Hutzler A (2018)
Publication Language: English
Publication Type: Thesis
Publication year: 2018
URI: https://opus4.kobv.de/opus4-fau/frontdoor/index/index/docId/10092
Liquid cell transmission electron microscopy (LCTEM) is a novel approach that enables the characterization of dynamic processes in liquid media at high spatial, temporal, and energetic resolution. In order to establish this particular method as standard approach, the architecture of liquid cells has to be optimized because most concepts thus far do not allow exploiting the performance limits of modern electron microscopes. Furthermore, distinct processes, like changes in the solution chemistry, induced by electron beam irradiation of liquid specimen have not yet been satisfactorily clarified. In the present work different liquid cell architectures are examined respecting their fabrication processes and applicability.
This is achieved by a fundamental analysis of advantages and drawbacks of different liquid cell architectures which allowed for a simplification and optimization of critical process routes. For example, the application of a photopatternable adhesive proved beneficial properties compared to direct bonding processes because of its lower sensitivity against surface roughness. Furthermore, strategies for a secure enclosure of the fluid specimen within the liquid cell are developed enabling an application of the liquid cells in transmission electron microscopes (TEM).
The influence of the electron beam on nanoparticles which were dispersed in aqueous solutions was the first subject of investigation. Here, the statistic motion of nanoparticles based on BROWNian motion was examined in detail. This investigation allowed for drawing conclusions about the properties of the fluid as well as about external influences like particle aggregation and charging effects. Furthermore, it was shown that the electron beam can be used to specifically influence the chemistry of the solution as well as to manipulate individual nanoparticles.
In the remainder of this thesis, a novel liquid cell architecture is described, which shows considerable benefits compared to other liquid cell designs respecting fabrication and versatility of application in TEM. The material graphene was utilized in order to confine the liquid specimen within the liquid cell. This material is particularly well-suited for its application in LCTEM because of its extraordinary conductivity, impermeability and extremely low thickness. Few-layer graphene which was utilized for this purpose was optically characterized via an analytical approach developed for enhancing the contrast of atomically thin layers on multilayer systems. Using this liquid cell design, growth and degradation of nanostructures were investigated. The experiments showed that this particular architecture does not only allow for high resolution imaging but also for compositional analysis via energy dispersive X-ray spectroscopy. This method was shown to be highly problematic in common liquid cell designs, mainly because of shadowing of the detectors caused by silicon edges of the liquid cell itself and by elements of the applied specimen holder. The new design benefits from a plane surface without shadowing features. Furthermore, the size of the electron transparent windows was extremely enlarged which enabled electron tomography in a liquid cell for the first time.
With this novel liquid cell architecture the mechanism of growth of silver shells on gold nanorods could be clarified in detail. In order to achieve this, a comprehensive study was conducted using various LCTEM methods. The specimen fluid under investigation contained gold nanorods which were stabilized with the surfactant cetrimonium bromide in an aqueous solution of silver nitrate. Silver ions were reduced by solved electrons arising from the electron beam induced radiolysis of water. It was shown that this particular reaction proceeds via a two-step process. Here, a precipitation of silver bromide occurred at first. This silver bromide dissolved layer-wise because of a disruption of the solution equilibrium caused by the reduction of free silver ions in the solution. The dissolution in turn leads to a release of further silver ions which deposit on the gold nanorods after reduction. In addition, an anisotropy in the growth of the silver shell was identified which is caused by bromide ions adsorbing at the surface of the nanorods. These bromide ions affect the surface energy of distinct crystal facets which causes a hindered growth of the silver shell along the longitudinal axis of the gold nanorods. The results of this study were validated by complementary experiments achieved applying UV-Vis absorption spectroscopy.
APA:
Hutzler, A. (2018). Development of advanced liquid cell architectures for high performance in situ transmission electron microscopy in materials sciences (Dissertation).
MLA:
Hutzler, Andreas. Development of advanced liquid cell architectures for high performance in situ transmission electron microscopy in materials sciences. Dissertation, 2018.
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