Research in Botton's Group
Botton's group focuses on the application and development of electron microscopy techniques to study materials at high spatial resolution. The core research is based on transmission electron microscopy but we also use a myriad of other characterization techniques to provide information on the structure and electronic properties of materials.
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Energy Materials
Key words: Fuel Cells, Li-ion Batteries, Machine Learning, CO oxidation, Electrocatalysis, Pt-alloy catalysts, Liquid-cell microscopy, In situ Annealing, Electron Tomography, Time-evolution studies, Durability tests, Charging/Discharging cycles, single-atom catalysis...
Contributors: Hanshuo Liu, Jie Yang, Sagar Prabhudev, Mike Chatzidakis, Sam Stambula... Contact us >
Selected Publications
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Liu, H, et al. (2016). Three-dimensional investigation of cycling-induced microstructural changes in lithium-ion battery cathodes using focused ion beam/scanning electron microscopy. Journal of Power Sources, 306, 300-308.
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Chatzidakis, M., et al. (2017). Bulk Immiscibility at the Edge of the Nanoscale. ACS nano, 11(11), 10984-10991.
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Liu, H. et al. (2016). Spatially resolved surface valence gradient and structural transformation of lithium transition metal oxides in lithium-ion batteries. Physical Chemistry Chemical Physics, 18(42), 29064-29075.
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Stambula, S., et al. Platinum single-atom and cluster catalysis of the hydrogen evolution reaction. Nature communications, 7.
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Prabhudev, S., et al (2013). Strained lattice with persistent atomic order in Pt3Fe2 intermetallic core–shell nanocatalysts. ACS nano, 7(7), 6103-6110.
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Zhu, G. Z., Prabhudev, S., et al. (2014). In Situ Liquid Cell TEM Study of Morphological Evolution and Degradation of Pt–Fe Nanocatalysts During Potential Cycling. The Journal of Physical Chemistry C, 118(38), 22111-22119.
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Chinchilla, L. et al (2017). Nanoscale analysis of structural and chemical changes in aged hybrid Pt/NbO x/C fuel cell catalysts. Journal of Power Sources, 356, 140-152.
The development of aberration correctors for the scanning transmission electron microscope has revolutionized the field of electron microscopy and dramatically improved the analytical “toolkit” of materials scientists. In particular, when combined with electron energy loss spectroscopy (EELS), scanning transmission electron microscopy (STEM) makes it possible to detect compositional and spectroscopic changes at the atomic level that can be used to understand the structure, and ultimately the performance of materials.
Using an FEI Titan (80-300 Cubed) microscope equipped with a monochromator and EELS spectrometer (Quantum 966) we have been able to image single Pt atoms on multilayer graphene nanosheets (GNS) and demonstrate that single Pt atoms are stabilized during atomic layer deposition on N-doped GNS. Similarly, quantitative STEM images have been used to detect atomic displacements on PtFe intermetallic core-shell nanoparticles that exhibit very high specific activity compared to pure Pt. Not only is elemental mapping at the atomic scale possible, but the high beam current and fast spectrometers also allow the acquisition of these maps with large sampling of the nanostructure. For instance, in the study of PtRu nanocatalysts used in fuel cells the Ru core-Pt shell structures can be very clearly mapped. In the same system, we have also shown that it is possible to obtain maps from the Ti K edge (4970eV loss) and Pt M45 edge (2120eV) using the dual-EELS capabilities of the spectrometer. Further studies with EELS demonstrate the detection of valence changes and mapping of valence in Li-ion battery materials.
Plasmonics
Key words: Fractal geometries, lithography, high-energy resolution EELS, plasmon edge modes and gap modes, coupling, monochromator excitation, silver nanostructures, plasmon hybridization, surface plasmons
Contributors: Edson Bellido, Isobel Bicket, Viktor Kapetanovic, Alex Pofeliski, David Rossouw, Matthieu Bugnet, Steffi Woo... Contact us >
Selected Publications
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Bellido, Edson Pazur, et al. Self-Similarity of Plasmon Edge Modes on Koch Fractal Antennas. ACS Nano (2017).
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Bellido, Edson P., et al. Plasmonic coupling of multipolar edge modes and the formation of gap modes. ACS Photonics (2017).
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Barrow, Steven J., et al. Electron Energy Loss Spectroscopy Investigation into Symmetry in Gold Trimer and Tetramer Plasmonic Nanoparticle Structures. ACS nano 10.9 (2016): 8552-8563.
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Bellido, E. P., et al. Very High Resolution Energy Loss Spectroscopy: Applications in Plasmonics. Microscopy and Microanalysis 22 (2016): 974.
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Bellido, Edson P., David Rossouw, and Gianluigi A. Botton. Toward 10 meV electron energy-loss spectroscopy resolution for plasmonics. Microscopy and Microanalysis 20.3 (2014): 767-778.
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Rossouw, David, and Gianluigi A. Botton. Plasmonic response of bent silver nanowires for nanophotonic subwavelength waveguiding. Physical review letters 110.6 (2013): 066801.
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Rossouw, D., et al. Multipolar plasmonic resonances in silver nanowire antennas imaged with a subnanometer electron probe. Nano letters 11.4 (2011): 1499-1504.
The Monochromated electron beam of the aberration-corrected microscopes has allowed the detailed study of plasmonic response of nanostructures. Achieving 0.06eV energy resolution with a sub-nm size probe, the CCEM instruments have been used to study surface plasmon resonances in metallic nanoscale wires that have potential use in photonic information transfer. Using the electron beam, surface plasmon polaritons are excited and a standing wave pattern is formed which can be simultaneously detected with the same electrons when analyzed with a high-resolution spectrometer. This electron excitation is directly related to the photonic density of states of the sample and is very effectively probed with an electron beam smaller than 1nm.
As demonstrated by Rossouw et al, in Physical Review Letters, the energy loss spectrum shows multiple excitations in energy range down to 0.17eV, the lowest energy features ever observed with an electron beam. By selecting the energy window for a given energy loss, the spatial resolution of the standing wave, of a given energy has also been mapped. The results show that, using the CCEM instrumentation, we can resolve optical excitation down to the mid-infra red regime and this by spatially resolving energy modes extended in space by few 10’s of nm. These features would hence be not detectable with photon-based techniques because some of the excitations would not couple to light (i.e. they are dark-modes) and would be significantly smaller than the free-space wavelength of light.
Heterostructures & Intefaces
Key words: Grain-boundary segregation, dopants, semiconductor materials, thin films, Internal oxidation, twin-boundaries, defects, voids, alloy clustering, atomic-ordering, heat-treatments, atomic-resolution imaging and chemical mapping....
Contributors: Alex Pofeliski, Shaobo Chen, Steffi Woo, Sharzhad Hosseini, Matthieu Bugnet, Guozhen Zhu, Karleen Dudeck, Sagar Prabhudev.... Contact us >
Selected Publications
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Zhu, G. Z., et al. (2012). Bonding and structure of a reconstructed (001) surface of SrTiO 3 from TEM. Nature, 490(7420), 384.
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Langelier, B., et al. (2017). Effects of boundary migration and pinning particles on intergranular oxidation revealed by 2D and 3D analytical electron microscopy. Acta Materialia, 131, 280-295.
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Bugnet, M., et al. (2014). Segregation and clustering of solutes at grain boundaries in Mg–rare earth solid solutions. Acta Materialia, 79, 66-73.
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Woo, S. Y., et al. (2015). Atomic Ordering in InGaN Alloys within Nanowire Heterostructures. Nano letters, 15(10), 6413-6418.
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Dudeck, K. J., et al. (2013). Sub-ångstrom Experimental Validation of Molecular Dynamics for Predictive Modeling of Extended Defect Structures in Si. Physical review letters, 110(16), 166102.
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Hosseini Vajargah, S., et al. (2012). Atomic-resolution study of polarity reversal in GaSb grown on Si by scanning transmission electron microscopy. Journal of Applied Physics, 112(9), 093101.
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Gauquelin, N., et al. (2014). Atomically resolved EELS mapping of the interfacial structure of epitaxially strained LaNiO 3/LaAlO 3 superlattices. Physical Review B, 90(19), 195140.
The development of aberration correctors for the scanning transmission electron microscope has revolutionized the field of electron microscopy and dramatically improved the analytical “toolkit” of materials scientists. In particular, when combined with electron energy loss spectroscopy (EELS), scanning transmission electron microscopy (STEM) makes it possible to detect compositional and spectroscopic changes at the atomic level that can be used to understand the structure, and ultimately the performance of materials.
Beyond the “simple” deduction of the distribution of elements in nanostructures from maps, quantification is essential to understand the detailed structure of defects and correlate compositional measurement with, for instance, the optical response of materials. The detailed quantification of the atomic position of a defect, for example, a so-called {311} defect [see Karleen Dudeck's work] generated by the implantation of ions in Si shows that an excellent agreement is obtained between the experimental atomic positions and molecular dynamics simulations with an accuracy of better than 0.05nm for more than 100 atomic columns. Similarly, quantitative analysis of SiGe alloys deposited on Si has allowed us to deduce compositional fluctuations and interdiffusion in proximity of interfaces with the substrate. Here a quantitative analysis with EELS can also be carried out, e.g. in the measurement of the composition of InGaN quantum dots in GaN nanowires. These deductions can be further supported with emission wavelengths measured from cathodoluminescence in STEM and photoluminescence measurements [see Steffi Woo's works].
Advanced Microscopy
Key words: Electron channeling, beam damage, momentum-dependent EELS, STEM-HAADF, ELNES fine structures, atomic-resolution imaging & spectroscopy, core-hole distribution, strain mapping...
Contributors: Alex Pofeliski, Shaobo Chen, Matthieu Bugnet, David Rossouw, Steffi Woo, Nicolas Gauquelin, Guozhen Zhu... Contact us >
Selected Publications
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Botton, G. A., et al. (2010). Elemental mapping at the atomic scale using low accelerating voltages. Ultramicroscopy, 110(8), 926-934.
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Botton, G. A., et al. (1995). Momentum dependent energy loss near edge structures using a CTEM: the reliability of the methods available. Ultramicroscopy, 59(1-4), 93-107.
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Botton, G. (2007). Analytical electron microscopy. In Science of Microscopy (pp. 273-405). Springer, New York, NY.
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Radtke, G., et al. (2006). High-resolution EELS investigation of the electronic structure of ilmenites. Physical Review B, 74(15), 155117.
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Pofelski, A., et al. (2017). 2D strain mapping using scanning transmission electron microscopy Moiré interferometry and geometrical phase analysis. Ultramicroscopy.
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Bugnet, M., et al. (2016). Real-space localization and quantification of hole distribution in chain-ladder Sr3Ca11Cu24O41 superconductor. Science advances, 2(3), e1501652.
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Lazar, S., et al. (2011). Atomic resolution imaging using the real-space distribution of electrons scattered by a crystalline material. Acta Crystallographica Section A: Foundations of Crystallography, 67(5), 487-490.
Following the development of new electron sources, stable electron microscopes, aberration correctors, and commercial monochromators, the applications of EELS in the two worlds of materials analysis and materials physics are now finally converging.
The capability of mapping at the atomic scale is not simply revealing local changes in composition but it allows us to identify the termination of the surface of substrates, and the chemical species that are in direct contact with the substrate. For the particular case of La2/3Ca1/3MnO3 (LCMO) grown on YBa2Cu3O7-d (YBCO), our work has shown that the last atomic plane in YBCO is Ba, while the first atomic plane in LCMO is Mn. Similarly, it is also possible to use EELS mapping to provide unambiguous information on the site preference of transition metals in oxides whereby, in a Ca2FeMnO5, Mn is found on octahedral sites and Fe on tetrahedral sides. In disordered systems, this approach has allowed us to directly map the distribution of implanted Pr atoms in SrTiO3 and has demonstrated the expected statistical distribution of atoms that cannot be resolved based on purely Z-contrast imaging. For surfaces, we have been able to determine the valence state of surface atoms in reconstructed SrTiO3. With the improved energy resolution, we have demonstrated that, simultaneous intense light irradiation (in-situ) and acquisition of energy-loss spectra, there is a significant change in the excitonic peak portion of the σ* fine structure. This high-sensitivity demonstrates that the local heating and the charge carriers generated by infra-red photons significantly modify the electronic structure of the nanotubes. At very low energy losses, we have also shown the detection of energy loss features down to 0.17eV, the lowest feature ever reported. In addition, using numerical deconvolution, we have been able to show improvements in the effective energy resolution of spectra down to a FWHM of 0.01eV.
