On the 25th of October 2019, Professor Wolfgang Neumann celebrated his 75th birthday. That this is the 75th Anniversary might already be surprising to most people in the scientific community since Wolfgang Neumann is still very active and visible in the community although it has been almost ten years since his retirement in 2010. I take it as a good sign.

Going further back to the year 1995, Wolfgang Neumann received the call for the C4 professorship on crystallography at the physics department of the Humboldt‐Universität zu Berlin (HU Berlin). At this time Wolfgang Neumann was member of the scientific staff of the Max‐Planck‐Institut (MPI) für Mikrostrukturphysik in Halle/Saale which was formerly the Institut für Festkörperphysik und Elektronenmikroskopie (IFE) headed by Professor Heinz Bethge and Professor Johannes Heydenreich. The personal reflections of Kurt Scheerschmidt and Reinhard Schneider, published on the occasion of Wolfgang Neumann's 65th and 70th birthday, respectively, are well worth a read, containing plenty of interesting facts about the time before 1995.^[1, 2^]

In September 1995 I was a PhD student at HU Berlin. I met Wolfgang Neumann for the first time in person at a workshop on “Crystallography of interfaces and crystal defects” held in Güntersberge/Harz. Knowing Wolfgang Neumann from his contributions to the book on “Electron Microscopy in Solid State Physics” by H. Bethge and J. Heydenreich, it was interesting to realize that the workshop was co‐organized by Wolfgang Neumann as speaker of the working group (Arbeitskreis) “Theoretical crystallography” of the German Society for Crystallography. Along with many great qualities, the fact that Wolfgang Neumann was active in both electron microscopy and crystallography most likely paved his way to the professorship at HU Berlin.

The research focus of the existing group was on defects in compound semiconductor bulk crystals mainly conducted by Dr. I. Hähnert, permanent staff member and manager of transmission electron microscopy laboratory. A second important focus was on the structural and chemical properties of epitaxially grown semiconductor layers. The transmission electron microscope (TEM) utilized for the research was a HITACHI H8110 operating at 200 kV and equipped with an LaB₆ electron source, scanning TEM (STEM) unit, and an energy‐dispersive X‐ray detector. The TEM was installed in 1993 and well equipped for solving crystallographic problems at the nanometer length scale. In particular, this TEM permitted a complete phase analysis delivering both, crystal structure and chemical composition of nanometer‐sized objects.

When Wolfgang Neumann started to lead the Crystallography group in 1996 he immediately got into the details of the ongoing research. His longstanding experience in combining his overarching insight in both electron microscopy and crystallography enabled him to quickly make progress and extend the field of research. For our discussions we usually sit at a round table where traditionally the oral exams were also taken. Rumors have circulated that this table is oaked with decades of students sweat. Remarkably, this table and other pieces furnished Professor Will Kleber's office in the 1960's during Wolfgang Neumann's mineralogy studies in Berlin. As a definite sign of his respect for the achievements of the predecessors this furniture was kept in daily use rather than sent to a museum. During our discussions it could happen that Wolfgang Neumann would jump up and pick the appropriate monograph or original paper which exactly fit to the topic we were discussing. This unique ability is a consequence of three (amongst numerous) of his excellent qualities. First, his diligence shows through his ability to read papers and books, second, he almost never forgets a thing. And third, he has a superior internal navigation system guiding him to the right reference, although it being hidden in an impressive pile of paperwork.

As result of Wolfgang Neumann's thoughts about the ongoing research in the group he figured out at least two important issues to work on. First was to strengthen the collaborations within the scientific landscape of Berlin and second to improve the existing TEM instrumentation. Soon new research projects were set up and turned out to be very successful. In particular the close cooperation with Professor Rolf Köhler was like a door opening to the Berlin‐wide collaborative research center SFB296 “Growth‐correlated properties of low‐dimensional semiconductor structures”. Moreover, a research project on Ni‐base superalloys succeeded together with the Hahn‐Meitner‐Institut Berlin. Concerning instrumentation a Gatan imaging filter (GIF) was attached to the existing microscope. The GIF largely extended the capabilities of analytical electron microscopy. By hiring Reinhard Schneider, now apl. Professor at Karlsruhe Institute of Technology and well‐known for his fundamental work in the field of electron energy loss spectroscopy, the group expertise was significantly increased.

A further important step into the direction of an internationally visible group was the move of the Institute of Physics from downtown Berlin to the science campus Berlin‐Adlershof in 2003. The new institute turned out to be a very attractive and innovative building making it a pleasure to do sciences therein. For the TEM laboratories a state‐of‐the‐art TEM JEOL 2200FS was purchased. It was fully equipped for the whole spectrum of analytical electron microscopy including energy‐dispersive X‐ray spectroscopy, electron energy loss spectroscopy and atomic‐number (Z) contrast STEM imaging. As a particular specialty a biprism for electron holography was installed. In combination with the in‐built Lorenz lens it allowed for the successful characterization of soft‐magnetic materials.

These outstanding capabilities even attracted international cooperation as, e.g., within the European framework project PARSEM (GaN‐based semiconductor structures), with Sławek Kret from the Polish academy of sciences (semiconductor nanowires), with Jan Neethling from Nelson Mandela Metropolitan University, Port Elizabeth, South Africa (electron crystallography), and with David Johnsen from University of Oregon, USA (Ferecrystals).

Another facet of Wolfgang Neumann's activities (and I can say it is almost a passion) is the organization of the Autumn Schools for Electron Microscopy. The longstanding tradition reaches back to the 1970s when the Autumn Schools were held at the IFE in Halle/Saale.^[2^] After the retirement of Johannes Heydenreich, Wolfgang Neumann was the remaining driving force of the Autumn Schools. From 1998 till 2002 the Schools alternated between MPI Halle and Fritz‐Haber‐Institut (FHI) Berlin. Concerning the organization it was a big step away from institutes of the Max Planck Society when the Autumn School was organized at HU Berlin in 2003 for the first time. Internationally renowned scientists were invited to teach the students of the school about the field of electron microscopy. The scope comprised modern developments of instrumentation, fundamentals of methods, and their application to materials science problems. It could be considered as a birthday gift that thanks to the engagement of Christoph C. Koch (HU Berlin), Michael Lehmann (Technical University Berlin), and Marc Willinger (FHI Berlin) there is a renaissance of the Autumn Schools. The organization is now done under the umbrella of the Berlin Electron Microscopy Network.

The Autumn Schools directly relate to teaching. This is one of the splendid skills of Wolfgang Neumann. Naturally connected to the Chair of Crystallography were lectures on geometrical and structural crystallography, crystal physics, and crystal defects. These lectures benefited from one of the most comprehensive crystallographic teaching collections all over Germany. I remember the enormous challenge to figure out which one of the more than 350 paperboard models is the tetragonal scalenohedron of point group $\overline{4}$m2 and not to mess it up with the trapezohedron of point group 422. By the way, I can state that this teaching collection is still in use and the students still struggle with morphology models made from wood during the so‐called “Klötzchenkunde”. I took over the lectures on geometrical structural crystallography. Part of it is also the layer groups for which no models exist. During the 25th European Crystallographic Meeting 2009 in Istanbul (Figure 1) we had the chance to admire the art of Islamic ornaments of the Sultan Ahmed mosque, Hagia Sophia museum and the Sultan's palace. This was the inspiration to document examples for each of the 17 layer groups which was successful to large extent. In particular, all the square layer groups were found. Interestingly enough, the p2gg layer group describing the well‐known herringbone pattern was not observed. Very likely this is due the fact that the squared shape of the tiles at walls and floors hardly fit to any other geometry. Presumably, we have to go to the Alhambra at Granada/Spain to verify all the layer groups in Islamic ornaments.

Wolfgang Neumann is still very active in the fields of crystallography and electron microscopy. He is senior research associate with David Johnsen at University of Oregon in Eugene where he was initially invited to give lectures on crystallography and to help with solving crystallographic problems. It turned out that Wolfgang Neumann could contribute a lot to the topic of ferecrystals. The list of further activities is long and very impressive. Amongst others, Wolfgang Neumann is Editor‐in‐chief of the journal Crystal Research and Technology. He is member of the German Societies for Electron Microscopy and for Crystallography (DGK). In the DGK he was chair of the board from 2006 till 2009, chair of the National Committee for Crystallography from 2003 till 2006, and a consultant of the Commission for Electron Crystallography of the International Union for Crystallography from 2005 till 2011.

For “his fundamental contributions to electron microscopy and electron diffraction of crystalline materials and its application to crystallographic questions” Wolfgang Neumann was awarded with the Carl‐Hermann‐Medal of the DGK in 2017. This medal “is intended to honor the life's work of outstanding scientific researchers in the field of crystallography in the broadest sense”.

As an additional sign for ongoing scientific activity and for pursuing the passion of teaching and transfer of knowledge Wolfgang Neumann and Klaus‐Werner Benz published a textbook on “Introduction to Crystal Growth and Characterization” in 2014. This textbook elegantly connects all the aspects of crystallography. In 2018 the book “Kristalle verändern die Welt” was published, addressing the reader not necessarily being a specialist in materials sciences. Considering a linear timeline of book publication after his retirement in 2010, what should we expect for the year 2022?

Finally, I would like to cite one of the almost famous statements of Wolfgang Neumann. Close to his retirement he said: “I started my career in Berlin Adlershof, at the end I am here again. The only difference is that I moved from one side of the Rudower Chaussee to the other one. Thus, I did not get very far in my scientific career.” In fact after finishing his studies in 1968 Wolfgang Neumann was an aspirant at the Central Institute for Physical Chemistry of the Academy of Sciences in Berlin‐Adlershof. But knowing what happened from 1968 till 2010 (and even after) it is quite easy to disprove this statement. Wolfgang, you got very far indeed and your way is by far not finished yet.

Best wishes to you and your entire family.

2019年10月25日，沃尔夫冈·诺伊曼（Wolfgang Neumann）教授庆祝了他的75岁生日。既然沃尔夫冈·诺伊曼（Wolfgang Neumann）自2010年退休以来已经过去了将近十年，所以这是75周年纪念日对于科学界的大多数人来说可能已经令人惊讶，因为沃尔夫冈·诺伊曼（Wolfgang Neumann）仍然非常活跃并在社区中可见。我认为这是一个好兆头。

追溯到1995年，沃尔夫冈·诺伊曼（Wolfgang Neumann）接到了柏林洪堡大学（HU Berlin）物理系晶体学C4教授职位的号召。沃尔夫冈·诺伊曼（Wolfgang Neumann）当时是哈勒/萨勒（Saale）麦克斯-普朗克研究所（MPI）的科学人员，该研究所以前是海因茨·贝特（Heinz Bethge）教授和约翰内斯·海登雷（Johannes Heydenre）教授领导的电子物理学和电子研究所（IFE）。分别在沃尔夫冈·诺伊曼（Wolfgang Neumann）诞辰65周年和70周年之际发表的Kurt Scheerschmidt和Reinhard Schneider的个人观点非常值得一读，其中包含有关1995年之前时间的许多有趣事实。^[ 1，2 ^]

1995年9月，我在柏林柏林大学获得博士学位。我在Güntersberge/ Harz举行的“界面和晶体缺陷的晶体学”研讨会上第一次亲自见了Wolfgang Neumann。了解H. Bethge和J. Heydenreich所著的《固态物理学中的电子显微镜》一书，沃尔夫冈·诺伊曼（Wolfgang Neumann）知道了这一点，很有趣的是，该研讨会是由沃尔夫冈·诺伊曼（Wolfgang Neumann）作为工作组的发言人（Arbeitskreis）共同组织的。 ）德国晶体学学会的“理论晶体学”。沃尔夫冈·诺伊曼（Wolfgang Neumann）在电子显微镜和晶体学领域都很活跃，这不仅具有许多出色的素质，而且很可能为HU Berlin的教授生涯铺平了道路。

现有小组的研究重点是化合物半导体块状晶体中的缺陷，主要由透射电子显微镜实验室的常任职员兼经理I.Hähnert博士进行。第二个重要的重点是外延生长的半导体层的结构和化学性质。用于研究的透射电子显微镜（TEM）是运行在200 kV的HITACHI H8110，配备了LaB ₆电子源，扫描TEM（STEM）单元和能量分散X射线探测器。TEM安装于1993年，设备齐全，可以解决纳米级的晶体学问题。尤其是，该TEM可以进行完整的相分析，从而提供纳米级物体的晶体结构和化学成分。

当沃尔夫冈·诺伊曼（Wolfgang Neumann）在1996年开始领导晶体学小组时，他立即了解了正在进行的研究的细节。他在将电子显微镜和晶体学方面的综合见解相结合方面的长期经验使他能够迅速取得进展并扩展研究领域。为了进行讨论，我们通常坐在圆桌旁，传统上也进行口试。有传言说这张桌子上已经堆满了几十年的学生汗水。值得注意的是，在沃尔夫冈·诺伊曼（Wolfgang Neumann）在柏林进行矿物学研究期间，这张桌子和其他作品为1960年代威尔·克莱伯（Will Kleber）教授的办公室提供了家具。这是他对前辈成就的尊重的明确标志，这种家具每天都在使用，而不是送到博物馆。在我们的讨论中，沃尔夫冈·诺伊曼（Wolfgang Neumann）可能会跳起来，选择与我们所讨论的主题完全相符的适当专着或原始论文。这种独特的能力是他（其中众多）出色品质中的三个的结果。首先，他的勤奋表现出他阅读论文和书籍的能力，其次，他几乎永远不会忘记任何事情。第三，他拥有出色的内部导航系统，可将其引导至正确的参考点，尽管该参考点被隐藏在令人印象深刻的文书工作中。他几乎永远不会忘记一件事。第三，他拥有出色的内部导航系统，可将其引导至正确的参考点，尽管该参考点被隐藏在令人印象深刻的文书工作中。他几乎永远不会忘记一件事。第三，他拥有出色的内部导航系统，可将其引导至正确的参考点，尽管该参考点被隐藏在令人印象深刻的文书工作中。

由于沃尔夫冈·诺伊曼（Wolfgang Neumann）对小组中正在进行的研究的想法，他找出了至少两个要研究的重要问题。首先是在柏林的科学领域内加强合作，其次是改善现有的TEM仪器。很快就建立了新的研究项目，结果非常成功。特别是与RolfKöhler教授的紧密合作就像是通往柏林范围的合作研究中心SFB296“低维半导体结构的生长相关特性”的大门。此外，与柏林哈恩-迈特纳研究所（Hahn-Meitner-Institut Berlin）一起成功开展了一项针对镍基高温合金的研究项目。关于仪器，Gatan成像滤镜（GIF）已连接到现有显微镜。GIF大大扩展了分析电子显微镜的功能。通过聘用现任公司Reinhard Schneider。卡尔斯鲁厄技术学院教授，​​以其在电子能量损失谱学领域的基础工作而闻名，该小组的专业知识得到了显着提高。

朝着国际知名组织方向迈出的又一个重要步骤是，物理研究所于2003年从柏林市中心迁至柏林科学园区-Adlershof。新的研究所原来是一座非常吸引人的创新建筑，使它成为一种愉悦的环境在其中做科学。为TEM实验室购买了最先进的TEM JEOL 2200FS。它配备齐全，可用于分析电子显微镜的整个光谱，包括能量色散X射线光谱，电子能量损失光谱和原子序数（TEM）STEM成像。作为特殊专业，安装了电子全息双棱镜。结合内置的Lorenz镜头，可以成功表征软磁材料。

这些出色的功能甚至吸引了国际合作，例如在欧洲框架项目PARSEM（基于GaN的半导体结构）中，与来自波兰科学院（半导体纳米线）的SławekKret，与来自伊丽莎白港的纳尔逊·曼德拉大都会大学的Jan Neethling ，南非（电子晶体学），以及美国俄勒冈大学的戴维·约翰森（David Johnsen）（铁晶体）。

沃尔夫冈·诺伊曼（Wolfgang Neumann）活动的另一个方面（我可以说这几乎是一种激情）是电子显微镜秋季学校的组织。悠久的传统可以追溯到1970年代，当时在哈雷/萨勒（Saale）的IFE举办了秋季学校。^[ 2 ^]约翰内斯·海登赖希（Johannes Heydenreich）退休后，沃尔夫冈·诺伊曼（Wolfgang Neumann）成为了秋季学校的剩余动力。从1998年到2002年，学校在MPI Halle和柏林的Fritz-Haber-Institut（FHI）之间交替。关于该组织，2003年秋天学校首次在柏林柏林成立时，距离马克斯·普朗克学会的机构迈出了一大步。邀请了国际知名的科学家向学校的学生讲授电子显微镜领域。范围包括仪器的现代发展，方法的基础及其在材料科学问题中的应用。由于Christoph C. Koch（柏林大学），Michael Lehmann（柏林工业大学）的参与，它可以被视为生日礼物。而马克·威林格（FHI柏林）则是秋季学校的复兴。现在，该组织是在柏林电子显微镜网络的保护下完成的。

秋季学校与教学直接相关。这是沃尔夫冈·诺伊曼（Wolfgang Neumann）出色的技能之一。与晶体学主席自然相关的是关于几何和结构晶体学，晶体物理学和晶体缺陷的讲座。这些讲座得益于整个德国最全面的晶体学教学资源之一。我记得要找出350多种纸板模型中的哪一种是点群的四边形正面体时面临的巨大挑战$\overline{4}$m2，而不是将其与点组422的梯形混合在一起。顺便说一句，我可以说这个教学集合仍在使用中，并且在所谓的“Klötzchenkunde”期间，学生们仍在努力使用木材制成的形态模型。我主持了关于几何结构晶体学的讲座。它的一部分也是没有模型的图层组。在2009年在伊斯坦布尔举行的第25届欧洲晶体学会议上（图1），我们有幸欣赏了苏丹艾哈迈德清真寺，圣索菲亚大教堂和苏丹宫殿的伊斯兰装饰艺术。这是为17个层组中的每个组记录示例的灵感，并在很大程度上取得了成功。特别地，发现了所有正方形层组。有趣的是，没有观察到描述众所周知的人字形图案的p2gg层组。这很可能是由于这样的事实，即墙和地板上瓷砖的方形形状几乎不适合任何其他几何形状。据推测，我们必须去西班牙格拉纳达的阿罕布拉核实伊斯兰装饰品中的所有层组。

沃尔夫冈·诺伊曼（Wolfgang Neumann）在晶体学和电子显微镜领域仍然非常活跃。他是俄勒冈州尤金大学戴维·约翰森（David Johnsen）的高级研究助理，最初应邀他参加了晶体学讲座，并帮助解决晶体学问题。事实证明，沃尔夫冈·诺伊曼（Wolfgang Neumann）可以为铁晶体这一主题做出很大贡献。进一步的活动清单很长，令人印象深刻。其中，沃尔夫冈·诺伊曼（Wolfgang Neumann）是《晶体研究与技术》杂志的主编。。他是德国电子显微镜和晶体学学会（DGK）的成员。在DGK中，他从2006年至2009年担任董事会主席，从2003年至2006年担任国家晶体学委员会主席，并于2005年至2011年担任国际晶体学联盟电子晶体学委员会的顾问。

沃尔夫冈·诺伊曼因其“对晶体材料的电子显微镜和电子衍射及其在晶体学问题中的应用的基础性贡献”，于2017年荣获DGK的卡尔·赫尔曼·梅德尔奖。该勋章“旨在表彰杰出的生命工作晶体学领域的科学研究人员”。

沃尔夫冈·诺伊曼（Wolfgang Neumann）和克劳斯·沃纳·本茨（Klaus-Werner Benz）于2014年出版了一本有关“晶体生长和表征简介”的教科书，这是正在进行的科学活动和追求教学和知识转移热情的又一标志。这本教科书巧妙地将晶体学的各个方面联系在一起。在2018年出版了《 Kristalleveränderndie Welt》一书，该书的读者不一定是材料科学专家。考虑到他于2010年退休后的线性出版时间，我们对2022年的期望是什么？

最后，我想引用沃尔夫冈·诺伊曼（Wolfgang Neumann）几乎是著名的声明之一。在退休后，他说：“我的职业生涯始于柏林阿德勒斯霍夫（Berlin Adlershof），最后我又回到了这里。唯一的区别是我从Rudower Chaussee的一侧移到了另一侧。因此，我的科学生涯并没有走太远。” 实际上，在1968年完成学业后，沃尔夫冈·诺伊曼（Wolfgang Neumann）是位于柏林-阿德勒斯霍夫（Abershof）的科学院中央物理化学研究所的一名志向。但是，知道从1968年到2010年（甚至之后）发生了什么，很容易反驳这一说法。沃尔夫冈，您的确走得很远，您的路还没有结束。

祝您和您的整个家庭幸福。