Micron-Size Two-Dimensional Methylammonium Lead Halide Perovskites

Hybrid lead halide perovskites with 2D stacking structures have recently emerged as promising materials for optoelectronic applications. We report a method for growing 2D nanosheets of hybrid lead halide perovskites (I, Br and Cl), with tunable lateral sizes ranging from 0.05 to 8 μm and a structure consisting of n stacked monolayers separated by long alkylamines, tunable from bulk down to n = 1. The key to obtaining such a wide range of perovskite properties hinged on utilizing the respective lead halide nanosheets as precursors in a hot-injection synthesis that afforded careful control over all process parameters. The layered, quantum-confined (n ≤ 4) nanosheets were comprised of major and minor fractions with differing n. Energy funneling from low to high n (high to low energy) regions within a single sheet, mediated by the length of the ligands between stacks, produced photoluminescent quantum yields as high as 49%. These large, tunable 2D nanosheets could serve as convenient platforms for future high-efficiency optoelectronic devices

Colloidal Quasi‐2D Methylammonium Lead Bromide Perovskite Nanostructures with Tunable Shape and High Chemical Stability

Control over the lateral dimensions of colloidal nanostructures is a complex task which requires a deep understanding of the formation mechanism and reactivity in the corresponding systems. As a result, it provides a well‐founded insight to the physical and chemical properties of these materials. In this work, the preparation of quasi‐2D methylammonium lead bromide nanostripes and discuss the influence of some specific parameters on the morphology and stability of this material is demonstrated. The variation in the amount of the main ligand dodecylamine gives a large range of structures beginning with 3D brick‐like particles at low concentrations, nanostripes at elevated and ultimately nanosheets at large concentrations. The amount of the co‐ligand trioctylphosphine can alter the width of the nanostripe shape to a certain degree. The thickness can be adjusted by the amount of the second precursor methylammonium bromide. Additionally, insights are given for the suggested formation mechanism of these anisotropic structures as well as for stability against moisture at ambient conditions in comparison with differently synthesized nanosheet samples

Thermodynamic calculations on the catalytic growth of multiwall carbon nanotubes

We have developed a thermodynamic model of the catalytic growth of multiwall carbon nanotubes from hydrocarbon precursors at elevated temperature. Using this model we have computed the heat distribution, and carbon concentration in the catalyst. Calculations delivered a analytical formula for the growth time and growth rate. We find that the growth is mainly driven by a concentration gradient within the catalyst, rather than a temperature gradient.Comment: 9 pages, 3 figures, 1 tabl

On the electric conductivity of highly ordered monolayers of monodisperse metal nanoparticles

Monolayers of colloidally synthesized cobalt-platinum nanoparticles of different diameters characterized by TEM (transmission electron microscopy) were deposited on structured silicon oxide substrates and characterized by SEM (scanning electron microscopy), GISAXS (grazing incidence x-ray scattering), and electric transport measurements. The highly ordered nanoparticle films show a thermally activated electron hopping between spatially adjacent particles at room temperature and Coulomb blockade at low temperatures. We present a novel approach to experimentally determine the particles charging energies giving values of 6.7-25.4 meV dependent on the particles size and independent of the interparticle distance. These observations are supported by FEM (finite element method) calculations showing the self-capacitance to be the determining value which only depends on the permittivity constant of the surrounding space and the particles radius.Comment: 6 pages, 5 figure

Charge Transfer Induced Polarity Switching in Carbon Nanotube Transistors

We probed the charge transfer interaction between the amine-containing molecules: hydrazine, polyaniline and aminobutyl phosphonic acid, and carbon nanotube field effect transistors (CNTFETs). We successfully converted p-type CNTFETs to n-type and drastically improved the device performance in both the ON- and OFF- transistor states utilizing hydrazine as dopant. We effectively switched the transistor polarity between p- and n- type by accessing different oxidation states of polyaniline. We also demonstrated the flexibility of modulating the threshold voltage (Vth) of a CNTFET by engineering various charge-accepting and -donating groups in the same molecule.Comment: 4 pages, 3 figure

Raman spectroscopy and field emission measurements on catalytically grown carbon nanotubes

We used microcontact printing to pattern a silicon surface with an iron-containing catalytic solution. Multi-wall carbon nanotubes were subsequently grown on the patterned areas by chemical vapor deposition at temperatures between 650 and 1000C. We demonstrate that the diameter of the catalytically grown multi-wall nanotubes increases with the deposition temperature. Raman spectroscopy has been used to investigate the crystalline character of the obtained structures and it is found that the fraction of the nano-crystalline shell increases with the temperatures. The measurement of the field emission properties shows a correlation between the tube diameter and the emission field values.Comment: 6 pages, 6 figures, 1 tabl

Oxygen and light sensitive field-effect transistors based on ZnO nanoparticles attached to individual double-wall carbon nanotubes

The attachment of semiconducting nanoparticles to carbon nanotubes is one of the most challenging subjects in nanotechnology. Successful high coverage attachment and control over the charge transfer mechanism and photo-current generation opens a wide field of new applications such as highly effective solar cells and fibre-enhanced polymers. In this work we study the charge transfer in individual double-wall carbon nanotubes highly covered with uniform ZnO nanoparticles. The synthetic colloidal procedure was chosen to avoid long-chained ligands at the nanoparticle-nanotube interface. The resulting composite material was used as conductive channel in a field effect transistor device and the electrical photo-response was analysed under various conditions. By means of the transfer characteristics we could elucidate the mechanism of charge transfer from non-covalently attached semiconducting nanoparticles to carbon nanotubes. The role of positive charges remaining on the nanoparticles is discussed in terms of a gating effect.Comment: 6 pages, 4 figure

Failure and success stories in intercultural Project management

Technisches Projektmanagement (PM) erfordert die fortlaufende individuelle Interpretation des zu erwartenden Projekterfolgs oder -misserfolgs. Dieser Artikel identifiziert Prozesse des narrativen Sinnmachens als Schlüsselfaktor bei der Interpretation von zukünftigem Projekterfolg oder -misserfolg. Basierend auf einer interpretativen Langzeitstudie eines interkulturellen Projekts in einem technischen Unternehmen, identifizieren wir drei Schritte des narrativen Sinnmachens. Diese sind: (1) Retrospektive Geschichten des Misserfolgs; (2) laufende Erzählprozesse des Misserfolgs; (3) kulturalisierte Geschichten des Misserfolgs/ des strategischen Erfolgs. Wir zeigen auf, dass kulturalisierte Interpretationen des Projekt-Misserfolgs oft im Bezug stehen zur individuellen Notwendigkeit, die Realität zu vereinfachen. Die Gefahr von kulturalisierten Interpretationen liegt darin, dass sie den potenziellen Bezug zu PM-Problemen vernachlässigen und der Entwicklung interkultureller PM zuwider laufen. Um zu vermeiden, dass kulturelle Interpretationen dominant werden, schlagen wir die Analyse von Projekt-Geschichten vor, speziell die der laufenden Erzählprozesse des Misserfolgs. Damit tragen wir zu Theorie und Praxis des Projektmanagements und der interkulturellen Kompetenzentwicklung bei.Technical project management (PM) requires constant individual interpretation with regard to expected project success or failure. This article shows that narrative sense-making with regard to PM is a crucial factor of how future project success/ failure is interpreted. Based on a long-term interpretative study of an intercultural project in a technical company, we identify three steps of narrative sensemaking: (1) retrospective failure stories; (2) ongoing failure storying; (3) culturalized failure stories/ culturalized strategic success stories. We show that culturalized interpretations of a project's failure are linked to the individual need to simplify reality. The danger of culturalized interpretations is that they neglect potential PM-related project issues and hinder the development of intercultural PM competencies. We suggest the analysis of stories, especially of ongoing failure storying, in order to prevent culturalized interpretations from prevailing, thereby contributing to theory and practice of PM and intercultural education and development