Video: Till Schürmann. German Video Clip.

Der neue Film des SFB 1083 nimmt den interessierten Laien mit auf eine Reise hinunter zur atomaren Skala und will ihm zeigen, wie die aktuelle Spitzenforschung dort im Bereich der Grenzflächen voranschreitet.

Das 6-minütige Video ist kein anspruchsvoller Lehrfilm, vielmehr wirkt es wie Wissenschafts-Science-Fiction direkt aus dem Kino, mit Kamerafahrten bis in den Nanometerbereich, mit Flügen durch leuchtende Moleküle, mit exotischen Exzitonen und raumfüllenden Laser-Apparaturen. Sehr eindrücklich auch die Musik, eigens für diesen Film wurden „Die Planeten“ von Gustav Holst (1874-1934) neu arrangiert.

Warum Grenzflächen?

„In unserer modernen Welt werden gewaltige Mengen an Daten übertragen,“ erläutert Prof. Ulrich Höfer, der Initiator und derzeitige Sprecher des SFB, „und Jahr für Jahr werden es mehr. Die ständige Miniaturisierung erlaubt uns, diese Datenmenge immer schneller und effizienter zu verarbeiten. Aber je kleiner die Bauteile werden, desto stärker tritt in den Vordergrund, wo auf der atomaren Skala die Information gesteuert wird: Die innere Grenzfläche zwischen zwei Materialien. Wer hier Fortschritte erzielen kann, setzt die Maßstäbe für die Welt von morgen.“

Der Film zeigt, dass Grenzflächen noch ganz andere Chancen bieten: Verbindungen von Elektronik und Organik versprechen völlig neue Möglichkeiten der Informationsverarbeitung, Nanometer-kleine Laser überbrücken immer weitere Strecken, und Solarzellen mit organischen Kristallen könnten unsere Energieversorgung auf ein neues Level heben. Oder mit den Worten von Prof. Stefanie Dehnen von der Uni Marburg: „Man möchte als Wissenschaftler immer Dinge entdecken und weiterentwickeln, die letztlich der Welt helfen können.“

Prof. Michael Dürr aus Gießen erklärt den hohen Anspruch des Film-Projekts: „Wir hatten den Ehrgeiz, die atomaren Prozesse schöner – und auch exakter – darzustellen, als man das bisher in dieser Art gesehen hat. Und dabei immer auch verständlich zu bleiben.“

Realisiert hat den Film der Gießener Filmemacher Till Schürmann. „Es macht ja immer viel Spaß, Wissenschaft so darzustellen, dass man auch die Begeisterung spürt, die die Wissenschaftler haben. Die sitzen ja nicht nur in ihren Laboren, die erleben immer wieder Nervenkitzel, die spüren Faszination und Freude genauso wie wir normalen Menschen“, erzählt er über seine Motivation. „Nur dass die Welt, in der sie sich bewegen, die Apparate, die Ergebnisse, dass die uns als pure Science Fiction erscheinen.“

Science Fiction, die durch die unermüdliche Arbeit der Forscher immer weniger – Fiction sein wird. Und die uns eines Tages vielleicht ganz selbstverständlich umgeben wird.

Was ist ein Sonderforschungsbereich?

Sonderforschungsbereiche sind langfristige Projekte aus der Grundlagenforschung, die von der Deutschen Forschungsgemeinschaft (DFG) aus Mitteln des Bundes und der Ländern gefördert werden.

Prof. Höfer erläutert das Besondere des Marburger Sonderforschungsbereichs 1083: “Das Verständnis innerer Grenzflächen gilt schon seit vielen Jahren als eines der Gebiete der Festkörperphysik mit dem drängendsten Forschungsbedarf. So sagte Herbert Kroemer bereits im Jahr 2000 bei seiner Nobelpreis-Vorlesung: ‘Die Grenzfläche ist das Bauteil’. Unser SFB überträgt dazu Methoden der Oberflächenphysik und Oberflächenchemie auf die Untersuchung von Grenzflächen. Durch diesen Ansatz und die Fokussierung auf Modellsysteme, die auf der atomaren Skala gut charakterisiert sind, haben wir uns als Verbund ein Alleinstellungsmerkmal erarbeitet. Aber auch bei der Entwicklung und Weiterentwickelten optischer Spektroskopien sind wir weltweit ganz vorne mit dabei.

Neben der Uni Marburg sind im SFB 1083 „Struktur und Dynamik innerer Grenzflächen“ noch die Uni Gießen, das Forschungszentrum Jülich und die Uni Münster mit an Bord. Insgesamt arbeiten hier 80 Wissenschaftler aus den unterschiedlichsten Disziplinen zusammen. Die jährlichen DFG-Fördergelder belaufen sich auf etwa 2.5 Millionen Euro.

„Der Film zeigt natürlich nur einen winzigen Ausschnitt unserer Aktivitäten“, sagt Höfer. „Bei insgesamt 18 Teilprojekten und 24 Professoren haben Sie eine ungeheure Bandbreite an Interessen und individuellen Forschungsschwerpunkten. Aber durch die Fokussierung auf die Grenzfläche erleben wir hier auch eine gewaltige gegenseitige Inspiration. So etwas ist eben nur durch einen Sonderforschungsbereich möglich, durch die langfristige Orientierung des gesamten Projekts.“

Video

Kontakt

In their study published in Nature Communications, the authors from three SFB-projects with expertise in interface chemistry, organometallic synthesis, and theoretical chemistry, jointly publish their research into template-controlled interfacial synthesis of unprecedented extended phthalocyanine dyes.

Interfacial template approach: control over the topology of the reaction products is achieved by using differently-sized metal templates in 2D confinement. (after publication-Fig. 1) Copyright by CC-BY 4.0.

Phthalocyanines possess unique optical and electronic properties and thus are widely used in (opto)electronic devices, coatings, photodynamic therapy, etc. Extending the π-conjugation of phthalocyanine dyes, while synthetically challenging, has the potential to produce desirable new molecular materials.

Here, Dr. Qitang Fan and coworkers use a templated interface approach to synthesize several extended phthalocyanine derivatives from the same building block, including an unprecedented lanthanide superphthalocyanine and an open-chain polycyanine (fig. left). The former represents the first superphthalocyanine without uranium center, while the latter provides an intriguing model for an organic semiconducting polymer with an absorption band in the visible range. Detailed study of these new materials by scanning tunneling microscopy, photoemission spectroscopy, and density functional theory calculations (fig. below), reveal their chemical structure and mechanical as well as electronic properties.

Orbitals: Lowest unoccupied molecular orbitals of Fe-NPc and Gd-SNPc, lowest unoccupied crystal orbital of polycyanine, from density-functional theory calculation. Copyright by CC-BY 4.0. 

See also natureresearch’s “Behind The Paper”-contribution by Michael Gottfried on “Synthesis in flatland: rings and chains grown on surfaces”.

Publication

Q. Fan, J.-N. Luy, M. Liebold, K. Greulich, M. Zugermeier, J. Sundermeyer, R. Tonner, J.M. Gottfried, Template‐controlled on‐surface synthesis of a lanthanide supernaphthalocyanine and its open‐chain polycyanine counterpart, Nature Commun. 10 (2019) 5049 DOI:s41467-019-13030-7

In their study published in Nanoscale Horizons, Maximilan Dreher, Dayeon Kang, Tobias Breuer and Gregor Witte introduce and validate a new concept to suppress the defect-driven fiber nucleation at surface steps by selective blocking of the active step sites using small molecules, so that the formation of crystalline, organic fibers is only governed by the intrinsic epitaxial growth on ideal, defect-free surface regions.

DNTT fiber structures grown on Ag(111) substrates without (left) and with (right) pre-exposition of oxygen to the surface. The oxygen suppresses the DNTT molecules to adsorb at the step edges, which leads to straight, elongated and epitaxially aligned fibers. (Image: M. Dreher). Reproduced with permission from the Royal Society of Chemistry.

Due to their anisotropic optoelectronic properties, crystalline organic fibers constitute an interesting class of nanoscale materials with great potential for integration into future optoelectronic devices based on organic-inorganic hybrid systems. While chemical synthesis allows for flexible tailoring of electronic molecular properties, well-established structuring methods such as, e.g. lithography are hardly applicable to most molecular materials. Therefore, self-organization is an important alternative route for structuring molecular materials especially for organic/inorganic hybrid architectures. While molecular materials often form crystalline fibers, their length and orientation is, however, limited by surface defects such as steps of the supports that cannot be prevented even on very perfect, single crystalline substrates, hence drastically restricting their use in device applications.

In their study the authors analyzed the influence of surface step edges on the initial growth of fibers for the case of the high performing organic semi¬conductor dinaphthothienothiophene (DNTT) and developed a new concept to suppress the defect–driven fiber nucleation. Based on a comparison of the organic film growth on densely packed, flat noble metal surfaces and on a regularly stepped, vicinal surface, they first showed how substrate steps affect the azimuthal molecular orientation in the seed layer and also the subsequent fiber formation. In a next step they demonstrate that this parasitical step-induced fiber nucleation that occurs also on densely packed Ag(111) surfaces can be suppressed by first exposing the metal support to oxygen, or even briefly to ambient condition, which causes a selective saturation of the active step sites. They show that this not only leads to an exclusive growth of epitaxial DNTT fibers but also strongly increases the fiber size to several hundreds of microns. This novel approach is quite versatile and allows a distinct improvement of template assisted growth and thereby the quality of organic/inorganic hybrids.

Publication

M. Dreher, D. Kang, T. Breuer and G. Witte,
Growth of extended DNTT fibers on metal substrates by suppression of step-induced nucleation
Nanoscale Horizons (2019) DOI:10.1039/C9NH00422J

Poster Award
The paper’s first author Maximilian Dreher is currently a Master’s student within SFB-project A2. We congratulate him on receiving the prize for his poster on the above research which he presented at the Cecam Workshop on “Fabrication processes and molecular organization in organic thin films: Theory and simulation meet experiments” held in Lecco, Italy from July 17-20, 2019.

Congratulations to Dr. Johannes Reimann, doctoral student in SFB-project B6 (Höfer), for being awarded a prize by Philipps- Universität Marburg for his excellent dissertation presented in 2018.

In his thesis entitled “Charge carried dynamics and photocurrents in the Dirac cone of topological insulators” Johannes Reimann investigated a novel class of materials, topological insulators. These materials, discovered only a decade ago, are insulating in the volume, but conductive at their surfaces and at their interfaces with conventional materials.

In the framework of his thesis, Johannes Reimann advanced the development of time- and angle-resolved photoelectron spectroscopy within the group of Prof. Höfer. In particular, his work is the first to combine this powerful technique with Terahertz excitation and to achieve subcycle time resolution. In collaboration with the group of Prof. Rupert Huber in Regensburg, he succeeded in taking band structure movies of electrical currents carried by Dirac electrons as they are driven by an intense THz wave. First results were published in Nature in September 2018 (see also SFB news, university press release.

The results of Johannes Reimann’s work hold great promise to realize new lightwave-driven electronics, a concept to increase the clock rates of conventional semiconductor devices by a factor of 1000 and more. Moreover, the successful demonstration of the combination of intense THz pulses as pump and angle-resolved photoelectron spectroscopy (ARPES) as probe, has triggered worldwide experimental efforts to take advantage of THz-APRES for time-resolved investigation of a variety of solids, surfaces and interfaces.

See here for details of the event.

In their review paper, Andreas Beyer and Kerstin Volz describe in detail their investigation of novel composite materials, which may eventually replace today’s silicon-based electronic devices. As the latter increasingly reach their performance limit, one option to overcome these largely physics-based limitations is to cover silicon with a different material layer.

Experimentally measured and simulated structure of the galliumphospide/silicon-interface at atomic resolution. Electron diffraction patterns allow to determine the interfacial charge distribution.

However, covering silicon with different material layers like, for example, well-suited III/V semiconductors (containing elements of the 3^rd and 5^th group of the periodic system) is challenging. In joining different materials with their individual physico-chemical properties their interface may be marked by defects. Here, for example, “erroneous” attachments may lead to unwished-for local charges – rendering the combined material as unsuitable for application in devices.

The group of Kerstin Volz closely studied galliumphosphide on silicon as a model system of III/V semiconductors on silicon. In their invited review the authors now describe the various electron-microscopy-based approaches employed in the study of the internal interface between the two materials and its defects. By means of transmission-electron-microscopy the researchers were able to show that the interface between the two materials is far from smooth; in fact, it more resembles a pyramidal structure affecting several atomic layers. In addition, it was also possible to “see” the erroneous atomic attachments which cause the unwished-for charge effect and link the phenomenon directly to changes in preparatory procedures.

The insights gained will be applied to perfecting preparation methods in order to reduce the number of defects and to fine-tuning the interface with a focus on raising the efficiency of existing devices and encouraging the development of novel applications.

Publication

A. Beyer and K. Volz,
Quantitative Electron Microscopy for III/V on Silicon Integration
Adv. Mater. Interfaces (2019) DOI: 10.1002/admi.201801951