Sven Oliver Müller

Laser action in nanowires: Observation of the transition from amplified spontaneous emission to laser oscillation

Direct evidence of the transition from amplified spontaneous emission to laser action in optically pumped zinc oxide (ZnO) nanowires, at room temperature, is presented. The optical power evolves from a superlinear to a linear regime as the pump power exceeds threshold, concomitant with a transition to directional emission along the nanowire and the emergence of well defined cavity Fabry–Perot modes around a wavelength of ≈385 nm, the intensity of which exceeds the spontaneous emission background by orders of magnitude. The laser oscillation threshold is found to be strongly dependent on nanowire diameter, with no laser oscillation observed for diameters smaller than ∼150 nm. Finally, we use an alternative “head on” detection geometry to measure the output power of a single nanowire laser.

Highly-Ordered Supportless Three-Dimensional Nanowire Networks with Tunable Complexity and Interwire Connectivity for Device Integration

The fabrication of three-dimensional assemblies consisting of large quantities of nanowires is of great technological importance for various applications including (electro-)catalysis, sensitive sensing, and improvement of electronic devices. Because the spatial distribution of the nanostructured material can strongly influence the properties, architectural design is required in order to use assembled nanowires to their full potential. In addition, special effort has to be dedicated to the development of efficient methods that allow precise control over structural parameters of the nanoscale building blocks as a means of tuning their characteristics. This paper reports the direct synthesis of highly ordered large-area nanowire networks by a method based on hard templates using electrodeposition within nanochannels of ion track-etched polymer membranes. Control over the complexity of the networks and the dimensions of the integrated nanostructures are achieved by a modified template fabrication. The networks possess high surface area and excellent transport properties, turning them into a promising electrocatalyst material as demonstrated by cyclic voltammetry studies on platinum nanowire networks catalyzing methanol oxidation. Our method opens up a new general route for interconnecting nanowires to stable macroscopic network structures of very high integration level that allow easy handling of nanowires while maintaining their connectivity.

Secondary phase segregation in heavily transition metal implanted ZnO

With micro-Raman spectroscopy and x-ray diffraction (XRD), we studied ZnO crystals implanted with Mn, Fe, Co, and Ni, respectively, with implantation concentrations from 4 up to 16 at. %. Using thermal treatments in air up to 700 °C, we analyzed the annealing effect on the ZnO crystal lattice as well as the onset of secondary phases and their microstructure on the sample surface. While the 500 °C treatment induces a considerable annealing, secondary phases are observed for transition metal (TM) concentrations ≥8 at. % after the treatment at 700 °C. Their microstructure strongly depends on the TM species. Various stoichiometric and nonstoichiometric TM oxide precipitates as well as elemental TM clusters are identified by their Raman and XRD signatures and their possible magnetic impact is discussed.

Intense white photoluminescence emission of V-implanted zinc oxide thin films

Pulsed laser deposited ZnO films were implanted with vanadium ions using ion energies between 30 and 250 keV with different fluences yielding vanadium concentrations in the range between 0.8 and 5 at. %. After annealing under oxygen ambient at 800 °C, a broad luminescence band observed by photoluminescence covers nearly the total visible spectral region. This luminescence is a superposition of different bands triggered by the incorporated V and remaining implantation defects. The visual impression of the bright whitish emission of the implanted ZnO has been quantified using the color space map of the Commission internationale de l’Eclairage. Furthermore, the intensity of the white emission strongly increases with increasing V concentration, whereas Ar-implanted reference sample shows only weak white emission.

Catalyst–nanostructure interaction and growth of ZnS nanobelts

Details of the vapour-liquid-solid Au droplet catalysed growth of ZnS nanobelts are elucidated in this work. The inclination of the Au droplet after solidification shows that it is indeed in the liquid state during nanobelt growth. Numerous stacking faults are observed when (0001) wurtzite is the side surface of the nanobelt. Compressive stress at the droplet-nanobelt-atmosphere triple interface is the cause of the stacking faults. Sawteeth-like structures are observed on the Zn-terminated polar (0001) side surface only. These surfaces are chemically active, while S-terminated [Formula: see text] surfaces and non-polar surfaces are not. On these active surfaces, autocatalysed vapour-solid growth leads to the formation of the observed sawteeth.

Structural and optical properties of (In,Ga)2O3 thin films and characteristics of Schottky contacts thereon

We report on structural and optical properties of a (InxGa)2O3 thin film having a monotonic lateral variation of the indium content x (). The growth condition for each In content is similar allowing precise determination of the dependence of material properties on x. For low In content () the thin film has monoclinic crystal structure; for highest In contents () the cubic bixbyite phase is predominant. For intermediate alloying we observe additionally the rhombohedral InGaO3(II) crystallographic phase. The optical band-gap decreases systematically with increasing indium content and has a linear dependency on x for parts of the sample having the monoclinic phase, only. Further, properties of Pt Schottky diodes are reported for monoclinic (InxGa)2O3 and photo response measurements for

Comparative study of deep defects in ZnO microwires, thin films and bulk single crystals

Electrical properties of a ZnO microwire grown by carbo-thermal evaporation, a ZnO thin film grown by pulsed-laser deposition and a hydrothermally grown ZnO bulk crystal are compared. Deep defects were investigated by means of deep-level transient spectroscopy. The defect level E3 was observed in all samples investigated. Additionally, a defect labelled T2 that preferentially forms under Zn-rich condition was detected in the microwire, the thin film and the bulk sample. Our results indicate that V Zn is likely involved in this defect.

Optical activation of implanted impurities in ZnS nanowires

Nanostructures of zinc sulfide (ZnS), a II-VI compound semiconductor with a direct band gap of 3.66eV in the cubic phase and 3.74eV in the wurtzite phase, show interesting optical properties, making it a promising candidate for optoelectronic devices. Single-crystalline nanobelts and nanowires were synthesized in a computer-controlled process according to the vapor-liquid-solid-mechanism. We investigated the morphology, structure, and composition by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The optical properties were studied by low-temperature photoluminescence (PL) and cathodoluminescence. The synthesized ZnS nanowires were implanted with nitrogen and boron as potential donor and acceptor, respectively. The implanted nanowires were investigated directly after ion implantation and showed a high quantity of defects resulting in nonluminescent material. Annealing procedures recovered the crystal structure and the luminescence, and we found emerging and varying P...

Einleitung: Musik als nationale und transnationale Praxis im 19. Jahrhundert

Introduction: Music as a National and Transnational Practice in 19th Century History During the 19th Century serious music was increasingly assessed in national terms. «National» music was created to fulfil political needs and to express cultural aspirations. People in all major European capitals tried to establish national schools of music and national opera traditions. The rise of «national» music meant to exchange, to communicate and to imitate styles and practices, but at the same time to demarcate differences between musical traditions. The nationalistic conflicts and enmities of the 19th century actually encouraged cultural transfers between nations rather than inhibited them. The importance of the assessment of music for the history of European culture allows for the study of common European practices and traditions.

Analysing musical culture in nineteenth-century Europe : Towards a musical turn?

The aim of this article is to establish the extent to which the history of music can offer new perspectives on the modern period. We need a change of perspective, moving away from the aesthetic debates on music to an investigation of actual experiences and practices of participants. Audience behaviour provides a link between musical production and society. In order to make opera houses and concert halls visible as social spheres, this article draws on examples from the musical life of Berlin and London in the 1800s. Music should no longer be regarded as a peripheral phenomenon, but instead as a potential historical question. The analysis of musical performances prompts at least one: music matters.