Pulse beam emission in a spin-polarized pulse-TEM (SP-TEM) was performed using a combination of a semiconductor photocathode and an ultra-short pulse laser, which has an ability of a time-resolved measurement. The photocathode has high quantum efficiency of the order of 10-3 comparing with other metal-type photocathode, which can realized a wide range of the pulse duration from a continuous emission to a pico-second pulse emission. The SP-TEM has several advantages of a high brightness of 3.1×108 A/cm2・sr, a narrow energy width of 114 meV and a long coherence length of 150 nm. In a pulse-mode operation, a pico-second pulse duration was realized with a newly developed ultra-short pulse laser system which consists of a mode-lock Ti-Sapphire laser, a compensator of a group velocity dispersion and a pulse-duration converter. Time-resolved TEM imaging and pulsed interference fringes were also conducted successfully with a stroboscopic acquisition technique. Consequently, in spite of a high current density, the pulsed electron beam emitted from the photocathode has enough coherence to realize a time-resolved holography that can observe phase information in a temporal space.
An ultrafast detection technique on 100 fs time scales over sub-nanometer (even atomic) spatial dimensions has long been a goal for the scientists to reveal and understand the ultrafast structural-change induced dynamics in materials. In this paper, a technique of particle acceleration based radio-frequency (RF) electron gun, the generation of femtosecond electron pulses using the RF gun and the first prototype of femtosecond time-resolved relativistic-energy ultrafast electron microscopy (UEM) at Osaka University are reported. Finally, both relativistic-energy electron diffraction and image measurements in the UEM prototype are presented.
The goal of the project is a contraction of a high-voltage transmission electron microscopy (TEM) by employing technologies of linear-accelerators driven by microwaves, which allow us to realize a compact and low-cost high-voltage TEM. The energy-spread of the beams by linear-accelerators is too large to utilize for TEMs directly, because the beams are accelerated by alternating electric field in resonance-cavities of microwaves. In this paper, we report several technologies, including RF-choppers, to solve the problems.
A next challenge for advanced electron microscopes is the development of high-speed electron microscope with the high time resolution. As the beginning, ultrafast electron diffraction has been studied. To observe phenomena of irreversible processes, intense short electron pulses must be indispensably developed, but there is an essential problem as the spread of the electron pulse by space charge effect. We are studying the interaction physics of intense femtosecond laser and matters to develop the instruments of ultrafast electron diffraction and deflectometry using laser generated and accelerated electron pulses. In this interaction, electrons (plasma) are instantaneously generated and accelerated in a target by an intense femtosecond laser pulse, and the electron bunch is available as an intense short pulse electron source. The electron pulse source will be intense and short enough for the ultrafast electron diffraction. In this article, the principle of laser acceleration, the compression of laser generated and accelerated electron pulses, the demonstration of imaging a diffraction pattern by a single pulse, and the observation of an laser induced surface wave by femtosecond electron deflectometry are reviewed.
A new time-resolved electron-diffraction technique has been developed by combining a reflection high-energy electron diffraction (RHEED) with a streak camera system. The developed compact system, named streak-camera RHEED, does not require a short-pulsed electron beam for the temporal resolution, and covers a wide range from sub-nano seconds to milli-seconds.
This year marks the 50th anniversary of the first launch of a commercial scanning electron microscope. Thanks to the utilization of the field emission gun, SEM has achieved a high resolution and it is widely used today. Low voltage SEM has become common because of the development of various beam deceleration techniques. These techniques are particularly useful for materials characterization due to the small penetration depth of the primary beam. Despite the usefulness of SEM, understanding SEM contrast is not straightforward: every SEM, even from the same manufacturer, gives different contrast when an identical specimen is observed. A change in both the accelerating voltage and the working distance results in a change in image contrast. In this review, I will present examples of rich microstructural images obtained by using a state of the art SEM. Then, I will take up again the topic of signal detection in the SEM, which was a crucial issue in its early development.
Single particle analysis can provide three-dimensional structure of biological macromolecules calculated from particle images taken by electron microscopy. Recently the achievable resolution by this technique has improved, and now atomic models have been obtained by this method. Here we introduce the technical improvements for the high resolution, such as electron direct detector, automated data acquisition, and software for image analysis. In these technical improvements, electron direct detector is the most important factor, but also advances of movie correction technique, automation of cryo-electron microscopy, and single particle analysis program that employs an empirical Bayesian approach, have enabled the structural analysis near atomic resolution. Details of the single particle analysis will be explained including our results, and sample preparation techniques are also introduced. This review could develop a better understanding and generate interest of this technique.
Cathodoluminescence (CL) spectroscopy in transmission electron microscopy (TEM) is a powerful method to analyze the atomistic properties (such as the localized energy levels and carrier lifetimes) of an individual nanostructure inside semiconducting materials, since the method enables us to obtain the optical property of the nanostructure by CL spectroscopy simultaneously with the atomic arrangement, composition, and morphology of the same nanostructure by TEM. We briefly summarize the principles underlying the generation and interpretation of CL signals, and then review the TEM-CL assessment for some semiconductor nanostructures.
Osteoblasts, bone-forming cells, synthesize a huge amount of type I collagen and mineralize extracellular matrix. Osteoblasts gradually differentiate into osteocytes embedded in bone matrix. Osteoblasts and osteocytes extend their cytoplasmic processes passing through the narrow passageway referred to as osteocytic canaliculi, consequently forming the functional syncytium. Osteoclasts, multinucleated giant cells, are responsible for bone resorption. Osteoclasts secrete abundant proton and proteolytic enzymes, e.g., cathepsin K and MMP-9 through the ruffled border, deeply folding of the cell membrane facing the bone surface. In a normal state, bone matrix is always metabolized: osteoclasts resorb old bone, while osteoblasts migrate and deposit new bone onto where osteoclasts previously resorbed. The replacement of old bone to new bone is called bone remodeling. Bone remodeling is based on cellular coupling between osteoclasts and osteoblasts.
Zirconium tungstate (ZrW2O8) exhibits negative coefficient of thermal expansion, which is not the case for most materials. It is believed that the negative thermal expansion should be closely related with geometrical alignment of WO4 tetrahedra in ZrW2O8. In this article, we introduce our recent study that revealed the spatial distribution of WO4 geometrical ordering state using dark-field transmission electron microscopy. It was found that the WO4 geometrical ordering is partly inverted and is partly disordered on the nanoscale.
Membrane proteins and biological macromolecular complexes often yield crystals too small or too thin for even the modern synchrotron X-ray beam and X-ray free electron laser. Electron crystallography could provide a powerful means for structure determination with such undersized crystals, as protein atoms diffract electrons 4 - 5 orders of magnitude more strongly than they do X-rays. Another important feature of electron scattering is that the diffraction pattern formed by elastically scattered electrons is directly related to the distribution of Coulomb potential. Thus, electron crystallography could provide a unique method to visualize the charged states of amino acid residues and metals. We have developed a methodology for electron crystallography of ultra-thin (only a few layers thick) 3D protein crystals and presented the Coulomb potential maps at 3.4 Å and 3.2 Å resolution, respectively, obtained from Ca2+-ATPase and catalase crystals. These maps demonstrate that it is indeed possible to build atomic models from such crystals and even to determine the charged states of amino acid residues in the Ca2+-binding sites of Ca2+-ATPase and that of the iron atom in the heme in catalase. Here we report the development and first results, and briefly discuss future applications toward structure determination with charges.
We have developed electron beam excitation assisted optical microscope and demonstrated its resolution higher than 50 nm. In the microscope, a light source in a few nanometers size is excited by focused electron beam in a luminescent film. The microscope makes it possible to observe dynamic behavior of living biological specimens in various surroundings, such as air or liquids. Scan speed of the nanometric light source is faster than that in conventional near-field scanning optical microscopes. The microscope enables to observe optical constants such as absorption, refractive index, polarization, and their dynamic behavior on a nanometric scale. We demonstrated the resolution evaluation with the numerical analysis based on the combination of Monte-Calro simulation and finite-differential time-domain method. The observation of dynamic movements of biological cells are also demonstrated. The microscope opens new microscopy applications in nano-technology and nano-science.