Tadahiro Kawasaki

Improved luminescence properties of Eu-doped GaN light-emitting diodes grown by atmospheric-pressure organometallic vapor phase epitaxy

We investigated the luminescence properties of Eu-doped GaN (GaN:Eu) grown by atmospheric-pressure organometallic vapor phase epitaxy. The GaN:Eu exhibited radiant red emission due to the intra-4f shell transition of Eu3+ ions at room temperature. The intensity of the dominant peak was about 4 times higher than that in the sample grown at 10 kPa, even though the Eu concentration was only half that of the 10 kPa sample. This was mainly caused by the enhancement of the energy transfer from the GaN host to Eu ions. The enhanced energy transfer resulted in improved luminescence properties of a GaN:Eu light-emitting diode.

Wave field restoration using three-dimensional Fourier filtering method.

A wave field restoration method in transmission electron microscopy (TEM) was mathematically derived based on a three-dimensional (3D) image formation theory. Wave field restoration using this method together with spherical aberration correction was experimentally confirmed in through-focus images of amorphous tungsten thin film, and the resolution of the reconstructed phase image was successfully improved from the Scherzer resolution limit to the information limit. In an application of this method to a crystalline sample, the surface structure of Au(110) was observed in a profile-imaging mode. The processed phase image showed quantitatively the atomic relaxation of the topmost layer.

Distorted surface and interface structures of catalytic gold nanoparticles observed by spherical aberration-free phase electron microscopy

The surface and interface atomic structure of catalytic gold nanoparticles was studied by analyzing a spherical aberration-free phase image. Typically, a catalytic gold particle forms a single crystal having a cuboctahedral shape. The atomic structure of the surface and interface is largely deformed from the bulk structure by stress produced by the atom missing row structure, the reconstructed surface structure, and strong interaction with the substrate. In addition, the structure inside the particle is also deformed by distortion of the surface and the interface.

Atomic level characterization of ultrathin flat cobalt disilicide film with three crystalline domains

The crystal structure and interface structure of ultrathin cobalt disilicide films, prepared on a Si(001) substrate at 400u200a°C, have been examined using transmission electron microscopy (TEM). Analysis of the electron diffraction data reveals that there are three general types of epitaxy between the silicon substrates and the cobalt disilicide films: (1) CoSi2(110)//Si(001), CoSi2[001]//Si[110]; (2) CoSi2(110)//Si(001), CoSi2[110]//Si[110]; and (3) CoSi2(001)//Si(001), CoSi2[110]//Si[110]. Using cross-sectional high-resolution TEM for all three types of epitaxy showed that (1) the cobalt disilicide films form an ultrathin flat layer and (2) the interface between the substrate and the film is abrupt with an atomic level for all three types of epitaxy. Dark-field observations also revealed unique localized distributions of three different types of crystalline domains. The domains of CoSi2(110) had elliptic and those of CoSi2(001) had round shapes that were several hundred nanometers in diameter. Each domain...

Development of Compact Cs/Cc Corrector with Annular and Circular Electrodes

The spherical aberration (Cs) correction is indispensable to improve the spatial resolution in the electron microscopes. Some types of Cs correction devices have been proposed and developed, and the Cscorrectors consisted of multi-pole lenses have successfully realized sub-angstrom resolution in (S)TEMs [1-2]. However, these correctors require complex control of multiple optical components with high accuracy and stability. They also demand reconfiguration of the microscope columns to insert rather large additional components, resulting in huge cost. In order to solve these problems, Ikuta had proposed a very simple and compact Cs-corrector with axially-symmetric electrostatic-filed formed between annular and circular electrodes [3-4], as schematically shown in Fig. 1(a). We called it “ACE corrector” (the Cscorrector using Annular and Circular Electrodes). Furthermore, this simple device has an additional capability to reduce the effect of the chromatic aberration (Cc). In the present paper, we report the principle of Cs/Cc correction and preliminary results of the ACE corrector in simulations and experiments.

STEM Phase Imaging by Annular Pixel Array Detector (A-PAD) Combined with Quasi-Bessel Beam

Tadahiro Kawasaki, Takafumi Ishida, Tetsuji Kodama, Takayoshi Tanji and Takashi Ikuta, 1. Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya, Japan 2. Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan 3. Global Research Center for Environment & Energy based on Nanomaterials Science, Tsukuba, Japan 4. Graduate School of Science & Technology, Meijo University, Nagoya, Japan 5. Faculty of Engineering, Osaka Electro-Communication University, Neyagawa, Japan

Simple and Compact Electrostatic Cs-Corrector using Annular and Circular Electrodes

1. Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya, Japan 2. Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan 3. Graduate School of Science & Technology, Meijo University, Nagoya, Japan 4. Vacuum Device Ltd., Mito, Japan 5. Faculty of Science and Engineering, Kinki University, Higashiosaka, Japan 6. Faculty of Engineering, Osaka Electro-Communication University, Neyagawa, Japan

Optical properties of Eu-implanted GaN and related-alloy semiconductors

We investigated the optical properties of Eu-implanted GaN and related-alloy semiconductors by photoluminescence (PL) and time resolved PL measurements at room temperature (RT). After thermal annealing, the red emission was observed in each sample due to the intra-4f transitions in Eu3+ ions. The PL intensity increases with Al incorporation into GaN while it decreases with In incorporation into GaN, indicating that the emission efficiency depends on the host materials while the emission wavelength is independent of the host materials. Since the decay times of Eu emission of the samples are found to be similar by time resolved PL measurements, the origin of the Eu emission of each sample is supposed to be same. Therefore, the difference in the PL intensity is attributed to the difference in the energy transfer efficiency because of the ion implantation damage and/or bandgap energy of the host materials.