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Electron microscopy analysis of nm- sized particles and segregations Frank Krumeich and Reinhard Nesper ETH Zurich, Laboratory of Inorganic Chemistry

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Presentation on theme: "Electron microscopy analysis of nm- sized particles and segregations Frank Krumeich and Reinhard Nesper ETH Zurich, Laboratory of Inorganic Chemistry"— Presentation transcript:

1 Electron microscopy analysis of nm- sized particles and segregations Frank Krumeich and Reinhard Nesper ETH Zurich, Laboratory of Inorganic Chemistry krumeich@inorg.chem.ethz.ch www.microscopy.ethz.ch  Electron microscopy: valuable tools for the characterization of nanomaterials  Scanning transmission electron microscopy STEM - HAADF-STEM - Combination with spectroscopic methods  Comparison of methods

2 Electron Microscopy Methods for the Characterization of Nanomaterials (Example: Vanadium Oxide Nanotubes) SEM: characterization of tubular morphology Cross-sections of VO x nanotubes: TEM and elemental maps obtained by electron spectroscopic imaging V map C map TEM: characterization of the wall structure EELS: composition

3 STEM detectors BF Bright Field detector ADF Annular Dark Field detector (Θ = 0.5 - 3°) Scanning Transmission Electron Microscopy (STEM) HAADF High Angle Annular Dark Field detector (Θ > 3°)

4 Scattering of Electrons at an Atom Strong Coulomb interaction of an electron with the nucleus  scattering into high angles or even backwards High angle annular dark field detector (HAADF-STEM)  atomic-number (Z) contrast:

5 HAADF-STEM of Small Metal Particles 50 nm 10 nm Au particles (bright contrast) on titania (Z contrast)

6 HAADF-STEM and EDXS: Point Analyses Pd/Pt particles on alumina Pt Pd Pt Cu Al O C Pt Pd Pt Cu Al O C

7 HAADF-STEM and EDXS WO 3 segregations in the oxidation product of Nb 4 W 13 O 47 (T ox =1000°C) Krumeich, Nesper, J. Solid State Chem. 179 (2006) 1658 matrix segregation

8 HAADF-STEM of Nb 4 W 13 O 49 HAADF-STEM: Elemental Distribution Single-crystal X-ray structure of Nb 7 W 10 O 47 ca. 80% Nb 100% W P2 1 2 1 2 a=12.26, b=36.63, c=3.95 Å (Krumeich, Wörle, Hussain, J. Solid State Chem. 149 (2000) 428)

9 High-Resolution Electron Microscopy WO 3 segregations in a bronze-type Nb-W oxide HRTEM 2 nm HAADF-STEM

10 Comparison: HRTEM ↔ HAADF-STEM HRTEMHAADF-STEM basics interference of coherently scattered electron waves incoherent scattering recording - time parallel 0.5 – 2 s serial 5-20 s (→ problems) cathodeLaB 6 (or FEG)FEG resolutionca. 2 Å obtainable information atomic positions (and elemental distribution) atomic positions and elemental distribution image interpretation comparison with simulations Scherzer defocus: atom columns dark direct atom columns always bright; intensity ~Z 2

11 Analytical Electron Microscopy Electron-matter interactions are mostly elastic  high electron doses necessary Long measuring times  high sample stability and absence of drift Ionization edges occur at different energies and are of different shape  not all methods are equally suitable for all elements Qualitative and quantitative information about the composition: EDXS, EELS Bonding, coordination, interatomic distances: Fine structure in EELS (ELNES, EXEFS) Spatially resolved information about composition: 1. STEM + EDXS and/or EELS 2. ESI Benefits Limitations

12 Transmission Electron Microscope Acknowledgements EMEZ: Electron Microscopy Center, ETH Hönggerberg www.emez.ethz.ch Tecnai F30 U acc = 300kV, field emission cathode (FEG) SuperTwin lens: C s = 1.15 mm, point resolution d < 0.2 nm Equipment: post-column imaging filter, STEM, energy-dispersive X-ray spectrometer Methods: TEM, HRTEM, STEM, ED, EDXS, EELS, ESI, EFTEM krumeich@inorg.chem.ethz.ch www.microscopy.ethz.ch Post-column filter

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