Multiple scattering effects of MeV electrons in very thick amorphous specimens

A precision dimple grinder-polisher produced by 3D printing

A precision dimple grinder-polisher has been designed and constructed using 3D printing. The purpose of the device is to produce a thin central area in 3 mm round samples for transmission electron microscopy before ion milling to electron transparency. The device can be self-made by any laboratory with a 3D printer for scientific research or teaching, and when combined with recycling and use of biodegradable filaments it can help labs reach their sustainable development goals. A novel sample holder design allows sample alignment without a monocular and thickness detection by light transmission. Novel solutions are developed for aligning the grinding disc and sample rotation motors and for fixing the polishing cloth to the polishing disc. The diameter-depth relationship is investigated for steel and plastic grinding discs. Design principles and materials are discussed, and the tool is evaluated by preparing samples from copper, silicon and tungsten, which are then examined in the transmission electron microscope to evaluate their quality.

Application of ultra-high voltage electron microscope tomography to 3D imaging of microtubules in neurites of cultured PC12 cells

Electron tomography methods using the conventional transmission electron microscope have been widely used to investigate the three-dimensional distribution patterns of various cellular structures including microtubules in neurites. Because the penetrating power of electrons depends on the section thickness and accelerating voltage, conventional TEM, having acceleration voltages up to 200 kV, is limited to sample thicknesses of 0.2 µm or less. In this paper, we show that the ultra-high voltage electron microscope (UHVEM), employing acceleration voltages of higher than 1000 kV (1 MV), allowed distinct reconstruction of the three-dimensional array of microtubules in a 0.7-µm-thick neurite section. The detailed structure of microtubules was more clearly reconstructed from a 0.7-µm-thick section at an accelerating voltage of 1 MV compared with a 1.0 µm section at 2 MV. Furthermore, the entire distribution of each microtubule in a neurite could be reconstructed from serial-section UHVEM tomography. Application of optimised UHVEM tomography will provide new insights, bridging the gap between the structure and function of widely-distributed cellular organelles such as microtubules for neurite outgrowth. LAY DESCRIPTION: An optimal 3D visualisation of microtubule cytoskeleton using ultra-high voltage electron microscopy tomography The ultra-high voltage electron microscope (UHVEM) is able to visualise a micrometre-thick specimen at nanoscale spatial resolution because of the high-energy electron beam penetrating such a specimen. In this study, we determined the optimal conditions necessary for microtubule cytoskeleton imaging within 0.7-µm-thick section using a combination with UHVEM and electron tomography method. Our approach provides excellent 3D information about the complex arrangement of the individual microtubule filaments that make up the microtubule network.

A Study of Membrane Impact on Spatial Resolution of Liquid In Situ Transmission Electron Microscope

Microchip technology with electron transparent membranes is a key component for in situ liquid transmission electron microscope (TEM) characterization. The membranes can significantly influence the TEM imaging spatial resolution, not only due to introducing additional material layers but also due to the associated bulging. The membrane bulging is largely defined by the membrane materials, thickness, and short dimension. The impact of the membrane on the spatial resolution, especially the extent of its bulging, was systematically investigated through the impact on the signal-to-noise ratio, chromatic aberration, and beam broadening. The optimization of the membrane parameters is the key component when designing the in situ TEM liquid cell. The optimal membrane thickness of 50 nm was found which balances the impact of membrane bulging and membrane thickness. Beyond this, the short membrane window dimension and the chip nominal spacing should be minimized. However, these two parameters have practical limitations in regards to chip handling.

Automatic system for electron tomography data collection in the ultra-high voltage electron microscope

In this study, we report an automatic system for collection of tilt series for electron tomography based on the ultra-HVEM in Osaka University. By remotely controlling the microscope and reading the observation image, the system can track the field of view and do focus in each tilt angle. The automatic tracking is carried out with an image matching technique based on normalized correlation coefficient. Auto focus is realized by the optimization of image sharpness. A toolkit that can expand the field of view with technique of image stitching is also developed. The system can automatically collect the tilt series with much smaller time consumption.

The influence of structure depth on image blurring of micrometres-thick specimens in MeV transmission electron imaging

This study investigates the influence of structure depth on image blurring of micrometres-thick films by experiment and simulation with a conventional transmission electron microscope (TEM). First, ultra-high-voltage electron microscope (ultra-HVEM) images of nanometer gold particles embedded in thick epoxy-resin films were acquired in the experiment and compared with simulated images. Then, variations of image blurring of gold particles at different depths were evaluated by calculating the particle diameter. The results showed that with a decrease in depth, image blurring increased. This depth-related property was more apparent for thicker specimens. Fortunately, larger particle depth involves less image blurring, even for a 10-μm-thick epoxy-resin film. The quality dependence on depth of a 3D reconstruction of particle structures in thick specimens was revealed by electron tomography. The evolution of image blurring with structure depth is determined mainly by multiple elastic scattering effects. Thick specimens of heavier materials produced more blurring due to a larger lateral spread of electrons after scattering from the structure. Nevertheless, increasing electron energy to 2MeV can reduce blurring and produce an acceptable image quality for thick specimens in the TEM.

Analysis of nonlinear intensity attenuation in bright-field TEM images for correct 3D reconstruction of the density in micron-sized materials

To obtain the correct tomographic reconstruction of micron-sized materials, the nonlinear intensity attenuation of bright-field transmission electron microscopy (BF-TEM) images was analyzed as a function of the sample thickness using a high-voltage electron microscope. The intensity attenuation was precisely measured relative to the projection thickness of carbon microcoils (CMCs) at acceleration voltages of 400-1000 kV using objective apertures (OAs) with radii of 2.1-28 nm(-1). The results show that the nonlinearity is strongly dependent on the OA size and the acceleration voltage. The influence of nonlinearity on tomographic reconstructions was also examined using a specially developed 360°-tilt sample holder. Sliced images of the reconstructed volumes indicated that an increase in the nonlinearity caused artificial fluctuations in the internal density of materials and inaccurate shapes of the objects in more significant cases. Conditions sufficient for reconstruction with the correct density have been estimated to be 0.67 of the minimum electron transmittance, and for reconstructions with correct shapes, 0.4. This information enables foreseeing the quality of the reconstruction from a single BF-TEM image prior to the tilt-series acquisition. As a result to demonstrate the appropriateness of these conditions, a CMC with a diameter of 3.7 µm was reconstructed successfully; i.e. not only the shape but also the internal density were correctly reproduced using electron tomography.

Electron tomographic resolution of microns-thick specimens in the ultrahigh voltage electron microscope

In this study, we determine the electron tomography (ET) resolution for microns-thick specimens by experiment in the ultra-high voltage electron microscope. A tilt series of projection images of a tilted 8μm thick epoxy-resin film are first acquired. Tomographic reconstructions are then calculated and the resolution is evaluated with the Fourier shell correlation method. The ET resolution of 32nm is achieved under the condition of 2MV accelerating voltage. We also demonstrate that some high tilt angle projections may be little useful for improving the final ET resolution because of the corresponding poor image qualities. These results are helpful to understand the possibility and limitation of ET applications in microns-thick specimens.

Note: direct measurement of the point-to-point resolution for microns-thick specimens in the ultrahigh-voltage electron microscope

We report on a direct measurement method and results of the point-to-point resolution for microns-thick amorphous specimens in the ultrahigh-voltage electron microscope (ultra-HVEM). We first obtain the ultra-HVEM images of nanometer gold particles with different sizes on the top surfaces of the thick epoxy-resin specimens. Based on the Rayleigh criterion, the point-to-point resolution is then determined as the minimum distance between centers of two resolvable tangent gold particles. Some values of resolution are accordingly acquired for the specimens with different thicknesses at the accelerating voltage of 2 MV, for example, 18.5 nm and 28.4 nm for the 5 μm and 8 μm thick epoxy-resin specimens, respectively. The presented method and results provide a reliable and useful approach to quantifying and comparing the achievable spatial resolution for the thick specimens imaged in the mode of transmission electron including the scanning transmission electron microscope.