Abstract
Start and first experiences in Stuttgart. My personal reminiscences of my “predecessor” Professor Predel. A brief history of the Max Planck Institute for Metals Research; processing of its Second World Wartime past in 2002. Move to the new building in 2002. Differences between manners and mores in “Delft” and “Stuttgart”; experiences with neighbours in private life. The unexpected restart of nitriding research, initiated by the discovery of amorphous nitride precipitates. The spectacular role of surface and interface energies in transformations at surface and interfaces; the model to predict, for real materials, quantitative values for these energies. The elimination of long held and widespread misconcepts: why the natural oxide layer on a metal (as aluminium) is amorphous and why whiskers are formed on a thin (tin) layer. Dean of the Study Course Materials Science; the “Kollegialprüfung”. The ambiguity of the relationship Max Planck Institute—University. Drafting the book “Fundamentals of Materials Science”. Colossal, internal stress gradients in thin films. Discovery of oscillating stress in a thin film: a quantum mechanical surprise of nature. The chapter ends with an example illustrating the perhaps greatest satisfaction for a materials scientist: the experience that his/her research of processes occurring in and with materials leads to fundamental, physical understanding of nature that allows utilization in technologically important applications.
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Notes
- 1.
In my first year in Stuttgart, Bertagnolli a couple of times urged me stringently to present an Inaugural Lecture to the Faculty/University. I stubbornly refused repeatedly, as I had just given a Farewell Lecture in Delft, where 12 years earlier I had already given an Inaugural Lecture on the occasion of my appointment as Professor in Delft. I couldn’t see the sense and certainly lacked any enthusiasm for an(other) Inaugural Lecture. After some time Bertagnolli gave up. In my Farewell Lecture in Stuttgart, 18 years later in 2016 (see Chap. 14), with Bertagnolli, in the meantime retired, present in the audience, I referred to this episode and remarked smilingly that this Farewell Lecture could be considered as redemption for the not given Inaugural Lecture in 1998 as well. During the reception afterwards Bertagnolli said to me that he had no clear memory of our friendly “skirmish” of so many years ago.
- 2.
Phase diagrams present fields of stability (i.e. states of equilibrium) for material phases as function of so-called “intensive” state variables. “Intensive” state variables are variables which do not depend on the size of the material system: for example, pressure, temperature and composition. “Extensive” state variables do depend on the size of the material system: for example: energy, mass and volume.
- 3.
Emil Heyn is a scientist known to me and others because he was one of the first to recognize that plastic deformation of a crystalline solid material can induce the emergence of locally strongly varying, internal stresses as a consequence of the intrinsic elastic and plastic anisotropy of the constituent crystals (also called “grains”, cf. footnote 12 in Chap. 8) of a solid material. Such stresses have sometimes been called “Heyn stresses”. Their measurement and analysis, by modern diffraction methods, is an important topic of also nowadays research devoted to the indicated “grain interaction” (e.g. see the book “Fundamentals of Materials Science”, 2nd Edition, Springer, Berlin-Heidelberg, 2021, pp. 350–352).
- 4.
This referred to book can be seen as the equivalent of an earlier book published by the Max Planck Society: R. Rürup, Schicksale und Karrieren (= Fates and Careers), Wallstein, Göttingen, 2008, devoted to the scientists of the Kaiser-Wilhelm-Gesellschaft (after the Second World War: Max-Planck-Gesellschaft) expelled by Germany under Nazi reign. We tend to think of very famous names as Albert Einstein and Lise Meitner, as examples of those scientists driven out of Germany (in case of Meitner it even was a genuine flight), but already only the thickness of both books, moreover recognizing that these books represent only those expelled from the University of Stuttgart and the Kaiser-Wilhelm-Gesellschaft, testifies of the enormous extent of the process of driving out scientists because of political and racist reasons in Nazi Germany: very many, very good and also less good scientists and students had to move and in many cases their careers were to be aborted for ever.
- 5.
As a pendant to the conduct of Werner Köster, the morally impeccable and, at a number of occasions, also already immediately after the “Machtergreifung” at the 30th January 1933, courageous behaviour by another scientist of “Stuttgart”, Paul Peter Ewald, can be considered. Ewald was married to a Jewish woman and also his four children were considered as being Jewish. He was a world famous scientist (one of the originators of the dynamical theory of (X-ray) diffraction; also see Chap. 5). Ewald was Chair Holder at the University of Stuttgart (since 1922), with an office more or less opposite to mine (but 70 years later) at the other side of the Seestrasse: a memorial plaque next to the entrance to his office and department refers to Ewald. He was Rector at the University from May 1932 till April 1933. After the “Machtergreifung” at the end of January 1933, in April 1933 at the Conference of the Rectors of the Universities of Germany in Wiesbaden, Ewald observed that his colleagues remained passive in view of the forthcoming, politically and racist motivated dismissals of colleagues. As a response, upon his return to Stuttgart he resigned from his assignment as Rector. In a later meeting at the University, in 1936, with compulsory attendance of all Professors and Lecturers, where a letter from the Minister of Science (= “Wissenschaft”), Education (= “Erziehung”) and National Education (= “Volksbildung”) was read, that centered around so-called “objective science”, Ewald became such appalled that he stood up and left the meeting hall. This was possibly the drop that made the bucket spill: soon thereafter, in the beginning of 1937, he was called to a meeting with the acting Rector and forced to request his dismissal. In the same year Ewald emigrated to England (see the referred to book in the main text).
- 6.
Whereas in English both a close friend or close family member and a stranger or somebody at higher social level can be addressed with “you” (so that one cannot guess upon usage of this word how small or large the social distance between the speaker/writer and the addressed one is), in, for example, the Dutch and German languages two words are in use for “you”: “du” and “Sie” in German and “jij” and “u” in Dutch. This explains the German verb “dutzen” (in Dutch “tutoyeren”) as characterizing people who use “du” or “jij”, respectively (close social distance), to address each other.
- 7.
This liberalism has its limits. Whereas the Dutch were forerunners in accepting and providing legal framework for, for example, abortion, formal marriage of homosexual or lesbian couples and self-determined death and they had a liberal drugs policy, in recent years some populist political parties have emerged in The Netherlands with anti-islam and anti-immigration programs that have drawn something like 25% of the votes in recent elections…
- 8.
The Swabians like their food specialties (as their tasteful “Maultaschen”, consisting of a cover of pasta filled with minced meat, spinach, bread, herbs and more) and their wine. And they are proud of it: On his first evening in Stuttgart (see “Start in Stuttgart” at the begin of this chapter) Eric was invited to join a meal in a restaurant with a couple of his future colleagues. One of these was a genuine Swabian. After having selected the wine, he informed Eric that all the wine that was produced in Swabia was consumed by the Swabians themselves. The message of this remark was clear: it should be interpreted as an indication of high quality of the wine, such that the Swabians would prefer to keep the wine for themselves rather than exporting it. Drinking this (red) wine, often a Lemberger or Trollinger or blends thereof, was not a positive experience for Eric; this red wine was much too “light” for his taste and generally did not impress at all. The thought, that a low rather than high quality of the Swabian wine then is the barrier for its exportation, imposes itself. To be fair and balance this critique, later, but rarely, Eric discovered also very good wines from Swabia, for example he enjoyed a delicious Kerner (white wine) from the “Felsengarten” (Neckar Basin) region.
- 9.
Within the (transmission) electron microscope (actually within the “column”; along its axis the electron beam passes that is used for image formation) magnetic fields occur due to the operation of the applied magnetic electron lenses. Interaction with the magnetic field invoked by the magnetic specimen complicates handling of the microscope. The effect can even cause the disintegration of the mechanically very vulnerable, thin, electron transparent specimens(foils), if these are magnetic. Thereby specimen fragments may be attracted and deposited onto the pole shoes of the magnetic lenses…., which is obviously undesired.
- 10.
The general reader of this booklet needs not to fully appreciate the meaning of these technical terms (and those in the following paragraph of the main text). For those interested here: The single-reflection collimating X-ray mirror is a multilayer optic of parabolic shape with respect to two mutually perpendicular planes and thereby the collimation is achieved, both “horizontally” and “vertically”, using a single (instead of two consecutive) Bragg reflections.
- 11.
If we would have had this equipment to our availability at the Laboratory of Metallurgy in Delft in the early nineties of past century, likely there would have not been the need to apply for measurement time at and to travel to one of the few storage rings worldwide for the production of synchrotron radiation (in that case to the United Kingdom; see “Iron Nitrides and Iron Carbides; Tempering of Steels and Pre-Precipitation Processes” in Chap. 10).
- 12.
The essence of the semi-empirical, “macroscopic atom” model is that an atom is considered to be a piece of material (in the model this piece is a Wigner–Seitz cell) with the macroscopic properties of that material. Strictly considered this is incorrect: only an aggregate of atoms of one kind exhibits macroscopic properties which identify the elemental material concerned. Bringing two such “macroscopic atoms”, each of a different element, into contact (as in a solid solution, which is the case originally considered by Miedema for the assessment of the enthalpy of formation of solid solutions, or as at the interface of two solids of different elements, which is the case of relevance to our work on the assessment of interface energies!) energy changes occur in association with a redistribution of electron density governed by the difference in electron density and the difference in chemical potential of both “macroscopic atoms”. Thereby available data on macroscopic properties can be used to calculate (predict) enthalpy of formation values.
- 13.
The book published in 1988 where the “macroscopic atom model” is elaborated with all available experimental verification available at the time (F.R. de Boer, R. Boom, W.C. M. Mattens, A.R. Miedema and A.K. Niessen, Cohesion in Metals: Transition Metal Alloys, 1988, Elsevier Science, North-Holland, Amsterdam) has been cited by now about 4000 times (personal communication by Rob Boom, now emeritus Professor at the Delft University of Technology and, by the way, the current possessor of my talar (see above under “Manners and Mores”)…).
- 14.
The crystallographic orientation of the surfaces has been indicated in Fig. 13.7 by the numbers within the braces: the so-called Miller indices (for the materials silicon (Si), aluminium (Al), chromium (Cr) and copper (Cu)) and the so-called Miller-Bravais indices (for the materials of hexagonal crystal symmetry, as titanium (Ti), zirconium (Zr) and magnesium (Mg)).
- 15.
The reader may try him/herself: having to write up oneself, in one’s own words, the essence/explanation of a scientific phenomenon, also a derivation of an equation, almost automatically and immediately brings about fathoming of the science involved.
- 16.
The Bologna agreement (1999) strives for unification of standards and levels (degrees) of university educations in Europe. This would lead to higher mobility of students so that an education began at university A in country C can be continued without barriers and loss of time, i.e. without more ado, at university B in country D. The University of Stuttgart (as held for all universities in Germany) was very late in adopting this system. We introduced the Bachelor/Master programme on Materials Science in 2008. The language of use in the Bachelor programme remained German; the language of use in the Master programme became English. Quite a number of years earlier the adaptation to the Bologna agreement had already been established at the universities in quite some countries of Europe, including The Netherlands and there the language of communication in both the Bachelor and Master courses is English.
One may not favour using English also in a Bachelor course. Native students may have difficulties if the lecturer speaks English, since this adds to the barrier the students experience in any case upon entering the university with its completely different way of “teaching and learning” as compared to the preceding “school”. Moreover the “English” of the lecturers may be of limited quality. Therefore in Stuttgart we maintained German as the language of communication in the Bachelor programme. As preparation for use of English both as the lingua franca of science and in the Master programme, we did advise English language textbooks for studying in also the Bachelor programme.
- 17.
In only one case I acted as the doctor father of a man distinctly older than I was: Aat Voskamp, who was 11 years my senior. Aat worked as an engineer at SKF Engineering and Research Centre in Nieuwegein, The Netherlands. He had an engineer degree from a polytechnic school (this degree was indicated with “Ing.” in The Netherlands (“Ing. (grad.)” in Germany), as a distinction with respect to an academic engineer graduated at a university of technology, leading to a degree indicated with “Ir.” (“Dipl.-Ing.” in Germany)). There was no doubt that Aat (yet) was of academic quality: he had published in the international scientific literature and in the course of time acquired an international reputation in his specialty: microstructural changes during rolling contact fatigue (as in ball bearings, which indicates the relevance for SKF). I knew Aat since my Ph.D. time, as he regularly came to Delft to perform texture measurements. Some 20 years later, in the beginning of the nineties, Aat approached me with the wish to start a Ph.D. project. From this cooperation with me a number of joint papers resulted and then the thesis was successfully defended in 1997, shortly before I left for Stuttgart. This academic promotion was remarkable, also because a special permission of the Delft University of Technology was required, since Aat had no academic qualification up till that time (I had to write an extensive application). This really was a special event, celebrated with a big party, also because Aat in 1997 was already 57 years. His thesis can indeed be considered as the crowning achievement of a lifelong career: a “life’s work” (see Chap. 6). With reference to the main text above, the second reason to include this footnote here is that also Aat no longer is amongst the living: he died from cancer in 2014 at the age of 75.
- 18.
This is the energy of the electrons in the metal which are not strongly bound to an atom but can move “freely” through the piece of metal. These so-called valence electrons move within a “potential well” confined by the surfaces of the crystal (here the interface with the substrate and the surface of the single-crystalline film. The (periodic) arrangement of the positively charged metal ions is ignored: the positive charge is taken to be smoothed out such that a uniform potential results (for some more details, see E.J. Mittemeijer, “Fundamentals of Materials Science”, Second Edition, Springer, 2021, pp. 68–79).
- 19.
If a bar is pulled along its axis, the lateral dimensions decrease somewhat. If the bar is compressed along its axis, the lateral dimensions increase somewhat. Similarly, if a thin film strives for thickness increase, then its lateral dimensions (i.e. the dimensions in the plane of the film) strive to decrease. If the film strives for thickness decrease, then its lateral dimensions strive to increase.
- 20.
The negative stress-depth gradient evokes a vacancy-concentration depth gradient which causes a mass flux (of tin atoms) from the bottom part of the film to the top part of the film, likely via the grain boundaries at the low (room) temperature considered (a process that resembles the one known in materials science as “Coble creep”). Then, to maintain the massive nature of the film, whisker growth occurs, to accommodate the Sn transported to the film surface along the more or less perpendicular grain boundary.
Upon closer consideration it must be recognized that not every grain boundary in the film can act as a “root” for whisker formation. Only those (few) surface adjacent grains which have grain boundaries inclined which respect to the surface (and are directly above a perpendicular grain boundary aiding Sn transport from the bottom of the film; see Fig. 13.12) can give rise to whisker formation: only along the inclined grain boundaries of such a surface grain shear stresses act (as consequence of the planar state of stress in the film), which support the outward transport of tin along these inclined grain boundaries by gliding (i.e. shearing) along these grain boundaries. The surface grain with its inclined grain boundaries thus becomes the “whisker root”.
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Mittemeijer, E.J. (2022). The Stuttgart Years; Science at the Max Planck Institute and the University. In: How Science Runs. Springer, Cham. https://doi.org/10.1007/978-3-030-90095-3_13
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