2,739 research outputs found
Local boron doping quantification in homoepitaxial diamond structures
The capability of transmission electronmicroscopy (TEM) using the high angle annular dark fieldmode (HAADF,also labelled Z-contrast) to quantify boron concentration, in the high doping range between 1019cm−3 and 1021cm−3, is demonstrated. Thanks to the large relative variation of atomic number Z between carbon and boron, doping concentration maps and profiles are obtained with a nanometer-scale resolution. A novel numerical simulation procedure allows the boron concentration quantification and demonstrates the high sensitivity and
spatial resolution of the technique.4 page
4D STEM: high efficiency phase contrast imaging using a fast pixelated detector
Phase contrast imaging is widely used for imaging beam sensitive and weak phase objects in electron microscopy. In this work we demonstrate the achievement of high efficient phase contrast imaging in STEM using the pnCCD, a fast direct electron pixelated detector, which records the diffraction patterns at every probe position with a speed of 1000 to 4000 frames per second, forming a 4D STEM dataset simultaneously with the incoherent Z-contrast imaging. Ptychographic phase reconstruction has been applied and the obtained complex transmission function reveals the phase of the specimen. The results using GaN and Ti, Nd- doped BiFeO3 show that this imaging mode is especially powerful for imaging light elements in the presence of much heavier elements
Spectroscopic imaging of single atoms within a bulk solid
The ability to localize, identify and measure the electronic environment of
individual atoms will provide fundamental insights into many issues in
materials science, physics and nanotechnology. We demonstrate, using an
aberration-corrected scanning transmission microscope, the spectroscopic
imaging of single La atoms inside CaTiO3. Dynamical simulations confirm that
the spectroscopic information is spatially confined around the scattering atom.
Furthermore we show how the depth of the atom within the crystal may be
estimated.Comment: 4 pages and 3 figures. Accepted in Phys.Rev.Let
How Fast is Your Detector? The Effect of Temporal Response on Image Quality
With increasing interest in high-speed imaging should come an increased
interest in the response times of our scanning transmission electron microscope
(STEM) detectors. Previous works have previously highlighted and contrasted
performance of various detectors for quantitative compositional or structural
studies, but here we shift the focus to detector temporal response, and the
effect this has on captured images. The rise and decay times of eight
detectors' single electron response are reported, as well as measurements of
their flatness, roundness, smoothness, and ellipticity. We develop and apply a
methodology for incorporating the temporal detector response into simulations,
showing that a loss of resolution is apparent in both the images and their
Fourier transforms. We conclude that the solid-state detector outperforms the
photomultiplier-tube (PMT) based detectors in all areas bar a slightly less
elliptical central hole and is likely the best detector to use for the majority
of applications. However, using tools introduced here we encourage users to
effectively evaluate what detector is most suitable for their experimental
needs
The atomic lensing model: new opportunities for atom-by-atom metrology of heterogeneous nanomaterials
The atomic lensing model has been proposed as a promising method facilitating
atom-counting in heterogeneous nanocrystals [KHW van den Bos et. al, Phys. Rev.
Lett. 116 (2016) 246101] Here, image simulations will validate the model, which
describes dynamical diffraction as a superposition of individual atoms
focussing the incident electrons. It will be demonstrated that the model is
reliable in the annular dark field regime for crystals having columns
containing dozens of atoms. By using the principles of statistical detection
theory, it will be shown that this model gives new opportunities for detecting
compositional differences
Characterization of the cytosolic tuberin-hamartin complex. Tuberin is a cytosolic chaperone for hamartin
Tuberous sclerosis (TSC) is an autosomal dominant disorder characterized
by a broad phenotypic spectrum that includes seizures, mental retardation,
renal dysfunction and dermatological abnormalities. Mutations to either
the TSC1 or TSC2 gene are responsible for the disease. The TSC1 gene
encodes hamartin, a 130-kDa protein without significant homology to other
known mammalian proteins. Analysis of the amino acid sequence of tuberin,
the 200-kDa product of the TSC2 gene, identified a region with limited
homology to GTPase-activating proteins. Previously, we demonstrated direct
binding between tuberin and hamartin. Here we investigate this interaction
in more detail. We show that the complex is predominantly cytosolic and
may contain additional, as yet uncharacterized components alongside
tuberin and hamartin. Furthermore, because oligomerization of the hamartin
carboxyl-terminal coiled coil domain was inhibited by the presence of
tuberin, we propose that tuberin acts as a chaperone, preventing hamartin
self-aggregation
- …