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The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
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Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 31 to 36 of 36 (0.034 seconds)| 31 |
Elektronentransport in Graphen-Nanobändern mit KantenrauheitRodemund, Tom 07 December 2018 (has links)
Diese Arbeit untersucht die Auswirkungen von Kantendefekten auf die Leitfähigkeit von Graphen-Nanobändern (GNRs). Es werden die Kantenatome von zigzag- und armchair-GNRs zufällig umverteilt. Mittels Tight-Binding-Verfahren und rekursivem Greenfunktions-Formalismus werden die Transmissionsspektren der Systeme berechnet und mit Landauer-Formalismus die Leitfähigkeit bei variierter Länge bestimmt. Aus der Leitfähigkeit in Abhängigkeit von der Länge wird die Lokalisierungslänge nach Anderson ermittelt. Es wurde berechnet, dass die Lokalisierungslänge bei rauhen zigzag-GNRs gegen einen konstanten Wert strebt. Bei armchair-GNRs wurde ein linearer Abfall der Lokalisierungslänge bei zunehmender Rauheit vorgefunden.:1. Einleitung
2. Physikalische Grundlagen
2.1 Graphen
2.2 Landauer-Formalismus
2.3 Tight-Binding-Verfahren
2.4 Greenfunktions-Formalismus
2.5 Anderson-Lokalisierung
3. Methoden
3.1 Bandstrukturen
3.2 Strukturerzeugung
3.2.1 Allgemeines
3.2.2 zigzag-GNRs
3.2.3 armchair-GNRs
3.3 Rauheitsparameter
3.4 Leitfähigkeit
3.5 Lokalisierungslänge
4. Ergebnisse
4.1 Atomumverteilung
4.2 Transmissionsspektren
4.3 Leitfähigkeit
4.4 Lokalisierungslängen
4.5 Weitere Rauheitsmaße
5. Zusammenfassung und Ausblick
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Efficient Finishing of Laser Beam Melting Additive Manufactured PartsZeidler, Henning, Aliyev, Rezo, Gindorf, Florian 12 July 2024 (has links)
In many cases, the functional performance of additively manufactured components can only be ensured by finishing the functional surfaces. Various methods are available for this purpose. This paper presents a procedure for selecting suitable processes for finishing laser beam melting additive–manufactured parts which is ultimately based on technological knowledge. It was experimentally proven that the use of several consecutive finishing processes is beneficial to achieve better surface quality. One finishing process chain was particularly effective (namely particle blasting/vibratory grinding/plasma electrolytic polishing) and the technological limits of this method were investigated in this study. The optimal parameters for this process combination ensured a surface roughness Sa < 1 µm.
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Analyse der Glättung rauer Oberflächen durch Dünnschichtdeposition / Analysis of smoothing of rough surfaces by thin film depositionRöder, Johanna 23 June 2009 (has links)
No description available.
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Multilagenbasierte Transmissionsoptiken für die Röntgenmikroskopie / Multilayer based transmission optics for x-ray microscopyLiese, Tobias 15 May 2012 (has links)
No description available.
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Thin films with high surface roughness: thickness and dielectric function analysis using spectroscopic ellipsometryLehmann, Daniel, Seidel, Falko, Zahn, Dietrich R.T. 06 March 2014 (has links)
An optical surface roughness model is presented, which allows a reliable determination of the dielectric function of thin films with high surface roughnesses of more than 10 nm peak to valley distance by means of spectroscopic ellipsometry. Starting from histogram evaluation of atomic force microscopy (AFM) topography measurements a specific roughness layer (RL) model was developed for an organic thin film grown in vacuum which is well suited as an example. Theoretical description based on counting statistics allows generalizing the RL model developed to be used for all non-conducting materials. Finally, a direct input of root mean square (RMS) values found by AFM measurements into the proposed model is presented, which is important for complex ellipsometric evaluation models where a reduction of the amount of unknown parameters can be crucial. Exemplarily, the evaluation of a N,N’-dimethoxyethyl-3,4,9,10-perylene-tetracarboxylic-diimide (DiMethoxyethyl-PTCDI) film is presented, which exhibits a very high surface roughness, i.e. showing no homogeneous film at all.
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The influence of physico-chemical surface properties and morphological and topological pore space properties on trapping (CCS) and recovery efficiency (EOR): a micromodel visualization studyGolmohammadi, Saeed 26 October 2023 (has links)
We theoretically and experimentally investigate the impact of pore space structure, wettability, and surface roughness on the displacement front, trapping, and sweeping efficiency at low capillary numbers. The microstructure of (i) 2D geologically-realistic media (2D natural sand and sandstone), (ii) a topological 3D-2D-transformation (2D sand analog), and (iii) geometrically representative media (Delaunay Triangulation) were studied over a wide range of wettability from water-wet to oil-wet systems provided by using various fluid-pairs. We observed the transition (compact to fractal) in the displacement front caused by local instabilities identified by Cieplak and Robbins. The trapping efficiency of 2D natural microstructures showed a non-monotonous dependency on wettability, whereas a crossover from no trapping to maximal trapping was observed in 2D patterns of circular grains. For the first time, we compared identical experimental microstructures with simulation, capturing the key elements of the invasion process. We demonstrated that corner flows occur particularly in low-porosity media, where the smaller grain-grain distance hindered the corner-flow bridging. These insights could improve the CO2 geological storage and Enhanced Oil Recovery processes.
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