Elmar Neumann

Incorporation of the acetylcholine receptor dimer from Torpedo californica in a peptide supported lipid membrane investigated by surface plasmon and fluorescence spectroscopy

The dimer species (M(r) 580,000) of the nicotinic acetylcholine receptor, isolated from the electric organ of Torpedo californica, was incorporated into a thiopeptide supported lipid bilayer. The incorporation was achieved by fusion of liposomes with reconstituted receptor onto a gold-supported thiopeptide lipid monolayer. Surface plasmon resonance spectroscopy (SPS) was used to monitor in real time the fusion process as well as the specific binding of the antagonist alpha-bungarotoxin. A recently developed extension of SPS offering enhanced sensitivity and specificity, surface plasmon fluorescence spectroscopy (SPFS), was then used to monitor subsequent binding of the monoclonal WF6 and polyclonal antibody, respectively. The latter was fluorescence labeled with Cy5. The different binding assays indicate the successful incorporation of the receptor in the lipid bilayer.

Interfacing electrogenic cells with 3D nanoelectrodes: position, shape, and size matter.

An in-depth understanding of the interface between cells and nanostructures is one of the key challenges for coupling electrically excitable cells and electronic devices. Recently, various 3D nanostructures have been introduced to stimulate and record electrical signals emanating from inside of the cell. Even though such approaches are highly sensitive and scalable, it remains an open question how cells couple to 3D structures, in particular how the engulfment-like processes of nanostructures work. Here, we present a profound study of the cell interface with two widely used nanostructure types, cylindrical pillars with and without a cap. While basic functionality was shown for these approaches before, a systematic investigation linking experimental data with membrane properties was not presented so far. The combination of electron microscopy investigations with a theoretical membrane deformation model allows us to predict the optimal shape and dimensions of 3D nanostructures for cell-chip coupling.

Realization of a vertical topological p-n junction in epitaxial Sb2Te3/Bi2Te3 heterostructures.

Three-dimensional (3D) topological insulators are a new state of quantum matter, which exhibits both a bulk band structure with an insulating energy gap as well as metallic spin-polarized Dirac fermion states when interfaced with a topologically trivial material. There have been various attempts to tune the Dirac point to a desired energetic position for exploring its unusual quantum properties. Here we show a direct experimental proof by angle-resolved photoemission of the realization of a vertical topological p–n junction made of a heterostructure of two different binary 3D TI materials Bi2Te3 and Sb2Te3 epitaxially grown on Si(111). We demonstrate that the chemical potential is tunable by about 200 meV when decreasing the upper Sb2Te3 layer thickness from 25 to 6 quintuple layers without applying any external bias. These results make it realistic to observe the topological exciton condensate and pave the way for exploring other exotic quantum phenomena in the near future.

Bi1Te1 is a dual topological insulator

Markus Eschbach, ∗ Martin Lanius, ∗ Chengwang Niu, ∗ Ewa M lyńczak, 2 Pika Gospodarič, Jens Kellner, Peter Schüffelgen, Mathias Gehlmann, Sven Döring, Elmar Neumann, Martina Luysberg, Gregor Mussler, Lukasz Plucinski, † Markus Morgenstern, Detlev Grützmacher, Gustav Bihlmayer, Stefan Blügel, and Claus M. Schneider Peter Grünberg Institute and JARA-FIT, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Krakow, Poland II. Institute of Physics B and JARA-FIT, RWTH Aachen University, 52074 Aachen, Germany Peter Grünberg Institute and Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany (Dated: May 2, 2016)New three-dimensional (3D) topological phases can emerge in superlattices containing constituents of known two-dimensional topologies. Here we demonstrate that stoichiometric Bi1Te1, which is a natural superlattice of alternating two Bi2Te3 quintuple layers and one Bi bilayer, is a dual 3D topological insulator where a weak topological insulator phase and topological crystalline insulator phase appear simultaneously. By density functional theory, we find indices (0;001) and a non-zero mirror Chern number. We have synthesized Bi1Te1 by molecular beam epitaxy and found evidence for its topological crystalline and weak topological character by spin- and angle-resolved photoemission spectroscopy. The dual topology opens the possibility to gap the differently protected metallic surface states on different surfaces independently by breaking the respective symmetries, for example, by magnetic field on one surface and by strain on another surface.

MBE growth of Al/InAs and Nb/InAs superconducting hybrid nanowire structures

We report the in situ growth of crystalline aluminum (Al) and niobium (Nb) shells on indium arsenide (InAs) nanowires. The nanowires are grown on Si(111) substrates by molecular beam epitaxy (MBE) without foreign catalysts in the vapor-solid (VS) mode. The metal shells are deposited by electron-beam evaporation in a metal MBE. High quality superconductor/semiconductor (SC/SM) hybrid structures such as Al/InAs and Nb/InAs are of interest for ongoing research in the fields of gateable Josephson junctions and quantum information related research. Systematic investigations of the deposition parameters suitable for metal shell growth are conducted. In the case of Al, the substrate temperature, the growth rate and the shell thickness are considered. The substrate temperature as well as the angle of the impinging deposition flux are explored for Nb shells. The core-shell hybrid structures are characterized by electron microscopy and X-ray spectroscopy. Our results show that the substrate temperature is a crucial parameter in enabling the deposition of smooth Al layers. Contrarily, Nb films are less dependent on substrate temperature but are strongly affected by the deposition angle. At a temperature of 200 °C Nb reacts with InAs, dissolving the nanowire crystal. Our investigations result in smooth metal shells exhibiting an impurity and defect free, crystalline SC/InAs interface. Additionally, we find that the SC crystal structure is not affected by stacking faults present in the InAs nanowires.

3D Au–SiO2 nanohybrids as a potential scaffold coating material for neuroengineering

We demonstrate the potential application of chemically synthesized 3D Au–SiO2 hybrid nanoparticles as a promising candidate for scaffold designing in neuroengineering. The hybrid nanospheres on substrates provide micro/nanotopography and the fine Au nanoparticles immobilized on SiO2 spheres together provide stable adhesion cue domains facilitating adhesion and viability of the cells as well as guidance of neurites. We also investigated the cell–nanohybrid interface and interaction mechanism by FIB-SEM for a better insight into the mode of adhesion.

Strain Compensation in Single ZnSe/CdSe Quantum Wells: Analytical Model and Experimental Evidence

The lattice mismatch between CdSe and ZnSe is known to limit the thickness of ZnSe/CdSe quantum wells on GaAs (001) substrates to about 2-3 monolayers. We demonstrate that this thickness can be enhanced significantly by using In0.12Ga0.88As pseudo substrates, which generate alternating tensile and compressive strains in the ZnSe/CdSe/ZnSe layers resulting in an efficient strain compensation. This method enables to design CdSe/ZnSe quantum wells with CdSe thicknesses ranging from 1 to 6 monolayers, covering the whole visible spectrum. The strain compensation effect is investigated by high resolution transmission electron microscopy and supported by molecular statics simulations. The model approach with the supporting experimental measurements is sufficiently general to be also applied to other highly mismatched material combinations for the design of advanced strained heterostructures.

Asymmetric, nano-textured surfaces influence neuron viability and polarity: ASYMMETRIC, NANO-TEXTURED SURFACES

Three dimensional, nanostructured surfaces have attracted considerable attention in biomedical research since they have proven to represent a powerful platform to influence cell fate. In particular, nanorods and nanopillars possess great potential for the control of cell adhesion and differentiation, gene and biomolecule delivery, optical and electrical stimulation and recording, as well as cell patterning. Here, we investigate the influence of asymmetric poly(dichloro-p-xylene) (PPX) columnar films on the adhesion and maturation of cortical neurons. We show that nanostructured films with dense, inclined polymer columns can support viable primary neuronal culture. The cell-nanostructure interface is characterized showing a minimal cell penetration but strong adhesion on the surface. Moreover, we quantify the influence of the nano-textured surface on the neural development (soma size, neuritogenesis, and polarity) in comparison to a planar PPX sample. We demonstrate that the nanostructures facilitates an enhancement in neurite branching as well as elongation of axons and growth cones. Furthermore, we show for the first time that the asymmetric orientation of polymeric nanocolumns strongly influences the initiation direction of the axon formation. These results evidence that 3D nano-topographies can significantly change neural development and can be used to engineer axon elongation.