TY - THES

T1 - Size and Shape Determination of Colloidal Nanocrystals with X-Ray Scattering Techniques

AU - Ritter, Maximilian

N1 - embargoed until null

PY - 2020

Y1 - 2020

N2 - The morphology of nanocrystals has a substantial influence on their highly diverse physical properties ranging from luminescence to biocompatibility. One key to success for the various applications and research areas is understanding the effect the morphology has on these properties and controlling the morphology during synthesis. Transmission electron microscopy has been the leading tool for analysing the morphology for the last decades. As modern-day nanocrystals are no longer used for purely fundamental research, the fact that it is extremely time consuming to analyse a substantial number of nanocrystals using transmission electron microscopy, has led to the developed of different methods. The properties of real-life nanocrystal applications do not depend on the morphology of a few selected ones analysed with transmission electron microscopy, but rather on the overall morphology of all nanocrystals in the application. Small angle X-ray scattering is a leading technique to analyse the morphology of colloidal nanocrystals with a sub-nanometre resolution. Using modern ab initio bead modelling the size, but more importantly also the 3D mean shape of at least 106 nanocrystals, seen in all directions, can be retrieved from the scattering data. To study the capability of shape retrieval from small angle X-ray scattering data, four superparamagnetic iron oxide nanocrystals with different shapes, ranging from a simple cube- like shape to a highly complex star-like shape are analysed. The results are then compared to transmission electron microscopy images to evaluate the success of the shape retrieval. X-ray diffraction is performed to complement and support the results. It is shown that without any a priori information about the shape, it is possible to extract the exact shape for simple structures and for complex structures the characteristic features are reproduced. Using either a priori information from e.g. transmission electron microscopy or the outcome of the first shape retrieval process, the results can be greatly enhanced by predefining the symmetry of the system, when applied with extreme caution. Then even the complex star-like shape can be retrieved, demonstrating that shape retrieval from small angle X-ray scattering data is a fiercely powerful tool and a definite alternative to transmission electron microscopy.

AB - The morphology of nanocrystals has a substantial influence on their highly diverse physical properties ranging from luminescence to biocompatibility. One key to success for the various applications and research areas is understanding the effect the morphology has on these properties and controlling the morphology during synthesis. Transmission electron microscopy has been the leading tool for analysing the morphology for the last decades. As modern-day nanocrystals are no longer used for purely fundamental research, the fact that it is extremely time consuming to analyse a substantial number of nanocrystals using transmission electron microscopy, has led to the developed of different methods. The properties of real-life nanocrystal applications do not depend on the morphology of a few selected ones analysed with transmission electron microscopy, but rather on the overall morphology of all nanocrystals in the application. Small angle X-ray scattering is a leading technique to analyse the morphology of colloidal nanocrystals with a sub-nanometre resolution. Using modern ab initio bead modelling the size, but more importantly also the 3D mean shape of at least 106 nanocrystals, seen in all directions, can be retrieved from the scattering data. To study the capability of shape retrieval from small angle X-ray scattering data, four superparamagnetic iron oxide nanocrystals with different shapes, ranging from a simple cube- like shape to a highly complex star-like shape are analysed. The results are then compared to transmission electron microscopy images to evaluate the success of the shape retrieval. X-ray diffraction is performed to complement and support the results. It is shown that without any a priori information about the shape, it is possible to extract the exact shape for simple structures and for complex structures the characteristic features are reproduced. Using either a priori information from e.g. transmission electron microscopy or the outcome of the first shape retrieval process, the results can be greatly enhanced by predefining the symmetry of the system, when applied with extreme caution. Then even the complex star-like shape can be retrieved, demonstrating that shape retrieval from small angle X-ray scattering data is a fiercely powerful tool and a definite alternative to transmission electron microscopy.

KW - small angle X-ray scattering

KW - nanocrystals

KW - super paramagnetic iron oxide nanocrystals

KW - shape retrieval

KW - small angle X-ray scattering

KW - nanocrystals

KW - super paramagnetic iron oxide nanocrystals

KW - shape retrieval

M3 - Master's Thesis

ER -