An electron microscope for the aberration-corrected era

Krivanek, Ondrej L.; Corbin, G.J.; Dellby, Niklas; Elston, B; Keyse, R.; Murfitt, Matthew F.; Own, Christopher S.; Szilágyi, Zoltán; Woodruff, J.W.

doi:10.1016/j.ultramic.2007.07.010

Cited by 291 publications

(211 citation statements)

References 13 publications

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“…A probe corrected Nion UltraSTEM 100 scanning transmission electron microscope 37 was used at an acceleration voltage of 100 kV in bright field (BF) and high-angle annular dark-field (HAADF) imaging mode, the latter to reveal single metal atoms in the samples as the intensity in HAADF images is to a good approximation proportional to the atomic number (Z) as Z n , n1.7.…”

Section: Methodsmentioning

confidence: 99%

Single Atoms of Pt-Group Metals Stabilized by N-Doped Carbon Nanofibers for Efficient Hydrogen Production from Formic Acid

et al. 2016

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Formic acid is a valuable chemical derived from biomass, as it has a high hydrogen-storage capacity and appears to be an attractive source of hydrogen for various applications. Hydrogen production via formic acid decomposition is often based on using supported catalysts with Pt-group metal nanoparticles. In the present paper, we show that the decomposition of the acid proceeds more rapidly on single metal atoms (by up to one order of magnitude). These atoms can be obtained by rather simple means through anchoring Pt-group metals onto mesoporous N-functionalized carbon nanofibers. A thorough evaluation of the structure of the active site by aberration-corrected scanning transmission electron microscopy (ac-STEM) in high-angle annular dark field (HAADF) mode, by CO chemisorption, X-ray photoelectron spectroscopy (XPS) and quantum-chemical calculations reveals that the metal atom is coordinated by a pair of pyridinic nitrogen atoms at the edge of graphene sheets. The chelate binding provides an ionic/electron-deficient state of these atoms prevents their aggregation and thereby leads to an excellent stability under the reaction conditions. Catalysts with single atoms have also shown very high selectivity. Evidently, the findings can be extended to hydrogen production from other chemicals and can be helpful for improving other energy-related and environmentally benign catalytic processes.

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Section: Methodsmentioning

confidence: 99%

Single Atoms of Pt-Group Metals Stabilized by N-Doped Carbon Nanofibers for Efficient Hydrogen Production from Formic Acid

et al. 2016

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“…Aberration-corrected STEM-ADF imaging was performed with a Nion Ultra STEM 100, equipped with a cold field emission electron source and a corrector of 3rd and 5th order aberrations 28 . The microscope was operated at 60 kV accelerating voltage, which is below the knock-on radiation damage threshold of graphene.…”

Section: Methodsmentioning

confidence: 99%

Direct visualization of reversible dynamics in a Si6 cluster embedded in a graphene pore

et al. 2013

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Clusters containing only a handful of atoms have been the subject of extensive theoretical and experimental studies, but their direct imaging has not been possible so far, with information about their structure provided mainly by theory. Here we report a direct atomically-resolved observation of a single Si 6 cluster trapped in a graphene nanopore. Furthermore, though electron-beam-induced irreversible atomic displacements have been reported before, here we report a sequence of images that show a reversible, oscillatory, conformational change: one of the Si atoms jumps back and forth between two different positions. Density-functional calculations show that the embedded cluster is exploring metastable configurations under the influence of the beam, providing direct information on the atomic-scale energy landscape. The capture of a Si cluster in a graphene nanopore suggests the possibility of patterning nanopores and assembling atomic clusters with a potential for applications.

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“…This means that if the temperature of the microscope (or of the sample rod) changes by just 0.1°C then the sample can drift by hundreds of nm. This results in image drift rates of the order of nm per minute being common with side-entry stages in all but the most stable environments.In order to minimize these kinds of problems, Nion's cartridge-based sample stage was designed to have an OL polepiece-to-sample mechanical path of 10 cm and a thermal expansion center that coincides with the microscope's optic axis [1]. The detachable sample cartridges have no direct link to the microscope's outside.…”

mentioning

confidence: 99%

“…In order to minimize these kinds of problems, Nion's cartridge-based sample stage was designed to have an OL polepiece-to-sample mechanical path of 10 cm and a thermal expansion center that coincides with the microscope's optic axis [1]. The detachable sample cartridges have no direct link to the microscope's outside.…”

mentioning

confidence: 99%

Stable and Flexible Side-Entry Stage for Nion STEMs

et al. 2017

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Aberration-corrected scanning transmission electron microscopes (STEMs) can resolve single atoms, probe them spectroscopically, and produce elemental and chemical maps with atomic resolution in 2D and 3D. When equipped with a monochromator and operating in an aloof mode, STEMs can record vibrational electron energy loss spectra (vib-EELS) to create nm-scale vibrational maps while avoiding radiation damage. These techniques require excellent short-term (vibration) and long-term (drift) stability of the microscope's sample stage.Typical side-entry stages are mounted on the side of the microscope in such a way that the sample is connected to the objective lens (OL) polepiece through a~30 cm long mechanical path. This means that if the temperature of the microscope (or of the sample rod) changes by just 0.1°C then the sample can drift by hundreds of nm. This results in image drift rates of the order of nm per minute being common with side-entry stages in all but the most stable environments.In order to minimize these kinds of problems, Nion's cartridge-based sample stage was designed to have an OL polepiece-to-sample mechanical path of 10 cm and a thermal expansion center that coincides with the microscope's optic axis [1]. The detachable sample cartridges have no direct link to the microscope's outside. These two innovations have resulted in drift rates smaller than 1 nm per hour and sample vibration amplitudes <0.1 Å r.m.s. [2]. Unfortunately, compared to a side-entry sample rod that supports the sample at one end and exits outside the microscope vacuum at the other end, a detachable cartridge in not as well suited for bringing in "services" to the sample such as cooling, heating, electrical, gases, liquids, straining, tilting, and nano-indenting.To combine the stability and freedom from drift of our centro-symmetric design with the flexibility of a side-entry sample rod, Nion has developed a new side-entry sample stage. The first version of the stage has been built for Orsay's CHROMATEM project: a high energy resolution monochromated STEM-EELS (HERMES) instrument, whose requirements include cathodo-luminescence (CL) capabilities with both light detection and injection [3], and a liquid nitrogen-cooled sample holder. A CL mirror can be introduced on the entrance side of the sample, in a 6 mm OL polepiece gap. The mirror is UHV-compatible and precisely moveable, so that the mirror's focal spot can be made to coincide with the "optimum probe formation spot" of the objective lens, about 0.5 x 0.5 x 2 µm in size (w x d x h). The mirror can couple out CL, or bring in laser illumination, as needed for instance for energy-gain spectroscopy. The cathodo-luminescence capabilities of the system are complemented by Nion's sub-10 meV energy resolution ground-potential monochromator [4], and a new Nion electron energy loss spectrometer optimized for vibrational studies.

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An electron microscope for the aberration-corrected era

Cited by 291 publications

References 13 publications

Single Atoms of Pt-Group Metals Stabilized by N-Doped Carbon Nanofibers for Efficient Hydrogen Production from Formic Acid

Single Atoms of Pt-Group Metals Stabilized by N-Doped Carbon Nanofibers for Efficient Hydrogen Production from Formic Acid

Direct visualization of reversible dynamics in a Si6 cluster embedded in a graphene pore

Stable and Flexible Side-Entry Stage for Nion STEMs

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