The lipid droplet (LD), an organelle that exists ubiquitously in various organisms, from bacteria to mammals, has attracted much attention from both medical and cell biology fields. The LD in white adipocytes is often treated as the prototype LD, but is rather a special example, considering that its size, intracellular localization and molecular composition are vastly different from those of non-adipocyte LDs. These differences confer distinct properties on adipocyte and non-adipocyte LDs. In this article, we address the current understanding of LDs by discussing the differences between adipocyte and non-adipocyte LDs.
The origins and the recent accomplishments of aberration correction in scanning transmission electron microscopy (STEM) are reviewed. It is remembered that the successful correction of imaging aberrations of round lenses owes much to the successful correction of spectrum aberrations achieved in electron energy loss spectrometers 2-3 decades earlier. Two noteworthy examples of the types of STEM investigation that aberration correction has made possible are shown: imaging of single-atom impurities in graphene and analyzing atomic bonding of single atoms by electron energy loss spectroscopy (EELS). Looking towards the future, a new all-magnetic monochromator is described. The monochromator uses several of the principles pioneered in round lens aberration correction, and it employs stabilization schemes that make it immune to variations in the high voltage of the microscope and in the monochromator main prism current. Tests of the monochromator carried out at 60 keV have demonstrated energy resolution as good as 12 meV and monochromated probe size of similar to 1.2 angstrom. These results were obtained in separate experiments, but they indicate that the instrument can perform imaging and EELS with an atom-sized probe <30 meV wide in energy, and that an improvement in energy resolution to 10 meV and beyond should be possible in the future.
Aim: This study aimed to identify the clinical, radiological and prognostic features of primary adrenal lymphoma (PAL) in order to diagnose the disease more accurately. Materials and methods: A retrospective multi-centre study was conducted on the clinical, biological and radiological features as well as the treatment and overall survival outcomes in PAL. Results: Between 1994 and 2014, 28 patients from five regions of eastern France were diagnosed with primary adrenal lymphoma. The revealing symptoms were a worsening general state (77%), weight loss (77%) and abdominal pain (42%). Biological features of PAL were almost omnipresent: increased LDH, b2 microglobulin, CRP or ferritinaemia levels. The PAL was bilateral in 20 cases (71%), adrenal insufficiency was searched for in 11 patients and found in eight (73%). CT scans showed masses of various sizes measuring up to 180mm. On MRI, the lesions were hypointense in T1 and hyperintense in T2. When done, positron emission tomography with fluorodeoxyglucose (FDG-PET) showed locations not seen on the CT and revealed extra- adrenal locations in 70% of examinations. Adrenalectomy brought no benefit. The overall survival rate was poor (61.9% at 2 years) despite polychemotherapy. Conclusion: The clinical presentation of PAL comprised major general symptoms. Adrenal insufficiency was very common in patients with bilateral involvement but was not systematically tested. PET was an efficient examination to visualize extra-adrenal locations. The preliminary results of MRI to distinguish between PAL and adrenocortical carcinoma should be confirmed. Further studies are needed to establish an optimal strategy for the management of these primary adrenal lymphomas.
We introduce digital holographic techniques and recent progress in multidimensional sensing. Digital holography can be used to perform multidimensional imaging of three-dimensional structure, dynamics, quantitative phase, multiple wavelengths, and polarization state of light and sensing of a holographic image of nonlinear light and a three-dimensional image of incoherent light. Abstract In this review, we introduce digital holographic techniques and recent progress in multidimensional sensing by using digital holography. Digital holography is an interferometric imaging technique that does not require an imaging lens and can be used to perform simultaneous imaging of multidimensional information, such as three-dimensional structure, dynamics, quantitative phase, multiple wavelengths and polarization state of light. The technique can also obtain a holographic image of nonlinear light and a three-dimensional image of incoherent light with a single-shot exposure. The holographic recording ability of this technique has enabled a variety of applications.
Abstract As an instrument, the scanning transmission electron microscope is unique in being able to simultaneously explore both local structural and chemical variations in materials at the atomic scale. This is made possible as both types of data are acquired serially, originating simultaneously from sample interactions with a sharply focused electron probe. Unfortunately, such scanned data can be distorted by environmental factors, though recently fast-scanned multi-frame imaging approaches have been shown to mitigate these effects. Here, we demonstrate the same approach but optimized for spectroscopic data; we offer some perspectives on the new potential of multi-frame spectrum-imaging (MFSI) and show how dose-sharing approaches can reduce sample damage, improve crystallographic fidelity, increase data signal-to-noise, or maximize usable field of view. Further, we discuss the potential issue of excessive data-rates in MFSI, and demonstrate a file-compression approach to significantly reduce data storage and transmission burdens.
We developed 300 kV TEM equipped with a fifth-order aberration corrector (delta corrector) for STEM. The contrast flat area in a Ronchigram expanded to 70 mrad. We demonstrated a spatial resolution of 40.5 pm by obtaining an ADF STEM image of GaN  with a convergence angle of 40 mrad. Abstract The achievement of a fine electron probe for high-resolution imaging in scanning transmission electron microscopy requires technological developments, especially in electron optics. For this purpose, we developed a microscope with a fifth-order aberration corrector that operates at 300 kV. The contrast flat region in an experimental Ronchigram, which indicates the aberration-free angle, was expanded to 70 mrad. By using a probe with convergence angle of 40 mrad in the scanning transmission electron microscope at 300 kV, we attained the spatial resolution of 40.5 pm, which is the projected interatomic distance between Ga–Ga atomic columns of GaN observed along  direction.
The short depth of focus of aberration-corrected scanning transmission electron microscopes (STEMs) could potentially enable 3D reconstruction of nanomaterials through acquisition of a through-focal series. However, the contrast transfer function of annular dark-field (ADF)-STEM depth sectioning has a missing-cone problem similar to that of tilt-series tomography. The elongation as a function of the probe-forming angle is found to be . For existing aberration-corrected STEMs operated at optimal imaging conditions, the elongation factor for depth sectioning is larger than 30. This large elongation factor results in highly distorted shapes of 3D objects and unexpected artifacts due to the loss of information. Depth-sectioning experiments using a 33-mrad 100 keV C 5-corrected aberration-corrected STEM demonstrate the elongation effect and the missing-cone problem in real and reciprocal space. The performance limits of different S TEM-based imaging modes are compared. There is a missing cone of information for bright-field S TEM, ADF-STEM, hollow-cone ADF-STEM and coherent scanning confocal electron microscopy (SCEM). Only incoherent SCEM fills the missing cone.
We investigate the excitation of surface optical vibrational modes in amorphous silicon dioxide films and magnesium oxide nanocubes in the long-wavelength regime with keV electrons. We show that the response of these nanosystems is strongly constrained by their size and shape and can be explained by the dielectric characteristics of the involved materials. Abstract Using spatially resolved Electron Energy-Loss Spectroscopy, we investigate the excitation of long-wavelength surface optical vibrational modes in elementary types of nanostructures: an amorphous SiO2 slab, an MgO cube, and in the composite cube/slab system. We find rich sets of optical vibrational modes strongly constrained by the nanoscale size and geometry. For slabs, we find two surface resonances resulting from the excitation of surface phonon polariton modes. For cubes, we obtain three main highly localized corner, edge, and face resonances. The response of those surface phonon resonances can be described in terms of eigenmodes of the cube and we show that the corresponding mode pattern is recovered in the spatially resolved EELS maps. For the composite cube/substrate system we find that interactions between the two basic structures are weak, producing minor spectral shifts and intensity variations (transparency behaviour), particularly for the MgO-derived modes.
Abstract High-resolution monochromated electron energy-loss spectroscopy has the potential to map vibrational modes at nanometer resolution. Using the SiO2/Si interface as a test case, we observe an initial drop in the SiO2 vibrational signal when the electron probe is 200 nm from the Si due to long-range nature of the Coulomb interaction. However, the distance from the interface at which the SiO2 integrated signal intensity drops to half its maximum value is 5 nm. We show that nanometer resolution is possible when selecting the SiO2/Si interface signal which is at a different energy position than the bulk signal. Calculations also show that, at 60 kV, the signal in the SiO2 can be treated non-relativistically (no retardation) while the signal in the Si, not surprisingly, is dominated by relativistic effects. For typical transmission electron microscope specimen thicknesses, surface coupling effects must also be considered.
We visualized lithium atom columns in LiV2O4 crystals by combining scanning transmission electron microscopy with annular bright field (ABF) imaging using a spherical aberration-corrected electron microscope (R005) viewed from the  direction. The incident electron beam was coherent with a convergent angle of 30 mrad (semi-angle), and the detector collected scattered electrons over 20-30 mrad (semi-angle). The ABF image showed dark dots corresponding to lithium, vanadium and oxygen columns.
In this paper, we employ the dimension reduction from multivariate analysis to evaluate EELS spectrum imaging data. Signal integration of the Sn-M4,5 edges with delayed onset and the profile of the Fe-L3 white line are quantitatively analysed based on supervision of three spectral components instead of individual pixels. Abstract Multivariate analysis is a powerful tool to process spectrum imaging datasets of electron energy loss spectroscopy. Most spatial variance of the datasets can be explained by a limited numbers of components. We explore such dimension reduction to facilitate quantitative analyses of spectrum imaging data, supervising the spectral components instead of spectra at individual pixels. In this study, we use non-negative matrix factorization to decompose datasets from Fe2O3 thin films with different Sn doping profiles on SnO2 and Si substrates. Case studies are presented to analyse spectral features including background models, signal integrals, peak positions and widths. Matlab codes are written to guide microscopists to perform these data analyses.
Here we report the use of an electron-counting direct-detection camera for EEL spectroscopy. We studied amorphous ice and proteins and obtained a signal noise ratio up to 10 times higher than with a conventional CCD allowing us to observe time-resolved chemical changes in situ while exposed by the electron beam. Abstract Since the development of parallel electron energy loss spectroscopy (EELS), charge-coupled devices (CCDs) have been the default detectors for EELS. With the recent development of electron-counting direct-detection cameras, micrographs can be acquired under very low electron doses at significantly improved signal-to-noise ratio. In spectroscopy, in particular in combination with a monochromator, the signal can be extremely weak and the detection limit is principally defined by noise introduced by the detector. Here we report the use of an electron-counting direct-detection camera for EEL spectroscopy. We studied the oxygen K edge of amorphous ice and obtained a signal noise ratio up to 10 times higher than with a conventional CCD. We report the application of electron counting to record time-resolved EEL spectra of a biological protein embedded in amorphous ice, revealing chemical changes observed in situ while exposed by the electron beam. A change in the fine structure of nitrogen K and the carbon K edges were recorded during irradiation. A concentration of 3 at% nitrogen was detected with a total electron dose of only 1.7 e−/Å2, extending the boundaries of EELS signal detection at low electron doses.
Phonon energy-loss spectroscopy using electrons has both short-range (high resolution) and long-range (low resolution) components. We discuss how these two contributions arise from a fundamental quantum mechanical perspective. The long-range interaction dominates in aloof beam imaging, a mode in which radiation damage can be avoided. Abstract Phonon energy-loss spectroscopy using electrons has both high resolution and low resolution components, associated with short- and long-range interactions, respectively. In this paper, we discuss how these two contributions arise from a fundamental quantum mechanical perspective. Starting from a correlated model for the atomic motion we show how short range ‘impact’ scattering and long range ‘dipole’ scattering arises. The latter dominates in aloof beam imaging, an imaging geometry in which radiation damage can be avoided.
We report a software tool for post-correcting the linear and nonlinear image distortions of atomically resolved 3D spectrum imaging as well as 4D diffraction imaging. This tool improves the interpretability of distorted scanning transmission electron microscopy spectrum/diffraction imaging data. Abstract Specimen and stage drift as well as scan distortions can lead to a mismatch between true and desired electron probe positions in scanning transmission electron microscopy (STEM) which can result in both linear and nonlinear distortions in the subsequent experimental images. This problem is intensified in STEM spectrum and diffraction imaging techniques owing to the extended dwell times (pixel exposure time) as compared to conventional STEM imaging. As a consequence, these image distortions become more severe in STEM spectrum/diffraction imaging. This becomes visible as expansion, compression and/or shearing of the crystal lattice, and can even prohibit atomic resolution and thus limits the interpretability of the results. Here, we report a software tool for post-correcting the linear and nonlinear image distortions of atomically resolved 3D spectrum imaging as well as 4D diffraction imaging. This tool improves the interpretability of distorted STEM spectrum/diffraction imaging data.
Energy-loss magnetic chiral dichroism (EMCD) is a versatile method for studying magnetic properties on the nanoscale. We study the theoretical possibilities of convergent beam EMCD, particularly the influence of detector position, convergence and collection angle on the detectable EMCD signal and the signal-to-noise ratio. Additionally, we give some guidelines for achieving optimal EMCD results. Abstract Energy-loss magnetic chiral dichroism (EMCD) is a versatile method for studying magnetic properties on the nanoscale. However, the classical EMCD technique is notorious for its low signal-to-noise ratio (SNR), which is why many experimentalists have adopted a convergent-beam approach. Here, we study the theoretical possibilities of using a convergent beam for EMCD. In particular, we study the influence of detector positioning as well as convergence and collection angles on the detectable EMCD signal. In addition, we analyse the expected SNR and give some guidelines for achieving optimal EMCD results.
A moire pattern is created in a scanning transmission electron microscope ( STEM) when the scan step is close to a crystalline periodicity. Usually, fringes are visible in only one direction, corresponding to a single set of lattice planes, but fringes can be formed in two directions or more. Using an accurate independent calibration, the strains in silicon devices have been determined from the spacing and orientation of one-directional STEM moire fringes. In this report, we first discuss the origin of the STEM moire, and then we show how an accurate calibration of the scan step can be obtained from the STEM moire pattern itself, providing that we know initially only an approximate scan step and the planar spacing. The new calibration scheme also makes the STEM moire experiments easier, since it can be applied for the moire where the scan direction is not precisely aligned with the crystalline lattice. Finally, we show how the two-dimensional strain information will be readily extracted from two one-directional moire patterns using the concept of geometric phase.
Novel spherical aberration (Cs) and chromatic aberration (Cc) correctors, which correct aberrations using a new principle, were developed. The asymmetric Cs correctors were designed for use in the probe-and image-forming systems at 300 kV to diminish undesired parasitic aberrations. The correctors composed of non-equivalent multipoles connecting with a demagnifying transfer doublet in the system. The axial aberrations were corrected well up to the fifth order except 6-fold astigmatism (A(6)) experimentally. Next, we developed superior Cs correctors for probe- and image-forming systems of low voltage microscope that uses triple dodecapoles to correct 6-fold astigmatism (A(6)). An important feature of this system is the rotation of the 3-fold astigmatism azimuth at the second dodecapole. The optimum rotation of the three hexapole fields for the compensation of A(6) was derived from theoretical calculations. The experimental results confirmed the compensation of A(6) and the third-order Cs. Finally, a unique Cc corrector, which utilized the concave lens effect formed by a long quadrupole field, was designed. The performance of the Cc corrector was investigated using a 30-kV transmission electron microscope. The results confirmed that Cc correction was achieved.
Abstract Internal modification induced in Si by a permeable pulse laser was investigated by transmission electron microscopy. A laser induced modified volume (LIMV) was a cylindrical rod along the track of a laser beam with the head at the focus of the laser beam. In the LIMV, beside voids, dislocations, micro-cracks and what had been supposed to be an unidentified high-pressure phase (hpp) of Si were observed in LIMV. The so-called ‘hpp’ was identified mostly as diamond Si.
Selected-area electron diffraction used for strain mapping at nanoscale. We used a two-dimensional stage-scanning system to acquire arrays of diffraction patterns at different positions of the sample under fixed beam conditions. Data processing with two-dimensional Gaussian fitting enabled the spot displacement (indicator of strain) to be measured with high precision. Abstract Unlike X-ray diffraction or Raman techniques, which suffer from low spatial resolution, transmission electron microscopy can be used to obtain strain maps of nanoscaled materials and devices. Convergent-beam electron diffraction (CBED) and nanobeam electron diffraction (NBED) techniques detect the deviation of a lattice constant (i.e. an indicator of strain) within 0.01%; however, their use is restricted to beam-insensitive samples. Selected-area electron diffraction (SAED) does not have such limitations but has low spatial resolution and precision. The use of a spherical aberration corrector and a nanosized selected-area aperture improves the spatial resolution, but the precision is still low. In this study, a two-dimensional stage-scanning system is used to acquire arrays of diffraction patterns at different positions of the sample under fixed beam conditions. Data processing with iterative nonlinear least-squares fitting enabled the spot displacement for each point of the scan area to be measured with precision comparable to that of the CBED or NBED technique. The precise strain determination, in combination with the simplicity of the measurement process, makes the nanosized SAED technique competitive with other methods for strain mapping at nanoscale dimensions.
A new generation of high-dynamic range pixel array detectors that collect the full scattering distribution let us record diffraction patterns from features as small as a single atom to large domains. By understanding these asymptotic limits of diffraction pattern formation, we can separate short from long-range features in center-of-mass imaging. Abstract What does the diffraction pattern from a single atom look like? How does it differ from the scattering from long-range potential? With the development of new high-dynamic range pixel array detectors to measure the complete momentum distribution, these questions have immediate relevance for designing and understanding momentum-resolved imaging modes. We explore the asymptotic limits of long-range and short-range potentials. We use a simple quantum mechanical model to explain the general and asymptotic limits for the probability distribution in both real and reciprocal space. Features in the scattering potential much larger than the probe size cause the bright field (BF) disk to deflect uniformly, while features much smaller than the probe size, instead of a deflection, cause a redistribution of intensity within the BF disk. Because long-range and short-range features are encoded differently in the diffraction pattern, it is possible to separate their contributions in differential phase–contrast (DPC) or center-of-mass (CoM) imaging. The shape profiles for atomic resolution CoM imaging are dominated by the shape of the probe gradient and not the highly singular atomic potentials or their local fields. Instead, only the peak height shows an atomic number sensitivity, whose precise dependence is determined by the convergence angle. At lower convergence angles, the contrast oscillates with increasing atomic number, similar to BF imaging. The range of collection angles impacts DPC and CoM imaging differently, with CoM being more sensitive to the upper cutoff limit, while DPC is more sensitive to the lower cutoff.