Ulrich Höfer is Plenary Speaker at DPG Spring Meeting, 2020

SFB 1083 spokesman Ulrich Höfer to give a plenary talk at the Annual Spring Meeting of the German Physical Society (DPG) in Dresden.

Ulrich Höfer, from the Department of Physics at Philipps-Universität Marburg, was invited by the Condensed Matter Section of the German Physical Society to give a plenary talk at this year’s Annual Spring Meeting of the German Physical Society (DPG) in Dresden March 15th-20th 2020. The title of his talk will be “THz-ARPES band structure movies of Dirac surface currents”.

The DPG-spring meeting in Dresden is Europe’s largest physics congress with more than 6000 participants in the past years.

Interfacial synthesis of novel phthalocyanine dyes – Publication by A4 (Gottfried), A6 (Tonner) & A7 (Sundermeyer)

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)

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.

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) 5049DOI:s41467-019-13030-7

Contact

Prof. Dr. Michael Gottfried
Philipps-Universität Marburg
SFB 1083 project A4
Tel.: 06421 28 22541
EMAIL

Metal chalcogenide clusters on doped TMDC-layers – Publication by A9 (Dehnen) & A6 (Tonner)

In their study published in the Journal of the American Chemical Society, Eike Dornsiepen, Fabian Pieck, Ralf Tonner, and Stefanie Dehnen report on the synthesis of molecular model systems for the up to now unknown adsorption of organotin chalcogenide cluster molecules on TMDC surfaces. Computational studies reveal similar covalent bonding interactions for the model system as well as for the adsorption on a TMDC surface.

Transition metal dichalcogenides (TMDCs) like MoS2 or WS2 have gained large interest for their potential in electronic applications. Combinations with other 2D materials in heterostructures have already been demonstrated as useful in various devices, such as tunneling transistors or solar cells. Hybrid systems combining 2D materials with layers of adsorbed molecules have proven to be interesting for optoelectronic applications, as they allow for tailoring of electronic properties and high photoabsorption of molecular materials. In most of these studies, the adsorbed molecules were organic molecules like pentacene or coordination compounds like phthalocyanines, which interacted with the surface by means of dispersion interactions. The interaction of larger organometallic systems with TMDCs, however, has not yet been studied. This is in part due to the fact that the chemisorption of molecules on TMDC surfaces is relatively weak, hence adsorbents tend to move randomly around.

With the aim to mimic the yet unknown covalent deposition of metal chalcogenide clusters on transition metal dichalcogenide MoS2 or WS2 layers, and thereby explore the interaction between the two systems and potential consequences for the physical properties of the TMDC material, the authors synthesized heterobimetallic model systems. The heterocubane-type cluster [(SnCl3) WCp)3S4], the organotin-sulfidomolybdate cluster [{(PhSn)3SnS6}{(MoCp)3S4}], and the corresponding tungstate [(PhSn)3SnS6{(WCp)3S4}] were obtained in ligand exchange reactions from [(PhSn)4S6] and [M(CO)3CpCl] (with M = Mo, W). Indeed, the {M3S4} cages in the three compounds resemble a section of the respective TMDC monolayers, altogether representing minimal molecular model systems for the adsorption of organotin sulfide clusters on MoS2 or WS2. The interaction between the {(MCp)3S4} and {(PhSn)3SnS6} subunits is characterized by multicenter bonding, rendering the respective Sn atom as Sn(II), hence driving the clusters into a mixed-valence Sn(IV)/Sn(II) situation, and the M atoms as M(IV) upon an in situ redox process. The attachment is thus weaker than via regular covalent M-S bonds, but definitely stronger than via van der Waals interactions that have been characteristic for all known interactions of clusters on TMDC surfaces so far. Calculations of a periodic model system that simulates the attachment of the {(PhSn3S6} fragment to MS2 surfaces reveal striking similarities in structure and bonding situation, given the MS2 surfaces are doped with titanium or other electron-poor metal atoms. This renders the new compounds as relevant molecular models for covalent attachment of larger organometallic systems on TMDCs.

Publication

E. Dornsiepen, F. Pieck, R. Tonner, S. Dehnen, [{(PhSn)3SnS6}{(MCp)3S4}] (M = W, Mo): minimal molecular models of the covalent attachment of metal chalcogenide clusters on doped transition metal dichalcogenide layers, J. Am. Chem Soc. (2019) DOI: 10.1021/jacs.9b09209

Contact

Prof. Dr. Stefanie Dehnen
Philipps-Universität Marburg
SFB 1083 project A9
Tel.: 06421 28 25751
EMAIL

Growth of extended DNTT fibers on metal substrates by suppression of step-induced nucleation – Publication by A2 (Witte)

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, rf. Dreher et al. (2019) in Nanoscale Horizons).

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.

Contact

Prof. Dr. Gregor Witte
Philipps-Universität Marburg
SFB 1083 project A2
Tel.: 06421 28 21384
EMAIL

Lisa Pecher awarded dissertation prize of Philipps-Universität Marburg

Congratulations to Dr. Lisa Pecher, former PhD-student of the SFB in the Tonner group (Project A6), for being awarded the Kurt-Dehnicke prize of the Department of Chemistry for her outstanding PhD thesis finalized in 2017.

Semiconductor surfaces are the basis for microtechnology and major applications like photovoltaics. Improving their efficiency and applicability toward future demands on materials requires functionalization with suitable molecules. Fundamental research can help here to understand the interaction between molecules and surfaces.

Lisa Pecher brought significant progress to the understanding of how organic molecules interact with semiconductor surfaces. In her thesis titled “Adsorption Dynamics and Bonding Analysis of Organic Molecules on Silicon(001) Surfaces” – funded and supported by SFB 1083 – she combined static and dynamic quantum-chemical methods with insightful qualitative and quantitative analysis of the electronic structure in extended systems to provide a unique view on the interaction between adsorbates and surfaces. She developed new, efficient approaches to tackle the complex interplay of atomic and electronic effects that need to be treated accurately to derive new insights. Inspired by chemical bonding concepts successfully used in molecular chemistry, she revealed surprising parallels in the realm of surface chemistry. For example, she pointed out for the first time that a well-known reaction mechanism for organic chemistry –second-order nucleophilic substitution – can be found in the reaction of ether molecules with silicon surfaces. This was the key insight explaining the product distribution and published in the chemistry flagship journal Angewandte Chemie (link).

In a further step towards actual device applications, the authors then transferred their findings and the developed preparation protocols to polycrystalline electrodes, demonstrating that the same work function changes can be observed also on “real-life” electrodes. With the end user in mind, the team also tested the air stability of their contact primers, proving that a sacrificial phthalocyanine multilayer serves well to protect the highly ordered mono- and bilayer contact primers during air transfer and can be removed by thermal desorption afterwards.

This was just one of nine publications in major scientific journals – all of them as first author, two of them highlighted on the cover pages. She summarized these impressive scientific results in a review article which was highlighted by science writers and bloggers worldwide (see the SFB news item for more details).

More coverage of the prize-giving event is found here (in German).

Johannes Reimann awarded dissertation prize of Philipps-Universität Marburg

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.

Novel single-atom sensitive imaging – Publication in Nature Materials by A12 (Tautz)

The team of researchers from Jülich, supported by SFB 1083 together with external partners, has developed a new method to measure the electric potentials of a sample with atomic accuracy. Using conventional methods, it was virtually impossible until now to quantitatively record the electric potentials that occur in the immediate vicinity of individual molecules or atoms. The new scanning quantum dot microscopy method, presented in the journal Nature Materials, also opens new ways of characterizing internal interfaces, as they often involve charge transfer and therefore show unique signatures in their electric potential.

Image from a scanning tunnelling microscope (STM, left) and a scanning quantum dot microscope (SQDM, right). Using a scanning tunnelling microscope, the physical structure of a surface can be measured on the atomic level. Quantum dot microscopy can visualize the electric potentials on the surface at a similar level of detail – a perfect combination. (Copyright: FZ Jülich, Christian Wagner)

The positive atomic nuclei and negative electrons of which all matter consists, produce electric potential fields that superpose and compensate each other, even over very short distances. Conventional methods do not permit quantitative measurements of these microscopic fields, which are responsible for many material and interface properties and functions at the nanoscale. Almost all established methods capable of imaging such potentials are based on the measurement of forces that are caused by electric charges. Yet these forces are difficult to distinguish from other forces that occur on the nanoscale, which prevents quantitative measurements.

Four years ago, however, the scientists from Forschungszentrum Jülich discovered a method based on a completely different principle. Scanning quantum dot microscopy involves attaching a single organic molecule – the “quantum dot” – to the tip of an atomic force microscope. The molecule is so small that individual electrons from the tip of the atomic force microscope can be attached to the molecule in a controlled manner. With the new method it is not only possible to visualize the electric fields of individual atoms and molecules, it is also possible to quantify them precisely.

Finally, scanning quantum dot microscopy is particularly well-suited to study internal interfaces. This is illustrated, e.g., by its ability to clearly resolve sub-surface defects, as the team around Stefan Tautz has already demonstrated. For such investigations, the long-range nature of electrostatic potentials is an asset.

Publication

C. Wagner, M.F.B. Green, M. Maiworm, P. Leinen, T. Esat, N. Ferri, N. Friedrich, R. Findeisen, A. Tkatchenko, R. Temirov, and F.S. Tautz, Quantitative imaging of electric surface potentials with single-atom sensitivity, Nature Materials (2019) DOI: 10.1038/s41563-019-0382-8

See also read-only access and German press release by FZ Jülich, as well as Nature Materials News & Views.

Contact

Prof. Dr. Stefan Tautz
Forschungszentrum Jülich
Peter Grünberg Institut
SFB 1083 project A12
Tel.: 02461 61 4561
EMAIL

Smaller, faster, more efficient? – Review by A5 (Volz)

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 3rd and 5th 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

Contact

Prof. Dr. Kerstin Volz
Philipps-Universität Marburg
SFB 1083 project A5
Tel.: 06421 28 22297
EMAIL

PI Seminar 2019 in Oberheimbach

As the first half of SFB 1083’s second funding period comes to a close it was time for its principal investigators to get together to discuss in depth their individual project’s progress and how interdisciplinary research and discussion across projects are developing.

The secluded setting in Oberheimbach provided the right framework for ample conversation in changing smaller and bigger groups and discussion of possible new research agendas for the third funding period of SFB 1083.

For details of the program please follow the link.

SFB 1083 in partnership with Chemikum Marburg supports Girls’ Day 2019

SFB 1083’s Ö-project closely cooperates with Chemikum Marburg e.V. by installing at its premises several new experiments and workshops providing hands-on insights into the SFB’s research objective and the study methods employed. In 2019, for a second time, the partnership supported Girls’ Day activities with dedicated offerings.

Girls’ Day 2019 with its 50 young (agegroup 10-16) female participants benefitted from these offerings, which included the application of acid-base-reactions, measuring thermal signatures of chemical reactions and electrical conductivity in various substances. The experiments provide insight into the central research aspect of SFB 1083: “What are the reactions taking place at the interface, that is the contact between two materials?”

“Girls’ Day allows us to showcase how researchers work. In interesting experiments and workshops we can entice enthusiasm for MINT-disciplines in female pupils”, state Prof. Stefanie Dehnen and Dr. Christof Wegscheid-Gerlach, director and co-director of Chemikum Marburg and principal investigators of SFB 1083’s Ö-project.

A special informatics-focused workshop, in cooperation with Michael Szabo (Fachdidaktik Informatik PUM/MLS), showcased how disciplines work together and how modern research needs detailed programming for optimal analytical results. The SFB’s Atomic Force Microscope (AFM), for example, needs a complex range of operational programming to realize its full potential. This was demonstrated using the Lego-model and it rapidly became obvious to the riveted audience how programming controls the instrument’s operation. 18 girls were then guided in developing their own little programs using the language scratch. At the end of the 3-hour workshop the young participants had all succeeded in letting their “dog run around the lake” and teasing out the impact of minor changes to their code.

See also a press release in German.

Contact

Dr. Christof Wegscheid-Gerlach
Chemikum Marburg
SFB 1083 project Ö
Tel.: 06421 28 25252
EMAIL

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