Lackinger M.,Deutsches Museum |
Lackinger M.,TU Munich
Chemical Communications | Year: 2017
Surface-assisted Ullmann coupling is the workhorse of on-surfaces synthesis. Among the various couplings that were successfully transferred from solution to solid surfaces, Ullmann coupling is arguably the most reliable, controllable, and widespread coupling reaction. The basic reaction scheme is straightforward: halogenated precursors are deposited onto solid surfaces, normally of coinage metals. In the adsorbed state the halogen substitutents are split off by virtue of the surface's reactivity, thereby generating acitvated species that subsequently recombine by forming C-C bonds. Ullmann coupling is well suited for reticular synthesis of novel organic nanostructures: ideally, the halogen substitution pattern of the precursor-which becomes the monomer upon dehalogenation-predetermines dimensionality and topology of the covalent nanostructures. Also in many relevant systems, side-reactions do not occur. However, in reality topological defects, competing C-H activation on more reactive surfaces, and reaction intermediates render this seemingly simple coupling reaction not only more complex, but also more interesting for fundamental research. This feature article aims to provide an account of the vast amount of already published work and tries to destill important findings and currents trends in surface-assisted Ullmann coupling. © 2017 The Royal Society of Chemistry.
Joas C.,Ludwig Maximilians University of Munich |
Eckert M.,Deutsches Museum
Annual Review of Condensed Matter Physics | Year: 2017
Arnold Sommerfeld (1868-1951), one of the founders of modern theoretical physics and a pioneer of quantum theory, was no condensed matter physicist. He nevertheless played a crucial role for the history of the field. Besides his important contributions to the study of condensed matter systems, among which his seminal electron gas theory of metallic conduction probably stands out, he influenced the field through his very approach to science, through his way of "doing" physics. Sommerfeld's specific style permeated not only his research but also his teaching and his promoting of physics. This has had a lasting influence on the practices of physicists to this day, and not only, but importantly, on those of condensed matter physicists. This article aims to provide a concise account of Sommerfeld's influence on the study of condensed matter systems, with regard to both his research and his practice. © 2017 by Annual Reviews. All rights reserved.
Eckert M.,Deutsches Museum
European Physical Journal H | Year: 2010
More than a hundred years ago William McFadden Orr and Arnold Sommerfeld conceived an approach to account for the transition from laminar to turbulent flow in terms of hydrodynamic stability theory. But the "turbulence problem", as this challenge became notoriously famous, could not be solved by this method. By 1920, it was widely recognized as an outstanding riddle. Although famous theoretical physicists like Werner Heisenberg dedicated a considerable effort to this problem, the "Orr-Sommerfeld method" has never found the attention of historians of science. This article describes its early perception and development in Germany, and how the "turbulence problem" reached center stage after the First World war as a major challenge for theorists with different perspectives. © EDP Sciences, Springer-Verlag 2010.
Eckert M.,Deutsches Museum
Acta Crystallographica Section A: Foundations of Crystallography | Year: 2012
The discovery of X-ray diffraction is reviewed from the perspective of the contemporary knowledge in 1912 about the nature of X-rays. Laues inspiration that led to the experiments by Friedrich and Knipping in Sommerfelds institute was based on erroneous expectations. The ensuing discoveries of the Braggs clarified the phenomenon (although they, too, emerged from dubious assumptions about the nature of X-rays). The early misapprehensions had no impact on the Nobel Prizes to Laue in 1914 and the Braggs in 1915; but when the prizes were finally awarded after the war, the circumstances of Laues discovery gave rise to repercussions. Many years later, they resulted in a dispute about the myths of origins of the community of crystallographers.
Buhler D.,Deutsches Museum
Proceedings of the ICE - Engineering History and Heritage | Year: 2016
Throughout history, civil engineers have created many admirable and long-lasting works that may rightly be considered a treasury of the merits and monumental highlights of their profession. Few of these buildings and constructions are regarded by official national, international and professional associations as deserving protection. The most important cornerstone for the protection of monuments is their identification, appreciation and eventual inscription in protection programmes such as the World Heritage List. The fact that few monuments have made it onto the list is not due to any lack of constructions that merit the civil engineering profession’s esteem, but reflects instead how little promotion engineering achievements receive. This paper focuses on the monuments of civil engineering that have been declared World Heritage Sites by the UN Educational, Scientific and Cultural Organization and outlines possible candidates deemed worthy of protection. © 2016, Thomas Telford Services Ltd. All rights reserved.
Walch H.,Ludwig Maximilians University of Munich |
Gutzler R.,Ludwig Maximilians University of Munich |
Sirtl T.,Ludwig Maximilians University of Munich |
Eder G.,Ludwig Maximilians University of Munich |
Lackinger M.,Deutsches Museum
Journal of Physical Chemistry C | Year: 2010
Adsorption of the brominated aromatic molecule 1,3,5-tris(4-bromophenyl) benzene on different metallic substrates, namely Cu(111), Ag(111), and Ag(110), has been studied by variable-temperature scanning tunneling microscopy (STM). Depending on substrate temperature, material, and crystallographic orientation, a surface-catalyzed dehalogenation reaction is observed. Deposition onto the catalytically more active substrates Cu(111) and Ag(110) held at room temperature leads to cleavage of carbon-bromine bonds and subsequent formation of protopolymers, i.e., radical metal coordination complexes and networks. However, upon deposition on Ag(111) no such reaction has been observed. Instead, various self-assembled ordered structures emerged, all based on intact molecules. Also sublimation onto either substrate held at ∼80 K did not result in any dehalogenation, thereby exemplifying the necessity of thermal activation. The observed differences in catalytic activity are explained by a combination of electronic and geometric effects. A mechanism is proposed, where initial charge transfer from substrate to adsorbate, followed by subsequent intramolecular charge transfer, facilitates C-Br bond homolysis. © 2010 American Chemical Society.
Eckert M.,Deutsches Museum
Studies in History and Philosophy of Science Part B - Studies in History and Philosophy of Modern Physics | Year: 2015
The radiation that is due to the braking of charged particles has been in the focus of theoretical physics since the discovery of X-rays by the end of the 19th century. The impact of cathode rays in the anti-cathode of an X-ray tube that resulted in the production of X-rays led to the view that X-rays are aether impulses spreading from the site of the impact. In 1909, Arnold Sommerfeld calculated from Maxwell[U+05F3]s equations the angular distribution of electromagnetic radiation due to the braking of electrons. He thereby coined the notion of "Bremsstrahlen." In 1923, Hendrik A. Kramers provided a quantum theoretical explanation of this process by means of Bohr[U+05F3]s correspondence principle. With the advent of quantum mechanics the theory of bremsstrahlung became a target of opportunity for theorists like Yoshikatsu Sugiura, Robert Oppenheimer, and-again-Sommerfeld, who presented in 1931 a comprehensive treatise on this subject. Throughout the 1930s, Sommerfeld[U+05F3]s disciples in Munich and elsewhere extended and improved the bremsstrahlen theory. Hans Bethe and Walter Heitler, in particular, in 1934 presented a theory that was later regarded as "the most important achievement of QED in the 1930s" (Freeman Dyson). From a historical perspective the bremsstrahlen problem may be regarded as a probe for the evolution of theories in response to revolutionary changes in the underlying principles. © 2015 Elsevier Ltd.
Eckerta M.,Deutsches Museum
European Physical Journal H | Year: 2014
Sommerfeld's extension of Bohr's atomic model was motivated by the quest for a theory of the Zeeman and Stark effects. The crucial idea was that a spectral line is made up of coinciding frequencies which are decomposed in an applied field. In October 1914 Johannes Stark had published the results of his experimental investigation on the splitting of spectral lines in hydrogen (Balmer lines) in electric fields, which showed that the frequency of each Balmer line becomes decomposed into a multiplet of frequencies. The number of lines in such a decomposition grows with the index of the line in the Balmer series. Sommerfeld concluded from this observation that the quantization in Bohr's model had to be altered in order to allow for such decompositions. He outlined this idea in a lecture in winter 1914/15, but did not publish it. The First World War further delayed its elaboration. When Bohr published new results in autumn 1915, Sommerfeld finally developed his theory in a provisional form in two memoirs which he presented in December 1915 and January 1916 to the Bavarian Academy of Science. In July 1916 he published the refined version in the Annalen der Physik. The focus here is on the preliminary Academy memoirs whose rudimentary form is better suited for a historical approach to Sommerfeld's atomic theory than the finished Annalen-paper. This introductory essay reconstructs the historical context (mainly based on Sommerfeld's correspondence). It will become clear that the extension of Bohr's model did not emerge in a singular stroke of genius but resulted from an evolving process. © EDP Sciences, Springer-Verlag 2014.
Song W.,Deutsches Museum |
Song W.,TU Munich |
Martsinovich N.,University of Warwick |
Heckl W.M.,Deutsches Museum |
And 3 more authors.
Journal of the American Chemical Society | Year: 2013
The driving force for self-assembly is the associated gain in free energy with decisive contributions from both enthalpy and entropy differences between final and initial state. For monolayer self-assembly at the liquid-solid interface, solute molecules are initially dissolved in the liquid phase and then become incorporated into an adsorbed monolayer. In this work, we present an adapted Born-Haber cycle for obtaining precise enthalpy values for self-assembly at the liquid-solid interface, a key ingredient for a profound thermodynamic understanding of this process. By choosing terephthalic acid as a model system, it is demonstrated that all required enthalpy differences between well-defined reference states can be independently and consistently assessed by both experimental and theoretical methods, giving in the end a reliable value of the overall enthalpy gain for self-assembly of interfacial monolayers. A quantitative comparison of enthalpy gain and entropy cost reveals essential contributions from solvation and dewetting, which lower the entropic cost and render monolayer self-assembly a thermodynamically favored process. © 2013 American Chemical Society.
Eckert M.,Deutsches Museum
Annual Review of Fluid Mechanics | Year: 2015
Sommerfeld's affiliation with fluid mechanics started when he began his career as an assistant of the mathematician Felix Klein at Göttingen. He always regarded fluid mechanics as a particular challenge. In 1904, he published a theory of hydrodynamic lubrication. Four years later, he conceived an approach for the analysis of flow instability (the Orr-Sommerfeld approach) as an attempt to account for the transition from laminar to turbulent flow. The onset of turbulence also became a major challenge for some of his pupils, in particular Ludwig Hopf and Fritz Noether. Both contributed considerably to elaborate the Orr-Sommerfeld theory. Heisenberg's doctoral work was another attempt in this quest. When Sommerfeld published his lectures on theoretical physics during World War II, he dedicated one of the six volumes to the mechanics of continuous media. With chapters on boundary layer theory and turbulence, it exceeded the scope of contemporary theoretical physics-revealing Sommerfeld's persistent appreciation of fluid mechanics. He resorted to Prandtl's Göttingen school of fluid mechanics in order to stay abreast of the rapid development of these specialties. Copyright © 2015 by Annual Reviews. All rights reserved.