Yoshizo Kitami

Ultra-high-resolution HVEM (H-1500) newly constructed at NIRIM: I. Instrumentation

Abstract Basic specifications and some experimental data of a new ultra-high-resolution HVEM (Hitachi H-1500), with a maximum accelerating voltage of 1300 kV, are described. A lattice fringe image of 0.07 nm is obtained from thin gold film, indicating excellent mechanical and electrical stability of the microscope. Spherical and chromatic aberration coefficients of the objective lens are 1.85 and 3.4 mm, respectively, at 1300 kV; and a theoretical point-to-point resolution, defined by the first-zero point of the contrast transfer function (CTF) curve under the Scherzer condition, is about 0.104 nm. A crystal structure image of silicon, in which each silicon site is observed as a black dot, is successfully obtained and the image agrees fairly with the results of computer simulations based on the above optical parameters.

Ultra-high-resolution HVEM (H-1500) newly constructed at NIRIM. II: Application to materials

Abstract We have recently constructed an ultra-high-resolution HVEM (H-1500), whose specifications are introduced in part I of this series. The point-to-point resolving power of the microscope is 1.0 A at an accelerating voltage of 1300 kV and 1.25 A at 1000 kV. Using the microscope at 1000 kV we have succeeded in imaging clearly not only Zr atoms but also oxygen atoms in zirconia ( ZrO 2 ). The contrast of oxygen atoms in a high- T c superconductor YBa 2 Cu 3 O 7− x is locally discriminated from that of cations in the image. A real structure image of Si [110] incidence is obtained at 1300 kV with a dark contrast at the Si atom sites and then used to analyze the structure at an initial stage of the damage due to electron irradiation.

Reduction Mechanism of Dislocation Density in GaAs Films on Si Substrates

Significant reduction of dislocation densities in GaAs films grown on Si substrates have been demonstrated. High-quality GaAs films on Si with average etch-pit density on the order of 104 cm-2 have been obtained by combining the low-temperature growth technique and the atomic hydrogen irradiation. The reduction mechanism of dislocation density in GaAs on Si as well as possible growth kinetics have been discussed based on reflection high-energy electron diffraction (RHEED) and transmission electron microscope (TEM) observations. Most of the threading dislocations have annihilated in the low-temperature grown GaAs layers by forming closed loops. As a consequence of the dislocation density reduction, the electron mobilities of GaAs films on Si have been improved.

New 300 kV Energy-Filtering Field Emission Electron Microscope

In order to observe high-spatial-resolution elemental images using inelastic electrons, a 300 kV energy-filtering transmission electron microscope with an omega-type energy filter has been developed. Some characteristic features of the new microscope are described. The accelerating voltage dependence of the inelastic images is calculated to confirm that the spatial resolution for the elemental images is improved with an increase in the voltage from 120 kV to 300 kV. It is shown that a single atomic layer of oxygen atoms in Al11O3N9 crystal is well imaged as a bright line with a periodic separation of 2.9 nm al the c-axis. The spatial resolution for the oxygen images is about 0.5 nm, which corresponds well with the theoretical calculation.

Needle-Like SiC Nanorods

SiC nanorods with a needle-like shape have been synthesized by carbothermal reduction of SiO at 1410°C, where the reductant is highly curled carbon nanotubes (CNTs) containing Fe nanoparticles approximately 10 nm in size. Each SiC nanorod has a rounded Fe–Si single crystalline tip 120–250 nm in size and a sharp SiC tip approximately 10 nm in size. Along the nanorod axis, the diameter decreases gradually from approximately 100 nm on the Fe–Si tip side to approximately 10 nm on the sharp SiC tip. A revised vapor-liquid-solid mechanism from Wagners mechanism is proposed to explain the formation of the SiC nanorods.

A 400 kV High Resolution-Analytical Electron Microscope Newly Constructed

A resolution limit of 0.23 nm has been achieved successfully by a newly constructed 400 kV analytical electron microscope equipped with an energy dispersive X-ray spectrometer. The characteristic of the new microscope is briefly described and structure images of H-Nb2O5- and 6H-SiC crystals are obtained to show the observation capability of high resolution structure imaging.

Some Results Obtained by a Newly Constructed Ultra-High-Resolution 1300 kV Electron Microscope

A new ultra-high-resolution electron microscope with a point-to-point resolution of 0.1 nm at 1300 kV was constructed. A lattice fringe image of 0.07 nm due to an interaction of two 220 reflections of gold was clearly observed, indicating good stability of the microscope. The so-called black-atom image of silicon was obtained. Direct observations of oxygen positions in Y-stabilized zirconia were also achieved successfully. All the metal atom positions in YBa2Cu3Oy superconductor were observed clearly as dark dots, while imaging of oxygen positions has not yet been successful.

High-resolution Observation of SrTiO3 Interface by Convergent Beam Illumination

The convergent beam illumination method has previously been proposed in order to determine the atomic arrangement in surface or interface structures on the sub-nanometer order. This method reduces interference fringes that appear at the surface or interface, and the fine structure can be analyzed. In this paper, the atomic arrangement near a SrTiO3 interface is determined from a transmission electron microscope image taken with convergent beam illumination. A cycloidal undulated structure can be found at the interface that is caused from misorientation of two crystals on each side of the interface. This structure cannot be found from images taken under conventional conditions, and therefore, it shows that the convergent beam illumination method is useful for analyzing the local structures.