Die Sammlung der zwei-dimensionalen (2D) Materialien ist begrenzt, da sehr wenige Verbindungen stabil bleiben, sobald sie nur aus Oberflächen bestehen. Aufgrund ihrer außergewöhnlichen Eigenschaften sind 2D Materialien jedoch nach wie vor überaus begehrt. Vor kurzem wurden atomar definierte, chemisch gesättigte SiO2 Bilagen auf verschiedenen Metalloberflächen präpariert. Eine solche ultradünne Silika-Lage wäre eine vielversprechende Ergänzung zur Familie der 2D Materialien, wenn sie unter Strukturerhalt vom Wachstumssubstrat isoliert werden kann. In dieser Arbeit untersuchen wir die Eigenschaften einer Silika-Bilage im Zusammenhang mit Anwendungen von 2D Materialien. Die Bilage besitzt kristalline und amorphe Regionen, die beide atomar glatt sind. Die kristalline Region besitzt ein hexagonales Gitter mit gleichmäßiger Porengröße, während die amorphe Region einer komplexeren Beschreibung bedarf. In einer Studie von Baublöcken zeigen wir, dass mittelreichweitige Struktureinheiten in Korrelation mit einem Parameter für die Bindungswinkelfrustration auftreten. Das Netzwerk verschiedener Nanoporen stellt eine größenselektive Membran dar, wie wir in einer Adsorptionsstudie zeigen. Pd- und Au-Atome durchdringen den Silikafilm abhängig von der Größe der zur Verfügung stehenden Nanoporen. Der ultradünne Film hält der Einwirkung verschiedener Lösungsmittel stand und die Beständigkeit der Struktur in Wasser wird analysiert. Diese Studien deuten die außergewöhnliche Stabilität dieser Struktur an. Wir entwickeln eine polymerbasierte mechanische Exfoliation, um den Film von seinem Wachstumssubstrat zu entfernen, und zeigen, dass der Film als intakte Einheit vom Substrat abgelöst wird. Wir präsentieren anschließend den Transfer des Silikafilms auf ein TEM-Gitter, wo er schraubenartig gewundene Formen annimmt. Weiterhin wurde der Film auf ein Pt(111)-Substrat transferiert. In diesem Fall wird unter Erhalt der Struktur ein Transfer in der Größenordnung von Millimetern erreicht. / The library of two-dimensional (2D) materials is limited, since only very few compounds remain stable when they consist of only surfaces. Yet, due to their extraordinary properties, the hunt for new 2D materials continues. Recently, an atomically defined, self-saturated SiO2 bilayer has been prepared on several metal surfaces. This ultrathin silica sheet would be a promising addition to the family of 2D materials, if it can be isolated from its growth substrate without compromising its structure. In this work, we explore the properties of a silica bilayer grown on Ru(0001) in the context of 2D technology applications. The bilayer sheet exhibits crystalline and amorphous regions, both being atomically flat. The crystalline region possesses a hexagonal lattice with uniform pore size, while the amorphous region requires a more complex description. In a building block study of the amorphous region, we find that medium range structural patterns correlate with a parameter describing the bond angle frustration. The resulting network of different nanopores represents a size-selective membrane, as illustrated in an adsorption study. Pd and Au atoms are shown to penetrate the silica film selectively, depending on the presence of appropriately sized nanopores. The ultrathin silica film is shown to withstand exposure to different solvents and the stability of the structure in water is analyzed. These studies indicate extraordinary stability of this nanostructure. We develop a polymer assisted mechanical exfoliation method for removing the film from the growth substrate, providing evidence that the film is removed as an intact sheet from the growth substrate. We subsequently present the transfer of the silica bilayer to a TEM grid, where it forms micro-ribbons. Further, the film is transferred to a Pt(111) substrate, where mm-scale transfer under retention of the structure is achieved.

Spin-polarized two-dimensional electron states (2DESs) at surfaces and interfaces of magnetically active materials attract immense interest because of the idea of exploiting fermion spins rather than charge in next generation electronics. Applying angle-resolved photoelectron spectroscopy, we show that the silicon surface of GdRh2Si2 bears two distinct 2DESs, one being a Shockley surface state, and the other a Dirac surface resonance. Both are subject to strong exchange interaction with the ordered 4f-moments lying underneath the Si-Rh-Si trilayer. The spin degeneracy of the Shockley state breaks down below ~90 K, and the splitting of the resulting subbands saturates upon cooling at values as high as ~185 meV. The spin splitting of the Dirac state becomes clearly visible around ~60 K, reaching a maximum of ~70 meV. An abrupt increase of surface magnetization at around the same temperature suggests that the Dirac state contributes significantly to the magnetic properties at the Si surface. We also show the possibility to tune the properties of 2DESs by depositing alkali metal atoms. The unique temperature-dependent ferromagnetic properties of the Si-terminated surface in GdRh2Si2 could be exploited when combined with functional adlayers deposited on top for which novel phenomena related to magnetism can be anticipated.

Microporous membranes act as selective barriers and play an important role in industrial gas separation and water purification. The permeability of such membranes is inversely proportional to their thickness. Synthetic two-dimensional materials (2DMs), with a thickness of one to a few atoms or monomer-units are ideal candidates for developing separation membranes. In this Progress Report, we present groundbreaking advances in the design, synthesis, processing, and application of 2DMs for gas and ion separations, as well as water desalination. After the introduction in Section 1, this report describes the syntheses, structures, and mechanical properties of 2DMs in Section 2. In Section 3, we will discuss the established methods for processing 2DMs into selective permeation membranes and address the separation mechanism and their performances. Finally, current challenges and emerging research directions, which need to be addressed for developing next generation separation membranes, are summarized in the Conclusion and Perspective.

For fiber-reinforced plastic composites, fiber-matrix adhesion is a significant aspect of composite properties. While conventional lightweight structures are always aiming for high fiber-matrix adhesion, innovative and unconventional functional constructions require different concepts. The research work treating adaptive fiber-reinforced plastic composites with shape memory alloy wires presented here uses the approach of actuators freely movable within the composite. This is supposed to prevent mechanical tensions in the interfaces of actuator and composite structure, which would otherwise cause damages of the composite. This work examines hybrid yarns based on friction spinning technology, with shape memory alloy wires as their core component as well as glass fibers, and partly polypropylene, as their sheath component. Additionally, the surface properties of the shape memory alloy wires being used are modified by sanding and coating. The results of a characterization by pull-out testing clearly show that a coating of the shape memory alloy wires with an abherent causes considerable decrease in adhesion and friction in the interface and leads to the mobility of the shape memory alloy wires in the later composite. An even greater effect is attained by sheathing the hybrid yarns in an additional layer of polypropylene, compacting the yarn cross-section. Thus, the pull-out force could be reduced to 35–40% of the reference structure.

Polymers capable of thermally controlled reversible bonding reactions are promising candidates for stimuli responsive materials, as required for self-healing or drug delivery materials. In order to investigate how the dynamic reactions can be controlled, effective analytical tools are demanded that are capable of analyzing not only the polymers but can also monitor the respective bonding reactions. Herein, we employ size exclusion chromatography in a newly developed temperature dependent mode (TD SEC) for the in situ characterization of polymers that undergo retro Diels-Alder (rDA) reaction at temperatures higher than 60 °C. Monitoring the evolution of the molar mass distribution of the polymers during the rDA reaction and evaluating the data quantitatively gives detailed information about the extent of the reaction and allows elucidating structural parameters that can be used for controlling the polymers debonding behavior. In contrast to spectroscopic techniques, TD SEC analyzes only the size of the polymers, hence the polymers do not need to fulfill any particular requirements (e.g. presence of detectable functional groups) but only need to be soluble in the TD SEC, which makes the method universally applicable. Side effects that might bias the results are minimized by using a high temperature chromatograph that allows performing the analysis in a broad temperature range (60 – 200 °C) and in different solvents. Thus, the analysis can be performed under the exact conditions that are required for the bonding reactions and an in situ image is provided.

In this work mesoporous organisilica materials are synthesized through the silica sol-gel process. For this a new class of precursors which are also surfactant are synthesized and self-assembled. This leads to a high surface area functionality which is analysized with copper (II) and water adsorption. / Im Rahmen dieser Arbeit werden mesoporöse Amin-funktionalisierte Organo-Silikate durch den Silika Sol-Gel Prozess hergestellt. Dabei werden neue Alkoxysilyl-Precursoren synthetisiert und condensiert die die gewünschte Funktion auf die Oberfläche dirigieren. Herstellt werden primäre, secundäre und chirale Amine. Die Oberflächenfunktionalität wird mit Kupfer (II) und Wasser Adsorption analysiert.

In this thesis, different aspects within the research field of protein spectro- and electro-chemistry on nanostructured materials are addressed. On the one hand, this work is related to the investigation of nanostructured transparent and conductive metal oxides as platform for the immobilization of electroactive enzymes. On the other hand the second part of this work is related to the immobilization of sulfite oxidase on gold nanoparticles modified electrode. Finally direct and mediated spectroelectrochemistry protein with high structure complexity such as the xanthine dehydrogenase from Rhodobacter capsulatus and its high homologues the mouse aldehyde oxidase homolog 1. Stable immobilization and reversible electrochemistry of cytochrome c in a transparent and conductive tin-doped and tin-rich indium oxide film with a well-defined mesoporosity is reported. The transparency and good conductivity, in combination with the large surface area of these materials, allow the incorporation of a high amount of electroactive biomolecules (between 250 and 2500 pmol cm-2) and their electrochemical and spectroscopic investigation. Both, the electrochemical behavior and the immobilization of proteins are influenced by the geometric parameters of the porous material, such as the structure and pore shape, the surface chemistry, as well as the protein size and charge. UV-Vis and resonance Raman spectroscopy, in combination with direct protein voltammetry, are employed for the characterization of cytochrome c immobilized in the mesoporous indium tin oxide and reveal no perturbation of the structural integrity of the redox protein. A long term protein immobilization is reached using these unmodified mesoporous indium oxide based materials, i.e. more than two weeks even at high ionic strength. The potential of this modified material as an amperometric biosensor for the detection of superoxide anions is demonstrated. A sensitivity of about 100 A M-1 m-2, in a linear measuring range of the superoxide concentration between 0.13 and 0.67 μM, is estimated. In addition an electrochemical switchable protein-based optical device is designed with the core part composed of cytochrome c immobilized on a mesoporous indium tin oxide film. A color developing redox sensitive dye is used as switchable component of the system. The cytochrome c-catalyzed oxidation of the dye by hydrogen peroxide is spectroscopically investigated. When the dye is co-immobilized with the protein, its redox state is easily controlled by application of an electrical potential at the supporting material. This enables to electrochemical reset the system to the initial state and repetitive signal generation. The case of negative charged proteins, which does not have a good interaction with the negative charged indium oxide based films, is also explored. The modification of an indium tin oxide film with a positive charged polymer and the employment of a antimony doped tin oxide film were investigated in this work in order to overcome the repulsion induced by similar charges of the protein and electrode. Human sulfite oxidase and its separated heme-containing domain are able to direct exchange electrons with the supporting material. A study of a new approach for sulfite biosensing, based on enhanced direct electron transfer of a human sulfite oxidase immobilized on a gold nanoparticles modified electrode is reported. The spherical gold nanoparticles were prepared via a novel method by reduction of HAuCl4 with branched poly(ethyleneimine) in an ionic liquid resulting in particles of about 10 nm in hydrodynamic diameter. These nanoparticles were covalently attached to a mercaptoundecanoic acid modified Au-electrode and act as platform where human sulfite oxidase is adsorbed. An enhanced interfacial electron transfer and electrocatalysis is therefore achieved. UV-Vis and resonance Raman spectroscopy, in combination with direct protein voltammetry, were employed for the characterization of the system and reveal no perturbation of the structural integrity of the redox protein. The proposed biosensor exhibited a quick steady-state current response, within 2 s and a linear detection range between 0.5 and 5.4 μM with high sensitivity (1.85 nA μM-1). The investigated system provides remarkable advantages, since it works at low applied potential and at very high ionic strength. Therefore these properties could make the proposed system useful in the development of bioelectronic devices and its application in real samples. Finally protein with high structure complexity such as the xanthine dehydrogenase from Rhodobacter capsulatus and the mouse aldehyde oxidase homolog 1 were spectroelectrochemically studied. It could be demonstrated that different cofactors present in the protein structure, like the FAD and the molybdenum cofactor, are able to directly exchange electrons with an electrode and are displayed as a single peak in a square wave voltammogram. Protein mutants bearing a serine substituted to the cysteines, bounding to the most exposed iron sulfur cluster additionally showed direct electron transfer which can be attributable to this cluster. On the other hand a mediated spectroelectrochemical titration of the protein bound FAD cofactor was performed in presence of transparent iron and cobalt complex mediators. The results showed the formation of the stable semiquinone and the fully reduced flavin. Two formal potentials for each single electron exchange step were then determined. / In dieser Arbeit werden verschiedenen Aspekte im Forschungsfeld der Protein-Spekro- und Elektro-Chemie an nanostrukturierte Materialien behandelt. Zum einen werden in dieser Arbeit nanostrukturierte, transparente und leitfähige Metalloxide als Basis für die Immobilisierung von elektroaktiven Enzym untersucht. Des Weiteren behandelt diese Arbeit die Immobilisierung von humaner Sulfitoxidase auf einer Gold-Nanopartikel-modifizierten Elektrode. Schließlich wird die direkte und die vermittelte Elektrochemie von Xanthindehydrogenase aus Rhodobacter capsulatus und Aldehydoxidase Homolog 1, aus Mause, vorgestellt. Im ersten Teil der Arbeit wird über die stabile Immobilisierung und reversible Elektrochemie von Cytochrom c in einem transparenten und leitfähigen Zinn-dotierten und Zinn-reichen Indiumoxid Film mit einer gut definierten Mesoporosität berichtet. Die Transparenz und gute Leitfähigkeit in Kombination mit der großen Oberfläche dieser Materialien erlauben die Inkorporation einer große Menge elektroaktiver Biomoleküle (zwischen 250 und 2500 pmol cm-2) und deren elektrochemische und spektroskopische Untersuchung. Das elektrochemische Verhalten und die Proteinimmobilisierung sind durch die geometrischen Parameter des porösen Materials, wie die Struktur und Porenform, die Oberflächenchemie, sowie die Größe und Ladung des Proteins beeinflusst. UV-Vis und Resonanz-Raman-Spektroskopie in Kombination mit direkter Protein-Voltammetrie werden für die Charakterisierung von Cytochrom c eingesetzt und zeigen keine Störung der strukturellen Integrität des Redox-Proteins durch die Immobilisierung. Eine langfristige Immobilisierung des Proteins von mehr als zwei Wochen auch bei hoher Ionenstärke wurde unter Verwendung dieser unmodifizierten mesoporösen Indiumoxid-basierten Materialien erreicht. Das Potential dieses modifizierten Materials für die Verwendung in einem amperometrischen Biosensor zum Nachweis von Superoxid-Anionen wurde aufgezeigt. Es wurde eine Empfindlichkeit von etwa 100 A M-1 m-2, in einem linearen Messbereich der Superoxidkonzentration zwischen 0,13 und 0,67 µM, erreicht. Außerdem wurde ein elektrochemisch umschaltbares Protein-basiertes optisches Gerät konzipiert mit Cytochrom c und der mesoporösen Indiumzinnoxidschicht. Ein redox-sensitiver Farbstoff wurde als schaltbare Komponente des Systems verwendet. Die Cytochrom c Oxidation des Farbstoffs durch Wasserstoffperoxid wurde spektroskopisch untersucht. Der Redox-Zustand des Farbstoffs, co-immobilisiert mit dem Protein, ist leicht durch das Anlegen eines elektrischen Potentials an das Trägermaterial kontrollierbar. Dadurch wird die elektrochemische Zurücksetzung des Systems auf den Anfangszustand und eine repetitive Signalerzeugung ermöglicht. Für negativ geladene Proteine, die keine gute Interaktion mit dem negativ geladenen Indiumoxid-basierten Film zeigen wurden die Modifikation der Indiumzinnoxidschicht mit einem positiv geladenen Polymer sowie die Verwendung eines Antimon-dotierten Zinnoxid Films vorgeschlagen. Dadurch konnte die Abstoßung induziert durch die ähnliche Ladung des Proteins und der Elektrode überwunden werden. Es gelang für die humane Sulfit-Oxidase und die separate Häm-haltige Domäne der Austausch von Elektronen mit dem Trägermaterial. Im zweiten Teil der Arbeit wird über eine neue Methode für die Biosensorik von Sulfit berichtet, bei der direkte Elektronentransfer von humaner Sulfitoxidase immobilisierten auf einer mit Gold-Nanopartikeln modifizierten Elektrode verstärkt wurde. Die sphärischen Gold-Nanopartikeln, von etwa 10 nm im Durchmesser, wurden über eine neue Methode durch Reduktion von HAuCl4 mit verzweigtem Polyethylenimin in einer ionischen Flüssigkeit synthetisiert. Diese Nanopartikel wurden kovalent an eine mit Mercaptoundecansäure modifizierten Gold-Elektrode immobilisiert und dienen als Basis für die Adsorption von Sulfitoxidase adsorbiert wurde. Dadurch wurde ein schneller heterogener Elektronen-Transfer und verbesserte Elektrokatalyse erreicht. Für die Charakterisierung des verwendeten Systems eingesetzt wurden UV-Vis und Resonanz-Raman-Spektroskopie in Kombination mit direkter Protein-Voltammetrie. Es wurde keine Störung der strukturellen Integrität des Redox-Proteins beobachtet. Der vorgeschlagene Biosensor zeigte eine schnelle steady-state Stromantwort innerhalb von 2 s, eine lineare Detektion im Bereich zwischen 0,5 und 5,4 µM Sulfit mit einer hohen Empfindlichkeit (1,85 nA µM-1). Das untersuchte System bietet bemerkenswerte Vorteile da es ermöglicht bei niedriger angelegter Spannung und bei sehr hoher Ionenstärke zu arbeiten. Aufgrund dieser Eigenschaften hat das vorgeschlagene System großes Potential für die Entwicklung von bioelektronischen Geräten und der Anwendung in realen Proben. Schließlich werden im letzten Teil der Arbeit die komplexeren Enzymen Xanthindehydrogenase aus Rhodobacter capsulatus und Maus Aldehydoxidase Homolog 1 spektro- und elektrochemisch untersucht. Es konnte gezeigt werden, dass verschiedene Kofaktoren in der Proteinstruktur, wie FAD und der Molybdän Kofaktor direkt Elektronen mit einer Elektrode austauschen können, was durch einzelne Peaks im Square Wave Voltammogramm angezeigt wird. Es konnte eine zusätzliche redoxaktive Gruppe mit direktem Elektronen-Transfer nach Austausch eines Cysteins durch Serin am exponierten Eisen-Schwefel-Cluster gezeigt werden. Außerdem wurde eine vermittelte spektroelektrochemische Titration des FAD-Kofaktors in Anwesenheit von Mediatoren der Klasse der Eisen und Kobalt-Komplexe durchgeführt. Die Ergebnisse zeigen, dass FAD in R. capsulatus XDH zu einem stabilen Semichinone reduziert werden kann. Es gelang die formalen Potentiale für die zwei einzigen Elektrontransferprozesse zu bestimmen.

The Institute of Resource Ecology (IRE) is one of the eight institutes of the Helmholtz-Zentrum Dresden – Rossendorf (HZDR). The research activities are mainly integrated into the program “Nuclear Waste Management, Safety and Radiation Research (NUSAFE)” of the Helmholtz Association (HGF) and focused on the topics “Safety of Nuclear Waste Disposal” and “Safety Research for Nuclear Reactors”. Additionally, various activities have been started investigating chemical and environmental aspects of processing and recycling of strategic metals, namely rare earth elements. These activities are located in the HGF program “Energy Efficiency, Materials and Resources (EMR)”. Both programs, and therefore all work which is done at IRE, belong to the research sector “Energy” of the HGF. The research objectives are the protection of humans and the environment from hazards caused by pollutants resulting from technical processes that produce energy and raw materials. Treating technology and ecology as a unity is the major scientific challenge in assuring the safety of technical processes and gaining their public acceptance. We investigate the ecological risks exerted by radioactive and nonradioactive metals in the context of nuclear waste disposal, the production of energy in nuclear power plants, and in processes along the value chain of metalliferous raw materials. A common goal is to generate better understanding about the dominating processes essential for metal mobilization and immobilization on the molecular level by using advanced spectroscopic methods. This in turn enables us to assess the macroscopic phenomena, including models, codes, and data for predictive calculations, which determine the transport and distribution of contaminants in the environment.

In this study a series of novel Fe-based materials derived from a bulk metallic glass-forming composition was investigated to improve the ductility of this high-strength glassy alloy. The interplay between the factors chemistry, structure and resulting mechanical properties was analyzed in detail. It has been recognized that subtle modifications of the chemical composition (carbon addition) lead to appreciable changes in the phase formation, which occurs upon solidification (from a single-phase structure to composite materials). As a consequence, significant differences in the mechanical response of the particular samples have been observed. The materials developed here were fabricated by centrifugal casting. To explore the structure features of the as-cast cylinders, manifold experimental techniques (X-ray diffraction, optical, as well as electron microscopy) were employed. The occurrence of the numerous reflections on the X-ray diffraction patterns has confirmed the crystalline nature of the studied Fe-based alloy systems. The subsequent extensive research on their deformation behavior (Vickers hardness and room temperature compression tests) has revealed that, although the glass-forming ability of the investigated compositions is not high enough to obtain a glassy phase as a product of casting, excellent mechanical characteristics (high strength - comparable to that of the reference bulk metallic glass (BMG) - associated with good ductility) were achieved for the “composite-like” alloys. In contrast, the single phase cylinders, subjected to compressive loading, manifested an amazing capacity for plastic deformation – no failure occurred. The fracture motives developed during deformation of the “composite-structured” samples were studied by scanning electron microscopy. The main emphasis has been put on understanding the mechanisms of crack propagation. Owing to the structural complexity of the deformed samples, it was crucial to elucidate the properties of the individual compounds. Based on the obtained results it was concluded that the coexistence of a soft f.c.c. γ-Fe phase in combination with a hard complex matrix is responsible for the outstanding mechanical response of the tested composites. While the soft particles of an austenite contribute to the ductility (they hinder the crack propagation and hence, cause unequivocal strain-hardening), the hard constituents of the matrix phase yield the strength.

Paper is renewable, recyclable, sustainable and biodegradable material and, as a result, paper-based materials are widely used in the world packaging market. However, paper-based materials cannot compete with plastics in terms of processability into various 3D shapes. This is due to poor formability of paper, which is closely associated with its toughness. To improve paper formability, we report on a facile and green method that combines fiber and paper mechanical modifications at different structural levels as well as biopolymer treatment via spraying. As a result, a remarkable elongation of ∼30% was achieved after proposed combined approach on the laboratory scale. At the same time, a significant increase in tensile strength and stiffness (by ∼306% and ∼690%, respectively) was observed. Overall, an inexpensive, green, and scalable approach is introduced to improve formability of fiber networks that in turn allows preparation of 3D shapes in the processes with fixed paper blanks such as vacuum forming, hydroforming, hot pressing, etc.