5 Sept 2016 : Benjamin Winter

Quantitative Electron Tomography of Functional Nanomaterials

Speaker : Dr Benjamin Winter, Friedrich-Alexander University Erlangen-Nuremberg

Venue    : Monday 5 Sept 2016, 3:30pm (Murdoch University, ECL1.031)

Functional nanomaterials owe their unique properties to structures on the nanometer scale and feature widespread applications ranging from optics, electronics, catalysis and sensor technology, to bionics and biomedical engineering. Since the development of these materials during the last years steadily led to more complex morphologies, novel techniques have to be employed that enable the characterization of these materials in three dimensions. Here, the potential of such a technique, namely electron tomography (ET), is demonstrated by applying it to a variety of technologically relevant nanoparticulate and nanoporous functional materials.

Detailed structural analyses are essential for the understanding of fundamental physical and chemical properties, which is necessary for the further optimization and development of these materials. Transmission electron microscopy (TEM) offers many different imaging and spectroscopic techniques allowing for comprehensive materials characterization. In the course of this, ET enables the three-dimensional (3D) reconstruction of the analyzed material derived from many individual projections recorded from different viewing angles. The realistic 3D representations of the samples with high spatial resolutions down to (1 nm)3, or even below, enable the examination of important structural properties. Each studied material system requires to devise and apply individually tailored characterization approaches, ranging from conventional TEM to advanced techniques like 360° ET.

On the one hand, quantum dot (QD)/low-dimensional hybrid materials with application in optoelectronics are characterized using TEM and ET techniques to unravel important material properties like QD size and morphology or interface cleanliness [1,2]. Furthermore, a novel routine to determine the approximate 3D atom distribution of nanoparticles within beam-sensitive hybrid structures is presented.

On the other hand, mesoporous titania thin films used as catalyst support [3] and nanoporous zeolite [4] and hematite particles are investigated. ET is employed to determine important parameters of these nanoporous functional materials such as pore size distribution, interconnectivity and porosity. Moreover, ET reconstructions can directly be used to understand and model physical and chemical properties and processes within catalysts, e.g., the mass transport and chemical reaction of gases. Here, the integration of ET into a so-called virtual prototyping process for mesoporous titania thin films is demonstrated, which combines experimental and computational approaches for an optimization of the pore system.

Furthermore, ET shows excellent applicability to investigate µm-thick and porous biological structures by revealing the coexistence of both gyroid chiralities and specific crystallographic texture of naturally occurring photonic crystals in wing scales of the butterfly Callophrys rubi [5].

The presented analyses combine different characterization techniques, whereat TEM and ET show their exceptional strength exclusively allowing for the examination of important structural properties. The resultant findings essentially contribute to a detailed understanding of the studied materials and, beyond this, are key to their further development and application.

1. J. Schornbaum, B. Winter, S. P. Schießl, B. Butz, E. Spiecker, J. Zaumseil. Controlled in situ PbSe quantum dot growth around single-walled carbon nanotubes: a noncovalent PbSe-SWNT hybrid structure. Chemistry of Materials, 25(13):2663-2669, 2013.

2. J. Schornbaum, B. Winter, S. P. Schießl, F. Gannott, G. Katsukis, D. M. Guldi, E. Spiecker, J. Zaumseil. Epitaxial growth of PbSe quantum dots on MoS2 nanosheets and their near-infrared photoresponse. Advanced Functional Materials, 24(37):5798-5806, 2014.

3. V. Novák, E. Ortel, B. Winter, B. Butz, B. Paul, P. Kočí, M. Marek, E. Spiecker, R. Kraehnert. Prototyping of catalyst pore-systems by a combined synthetic, analytical and computational approach: application to mesoporous TiO2. Chemical Engineering Journal, 248(0):49-62, 2014.

4. A. G. Machoke, A. M. Beltrán, A. Inayat, B. Winter, T. Weissenberger, N. Kruse, R. Güttel, E. Spiecker,
W. Schwieger.
Micro/macroporous system: MFI-type zeolite crystals with embedded macropores. Advanced Materials, 27(6):1066-1070, 2015.

5. B. Winter, B. Butz, C. Dieker, G. E. Schröder-Turk, K. Mecke, E. Spiecker. Coexistence of both gyroid chiralities in individual butterfly wing scales of Callophrys rubi. PNAS, 112(52):12911-12916, 2015.

Acknowledgement: German Research Foundation (DFG) Cluster of Excellence “Engineering of Advanced Materials” (EXC 315), DFG SPP 1570.