Prof. Dr. Volker Presser

INM - Leibniz-Institut für Neue Materialien gGmbH
Saarland University, Germany

21.06.2024,      
N 007, Eißendorfer Straße 40, TUHH

Prof. Dr. Linnea Hesse

Wood Physics
Institute of Wood Science,
University of Hamburg, Germany

08.05.2024, 17.00h      
K0506, Denickestraße 15, TUHH
pdf Version

3D imaging in plant biomimetics: Drawing inspiration from plants for a technical transfer

Plants are multiscale living material systems that generate diverse functions through a finely tuned passive and actively adaptable and controllable interaction with water. I will present examples of how targeted water flow and optimized fiber composite design in plants provide solutions for technical material systems and move architecture.

Jun.-Prof. Dr. Jens Bauer

Nanoarchitected Metamaterials Laboratory,
Institute of Nanotechnology,
Karlsruhe Institute of Technology (KIT), Germany

26.04.2024, 10.00h      
K0506, Denickestraße 15, TUHH
pdf Version

Nanoprinted Materials & Metamaterials

One- and two-dimensional nanoscale objects, such as nanowires and thin films, can possess exceptional physical properties. However, these characteristics are intrinsically coupled to their small size and generally challenging to harness in conventional monolithic solids. Metamaterials go beyond classical material design approaches and are structured from building blocks with rationally designed spatial architectures, such as lattice-trusses. Rather than the used base material, these architectures grant metamaterials many conventionally inaccessible properties. High-resolution 3Dprinting techniques, such as 2-photon polymerization (2PP) facilitate the miniaturization of metamaterial architectures down to the nanometer-scale. In addition to topological characteristics, this nanoarchitecture enables metamaterials to harness and tailor strong material size-effects in their constituent solids, such as extreme mechanical strength, with the perspective to exploit such beneficial nano-properties in volumetric materials. This talk focuses on our recent progress in the development of novel additive manufacturing routes to synthesize micro- and nanostructures, including metamaterials, from technologically relevant inorganic materials. Nanoarchitected metamaterials from such are presented and their design, characterization, and mechanical properties are discussed.

Dr. Alexander Schlaich

Multiscale Materials Modeling
University of Stuttgart, Germany

18.04.2024, 17.00h      
M 0526, Eißendorfer Straße 42, TUHH
pdf Version

Humidity-dependent water structure and dynamics in compliant porous materials

The structure and dynamics of fluids - and especially water - at interfaces remains puzzling in many aspects. Simulations and theoretical models yield microscopic insights where experimental information is scare. In this talk I will report on our recent work on the dynamics of soil salinization, a multi-scale problem where atomistic details govern the field-scale behavior. In detail, we showed that the water dynamics can be fully explained by combining classical statistical mechanics models and continuum hydrodynamics [1]. The porous salt leads to a strong reduction of the water dynamics which can be probed by combined experimental/theoretical analysis of the dipolar NMR relaxation [2]. However, the length- and time-scales that are accessible atomistically typically prohibit a full characterization of the system, thus coarse-graining approaches are necessary and microscopic details need to be reconstructed to determine the desired observables [3]. Moreover, the impact of the compliance of nano-porous materials on the swelling and water transport properties is currently gaining significant interest. We have observed that the water structure in such materials strongly impacts the macroscopic permeance [4]. We derive a consistent link between the latter and the microscopic dynamics that can be probed e.g. by quasi-elastic coherent neutron scattering.

References

[1] Gravelle, Holm & Schlaich, J. Chem. Phys. 157, 104702 (2022).
[2] Gravelle, Haber-Pohlmeier, Mattea, Stapf, Holm & Schlaich, Langmuir 39, 7548–7556 (2023).
[3] Gravelle, Beyer, Brito, Schlaich, & Holm, J. Phys. Chem. B 127, 5601–5608 (2023).
[4] Schlaich, Plazanet, Vandamme & Coasne, arXiv:2403.19812 (2024)

Prof. Dr. Dr.h.c. Peter Fratzl

Max Planck Institute of Colloids and Interfaces,
Potsdam, Germany

10.04.2024, 17.00h      
K0506, Denickestraße 15, TUHH
pdf Version

Force and shape generation in biological extracellular matrix by water-driven contractility

Molecular-scale contractility plays an essential role in shape-forming as well as for the motility of biological tissues. This is true in plants where osmotic pressure actuates leaves and controls cell growth. But even in dead plant tissue, such as seed dispersal systems, humidity uptake from air results in volume changes of the cell walls and, thereby, in force generation and actuation. Molecular motors, such as myosin coupled to actin filaments, generate contractile forces in animal tissues and help generating complex shapes in growing tissues. But other molecular systems, such as collagen fibrils, generate contractile stress when subjected to osmotic pressure or to mineralization that is known to replace water in these fibrils. The talk reviews some recent work on how the chemical potential of water is converted into molecular-scale contractility in biological tissues.

Prof. Raynald Gauvin, Ph.D., Ing.

Department of Materials Engineering,
McGill University,
Montréal, Québec,
Canada, H3A 0C5

20.03.2024, 17.00h      
M 2589, Eißendorfer Straße 42, TUHH
pdf Version

Chemical Analysis of Nanomaterials and Lithium of Battery Materials with high spatial resolution using EDS and EELS in low voltage SEM and STEM

This seminar will present the scanning transmission electron microscope (STEM) SU-9000 from Hitachi which characterizes thin and massive samples with electron beam energies ranging from 0.1 to 30 keV. This microscope is equipped with an electron energy loss spectroscopy (EELS) detector which allows the detection of Lithium. High spatial resolution images are possible with a resolution of 0.16 nm. Many examples will be presented on Li materials and nano-materials. This microscope is equipped with an EDS detector of lithium (Extreme, Oxford Instrument), and the microanalysis of lithium compounds, which is very difficult and challenging, will also be covered. The preparation of thin films by focus ion beam (FIB) for high spatial resolution images in STEM will be also shown with the newly acquired Hitachi NX-5000 FIB. The quantification of images and EDS spectra from electron microscopy with deep learning and Monte Carlo simulations will also be covered. Finally, aspects of Fractal Geometry on electron scattering and the microstructure of materials will be lightly covered.

Prof. Carl E. Krill III, Ph.D.

Institute of Functional Nanosystems,
Ulm University,
89081 Ulm, Germany

14.03.2024, 17.00h      
K0506, Denickestraße 15, TUHH
pdf Version

When grains go wild! Tracing microstructural outcomes back to possible mechanisms for abnormal grain growth

Usually, the coarsening of a polycrystalline material is a rather civilized affair, with adjacent grains swiping atoms from each other so surreptitiously that relative growth rates remain moderate, and the mutual boundary stays smooth. In some cases, however, certain participants in this competition manifest a seemingly unlimited hunger for growth! The result is a subpopulation of large, “abnormal” crystallites embedded in a matrix of much smaller grains, whereby the abnormal/matrix interface can be anywhere from perfectly flat to fractally convoluted. The formation of such a microstructure is the telltale signature of abnormal grain growth (AGG). Although the most prominent feature of AGG is the shape of the abnormal grains themselves—which can range from prismatic to dendritic— computational simulations indicate that the mechanism of AGG is encoded to a greater extent in the morphology of the interfaces between abnormal and matrix grains. Based on this finding, we propose a classification scheme for inferring the possible mechanism(s) underlying any experimentally observed case of (sufficiently extreme) AGG. The scheme can be applied to 2D metallographic sections but also to recent efforts exploiting diffraction contrast tomography (DCT) to capture AGG in 3D. Surprisingly, for most forms of AGG that we have encountered, the microstructural outcomes point to boundary-to-boundary mobility variation as the primary factor governing the phenomenon.

Dr.‐Ing. Ingmar Bösing

Group Leader Electrochemistry and Reaction Engineering
in the Department of Chemical Process Engineering
Universität Bremen, Germany

29.11.2023, 17.00h      
K0506, Denickestraße 15, TUHH
pdf Version

Kinetic Modeling of Electrochemical Oxide Film Growth

We are surrounded by metal oxides everywhere in our daily life and our technological world wouldn’t be possible without them. Metal oxides can be found in semiconductor devices, as (electro-)catalysts, color pigments or as corrosion products and corrosion protection. The spontaneous formation of a dense oxide film on a metal surface is called passivation, slows down corrosion reaction about three orders of magnitude and thus enables the metal-based civilization we live in. Despite the great importance of metal oxides and passive films, the mechanisms behind electrochemical oxide film formation are still not fully understood. Here we present a kinetic model, which describes oxide film growth, dissolution and breakdown of films by interfacial reactions at the metal/film and film/solution interfaces and by transport of crystal defects and electrons and holes through the oxide. The model allows insights in oxide film properties for corrosion prediction, the understanding of critical processes as pitting corrosion and gives general insights in processes at metal/semiconductor interfaces under potential control.

Prof. Dr.‐Ing. Rainer Helmig

Institute for Modelling Hydraulic and Environmental Systems,
Universitaet Stuttgart, Germany

09.03.2023, 17.00h      
K0506, Denickestraße 15, TUHH
pdf Version

Porous Media Free‐Flow Coupling – from REV to Pore Scale and back

Coupled systems of free ow adjacent to a porous‐medium appear ubiquitously in nature and in technical applications. Examples for interface‐driven transport and exchange processes include soil evaporation, fuel cell water management, self‐cooling of turbans or food drying.
One of the key challenges for coupled free flow and porous‐medium flow arises from the fact that the overall effective behaviour depends strongly on interface processes that occur on small spatial scales (pore scale), although the overall system of interest is often too large to resolve these processes explicitly in detail. REV‐scale models are usually not able to capture all the relevant physical processes for such coupled systems. In addition, pore‐scale interface roughness, macro‐scale surface topologies, and boundary layers strongly influence the flow behaviour inside the porous medium and the freeflow region near the common interface. Pore‐scale models are in turn not suitable for large‐scale problems because of the high computational costs involved, rendering them applicable only to model domains in the range of micrometers to centimeters. For the accurate description of interface phenomena, it is therefore necessary to develop model concepts that combine information gained through pore‐scale and REV‐scale models. The results will be compared and discussed with experimental measurements on different scales.

Markus Valtiner

Institute for Applied Physics,
TU Wien, Austria

11.01.2023, 17.00h      
K0506, Denickestraße 15, TUHH
pdf Version

Probing reactive processes and molecular adsorption at solid/liquid interfaces

Function and properties at biologic as well as technological interfaces are controlled by a complex and concerted competition of specific and unspecific interaction of reactive surfaces with ions, molecules and water in the electrolyte. Atomic force microscopy techniques provide an unprecedented resolution of surface structures, in both gaseous and aqueous environments. Here, I will discuss our understanding of ion exchange processes, and competitive molecular interaction at the interface of Muscovite mica. Muscovite mica, KAl₂(Si₃Al)O₁₀(OH)₂, a layered phyllosilicate with perfect cleavage planes, has been one of the prime model‐surfaces for probing molecular resolution imaging at the solid/liquid interface in 3D. Starting from highly resolved data of freshly cleaved mica surface, all the way to competitive adsorption at this well‐defined solid/liquid interface, quantitative and even thermodynamic information can be derived from experiments based on SPM techniques. In particular, to date it is not possible to directly estimate by experiment the interfacial binding energies of surface‐active species at the solid/liquid boundary in a consistent approach, thus limiting our understanding of how surface interactions in complex media are moderated. I will show how force probe experiments can be utilised to derive a quantitative and visual model for describing surface/ion interactions, using a competing Langmuir isotherm model, which can describe concentration‐dependent competitions of ions and functional molecules at a solid/liquid interface. In essence, this enables extraction of thermodynamic interaction energies and kinetic parameters of ionic species during monolayer level interactions at a solid|liquid interface. I will then further discuss how complementary surface analysis methods may be utilised to complement our data.

Institute of Physical Chemistry,
University of Hamburg,
Hamburg, Germany

24.11.2021, 17.00h      
via Zoom, for dial-in details please contact Pia Fischer.
pdf version

Self‐organization of inorganic nanoparticles and biomolecular building blocks into biohybrid nanomaterials

Self‐organization is a key tool for the construction of functional nanomaterials. We have recently established a novel method for the self‐organization of biomolecular building blocks and nanoparticles. Here, protein containers, engineered with opposite surface charge, are used as an atomically precise ligand shell for the assembly of inorganic nanoparticles.[1] The assembly of these protein‐nanoparticle composites yields highly ordered nanoparticle superlattices with unprecedented precision. The structure of the protein scaffold can be tuned with external stimuli such as metal ion concentration.[2] Importantly, these composite materials show catalytic activity inside the porous material.[3] Along these lines, the protein containers used as a scaffold offer a viable route towards renewable materials.[4] For the formation of these biohybrid materials, the inorganic cargo has to be synthesized or encapsulated into the protein containers. Here, we demonstrate that the highly specific cargo‐loading mechanism of the bacterial nanocompartment encapsulin can be employed for encapsulation of artificial cargo such as inorganic nanoparticles.[5] For this purpose, gold nanoparticles were decorated with cargo‐loading peptides. By lock‐andkey interaction between the peptides and the peptide‐binding pockets on the inner container surface, the nanoparticles are encapsulated with extremely high efficiency. Importantly, the container does not change, as shown by electron microscopy. Most notably, the supramolecular peptide binding is independent from external factors such as ionic strength.[5] Cargo‐loading peptides may serve as generally applicable tool for efficient and specific encapsulation of cargo molecules into a protein compartment. Moreover, these nanoparticle proteincontainer composites are suitable for applications as building blocks in materials, exploiting the plasmonic properties of gold nanoparticles for light manipulation or sensing.

[1] M. Künzle, T. Eckert, T. Beck, J. Am. Chem. Soc. 2016, 138, 12731‐12734.
[2] M. Künzle, T. Eckert, T. Beck, Inorg. Chem. 2018, 57, 13431‐13436.
[3] M. Lach, M. Künzle, T. Beck, Chem. Eur. J. 2017, 23, 17482‐17486.
[4] a) M. Künzle, M. Lach, T. Beck, Dalton Transactions 2018, 47, 10382‐10387;
     b) M. Lach, M. Künzle, T. Beck, Biochemistry, 2019, 58, 140.
[5] M. Künzle, J. Mangler, M. Lach, T. Beck, Nanoscale 2018, 10, 22917‐22926..

Max-Planck-Institut für Eisenforschung
Düsseldorf, Germany

26.05.2021, 17.00h      
via Zoom, for dial-in details please contact Pia Fischer.
pdf Version

Materials design by exploiting high-dimensional chemical and structural configuration spaces

The chemical and structural complexity employed in modern engineering materials presents a challenge to their design since experimental trial-and-error approaches as successfully used in the past are often no longer feasible. Ab initio approaches provide perfect tools to new design routes but face serious challenges when having to systematically sample high-dimensional chemical and structural configuration spaces. Combining advanced sampling approaches with our python based framework pyiron allows us in a highly automated way to combine first principles calculations with big data analytics and to obtain accurate ab initio descriptors. The flexibility and the power of these approaches will be demonstrated for a few examples: The design of ductile Mg alloys, overcoming mutually exclusive properties in high entropy alloys, and the discovery of general rules for interstitials in metals.

Deutsches Elektronen-Synchrotron (DESY) &
KTH Royal Institute of Technology, 
Department of Fibre and Polymer Technology
Stockholm, Sweden

12.05.2021, 17.00h      
via Zoom, for dial-in details please contact Pia Fischer.
pdf Version

Hybrid and biopolymeric functional thin films - fabrication, characterization and nanostructure – optical properties relationship

The development of novel functional materials crucially relies on observing the materials structural transformations in situ from the nano- to the microscale during materials’ synthesis, self-assembly and subsequent device fabrication. These changes must be related to their (macroscopic) functionality. To start with, I focus on cellulose as renewable resource. Introducing spray deposition as versatile process, ultrasmooth cellulose nanofibril films with controlled thickness are investigated [1,2]. Depending on their charge and roughness, the wettability can be controlled. This is crucial for optimizing the fabrication of hybrid materials, typical for energy conversion and storage as well as sensor applications [3]. The tailoring of wettability is further pursued by surface functionalization of water-based latex colloids. These materials offer the possibility to tailor and fine-tune the wettability by tuning the core-shell colloid morphology in thin films, providing a facile template methodology for repellent surfaces of devices [4]. Electronic properties manifest themselves for example in electrical conductivity changes and optical response. The electronic properties are governed by the nanoscale morphology. Imaging via scattering methods allows to extract the granular morphology up to and beyond the percolation threshold in situ during fabrication. At the same time, this analysis allows to predict the electrical behavior of hybrid composites and their optimization for example as electrodes in such devices [5,6]. Silver nanowires offer electrical conductivity, mechanical flexibility as well as well high optical transparency when applied as meshes in top electrodes. Here, printing applications offer great potential for photovoltaics and flexible electronics [7]. From a fundamental point, towards 3D printing, the photopolymerization process itself is imaged in real time using X-rays thus relating physical and chemical transformations [8].

References
[1] C. J. Brett et al., Macromolecules 52, 4721 (2019)
[2] W. Ohm et al., J. Coat. Technol. Res. 15, 759 (2018)
[3] Q. Chen et al., ACS Appl. Nano Mater.  4, 503 (2021)
[4] J. Engström et al., Adv. Funct. Mater. 30, 1907720 (2020)
[5] M. Gensch et al., ACS Appl. Nano Mater. 4, 4245 (2021)
[6] S. V. Roth et al., ACS Appl. Mater. Interfaces 7, 12470 (2015)
[7] T. E. Glier et  al., Scientific Reports 9, 6465 (2019)
[8] C. J. Brett et al., Commun. Chem. 3, 88 (2020)

Center for Hybrid Nanostructures
University of Hamburg
Hamburg, Germany

24.03.2021, 17.00h      
via Zoom, for dial-in details please contact Pia Fischer.
pdf Version

Transforming traditional fiber drawing into highly sophisticated
NANOMANUFACTURING TOOLBOX:
Kilometer-long nanostructures for photonics, electronics, mechanics

In this talk I will present and discuss our recent works on fiber-based nanomaterials, sensors, and devices including
– advanced multi-material fiber-based devices [1, 2, 3, 4, 5]
– realization of a radically new top-to-bottom nanofabrication technique6 and their applications in electronics, photonics and mechanics [7, 8, 9]
– piezoelectric polymer nanostructures for artificial skin, cardiac sensors, and energy harvesting applications [9, 10]
– triboelectric sensors and nanogenerators [11, 12]
– nanospring absorbers as a light-harvesting platform [13]
– smart nanostructures and surfaces for open microfluidics [14, 15]
– on-chip chalcogenide microresonators [16, 17]
– digitizing the smell (digital photonic nose) [18, 19]

I will also briefly discuss some of the future projects on next-generation fiber-based nanostructured probes for cells and neural networks, supercapacitors for flexible electronics and smart textiles and phase change nanowire synaptic devices for brain-inspired computing.

References
... see pdf version.

John A. Paulson School of Engineering and Applied Sciences
and
Wyss Institute for Biologically Inspired Engineering
Harvard University
Cambridge, MA, USA

03.03.2021, 17.00h      
via Zoom, for dial-in details please contact Pia Fischer.
pdf Version

Utilizing Digital Fabrication to drive innovation in (Multi-)Functional Materials

Human creativity paired with modern, computational tools can derive the most captivating designs. The physical realization, however, remains a challenge. On the other end, the grand challenge in manufacturing is to create a process that is economical, fast, repeatable, and that enables the desired design freedom. Digital Fabrication and, in particular, Additive Manufacturing (AM) has emerged as a potent alternative to conventional manufacturing and is considered by many the holy grail. Despite the hype, however, AM still lacks behind the expectations and is often not able to handle the required complexity, which significantly limits progress in major research fields. The first part of the talk will address both the digital design of novel materials and structures with outstanding properties, and the fabrication thereof. I will show how the mutual exclusivity between strength and toughness can be overcome and how (multi-)functionality, such as actuation and sensing, can be integrated on a materials level. This requires AM-based solutions specifically tailored to such complex designs that cannot be fabricated in any other way. I will then address the general limitations of AM and show how they can be overcome, with the ultimate goal of solving the grand challenge.

Materials Research Department
GSI Helmholtz Centre for Heavy Ion Research 
Darmstadt, Germany

20.01.2021, 17.00h      
via Zoom, for dial-in details please contact Pia Fischer.
pdf Version

Three-dimensional free-standing nanowire networks with tailored parameters fabricated by ion-track nanotechnology

The implementation of metal and semiconductor nanostructures in devices for e.g. catalysis, sensing, and energy conversion benefits from a controlled geometry, crystallinity and composition of the individual nanostructures, as well as its successful assembly into 3-D architectures. In particular, nanowire ensembles offer important advantages compared to planar films including e.g. larger surface area and surface to volume ratio, and better crystalline quality. This talk will illustrate how ion-track nanotechnology provides an excellent platform to (i) fabricate tailored porous polymer membranes and (ii) develop three-dimensional nanowire networks as tailored porous systems. Etched ion-track membranes are synthesized in two separate process steps: (i) sequential irradiation of polymer foils from one or various directions with swift heavy ions resulting in the creation of damage tracks, (ii) converting the ion tracks into nanochannels by selective chemical etching. Channel density and orientation, as well as diameter and geometry are adjusted by the irradiation and etching conditions, respectively. By electrodeposition in the nanochannels and subsequent removal of the polymer template 3-D nanowire networks are synthesized. Since the nanowires adopt the exact shape of the host channel, their diameter can be adjusted between ~15 nm and a few µm, and their length between ~1 and several tens of µm. Their interconnectivity is tailored also by the nanowire density. Recent developments achieved on the electrodeposition of metal (Cu, Au1-xAgx), semiconductor (ZnO and Cu2O) and semimetal (Bi, Sb) nanowire networks, their characterization, and the investigation of their photoelectrochemical and catalytical properties will be presented.

Department of Molecular Design & Engineering
Graduate School of Engineering, Nagoya University
Nagoya, Japan

22.04.2020, 17.00h      
H 0.09, Am Schwarzenberg-Campus 5, TUHH
pdf Version

Environmentally friendly Structural Colored Materials by Black and White Materials

Our lives in the present age are full of colorful items. However, when many coloring materials cannot be used due to environmental concerns, this colorful life that has been constructed will be diminished. Maintaining our rich lifestyle necessitates the development of a technology that can make safe and secure color materials from materials with less burden on people and the environment. Our group reveals that structural colored materials with little angle dependence can be prepared by using various materials with a short-range order in the refractive index, comparable to the wavelength of visible light, and with the aid of a black substance. This approach enables the preparation of colorful materials from materials with low environmental burdens and that are non-toxic to living things; examples of such materials include silica, carbon black, and iron oxide. Environmentally friendly green color materials are expected to promote sustainable development. I will also introduce the latest research results.

References
[1] Chemical Communications, 54, 4905-4914 (2018).
[2] Small, 14, 1800817(1-8) (2018)
[3] ytakeoka.xcience.jp

Laboratory for Nanometallury
Department of Materials, ETH
Zürich, Switzerland

27.11.2019, 17.00h      
K0506, Denickestraße 15, TUHH
pdf Version

Scalability of functional nanomaterials? – between architecture and self-organization

We are approaching a point where we will be able to design materials from the bottom up, ideally determining very every single atom has its place. However, once we are able to do this, creating tangible materials will take a very long time.
In my talk I will address the issue of when it is useful to architect materials and when self-organized materials are preferred, where we can control nanoscale structures by external parameters such as temperature and time. While most of the presentation will focus on functional materials, where the optical response can be tuned, with case studies on “mood” materials (materials that show their internal structure by their color), color effects by phase-change media and epsilon near zero materials, a bridge to mechanical properties will be built via reflectance anisotropy spectroscopy. This technique is highly sensitive to small deviations from isotropy, which can result from elastic distortion, the formation of plasmonic cracks and also a change in phase.
Finally, mechanics and optics will be combined by the introduction of a 3D printing process that allows for a chemical and structural change on a voxel to voxel basis with a 100 nm voxel diameter. This process allows for a combination of architecture and self-organization.

Theory Department
Fritz-Haber-Institut
Berlin, Germany

22.05.2019, 17.00h      
H0.09, Am Schwarzenberg-Campus 5, TUHH
pdf version

Adressing the nuclear and electronic structure of weakly bonded Interfaces

Weakly bonded systems composed by organic constituents are ubiquitous in nature and nowadays also in technological applications. In particular, the use of organic components interfaced with inorganic materials offers the possibility of enhancing the efficiency and versatility of devices. One aspect that hinders advances in this field is the lack of understanding about how the electronic and atomic degrees of freedom cooperate or compete to yield the desired interface properties. From a theoretical perspective, addressing these systems involves efforts in finding the relevant structural motifs, evaluating their dynamical evolution and evaluating the associated electronic properties. These tasks are especially challenging in these systems due to the large conformational space they can explore at finite temperatures, and the inherent anharmonicity of their intra and intermolecular interactions. In this talk, I will discuss our recent efforts to address the challenges mentioned above, based on density functional theory and ab initio molecular dynamics simulations. I will present strategies for conformational space sampling of organic/inorganic interfaces, techniques to include anharmonicity in vibrational fingerprints, and our recent methodological developments that allow the inclusion quantum nuclear effects in high-dimensional systems using path integral molecular dynamics.

Computer Chemistry Center
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Germany

15.05.2019, 17.00h      
H-0.09 , Am Schwarzenberg-Campus 5, TUHH
pdf version

Molecular Simulations of crystal nucleation, growth and functionalization: From understanding to tailoring

Molecular dynamics simulations allow the rationalization of collective molecular interactions during the self-organisation of bulk liquid/solid phases, interfaces and surfaces including self-assembled monolayers. Insights include the mechanisms of crystal nucleation and growth, the re-organisation upon proton transfer and redox-reactions and the in-depth assessment of surfactant assembly for functionalizing nanomaterials. We outline these perspectives for supporting the rationalization of mechanisms and the tailoring of new experiments and industrial developments..

Physical Chemistry I
University of Bayreuth, Germany

24.04.2019, 17.00h      
H0.09, Am Schwarzenberg-Campus 5, TUHH
pdf version

Functional Colloidal Mesostructures: From Optics to Thermal Transport

Self-assembly is a powerful tool to access well-defined nanostructured materials, which exhibit unique mechanical, optical, or thermal properties. When working with colloidal latex or silica particles structural length scales from a few tens up to few micrometers can be addressed.In this presentation, I will elaborate on three topics. At first, I will present our latest results on the self-assembly process and nanostructured material fabrication itself. I introduce a new way to break the ever-occurring six-fold symmetry in colloidal monolayers and a new method to access transferable and free-standing nanostructures. Secondly, I will talk about nanophotonic properties of plasmonic hole arrays and Mie scattering of hollow silica nanoparticles. In the third part, I will talk about three-dimensional colloidal structures and their thermal transport properties. This is a rather underexplored field, yet, colloidal superstructures are ideally suited to design the thermal properties of nanostructured materials rationally. Our recent results show how to engineer highly insulating materials. First results on switchable anisotropy and programmable temperature-dependent thermal conductivity pave the way towards intriguing thermal devices such as thermal diodes or Switches.

Department of Chemistry
Emory University
Atlanta, USA

17.04.2019, 17.00h      
H0.09, Am Schwarzenberg-Campus 5, TUHH
pdf version

Efficient Plasmon Induced Hot Electron Transfer

It has been well-established that excitation of plasmons in metal nanostructures can lead to the injection of hot electrons and holes into semiconductors or adsorbed molecules to drive photocatalysis. Therefore plasmonic hot carriers can access highly energetic and reactive states of metals that is difficult to access with thermal chemistry. However, plasmon-induced hot electron transfer are often inefficient because of unfavorable initial hot electron distribution and the competing ultrafast hot electron relaxation processes within the metallic domain. In this talk, we discuss two approaches to enhance the efficiency of plasmon induced hot electron transfer. In the first approach, we explore the possibility of enhancing hot electron distribution by decreasing the size of plasmonic Au particles. Using CdS/Au nanorod heterostuctures, we show that the hot electron injection efficiency increases at smaller Au particle size. We attribute this size dependence to increasing contribution of surface assisted plasmon damping, which generates more hot electrons compared to damping by interband transition. In the second approach, we demonstrate that in CdSe/Au hetersostructureswith strong metal/semiconductor coupling, the plasmon decays by direct excitation of an electron from the metal to semiconductor, i.e. plasmon induced interfacial charge transfer transition (PICTT). The new plasmon damping pathway can be very efficient because it bypasses the competition with hot electron relaxation within the metal satisfies both the energy and momentum conservation. We will discuss whether PICTT can be a general scheme for efficient hot electron transfer.

Institute of Materials Physics
Graz University of Technology
Graz, Austria

20.02.2019, 17.00h      
M 1582, Eißendorfer Str. 42, TUHH
pdf version

In-Situ Studies on the Formation as well as on Tunable Electronic and Magnetic Properties of Nanoporous Metals Produced by Electrochemical Dealloying

The high surface-to-volume ratio of nanoporous (np)  metals makes this class of materials sensitive to electrochemical stimuli, e.g., for property tuning. Recent studies of nanoporous metals by in-situ magnetometry and in-situ resistometry will be presented. For np-Au, the charging-induced resistance variation in the range of several ten percents is found to be dependent on the degree of porosity and the amount of residual Ag
[1]. In-situ resistometry could also be applied for analyzing the etching progress during electrochemical dealloying, supporting ex-situ studies according to which dealloying occurs in two steps referred to as ‘primary (or bulk) dealloying’ and ‘secondary (or ligament) dealloying’ [2]. Regarding the electrochemical control of magnetism, dealloyed Pd(Co) is chosen as model system. The idea is to bring the system - by properly adjusting the residual Co concentration - into a state from which it can be driven to ferromagnetism by electrochemical stimuli. Upon voltammetric cycling in the regime of hydrogenation and dehydrogenation, the net magnetization can be reversibly changed by several hundred percents [3].Part of this work is financially supported by the Austrian Science Fund (FWF): P30070-N36.

[1] E.-M. Steyskal, M. Seidl, S. Simic, R. Würschum, Langmuir 34 (2018) 13110-13115.
[2] E.-M. Steyskal, M. Seidl, M. Graf, R. Würschum, Phys. Chem. Chem. Phys. 19 (2017) 29880-29885.
[3] M. Gößler, M. Albu, H. Krenn, R. Würschum, to be published.

Institute for Materials Research (IMO-IMOMEC)
Hasselt University
Diepenbeek, Belgium

30.01.2019, 17.00h     
K 0506, Denickestr. 15, TUHH
pdf version


Approaching from the surface: Using surfactant inhibitors to create hierarchical nanoporous surfaces

Nanoporous metals can be prepared by chemical or electrochemical dealloying of noble or relatively noble alloys such as Cu-Au or Cu-Zn. Nanoporous metal structures have been proposed for applications, but dealloying is also and originally among the prime fundamental corrosion processes studied. Moreover, the evolving nanoscale porosity is as well an interesting subject for advancing our understanding of nanomaterials behaviour in itself [1].  Surfactants are used in both, corrosion inhibition and nanotechnology, but the exact mechanisms of their action are still under debate. Surfactant inhibitors such as thiols or selenides readily adsorb on Au and Cu surfaces and eventually form well-ordered self-assembled monolayers. Modification of these organic films is possible for instance by molecular microcontact printing [2], and can be employed to create structurally heterogeneous films with well-controlled defect patterns.In this presentation I will report on the formation and behaviour of inhomogeneous self-assembled thiol films on Au-based and Cu-based alloys. Such films inhibit the initial  dealloying reactions on the alloy surfaces leading to a localized dealloying process and resulting heterogeneous or hierarchical nanoporous materials on the surfaces of the alloys.

[1] F. U. Renner et al, Adv. Mater. 27 (2015), 4877–4882.
[2] S. Neupane et al, Langmuir. 34 (2018), 66–72.

Hybrid Materials Interfaces Group
University of Bremen, Germany

23.01.2019, 17.00h     
K 0506, Denickestr. 15, TUHH
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A novel coarse-grained model for the discrete element simulation of aggregated TiO₂ nanoparticle films

Oxide nanoparticle films produced by flame-based methods find applications in battery or fuelcell electrodes, gas sensors, and catalysts. We have developed a coarse-grained contact model for the Discrete Element Modelling of TiO₂ nanoparticle films under mechanical stress. The particles can interact both via elastic sinter bridges or weaker capillary and solvation forces. The model’s mathematical terms and parameters are derived in a self-consistent and physically sound way from all-atom Molecular Dynamics simulations of interacting particles and surfaces. In particular, the nature of atomic-scale friction and dissipation effects is taken into account by explicit modelling of the surface features and water adsorbate layers that strongly mediate the particle-particle interactions. The predictive power of the model is validated against atomic force microscopy (AFM) and mechanical compaction experiments, revealing previously unknown details into the film restructuring due to the application of external loads.

Laboratory of Computational Science and Modelling (COSMO)
École polytechnique fédérale de Lausanne, Switzerland

12.12.2018, 17.00h     
K 0506, Denickestr. 15, TUHH
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Machine learning like a physicist

Statistical regression techniques have become very fashionable as a tool to predict the properties of systems at the atomic scale, sidestepping much of the computational cost of first-principles simulations and making it possible to perform simulations that require thorough statistical sampling without compromising on the accuracy of the electronic structure model.

In this talk I will argue how data-driven modelling can be rooted in a mathematically rigorous and physically-motivated framework, and how this is beneficial to the accuracy and the transferability of the model. I will also highlight how machine learning - despite amounting essentially at data interpolation - can provide important physical insights on the behavior of complex systems, on the synthesizability and on the structure-property relations of materials.

I will give examples concerning all sorts of atomistic systems, from semiconductors to molecular crystals [1], and properties as diverse as drug-protein interactions[2], dielectric response of aqueous systems[3] and NMR chemical shielding in the solid state[4].

 References
[1] F. Musil, S. De, J. Yang, J. E. J. E. Campbell, G. M. G. M. Day, and M. Ceriotti, Chem. Sci. 9 (2018) 1289
[2] A. P. A. P. Bartók, S. De, C. Poelking, N. Bernstein, J. R. J. R. Kermode, G. Csányi, and M. Ceriotti, Sci. Adv. 3, (2017) e1701816
[3] A. Grisafi, D. M. Wilkins, G. Csányi, and M. Ceriotti, Phys. Rev. Lett. 120 (2018) 36002
[4] http://shiftml.org

Institute for Solar Fuels
Helmholtz-Zentrum Berlin für Materialien und Energie, Germany

05.12.2018, 17.00h     
K 0506, Denickestr. 15, TUHH
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Solar water splitting with ternary metal oxide semiconductors: Recent insights in bulk and surface properties

The direct photo-electrochemical conversion of water and CO₂ into chemical fuels represents an exciting new pathway for the combined conversion and storage of solar energy. One of the main challenges in this field is to find semiconducting light absorbers that are efficient, chemically stable, and easy to synthesize. Efforts in our group are focused on multinary oxides, a large but still little-explored class of semiconductors. Examples of promising ternary oxides are BiVO₄, CuBi₂O₄, and alpha-SnWO₄. I will show how novel doping strategies can be used to enhance the bulk charge separation in these materials. Time-resolved spectroscopy on fs – ms time scales reveals that the carrier dynamics in these oxides is fundamentally different from those in classical semiconductors. This has important implications for the design of efficient photoelectrodes. To enhance the reaction kinetics, the surfaces of these semiconductors are typically modified with electrocatalysts. Our understanding of the semiconductor/electrocatalyst is, however, still far from complete. For example, we found that certain catalysts do not enhance the charge transfer kinetics, but instead electronically passivate the surface. I will discuss our recent progress on understanding charge transfer and recombination processes and show how synchrotron-based ambient pressure photoemission techniques can help us to get better insights in how the solid/liquid interface behaves under illumination.

Center for Hybrid Nanostructures
Institute for Nanostructure and Solid State Physics
University of Hamburg, Germany

*New date* 04.07.2018, 17.00h     

H 009, Am Schwarzenberg-Campus 5, TUHH
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From nanoparticles synthesis in solution to functional devices – a perspective based on in situ synchrotron studies

Over the past years we have developed various approaches to fabricate materials with sophisticated chemical and structural complexity. We have focused on synthesis in non-aqueous solution since this approach is not limited to one particular class of materials. Thus, it gives us flexibility to tailor the composition and properties of materials in respect to the application.

In this talk, I will present how X-ray synchrotron methods, far from merely providing new tools, are extending the ways we study, understand and design such complex structures. Particularly, combination of spectroscopic and scattering methods and rapid data acquisition help to uncover the complex chemical world behind the synthesis of functional materials. It gives complementary information about chemical reaction in solution and nucleation, growth and crystal phase transition of nanoparticles.[1-2]

Moreover, I will discuss how the possibility to select with high-energy resolution the incident and emission X-ray energies offers unprecedented site selectivity and give access to determine structure – function relationship of electrochemical materials. [3,4,5]

References
[1] Staniuk M., Hirsch O., Kränzlin N., Böhlen R., van Beek W., Abdala P. M., and Koziej D. Chem. Mater. 26, 2014, 2086.
[2] Kränzlin N., van Beek W., Niederberger M. and Koziej D., Adv. Mater. Interfaces 2015, 2,1500094.
[3] Hirsch O., Kvashnina K.O., Luo L., Süess M.J., Glatzel P., and Koziej D. PNAS, 2015, 112, 15803.
[4] Hirsch O., Kvashnina K., Willa C., D Koziej, Chem. Mater. 29 (4), 2017, 1461-1466
[5] Koziej D., Chem. Mater. 28 (8), 2016, 2478-2490

Institute of Inorganic and Applied Chemistry
University of Hamburg, Germany

02.05.2018, 17.00h     
H 009, Am Schwarzenberg-Campus 5, TUHH
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Periodic Mesoporous Organosilicas: Porosity meets Functionality

Periodic mesoporous organosilicas (PMOs) have been of interest for the last 18 years because of the attractive combination of a robust inorganic framework with the enormous functional variability of the organic bridges paired with tunable nanoporosity. Various research groups worldwide are developing new PMOs for the usage as heterogeneous catalysts, adsorbents, sensors, drug containers and optical materials. Comparable to silica based materials it is also possible to shape PMOs in order to obtain thin films, monoliths, nanoparticles, hollow spheres, core/shell systems and inverse opal morphologies with hierarchical pore structures. The research focus of our group is on PMO materials with different functionalities and morphologies which covers the range from optical materials over highly efficient adsorbents for toxic gases to the usage as model host structures for investigating the properties of water in confining hybrid nanopores.

References
[1] J.B. Mietner, F.J. Brieler, Y.J. Lee, and M. Fröba, Angew. Chem. Int. Ed. 2017, 56, 12348-12351.
[2] T. Simon, F.J. Brieler, M. Fröba, J. Mater. Chem. C 2017, 5, 5263-5268.
[3] L. Grösch, Y.J. Lee, F. Hoffmann, M. Fröba, Chem. Eur. J. 2015, 21, 331-346.
[4] F. Hoffmann and M. Fröba, Chem. Soc. Rev. 2011, 40, 608-620.
[5] F. Hoffmann, M. Cornelius, J. Morell, M. Fröba, Angew. Chem. Int. Ed. 2006, 45, 3216-3251.

Institute of Applied Physics
TU Wien, Austria

18.04.2018, 17.00h     
H 009, Am Schwarzenberg-Campus 5, TUHH
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Iron-Oxide Surfaces and their Reactivity to Water

The interaction of water with iron oxide surfaces underlies geochemistry, corrosion, and weathering processes, and there are numerous technologies where iron oxide reactivity plays an important role. For example, the industrial catalyst for the water-gas shift reaction (CO+H₂O ⇌ CO₂+H₂) is based on magnetite (Fe₃O₄), and hematite (α-Fe₂O₃) is a promising photoanode for photoelectrochemical water splitting and artificial photosynthesis devices. In this talk, I will describe our recent efforts to understand the adsorption of water on iron oxides at the atomic scale, with a focus on Fe₃O₄(001), (111), and (110) surfaces, as well as the α-Fe₂O₃(012). Using a combination of experimental techniques and density functional theory based calculations, I will show that partially dissociated water dimers are common to all these surfaces. I will discuss how the different surface structures dictate the evolution of the water overlayer as the coverage increases, address what might happen in high pressure and liquid environments, and attempt to put these results into the context of what is known about water adsorption on other metal oxide surfaces.

Leibniz-Institut für Polymerforschung Dresden e.V.
Dresden, Germany

31.01.2018, 17.00h     
K 0506, Denickestr. 15, TUHH
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Colloidal surface assemblies: Nanotechnology meets Bioinspiration

A: Well-defined Ag/Au nanorods with tuneable shape and spectroscopic response [1] B: Ordered assemblies of nanorods up to macroscopic areas [2]

Colloidal nanoparticles offer a range of interesting optical and electronic effects. A prominent example is the localized surface plasmon resonance (LSPR) of metal nanoparticles due to resonant excitations of vibrations of the particles’ free-electron cloud by light. Due to the LSPR, plasmonic nanoparticles provide excellent means for controlling electromagnetic near-fields at optical frequencies, which has led to a broad range of applications in various field such as surface enhanced spectroscopy, light harvesting or photonics.

While much research is dedicated to understanding nanoparticle synthesis and tailor their LSPR on the single particle level [1], ordering particles on surfaces opens another powerful avenue towards optical and electronic functionality. Plasmonic particles can couple locally, altering their LSPR, but as well collective long range phenomena can give rise to novel effects. In this context, methods for ordering particles that are scalable to macroscopic areas are of great interest.

We discuss, how biomimetic approaches can contribute to solving this technological challenge. In particular we focus on controlled wrinkling as a versatile means for surface patterning and its application in template assisted self assembly [2]. We discuss the underlying physico-chemical effects and perspectives for applications in Surface Enhanced Raman Spectroscopy and Photonics, as well as approaches towards tuning of plasmonic coupling effects by mechanical strains.

References
[1] Mayer, M.; et al. Nano Letters 2015, 15, 5427-5437; Mayer, M. et al., Angewandte Chem. Int. Ed., 2017, DOI: 10.1002/anie.201708398
[2] Steiner, A., et al, ACS Nano 2017, 11(9), 8871–8880, Tebbe, M.; et al. Faraday Discussions 2015, 181, 243-260; Hanske, C.; et al. Nano Letters 2014, 14 (12), 6863 – 6871

European XFEL
Schenefeld, Germany

22.11.2017, 17.00h     
K 0506, Denickestr. 15, TUHH
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New science by X-ray imaging and ultrafast dynamics experiments at the European XFEL

The European X-Ray Free-Electron Laser in Hamburg-Schenefeld was inaugurated on 1st Sept this year after 8 years of construction work. It is the most powerful X-ray laser in the world and the result of an international collaboration with 12 contributing countries. This new facility will provide users with X-rays of unprecedented peak brilliance and coherence. Access to the European XFEL is provided through an open application procedure with the selection of experiments based on scientific excellence via peer review. In the seminar I will discuss the novel opportunities for X-ray experiments that emerge, with particular focus on the experimental capabilities of the MID station (MID: Materials Imaging and Dynamics) which will open for users in 2018. Combining ultrafast experiments with X-ray coherence provides new possibilities both for imaging and dynamics experiments is the areas of materials science, physics, chemistry, and biology.

Department of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa

25.10.2017, 17.00h     
K 0506, Denickestr. 15, TUHH
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Interfacial complexions & thermodynamic transitions at interfaces as characterized by electron microscopy

Since the 1980s it has been recognized that the structure of grain boundaries in polycrystalline ceramics can have a diffuse nature, characterized by a ~1nm thick nominally amorphous film. More recently, the structure of grain boundaries has been described following diffuse interface theory, stating that the structure and chemistry of grain boundaries, interfaces and surfaces can go through two dimensional transitions between thermodynamic states (sometimes termed complexions). As an example, surface reconstruction is a first order complexion transition, equivalent to a discontinuous change in the level of adsorbed excess. As such complexions for interfaces are analogous to phases in bulk, although they are not bulk phases. In the past these conclusions have been reached based on structural characterization of grain boundaries and interfaces correlated with mechanical and electrical properties, and more recently it has been shown that specific complexions can have a significant influence on grain boundary mobility, and thus the morphology of an evolving microstructure.

To date, almost all of these studies have been conducted at grain boundaries in single phase polycrystalline systems, which by definition are not at equilibrium, and in some cases it is not even clear if the identified complexions are at steady-state. Similar questions have been raised for studies focusing on metal-ceramic interfaces from thin film studies, where the deposition process used to form the samples may be very far from equilibrium.

This presentation will focus on an experimental approach to address the structure, chemistry and energy of complexions at (metal-ceramic) interfaces which are fully equilibrated, from which it can be demonstrated that formation of a complexion at equilibrium minimizes interface energy. This will be compared with complexions at solid-liquid interfaces, where a region of ordered liquid exists adjacent to the interface at equilibrium, and the details of a reconstructed solid-solid interface where the reconstructed interface structure accommodates lattice mismatch for a nominally incoherent interface. These three systems will be compared to known reconstructed solid surfaces, which can also be described as complexions, within a more generalized Gibbs adsorption isotherm.

INM Leibniz Institute for New Materials, Saarbrücken

17.05.2017, 17.00h     
H 009, Am Schwarzenberg-Campus 5, TUHH
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Self-assembly of particle-based materials: Mechanisms and their application for flexible electronics

Concrete, paint, rubber, and many other important materials are prepared from mixtures of particles, polymers, solvents, and additives. Their microstructures are often heterogeneous and hard to predict; they limit the performance. This talk will discuss how self‐assembly can be used to gain control over microstructure and properties of particlebased materials. We seek self‐assembly mechanisms that work with relevant materials, do not require complex chemistry, and are compatible with established materials manufacturing processes such as spray coating, doctor blading, and inkjet printing.

I will discuss particle‐based electronic materials that illustrate our strategy. Metal spheres, rods, and wires with characteristic dimensions between 2 nm and 50 nm and narrow size distributions were chemically synthesized and coated with organic shells of varying thickness, density, and chemical nature. We determined shape and size using electron microscopy and scattering techniques. Colloidal interactions between the hybrid particles in different solvents were systematically quantified through concentration‐ and temperature‐dependent light and X‐ray‐scattering experiments. We study the onset of agglomeration, agglomeration rates, and the geometry of the agglomerates. Interfaces are used to confine the particles and template self‐assembly. I will show that monolayers and multilayers of nanoparticles, supraparticles and structured nanocomposites can be deposited using the right combination of interactions and confinement.

Figure: I will discuss how the self‐assembly of chemically synthesized nanoparticles (for example, metals) can be tuned through chemistry, confinement, and external stimulation to yield functional structures for electronics

We find that mobility and interaction at different length scales are central features of self‐assembly mechanisms for particle‐based materials. Their interplay affects whether the resulting materials reach equilibrium structures or are kinetically dominated. In practice, viscosity and time scales are often not freely adjustable– there are large differences, for example, between inkjet printing and 3D printing via fused deposition modeling–and rule out certain self‐assembly mechanisms. I will discuss such boundary conditions on the example of transparent electrode layers that self‐assemble from ultrathin gold wires.

As an outlook, I will discuss particle‐based structures that can reconfigure in the material during its lifetime. First examples of “active” nanocomposites based on self‐assembly and on disassembly of particles can change their properties upon stimulation. We explore such materials for a digital world where even materials are connected to networks.

Interdisciplinary Centre for Advanced Materials Simulation (ICAMS),
Ruhr-Universität Bochum

03.05.2017, 17.00h     
H 009, Am Schwarzenberg-Campus 5, TUHH
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Grain boundary properties: Insights from atomistic simulations and their use in mechanical modeling of materials

Modern structural materials are seldom single crystals, but exhibit a polycrystalline, multiphase, often hierarchical microstructure. The thus occurring interfaces in the microstructure have significant influence on the macroscopic properties. Nowadays even tailored microstructures, containing certain arrangements of grain boundaries with specific properties that can be tuned by segregation engineering, are within experimental reach. This gives additional impetus to the development of predictive material models that bridge between the atomistic details of grain boundaries and the effective properties of the microstructure, and can help to identify microstructures with optimized mechanical properties.

Numerical simulation methods, that either allow the study of relevant processes on their characteristic length scale, or can be used to pass on information from finer to coarser length scales, are common tools in this respect. In the presentation some examples of atomistic studies of grain boundaries will be given that illustrate current developments and the challenges that one has to face when trying to extract effective mechanical behavior and to link it to fundamental physical and geometrical properties of the interfaces. The focus will be on lamellar TiAl alloys, in which the high density of interfaces can rule the overall mechanical behavior. High resolution experimental methods exist to analyze the underlying atomistic processes. However, since these processes are not independent, often several of them occur at the same time. To isolate the intrinsic deformation mechanisms of grain boundaries we have carried out molecular statics and molecular dynamics simulations of bicrystal shear at different boundaries. Four distinct mechanisms could be identified, namely rigid grain sliding, grain boundary migration, coupled sliding and migration, and dislocation nucleation and emission – that could be related to structural features of the grain boundaries as well as physical properties of the material. Their relevance for some of the experimentally observed phenomena will be discussed.

Physikalische Chemie,
Universität Konstanz

05.04.2017, 17.00h     
H 009, Am Schwarzenberg-Campus 5, TUHH
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Bio-Inspired Organic-Inorganic Hybrid Materials

Biominerals teach excellent lessons about advanced materials design. Their structural design is optimized for the specific materials purpose and often, the beneficial properties are generated on several hierarchy levels. Consequently, Biominerals are an intense subject of research to reveal the design principles. This led to the discovery of amorphous or even liquid precursors to single crystals in Biomineralization and additive controlled crystallization events. Non classical particle mediated crystallization pathways were found to be important besides the classical crystallization path.

This presentation begins with Nacre mimics and self-assembled hierarchical layered materials from anisotropic nanoparticles aligned by modified self-assembling polyoxazoline polymers with mesogens forming liquid crystals as driving force towards crystallization. Furthermore, an attempt towards combination of several advantageous biomineral properties, namely the fracture resistance of Nacre, the wear resistance of chiton teeth and the magnetic properties of magnetotactic bacteria will be reported. The third example is bio-inspired elastic cement synthesized via a non-classical crystallization pathway. Calcium-silicate-hydrate (C-S-H) nanoparticles, the glue in concrete, are stabilized by copolymers with anionic groups and moieties able to form hydrogen bonds. These polymers bind to C-S-H nanoparticles at pH 12 and stabilize them. Further pH increase leads to destabilization and subsequent nanoparticle aggregation in crystallographic register forming a mesocrystal with a similar structure to a sea urchin spine. This mesocrystal is elastic and can be bent without breaking. This is a further demonstration that bio-inspired synthesis and structuration of organic-inorganic hybrid materials can lead to significant materials improvement – even for the most used synthetic material.

Bending by micromanipulation of bio-inspired mesocrystalline elastic cement.

Department of Chemistry and Pharmacy,
Friedrich-Alexander Universität Erlangen-Nürnberg

25.01.2017, 17.00h     
H 009, Am Schwarzenberg-Campus 5, TUHH
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Functional molecular layers on atomically-defined oxide surfaces and nanoparticles

Functional molecular films on oxide surfaces are at the heart of emerging technologies. Potential fields of application include molecular electronics, solar energy conversion, catalysis, sensor development, or biointerfacial engineering. In spite of this future potential, our understanding of molecule-oxide interfaces is still poor at the atomic level. Whereas the surface science approach has provided a wealth of knowledge on organic film growth on metals, organic-oxide interfaces have remained largely unexplo­red, a situation which we denote as the materials gap in organic thin film science.

In this presentation, selected results from the DFG Research Unit FOR 1878 “funCOS – Functional Molecular Structures on Complex Oxide Surfaces” are reviewed. funCOS started in 2013, aiming to fill the above mentioned gap and to provide the fundamental knowledge basis to design tailor-made functional films on oxides. funCOS follows a knowledge-driven strategy, starting from a rigorous surface science approach. The Research Unit comprises a team of 15 research groups from experimental and theoretical surface and interface science. Combining complementary surface spectroscopies and microscopies, we start from ultrahigh vacuum experiments on ordered single crystal surfaces and bridge the gap between ideal and real conditions by exploring anchoring of molecular films up to ambient pressure and in liquid environments. In the first step, the reaction mechanisms, bonding geometries, energetics and the kinetics of molecular anchoring is investigated with simple test molecules on prototype oxides. Subsequently, this knowledge is transferred the anchoring of porphyrin derivatives. Exemplifying reactions with carboxylate linkers, we explore role of substitution patterns, multiple anchoring, and chelating anchors to control the molecular orientation, formation kinetics, and stability of the films. Interestingly, a strong dependence on the surface structure is observed which can be rationalized on the basis of the cation arrangement and their accessibility at the surface. Finally, we discuss the influence of the molecular orientation and surface structure on metalation reactions and the role of water and hydroxyl groups in molecular anchoring reactions.

Institute of Functional Interfaces (IFG),
Karlsruhe Institute of Technology (KIT)

18.01.2017, 17.00h     
K 0506, Denickestr. 15, TUHH
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Programmed assembly of molecular frameworks: A new class of designer solids?

The demand for advanced materials with novel combinations of different functionalities requires the development of new types of solids. In this context, supramolecular chemistry holds unique prospects. Self-assembly of one or different types of functional units can be employed to fabricate crystalline arrangements, yielding complex but at the same time structurally well defined, highly ordered “Designer Solids”, which exhibit functionalities going well beyond that provided by the individual building blocks. In this presentation, it will become evident that a recently introduced class of supramolecular materials, metal-organic frameworks, or MOFs, carry an enormous potential with regard to the fabrication of solids with unusual physical properties [1]. MOFs are stable materials, with decomposition temperatures well above 200°C (in some cases > 500°C). Using selected examples, we will demonstrate the interesting, and often surprising (e.g. negative thermal expansion coefficient), mechanical, electronic, magnetic and optical properties of these molecular, crystalline materials.
This fairly recent class of porous solids, introduced in the 1990s, is very large in number, already more than 50.000 different structures have been reported. In order to exploit the properties of these materials for applications in solid state physics, we have developed a liquid phase epitaxy (LPE) process, which allows growing MOFs on modified substrates using a layer-by-layer procedure [1]. The availability of cm-sized, highly oriented MOF thin films with thickness in the µm-regime allows to determine the basic physical properties (mechanical [2], optical [3], electronic [4], magnetic [5]) of these porous, molecular solids using standard methods. A unique feature of the LPE-process is the ability to use heteroepitaxy [6] to add further functionality to these materials by creating multilayer systems [7].
The porous nature of these crystalline solids opens up the prospect of adding additional functionality by placing molecules [8] or nanoobjects inside the voids within the MOFs, e.g. metal clusters or dye molecules [9]. We will demonstrate the potential of this approach by loading the three-dimensional porous scaffolds, or “designer solids”, with metal-containing molecules such as ferrocene and then determining the change in conductivity using electrochemistry [10].

[1] H. Gliemann und Ch. Wöll, Materials Today 15, 110 (2012)
[2] S. Bundschuh, O. Kraft, H. Arslan, H. Gliemann, P. Weidler, C. Wöll, Appl. Phys. Lett. 101, 101910 (2012)
[3] E. Redel, Z. Wang, S. Walheim, J. Liu, H. Gliemann, Ch. Wöll, Appl. Phys. Lett., 103, 091903 (2013)
[4] J.Liu, W.Zhou, J.Liu, I.Howard, G.Kilibarda, S.Schlabach, D.Coupry, M.Addicoat, S.Yoneda, Y.Tsutsui, T. Sakurai, S.Seki, Z.Wang, P.Lindemann, E.Redel, T.Heine, C.Wöll, Angew. Chemie, 54, 7441 (2015)
[5] M.E. Silvestre, M. Franzreb, P.G. Weidler, O.Shekhah, Ch. Wöll, Adv. Funct. Materials, 23, 1093 (2013)
[6] Z.Wang, J. Liu, B. Lukose, Z. Gu, P.Weidler, H.Gliemann, T. Heine, C. Wöll, Nano Letters, 14, 1526 (2014)
[7]. J.P. Best, J. Michler, J. Liu, Zh. Wang, M. Tsotsalas, X. Maeder, S. Röse, V. Oberst, J. Liu, S. Walheim, H. Gliemann, P.G. Weidler, E. Redel, Ch. Wöll, Appl. Phys. Lett., 107, 101902 (2015)
[8] L. Heinke, Z. Gu, Ch. Wöll, Nature Comm., 5, 4562 (2014)
[9] W. Guo, J. Liu, P.G. Weidler, J. Liu, T. Neumann, D. Danilov, W. Wenzel, C. Feldmann, Ch. Wöll, Phys.Chem.Chem.Phys., 16, 17918 (2014)
[10] A. Dragässer, O. Shekhah, O. Zybaylo, C. Shen, M. Buck, C. Wöll, D. Schlettwein, Chem.Comm. 48, 663 (2012)

A³BMS Lab – Adaptive, Active and Autonomous Bioinspired Material Systems,
Institute for Macromolecular Chemistry,
Freiburg Materials Research Center (FMF), and Freiburg Institute for Interactive Materials and Bioinspired Technologies (FIT),
Albert-Ludwigs-University Freiburg

11.01.2017, 17.00h     
H 009, Am Schwarzenberg-Campus 5, TUHH
pdf version

Static and dynamic bioinspired self-assembled material systems

Biology is a source of inspiration for materials science by demonstrating macroscopic materials with advanced functionalities and excellent mechanical properties. However, although these rather static architectures stimulate large interest, even more thoughtprovoking are the dynamic, kinetically controlled processes and temporal evolution of structures in complex biological systems. These are orchestrated through feedback loops and require energy input and dissipation to allow non-equilibrium materials and full spatiotemporal control.
In man made self-assemblies we have mastered to a large extent near-equilibrium structure formation in space and have gained an increasing understanding of how to construct very complex, hierarchically structured soft matter by using co-assemblies, competing interactions and hierarchical length scales. This has allowed to create real-life materials with unprecedented functionalities, inaccessible without delicate control over molecular interactions and sophisticated nano- and mesostructuration. The next step is to master temporal control in self-assemblies. This requires kinetic control of opposing reactions (builtup/ destruction), internal feedback systems or the use of energy dissipation to sustain structures only as long as a chemical fuel is available. These approaches keep systems forcefully away from equilibrium and potentially allow neat access to temporal control.
In this talk I will present concepts for bioinspired materials formed in both static and dynamic conditions. The first part will deal with rather static, nacre-inspired high-performance nanocomposites, in which lightadaptive properties can be encoded through co-assembly and energy transfer approaches. The second part will focus on a platform concept, which allows to program self-assembling systems outside equilibrium with a lifetime by kinetic control of promoter/deactivator pairs and a simple internal feedback system. This will be showcased for different self-assembling systems.

Recent references:
[1] Self-Assembled Artificial Nacre: Nano Lett. 2016, 16, 5167, Angew. Chem. Int. Ed. 2015, 54, 8653; Nat. Commun. 2015, 6, 5967; ACS Appl. Mater. Interfaces 2013, 5, 3738; Adv. Mater. 2013, 25, 5055;
[2] Time Programmed Dynamic Materials: Nano Lett., 2015, 15, 2213, Angew. Chem. 2015, 54, 13258 , Review: Soft Matter 2015, 11, 7857.

Nanostructured Particles Group,
Friedrich-Alexander Universität Erlangen-Nürnberg, Germany

07.12.2016, 17.00h     
H 009, Am Schwarzenberg-Campus 5, TUHH
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Crystal growth on curved surfaces: Novel approaches for the synthesis of anisotropic nanostructured materials

Small particles are widely exploited in a broad range of functional materials, ranging from dense, close-packed layers to dilute dispersions. The interactions involved in such particle ensembles are generally isotropic and the properties of the resulting material can often be regarded as equivalent to those of an effective, isotropic medium. There is however, a rapidly growing interest in the development of particles with anisotropic character. This is driven, in part, by the promise of using such particles as components of adaptive devices or as building blocks for the self- or directed assembly of complex and functionally optimized hierarchical structures in applications as diverse as catalysts, special effect pigments, sensors and biomedical diagnostics and therapeutics.

In this presentation I will focus on the creation of interfacial anisotropy, a topic which has received rapidly growing attention in recent years. In particular the exciting promise for fundamental and applied research of so-called patchy and Janus particles will be introduced. In this regard, my own research group’s activities to synthesise patchy particles by extremely simple and scalable approaches will be highlighted. In contrast to most other reported methods, we avoid the use of templates and phase boundaries but rather employ electroless metallization reactions. Here we rely on the enrichment of the metal precursor and reducing agent at the core particle surface and subsequent heterogeneous nucleation and surface diffusion driven conformal growth of the metal. To ensure a narrow distribution of metal patch numbers and coverages, we have undertaken a programme of replacing the initially-developed batch processes^1,2 with setups based on a continuous flow static mixers³. On the one hand, this has enabled systematic studies of the materials chemistry behind the surface conformal crystal growth. Here I will illustrate our use of advanced characterisation techniques such as analytical ultracentrifugation. On the other hand, we have expanded beyond the original core particle systems of colloidal silica¹ and polystyrene² to demonstrate our fabrication methodology for technical substrates of various compositions. Target applications are wide ranging, from plasmonic sensors and photovoltaic enhancement to catalysis and biomaterials.

[1] H. Bao, R. N. Klupp Taylor, W. Peukert, One-pot Colloidal Synthesis of Plasmonic Patchy Particles, Adv. Mater. 2011, 23, 2644
[2] H. Bao, T. Bihr, A.-S. Smith, R. N. Klupp Taylor, Facile colloidal coating of polystyrene nanospheres with tunable gold dendritic patches, Nanoscale 2014, 6, 3954.
[3] T. Meincke, H. Bao, L. Pflug, M. Stingl, R.N. Klupp Taylor, Heterogeneous nucleation and surface conformal growth of silver nanocoatings on colloidal silica in a continuous flow static T-mixer Chem. Eng. J. 2017, 308, 89.

Institute for Materials Testing, Materials Science and Strength of Materials (IMWF),
University of Stuttgart, Germany

01.06.2016, 16.30h     
O 018, Eißendorfer Str. 38, TUHH
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Multiscale Materials Modelling
Procedures-Examples-Challenges

In the recent past, multiscale materials modelling became a central idea in understanding present day complex composites and in making progress in the development of advanced materials. There exists, however, a discrepancy between available results described in literature and the expression “multiscale modelling”, because typically cases are treated with two length scales only and some­times additional one or two time scales.

This presentation will describe several successfully running multiscale examples which are used in ana­lyzing pipeline steel weldments, metal/ceramic interfaces and fatigue problems of metals which are employed for a better understanding of physical phenomena in the materials leading to their de­for­mation and fracture behavior. It will be shown that not only several length and time scales are re­quired but also several methods have to be involved for performing successful hierarchical analy­ses with quantitative results in the field of modern materials research.

In addition, studies will be shown which provide the basis for the development of new material alloys when taking ab initio, Monte Carlo or Molecular Dynamics modelling approaches into account. As examples solid solution hardening is considered for Fe-base ma­te­rials or fatigue loading for polycrystalline steels where property predictions are in close agree­ment to experimental findings.

S. Schmauder, D. Uhlmann, G. Zies, "Experimental and numerical investigations of two material states of the material 15 NiCuMoNb (WB 36)", Computational Materials Science 25, pp. 174-192 (2002).
S. Schmauder, "Simulation als Instrument der Werkstoffentwicklung", Metall 63, pp. 295-297 (2009).
S. Schmauder, C. Kohler, "Atomistic simulations of solid solution strengthening of α-iron", Computational Materials Science 50, pp. 1238-1243 (2011).
S. Schmauder, U. Weber, A. Reuschel, M. Willert, "Simulation of the Mechanical Behaviour of Metal Matrix Composites", Materials Science Forum 678, pp. 49-60 (2011).
Z. Bozic, S. Schmauder, M. Mlikota, M. Hummel, „Multiscale fatigue crack growth modelling for welded stiffened panels”, Fatigue & Fracture of Engineering Materials & Structures 00, pp. 1-12 (2014).

Center for Materials Physics and Technology, Naval Research Laboratory, Washington, DC, USA

25.05.2016, 17.00h     
O 018, Eißendorfer Str. 38, TUHH

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Mechanical effects of fluids adsorption by nanoporous materials

In my talk I will focus on two mechanical effects related to fluid adsorption by porous materials: adsorption-induced deformation and change of elastic properties of fluids during adsorption. I will start from reviewing recent experimental findings and continue with presenting my theoretical models for them. The development of quantitative theories of these effects will provide the opportunity to employ them for new sensing technologies and new approaches for the characterization of nanoporous materials [1].

Adsorption-induced deformation is a change of shape or volume of a porous sample during adsorption. It could be either expansion or contraction, and while the former is well understood, the latter is still puzzling due to the apparent contradiction with the Gibbs adsorption equation [2]. I will show how this apparent contradiction can be resolved by relating the strain of the solid to the change of the surface stress due to adsorption. I will present the results of the surface stress calculations based on ab initio molecular dynamics simulations.

In the second part of my talk I will focus on the effects of nanoconfinement on the mechanical properties of the adsorbed fluid. Recent ultrasonic experiments have shown that the elastic modulus of argon adsorbed in nanoporous glass noticeably differs from the elastic modulus of bulk liquid argon. I will present the results of a molecular modeling study which explains these experimental observations and sheds light on possibilities of ultrasonic investigation of nanoporous materials [3].

1. Gor, G. Y.; Bertinetti, L.; Bernstein, N.; Hofmann, T.; Fratzl, P. & Huber, P. Appl. Phys. Lett., 2015, 106, 261901
2. Gor, G. Y. & Bernstein, N. Phys. Chem. Chem. Phys., 2016, 18, 9788-9798
3. Gor, G. Y.; Siderius, D. W.; Rasmussen, C. J.; Krekelberg, W. P.; Shen, V. K. & Bernstein, N. J. Chem. Phys., 2015, 143, 194506

Laboratory for Multiscale Mechanics Modeling, EPFL, Switzerland

27.04.2016, 17.00h     
O 018, Eißendorfer Str. 38, TUHH

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Microstructural design of fiber composites

Composites reinforced with ceramic fibers are often brittle and fail without warning. One route for improving the composite response involves design of the composite microstructure using multiple fiber types, directions of reinforcement, and/or length scales. Some of these concepts can now be realized in the lab, via techniques such as additive manufacturing. However, the space of possible microstructures is too large to be explored by trial-and-error alone; thus, mechanics models are needed to guide composite manufacturing efforts. These models should connect the overall composite properties to the constituent properties and composite microstructure.

In this talk, I will present one such class of mechanics models, known as global load sharing (GLS) theory. I will apply GLS theory to two types of fiber composites --- “hybrid” composites, which use fibers of multiple types (e.g., carbon and glass), and “hierarchical” composites, in which fibers span multiple length scales. In both cases, I show that the added microstructural complexity allows different properties, such as strength and toughness, to be traded-off. In the case of hybrid composites, I have identified optimal composites that are stronger, stiffer, and tougher than the corresponding single-fiber-type composite. As an added benefit, these composites are “pseudo-ductile,” exhibiting non-linear behavior before fracture. Preliminary comparisons of the model with experimental results on discontinuous-fiber hybrid composites are also generally good. In the case of hierarchical composites, I have demonstrated that the optimal composites are quite complex, comprising long fibers at lower scales and discontinuous fibers at the highest. Although making such composites in the lab will be challenging, they promise to be substantially tougher and more damage-tolerant than their non-hierarchical counterparts.

Materials Research Centre, Indian Institute of Science, Banglore, India

27.01.2016, 16.15h     
K 0506, Denickestr. 15, TUHH

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Structural, microstructural and interfacial engineering of nanostructures and hybrids for applications

Nucleation and growth processes play a key role in controlling the structure, microstructure and chemistry and consequently every conceivable property of advanced functional materials. Our group has been working on wet-chemical methods for the synthesis of nanostructures and hybrids. While these methods are simple and undoubtedly very powerful, the mechanisms of nucleation and growth are poorly understood. In particular, there is an over-emphasis on the role of specific reagents rather than broad principles that are applicable for a wide variety of systems. My talk will focus on three specific issues. In the first part, I will discuss some general principles of morphology evolution during wet chemical synthesis. In particular, the formation of anisotropic structures of high symmetry materials and the associated symmetry breaking mechanisms will be discussed. Specific examples include the growth of ultrathin single crystalline Au nanowires and the formation of plate-shaped structures. I will present some of the newer results on the intriguing structure and properties of the ultrathin metal nanowires. In the second part, I will discuss a general method for the synthesis of nanoporous materials and discuss some of their applications. Some unexpected and interesting results on the stability of these nanoporous systems will be presented. In the third part, I will discuss about the role of heterogeneous nucleation for controlled synthesis of nanoscale hybrids for a variety of applications including catalysis and photovoltaic applications.The overall emphasis will be on illustrating general principles that we have been able to extract based on our research over the past few years and also some thoughts on future directions, applications and possible collaborations.

Simulation Engineering (MOSE) Laboratory, Department of Engineering and Architecture, University of Trieste, Italy

13.01.2016, 16h
K 0506, Denickestr. 15, TUHH

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Materials by design: multiscale molecular modeling of nanostructured materials

One of the major goals of computational material science is the rapid and accurate prediction of properties of new materials. In order to develop new materials and compositions with designed new properties, it is essential that these properties can be predicted before preparation, processing, and characterization. Despite the tremendous advances made in the modeling of structural, thermal, mechanical and transport properties of materials at the macroscopic level (finite element (FE) analysis of complicated structures), there remains a tremendous uncertainty about how to predict many critical properties related to performance. The fundamental problem here is that these properties depend on the structure that the material exhibits at a length scale ranging from few to some dozens of nanometers, and this structure depends strongly on the interactions at atomistic scale. In order to substantially advance the ability to design useful high performance materials, it is essential that we insert the chemistry into the mesoscopic (MS) modeling. Currently, atomistic level simulations such as molecular dynamics (MD) or Monte Carlo (MC) techniques allows to predict the structure and properties for systems of considerably large number of atoms and time scales of the order of microseconds. Although this can lead to many relevant results in material design, many critical issues in materials design still require time and length scales far too large for practical MD/MC simulations. Given these concepts, it is than necessary to carry out calculations for realistic time scales fast enough to be useful in design. This requires developing techniques useful to design engineers, by incorporating the methods and results of the lower scales (e.g., MD) to mesoscale simulations [1]. To this aim, we have developed a multiscale molecular modeling protocol, based on the combination of different techniques each of them suitable for the simulation at a given time and length scale. The protocol is able to predict macroscopic properties taking into account the nanostructure and the effect of the interphases/interfaces at nanoscale, thus resulting in a powerful tool for designing nanostructured systems [2]. The talk will describe the details of the multiscale molecular simulation framework, and will focus on some examples of industrial relevance both in material science and in life science [3].

References:

[1] Fermeglia M., Pricl S., Multiscale molecular modeling in nanostructured material design and process system engineering, Computers & Chem.Eng, 33:1701-1710 (2009).

[2]Posocco P., Pricl S., Fermeglia M., In "Modeling and Prediction of Polymer Nanocomposite Properties" edited by Vikas Mittal, Wiley-VCH Verlag GmbH & Co, 1:95-128 (2013)

[3] Scocchi G., Posocco P., Handgraaf J.W., Fraaije J.G.E.M., Fermeglia M., Pricl, S., A complete multiscale modelling approach for polymer-clay nanocomposites, Chemistry - A European Journal, 15:7586-7592(2009).

Mechanical Engineering Department, University of California, Santa Barbara, USA

11.11.2015, 17ct      
K0506, Denickestr. 15, TUHH

pdf version

Metamaterials with extreme stiffness and strength

Metamaterials have mechanical properties that are a function of their geometry on the mesoscale, the intermediate scale between microsctructural features of the constituent material(s) and the macroscale on which loads and parts are described. These materials can fill an otherwise unpopulated region of property space in terms of low density and high stiffness and strength. A material geometry has been identified that achieves theoretical bounds for isotropic stiffness, over a wide range of relative densities, giving it nearly ideal properties, and is capable of filling this hole in property space. This closed cell geometry, while being relatively simple, presents challenges in terms of fabricablity when compared to open cell geometries which allow for fluid transport, facilitating infiltration and exfiltration of materials during and after processing. A second disparate material system has been measured to have the highest specific stiffness and strength for its density. This material is formed by self-assembly on the nanoscale to produce an inverse FCC geometry. These opaline structures are then coated with TiO2 by atomic layer deposition. The addition of this second stiff phase greatly increases the ultimate performance, while having a mixed influence on structural efficiency.  While this material has been measure to have extremal properties its performance is poor compared to an ideal geometry. We investigate the morphological features associated with high performance by comparing these two material systems. Finite element homogenization is used to compute the properties and resolve strain energy distributions. Uniform strain energy distributions in stiff networks of members aligned with principle stresses are key to high performance. Two and three phase theoretical bounds are used as metrics for performance, with three phase systems having a significant advantage in ultimate performance when compared to the Voight bound. Compromises between constituent properties, fabrication techniques, mesoscale geometry, scale, and other factors are currently necessary in realizing materials that can achieve extremal properties beyond current possibilities.

Institute of Applied Physics, TU Vienna, Austria

24.06.2015, 17ct      
N 0008, Eißendorfer Str. 40, TUHH

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Surface Science Studies of Magnetite Fe₃O₄

Magnetite, Fe₃O₄, is an abundant material with interesting electronic, magnetic, and chemical properties that make it promising for many applications. The talk will focus on the (001) surface of Fe₃O₄ single crystals.  This surface forms a reconstruction with (√2x√2)R45° symmetry that was solved recently [1].  Subsurface iron atoms are missing in a regular fashion, which gives rise to a peculiar – and rather useful – adsorption behavior on the surface:  vapor-deposited metal atoms, e.g., Au [2], Ag [3] Pd [4], Pt , Fe, Co, Ti , etc., stick strongly to one specific site within the reconstructed unit cell.  Noble metals do not diffuse until the reconstruction is lifted around 700 K [5], while more reactive metals move subsurface filling the cation vacancy sites. This property enables one to follow aggregation and sintering phenomena at the atomic scale [3, 4] with Scanning Tunneling Microscopy (STM).  The Fe₃O₄(001)–(√2x√2)R45°) is also an excellent model system for observing surface reactions that are relevant in catalysis. 

[1] R.  Bliem, et al. Science, 346 (2014) 1215
[2] Z. Novotný, et al. Physical Review Letters, 108 (2012) 216103
[3] R. Bliem, et al. ACS Nano 8(7) (2014), 7531–7537
[4] G. S. Parkinson, et al., Nature Materials, 12 (2013) 724 - 728
[5] N.C. Bartelt, Phys. Rev. B 88, 235436 (2013).

Institut für Baustoffe (IfB), ETH Zürich, Switzerland

10.06.2015, 17ct      
N 0008, Eißendorfer Str. 40, TUHH

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Bio-inspired wood materials

The fabrication of renewable materials with superior properties and novel functionalities is one of the key challenges for a transition to sustainable societies. Among the materials available from nature, wood is a rather exceptional material that has been used for thousands of years. The mechanical performance of trees predominately originates from a sophisticated cell wall assembly, the hierarchical structure of the wood body as well as adaptive growth processes. An unravelling of the underlying structure-function relationships of wood allows for transferring the crucial principles and mechanisms for the design of bio-inspired materials. The bulk wood structure can be functionalized at the nano-and microscale to improve wood properties or to add new functions to the engineering material for novel applications. This concept is presented by means of various wood modification approaches such as in-situ polymerization techniques and mineralization processes at the cell wall level or magnetic hybrid wood composites with an anisotropic material profile. Principles of hydro-actuation in plants are presented and transferred for the design of autonomously deforming wood structures, which are driven by daily humidity changes and can be utilized as bio-based and bio-inspired facade elements.

DESY NanoLab and University of Hamburg, Physics Department, Hamburg, Germany

12.11.2014, 17ct      
K 0506, Denickestr. 15, TUHH

pdf version

The Atomic Structure of Nano-Objects:
What X-Rays Can Tell

The atomic structure determination of nano-objects with dimensions in the sub-100 nm regime is a formidable task for today’s diffraction, imaging and scanning probe techniques. Such a detailed structural and compositional analysis is mandatory for a correlation with the nano- object’s functionality e.g. as heterogeneous catalysts, magnetic storage material or light emitting device. In conventional x-ray diffraction experiments on powder samples the structural analysis is hampered by a random nanoparticle orientation and often by background scattering from the supporting material. Here I will present different ensemble averaging in-situ synchrotron radiation based x-ray diffraction schemes delivering quantitative information on the nanoparticle size, shape and facet surface structures under varying gas surroundings:
First I will discuss high resolution reciprocal space mapping from epitaxial Rh and Pt-Rh nanoparticles under oxidizing and reducing conditions, as well as during CO oxidation at near ambient pressures [1]. As a second approach I will present a combinatorial high energy x-ray diffraction scheme (85 keV photon energy) allowing a systematical screening of particle size or composition under identical reaction conditions, which we used to follow the CO oxidation induced sintering process of PtRh nanoparticles as a function of their composition [2]. Finally, I will demonstrate how graphene templated growth of nanoparticles with diameter < 2 nm opens the door for x-ray diffraction experiments with high crystallographic precision and monitoring of nanoparticle / gas molecule interactions [3].

[1] P. Nolte, A. Stierle, N. Y. Jin-Phillipp, N. Kasper, T. U. Schulli, H. Dosch, Science 321, 1654-1658 (2008).

[2] P. Müller, U. Hejral, U. Rütt and A. Stierle, Phys. Chem. Chem. Phys. 16, 13866 (2014).
[3] D. Franz, S. Runte, C. Busse, S. Schumacher, T. Gerber, T. Michely, M. Mantilla, V. Kilic, J. Zegenhagen, und A. Stierle, Phys. Rev. Lett. 110, 065503 (2013).

CANCELED

Materials Department and Department of Mechanical Engineering, University of California, Santa Barbara, USA

09.07.2014, 17ct
K 0506, Denickestr. 15, TUHH

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GPU-Based Simulations of Fracture in Idealized Brick and Mortar Microstructures
This talk will describe simulations of fracture in idealized brick and mortar microstructures comprising extremely stiff bricks bonded together with compliant, ductile mortar. The objective is to guide the development of ‘synthetic nacres’ by providing quantitative connections between brick hierarchy (i.e. size distributions, stacking sequences, etc.), interface behaviors, and macroscopically-defined fracture toughness. The simulations are created using an idealized framework tracks individual brick displacements and rotations and accounts for brick interactions using a non-linear cohesive law that spans elastic response, perfectly plastic yielding, and rupture. Micromechanical models will be presented that indicate the range of constituent properties for which microstructural idealization is expected to be valid. A novel incremental Monte-Carlo minimization scheme will be described to simulate cracking without a priori assumptions of the interaction between crack path and brick arrangement; the framework is specifically tailored to using graphical processing units (GPUs) to exploit highly parallel computations. Simulations of fracture in specimens with various brick/interface alignments, size distributions, strength distributions, etc. are used to extract the relationships between these features and the macroscopically-defined intitation toughness, strength and modulus. The results demonstrate that the fracture toughness and strength are a strong function of the orientation between microstructural features and loading direction, which dictates active fracture mechanisms observed elsewhere in experiments (e.g. splitting, staircases, bridging). The results also demonstrate that statistical distributions in constituent properties can have a profound impact on inferred macropscopic properties, even though the latter are essentially deterministic.

School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, USA

25.06.2014, 17ct      
K 0506, Denickestr. 15, TUHH

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Nanogenerators as new energy technology and piezotronics for functional systems
Developing wireless nanodevices and nanosystems is of critical importance for sensing, medical science, environmental/infrastructure monitoring, defense technology and even personal electronics. It is highly desirable for wireless devices to be self-powered without using battery. Nanogenerators (NGs) have been developed based on piezoelectric, trioboelectric and pyroelectric effect, aiming at building self-sufficient power sources for mico/nano-systems. The output of the nanogenerators now is high enough to drive a wireless sensor system and charge a battery for a cell phone, and they are becoming a vital technology for sustainable, independent and maintenance free operation of micro/nano-systems and mobile/portable electronics. This talk will focus on the fundamentals and novel applications of NGs.
For Wurtzite and zinc blend structures that have non-central symmetry, such as ZnO, GaN and InN, a piezoelectric potential (piezopotential) is created in the crystal by applying a strain. Such piezopotential can serve as a “gate” voltage that can effectively tune/control the charge transport across an interface/junction; electronics fabricated based on such a mechanism is coined as piezotronics, with applications in force/pressure triggered/controlled electronic devices, sensors, logic units and memory. By using the piezotronic effect, we show that the optoelectronc devices fabricated using wurtzite materials can have superior performance as solar cell, photon detector and light emitting diode. Piezotronics is likely to serve as a “mechanosensation” for directly interfacing biomechanical action with silicon based technology and active flexible electronics. This lecture will focus on the fundamental science and novel applications of piezotronics in sensors, touch pad technology, functional devices and energy science.

Zoological Institute, Kiel University

18.06.2014, 17ct
K0506, Denickestr. 15, TUHH

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Fly on the ceiling:
Animal attachment devices and biologically-inspired adhesives
Why does the fly not fall from the ceiling? Animal attachment systems demonstrate their excellent adhesion and high reliability of contact. The structural background of this functional effect will be discussed. It will be demonstrated how comparative experimental biological approach can aid in development of novel tribological materials and systems. Biomimetic mushroom-shaped fibrillar adhesive microstructure inspired by these systems was characterized using a variety of measurement techniques and compared with a control flat surface made of the same material. Results revealed that pull-off force and peel strength of the structured specimens are more than twice those of the flat specimens. Based on the combination of several geometrical principles found in biological attachment devices, the presented microstructure exhibits a considerable step towards the development of an industrial dry adhesive.

Department of Materials Science and Metallurgy, University of Cambridge, UK

07.05.2014, 17ct
K0506, Denickestr. 15, TUHH

pdf version

Electron Tomography in Materials Science:
3D Imaging at the Nanoscale

Although its origins lie in the life sciences as a technique to investigate the 3D ultrastructure of cells, viruses and bacteria, electron tomography has become a method used by many in materials science to routinely characterise 3D morphology at the nanoscale. The need to study ever-more complex materials structures, especially at the nanoscale, led to the introduction first of STEM HAADF tomography and later, through the combination of tomography with other imaging and spectroscopy techniques, methods for 3D mapping of composition, dislocation networks and electromagnetic potentials. More recently, there is a growing need not only for higher spatial resolution but also for improved quantification of tomograms which has led to novel reconstruction algorithms yielding more reliable and obust 3D information. Developments in the efficiency and speed of detectors and spectrometers has led to advances in ‘spectrum-tomography’ where 4D data sets (with spatial and energy dimensions) contain a wealth of information not only about 3D morphology but also the composition and chemistry at the nanoscale. This seminar will discuss progress made to date, highlighting key advances with illustrations from a broad spectrum of materials science. Challenges and opportunities that lie ahead will also be considered, focussing on how recent technical developments, both hardware and software, should allow new insights into the understanding of materials at the nanoscale.

Department of Mechanical Engineering McGill University, Montreal, Canada

29.01.2014, 17ct
K0506, Denickestr. 15, TUHH

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Overcoming brittleness trough bio-inspiration and microarchitecture

Natural structural materials such as bone and seashells are made of weak and brittle “building blocks”, yet they exhibit unique combinations of mechanical properties currently unmatched by their engineering counterparts. This performance can be largely explained by their “staggered microstructure”, a brick wall-like arrangement of stiff inclusions of high aspect ratio parallel to each other with some overlap, and bonded by a softer matrix. Here I will discuss how this seemingly simple microstructure generates high stiffness, high strength and attractive post-yielding behaviors by gliding of the inclusions on one another, and how this attractive micro-mechanism propagates over large volumes within the material ensuring high properties at the macroscale. I will also discuss, through experiments and modeling, how the staggered structure “amplifies” the toughness of its constituents through crack deflection along weak interfaces, crack bridging and process zone mechanisms. As a result, a material like nacre is several orders of magnitude tougher than calcium carbonate, its main consistent.
Duplicating the structures and mechanisms of natural materials into “biomimetic materials” represents formidable challenges in terms of fabrication, which we are addressing using two different approaches. In the “inclusion-based” approach we align and assemble microscopic ceramic inclusions using a simple doctor blading technique. We used this method to produce nacre-like films, and cylinders with a structural hierarchy similar to bone osteons. On the other hand, the “interface-based” approach is a topdown approach where weaker interfaces are carved directly within the bulk of glass using threedimensional laser engraving. The architecture and the toughness of the interfaces is designed to channel cracks into controlled sliding and toughening configurations, which resulted in a deformable material made of 99% glass, but 300 tougher. These micro-architectured glasses can be further combined with elastomers and other polymers with attractive rheologies to produce nacre-like glasses and other twoand three dimensional bio-inspired materials with unusual behavior and mechanical performance.

Department of Materials Science and Engineering, Stanford University, USA

30.10.2013, 17ct
K0506, Denickestr. 15, TUHH

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Hybrid Films in Nano- and Bio-Technologies:
Molecular Design and Thermo-Mechanical Properties

Hybrid films comprising inorganic and organic components tailored at molecular length scales are used in a wide range of emerging nano-technologies. These range from protective transparent (conductive) coatings in display and photovoltaic devices, membranes in fuel cells, dielectric layers in microelectronics and adhesive layers in high-performance laminates.  They operate near the envelope of their mechanical and adhesive properties with remarkably high levels of film stress.  Reliability integrating new multi-functional hybrid films requires a new understanding of their mechanical properties and how they are related to underlying molecular structure. Similarly, some biological tissues like human skin are layered structures in which biomechanical properties of component layers are crucial in understanding biophysical function. Skin hybrid constructs that incorporate inorganic UV absorbing nanoparticles can be designed to prevent damage after solar exposure.

We will describe some of our research by selecting several examples involving hybrid materials in emerging nanoscience, energy and bioscience technologies.  Specifically, we will discuss molecular design of multi-functional hybrids for resistance to moisture assisted cracking, the fracture behavior of materials in active layers and modules of photovoltaic devices exposed to hostile solar conditions, and finally, discuss the biomechanical function of human skin and the effects of treatments and technologies to reduce skin damage and promote regeneration.

Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany

03.07.2013, 17ct
K0506, Denickestr. 15, TUHH

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Intrinsic Nanostructures in 1 Billon Tons:
Interface Engineering in Complex Steels and Biological Nanocomposites

Two topics will be addressed in this contribution: advanced near-atomic scale interface analysis in Fe-Mn steels and in biological chitin-based nanocomposites. First, we present novel approaches to the atomic-scale understanding and design of advanced steels. Our scientific interest follows 3 directions: (1) Steels are complex alloys where minor chemical or structural changes can dramatically alter their behavior. (2) Steels can undergo multiple phase transformations that lead to specific nanostructure and property profiles. (3) We increasingly observe that steels can be bottom-up designed by exploiting and designing partitioning, equilibrium defect segregation, and displacive transformation at an atomic scale. Smart use of these effects allows us to better understand and tailor mankind’s most important mass produced material via self organization, lattice defect-, phase-, and interface-design from an atomic perspective. We give exemplary examples from the fields of maraging TRIP steels, TWIP steels, pearlite, and soft magnetic steels. In the second part of the talk a cross-hierarchical analysis and theoretical treatment of calcite-reinforced chitin-based biological nanocomposites will be presented. The background of this work is the analysis of the structure and the mechanical properties of the arthropod cuticle, which serves as the main structural material for more than 90% of all species on the planet.

Optical Materials Engineering Laboratory ETH Zürich, Schweiz

26.06.2013, 17ct
K0506, Denickestr. 15, TUHH

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Template-Stripped Plasmonic Films For Energy Conversion

In general, template stripping utilizes the fact that coinage metals (e.g., silver, gold, and copper) will wet silicon substrates well but adhere poorly. Thus, by depositing such a metal on a patterned silicon wafer, the metal film can then be “stripped” off to reveal a smooth patterned interface that was templated by the substrate. Previously, we demonstrated that silver interfaces obtained via this approach could be ultra-smooth and exhibit improved properties for photonic applications. In particular, such metallic films can be patterned to manipulate electromagnetic waves known as surface plasmons that exist at the interface of the metal. The field of plasmonics has been using patterned metals to channel, concentrate, or otherwise manipulate these waves. However, surface roughness and other inhomogeneities can impede the propagation of the surface plasmons, limiting performance. Template stripping can provide a simple high-throughput method for obtaining high quality patterned metals to avoid these issues. Moreover, we have recently demonstrated that template stripping can be extended beyond the coinage metals to refractory metals, semiconductors, and oxides, enabling a variety of structures. In this talk, we will discuss the use of these template-stripped films for photovoltaic applications. For example, because heat can be used to generate surface plasmons, we have been studying hot plasmonic structures for obtaining new and useful optical behavior. We have shown that metallic bull's eye patterns can lead to thermal emission that is amazingly narrow, both in terms of its spectrum and its angular divergence. Thus, a simple metallic foil can generate a highly directional beam of monochromatic light by a thermal process. This effect has implications for creating efficient thermophotovoltaic devices, which convert heat into electricity. Structured stacks of metallic and semiconductor layers can also have implications for photovoltaic devices.

Max-Planck-Institut für Kolloid- und Grenzflächenforschung, Golm (Potsdam), Department of Biomaterials, Germany

23.01.2013, 17ct
K 0506, Denickestr. 15, TUHH

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Multi-scale structure and interface design in biological materials

Most load-bearing biological tissues, such as bones, plant stems, glass sponges or protein fibers have a multi-scale architecture resulting from the assembly of building blocks. This allows the fine-tuning of (generally multi-functional) properties but also requires specific interface structures to allow proper load transfer between the building blocks. The lecture reviews recent work on determining structure, composition and functionality of interfaces in a variety of biological materials.

Christian-Albrechts-Universität zu Kiel, Institut für Experimentelle und Angewandte Physik, Germany

28.11.2012, 17ct
K 0506, Denickestr. 15, TUHH

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Surface X-ray scattering studies of deeply buried interfaces in condensed matter: Functional composites, electrochemical growth, and liquid interface structure