Advanced electron tomography to investigate the growth of homogeneous and heterogeneous nanoparticles
2 October 2018
Campus Groenenborger, U0.24 - Groenenborgerlaan 171 - 2020 Antwerpen (route: UAntwerpen, Campus Groenenborger
Organization / co-organization:
Department of Physics
PhD defence Naomi Winckelmans - Faculty of Science, Department of Physics
Since the properties of nanoparticles heavily depend on their morphology, the design of nanoparticles with a predetermined shape is of high importance. In the past, specific particle morphologies were synthesized by trial and error. Nowadays, much effort is devoted toward a more rational design for which it is of key importance to understand the fundamental parameters that influence the growth mechanism and the end morphology of the nanoparticles. In this thesis, the growth of homogeneous and heterogeneous metallic nanoparticles is investigated by different 2D and 3D electron microscopy techniques.
The first part of the thesis is devoted to the investigation of homogeneous Au nanoparticles. It was essential to develop a method which enabled the visualization of twinning planes, which is not possible with standard electron microscopy techniques. Different techniques have been optimized, but multimode tomography was clearly superior and therefore used to investigate twinning planes in Au nanoparticles. By applying the multimode technique on Au nanoparticles grown from a Pd containing nuclei, we were capable to investigate their growth mechanism. In a second investigation, the growth of branched Au nanoparticles is discussed. Such nanoparticles are of high interest due to their strong Plasmon resonances, making them ideal substrates for surface enhanced Raman spectroscopy. On the end of the first part, first steps have been made to optimize the acquisition of the (multimode) tomography. By continuously rotating and focusing during the acquisition, the time is reduced ten times. Also, first results are shown obtained by a novel 4D detector which enabled the visualization of a thin Ag layer surrounding Au nanorods.
In the second part of the thesis, heterogeneous nanoparticles are characterized in 3D. By the use of EDX tomography and multimode tomography we enabled the visualization of Au/FeOx Janus nanoparticles. An increasing optical absorption was observed for increasing [Au]/[Fe] ratio. By the use of electron tomography we enabled to connect these optical features to the morphology of the Janus nanoparticles. Because these nanoparticles are efficient light to heat converters, they are promising candidates for cancer treatment. In such applications the Au nanoparticles are often heated and unwanted morphological changes might occur. To investigate if the Janus nanoparticles are useful in such applications, electron tomography is performed to investigate if the nanoparticles morphology changed upon heating. The investigation of heterogeneous nanoparticles became even more challenging when the nanoparticles contain domains that differ only in valency. Core/shell ironoxide/ironoxide nanoparticles are of high interest for medical diagnostics and cancer treatment. By applying advanced spectroscopic techniques we were able to visualize the core and the shell. Furthermore, the influence of small modifications during the synthesis procedure (for example, post synthesis heating) on the morphology is investigated in 3D.