139 research outputs found
FEI Titan G3 50-300 PICO
The FEI Titan G3 50-300 PICO is a unique fourth generation transmission electron microscope which has been specifically designed for the investigation of a wide range of solid state phenomena taking place on the atomic scale and thus necessitating true atomic resolution analysis capabilities. For these purposes, the FEI Titan G3 50-300 PICO is equipped with a Schottky type high-brightness electron gun (FEI X-FEG), a monochromator unit, and a Cs probe corrector (CEOS DCOR), a Cs-Cc achro-aplanat image corrector (CEOS CCOR+), a double biprism, a post-column energy filter system (Gatan Quantum 966 ERS) as well as a 16 megapixel CCD system (Gatan UltraScan 4000 UHS). Characterised by a TEM and STEM resolution well below 50 pm at 200 kV, the instrument is one of the few chromatically-corrected high resolution transmission electron microscopes in the world. Typical examples of use and technical specifications for the instrument are given below
FEI Titan 80-300 TEM
The FEI Titan 80-300 TEM is a high-resolution transmission electron microscope equipped with a field emission gun and a corrector for the spherical aberration (CS) of the imaging lens system. The instrument is designed for the investigation of a wide range of solid state phenomena taking place on the atomic scale, which requires true atomic resolution capabilities. Under optimum optical settings of the image CS-corrector (CEOS CETCOR) the point-resolution is extended up to the information limit of well below 100 pm with 200 keV and 300 keV electrons. A special piezo-stage design allows ultra-precise positioning of the specimen in all 3 dimensions. Digital images are acquired with a Gatan 2k x 2k slow-scan charged coupled device camera
3D sub-nanoscale imaging of unit cell doubling due to octahedral tilting and cation modulation in strained perovskite thin films
Determining the 3-dimensional crystallography of a material with
sub-nanometre resolution is essential to understanding strain effects in
epitaxial thin films. A new scanning transmission electron microscopy imaging
technique is demonstrated that visualises the presence and strength of atomic
movements leading to a period doubling of the unit cell along the beam
direction, using the intensity in an extra Laue zone ring in the back focal
plane recorded using a pixelated detector method. This method is used together
with conventional atomic resolution imaging in the plane perpendicular to the
beam direction to gain information about the 3D crystal structure in an
epitaxial thin film of LaFeO3 sandwiched between a substrate of (111) SrTiO3
and a top layer of La0.7Sr0.3MnO3. It is found that a hitherto unreported
structure of LaFeO3 is formed under the unusual combination of compressive
strain and (111) growth, which is triclinic with a periodicity doubling from
primitive perovskite along one of the three directions lying in the
growth plane. This results from a combination of La-site modulation along the
beam direction, and modulation of oxygen positions resulting from octahedral
tilting. This transition to the period-doubled cell is suppressed near both the
substrate and near the La0.7Sr0.3MnO3 top layer due to the clamping of the
octahedral tilting by the absence of tilting in the substrate and due to an
incompatible tilt pattern being present in the La0.7Sr0.3MnO3 layer. This work
shows a rapid and easy way of scanning for such transitions in thin films or
other systems where disorder-order transitions or domain structures may be
present and does not require the use of atomic resolution imaging, and could be
done on any scanning TEM instrument equipped with a suitable camera.Comment: Minor fixes, especially in reference
Los números
128 páginas.La teorÃa de los números ocupa un peculiar y distinguido lugar entre las diversas ramas de las matemáticas. Que su objetivo principal sea el estudio de algo tan conocido y familiar como son los enteros, sus propiedades y sus relaciones, explica el interés que ha suscitado siempre entre muchos ciudadanos, quienes, aun careciendo de la formación matemática apropiada, se sienten fascinados por sus problemas, tan fáciles de enunciar y, sin embargo, tan difÃciles a veces de resolver. Este libro no pretende ser, ni mucho menos, un tratado de la teorÃa de los números, sino tan sólo un vehÃculo que permita al lector pasear por algunos de sus parajes más asequibles. Una especie de guÃa turÃstica para aritméticos aficionados y para todos aquellos que tengan curiosidad acerca de las propiedades de los números y aprecien el arte de engarzar las ideas que conlleva todo razonamiento matemático.Peer reviewe
Lessons from the harmonic oscillator -- a reconciliation of the Frequency-Resolved Frozen Phonon Multislice Method with other theoretical approaches
We compare the Frequency-Resolved Frozen Phonon Multislice (FRFPMS) method,
introduced in Phys. Rev. Lett. 124, 025501 (2020), with other theoretical
approaches used to account for the inelastic scattering of high energy
electrons, namely the first-order Born approximation and the quantum excitation
of phonons model. We show, that these theories lead to similar expressions for
the single inelastically scattered intensity as a function of momentum transfer
for an anisotropic quantum harmonic oscillator in a weak phase object
approximation of the scattered waves, except for a too small smearing of the
scattering potential by the effective Debye-Waller factor (DWF) in the FRFPMS
method. We propose that this issue can be fixed by including an explicit DWF
smearing into the potential and demonstrate numerically, that in any realistic
situation, a FRFPMS approach revised in this way, correctly accounts for the
single inelastically scattered intensity and the correct elastic scattering
intensity. Furthermore our simulations illustrate that the only requirement for
such a revised FRFPMS method is the smallness of mean squared displacements for
all atomic species in all frequency bins. The analytical considerations for the
FRFPMS method also explain the -scaling of FRFPMS spectra observed
in Phys. Rev. B 104, 104301 (2021) by the use of classical statistics in the
molecular dynamics simulation. Moreover, we find that the FRFPMS method
inherently adds the contributions of phonon loss and gain within each frequency
bin. Both of these issues related to the frequency-scaling can be fixed by a
system-independent post-processing step
Measurement of directional atomic modulation direction using the azimuthal variation of first order Laue zone electron diffraction
Data that generates the figures in the associated article and shows how the calculations are done
Measurement of directional atomic modulation direction using the azimuthal variation of first order Laue zone electron diffraction
We show that diffraction intensity into the First Order Laue Zone (FOLZ) of a
crystal can have a strong azimuthal dependence, where this FOLZ ring appears
solely because of unidirectional atom position modulation. Such a modulation
was already known to cause the appearance of elliptical columns in atom
resolution images, but we show that measurement of the angle via 4-dimensional
Scanning Transmission Electron Microscopy (4DSTEM) is far more reliable and
allows the measurement of the modulation direction with a precision of about
1{\deg} and an accuracy of about 3{\deg}. This method could be very powerful in
characterising atomic structures in 3 dimensions by 4DSTEM, especially in cases
where the structure deviates from that found in bulk crystals.Comment: To be submitted to PR
Atomic resolution mapping of localized phonon modes at grain boundaries
Phonon scattering at grain boundaries (GBs) is significant in controlling
nanoscale device thermal conductivity. However, GBs could also act as
waveguides for selected modes. To measure localized GB phonon modes, meV energy
resolution is needed with sub-nm spatial resolution. Using monochromated
electron energy loss spectroscopy (EELS) in the scanning transmission electron
microscope (STEM) we have mapped the 60 meV optic mode across GBs in silicon at
atomic resolution and compared it to calculated phonon densities of states
(DOS). The intensity is strongly reduced at GBs characterised by the presence
of five- and seven-fold rings where bond angles differ from the bulk. The
excellent agreement between theory and experiment strongly supports the
existence of localized phonon modes and thus of GBs acting as waveguides
Microwave-assisted synthesis of iridium oxide and palladium nanoparticles supported on a nitrogen-rich covalent triazine framework as superior electrocatalysts for the hydrogen evolution and oxygen reduction reaction
Iridium oxide (IrOx-NP) and palladium nanoparticles (Pd-NP) were supported on a 2,6-dicyanopyridine-based covalent-triazine framework (DCP-CTF) by energy-saving and sustainable microwave-assisted thermal decomposition reactions in propylene carbonate and in the ionic liquid [BMIm][NTf2]. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) confirm well-distributed NPs with sizes from 2 to 13 nm stabilized on the CTF particles. Metal contents between 10 and 41 wt% were determined by flame atomic absorption spectroscopy (AAS). Nitrogen sorption measurements of the metal-loaded CTFs revealed Brunauer–Emmett–Teller (BET) surface areas between 904 and 1353 m2 g−1. The composites show superior performance toward the hydrogen evolution reaction (HER) with low overpotentials from 47 to 325 mV and toward the oxygen reduction reaction (ORR) with high half-wave potentials between 810 and 872 mV. IrOx samples in particular show high performances toward HER while the Pd samples show better performance toward ORR. In both reactions, electrocatalysts can compete with the high performance of Pt/C. Exemplary cyclic voltammetry durability tests with 1000 cycles and subsequent TEM analyses show good long-term stability of the materials. The results demonstrate the promising synergistic effects of NP-decorated CTF materials, resulting in a high electrocatalytic activity and stability
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