Institut für Festkörperphysik

157 Items

Recent Submissions
Photolumineszenz- und Raman-Spektroskopie von zweidimensionalem MoS2

Scheuschner, Nils (2017)

In this work the electronic and vibrational properties of two-dimensional molybdenum disulfide (MoS2) are examined using Raman- and photoluminescencespectroscopy (PL). Spatially resolved measurements of suspended MoS2 and Si/SiO2 supported MoS2 show an increase of the charge carrier concentration of the MoS2 in the supported areas. Furthermore the indirect band gap energy of bilayer MoS2 is dec...

Unconventional magnetic properties of low-dimensional antiferromagnets BaNi2V2O8 and BaCu2V2O8

Klyushina, Ekaterina (2017)

This work explores the magnetic properties of two novel compounds BaCu2V2O8 and BaNi2V2O8 which both provide rare physical realizations of model magnetic systems that are characterized by unconventional magnetic behaviour at finite temperatures. BaNi2V2O8 has an ideal honeycomb crystal structure where S=1 nickel magnetic ions are arranged on well isolated honeycomb layers. The nearest neighbour...

Magnetic properties of rare earth zirconate pyrochlores

Xu, Jianhui (2017)

Diese Dissertation behandelt experimentelle Untersuchungen an drei magnetischen Pyrochloren, Nd2Zr2O7, Sm2Zr2O7 and Gd2Zr2O7. Es wurden einkristalline und pulverförmige Proben hergestellt wobei die zwei erstgenannten Substanzen in der Pyrochlor Struktur kristallisieren, während Gd2Zr2O7 einige Platzwechsel-Defekte von Gd/Zr aufweist. Alle Verbindungen zeigen in den makroskopischen Eigenschaften...

Effects of magnetic field gradients on the aggregation dynamics of colloidal magnetic nanoparticles

Heinrich, Dirk ; Goñi, Alejandro R. ; Osán, Tristán ; Cerioni, L. M. C. ; Smessaert, Anton ; Klapp, Sabine H. L. ; Faraudo, Jordi ; Pusiol, Daniel Jose ; Thomsen, Christian (2015)

We have used low-field H-1 nuclear-magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) to investigate the aggregation dynamics of magnetic particles in ionic ferrofluids (IFFs) in the presence of magnetic field gradients. At the beginning of the experiments, the measured NMR spectra were broad and asymmetric, exhibiting two features attributed to different dynamical environments o...

Design, Epitaxie und Charakterisierung AlGaN-basierter Leuchtdioden mit Emissionswellenlängen unterhalb von 250 nm

Mehnke, Frank (2017)

Diese Arbeit befasst sich mit der Realisierung von AlGaN-basierten ultravioletten Leuchtdioden (LEDs) mit Emissionswellenlängen unterhalb von 250 nm sowie der Analyse ihrer strukturellen und elektrooptischen Eigenschaften. Ziel war es, eine LED mit einer mit möglichst maximaler spektraler Leistungsdichte bei 226 nm zu realisieren, welche es ermöglicht, Absorptionsmessungen innerhalb eines Stick...

Towards non-volatility in quantum-dot-based memories

Bonato, Leo (2017)

The aim of this work is the extension of the hole storage time at room temperature in self-organised semiconductor quantum dots (QDs), with the long-term goal of achieving non-volatility in said QDs in order to develop a novel charge-storage memory architecture. Static capacitance spectroscopy (C--V profiling) and time-resolved capacitance spectroscopy (deep level transient spectroscopy, DLTS) ...

Periodic lateral polar structure-based waveguides in III-nitrides for quasi-phase matched second harmonic generation

Alden Angeles, Dorian Eduardo (2017)

Lasers emitting in the ultraviolet spectrum below 300 nm are desired for a variety of applications. Currently available deep UV laser systems are expensive, inefficient, stationary, require frequent maintenance and have a high operation cost. Alternatively, UV laser light can be obtained through frequency doubling as second harmonic generation using nonlinear crystals. The III-Nitrides are attr...

Blind testing of cross-linking/mass spectrometry hybrid methods in CASP11

Schneider, Michael ; Belsom, Adam ; Rappsilber, Juri ; Brock, Oliver (2016)

Hybrid approaches combine computational methods with experimental data. The information contained in the experimental data can be leveraged to probe the structure of proteins otherwise elusive to computational methods. Compared with computational methods, the structures produced by hybrid methods exhibit some degree of experimental validation. In spite of these advantages, most hybrid methods h...

Few-layer antimonene by liquid-phase exfoliation

Gibaja, Carlos ; Rodriguez-San-Miguel, David ; Ares, Pablo ; Gómez-Herrero, Julio ; Varela, Maria ; Gillen, Roland ; Maultzsch, Janina ; Hauke, Frank ; Hirsch, Andreas ; Abellán, Gonzalo ; Zamora, Félix (2016)

We report on a fast and simple method to produce highly stable isopropanol/water (4: 1) suspensions of few-layer antimonene by liquid-phase exfoliation of antimony crystals in a process that is assisted by sonication but does not require the addition of any surfactant. This straightforward method generates dispersions of few-layer antimonene suitable for on-surface isolation. Analysis by atomic...

Deterministische Quantenpunktmikrolinsen als effiziente Quantenlichtquellen

Thoma, Alexander (2017)

Quantenbits, häufig auch als Qubits bezeichnet, bilden die Grundlage der Quanteninformatik. In der Regel können diese durch jedes beliebige quantenmechanische Zweiniveausystem repräsentiert werden. Protokolle zur sicheren Datenübertagung mittels Verfahren der Quantenschlüsselverteilung beruhen jedoch auf sogenannten flying qubits - den Photonen. In den letzten Jahren haben sich Halbleiterquan...

Breitbandige VCSEL mit minimalem Energieverbrauch für kommerzielle Anwendungen

Larisch, Gunter (2017)

Ziel der vorliegenden Arbeit ist eine allumfassende Optimierung oberflächenemittierender Halbleiterlaser mit vertikaler Kavität im Hinblick auf zukünftige, kommerzielle Anwendungen. Dabei sind sowohl hohe Übertragungsraten und Energieeffizienz als auch optische Leistung und Stromdichte des Lasers sowie die Anforderungen an die zum Betrieb des Lasers nötige Infrastruktur gleichrangige Leistungsm...

Charakterisierung von dotierten Zinnoxidschichten für die Detektion von Gasen durch ellipsometrische Messung der Oberflächenplasmonenresonanz

Fischer, Daniel (2017)

In der vorliegenden Dissertation wird die Verbesserung von Gassensoren durch Beschichtung mit dotierten Zinnoxidschichten untersucht, wobei zur Messung der Gase die Methode der oberflächenplasmonenresonanzverstärkten Ellipsometrie (SPREE) angewendet wurde. Die vorgestellten Ergebnisse unterteilen sich dabei in drei Schritte: Herstellung der Schichtsysteme, Analyse der chemischen, strukturellen ...

Anisotropic plasmonic nanoparticle arrays for surface-enhanced biosensors

Gkogkou, Dimitra (2017)

Plasmonic structures exhibiting surface enhancement properties can lead to hypersensitive, label-free and analyte-specific detection of organic molecules. The motivation of this work is the realization and study of optically anisotropic plasmonic substrates for combining SERS (surface enhanced Raman scattering) and SEIRA (surface enhanced infrared absorption) spectroscopy. These properties can ...

Temperature-dependent recombination coefficients in InGaN light-emitting diodes

Nippert, Felix ; Karpov, Sergey Yu. ; Callsen, Gordon ; Galler, Bastian ; Kure, Thomas ; Nenstiel, Christian ; Wagner, Markus R. ; Strassburg, Martin ; Lugauer, Hans-Jürgen ; Hoffmann, Axel (2016)

We obtain temperature-dependent recombination coefficients by measuring the quantum efficiency and differential carrier lifetimes in the state-of-the-art InGaN light-emitting diodes. This allows us to gain insight into the physical processes limiting the quantum efficiency of such devices. In the green spectral range, the efficiency deteriorates, which we assign to a combination of diminishing ...

Determination of recombination coefficients in InGaN quantum-well light-emitting diodes by small-signal time-resolved photoluminescence

Nippert, Felix ; Karpov, Sergey ; Pietzonka, Ines ; Galler, Bastian ; Wilm, Alexander ; Kure, Thomas ; Nenstiel, Christian ; Callsen, Gordon ; Strassburg, Martin ; Lugauer, Hans-Jürgen (2016)

We suggest a novel technique for the evaluation of the recombination coefficients corresponding to Shockley–Read–Hall, radiative, and Auger recombination that occur in InGaN/GaN-based light-emitting diodes (LEDs). This technique combines the measurement of the LED efficiency as a function of LED drive current with a small-signal time-resolved photoluminescence measurement of the differential ca...

Polarization-induced confinement of continuous hole-states in highly pumped, industrial-grade, green InGaN quantum wells

Nippert, Felix ; Nirschl, Anna ; Schulz, Tobias ; Callsen, Gordon ; Pietzonka, Ines ; Westerkamp, Steffen ; Kure, Thomas ; Nenstiel, Christian ; Strassburg, Martin ; Albrecht, Martin ; Hoffmann, Axel (2016)

We investigate industrial-grade InGaN/GaN quantum wells (QWs) emitting in the green spectral region under high, resonant pumping conditions. Consequently, an ubiquitous high energy luminescence is observed that we assign to a polarization field Confined Hole Continuum (CHC). Our finding is supported by a unique combination of experimental techniques, including transmission electron microscopy, ...

Spektrale und transiente Eigenschaften der Lumineszenz von Cu2ZnSn(S,Se)4-Dünnschichten

Kretzschmar, Steffen (2017)

Um die auf der Pariser Klimakonferenz 2015 vereinbarten Ziele zu erreichen, muss die photovoltaische Energieerzeugung weltweit deutlich ausgebaut werden, da diese unter den regenerativen Energiequellen das höchste Potenzial hat, den wachsenden globalen Bedarf an elektrischer Energie zu decken. Dafür werden Solarzellen benötigt, die aus Elementen bestehen, die in ausreichendem Maße zur Verfügung...

Non-radiative loss mechanisms in InGaN/GaN multiple quantum well light-emitting diodes

Nippert, Felix (2017)

InGaN/GaN quantum wells (QWs) are commonly used for blue and green light-emitting diodes (LEDs), for example in solid-state lighting (SSL). While such structures are already in mass-production, there are still several open questions. They show drastic reductions in internal quantum efficiency (IQE) towards longer wavelengths (“green gap”), as well as with increased drive current (“droop”). In a...

Many body effects in heavily doped GaN

Nenstiel, Marc Christian Siegfried (2017)

In this work the fundamental optical signatures of highly Germanium doped GaN are investigated. This work gives fundamental new insights in interactions of carriers in a three dimensional degenerated electron gas. The first part of this thesis is dedicated to the investigation of compensation mechanisms in GaN samples with Germanium concentrations up to 1021 cm‐3. The combination of Hall effec...

Vibrational properties of low-dimensional inorganic layered materials

Staiger, Matthias (2017)

The family of low-dimensional inorganic layered materials covers a wide spectrum of properties, structurally and electronically. Ever since their synthesis as nanotubes and their preparation as mono- and few-layers these inorganic analogues to carbon nanotubes and graphene, respectively, have attracted a lot of interest both because of their importance for fundamental research as well as for th...