Method field C: Nanotools

Dip-pen lithography

Coordinator: Harald Fuchs, Physics Institute

This mothod field forms the general methodical platform within the SoN. Both research fields A and B require nanotools to prepare functional nanomaterials and to analyze their structure and function. For that purpose, nanofabrication methods, including self-assembly and lithography, as well as analytical methods adapted to the SoN environment shall be developed far beond the current state. Nanotools can be divided into two groups:

  1. Tools for a controlled preparation of functinal nanomaterials to self-assemble nanosystems in an active and controlled manner
  2. Nanoanalytic techniques for local specroscopy and structure investigations at freely selectable positions with nanometer precision and up to an atomic resolution.

The development of nanotools in Münster has a long tradtion, whereas within some fields an international leading position is occupied. Beside the development of specific procedures relevant in fundamental research, for a range of cases it was possible to bring procedures to maket maturity and to market them with great success.

Reference: Fuchs,  NatureNano.

© H.F. Arlinghaus

Heinrich F. Arlinghaus, Institute of Physics
Nanoanalysis with ToF-SIMS/Laser-SNMS

To understand the important physical and chemical properties of molecular nanostructures, it is essential to know the 3D chemical composition of the materials. This requires answering three central questions: Which elements, isotopes, functional groups and molecular compounds are present? What are the concentrations of these chemical constituents? How are these components distributed in three dimensions? To answer these questions, the Arlinghaus research group is investigating two mass spectrometric imaging techniques as nanoanalysis tools, time-of-flight secondary ion mass spectrometry (ToF-SIMS) and laser post-ionization secondary neutral mass spectrometry (Laser-SNMS). The group has developed a unique combined cryo-ToF-SIMS/Laser-SNMS instrument with integrated high vacuum cryo-preparation/cryo-sectioning for nanoanalytical applications in life sciences. Fundamental research in sputtering and ionization as well as specific life science applications are being investigated. The Arlinghaus group, in interdisciplinary cooperation with numerous academic and industrial partners, has already applied these methods to solve a range of different technologically relevant analytical problems. Examples include trace molecular analysis, synthesis of molecular functional layers to develop DNA/PNA/protein/peptide biosensors, differential diagnosis and pharmacokinetic studies in cell tissues, biomineralization, and characterization of nanoparticles in the environment and within cells. Using these techniques organic compounds can be detected and identified with attomol sensitivity. Trace amounts of pharmaceutical compounds and their degradation products can be localized and quantified in cell cultures and tissue cells with nanometer scale 3D resolution.

Relevant preliminary work:

  1. “Improved 3D-imaging of a sirolimus/probucol eluting stent coating using laser postionization secondary neutral mass spectrometry and time-of-flight secondary ion mass spectrometry.” A. Pelster, B. J. Tyler, M. Körsgen, R. Kassenböhmer, R. E. Peterson, M. Stöver, W. E. S. Unger, H. F. Arlinghaus, Biointerphases 2016, 11, 041001/1-10.
  2. "ToF-SIMS and laser-SNMS analysis of Madin-Darby canine kidney II cells with silver nanoparticles using an argon cluster ion beam.” R. Nees, A. Pelster, M. Körsgen, H. Jungnickel, A. Luch, H. J. Galla, H. F. Arlinghaus, Biointerphases 2016, 11, 02A305/1-5.
  3. “Characterization of freeze-fractured epithelial plasma membranes on nanometer scale with ToF-SIMS.” F. Draude, M. Körsgen, A. Pelster, T. Schwerdtle, J. Müthing, H. F. Arlinghaus, Anal. Bioanal. Chem. 2015, 407, 2203-2211.

Figure: Drug eluting stents (DES) are among the most widely used drug-releasing systems worldwide. The 3D ToF-SIMS image (lateral resolution ~150 µm) of a dual DES coating shows the outer ~1 µm of the coating. An overlay of signals for C5H10N+ (sirolimus, releasing drug: green) and C17H27SO+ (probucol, matrix: blue) is shown. Additionally, the different sputter ion dose densities (SpIDD) are depicted with the corresponding layer depth up to a depth of 1 µm. It can be seen that sirolimus (green) dominates at the surface. At a depth of about 40 nm, distinct areas of probucol appear which are surrounded by sirolimus. Below a depth of 150 nm, a nearly uniform mixture of drug and matrix is observed. However, small channels of concentrated sirolimus persist to a depth of 1 µm. Beneath this, probucol and sirolimus are homogeneously distributed throughout the entire drug-eluting coating (not shown).

Reference: [1]

Functionalization of a gold dot-structured surface with different organic molecules

Lifeng Chi, Physics Institute
Nanostructured biochemical surfaces

Patterned surfaces with micro/nano sized structures have been demonstrated to be a powerful platform for providing molecular engineering of cellular environments. Increased efforts have been made to study the influence of structured surfaces on cell behaviors such as adhesion, differentiation, proliferation and so on. These studies aim at creating biomimetic environments with defined chemical and physical properties in order to gain deeper understandings on how cells interact with their environment.

We are well experienced in the fabrication of structured surfaces with feature sizes ranging from micrometers down to nanometers, based on bottom-up and top-down strategies, as well as their combinations, and further chemical modifications. The application of these structured surfaces in cell culture has been conducted in our group in the recent years to demonstrate their influence on cell behaviors. For instance, osteoblasts, phytopathegenic fungi Magnaporthe Grisea and Pucinnia Graminis cells show clear alignment along topography patterns made by Langmuir-Blodgett Lithography (LBL); Human embryonic stem cells (hESC), which have the ability to differentiate into three germ layers, differentiate preferably towards neuronal lineage on structured surfaces with linear shapes; the growth of some cancer cells can be effectively depressed on nanostructured surfaces.

In future works, we are going to focus on the fate of embryonic stem cells and cancer cells on structured surfaces - in collaboration with the Max-Planch-Institute of Molecular Biomedicine (MPI Münster) and medical/biological groups of WWU - together with chemical modifications of the surfaces. Furthermore the application of external forces such as mechanical forces and electrical fields is in planning. Based on the understanding of the mechanisms behind the effects, the long term goal is to develop applicable surfaces/interfaces for clinical regenerative medicine.

Relevant preliminary work:

  1. “Tunable organic hetero-patterns via molecule diffusion control.” H. Wang, W. Wang, L. Li, M. Hirtz, C. G. Wang, Y. Wang, Z. Xie, H. Fuchs, L. Chi, Small 2014, 10, 3045-3049.
  2. “Addressable organic structure by anisotropic wetting.” W. Wang, C. Du, L. Li, H. Wang, C. Wang, Y. Wang, H. Fuchs, L. Chi, Adv. Mater. 2013, 25, 2018-2023.
  3. “Patterned nucleation control in vacuum deposition of organic molecules.” W. C. Wang, D. Y. Zhong, J. Zhu, F. Kalischewski, R. F. Dou, K. Wedeking, Y. Wang, A. Heuer, H. Fuchs, G. Erker, L. F. Chi, Phys. Rev. Lett. 2007, 98, 225504.

Reference: “Tunable multicolor ordered patterns with two dye molecules.” W. Wang, C. Du, H. Bi, Y. Sun, Y. Wang, C. Mauser, E. Da Como, H. Fuchs, L. Chi, Adv. Mater. 2010, 22, 2764-2769.

Harald Fuchs, Physics Institute
Constructive lithography for biomimetic surfaces

Scanning-probe technologies have unique potential for directly characterizing and functionalizing interfaces with biological materials at ultrahigh resolution because of their ability to function in humid air and aqueous environments. Massively parallel tip array systems with several tens of thousands of tips are available allowing to deposited surface areas with nanostructures as large as several cm² per minute.

Using this technique biomimetic systems can be written, which may vary chemically from spot to spot. Systems such as sensor arrays which undergo structural changes after specific molecular adsorption, allergen arrays as well as artificial anchor-patches for biological cells and model systems for membrane rafts can be developed. It is clear that these opportunities require the intense cooperation between Physics, Chemistry and biology, and is, therefore, a valuable tool within the SoN-center, which is complemented by all other scanning probe technique, high resolution far field optics, electron Microscopy, and surface characterization methods.

Christiane Höppener, Physics Institute
Near-field optical microscopy

The research focus of the ‘NanoBioPhotonics’ junior group is on the investigation of the interaction of light and matter on the nanometer scale. The objective is to develop high-resolution microscopic procedures und to apply these for specific biological issues. Beside the spatial resolution, strengthening effects play a role in the improvement of the sensitivity and the detection limit. For this purpose the key element includes optical antennas, which can change the local confinement of optical fields as well as the local density of states of the quantum emitters’ environment, and thus influence the transition rates. This allows an investigation of systems featuring a low quantum yield of photoluminescence. For that reason, antenna-enhanced optical microscopy/spectroscopy allow the possibility to identify and address natural fluorescent proteins and protein complexes at submicroscopic resolution.

Jürgen Klingauf, Institute of Medical Physics and Biophysics

The rational control of the growth of neurons and cells as well as the formation of synaptic contacts on functionalized substrates is a present challenge, which could enable the development of particular cell systems. The results of these experiments deepen the fundamental understanding of synaptic dynamics and plasticity and, in the long term, generate impulses for the development of neuronal interfaces. Chiral surfaces or surfaces modified with proteins and synthetic biocompatible gels control the cell growth for i.a. implants. Within this thematic field, the existing cooperation with the MPI of Molecular Biomedicine and the excellence cluster “Cells in Motion” can be employed. The application of adaptive and responsive materials in the regenerative medicine can be regarded as a long term perspective, whereas it is aimed at a synthetic substitution of the epithelial barrier.

Schematic representation of a light emitting carbon nanotube coupled to an optical waveguide (blue). The carbon nanotube is electrically contacted with metal electrodes (yellow)

Wolfram Pernice, Institute of Physics
Nanophotonics and single photon detection

Using nanophotonic building blocks we develop optical integrated circuits which are able to process optical signals in analogy to electronic circuits. In such photonic circuits electrical wires are replaced by waveguides which guide light across the chip surface. This allows for realizing complex optical components, consisting of individually optimized fundamental units which are interconnected to intelligent systems. Such devices comprise for example of nanoresonators, integrated spectrometers and optical memories. Nanostructured systems are particularly interesting for nanoanalytic applications because they allow for measuring surface effects in the optical near field with highest precision. Especially hybrid optical circuits which combine traditionally passive materials such as silicon and dielectrics with functional nanocomponents offer unprecedented possibilities for chipbased sensing, metrology and surface analytics. We analyze such systems with photonic measurement techniques and combine them with novel sensing concepts which exploit radiation pressure. This way additional mechanical degrees of freedom become accessible for optical devices and offer new possibilities to realize tunable components.

Complementary to hybrid nanophotonic systems, we investigate photonic structures at ultralow intensities, down to the single photon level. For this purpose we develop high performance single photon detectors integrated atop nanophotonic waveguides, leading to near-unity efficiency, negligible dark count rates and highest timing resolution. Because such detectors are realized with scalable nanofabrication techniques, we combine efficient detector arrays with nanophotonic circuits to realize functional single photon systems. Essential for such research directions are precision nanofabrication under cleanroom conditions, precision measurements and efficient simulation techniques to predict the optical behavior of nanophotonic circuits.

Relevant preliminary work:

  1. “Fully integrated quantum photonic circuit with an electrically driven light source.” S. Khasminskaya, F. Pyatkov, K. Slowik, S. Ferrari, O. Kahl, V. Kovalyuk, P. Rath, A. Vetter, F. Hennrich, M. M. Kappes, G. Goltsman, A. Korneev, R. Krupke, W. H. P. Pernice, Nat. Photon. 2016, 10, 727-732.
  2. “Cavity-enhanced light emission from electrically driven carbon nanotubes.” F. Pyatkov, V. Fütterling, S. Khasminskaya, B. S. Flavel, F. Hennrich, M. M. Kappes, R. Krupke, W. H. P. Pernice, Nat. Photon. 2016, 10, 420-427.
  3. “Integrated all-photonic nonvolatile multi-level memory.“ C. Ríos, M. Stegmaier, P. Hosseini, D. Wang, T. Scherer, C. D. Wright, H. Bhaskaran, W. H. P. Pernice, Nat. Photon. 2015, 9, 725-732.

Reference: W. Pernice.

Scanning electron microscopy image of an ultrathin anodic alumina membrane. (upper right) elektro-deposited Ni-Nanowires in porous alumina (upper left). Regular pore structure with a pore diameter of only 15 nm (lower left). Anodic alumina membrane: pores filled with DAR Resin + PAA: poly acrylic acid + POR: porphine tetratosylate (lower right)

Gerhard Wilde, Institute of Materials Physics
Functional surface nanostructures

Nanostructured inorganic/organic hybrid materials offer an increased and new potential for diverse applications in a broad range of fields, such as gas sensing or bio-sensing, optically active or optically responsive surfaces, with regard to novel solar cells of organic light-harvesting complexes or the wide range of organic electronics. All such hybrid systems have complex electronic interactions at the interface between an inorganic substrate, which is structured in many cases, and complex functional molecules or organic/biological building blocks in common. Moreover, non-linear back couplings through this complex interface are of particular significance regarding the functionality and stability of the hybrid systems.

These non-linear back coupling mechanisms result, for example, from the charge transport through the interface, since a charge transport causes local structural modifications, which again cause modifications of the charge transport. In general, such kind of mechanisms need to be considered for the transport of information (photons, charges, masses) through complex interfaces. However, these mechanisms, which are crucial for the functionality and efficiency as well as the stability and lifetime of complex hybrid systems, are not completely understood so far. To experimentally investigate such kind of complex interactions, it is necessary to prepare preferably precise and controlled hybrid systems, which can be analyzed regarding the atomic and electronic structure of the interface applying spatially high-resolution methods. These results are then being incorporated in a model-like description of ensemble properties, which can be directly compared to results obtained from macroscopically averaged experimental procedures.

Exactly at this point the work of the AG Wilde within the SoN starts: We synthesize semi-conducting substrates, isotope-hetero structures, nanostructured semi-conducting, isolating and metal surfaces as well as nanoporous templates of a precisely controlled, highly regulated topology and microstructure. The structures provide carrier systems to immobilize complex molecular functions, which are synthesized by the chemical working groups of the SoN (AG Glorius, AG Ravoo, AG Schönhoff, AG Strassert and AG Studer), yielding in the formation of inorganic/organic functional units. In cooperation with the physical working groups, the resulting hybrid systems will be analyzed with regard to the atomic structure of the interface. Here, the expertise of materials physics is of particular importance, not only to quantitatively explore the topology but also the complex structure of defects at and within the interface. Essential for these studies is the possibility to perform high-resolution transmission electron microscopy without the delocalization of structural information by spherical aberration on “edge-on” oriented interfaces.

Moreover, in cooperation with AG Fuchs and AG Zacharias high-resolution AFM/STM techniques and methods to analyze the electronic structure of areas close to the surface (XPS, Auger electron spectroscopy, photoelectron spectroscopy), respectively,  will be applied. Regarding the experimental analysis of the ensemble properties, measurements of the photoluminescence of organic complexes in nanoporous templates, investigations of nanostructured semi-conductors on nanostructured surfaces applying impedance spectroscopy as well as studies of the efficiency of charge injection of biological light-harvesting complexes in ordered TiO2/Ru-nanowire assemblies are planned for the start, because this experimental analysis is directly linked to our long-time expertise in the field of materials characterization. The model-like description of the experimental results, which only leads to a broadened understanding, is planned to be performed together with theoretical groups regarding the non-linear coupling and shall further be supported by molecular dynamic simulations (AG Doltsinis).

Relevant preliminary work:

  1. “Surface Patterning using Templates: Concept, Properties and Device Applications.” Y. Lei, S. Yang, M. Wu, G. Wilde, Chem. Soc. Rev. 2011, 40, 1247-1258.
  2. “Template-Confined Dewetting Process to Surface Nanopatterns: Fabrication, Structural Tunability, and Structure-Related Properties.” S. K. Yang, F. Xu, S. Ostendorp, G. Wilde, H. Zhao, Y. Lei, Adv. Funct. Mater. 2011, 21, 2446-2455.
  3. "Non-destructive functionalisation for atomic layer deposition of metal oxides on carbon nanotubes: effect of linking agents and defects.” N. Kemnade, C. J. Shearer, D. J. Dieterle, A. S. Cherevan, P. Gebhardt, G. Wilde, D. Eder, Nanoscale 2015, 7, 3028-3034.

Reference: G. Wilde

Electron spinfiltering by organized oligo dsDNA.
© H. Zacharias

Helmut Zacharias, Physics Institute
Electron transfer in functional organic films

We are investigating energy, charge and spin transfer processes in organized functional organic films on, e.g., SiC, a bio-inert substrate material of interest also for electronic applications. To understand the interplay between the adsorbates and the substrate as well as interactions within functional constituents of adsorbates the lifetimes of occupied and unoccupied states are investigated. SiC substrates functionalized via organic linkers with several organic dyes by wet chemistry as well as evaporation in vacuum have been characterized by inverse photoemission, X-ray photoelectron spectroscopy, and picosecond time-resolved fluorescence microscopy. The latter already yields spatially resolved positions of fluorophores.

Ultrafast electron transfer processes are studied by time-resolved two-photon photoemission (2PPE), employing laser radiation with pulse durations of a few tens of femtoseconds. Standard 2PPE spectroscopy does not yield any spatial information, because the recorded signal integrates over the whole light spot on the sample. In order to investigate structural dependencies of electron transfer processes a photoemission electron microscope (PEEM) is employed. This may yield a spatial resolution of 20 nm or better, depending on the type of instrument. In the experiments we use an optical parametric amplifier (OPA) pumped by a Ti:sapphire laser with pulse energies up to 1.1 mJ, a pulse duration of 30 fs and repetition rates between 1 and 10 kHz. The OPA is continuously tunable from 230 nm to 2700 nm with pulse durations between 30 fs and 120 fs and pulse energies between 2 µJ and 250 µJ, depending on the desired output wavelength. A motorized delay stage with a Michelson-type interferometer splits the resulting pulses into two separate ones and thus introduces an adjustable delay with femtosecond resolution.

Lifetime measurements allow to sensitively assess different binding environments. It is therefore expected that changes in the binding of non-covalently bound buildings blocks of functional materials can be revealed.

Relevant preliminary work:

  1. “Spin selectivity in electron transmission through self-assembled monolayers of double-stranded DNA.” B. Göhler, V. Hamelbeck, T. Z. Markus, M. Kettner, G. F. Hanne, Z. Vagner, R. Naaman, H. Zacharias, Science 2011, 331, 894-897.
  2. “Femtosecond Electron Dynamics in Dye-Functionalized 6H-SiC(0001).” N. F. Kleimeier, D. K. Bhowmick, H. Zacharias, J. Phys. Chem. C 2015, 119, 27489-27495.
  3. “Fluorescence Properties of Perylene and Pyrene Dyes Covalently Linked to 6H-SiC(0001) and Silicate Surfaces.” D. K. Bhowmick, L. Stegemann, M. Bartsch, C. Strassert, H. Zacharias, J. Phys. Chem. C  2016, 120, 3275-3288.

Reference: H. Zacharias.