics concepts and together with H. Meekes, he was able to tackle the habits of real crystal structures in detail using computer programs. He was also mesmerized by the morphology of incommensurate crystals and collaborated on this topic with the well-known expert, A. Janner (University of Nijmegen). Of course, also “common” crystals, such as paraffin and other organic crystals, salts grown from aqueous solution, semiconductors and even fractals received his attention. Due to this, he kept in touch with many industries and collaborated on the more fundamental aspects of industrial crystallization with G. van Rosmalen’s group at Delft University of Technology. In 1995 Piet Bennema received the Frank Award in 1995 from the International Organization for Crystal Growth.
Piet Bennema had a special relationship with Japan. He was born in Indonesia (then called the Dutch East Indies) and as a child was interned in a Japanese camp during World War II. Despite this experience, he made his first journey to Japan in 1975 and started a warm hearted collaboration with the Japanese crystal growth community in general and with Prof. Sunagawa in particular.
Ichiro Sunagawa (1924-2012) was invited to Tohoku University as a Professor in Mineralogy in 1971 after 23 years at the Geological Survey of Japan. He became interested in the morphological change of minerals due to the change of environments. In order to understand the morphological change of minerals, he wanted to introduce the concept of ecology in biology to the field of mineralogy. “I was inspired by an ecologist in Tohoku University when I was a student”, he later said to me. This is the reason why he liked the words, “Snow is a letter from sky” given by Professor Ukichiro Nakaya.
He went to London University in 1957 to study crystal growth in the laboratory of Tolansky, who was famous for developing multiple-beam interferometry and Frank who was known for his theory of spiral growth. Ichiro Sunagawa brought an Olympus phase-contrast microscope from Japan to the field of crystal growth in London. Using the microscope, he observed surfaces of various crystals like hematite, quartz, SiC and diamonds. These surfaces were too flat and thus no steps could be seen by other scientists. However he could observe beautiful spiral steps on these crystals with the Olympus microscope. The microscope was therefore jokingly said to be equipped with built-in spiral patterns in the optical path. The Japan Mineralogical Society awarded him the Japan Geological Prize in 1963 for his pioneering works on crystal growth mechanisms through surface observations.
In 1971 he started his new job as a Professor in Tohoku University which he held for the next 17 years. I clearly remember his first lecture when I was a third-year student of the undergraduate course. A colorful thin section of the mineral tourmaline attracted me so much during his lecture. This was a memorable slide that led me to work in the field of crystal growth. Without this slide, I would not have come into this field. While Ichiro Sunagawa was in Tohoku University he studied crystal growth in various fields with students. During this17 year period, 107 undergraduate and postgraduate students studied in his laboratory. He also activated the crystal growth community by starting the JSPS project “Materials Science in The Depth of the Earth.” This was the first big project in the field of Earth Science in Japan.
In 1982, he was nominated as a Council Member of Japan. He also acted as president in various societies, including the Mineralogical Society of Japan, the Japan Association of Crystal Growth and the Japan Gem Society. For these activities, the University of Marseille awarded him the honorary degree of Doctor of Science. He is also an honorary member of the Bulgarian Academy of Science.
After retiring, he became President of Gem Material School of Yamanashi prefecture. In the meantime, he spent time for the organization of ICCG4 in Sendai. We expected 400 participants before the conference but over 1300 participants attended. That was also an unforgettable memory for us. He was awarded the Distinguished Service Award from the IOCG in 2007. I still remember the ceremony. The daughter of old Sunagawa accompanied him for assistance. She dressed in a Kimono beside him. Although he could be strict, Sunagawa’s smile always gave us courage to overcome various barriers and to continue new directions in science and technology. His generosity of spirit affected everyone and we would very much appreciate to see his smile again, we hope.