Computer Image and Spectrum Acquisition on an HB501A STEM

ELS and XPS study of Pd/PdO methane oxidation catalysts

Quantitative EMCD by use of a double aperture for simultaneous acquisition of EELS

Smart acquisition EELS

At present transmission electron energy loss spectrum (EELS) analysis is only carried out in dedicated research instruments such as transmission electron microscopes (TEMs) or scanning transmission electron microscopes. This article presents a new design of second-order geometric aberration corrected EELS spectrometer attachment using split plates, which enables conventional scanning electron microscopes (SEMs) to provide TEM-like EELS spectra. Correction to a third-order dominant geometric aberration pattern has been achieved, which indicates that most of the second-order geometric aberration component is eliminated. This second-order aberration corrected spectrometer attachment design can enable SEMs to provide transmission EELS spectrums.

Auger and electron energy loss spectra of adsorbed species: α and β states of carbon monoxide and nitrogen on W(100)

In scanning transmission electron microscopy (STEM), one can obtain a variety of STEM images such as bright‐field (BF) and annular dark‐field (ADF) STEM images by changing the shape of the scintillator. However, the intensity distribution of convergent beam electron diffraction (CBED) patterns at the detector plane is yet to be fully utilized. Meanwhile, direct electron detectors with fast frame rate have recently been commercialized and used in electron microscopy. Such detectors, when used for recording CBED pattern images for each STEM probe position, are called pixelated STEM detectors. With the obtained 4‐dimensional (4D) dataset, any shape of STEM detector can be synthesized in a post processing by a free selection of the integration area. Therefore, we can synthesize variety of STEM images such as differential phase contrast (DPC) and annular bright field (ABF) images, if we once record the image signal with a pixelated detector. The 4D dataset can also be used for the advanced image processing techniques such as ptychography, which has been shown to provide high efficiency for reconstructing the phase image of an object [1,2]. Using ptychography, not only the phase contrast can be enhanced but also the effect of lens aberrations to the image such as defocus can be corrected by the post processing using the information collected by a pixelated detector. Experiments were performed using an aberration corrected microscope (JEOL JEM‐ARM200F) equipped with a pixelated detector (pnDetector pnCCD), the fast direct electron detector, which can record images at a speed of 1,000 fps in a full frame mode (264 x 264 pixels). Binning or windowing can increase the speed. The camera was placed below the ADF detector to enable simultaneous recording. Figure 1 shows STEM images of a monolayer graphene obtained at 80 kV. Fig. 1a shows an ADF image obtained with the probe current of approximately 0.2 pA and the dwell time for a pixel of 0.5 ms. Because of a combination of low dose and residual uncorrected aberrations, the lattice contrast of graphene is almost buried in the noise originated from 50 Hz commercial frequency. Fig. 1b shows a reconstructed phase image using ptychography. The image contrast is significantly improved compared to the simultaneous ADF image, but the contrast transfer of the image (see the Fourier transform displayed in the inset) is anisotropic, resulting in uncertain positions of carbon atoms. This is because there remains large two‐fold astigmatism and defocus in the image shown in Fig. 1(b), because we could not adjust those by observation of the ADF image due to the weak image signal. Fig. 1c is a phase image in which the aberrations are corrected through post processing using the same 4D dataset by applying correction functions in the spatial frequency domain. The image is no longer anisotropic and the carbon atomic positions can be unambiguously determined. Although the same amount of electron dose is used to form the ADF and the corrected phase images, the result clearly shows the benefit of ptychographic phase reconstruction in improving image signal to noise and being able to correct aberrations through post processing. Figure 2 shows the ptychographic phase maps of the 4D dataset at a certain spatial frequency. With an aberration‐free electron probe, they would be flat phase on the two sidebands, and the phase difference between the bands be π. In Fig. 2a, the map of the original dataset, there is a phase gradient inside each sideband because the aberrations were present in the electron probe. Fig. 2b is the correction function that compensates for the aberration seen in Fig. 2a. Fig. 2c is the corrected phase map and corresponding to the image in Fig. 1c. Here, only defocus and two‐fold astigmatism are corrected but corrections of other higher order aberrations are in principle possible. Figure 3 shows through focus images created in the same way as above. As we know the full information on the electron wave at the condenser aperture plane, we can induce any aberrations such as defocus.

Development and application of STEM for the biological sciences

Scanning transmission electron microscopy (STEM) has been widely utilized with annular detectors such as annular dark field (ADF) and annular bright field (ABF).Recently, segmented and pixelated detectors have allowed for the detection of detailed electron scattering intensity in the diffraction plane.Utilizing this richer information, low-dose STEM imaging capabilities have been discussed [1,2].Optimum-bright field (OBF) STEM, a non-iterative imaging technique developed recently, uses a segmented or pixelated detector for low-dose observation [3].OBF images are reconstructed from multiple images recorded simultaneously with a segmented/pixelated detector (Fig. 1).The reconstruction process ensures that the reconstructed image achieves the maximum signal-to-noise ratio (SNR) under the weak phase object approximation (WPOA).As the reconstruction process is noniterative, OBF images can be displayed synchronously with the probe scan.OBF STEM is starting to be used as a dose-efficient imaging technique for beam-sensitive materials.Recently, we demonstrated low-dose atomic resolution observations of FAU-type zeolite using OBF STEM, successfully visualizing all atomic sites [4].Figure 2 compares the OBF image with integrated differential phase contrast (iDPC), annular bright field (ABF), and bright field (BF) imaging techniques.The OBF image displays the highest SNR, clearly visualizing both oxygen and silicon sites.Additionally, since the noise in the OBF image can be considered as white noise, its interpretation is straightforward.In contrast, noise in the iDPC image is intensified in the low-frequency region, leading to reduced image contrast.Although OBF STEM is a promising technique for low-dose observations, adjusting observation conditions such as aberrations and crystal orientations for beam-sensitive specimens remains challenging.However, OBF reconstruction can account for residual aberrations and crystal misorientation.We developed a method to estimate actual observation conditions, including residual aberrations, crystal misorientation, and specimen thickness, using data recorded by a pixelated detector.Under the conditions of a thick weak phase object approximation (tWPOA) [5,6], we formulated a mathematical expression that defines the relationship between the 4D dataset and observation condition parameters.We found that it is possible to estimate these parameters separately by fitting the dataset to the corresponding mathematical expressions.We tested this method on a low-dose observation of FAU-type zeolite, with the dataset intentionally recorded under suboptimal observation conditions.The OBF reconstructed image assuming ideal observation conditions appeared opaque due to residual aberrations and crystal misorientation.In contrast, the OBF image that took into account the estimated observation condition parameters accurately visualized all atomic sites of FAU-type zeolite.This method significantly enhances the efficiency of low-dose observations.Moreover, if real-time estimation becomes feasible, the dataset could be recorded under nearly ideal conditions by adjusting the electron microscope based on the estimated parameters [7].

Strategy for optimizing experimental settings for studying low atomic number colloidal assemblies using liquid phase scanning transmission electron microscopy

FePt nanodendrites with high-index facets as active electrocatalysts for oxygen reduction reaction

An ultra-high resolution pole piece with a coefficient of spherical aberration Cs=0.7mm. was previously designed for a Vacuum Generators HB-501A Scanning Transmission Electron Microscope (STEM). This lens was used to produce bright field (BF) and annular dark field (ADF) images of (111) silicon with a lattice spacing of 1.92 Å. In this microscope the specimen must be loaded into the lens through the top bore (or exit bore, electrons traveling from the bottom to the top). Thus the top bore must be rather large to accommodate the specimen holder. Unfortunately, a large bore is not ideal for producing low aberrations. The old lens was thus highly asymmetrical, with an upper bore of 8.0mm. Even with this large upper bore it has not been possible to produce a tilting stage, which hampers high resolution microscopy.

Investigating the atomic scale structure and chemistry of grain boundaries in high-Tc superconductors

From the front cover and continuing on to the back, the images shown are, respectively: (1) Two-dimensional (2D) electron energy loss spectra (EELS) from a silicon oxide-nitride-oxide (ONO) stack, in which the horizontal dimension corresponds to energy loss, and the vertical represents a spatial coordinate; that is, each 2D spectrum represents a collection of EELS spectra spatially-resolved across the interfaces. From "Nanoscale Structural / Compositional Characterization of Ultra-Thin Films; (2) Tensile test specimen -MEMS polysilicon thickness 4 micrometers; (3) Magneto-optical image of domain patterns in a new "synthetic antiferromagnet" Co/Ru /Co trilayer showing two different types of domains separated by novel non-180 degree walls. Similar trilayers are used in high density recording media; (4) Color representation of one normal mode of magnetization vibration calculated for a 50 nm thick film of Permalloy with 20 nm defects; and (5) A synchrotron x-ray scattering pattern of a nanostructured thin film for electronic applications.

Quantitative analysis of the effect of probe convergence on electron energy loss spectra of anisotropic materials

Electron energy loss spectra of microscopy regions of quasicrystalline and crystalline Al 86Mn 14 alloys