Prof. Dr. Johannes Heydenreich

This issue contains a collection of papers dedicated to Professor Dr. Johannes Heydenreich on the occasion of his 70^th birthday. The large number of contributions reflects his international reputation in the scientific community of electron microscopy, solid state physics and crystallography. This collection of original papers is a colourful bouquet of scientific results of former collaborators, colleagues and friends from East and West honouring the scientist Johannes Heydenreich.

Johannes Heydenreich was born on June 20^th, 1930 in Plauen/Vogtland near Dresden. He studied physics at the Pedagogical Hochschule Potsdam, where he obtained his "Dipl. Phys." in 1958 and his doctorate in 1961. In 1969 he obtained the Habilitation degree at the Martin Luther University in Halle.

In Potsdam, Heydenreich´s scientific interests were mainly influenced by Prof. Picht, one of the pioneers in electron optics. A fruitful collaboration with Prof. Heinz Bethge began during the time when Johannes Heydenreich did the experimental work for his Diploma at the Institute for Experimental Physics at the University of Halle.

The Institute for Solid State Physics and Electron Microscopy of the Academy of Sciences of the GDR, in Halle, was founded fourty years ago in 1960. Two years later Heydenreich joined the team of this institute which was directed by Prof. Bethge.

Heydenreich, as Assistant Director, was the ideal counterpart to Heinz Bethge, and played a crucial role in introducing and organising the various techniques of electron microscopy in the institute. The Bethge-Heydenreich partnership was defined fittingly by Tom Mulvey, Aston University of Birmingham: "They were of like mind, physicists striving for excellence in physics, Bethge more outspoken, Heydenreich more diplomatic, but neither of them compromised their personal integrity in a political system that often put loyality to the Party before scientific excellence. The two of them complemented each other in skill, firmness, ingenuity and diplomacy to forge the growing organisation into a research institute with an internationally acknowledged reputation, attracting and encouraging scientists from both East and West to work there."

The research activities of Prof. Heydenreich have covered a broad spectrum. At the beginning of his career he made significant contributions in the field of electron mirror microscopy. After that his main interests were focused on transmission electron microscopy, ranging from diffraction contrast analysis of crystal defects to high resolution electron microscopy and image processing. His favourite field concerned studies of defect-induced phenomena in advanced materials. The so-called Bethge-Heydenreich, the book "Electron Microscopy in Solid State Physics", published by Elsevier in 1987, provides an excellent overview both of Heydenreich´s work and of the spectrum of the Institute of Solid State Physics and Electron Microscopy in Halle.

After the re-unification of Germany this institute was transformed into the Max Planck Institute of Microstructure Physics, the first institute of the Max Planck Society in the eastern part of Germany. From the beginning, Prof. Heydenreich was on the Board of Directors and was the Executive Director from 1993 until his retirement in 1995.

A remarkable and time-consuming part of Heydenreich´s work was connected with the International Centre of Electron Microscopy at the institute in Halle, which was founded in 1975. Young scientists from Eastern Europe were taught in annual spring and summer meetings including practical exercises on the microscopes. All in all, Johannes Heydenreich conducted 35 of such schools! From the beginning, he was a member of the Scientific Council of the Centre, and from 1985 the Director of the Centre. The centre could continue its work under the auspices of the Max Planck Society and is now a real scientific bridge between Eastern and Western Europe.

Furthermore, Johannes Heydenreich had been active as a leading member of various scientific boards for many years. Thus, he was a co-editor of several journals covering electron microscopy, solid state physics and crystallography. As a member of the Executive Committee of the European Society for Electron Microscopy (CESEM) for many years, and as a member of the Executive Board of the German Society for Electron Microscopy, Johannes Heydenreich had invested a great deal of time and effort for the welfare of the scientific community. Over the course of nearly three decades Prof. Heydenreich taught the fundamentals and applications of electron microscopy at the Universities of Halle and Leipzig. Generations of students have admired his excellent lectures with clear representation and rigorous scholarship.

The scientific work of Johannes Heydenreich had been honoured by his election to the Academy of Natural Scientists Leopoldina where he worked as a Secretary of natural science for many years. The Technical University of Chemnitz confered an honory doctors degree on Prof. Heydenreich in recognition of his scientific work.

I also acknowledge with gratitude the time of inspiring collaboration in Halle. All his friends, colleagues, and generations of his students wish him many further years of good health. The Editors of Crystal Research and Technology join with these wishes and add their gratefulness for his long-standing engagement as a member of the Advisory Board.

W. Neumann, Berlin