Low-voltage TEM is used for analyzing low-dimensional materials which are damaged by high energy electrons. However, spatial resolution at low voltages is severely degraded by geometric and chromatic aberrations. Here we developed low-voltage TEM equipped with delta-type aberration correctors and a monochromator to suppress the effect of these aberrations. By using the TEM, an atomic distance of 0.142 nm in monolayer graphene was resolved at 15–60 kV. In addition, Fourier transform of monolayer WS2 image at 15 kV shows spots corresponding to less than 10 times the electron wavelength. Observation of carbon atomic chains indicated that dynamic observation with large field of view is available with atomic resolution. Various kinds of low-dimensional materials will be analyzed by using this atomic-resolution low-voltage TEM.
Qualitative epitaxial graphene is fabricated directly over large area of semi-insulating substrate by thermal decomposition of SiC, which leads to possible application in the field of high frequency transistor devices. However, hence it is a remaining important subject that carriers in graphene are scattered by phonon on the surface of substrate. In this study, to modify this graphene/SiC interface structure, formation of novel periodical atomic-layer interface structures by nitridation and establishment of quasifreestanding technique of graphene by rapid-cooling treatment using its negative thermal expansion coefficient were carried out. In this paper, in particular, a process of assignment of the nitrided interface structure by direct observation of the interface using high-resolution transmission electron microscopy (HRTEM) is introduced, and effectiveness and importance of HRTEM observation for the structure analysis of graphene are referred.
Two-dimensional materials consisting of mono-atomic layer are attracting a great interest as fundamental materials of next-generation high-performance semiconductor devices due to new physical properties and functionality. In this paper, we will focus on graphene in particular, while also mentioning a single layer h-BN nanosheet. We will outline the methods of synthesis through solid surfaces such as surface segregation and surface reaction of doped elements. The optical and electronic properties of graphene depend on the number of layers, the dopant, the defect and the bond with the substrate. Since monolayer, bilayer, and tri-layer graphene nanosheets show different electronic states and functions, specifying the number of graphene layers is indispensable for material research focusing on novel device applications. Therefore, confocal Raman microscopy, scanning tunneling microscopy, scanning Auger microscopy, helium ion microscopy, and Kelvin probe force microscopy, which can perform microscopic analyses of structure and physical properties such as layer number, atomic structure, local density of states, chemical state, work function and so on, are introduced with the actual examples.
Although periodic atomic displacements in transition metal dichalcogenides formed due to the commensurate charge density wave (CCDW) phase transition have been modeled by diffractometric methods, they have not been confirmed by direct observation in real space. Against this background, we have attempted direct observation of the periodic atomic displacements in real space by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) of the CCDW phase of 1T-TaSe2. In consequence, periodic image contrast with six-fold symmetry superimposed on the image contrasts due to the atomic columns is observed in HAADF-STEM image of the CCDW phase of 1T-TaSe2. The periodicity of the image contrast corresponds to that of the long range ordered structure formed in the CCDW phase of 1T-TaSe2. Also it is confirmed that the periodic image contrast is disappeared at 673 K, which is the phase transition temperature of the 1T-TaSe2, or higher temperature by HAADF-STEM observation of the 1T-TaSe2 at elevated temperatures. These experimental results and comparison of the experimental HAADF-STEM image with simulated image calculated by the multi slice method suggests that the periodic image contrast reflects the static displacement of Ta atom positions. These results show that the periodic atomic displacement, which corresponds with the model predicted by the diffractometric methods, is observed experimentally in the CCDW phase of 1T-TaSe2 shown by HAADF-STEM observation.
The development of long-range order in disordered Co-Pt alloy nanoparticles has been atomically resolved in situ with an ultra-high voltage electron microscope equipped with a direct electron detection camera. Electron-irradiation-enhanced ordering occured at 573 K with 1 MeV electrons at a dose rate of 8.9 × 1024 e/m2s. High-speed (400 frames/s) imaging revealed fluctuations of the c-axis orientation of the L10–type ordered structure. Specifically, the c-axis orientation changes occurred at 2.5-msec intervals. Thus, the atomic ordering rate at 573 K is deduced to be 3 × 10-17 m2/s, which is 1013 times higher than that estimated for interdiffusion in a bulk Co-Pt alloy. The observed kinetic ordering temperature of 573 K is significantly lower than that reported previously (> 800 K). The low-temperature ordering may be the result of enhanced atom migration via excess vacancies, 106 times higher than that at thermal equilibrium, introduced by the high-energy electron irradiation. We have demonstrated that time-resolved electron imaging can directly reveal rapid spatiotemporal fluctuations.
Kinesin superfamily proteins move along the microtubules to accomplish the various functions including intracellular transport, mitosis, left-right determination, ciliary length control, and so on. I've solved the several kinesin structures complexed with the microtubules to elucidate the structural basis of the multiple functions of kinesin motors. In this review, I introduce four kinesin motors with the different characteristics, the plus-end directed Kinesin-3, the minus-end directed Kinesin-14, the microtubule depolymerizing Kinesin-13, and the dual functional Kinesin-8 which not only moves along the microtubule but also depolymerizes the microtubule. All kinesin motors utilize the conserved strategy, the attachment/detachment on/from the microtubule during the ATPase cycle. However, they have acquired multiple functions along the course of evolution, by the local conformational changes as well as the insertion of specific amino-acids at the microtubule-binding region or by the addition of the helical structures outside the motor domain to amplify the conformational changes occurring inside the motor domain.
An inference technique in which a posterior probability calculated by the Bayesian theorem is used is called Bayesian inference. We introduce an image super-resolution technique based on Bayesian inference. The compound Bayesian super-resolution proposed by Kanemura et al. is explained in particular. In Bayesian super-resolution, subpixel details can be reproduced because shifts and rotations of observed images are utilized positively. Furthermore, edge reproduction is realized by the line process in compound Bayesian super-resolution. In this paper, we describe the outline of compound Bayesian super-resolution and show experimental results.