Dahmen, Tim | Kohr, Holger | de Jonge, Niels | Slusallek, Philipp
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Combined tilt- and focal series scanning transmission electron microscopy is a recently developed method to obtain nanoscale three-dimensional (3D) information of thin specimens. In this study, we formulate the forward projection in this acquisition scheme as a linear operator and prove that it is a generalization of the Ray transform for parallel illumination. We analytically derive the corresponding backprojection operator as the adjoint of the forward projection. We further demonstrate that the matched backprojection operator drastically improves the convergence rate of iterative 3D reconstruction compared to the case where a backprojection based on heuristic weighting is used. In addition, we show that the 3D reconstruction is of better quality.
Dahmen, Tim | Kohr, Holger | de Jonge, Niels | Slusallek, Philipp
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DOI:Frigge, Tim | Hafke, Bernd | Tinnemann, Verena | Krenzer, Boris | Horn-von Hoegen, Michael
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The thermal transport properties of crystalline nanostructures on Si were studied by ultra-fast surface sensitive time-resolved electron diffraction. Self-organized growth of epitaxial Ge hut, dome, and relaxed clusters was achieved by in-situ deposition of 8 monolayers of Ge on Si(001) at 550 °C under UHV conditions. The thermal response of the three different cluster types subsequent to impulsive heating by fs laser pulses was determined through the Debye-Waller effect. Time resolved spot profile analysis and life-time mapping was employed to distinguish between the thermal response of the different cluster types. While dome clusters are cooling with a time constant of τ = 150 ps, which agrees well with numerical simulations, the smaller hut clusters with a height of 2.3 nm exhibit a cooling time constant of τ = 50 ps, which is a factor of 1.4 slower than expected.
Hermannsdörfer, Justus | de Jonge, Niels
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DOI:Hermannsdörfer, Justus | de Jonge, Niels | Tinnemann, Verena | Alansary, Dalia | Niemeyer, Barbara A. | Korf, Ulrike | Peckys, Diana B.
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DOI:Hermannsdörfer, Justus | de Jonge, Niels | Verch, Andreas
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It was studied how the chemistry of gold nanoparticles in water is influenced by solution parameters such as the pH or the NaCl concentration under electron beam irradiation. We found that depending on these parameters the gold nanoparticles either dissolved, merged or remained unchanged.
Peckys, Diana B. | de Jonge, Niels
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This protocol describes the labeling of epidermal growth factor receptor (EGFR) on COS7 fibroblast cells, and subsequent correlative fluorescence microscopy and environmental scanning electron microscopy (ESEM) of whole cells in hydrated state. Fluorescent quantum dots (QDs) were coupled to EGFR via a two-step labeling protocol, providing an efficient and specific protein labeling, while avoiding label-induced clustering of the receptor. Fluorescence microscopy provided overview images of the cellular locations of the EGFR. The scanning transmission electron microscopy (STEM) detector was used to detect the QD labels with nanoscale resolution. The resulting correlative images provide data of the cellular EGFR distribution, and the stoichiometry at the single molecular level in the natural context of the hydrated intact cell. ESEM-STEM images revealed the receptor to be present as monomer, as homodimer, and in small clusters. Labeling with two different QDs, i.e., one emitting at 655 nm and at 800 revealed similar characteristic results.
Peckys, Diana B. | Hermannsdörfer, Justus | Tinnemann, Verena | Korf, Ulrike | de Jonge, Niels
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DOI:van de Put, Marcel W. P. | Carcouët, Camille C. M. C. | Bomans, Paul H. H. | Friedrich, Heiner | de Jonge, Niels | Sommerdijk, Nico A. J. M.
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Silica nanoparticles are imaged in solution with scanning transmission electron microscopy (STEM) using a liquid cell with silicon nitride (SiN) membrane windows. The STEM images reveal that silica structures are deposited in well-defined patches on the upper SiN membranes upon electron beam irradiation. The thickness of the deposits is linear with the applied electron dose. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrate that the deposited patches are a result of the merging of the original 20 nm-diameter nanoparticles, and that the related surface roughness depends on the electron dose rate used. Using this approach, sub-micrometer scale structures are written on the SiN in liquid by controlling the electron exposure as function of the lateral position.
Tilgner, Dominic | Friedrich, Martin | Hermannsdörfer, Justus | Kempe, Rhett
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Porous coordination polymers or metal–organic frameworks have been proposed as promising catalyst materials since their discovery. A fundamental problem associated with MOF-based catalysts is the stability during their catalytic performance, especially in liquid-phase catalysis. Herein, we report on the controlled incorporation of nanoscale palladium and titanium dioxide inside MIL-101 (Cr). The introduction of the metal species was accomplished by metal-organic chemical vapor deposition and can be varied over a large weight-percentage range. The enhanced catalytic activity and the improved reusability of the resulting Pd/TiO2@MIL-101 composite materials were demonstrated in hydrogenation and dehydrogenation reactions. Furthermore, the presence of TiO2 (amorphous) allowed observing an enhanced photocatalytic activity.