Highlights aus der Forschung

Forschungsprojekte

  • Colloidal 2D PbSe Nanoplatelets with Efficient Emission Reaching the Telecom O-, E- and S-band
    Colloidal two dimensional (2D) lead chalcogenide nanoplatelets (NPLs) represent highly interesting materi-als for near- and short wave-infrared applications including innovative glass fiber optics exhibiting negligi-ble attenuation. However, the direct synthetic access of these optoelectronic materials is still scarce. In this work, we demonstrate a colloidal synthesis route for 2D PbSe NPLs with cubic rock salt structure at low reaction temperatures of 0 °C and room temperature. A lateral size tuning of the PbSe NPLs leads to excitonic absorption features in the range of 1.55 – 1.24 eV (800 – 1000 nm) and narrow photolumines-cence (PL) reaching the telecom O-, E- and S-band (1.38 – 0.86 eV, 900 – 1450 nm). The PL quantum yield of the as-synthesized PbSe NPLs is doubled by a postsynthetic treatment with CdCl2 (e.g. from 14.7 % to 37.4 % for NPLs emitting at 980 nm with a FWHM of 214 meV). Our results open up new pathways for a direct synthesis and straightforward incorporation of colloidal PbSe NPLs as efficient infrared emitters at technologically relevant telecom wavelengths.
    Leitung: Hübner & Lauth
    Jahr: 2022
  • Thickness-dependent gap energies in thin layers of HfTe5
    Hafnium pentatelluride (HfTe5) is a layered two-dimensional material with various exotic properties. One of these properties is a unique resistivity anomaly, which can be explained by a change in the band structure. Also, it is predicted that HfTe5 is a topological insulator (TI) with a transition between weak to strong TI. Moreover, one of the most prominent predicted features of HfTe5 is that its single layer is a quantum spin Hall insulator. To observe the quantum spin Hall effect at room temperature a large bandgap is essential. In this project, we measured band gap energies for samples with varying thicknesses and found a clear increase of gap energies for thinner samples.
    Leitung: Behrens & Haug
    Jahr: 2022
  • Single photon emission from ODT passivated near-surface GaAs quantum dots
    Epitaxially grown semiconductor quantum dots (QDs) are one of the most promising candidates for efficient quantum light sources. Excellent optical properties can typically be ensured only if these so-called ‘artificial atoms’ are buried deep inside the semiconductor host material (≥ 100 nm). The optical properties of semiconductor micro- and nanostructures are greatly affected by their surface. Defects in the crystal lattice usually result in additional electron-ic states in the bandgap (so-called surface states) which is detrimental for radiative recombination processes and charge carrier transport. Quantum dots grown close to the surface are prone to charge carrier fluctuations and trap states on the surface, degrading the brightness, coherence and stability of the emission. However, some hybrid nanophotonic devices with near-field coupling, such as QDs coupled with surface plasmons or a single photon transis-tor, require a very small distance (< 25 nm) between the plasmon and the QD emitter. This raises the need for effec-tive surface passivation methods to recover the optical properties for near-surface QDs.
    Leitung: Haug & Ding
    Jahr: 2022
  • Room Temperature Micro-Photoluminescence Studies of Colloidal WS2 Nanosheets
    Wet-chemical syntheses of quasi two-dimensional (2D) transition metal dichalcogenides (TMDs) are emerging as promising methods for straightforward solution processing and upscaling of the materials. However, the photoluminescence (PL) properties of colloidal TMDs are virtually unexplored due to typically non-emissive TMD synthesis products. In this project, we demonstrate the first room temperature micro-PL characterization of delicate colloidal ultrathin colloidal WS2 nanosheets, rendering the wet-chemical synthesis as a simple and versatile alternative to existing methods including exfoliation and chemical vapor deposition (CVD).
    Leitung: Oestreich & Lauth
    Jahr: 2021
  • Modification of Nanocrystal-based Network Structures
    The transformation of colloidally dispersed nanocrystals into porous network structures, called gels, can be seen as way to bring these nanoscopic particles into the macroscopic world without losing their size-dependent properties. This means one is able to generate a macroscopic structure which still has the high surface to volume ratio and tunable optics inherent to the nanoparticulate building blocks. The improvement of their mechanical properties which is an important step in the way towards application of theses structures could be demonstrated and these new structures allowed further insight into the electronic processes.
    Leitung: Behrens & Dorfs & Bigall
    Jahr: 2020
  • Metal-Organic Framework-based resistive gas sensor
    Metal-organic frameworks (MOFs) do not conduct electric charges, i.e. they are insulators. However, when the pore volume of a MOF of the structure type Co-MOF-74 is filled with an electrically conducting guest molecules like tetrathiafulvalene (TTF) or tetracyanoquinodimethane (TCNQ), the MOF becomes conduct-ing. In this MOF type with one-dimensional pore structure, the Co2+ are accessible for gas molecules. These gas molecules compete with TTF for the Co2+ interaction. We expected that adsorption of guest molecules from the gas phase will alter the conductivity. We have indeed found that the resistivity is al-tered by adsorption of guest molecules from a surrounding atmosphere like CO2 or CH4.
    Leitung: Bigall & Caro
    Jahr: 2019
  • Metal-Organic Framework nano-layers for capacitive gas sensing
    In this project, novel metal-organic frameworks (MOFs) will be evaluated for the implementation into gas sensing devices. MOFs are molecular sieves with pores in the nm-range. A MOF layer with a thickness of several nanometres shall be coated on a Si-based capacitor. If molecules from a gas mixture enter selec-tively the MOF layer, the capacity of the capacitor will change in a characteristic way. There are two main routes for selective gas sensing using (i) the molecular sieve effect, which means that only molecules smaller than the pores can become adsorbed, or (ii) strong adsorption on specific sorption sites like ac-cessible metal ions in the walls of the MOF structure.
    Leitung: Caro & Osten
    Jahr: 2019
  • Atomchips mit integrierten optischen Gittern zur Erzeugung von Bose-Einstein-Kondensaten
    Die Nutzung von hochpräzisen Materiewelleninterferometern im Feld oder unter Weltraumbedingungen bedingt eine Miniaturisierung des Gesamtsystems. Insbesondere der Einsatz auf Satelliten und Forschungsraketen erfordert eine Begrenzung der Masse und des Volumens der Nutzlast. Durch die Gittertechnologie wird die Aufteilungsoptik hinter den Lasern und das Heranführen des Lichts an die Atome vereinfacht. Anstelle das Licht auf vier Wege aufzuteilen und diese zueinander und auf die Atome justieren zu müssen, bleibt lediglich ein Strahl übrig, der auf die Atome justiert werden muss. Ferner bedingt die mikrotechnologische Integration solcher Gitter in die Atomchip-Oberfläche einen Verzicht auf adhäsive Fügeverfahren und reduziert somit die Ausgasrate im Vakuum.
    Leitung: Rasel & Wurz
    Jahr: 2019
  • Selective Detection of NO2 with a Novel Calixarene-based Metal-organic Framework
    This work introduces a novel principle to the application of Metal-organic Frameworks (MOFs) as sensors, namely the transfer of highly specific reactions into MOFs where one of the reaction partners is exposed by being part of the porous framework, leading to sensor materials of highest selectivity. A Novel Calixarene-based MOF is presented that is selective to NO2, which is good visible by a color change of the material.
    Leitung: Zimmermann & Schaate
    Jahr: 2019
  • Delamination and Photochemical Modification of a Novel Two-Dimensional Zr-based MOF
    Metal-organic frameworks (MOFs) are currently one of the most intensely researched class of materials. Here, we present a novel two-dimensional Zr-based metal-organic framework which offers the possibility for postsynthetic photochemical modification at the linker molecule. Delamination and adaptation of the surface chemistry open up novel ways for shaping MOFs, e.g. for the incorporation into polymer composites, and pave the way for various applications.
    Leitung: Schaate, Haug & Behrens
    Jahr: 2019
  • Macrophage entrapped silica coated superparamagnetic iron oxide particles for controlled drug release in a 3D cancer model
    Targeted delivery of drugs is a major challenge in treatment of diverse diseases. Systemically adminis-tered drugs demand high doses and are accompanied by poor selectivity and side effects on non-target cells. In a joint research programme between LNQE, BMWZ at Leibniz Universität Hannover and theHelmholtzzentrum für Infektionsforschung (HZI) in Braunschweig werecently introduceda new principle for targeted drug delivery. It is based on macrophages as transporters for nanoparticle-coupled drugs as well as controlled release of drugs by hyperthermia mediated disruption of the cargocells and simultane-ous deliberation of nanoparticle-linked drugs.
    Leitung: Behrens & Kirschning
    Jahr: 2019
  • On the interaction of guest molecules with Co-MOF-74: A Vis/NIR and Raman approach
    We were able to demonstrate the strongly anisotropic absorption behavior of Co-MOF-74 rod like crystals with a length of several hundred micrometers illuminated by polarized light. Afterwards Co-MOF-74 has been evaluated for selective gas sensing. Several gases (CO2, propene, propane, Ar, MeOH, H2O) can be detected and distinguished by Co-MOF-74 due to their interactions with the Co2+- centers.
    Leitung: Dorfs & Caro
    Jahr: 2018
  • Prozesstechnik und Modellierung der Synthese maßgeschneiderter ZrO2-Nanopartikel
    Nanostrukturiertes Zirconium(IV)-Oxid ist aufgrund seiner hohen chemischen und thermischen Stabilität, seiner geringen Toxizität und seiner vorteilhaften mechanischen Eigenschaften von großem Interesse für verschiedenste Anwendungen auf den Gebieten der technischen Keramik, für Katalysatoren oder Elektronikkomponenten. Jedoch ist seine Performance maß-geblich von den spezifischen Eigenschaften der zugrunde liegenden Nanopartikel abhängig. Insbesondere deren Partikelgröße und Kristallitgröße, Morphologie oder Phasenzusammensetzung sind von großer Bedeutung und müssen somit genau kontrolliert werden.
    Leitung: Bigall & Garnweitner
    Jahr: 2018
  • Development of 3D human cells-based microvessels microfluidic model for replacement of ani-mals in microvascular disease study
    It has been recognized that microcirculation plays an important role in pathogenesis of many diseases. Understand-ing and regulation of microvasculature are urgently needed for developing effective therapeutic strategies. Howev-er, suitable models allowing in depth biomedical research of microcirculation are missing. Most of the research is performed with the use of animal models. The main aim of the project is to develop human cells-based microvessel microfluidic model (HZ-MMM). Vessels are grown from microvascular endothelial cells (EC) and accompanying cells in a microfluidic device by the process of angiogenesis. The model is adjusted for applications in basic research and drug development.
    Leitung: Chichkov
    Jahr: 2017
  • Improved hydrogen selectivity of Surface Modified Graphite (SMG) membranes: Permeation experiments and characterisation by micro-Raman spectroscopy and XPS
    Graphit ist ein preiswertes 2D-Kohlenstoffmaterial, dessen Flocken sich durch uniaxiales Pressen relativ leicht zu etwa 1mm dicken Scheiben verformen lassen. Diese verpressten Graphitscheiben wurden als gastrennende Membran evaluiert. Bereits ohne jegliche Oberflächenbehandlung ergaben sich überraschend hohe Trennfaktoren in der Abtrennung von Wasserstoff aus den Gemischen mit Kohlendioxid und Wasserdampf. Im Projekt zeigen wir, dass durch Oberflächensilanierung dieser Trenneffekt weiter gesteigert werden kann . Durch Zusammenarbeit im LNQE konnte durch XPS und Micro-Raman der molekulare Mechanismus der Wechselwirkung aufgeklärt und verstanden, und dadurch letztlich optimiert werden. Die oberflächenmodifizierten Graphite werden „surface modified graphite“ (SMG) genannt.
    Leitung: Tegenkamp & Caro
    Jahr: 2017
  • Spin and reoccupation noise beyond the fluctuation-dissipation theorem
    we have measured the non-equilibrium spin noise of a homogeneously broadened single quantum dots in a microcavity. The measurements in combination with a theoretical analysis beyond the fluctuation-dissipation theorem reveal the spin dynamics in the ground and the excited state of the strongly driven artificial atom which is potentially useful for spin-photon interfacing.
    Leitung: Oestreich
    Jahr: 2017
  • Graphene ähnliche und leitfähige 2D Metallorganische Gerüstverbindungen als Nanosensoren
    In den letzten Jahren haben sich die metallorganischen Gerüstverbindungen (engl.: metal-organic frameworks, MOFs) zu einem sehr großen Forschungsbereich entwickelt. Besonders die zum Teil extrem hohen spezifischen Oberflächen in Kom-bination mit der Möglichkeit zur chemischen Modifizierbarkeit des gesamten Materials machen diese Materialklasse attraktiv für verschiedene Anwendungsgebiete, da die MOFs auf die gewünschte Fragestellung angepasst werden können. Vorversuche haben gezeigt, dass es möglich ist sehr sensitive Oberflächen zu erhalten, die schnell auf Testgase wie Kohlenstoffdioxid sowie Methanol in einem Trägergasstrom reagieren. In diesem Teilprojekt ist vor allem von Interesse diese Materialien auf Interdigitalelektroden aufzubringen und quantitative Messungen mit verschiedenen Analytkonzentrationen durchzuführen, sodass diese Materialien in Sensoren eingesetzt werden können.
    Leitung: Haug, Zimmermann & Behrens
    Jahr: 2017
  • Lokalisierte Oberflächenplasmonenresonanz verschiedener Nickelsulfid Nanostrukturen
    Es konnten erfolgreich plasmonische Nanostrukturen aus zwei unterschiedlichen Nickelsulfid-Phasen hergestellt werden, welche lokalisierte Oberflächenplasmonenresonanzen im sichtbaren Bereich des elektromagnetischen Spektrums aufweisen. Damit konnte das Forschungsgebiet der Materialien mit Resonanzfrequenzen in diesem Bereich, welches bisher vornehmlich von Edelmetallpartikeln dominiert wurde, durch deutlich kostengünstigere Materialien erweitert werden.
    Leitung: Dorfs
    Jahr: 2017
  • Gold-Aerogele zur Detektion von elementarem Quecksilber in der Gasphase
    Quecksilber wird in großen Mengen durch industrielle Prozesse freigesetzt. Da Quecksilber sehr toxisch ist, werden zum Schutz des Menschen Sensoren benötigt, welche in der Lage sind, geringe Quecksilberkonzentrationen zu detektieren. Der Quecksilbersensor in diesem Projekt besteht aus zwei Kupferelektroden auf einer Leiterplatte, zwischen denen in einem Spalt ein Gold-Aerogel aufgebracht ist. Der Sensor nutzt die Bildung eines Amalgams beim Kontakt von Quecksilber mit Gold als Messeffekt aus und detektieren eine Masse- bzw. Widerstandsänderung.
    Leitung: Bigall & Zimmermann
    Jahr: 2017
  • Azobenzene Guest Molecules as Light-Switchable CO2 Valves in an Ultrathin UiO-67 Membrane
    an UiO-67 membrane was prepared and characterized for the first time in terms of its H2 purification properties. Further, a light switchable guest molecule was introduced into the MOF network, which could be used to switch the gas transport of CO2 by light over the permeance of H2, resulting in selectivity changes. Thereby, an easy and cheap way of making a switchable membrane was achieved and functionally tested.
    Leitung: Behrens & Caro
    Jahr: 2017
  • Optionen zur Realisierung von Si-Solarzellen mit Effizienzen über 26%
    Der Wirkungsgrad von Solarzellen wird, angesichts des immer größer werdenden Anteils der BOS (balance of system)-Kosten an einem PV-System, zum entscheidenden Faktor für eine weitere Reduktion der PV-Stromgestehungskosten. In dem „26+“-Projekt sollen „Leuchtturmeffizienzen“ von über 26% erreicht werden. Wir verfolgen den Ansatz, passivierende Kontakte aus polykristallinem Silizium auf Oxid (POLO) anstatt amorphes Silizium zu verwenden, da die POLO-Kontakte temperaturstabiler und somit mit einer konventionellen Siedruckmetallisierung vereinbar sind.
    Leitung: Brendel & Osten
    Jahr: 2016
  • Strong suppression of shot noise in a feedback controlled single-electron transistor
    We demonstrate the strong suppression of shot noise in a single-electron transistor using an exclusively electronic closed-loop feedback. The occurrence of shot-noise, due to the random emission of electrons with the quantized charge e-, was first postulated in vacuum diodes by W. Schottky in 1918 and is becoming the dominant source of noise in present-day mesoscopic conductors. Our technique is analog to the generation of squeezed light in quantum optics, using in-loop photo detection.
    Leitung: Haug
    Jahr: 2016
  • Plasmonic Semiconductor Nanoparticles in a Metal-Organic Framework Structure and their In Situ Cation Exchange
    In this work we present the successful integration of two plasmonic semiconductor systems into the nanoporous MOF type ZIF 8. Both systems are potentially interesting for sensory application in which the ZIF network is size discriminating the access to the LSPR particles and can be either used for optical sensing of redox active substances or for simply sensing changes in the dielectric surrounding.
    Leitung: Caro & Dorfs
    Jahr: 2016
  • Amorphous, turbostratic and crystalline carbon membranes with hydrogen selectivity
    Hydrogen production by catalytic steam reforming of renewable hydrocarbons like bio-methane or bio-ethanol has become an attractive goal of sustainable chemistry. Side reactions as in ethanol steam re-forming decrease the hydrogen selectivity. A low-temperature catalytic membrane reactor with a hydrogen-selective membrane is expected to solve this problem. Three different carbon membranes are investigated with respect to their performance to extract hydrogen selectively.
    Leitung: Tegenkamp & Caro
    Jahr: 2016
  • Self-Assembly of CdSe and CdSe/CdS Nanoplatelets to Form Highly Porous Fluorescent Aerogels
    A synthetic strategy to obtain highly porous aerogels from quasi 2D 5 ML thick CdSe and CdSe/CdS NPLs is presented. The aerogels partially exhibit the quantum confinement properties of their initial building blocks with a highest absolute quantum yield of 10.3%. The aerogels solely exhibit (111) as the exposed crystal facet. This type of extremely lightweight aerogels with high porosities and BET specific surface areas are promising for future applications for e.g., facet dependent catalytic reactions or in sensing chemicals.
    Leitung: Behrens & Bigall
    Jahr: 2016
  • Versatile fabrication method for aerogels by freezing and subsequent freeze-drying of colloidal nanoparticle solutions
    We present a novel approach for synthesizing aerogels by shock-freezing colloidal nanoparticle in liquid nitrogen and subse-quent freeze drying. With this simple method it is possible to assemble nanoparticle into macroscopic voluminous monoliths, while retaining most of their properties such as size, shape or optical properties. In comparison to state of the art techniques it is a lot faster and easier to handle. This procedure might bridge the gap for scaled-up production and might enable industrial applications.
    Leitung: Bahnemann & Behrens & Bigall
    Jahr: 2016
  • Aerogels from CdSe/CdS Nanorods with Ultra-long Exciton Lifetimes and High Fluorescence Quantum Yields
    Hydrogels and aerogels from CdSe/CdS nanorods have been fabricated. By precisely controlling the gelation process, gels with high photoluminescence quantum yield and ultra-long exciton lifetime can be obtained. Thus, this type of assemblies represents a very promising way to fabricate materials that present new or improved characteristics with respect to both the colloidal solution and the bulk.
    Leitung: Dorfs & Bigall
    Jahr: 2015
  • Raman spectroscopy and tunneling microscopy on epitaxially grown graphene nanoribbons
    We have characterized in this joint collaboration Graphene nanoribbons, grown selectively on the sidewalls of SiC mesa. The identification of charge neutrality, monolayer thickness as well as the zig-zag orientation is important and a prerequsiste for the ballisitic transport behavior.
    Leitung: Oestreich & Tegenkamp
    Jahr: 2015
  • Oxidations of Alcohols under Inductively-Heated Flow Conditions with Gold-Doped Superparamagnetic Nanoparticles as Catalyst and Oxygen as Oxidant
    A continuous flow protocol for the oxidation of alcohols to aldehydes and ketones, respectively, using oxygen gas or atmospheric air is reported. The key features of this work are gold nanoparticles that are attached to the surface of nanostructured core shell particles composed of an Fe3O4-containing core and a silica shell. These nanostructured particles exert superparamagnetic properties and thus inductively heat up in an external oscillating electromagnetic field, conditions under which the gold cata-lyst is able to perform these oxidation reactions.
    Leitung: Kirschning
    Jahr: 2015
  • Microfabricated atom traps for quantum information science and precision measurements
    Microfabrication holds great promise for a new class of atomic and molecular quantum systems based on scalable and compact trapping structures. These systems have found applications both in quantum information science, novel types of quantum sensors and precision experiments. We design, fabricate, characterize and operate microfabricated neutral atom and ion chip-scale traps both at LNQE and in the PTB cleanroom facility.
    Leitung: Ospelkaus & Rasel
    Jahr: 2015
  • Site-Selective Noble Metal Growth on CdSe Nanoplatelets
    In this work, we have grown Au, Pd, and Pt metal domains site-selectively on quasi 2D CdSe nanoplatelets of 5 monolayer thickness. Au and Pd domains are found mainly at the corner and at the shorter edges of the NPLs, whereas the Pt domains are all around the edges of the nanoplatelets. The different morphologies obtained for different metals are attributed to the type of metal precursor and to the varied reaction parameters.
    Leitung: Bigall
    Jahr: 2015
  • Superlattice Structures in Twisted Bilayers of Folded Graphene
    The electronic properties of bilayer graphene strongly depend on relative orientation of the two atomic lattices. Whereas Bernal-stacked graphene is most commonly studied, a rotational mismatch between layers opens up a whole new field of rich physics, especially at small interlayer twist. We investigate magnetotransport measurements on twisted graphene bilayers, prepared by folding of single layers. These reveal a strong dependence on the twist angle, which can be estimated by means of sample geometry.
    Leitung: Haug
    Jahr: 2014
  • Micro- and Mesoporous Silica and Titania for Catalysis, Biomedizin, Photonics
    The results presented here show novel possibilities to combine the laser-based top-down approach of structuring materials on the micrometer scale by two-photon polymerization (2PP) technique with a chemical bottom-up self-organization process for producing artificial hierarchically ordered porous media for applications in chemistry, biomedicine, and photonics.
    Leitung: Chichkov & Behrens
    Jahr: 2014
  • Oxidations of Allylic and Benzylic Alcohols under Inductively-Heated Flow Conditions with Gold-Doped Superparamagnetic Nanostructured Particles as Catalyst and Oxygen as Oxidant
    A continuous flow protocol for the oxidation of alcohols to aldehydes and ketones, respectively, using oxygen gas or atmospheric air is reported. The key features of this work are gold nanoparticles that are attached to the surface of nanostructured core shell particles composed of an Fe3O4-containing core and a silica shell. These nanostructured particles exert superparamagnetic properties and thus inductively heat up in an external oscillating electromagnetic field, conditions under which the gold catalyst is able to perform these oxidation reactions.
    Leitung: Kirschning
    Jahr: 2014
  • Carrier-selective junctions based on junctions between polycrystalline and monocrystalline silicon – a key building block for ultrahigh efficient Si solar cells
    Despite of the numerous investigations of poly-Si/c-Si junctions performed in bipolar microelectronics, the current transport mechanism across these types of junctions is still not fully understood. Existing models assuming a tunneling of charge carriers through an interfacial oxide between the poly-Si and the c-Si fail to describe consistently the behavior of junctions with n-doped and p-doped poly-Si. Therefore, we have developed an alternative, rather simple analytical model assuming a dominant current flow through pinholes in the interfacial oxide.
    Leitung: Wietler & Brendel
    Jahr: 2014
  • Segmented CdSe@CdS/Zns Nanorods Synthesized via a Partial Ion Exchange Sequence
    We have shown the first synthetic pathway towards CdSe@CdS/ZnS nanorods with a sharp boundary between the CdS and the ZnS parts of the rods. The concept of sequential cation exchange reactions has been herewith extended to another interesting material combination which was not directly accessible. These new types of nanorods are promising candidates for applications where a good electronic insulation of the CdSe core is necessary and where the nanorods are contacted end-on.
    Leitung: Dorfs
    Jahr: 2014
  • Investigations on Platinum Group Metal Nanoparticle Separation with Magnetic Beads
    We propose an approach for the magnetic bead-based capture and release of metallic nanoparticles of the platinum group, which can be interesting for many small-scale synthesis reactions e.g. in the area of fine chemical production. The application of magnetic beads for the capture and manipulation of metallic nanoparticles has hardly been under investigation so far. The development of a microfluidic magnetic bead-based separation system might allow for a re-use of the Pd catalyst, which would be of high industrial impact. The investigations described here can be used for both, Pd and Pt particles featuring similar chemical properties.
    Leitung: Bigall & Rissing
    Jahr: 2014
  • Untersuchungen zur photokatalytischen Wasserspaltung an La-dotierten NaTaO3 Partikeln
    Die photoinduzierte Spaltung von Wasser bietet die Möglichkeit, mit Hilfe von Sonnenlicht direkt den Brennstoff Wasserstoff zu erzeugen. Dies stellt einen eleganten Weg dar, regenerative Energie zu erzeugen, zu speichern und transportabel zu machen. Die photokatalytische Wasserspaltung erfolgt in drei wichtigen Schritten. Im ersten Schritt absorbiert der Halbleiter Licht mit einer Energie, die gleich oder größer als die Energie der Bandlücke des halbleitenden Photokatalysators ist. Dadurch werden Ladungsträger (Elektronen und Löcher) erzeugt, die im zweiten Schritt an die Oberfläche des Halbleiterteilchens wandern. Im dritten Schritt können die gebildeten Ladungsträger an der Grenzfläche zwischen den Halbleiterteichen und der umgehenden wässrigen Phase Redoxreaktionen eingehen, wodurch aus Wasser molekularer H2 und O2 gebildet wird.
    Leitung: Bahnemann
    Jahr: 2014
  • Cost-efficient High-throughput Ion-Implantation for Photovoltaics - CHIP
    Die aktuelle Entwicklung von kristallinen Siliziumsolarzellen ist gekennzeichnet durch die Reduktion der Herstellungskosten einerseits und die sukzessive Erhöhung des Zellwirkungsgrades andererseits. Eine interessante Alternative von bisherigen Standardzellkonzepten von Siliziumsolarzellen ist die Dotiertechnik der Ionenimplantation, die die Mikroelektronik seit mehreren Jahrzehnten zur Dotierung verwendet. Grundlegendes Ziel des CHIP-Projektes ist es, die Ionen-Implantation für die Herstellung von industrienahen Silizium-Solarzellen zu evaluieren. Hierzu ist Grundlagenforschung zu den Mechanismen der Ausheilprozesse der Kristallschäden notwendig, um einerseits exzellente Bauelementcharakteristiken zu erhalten, andererseits die dafür not-wendige Prozesszeit zu minimieren und die Prozesse so wirtschaftlich zu gestalten.
    Leitung: Brendel & Osten
    Jahr: 2014
  • Al2O3-passivation layers for Si-based solar cells
    One of the key parameter for solar cells is the surface recombination velocity of the charge carriers which limits the efficiency of photovoltaic devices. Therefore, a homogenous surface passivation with excellent electronic properties is demanding for future applications. There are two complementary contributions for a reduction in the surface recombination velocity: a reduction in the density of electronic surface states (‘chemical passivation’) and, secondly, a reduction in the electron or hole concentration near the surface, e.g., by a band bending in Si-surface toward the interface (‘field-effect passivation’). Al2O3 films grown by atomic layer deposition (ALD) on crystalline silicon (c-Si) were shown to exhibit both contributions due to a well-defined interface structure and a high negative fixed charge density localized with in 1nm of the interface. In this joint project the chemical and electrical properties of passivation films have been studied by means of X-ray photoelectron spectroscopy (XPS) and capacitance-voltage (CV) analysis, respectively.
    Leitung: Tegenkamp & Brendel
    Jahr: 2014

Forschungsprojekte

  • Colloidal 2D PbSe Nanoplatelets with Efficient Emission Reaching the Telecom O-, E- and S-band
    Colloidal two dimensional (2D) lead chalcogenide nanoplatelets (NPLs) represent highly interesting materi-als for near- and short wave-infrared applications including innovative glass fiber optics exhibiting negligi-ble attenuation. However, the direct synthetic access of these optoelectronic materials is still scarce. In this work, we demonstrate a colloidal synthesis route for 2D PbSe NPLs with cubic rock salt structure at low reaction temperatures of 0 °C and room temperature. A lateral size tuning of the PbSe NPLs leads to excitonic absorption features in the range of 1.55 – 1.24 eV (800 – 1000 nm) and narrow photolumines-cence (PL) reaching the telecom O-, E- and S-band (1.38 – 0.86 eV, 900 – 1450 nm). The PL quantum yield of the as-synthesized PbSe NPLs is doubled by a postsynthetic treatment with CdCl2 (e.g. from 14.7 % to 37.4 % for NPLs emitting at 980 nm with a FWHM of 214 meV). Our results open up new pathways for a direct synthesis and straightforward incorporation of colloidal PbSe NPLs as efficient infrared emitters at technologically relevant telecom wavelengths.
    Leitung: Hübner & Lauth
    Jahr: 2022
  • Thickness-dependent gap energies in thin layers of HfTe5
    Hafnium pentatelluride (HfTe5) is a layered two-dimensional material with various exotic properties. One of these properties is a unique resistivity anomaly, which can be explained by a change in the band structure. Also, it is predicted that HfTe5 is a topological insulator (TI) with a transition between weak to strong TI. Moreover, one of the most prominent predicted features of HfTe5 is that its single layer is a quantum spin Hall insulator. To observe the quantum spin Hall effect at room temperature a large bandgap is essential. In this project, we measured band gap energies for samples with varying thicknesses and found a clear increase of gap energies for thinner samples.
    Leitung: Behrens & Haug
    Jahr: 2022
  • Single photon emission from ODT passivated near-surface GaAs quantum dots
    Epitaxially grown semiconductor quantum dots (QDs) are one of the most promising candidates for efficient quantum light sources. Excellent optical properties can typically be ensured only if these so-called ‘artificial atoms’ are buried deep inside the semiconductor host material (≥ 100 nm). The optical properties of semiconductor micro- and nanostructures are greatly affected by their surface. Defects in the crystal lattice usually result in additional electron-ic states in the bandgap (so-called surface states) which is detrimental for radiative recombination processes and charge carrier transport. Quantum dots grown close to the surface are prone to charge carrier fluctuations and trap states on the surface, degrading the brightness, coherence and stability of the emission. However, some hybrid nanophotonic devices with near-field coupling, such as QDs coupled with surface plasmons or a single photon transis-tor, require a very small distance (< 25 nm) between the plasmon and the QD emitter. This raises the need for effec-tive surface passivation methods to recover the optical properties for near-surface QDs.
    Leitung: Haug & Ding
    Jahr: 2022
  • Room Temperature Micro-Photoluminescence Studies of Colloidal WS2 Nanosheets
    Wet-chemical syntheses of quasi two-dimensional (2D) transition metal dichalcogenides (TMDs) are emerging as promising methods for straightforward solution processing and upscaling of the materials. However, the photoluminescence (PL) properties of colloidal TMDs are virtually unexplored due to typically non-emissive TMD synthesis products. In this project, we demonstrate the first room temperature micro-PL characterization of delicate colloidal ultrathin colloidal WS2 nanosheets, rendering the wet-chemical synthesis as a simple and versatile alternative to existing methods including exfoliation and chemical vapor deposition (CVD).
    Leitung: Oestreich & Lauth
    Jahr: 2021
  • Modification of Nanocrystal-based Network Structures
    The transformation of colloidally dispersed nanocrystals into porous network structures, called gels, can be seen as way to bring these nanoscopic particles into the macroscopic world without losing their size-dependent properties. This means one is able to generate a macroscopic structure which still has the high surface to volume ratio and tunable optics inherent to the nanoparticulate building blocks. The improvement of their mechanical properties which is an important step in the way towards application of theses structures could be demonstrated and these new structures allowed further insight into the electronic processes.
    Leitung: Behrens & Dorfs & Bigall
    Jahr: 2020
  • Metal-Organic Framework-based resistive gas sensor
    Metal-organic frameworks (MOFs) do not conduct electric charges, i.e. they are insulators. However, when the pore volume of a MOF of the structure type Co-MOF-74 is filled with an electrically conducting guest molecules like tetrathiafulvalene (TTF) or tetracyanoquinodimethane (TCNQ), the MOF becomes conduct-ing. In this MOF type with one-dimensional pore structure, the Co2+ are accessible for gas molecules. These gas molecules compete with TTF for the Co2+ interaction. We expected that adsorption of guest molecules from the gas phase will alter the conductivity. We have indeed found that the resistivity is al-tered by adsorption of guest molecules from a surrounding atmosphere like CO2 or CH4.
    Leitung: Bigall & Caro
    Jahr: 2019
  • Metal-Organic Framework nano-layers for capacitive gas sensing
    In this project, novel metal-organic frameworks (MOFs) will be evaluated for the implementation into gas sensing devices. MOFs are molecular sieves with pores in the nm-range. A MOF layer with a thickness of several nanometres shall be coated on a Si-based capacitor. If molecules from a gas mixture enter selec-tively the MOF layer, the capacity of the capacitor will change in a characteristic way. There are two main routes for selective gas sensing using (i) the molecular sieve effect, which means that only molecules smaller than the pores can become adsorbed, or (ii) strong adsorption on specific sorption sites like ac-cessible metal ions in the walls of the MOF structure.
    Leitung: Caro & Osten
    Jahr: 2019
  • Atomchips mit integrierten optischen Gittern zur Erzeugung von Bose-Einstein-Kondensaten
    Die Nutzung von hochpräzisen Materiewelleninterferometern im Feld oder unter Weltraumbedingungen bedingt eine Miniaturisierung des Gesamtsystems. Insbesondere der Einsatz auf Satelliten und Forschungsraketen erfordert eine Begrenzung der Masse und des Volumens der Nutzlast. Durch die Gittertechnologie wird die Aufteilungsoptik hinter den Lasern und das Heranführen des Lichts an die Atome vereinfacht. Anstelle das Licht auf vier Wege aufzuteilen und diese zueinander und auf die Atome justieren zu müssen, bleibt lediglich ein Strahl übrig, der auf die Atome justiert werden muss. Ferner bedingt die mikrotechnologische Integration solcher Gitter in die Atomchip-Oberfläche einen Verzicht auf adhäsive Fügeverfahren und reduziert somit die Ausgasrate im Vakuum.
    Leitung: Rasel & Wurz
    Jahr: 2019
  • Selective Detection of NO2 with a Novel Calixarene-based Metal-organic Framework
    This work introduces a novel principle to the application of Metal-organic Frameworks (MOFs) as sensors, namely the transfer of highly specific reactions into MOFs where one of the reaction partners is exposed by being part of the porous framework, leading to sensor materials of highest selectivity. A Novel Calixarene-based MOF is presented that is selective to NO2, which is good visible by a color change of the material.
    Leitung: Zimmermann & Schaate
    Jahr: 2019
  • Delamination and Photochemical Modification of a Novel Two-Dimensional Zr-based MOF
    Metal-organic frameworks (MOFs) are currently one of the most intensely researched class of materials. Here, we present a novel two-dimensional Zr-based metal-organic framework which offers the possibility for postsynthetic photochemical modification at the linker molecule. Delamination and adaptation of the surface chemistry open up novel ways for shaping MOFs, e.g. for the incorporation into polymer composites, and pave the way for various applications.
    Leitung: Schaate, Haug & Behrens
    Jahr: 2019
  • Macrophage entrapped silica coated superparamagnetic iron oxide particles for controlled drug release in a 3D cancer model
    Targeted delivery of drugs is a major challenge in treatment of diverse diseases. Systemically adminis-tered drugs demand high doses and are accompanied by poor selectivity and side effects on non-target cells. In a joint research programme between LNQE, BMWZ at Leibniz Universität Hannover and theHelmholtzzentrum für Infektionsforschung (HZI) in Braunschweig werecently introduceda new principle for targeted drug delivery. It is based on macrophages as transporters for nanoparticle-coupled drugs as well as controlled release of drugs by hyperthermia mediated disruption of the cargocells and simultane-ous deliberation of nanoparticle-linked drugs.
    Leitung: Behrens & Kirschning
    Jahr: 2019
  • On the interaction of guest molecules with Co-MOF-74: A Vis/NIR and Raman approach
    We were able to demonstrate the strongly anisotropic absorption behavior of Co-MOF-74 rod like crystals with a length of several hundred micrometers illuminated by polarized light. Afterwards Co-MOF-74 has been evaluated for selective gas sensing. Several gases (CO2, propene, propane, Ar, MeOH, H2O) can be detected and distinguished by Co-MOF-74 due to their interactions with the Co2+- centers.
    Leitung: Dorfs & Caro
    Jahr: 2018
  • Prozesstechnik und Modellierung der Synthese maßgeschneiderter ZrO2-Nanopartikel
    Nanostrukturiertes Zirconium(IV)-Oxid ist aufgrund seiner hohen chemischen und thermischen Stabilität, seiner geringen Toxizität und seiner vorteilhaften mechanischen Eigenschaften von großem Interesse für verschiedenste Anwendungen auf den Gebieten der technischen Keramik, für Katalysatoren oder Elektronikkomponenten. Jedoch ist seine Performance maß-geblich von den spezifischen Eigenschaften der zugrunde liegenden Nanopartikel abhängig. Insbesondere deren Partikelgröße und Kristallitgröße, Morphologie oder Phasenzusammensetzung sind von großer Bedeutung und müssen somit genau kontrolliert werden.
    Leitung: Bigall & Garnweitner
    Jahr: 2018
  • Development of 3D human cells-based microvessels microfluidic model for replacement of ani-mals in microvascular disease study
    It has been recognized that microcirculation plays an important role in pathogenesis of many diseases. Understand-ing and regulation of microvasculature are urgently needed for developing effective therapeutic strategies. Howev-er, suitable models allowing in depth biomedical research of microcirculation are missing. Most of the research is performed with the use of animal models. The main aim of the project is to develop human cells-based microvessel microfluidic model (HZ-MMM). Vessels are grown from microvascular endothelial cells (EC) and accompanying cells in a microfluidic device by the process of angiogenesis. The model is adjusted for applications in basic research and drug development.
    Leitung: Chichkov
    Jahr: 2017
  • Improved hydrogen selectivity of Surface Modified Graphite (SMG) membranes: Permeation experiments and characterisation by micro-Raman spectroscopy and XPS
    Graphit ist ein preiswertes 2D-Kohlenstoffmaterial, dessen Flocken sich durch uniaxiales Pressen relativ leicht zu etwa 1mm dicken Scheiben verformen lassen. Diese verpressten Graphitscheiben wurden als gastrennende Membran evaluiert. Bereits ohne jegliche Oberflächenbehandlung ergaben sich überraschend hohe Trennfaktoren in der Abtrennung von Wasserstoff aus den Gemischen mit Kohlendioxid und Wasserdampf. Im Projekt zeigen wir, dass durch Oberflächensilanierung dieser Trenneffekt weiter gesteigert werden kann . Durch Zusammenarbeit im LNQE konnte durch XPS und Micro-Raman der molekulare Mechanismus der Wechselwirkung aufgeklärt und verstanden, und dadurch letztlich optimiert werden. Die oberflächenmodifizierten Graphite werden „surface modified graphite“ (SMG) genannt.
    Leitung: Tegenkamp & Caro
    Jahr: 2017
  • Spin and reoccupation noise beyond the fluctuation-dissipation theorem
    we have measured the non-equilibrium spin noise of a homogeneously broadened single quantum dots in a microcavity. The measurements in combination with a theoretical analysis beyond the fluctuation-dissipation theorem reveal the spin dynamics in the ground and the excited state of the strongly driven artificial atom which is potentially useful for spin-photon interfacing.
    Leitung: Oestreich
    Jahr: 2017
  • Graphene ähnliche und leitfähige 2D Metallorganische Gerüstverbindungen als Nanosensoren
    In den letzten Jahren haben sich die metallorganischen Gerüstverbindungen (engl.: metal-organic frameworks, MOFs) zu einem sehr großen Forschungsbereich entwickelt. Besonders die zum Teil extrem hohen spezifischen Oberflächen in Kom-bination mit der Möglichkeit zur chemischen Modifizierbarkeit des gesamten Materials machen diese Materialklasse attraktiv für verschiedene Anwendungsgebiete, da die MOFs auf die gewünschte Fragestellung angepasst werden können. Vorversuche haben gezeigt, dass es möglich ist sehr sensitive Oberflächen zu erhalten, die schnell auf Testgase wie Kohlenstoffdioxid sowie Methanol in einem Trägergasstrom reagieren. In diesem Teilprojekt ist vor allem von Interesse diese Materialien auf Interdigitalelektroden aufzubringen und quantitative Messungen mit verschiedenen Analytkonzentrationen durchzuführen, sodass diese Materialien in Sensoren eingesetzt werden können.
    Leitung: Haug, Zimmermann & Behrens
    Jahr: 2017
  • Lokalisierte Oberflächenplasmonenresonanz verschiedener Nickelsulfid Nanostrukturen
    Es konnten erfolgreich plasmonische Nanostrukturen aus zwei unterschiedlichen Nickelsulfid-Phasen hergestellt werden, welche lokalisierte Oberflächenplasmonenresonanzen im sichtbaren Bereich des elektromagnetischen Spektrums aufweisen. Damit konnte das Forschungsgebiet der Materialien mit Resonanzfrequenzen in diesem Bereich, welches bisher vornehmlich von Edelmetallpartikeln dominiert wurde, durch deutlich kostengünstigere Materialien erweitert werden.
    Leitung: Dorfs
    Jahr: 2017
  • Gold-Aerogele zur Detektion von elementarem Quecksilber in der Gasphase
    Quecksilber wird in großen Mengen durch industrielle Prozesse freigesetzt. Da Quecksilber sehr toxisch ist, werden zum Schutz des Menschen Sensoren benötigt, welche in der Lage sind, geringe Quecksilberkonzentrationen zu detektieren. Der Quecksilbersensor in diesem Projekt besteht aus zwei Kupferelektroden auf einer Leiterplatte, zwischen denen in einem Spalt ein Gold-Aerogel aufgebracht ist. Der Sensor nutzt die Bildung eines Amalgams beim Kontakt von Quecksilber mit Gold als Messeffekt aus und detektieren eine Masse- bzw. Widerstandsänderung.
    Leitung: Bigall & Zimmermann
    Jahr: 2017
  • Azobenzene Guest Molecules as Light-Switchable CO2 Valves in an Ultrathin UiO-67 Membrane
    an UiO-67 membrane was prepared and characterized for the first time in terms of its H2 purification properties. Further, a light switchable guest molecule was introduced into the MOF network, which could be used to switch the gas transport of CO2 by light over the permeance of H2, resulting in selectivity changes. Thereby, an easy and cheap way of making a switchable membrane was achieved and functionally tested.
    Leitung: Behrens & Caro
    Jahr: 2017
  • Optionen zur Realisierung von Si-Solarzellen mit Effizienzen über 26%
    Der Wirkungsgrad von Solarzellen wird, angesichts des immer größer werdenden Anteils der BOS (balance of system)-Kosten an einem PV-System, zum entscheidenden Faktor für eine weitere Reduktion der PV-Stromgestehungskosten. In dem „26+“-Projekt sollen „Leuchtturmeffizienzen“ von über 26% erreicht werden. Wir verfolgen den Ansatz, passivierende Kontakte aus polykristallinem Silizium auf Oxid (POLO) anstatt amorphes Silizium zu verwenden, da die POLO-Kontakte temperaturstabiler und somit mit einer konventionellen Siedruckmetallisierung vereinbar sind.
    Leitung: Brendel & Osten
    Jahr: 2016
  • Strong suppression of shot noise in a feedback controlled single-electron transistor
    We demonstrate the strong suppression of shot noise in a single-electron transistor using an exclusively electronic closed-loop feedback. The occurrence of shot-noise, due to the random emission of electrons with the quantized charge e-, was first postulated in vacuum diodes by W. Schottky in 1918 and is becoming the dominant source of noise in present-day mesoscopic conductors. Our technique is analog to the generation of squeezed light in quantum optics, using in-loop photo detection.
    Leitung: Haug
    Jahr: 2016
  • Plasmonic Semiconductor Nanoparticles in a Metal-Organic Framework Structure and their In Situ Cation Exchange
    In this work we present the successful integration of two plasmonic semiconductor systems into the nanoporous MOF type ZIF 8. Both systems are potentially interesting for sensory application in which the ZIF network is size discriminating the access to the LSPR particles and can be either used for optical sensing of redox active substances or for simply sensing changes in the dielectric surrounding.
    Leitung: Caro & Dorfs
    Jahr: 2016
  • Amorphous, turbostratic and crystalline carbon membranes with hydrogen selectivity
    Hydrogen production by catalytic steam reforming of renewable hydrocarbons like bio-methane or bio-ethanol has become an attractive goal of sustainable chemistry. Side reactions as in ethanol steam re-forming decrease the hydrogen selectivity. A low-temperature catalytic membrane reactor with a hydrogen-selective membrane is expected to solve this problem. Three different carbon membranes are investigated with respect to their performance to extract hydrogen selectively.
    Leitung: Tegenkamp & Caro
    Jahr: 2016
  • Self-Assembly of CdSe and CdSe/CdS Nanoplatelets to Form Highly Porous Fluorescent Aerogels
    A synthetic strategy to obtain highly porous aerogels from quasi 2D 5 ML thick CdSe and CdSe/CdS NPLs is presented. The aerogels partially exhibit the quantum confinement properties of their initial building blocks with a highest absolute quantum yield of 10.3%. The aerogels solely exhibit (111) as the exposed crystal facet. This type of extremely lightweight aerogels with high porosities and BET specific surface areas are promising for future applications for e.g., facet dependent catalytic reactions or in sensing chemicals.
    Leitung: Behrens & Bigall
    Jahr: 2016
  • Versatile fabrication method for aerogels by freezing and subsequent freeze-drying of colloidal nanoparticle solutions
    We present a novel approach for synthesizing aerogels by shock-freezing colloidal nanoparticle in liquid nitrogen and subse-quent freeze drying. With this simple method it is possible to assemble nanoparticle into macroscopic voluminous monoliths, while retaining most of their properties such as size, shape or optical properties. In comparison to state of the art techniques it is a lot faster and easier to handle. This procedure might bridge the gap for scaled-up production and might enable industrial applications.
    Leitung: Bahnemann & Behrens & Bigall
    Jahr: 2016
  • Aerogels from CdSe/CdS Nanorods with Ultra-long Exciton Lifetimes and High Fluorescence Quantum Yields
    Hydrogels and aerogels from CdSe/CdS nanorods have been fabricated. By precisely controlling the gelation process, gels with high photoluminescence quantum yield and ultra-long exciton lifetime can be obtained. Thus, this type of assemblies represents a very promising way to fabricate materials that present new or improved characteristics with respect to both the colloidal solution and the bulk.
    Leitung: Dorfs & Bigall
    Jahr: 2015
  • Raman spectroscopy and tunneling microscopy on epitaxially grown graphene nanoribbons
    We have characterized in this joint collaboration Graphene nanoribbons, grown selectively on the sidewalls of SiC mesa. The identification of charge neutrality, monolayer thickness as well as the zig-zag orientation is important and a prerequsiste for the ballisitic transport behavior.
    Leitung: Oestreich & Tegenkamp
    Jahr: 2015
  • Oxidations of Alcohols under Inductively-Heated Flow Conditions with Gold-Doped Superparamagnetic Nanoparticles as Catalyst and Oxygen as Oxidant
    A continuous flow protocol for the oxidation of alcohols to aldehydes and ketones, respectively, using oxygen gas or atmospheric air is reported. The key features of this work are gold nanoparticles that are attached to the surface of nanostructured core shell particles composed of an Fe3O4-containing core and a silica shell. These nanostructured particles exert superparamagnetic properties and thus inductively heat up in an external oscillating electromagnetic field, conditions under which the gold cata-lyst is able to perform these oxidation reactions.
    Leitung: Kirschning
    Jahr: 2015
  • Microfabricated atom traps for quantum information science and precision measurements
    Microfabrication holds great promise for a new class of atomic and molecular quantum systems based on scalable and compact trapping structures. These systems have found applications both in quantum information science, novel types of quantum sensors and precision experiments. We design, fabricate, characterize and operate microfabricated neutral atom and ion chip-scale traps both at LNQE and in the PTB cleanroom facility.
    Leitung: Ospelkaus & Rasel
    Jahr: 2015
  • Site-Selective Noble Metal Growth on CdSe Nanoplatelets
    In this work, we have grown Au, Pd, and Pt metal domains site-selectively on quasi 2D CdSe nanoplatelets of 5 monolayer thickness. Au and Pd domains are found mainly at the corner and at the shorter edges of the NPLs, whereas the Pt domains are all around the edges of the nanoplatelets. The different morphologies obtained for different metals are attributed to the type of metal precursor and to the varied reaction parameters.
    Leitung: Bigall
    Jahr: 2015
  • Superlattice Structures in Twisted Bilayers of Folded Graphene
    The electronic properties of bilayer graphene strongly depend on relative orientation of the two atomic lattices. Whereas Bernal-stacked graphene is most commonly studied, a rotational mismatch between layers opens up a whole new field of rich physics, especially at small interlayer twist. We investigate magnetotransport measurements on twisted graphene bilayers, prepared by folding of single layers. These reveal a strong dependence on the twist angle, which can be estimated by means of sample geometry.
    Leitung: Haug
    Jahr: 2014
  • Micro- and Mesoporous Silica and Titania for Catalysis, Biomedizin, Photonics
    The results presented here show novel possibilities to combine the laser-based top-down approach of structuring materials on the micrometer scale by two-photon polymerization (2PP) technique with a chemical bottom-up self-organization process for producing artificial hierarchically ordered porous media for applications in chemistry, biomedicine, and photonics.
    Leitung: Chichkov & Behrens
    Jahr: 2014
  • Oxidations of Allylic and Benzylic Alcohols under Inductively-Heated Flow Conditions with Gold-Doped Superparamagnetic Nanostructured Particles as Catalyst and Oxygen as Oxidant
    A continuous flow protocol for the oxidation of alcohols to aldehydes and ketones, respectively, using oxygen gas or atmospheric air is reported. The key features of this work are gold nanoparticles that are attached to the surface of nanostructured core shell particles composed of an Fe3O4-containing core and a silica shell. These nanostructured particles exert superparamagnetic properties and thus inductively heat up in an external oscillating electromagnetic field, conditions under which the gold catalyst is able to perform these oxidation reactions.
    Leitung: Kirschning
    Jahr: 2014
  • Carrier-selective junctions based on junctions between polycrystalline and monocrystalline silicon – a key building block for ultrahigh efficient Si solar cells
    Despite of the numerous investigations of poly-Si/c-Si junctions performed in bipolar microelectronics, the current transport mechanism across these types of junctions is still not fully understood. Existing models assuming a tunneling of charge carriers through an interfacial oxide between the poly-Si and the c-Si fail to describe consistently the behavior of junctions with n-doped and p-doped poly-Si. Therefore, we have developed an alternative, rather simple analytical model assuming a dominant current flow through pinholes in the interfacial oxide.
    Leitung: Wietler & Brendel
    Jahr: 2014
  • Segmented CdSe@CdS/Zns Nanorods Synthesized via a Partial Ion Exchange Sequence
    We have shown the first synthetic pathway towards CdSe@CdS/ZnS nanorods with a sharp boundary between the CdS and the ZnS parts of the rods. The concept of sequential cation exchange reactions has been herewith extended to another interesting material combination which was not directly accessible. These new types of nanorods are promising candidates for applications where a good electronic insulation of the CdSe core is necessary and where the nanorods are contacted end-on.
    Leitung: Dorfs
    Jahr: 2014
  • Investigations on Platinum Group Metal Nanoparticle Separation with Magnetic Beads
    We propose an approach for the magnetic bead-based capture and release of metallic nanoparticles of the platinum group, which can be interesting for many small-scale synthesis reactions e.g. in the area of fine chemical production. The application of magnetic beads for the capture and manipulation of metallic nanoparticles has hardly been under investigation so far. The development of a microfluidic magnetic bead-based separation system might allow for a re-use of the Pd catalyst, which would be of high industrial impact. The investigations described here can be used for both, Pd and Pt particles featuring similar chemical properties.
    Leitung: Bigall & Rissing
    Jahr: 2014
  • Untersuchungen zur photokatalytischen Wasserspaltung an La-dotierten NaTaO3 Partikeln
    Die photoinduzierte Spaltung von Wasser bietet die Möglichkeit, mit Hilfe von Sonnenlicht direkt den Brennstoff Wasserstoff zu erzeugen. Dies stellt einen eleganten Weg dar, regenerative Energie zu erzeugen, zu speichern und transportabel zu machen. Die photokatalytische Wasserspaltung erfolgt in drei wichtigen Schritten. Im ersten Schritt absorbiert der Halbleiter Licht mit einer Energie, die gleich oder größer als die Energie der Bandlücke des halbleitenden Photokatalysators ist. Dadurch werden Ladungsträger (Elektronen und Löcher) erzeugt, die im zweiten Schritt an die Oberfläche des Halbleiterteilchens wandern. Im dritten Schritt können die gebildeten Ladungsträger an der Grenzfläche zwischen den Halbleiterteichen und der umgehenden wässrigen Phase Redoxreaktionen eingehen, wodurch aus Wasser molekularer H2 und O2 gebildet wird.
    Leitung: Bahnemann
    Jahr: 2014
  • Cost-efficient High-throughput Ion-Implantation for Photovoltaics - CHIP
    Die aktuelle Entwicklung von kristallinen Siliziumsolarzellen ist gekennzeichnet durch die Reduktion der Herstellungskosten einerseits und die sukzessive Erhöhung des Zellwirkungsgrades andererseits. Eine interessante Alternative von bisherigen Standardzellkonzepten von Siliziumsolarzellen ist die Dotiertechnik der Ionenimplantation, die die Mikroelektronik seit mehreren Jahrzehnten zur Dotierung verwendet. Grundlegendes Ziel des CHIP-Projektes ist es, die Ionen-Implantation für die Herstellung von industrienahen Silizium-Solarzellen zu evaluieren. Hierzu ist Grundlagenforschung zu den Mechanismen der Ausheilprozesse der Kristallschäden notwendig, um einerseits exzellente Bauelementcharakteristiken zu erhalten, andererseits die dafür not-wendige Prozesszeit zu minimieren und die Prozesse so wirtschaftlich zu gestalten.
    Leitung: Brendel & Osten
    Jahr: 2014
  • Al2O3-passivation layers for Si-based solar cells
    One of the key parameter for solar cells is the surface recombination velocity of the charge carriers which limits the efficiency of photovoltaic devices. Therefore, a homogenous surface passivation with excellent electronic properties is demanding for future applications. There are two complementary contributions for a reduction in the surface recombination velocity: a reduction in the density of electronic surface states (‘chemical passivation’) and, secondly, a reduction in the electron or hole concentration near the surface, e.g., by a band bending in Si-surface toward the interface (‘field-effect passivation’). Al2O3 films grown by atomic layer deposition (ALD) on crystalline silicon (c-Si) were shown to exhibit both contributions due to a well-defined interface structure and a high negative fixed charge density localized with in 1nm of the interface. In this joint project the chemical and electrical properties of passivation films have been studied by means of X-ray photoelectron spectroscopy (XPS) and capacitance-voltage (CV) analysis, respectively.
    Leitung: Tegenkamp & Brendel
    Jahr: 2014