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Abstract
In this dissertation, factors affecting electron holographic measurements of the mean inner potential are explored. Electron holography in the transmission electron microscope (TEM) allows for quantitative retrieval of the amplitude and phase of the electron beam. Both the amplitude and the phase reflect properties of the specimen. The phase can yield quantitative measurements of nanoscale electric and magnetic potentials. One such electrostatic potential is called the mean inner potential. The mean inner potential is the average electrostatic potential measured between the bulk of a material and vacuum far from the specimen, and is nonzero for all materials. However, previous mean inner potential measurements have disagreed for the same material measured by different groups. Additionally, experiment and image simulation are known to differ for highresolution TEM, but not for electron holography, and this difference is known as the Stobbs factor  therefore, a dataset that allows for good comparison between image simulation and experiment might highlight possible improvements in the simulation software.
The factors that affect the mean inner potential are explored through both experiment and simulation. Thickness measurements using different tomographic algorithms (algebraic, geometric, and discrete tomography) and nontomographic methods are compared on an InAs nanowire. A selfcalibrating tiltseries of holograms on the same InAs nanowire is acquired and compared with image simulations to analyze diffraction effects on the amplitude and the phase. There is relatively good comparison between image simulation and experimental data, but the experimental absorption parameter is found to differ between strongly and weakly diffracting conditions. Density functional theory simulations of the mean inner potential are carried out using the GPAW program, allowing for exploration of the surface dependence of the mean inner potential. Factors including surface facet, structure optimization (atomic position relaxation), adsorbates, and fringing fields at corners are all examined. Finally, surface modification is attempted on an InAs/InP nanowire, but leads to nanowire dissolution instead  this dissolution is briefly characterized for GaAs nanowires.
The factors that affect the mean inner potential are explored through both experiment and simulation. Thickness measurements using different tomographic algorithms (algebraic, geometric, and discrete tomography) and nontomographic methods are compared on an InAs nanowire. A selfcalibrating tiltseries of holograms on the same InAs nanowire is acquired and compared with image simulations to analyze diffraction effects on the amplitude and the phase. There is relatively good comparison between image simulation and experimental data, but the experimental absorption parameter is found to differ between strongly and weakly diffracting conditions. Density functional theory simulations of the mean inner potential are carried out using the GPAW program, allowing for exploration of the surface dependence of the mean inner potential. Factors including surface facet, structure optimization (atomic position relaxation), adsorbates, and fringing fields at corners are all examined. Finally, surface modification is attempted on an InAs/InP nanowire, but leads to nanowire dissolution instead  this dissolution is briefly characterized for GaAs nanowires.
Original language  English 

Place of Publication  Kgs. Lyngby 

Publisher  Technical University of Denmark 
Number of pages  245 
Publication status  Published  2012 
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Projects
 1 Finished

Insitu TEM observation of growth and properties of groupIV doped and SiGe heterostructure nanowires
Pennington, R. S., Hansen, J. O. B., Boothroyd, C., DuninBorkowski, R. E., Wagner, J. B., Thygesen, K. S., Rosenauer, A. & Rouviere, J.
01/01/2009 → 30/04/2012
Project: PhD