Recent Research Highlights

Phase Contrast in STEM

Phase-contrast STEM imaging in an aberration-corrected microscope represents an increasingly important alternative to the well-established HRTEM method. In both methods, the image contrast is coherently generated and thus depends not only on illumination and collection angles but on defocus and specimen thickness as well. This can be understood on the basis of the reprocity principle as demonstrated in this review. The contrast inversion in the PC-STEM images of an Au nanoparticle show above exemplifies the defocus dependence.

Phase-contrast imaging in aberration-corrected scanning transmission electron microscopy
F. Krumeich, E. Müller, and R. A. Wepf
Micron 2013, 49, 1-14 DOI

Tin Nanocrystals for Battery Applications

Uniform and monodisperse Sn and Sn/SnO₂ nanoparticles can be obtained with sizes in the range 9-23 nm. In electrochemical measurements 10 nm Sn/SnO₂ nanocrystals have demonstrated high Li insertion/removal cycling stability superior to commercial 100−150 nm powders of Sn and SnO₂.

Monodisperse and Inorganically Capped Sn and Sn/SnO₂ Nanocrystals for High Performance Li-ion Battery Anodes
K. Kravchyk, L. Protesescu, M. Bodnarchuk, F. Krumeich, M. Yarema, M. Walter, C. Guntlin, and M. Kovalenko
J. Am. Chem. Soc., 2013, 135, 4199-420 DOI

see also ETH Life

The persistence of nanoparticles during waste combustion was probed by introducing nano-CeO₂ (image) into the waste or the gas stream exiting the furnace of a muncipal waste incineration plant. The analysis of the residues show the presence of the unaltered nanoparticles in the slag and fly ash. Thus, although the nanoparticles are efficiently filtered from the cleaned gas, they still remain in the solid residues which has to be taken care of before deposition.

Persistence of Engineered Nanoparticles in a Municipal Solid-Waste Incineration Plant
T. Walser, L. K. Limbach, R. Brogioli, E.Erismann, L. Flamigni, B. Hattendorf, M. Juchli, F. Krumeich, C. Ludwig, K. Prikopsky, M. Rossier, D. Saner, A. Sigg, S. Hellweg, D. Günther, and W. J. Stark
Nature Nanotechn. 7 (2012) 520-524 DOI

see also ETH Life

Dodecagonal Tantalum Tellurides

Phase-contrast imaging performed on an aberration-corrected scanning transmission electron microscope (STEM) represents a means to characterize the structure of dd-(Ta,V)_1.6Te phases. The basic (Ta,V)₁₅₁Te₇₄ clusters can be visualized with high resolution with the image contrast depending on defocus and specimen thickness like in HRTEM. In thin areas, the projected crystal potential is basically imaged and square-triangle tilings can be derived in which each vertex corresponds to a cluster center (an example is marked by arrow in the image).

The structure of Dodecagonal (Ta,V)_1.6 Te imaged by Phase-Contrast Scanning Transmission Electron Microscopy
F. Krumeich, E. Müller, R.A. Wepf, M. Conrad, C. Reich, B. Harbrecht und R. Nesper, J. Solid State Chem. 194 (2012) 106-112 DOI

Coated Nanoparticles

Composite nanoparticles and Coated nanoparticles can be synthesized by flame spray pyrolysis of corresponding precorsor solutions (for detailed information, see PTL). The image shows silica coated Ag particles. In this case, the coating modifies the antibacterial activity of Ag.

Non-toxic Dry-coated Nanosilver for Plasmonic Biosensors
G. A. Sotiriou, T. Sannomiya, A.Teleki, F. Krumeich, J. Vörös, and S. E. Pratsinis, Adv. Funct. Mater. 20 (2010) 4250–4257 DOI

Nanosilver on Nanostructured Silica: Antibacterial Activity and Ag Surface Area
G. Sotiriou, A. Teleki, A. Camenzind, F. Krumeich, A. Meyer, S. Panke, and S.E. Pratsinis, Chem. Eng. J. 170 (2011) 547–554 DOI

Catalyst Characterization

Aberration-corrected scanning transmission electron microscopy (STEM) combines sub-Angstrom resolution with outstanding analytical capabilities and thus provide an excellent tool for the characterization of heterogeneous catalysts. Images can be recorded with bright field (BF), annular dark field (ADF) and secondary electron (SE) detectors using various signals. The image shows Pd particles distributed on a (Si,Al)O_x support. All particles are visible in the ZC image, only those at the upper surface appear in the SE image giving some idea about the 3D structure.

Characterization of Catalysts in an Aberration-Corrected Scanning Transmission Electron Microscope
F. Krumeich, E. Müller, R. A. Wepf, and R. Nesper, J. Phys. Chem C 115 (2011) 1080–1083 DOI

Surface Properties and Morphology of Supported, Colloid-Derived Gold/Palladium Mono- and Bimetallic Nanoparticles
S. Marx, F. Krumeich, and A. Baiker, J. Phys. Chem. C 115 (2011) 8195-8205 DOI

Characterization of AuPd Nanoparticles by Probe-Corrected Scanning Transmission Electron Microscopy and X-Ray Absorption Spectroscopy
F. Krumeich, S. Marx, A. Baiker, and R. Nesper, Z. anorg. allg. Chem. 637 (2011) 875–881 DOI

Optimization of Catalysts

RuO₂ nanocrystals grown on SnO₂ microcrystal provide superior catalytic efficiency for the oxidation of HCl. In addition to the published results in this manuscript, EDXS analyses with high lateral resolution proved the expected elemental distribution (link).

Shaped RuO₂/SnO₂-Al₂O₃ Catalyst for Large-Scale Stable Cl₂ Production via HCl Oxidation
C. Mondelli, L. D. Pachón, A. Amrute, T. Schmidt, F. Krumeich, and J. Pérez-Ramírez, ChemCatChem 3 (2011) 657-660 DOI

Cation Ordering in Perovskites

The results of a combined HRTEM and HAADF-STEM study of the complex perovskites NaNb_1-xTa_xO₃ (0.4 ≤ x ≤ 0.6) revealed the formation of extended crystal areas with niobium and tantalum order and allowed us to develop a structural model explaining the experimental findings.

Transmission Electron Microscopy Evidence of Spontaneous B-Cation Layered Distribution in NaNb_1-xTa_xO₃
A. Torres-Pardo, F. Krumeich, J. M. González-Calbet, and E. García-González, J. Am. Chem Soc. 132 (2010) 9843-9849 DOI

Leaching of ZSM-5 Zeolithes

The treatment of ZSM-5 crystals with NaOH leads to an inhomogeneous dissolution with the inner core disappearing more rapidly than the crystal rim (image) indicating an inhomogeneous Al-Si distribution. It could indeed be shown by EDXS mapping that Al is enriched at the rim.

Where are the Active Sites in Zeolites? Origin of Aluminum Zoning in ZSM-5
N. Danilina, F. Krumeich, S. A. Castelanelli, and J. A. van Bokhoven
J. Phys. Chem. C 114 (2010) 6640-6645 DOI

Cytoxicity of Nanoparticles

The effect of metallic nanoparticles on cells was probed by treating two cell lines with C-coated Cu nanoparticles. The up-take of these nanoparticles was shown by HAADF-STEM that reveal them as bright patches inside the cells (s. image).

Nanoparticle Cytotoxicity Depends on Intracellular Solubility: Comparison of Stabilized Copper Metal and Degradable Copper Oxide Nanoparticles
A. M. Studer, L. K. Limbach, L. Van Duc, F. Krumeich, E. K. Athanassiou, L. C. Gerber, H. Moch, and W. J. Stark
Toxicology Lett. 197 (2010) 169-174 DOI

The reciprocal lattice of a new bismuth oxysulfate was determined by tilting experiments on single crystalline fibers (a=1.221, b=1.961, c=0.584 nm; SG Ccc2). The analogy to Bi₆Cr₂O₁₅ results in a structural model. Simulations calculated with the corresponding parameters and the experimental images match well (see figure; [100] left, [110] right).

Hydrothermal Synthesis of Bi₆S₂O₁₅ Nanowires: Structural, in situ EXAFS, and Humidity-Sensing Studies
Y. Zhou, J.-D. Grunwaldt, F. Krumeich, K. Zheng, G. Chen, J. Stoetzel, R. Frahm, and G. R. Patzke, Small 6 (2010) 1173-117 DOI