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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the 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.

Analysis of microstructures and defects of GaN grown on sapphire substrates

Li, Jyun-yu 25 August 2009 (has links)
The study aims at investigating the microstructures of GaN grown on sapphire substrate, including the interface between GaN and substrate as well as the InGaN/GaN multi quantum well (MQW) in GaN film. Some tiny straight lines on the surface of GaN film produced from epitaxy process can be observed by optical microscope. The scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to analyze the lines. When analyzing the GaN film, we discovered some V-shape defects in the InGaN/GaN and above which the roughening hollows corresponded to the defects. Therefore, we used Cathodoluminescence and TEM to further analyze the influence of V-shape defects on the growth of GaN film.

The microstructure analysis of Au nano particles

LEE, NI-HSING 23 July 2007 (has links)

TEM-Zellen zur Kalibration von elektromagnetischen Feldsensoren /

Groh, Christine. January 2002 (has links) (PDF)
Univ., Diss.--Hannover, 2002. / Literaturverz. S. 176 - 185. Nebensacht.: TEM-Zellen zur Kalibration von Feldsensoren.

Qualifikation beladener TEM-Wellenleiter /

Kärst, Jens Peter. January 2002 (has links) (PDF)
Univ., Diss.--Hannover, 2002. / Literaturverz. S. 151 - 156.

Microstructure of Al2O3/5 vol% SiC with Transmission Electron Microscope

Yeh, Jhy-Shyong 11 July 2002 (has links)
Hot-pressing sintering Al2O3/5 vol% SiC gets detail research. Sub-boundaries and dislocations observed in grains. Most Burgers vectors are ¡Õ1120¡Ö.

Self-masked epitaxial lateral overgrowth of ZnO

Chen, Zheng-huan 30 July 2009 (has links)

Combined TEM-cathodoluminescence study of nitride semiconductor structures

Boyall, Nicholas Matthews January 2003 (has links)
This work presents the results of an investigation into the technique of combined TEM-Cathodoluminescence and its application to the study of GaN epitaxial layers grown by MOVPE and PAMBE on sapphire and LiAlO(_2) substrates respectively - and MOVPE grown In(_x)Ga(_1-x)N/GaN/A1(_2)O(_3) QW structures. The measurement of CL in a TEM allows spectral information to be correlated with structural information. In-situ electron beam degradation curves of panchromatic CL from GaN epilayers and In(_0.1)Ga(_0.9)N QW emission revealed a decline in the luminescence which could be attributed to the introduction of non-radiative recombination centres. The influence of thickness on both CL spectra and images was investigated experimentally and by modelling. A method of normalising STEM-CL images for thickness contrast was developed. Application of this normalisation to In(_0.1)Ga(_0.9)N QWs in cross-section revealed inhomogeneous CL with bright regions 200-700nm in width. No systematic relationship was identified between luminescence at the QW peak emission wavelength, QW(_A), and luminescence at QW(_A) ±10nm. This finding does not support the hypothesis that variation in QW CL brightness is due to local compositional fluctuation. However, clusters of threading dislocations were shown to suppress QW luminescence and are suggested as a cause for the observed inhomogeneity in luminescence. A statistical analysis of (dislocation related) V-pits in In(_x)Ga(_1-x)N MQW samples revealed clustering of pits on a length scale of 60-120nm, but no long range clustering indicative of sub-grain boundaries was found. Finally TEM-CL spectra and monochromatic line-scans were used to show that bundles of basal plane stacking faults in M-plane GaN epitaxial layers grown on LiAlO(_2) emit radiatively at 3.3-3.35eV (l00K). The radiative transition energy is consistent with models in the literature that consider basal plane stacking faults to be layers of cubic GaN in the wurtzite matrix which act as type II QWs.

Investigating Ceria Nanocrystals Uptake by Glioblastoma Multiforme Cells and its Related Effects: An Electron Microscopy Study

Aloufi, Bader 22 January 2017 (has links)
Cerium oxide nanoparticles have been utilized widely nowadays in cancer research. It has been suggested by many studies that these nanoparticles are capable of having dual antioxidant behavior in healthy and cancer microenvironment; where in physiological condition, they act as antioxidant and do not affect the healthy cells, while in tumor-like condition; they act as an oxidase, and result in a selective killing for the cancer cells. In this experiment, the interaction of nanoceria with glioblastoma and healthy astrocyte cells was examined, and further correlated with the in vitro cytotoxic effects of various nanoceria concentrations (100 and 300 µg/ml) and exposure times (12, 24, and 48 hours). Electron microscopes were used to investigate the cellular-NPs interactions, and to examine the related cytotoxic effects in combination with trypan blue and propidium iodide viability assays. Our data suggest the following results. First, the two cell lines demonstrated capability of taken up the ceria through endocytosis pathway, where the NPs were recognized engulfed by double membrane vesicles at various regions over the cellular cytoplasm. Secondly, cerium oxide nanoparticles were found to affect the glioblastoma cells, but not so severely the corresponding healthy astrocytes at the various concentrations and incubation times, as revealed by the viability assays and the electron microscopy analysis. Thirdly, the viability of the glioblastoma cells after the treatment displayed a declined trend when increasing the ceria concentrations, but did not show such dependency with regard to the different time points. In all cases, the healthy astrocyte cells showed slight alterations in mitochondrial shape which did not influence their viability. Among the various nanoceria concentrations and exposure times, the most efficient dose of treatment was found to be with a concentration of 300 µg/ml at a time point of 24-hour, where higher reduction on the viability of glioblastoma cells was achieved, with minimal toxicity to the healthy astrocyte cells.

Ultrastructural Analysis of Human Breast Cancer Cells during Their Overtime Interaction with Cerium Oxide Nanoparticles

AlAbbadi, Shatha H. 12 1900 (has links)
Cerium oxide nanoparticles have been proposed as an anticancer agent, thanks to their ability of tuning the redox activity in accordance to different conditions, which lead to selective roles on healthy and cancer cells. Recent evidence suggested the ability of these nanoparticles to be toxic against cancer cells, while confer protection from oxidative stress, toward healthy cells. The main focus of this study was to determine the ultrastructural effects of cerium oxide nanoparticles over multiple incubation time of 1, 3, and 7 days on breast healthy and cancer cells. Cellular characterizations were carried out using electron microscopes, both transmission and scanning electron microscopes, while the viability assessments were performed by propidium iodide and trypan blue viability assays. The obtained results of the viability assays and electron microscopy suggested higher toxic effects on the cancer cell line viability by using a nanoceria dose of 300 μg/mL after 1 day of treatment. Such effects were shown to be preserved at 3 days, and in a longer time point of 7 days. On the contrary, the healthy cells underwent less effects on their viability at time point of 1 and 7 days. The 3 days treatment demonstrated a reduction on the number of cells that did not correlate with an increase of the dead cells, which suggested a possible initial decrease of the cell growth rate, which could be due to the high intracellular loading of nanoparticles. To conclude, the overall result of this experiment suggested that 300 μg/mL of CeO2 nanoparticles is the most suitable dose, within the range and the time point tested, which induces long-lasting cytotoxic effects in breast cancer cells, without harming the normal cells, as highlighted by the viability assays and ultrastructural characterization of electron microscopy analysis.

Flagellar sensilla of females of selected species of Vespidae (Hymenoptera)

McCaskill, Andrew Oliver 02 May 2009 (has links)
Little information regarding the flagellar sensilla of the Vespidae, particularly Polistes, exists in the literature. A variety of social behaviors in vespids, such as alarm pheromones and pheromone response, involve intraspecific communication. Therefore, an understanding of sensory receptors in social wasps would benefit further behavioral and neurological studies of wasps. The flagellar sensilla of female paper wasps Polistes dorsalis, Polistes metricus, and the solitary wasp Monobia quadridens were examined by scanning and transmission electron microscopy. A number of olfactory receptors, contact chemoreceptors, and mechanoreceptors were named and described. Possible functions of these receptors were proposed based on morphological and ultrastructural data for each type of sensillum. Counts of several sensilla were made over the whole of five flagellae of each species and results were compared among species, flagellomeres, medial and lateral surfaces.

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