Complementary 2D/3D Imaging of Functional Materials using X-ray & Electron Microscopy

Catalysts and other functional materials are generally hierarchically structured materials. Hence, the detailed
characterization at different length scales, and especially under reaction conditions, are necessary
to unravel their mechanisms and to improve their performance and catalytic activities. Besides, a combination
of several techniques is required to acquire complementary information owing to the lack of a
single technique able to cover all the length scales. With respect to length, the best way to investigate is
by microscopy either in 2D or more preferably in 3D. The work began with an exploration of three different
3D imaging techniques, i.e. ptychographic X-ray computed tomography, electron tomography, and
focused ion beam slice-and view. Using nanoporous gold as the model, this study aimed to exhibit the
versatility of 3D microscopy as a method beyond imaging as well as to confirm the necessity of complementary
nature between them, where electron offers better spatial resolution and X-ray provides larger
field of view. The study then continued by utilizing ptychographic X-ray computed tomography for quasi
in situ thermal treatment of the same materials under atmospheric pressure. ... mehrThis study highlighted its
ease of use of implementing in situ studies, complemented by electron tomography to prove its powerful
ability to resolve what ptychographic tomography cannot. The resulting 3D volumes were then used for
air permeability and CO2 diffusion simulations, along with material’s electrical and thermal conductivity
simulations in order to further expose another excellent benefit from 3D microscopy. Ultimately, the work
proceeded into developing two cells in order to perform full in situ investigations under controlled temperatures
and atmospheres, where one cell was built for 2D only (X-ray) ptychography experiments with
simultaneous X-ray fluorescence mapping, and the other was constructed with an additional capability
for 3D limited-angle ptychographic tomography experiments. The feasibility tests were conducted using
several functional materials, i.e. nanoporous gold, zeolite, and cobalt-manganese-oxides hollow sphere,
as the models for thermal annealing process under specific atmospheres. This work eventually attests the
importance of in situ studies in precisely determining the onset annealing temperatures under particular
environments, to visualize the morphology online either in 2D or 3D, and to simultaneously map elemental
distributions live. Moreover, a complementary technique via transmission electron microscopy
was also demonstrated on the same sample, adding up another advantage in using the cells. Despite the
preliminary results from in situ limited-angle ptychographic tomography experiments for limitation in data
reconstruction, a new tomographic reconstruction technique was recently developed as a solution to acquire
3D images with shortened acquisition times. In conclusions, the work here converges into the ideal
case of performing all-around in situ 3D imaging of functional materials for quantitative analysis and simulation.