Fak. 2 Mathematik und Naturwissenschaften

2294 Items

Recent Submissions
Theoretical studies for the development of a better understanding of cofactor-structure and mechanistic properties of photoreceptors and metallo-enzymes with quantum chemical and molecular dynamical approaches

Belger, Dennis Heinz (2020)

In this work two phytochromes, namely Cyanobacterial phytochrome Cph1 and Agrobacterium tumefaciens phytochrome Agp2, as well as formate dehydrogenase of Rhodobacter Capsulatus (RcFDH), are investigated. Part III shows the development and its application of a new polarized force field (polff) for the chromophore-binding domain (CBD) of Cph1, derived by QM-computations of Mulliken charges. This ...

Calibration of Polarization Fields and Electro-Optical Response of Group-III Nitride Based c-Plane Quantum-Well Heterostructures by Application of Electro-Modulation Techniques

Papadimitriou, Dimitra N. (2019-12-27)

The polarization fields and electro-optical response of PIN-diodes based on nearly lattice-matched InGaN/GaN and InAlN/GaN double heterostructure quantum wells grown on (0001) sapphire substrates by metalorganic vapor phase epitaxy were experimentally quantified. Dependent on the indium content and the applied voltage, an intense near ultra-violet emission was observed from GaN (with fundamenta...

Graphene Quantum Dot-Based Electrochemical Immunosensors for Biomedical Applications

Mansuriya, Bhargav D. ; Altintas, Zeynep (2019-12-23)

In the area of biomedicine, research for designing electrochemical sensors has evolved over the past decade, since it is crucial to selectively quantify biomarkers or pathogens in clinical samples for the efficacious diagnosis and/or treatment of various diseases. To fulfil the demand of rapid, specific, economic, and easy detection of such biomolecules in ultralow amounts, numerous nanomateria...

The Alanine World Model for the Development of the Amino Acid Repertoire in Protein Biosynthesis

Kubyshkin, Vladimir ; Budisa, Nediljko (2019-11-05)

A central question in the evolution of the modern translation machinery is the origin and chemical ethology of the amino acids prescribed by the genetic code. The RNA World hypothesis postulates that templated protein synthesis has emerged in the transition from RNA to the Protein World. The sequence of these events and principles behind the acquisition of amino acids to this process remain elu...

Generation of maximally entangled states and coherent control in quantum dot microlenses

Bounouar, Samir ; Haye, Christpoh de la ; Strauß, Max ; Schnauber, Peter ; Thoma, Alexander ; Gschrey, Manuel ; Schulze, Jan-Hindrik ; Strittmatter, André ; Rodt, Sven ; Reitzenstein, Stephan (2018-04-12)

The integration of entangled photon emitters in nanophotonic structures designed for the broadband enhancement of photon extraction is a major challenge for quantum information technologies. We study the potential of quantum dot (QD) microlenses as efficient emitters of maximally entangled photons. For this purpose, we perform quantum tomography measurements on InGaAs QDs integrated determinist...

Efficient single-photon source based on a deterministically fabricated single quantum dot - microstructure with backside gold mirror

Fischbach, Sarah ; Kaganskiy, Arsenty ; Tauscher, Esra Burcu Yarar ; Gericke, Fabian ; Thoma, Alexander ; Schmidt, Ronny ; Strittmatter, André ; Heindel, Tobias ; Reitzenstein, Stephan (2017-07-05)

We present an efficient broadband single-photon source which is fabricated by a flip-chip gold-bonding technique and in-situ electron beam lithography. The device comprises a single InGaAs quantum dot that is centered at the bottom of a monolithic mesa structure and located above a gold mirror for enhanced photon-extraction efficiency. We show a photon-extraction efficiency of ηext=(18±2) % int...

Resonance fluorescence of a site-controlled quantum dot realized by the buried-stressor growth technique

Strauß, Max ; Kaganskiy, Arsenty ; Voigt, Robert ; Schnauber, Peter ; Schulze, Jan-Hindrik ; Rodt, Sven ; Strittmatter, André ; Reitzenstein, Stephan (2017-03-12)

Site-controlled growth of semiconductor quantum dots (QDs) represents a major advancement to achieve scalable quantum technology platforms. One immediate benefit is the deterministic integration of quantum emitters into optical microcavities. However, site-controlled growth of QDs is usually achieved at the cost of reduced optical quality. Here, we show that the buried-stressor growth technique...

Enhanced photon-extraction efficiency from InGaAs/GaAs quantum dots in deterministic photonic structures at 1.3 μm fabricated by in-situ electron-beam lithography

Strocka, N. ; Musiał, A. ; Schneider, P.-I. ; Mrowiński, P. ; Holewa, P. ; Burger, S. ; Quandt, D. ; Strittmatter, André ; Rodt, Sven ; Reitzenstein, Stephan ; Sęk, G. (2018-08-07)

The main challenge in the development of non-classical light sources remains their brightness that limits the data transmission and processing rates as well as the realization of practical devices operating in the telecommunication range. To overcome this issue, we propose to utilize universal and flexible in-situ electron-beam lithography and hereby, we demonstrate a successful technology tran...

Micropillars with a controlled number of site-controlled quantum dots

Kaganskiy, Arsenty ; Gericke, Fabian ; Heindel, Tobias ; Porte, Xavier ; Reitzenstein, Stephan (2018-02-12)

We report on the realization of micropillars with site-controlled quantum dots (SCQDs) in the active layer. The SCQDs are grown via the buried stressor approach which allows for the positioned growth and device integration of a controllable number of QDs with high optical quality. This concept is very powerful as the number and the position of SCQDs in the cavity can be simultaneously controlle...

Quantum-optical influences in optoelectronics - an introduction

Chow, Weng W. ; Reitzenstein, Stephan (2018-10-26)

This focused review discusses the increasing importance of quantum optics in the physics and engineering of optoelectronic components. Two influences relating to cavity quantum electrodynamics are presented. One involves the development of low threshold lasers, when the channeling of spontaneous emission into the lasing mode becomes so efficient that the concept of lasing needs revisiting. The ...

Fabrication of dense diameter-tuned quantum dot micropillar arrays for applications in photonic information processing

Heuser, Tobias ; Große, Jan ; Kaganskiy, Arsenty ; Brunner, Daniel ; Reitzenstein, Stephan (2018-09-28)

We report on the realization of a dense, large-scale array of 900 quantum dot micropillar cavities with high spectral homogeneity. We target applications in photonic information processing such as optical reservoir computing which can be implemented in large arrays of optically coupled microlasers. To achieve the required spectral homogeneity for the underlying optical injection locking, we cal...

Methanogenic Archaea Can Produce Methane in Deliquescence-Driven Mars Analog Environments

Maus, Deborah ; Heinz, Jacob ; Schirmack, Janosch ; Airo, Alessandro ; Kounaves, Samuel P. ; Wagner, Dirk ; Schulze-Makuch, Dirk (2020-01-08)

The current understanding of the Martian surface indicates that briny environments at the near-surface are temporarily possible, e.g. in the case of the presumably deliquescence-driven Recurring Slope Lineae (RSL). However, whether such dynamic environments are habitable for terrestrial organisms remains poorly understood. This hypothesis was tested by developing a Closed Deliquescence System (...

O−O Bond Formation and Liberation of Dioxygen Mediated by N5‐Coordinate Non‐Heme Iron(IV) Complexes

Kroll, Nicole ; Speckmann, Ina ; Schoknecht, Marc ; Gülzow, Jana ; Diekmann, Marek ; Pfrommer, Johannes ; Stritt, Anika ; Schlangen, Maria ; Grohmann, Andreas ; Hörner, Gerald (2019-08-13)

Formation of the O−O bond is considered the critical step in oxidative water cleavage to produce dioxygen. High‐valent metal complexes with terminal oxo (oxido) ligands are commonly regarded as instrumental for oxygen evolution, but direct experimental evidence is lacking. Herein, we describe the formation of the O−O bond in solution, from non‐heme, N5‐coordinate oxoiron(IV) species. Oxygen evo...

Anti‐Stokes Photoluminescence of Monolayer WS2

Pierret, Aurélie ; Tornatzky, Hans ; Maultzsch, Janina (2019-10-09)

Anti‐Stokes photoluminescence excitation of a WS2 monolayer flake between 10 and 300 K is reported herein. Even with continuous‐wave lasers at low power, the emission of the exciton at excitation 100 meV below its emission energy at room temperature is observed. A mechanism which involves the trions as the intermediate state is proposed, leading to an efficient up‐conversion process. In additio...

A Reaction‐Induced Localization of Spin Density Enables Thermal C−H Bond Activation of Methane by Pristine FeC4+

Geng, Caiyun ; Li, Jilai ; Weiske, Thomas ; Schwarz, Helmut (2019-08-13)

The reactivity of the cationic metal‐carbon cluster FeC4+ towards methane has been studied experimentally using Fourier‐transform ion cyclotron resonance mass spectrometry and computationally by high‐level quantum chemical calculations. At room temperature, FeC4H+ is formed as the main ionic product, and the experimental findings are substantiated by labeling experiments. According to extensive...

Direct Identification of Acetaldehyde Formation and Characterization of the Active Site in the [VPO4].+/C2H4 Couple by Gas‐Phase Vibrational Spectroscopy

Li, Ya-Ke ; Debnath, Sreekanta ; Schlangen, Maria ; Schöllkopf, Wieland ; Asmis, Knut R. ; Schwarz, Helmut (2019-11-08)

The gas‐phase reaction of the heteronuclear oxide cluster [VPO4].+ with C2H4 is studied under multiple collision conditions at 150 K using cryogenic ion‐trap vibrational spectroscopy combined with electronic structure calculations. The exclusive formation of acetaldehyde is directly identified spectroscopically and discussed in the context of the underlying reaction mechanism. In line with comp...

Influence of Adding Molybdenum on Structure and Performance of FexOy/SBA‐15 Catalysts in Selective Oxidation of Propene

Genz, Nina Sharmen ; Ressler, Thorsten (2019-08-21)

Mixed iron and molybdenum oxide catalysts supported on nanostructured silica, SBA‐15, were synthesized with various Mo/Fe atomic ratios ranging from 0.07/1.0 to 0.57/1.0. Structural characterization of as‐prepared MoxOy_FexOy/SBA‐15 samples was performed by nitrogen physisorption, X‐ray diffraction, and DR‐UV‐Vis spectroscopy. Adding molybdenum resulted in a pronounced dispersion effect on supp...

Vinylene-Linked Covalent Organic Frameworks by Base-Catalyzed Aldol Condensation

Acharjya, Amitava ; Pachfule, Pradip ; Roeser, Jérôme ; Schmitt, Franz-Josef ; Thomas, Arne (2019-09-09)

Two 2D covalent organic frameworks (COFs) linked by vinylene (−CH=CH−) groups (V‐COF‐1 and V‐COF‐2) are synthesized by exploiting the electron deficient nature of the aromatic s‐triazine unit of C3‐symmetric 2,4,6‐trimethyl‐s‐triazine (TMT). The acidic terminal methyl hydrogens of TMT can easily be abstracted by a base, resulting in a stabilized carbanion, which further undergoes aldol condensa...

Boosting water oxidation through in situ electroconversion of manganese gallide: an intermetallic precursor approach

Menezes, Prashanth W. ; Walter, Carsten ; Hausmann, Jan Niklas ; Beltrán-Suito, Rodrigo ; Schlesiger, Christopher ; Praetz, Sebastian ; Yu. Verchenko, Valeriy ; Shevelkov, Andrei V. ; Driess, Matthias (2019-10-15)

For the first time, the manganese gallide (MnGa4) served as an intermetallic precursor, which upon in situ electroconversion in alkaline media produced high‐performance and long‐term‐stable MnOx‐based electrocatalysts for water oxidation. Unexpectedly, its electrocorrosion (with the concomitant loss of Ga) leads simultaneously to three crystalline types of MnOx minerals with distinct structures...

Lewis acid catalyzed transfer hydromethallylation for the construction of quaternary carbon centers

Walker, Johannes C. L. ; Oestreich, Martin (2019-09-12)

The design and gram‐scale synthesis of a cyclohexa‐1,4‐diene‐based surrogate of isobutene gas is reported. Using the highly electron‐deficient Lewis acid B(C6F5)3, application of this surrogate in the hydromethallylation of electron‐rich styrene derivatives provided sterically congested quaternary carbon centers. The reaction proceeds by C(sp3)−C(sp3) bond formation at a tertiary carbenium ion ...