•A large-area SDD and a virtual-pivot double-tilt specimen holder are tested.•The specimen holder designs and materials are optimized.•Shadowing-free EDS measurements have been demonstrated.•A specimen holder made of polyetheretherketone yields the lowest system noise.This paper describes the effective solid angle improvement achieved using a large-area silicon drift detector together with a virtual-pivot double-tilt specimen holder. The virtual-pivot mechanism enables various designs of specimen-retaining and can reduce the shadowing effect. Energy-dispersive X-ray spectra were measured and converted into effective solid angles using different types of specimen holders and specimens. The investigated shadowing-free mechanical system yielded effective solid angles approaching the nominal solid angle of 0.464 sr. In addition, we have demonstrated the availability of the plastic (polyetheretherketone) specimen holder for low system noise.

•A rapid method for measuring low-order aberrations of STEM is proposed.•The aberrations are evaluated using Fourier transforms of crystalline Ronchigrams.•The first- and second-order aberrations are determined using two Ronchigrams.•The time dependences of focus and twofold astigmatism are examined.The aberrations of the objective lens should be measured and adjusted to realize high spatial resolution in scanning transmission electron microscopy (STEM). Here we report a method of measuring low-order aberrations using the Fourier transforms of Ronchigrams of an arbitrary crystal such as a specimen of interest. We have applied this technique to measure first- and second-order geometrical aberrations using typical standard specimens. Focus and twofold astigmatism are measured using two Ronchigrams obtained under different foci. Axial coma and threefold astigmatism are evaluated using the Fourier transforms of small subareas of a Ronchigram. The time dependences of focus and twofold astigmatism are examined using this technique for an aberration-corrected microscope.

•We assess the temporal partial coherence of TEM using a 3-dimensional (3D) Fourier transform (FT) of through-focus images.•We apply the 3D FT method with intentionally tilted incidence to normalize various factors associated with a TEM specimen and an imaging device.•The spatial frequency at which information transfer decreases to 1/e2 (13.5%) is determined for two lower-voltage TEM systems.We evaluate the temporal partial coherence of transmission electron microscopy (TEM) using the three-dimensional (3D) Fourier transform (FT) of through-focus images. Young's fringe method often indicates the unexpected high-frequency information due to non-linear imaging terms. We have already used the 3D FT of axial (non-tilted) through-focus images to reduce the effect of non-linear terms on the linear imaging term, and demonstrated the improvement of monochromated lower-voltage TEM performance [Kimoto et al., Ultramicroscopy 121 (2012) 31–39]. Here we apply the 3D FT method with intentionally tilted incidence to normalize various factors associated with a TEM specimen and an imaging device. The temporal partial coherence of two microscopes operated at 30, 60 and 80 kV is evaluated. Our method is applicable to such cases where the non-linear terms become more significant in lower acceleration voltage or aberration-corrected high spatial resolution TEM.

We assess the imaging performance of a transmission electron microscopy (TEM) system operated at a relatively low acceleration voltage using the three-dimensional (3D) Fourier transform of through-focus images. Although a single diffractogram and the Thon diagram cannot distinguish between the linear and non-linear TEM imaging terms, the 3D Fourier transform allows us to evaluate linear imaging terms, resulting in a conclusive assessment of TEM performance. Using this method, information transfer up to 98 pm is demonstrated for an 80 kV TEM system equipped with a spherical aberration corrector and a monochromator. We also revisit the Young fringe method in the light of the 3D Fourier transform, and have found a considerable amount of non-linear terms in Young fringes at 80 kV even from a typical standard specimen, such as an amorphous Ge thin film.Highlights► We assess the performance of TEM using 3D Fourier transform of through-focus images. ► The method can discriminate between the linear and non-linear TEM imaging terms. ► High resolution of 98 pm is achieved using 80 kV Cs-corrected TEM with monochromator. ► We also revisit the Young fringe method in the light of the 3D Fourier transform.

We demonstrate spatially resolved diffractometry in which diffraction patterns are acquired at two-dimensional positions on a specimen using scanning transmission electron microscopy (STEM), resulting in four-dimensional data acquisition. A high spatial resolution of about 0.1 nm is achieved using a stabilized STEM instrument, a spherical aberration corrector and various post-acquisition data processings. We have found a few novel results in the radial and the azimuthal scattering angle dependences of atomic-column contrast in STEM images. Atomic columns are clearly observed in dark field images obtained using the excess Kikuchi band intensity even in small solid-angle detection. We also find that atomic-column contrasts in dark field images are shifted in the order of a few tens of picometers on changing the azimuthal scattering angle. This experimental result is approximately interpretable on the basis of the impact parameter in Rutherford scattering. Spatially resolved diffractometry provides fundamental knowledge related to various STEM techniques, such as annular dark field (ADF) and annular bright field (ABF) imaging, and it is expected to become an analytical platform for advanced STEM imaging.Research highlights► We demonstrated spatially resolved diffractometry with high spatial resolution using STEM. ► Atomic columns are clearly observed in dark field images obtained using the excess Kikuchi band even in small solid-angle detection. ► Atomic-column contrasts in dark field images are shifted by changing the azimuthal scattering angle. ► It is interpretable on the basis of the impact parameter in Rutherford scattering.

Titanium oxide nanosheets have been attracting much attention owing to their photocatalytic property. Here, we synthesized a Ti2O3 nanosheet by the reduction of a titania nanosheet (Ti0.87O2) that was one or two atoms in thickness. The atomic structure of the Ti2O3 nanosheet was quantitatively revealed by electron diffraction analysis, electron energy-loss spectroscopy, and high-resolution transmission electron microscopy (TEM). A titania nanosheet (Ti0.87O2) consisting of edge-shared TiO6 octahedra was transformed to a Ti2O3 nanosheet consisting of face-shared octahedra by electron beam irradiation. This represents a stable crystal phase of titania nanosheets like the Magneli phase in oxygen-deficient environments. The atomic arrangement of the Ti2O3 nanosheet was directly observed by newly developed aberration-corrected TEM.Keywords: high-resolution transmission electron microscopy; Magneli phase; reducing atmosphere; TiO6 octahedron; titania nanosheet;

We report a local crystal structure analysis with a high precision of several picometers on the basis of scanning transmission electron microscopy (STEM). Advanced annular dark-field (ADF) imaging has been demonstrated using software-based experimental and data-processing techniques, such as the improvement of signal-to-noise ratio, the reduction of image distortion, the quantification of experimental parameters (e.g., thickness and defocus) and the resolution enhancement by maximum-entropy deconvolution. The accuracy in the atom position measurement depends on the validity of the incoherent imaging approximation, in which an ADF image is described as the convolution between the incident probe profile and scattering objects. Although the qualitative interpretation of ADF image contrast is possible for a wide range of specimen thicknesses, the direct observation of a crystal structure with deep-sub-angstrom accuracy requires a thin specimen (e.g., 10 nm), as well as observation of the structure image by conventional high-resolution transmission electron microscopy.

We demonstrate atomic-column imaging by scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). The silicon atomic-columns of a β-Si3N4 (0 0 1) specimen are clearly resolved. The atomic-site dependence and the energy-loss dependence of the spatial resolution are elucidated on the basis of the experimental results and multislice calculations. We describe two decisive factors for realizing atomic-column imaging in terms of localization in elastic and inelastic scattering. One is the channeling of the incident probe due to dynamical diffraction, which has atomic-site dependence. The other is the localization in inelastic scattering; in addition to the energy-loss dependence of delocalization, we point out its dependence on the offset energy from the ionization energy, i.e., an additional localization factor concerning the Bethe surface. The present atomic-column observation of the Si–L core-loss image indicates that the local approximation, which can be interpreted intuitively, is achievable under appropriate experimental conditions, such as high-energy-loss, a small convergence angle and a large collection angle (e.g., 400 eV, 15 and 30 mrad, respectively).

We demonstrate atomic-column imaging by scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). The silicon atomic-columns of a β-Si3N4 (0 0 1) specimen are clearly resolved. The atomic-site dependence and the energy-loss dependence of the spatial resolution are elucidated on the basis of the experimental results and multislice calculations. We describe two decisive factors for realizing atomic-column imaging in terms of localization in elastic and inelastic scattering. One is the channeling of the incident probe due to dynamical diffraction, which has atomic-site dependence. The other is the localization in inelastic scattering; in addition to the energy-loss dependence of delocalization, we point out its dependence on the offset energy from the ionization energy, i.e., an additional localization factor concerning the Bethe surface. The present atomic-column observation of the Si-L core-loss image indicates that the local approximation, which can be interpreted intuitively, is achievable under appropriate experimental conditions, such as high-energy-loss, a small convergence angle and a large collection angle (e.g., 400 eV, 15 and 30 mrad, respectively).

Microstructure characterization has become indispensable to the study of complex materials, such as strongly correlated oxides, and can obtain useful information about the origin of their physical properties. Although atomically resolved measurements have long been possible, an important goal in microstructure characterization is to achieve element-selective imaging at atomic resolution. A combination of scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS)1, 2 is a promising technique for atomic-column analysis. However, two-dimensional analysis has not yet been performed owing to several difficulties, such as delocalization in inelastic scattering or instrumentation instabilities. Here we demonstrate atomic-column imaging of a crystal specimen using localized inelastic scattering and a stabilized scanning transmission electron microscope3. The atomic columns of La, Mn and O in the layered manganite La1.2Sr1.8Mn2O7 are visualized as two-dimensional images.

The practical advantages of a monochromator for electron energy-loss spectroscopy (EELS) in transmission electron microscopy are reviewed. The zero-loss peaks (ZLPs) of a monochromator and a cold field emission gun are compared in terms of bandgap measurement performance. The intensity of the ZLP tails at the bandgap energy is more important than the full-width at half maximum of the ZLP, and a monochromator is preferable to conventional electron sources. The silicon bandgap of 1.1 eV is evaluated from the onset in the EEL spectrum obtained using the monochromator without a numerical procedure. We also show a high-speed instability-correction technique to realize the inherent energy resolution of the monochromator, in which instabilities of less than 335 Hz are corrected using 512 EEL spectra obtained with an exposure time of 1.4 ms. It will be useful in bandgap measurements and advanced studies for elucidating sub-eV EEL spectra.

We demonstrate that a high energy resolution of 0.23 eV is possible by using a cold field-emission electron gun (CFEG) without a monochromator. We have used a 300 kV transmission electron microscope (Hitachi, HF-3000) equipped with a CFEG and an energy filter (Gatan, GIF2002). Since energy instability is critical for high energy resolution in electron energy-loss spectroscopy, we have applied a high-speed ‘streak imaging’ acquisition technique, in which a series of time-resolved spectra are acquired as a two-dimensional spectrum. With this technique, we can easily record 1000–20,000 spectra with an exposure time of 0.353 ms per spectrum. Instability of less than 1.4 kHz has been corrected in the time-resolved spectra, allowing the inherent performance of the CFEG to be realized.

The practical procedure for coma-free alignment using a single defocused transmission electron microscopy (TEM) image is presented. Caustic figures observed in the defocused TEM image of a focused probe are utilized. Coma-free alignment can be carried out by coinciding a bright-field spot with the center of a caustic curve as observed in an underfocus TEM image. With this method, beam tilt misalignment is reduced to the sub-mrad order (e.g. 0.3 mrad for 300 kV FEG–TEM). This can be done without intentional beam tilting, an amorphous specimen, high-resolution TEM images, or fast Fourier transform for diffractogram or cross-correlation, which are used in previous methods. Residual coma aberration is detected using the multiple Bragg images of a known crystal. Similarity between the present coma-free alignment and well-known STEM alignment using shadow image is discussed.

Phase contrast formed by inelastically scattered electrons in a crystal has been investigated using spatially resolved EELS, which enables simultaneous observation of lattice fringes formed by electrons of various energy losses. Lattice fringes produced by low-loss electrons overlap on an elastic TEM image like Fourier images. This means that the exit wave is preserved in low-loss scattering. Similar Fourier images occur for electrons suffering core-losses in the range 50–400 eV, which indicates delocalization and spatial coherence in those core-loss scattering events. The spatial coherence of inelastically scattered electrons is estimated from the focus dependence of energy-filtered lattice fringe contrast. Spatial coherence widths shorten with increasing energy-loss, and their energy-loss dependence is similar to diffraction errors derived from the characteristic angle for inelastic scattering.