Aki Miyake

Preparation of ZnO thin films for high-resolution field emission display by electron beam evaporation

The dependence of the structural, photoluminescent and cathodoluminescent properties of ZnO thin films deposited by electron beam evaporation on the preparation conditions has been investigated. Both as-deposited and annealed thin films deposited at substrate temperatures higher than 200°C showed c-axis orientation, and their crystallinity was improved with increasing annealing temperature. The films showed the emission with a peak at around 510 nm in photoluminescence (PL) and cathodoluminescence (CL) except for the film annealed at 800°C in air. The emission seems to be well-known blue-green emission due to ZnO:Zn phosphor. The strong green emission with a peak at around 540 nm was obtained from the film annealed at 800°C in air. The origin of the emission is not understood. The film showed CL luminance of about 60 cd/m2 under excitation of 2 kV, 400 μA/cm2. Moreover, it showed CL under excitation even at 250 V without charging-up.

p-Type ZnO Layer Formation by Excimer Laser Doping

A p-type ZnO layer was fabricated by excimer laser doping technique using thermally oxidized ZnO films. Epitaxial ZnO(0001) films were formed by thermal oxidation of epitaxial ZnSe films on Si(111) substrate grown by remote plasma enhanced metal-organic chemical vapor deposition. The p-type ZnO was fabricated by excimer laser irradiation with Sb as a dopant source. A good Ohmic contact was obtained between Sb doped ZnO layer and gold metal electrodes. The Sb doped ZnO layer showed positive Hall coefficient, the resistivity was 8 × 10 -3 Ω cm with a hole mobility of 1.5 cm 2 /Vs and an acceptor concentration of 5 x 10 20 cm -3 as p-type, respectively.

Growth of Epitaxial ZnO Thin Film by Oxidation of Epitaxial ZnS Film on Si(111) Substrate

The growth of an epitaxial ZnO thin film on a Si substrate by oxidation of an epitaxial ZnS film is a novel method and we are reporting it for the first time. The merits of using the Si substrate are to make the driving voltage of light-emitting diodes (LEDs) lower and the cost of the LEDs less expensive than that using a sapphire substrate. In this study, the epitaxial ZnO thin film could be successfully grown on the Si substrate. The epitaxial films showed a strong near-ultraviolet emission with a peak at around 3.32 eV at room temperature under 325 nm excitation.

Dynamic autofluorescence imaging of intracellular components inside living cells using direct electron beam excitation

We developed a high-resolution fluorescence microscope in which fluorescent materials are directly excited using a focused electron beam. Electron beam excitation enables detailed observations on the nanometer scale. Real-time live-cell observation is also possible using a thin film to separate the environment under study from the vacuum region required for electron beam propagation. In this study, we demonstrated observation of cellular components by autofluorescence excited with a focused electron beam and performed dynamic observations of intracellular granules. Since autofluorescence is associated with endogenous substances in cells, this microscope can also be used to investigate the intrinsic properties of organelles.

Study on the structural transformation process from ZnS epitaxial film grown on Si substrate to ZnO epitaxial film by oxidation

ZnO epitaxial thin film was successfully obtained by oxidation of ZnS epitaxial thin film with the orientation of (0002),[1120]ZnO∥(111),[110]Si. The ZnS film was completely oxidized at 800°C for 1 h in O 2 flow. An interface layer was formed between the ZnO layer and the Si substrate by excess annealing. The ZnO layer showed near ultraviolet emission due to exciton in addition to visible emission, and by annealing for 5 h, strong exciton emission without the visible emission.

Nanometric light spots of cathode luminescence in Y 2 O 3 :Eu 3+ phosphor thin films excited by focused electron beams as ultra-small illumination source for high-resolution optical microscope

We present an Electron-beam-eXcitation-Assisted (EXA) optical microscope with a nanometric illumination light source consisting of red cathode luminescence (CL) lights emitted by a Y2O3:Eu3+ phosphor thin film excited by a high-energy focused electron beams. Phosphor films a few hundred nanometers thick were fabricated on 50-nm Si3N4 membranes using electron beam evaporation. The film preparation conditions for brighter CL emissions were examined in terms of the post-annealing temperatures and film thickness. We succeeded in spatially resolving gold nanoparticles with average diameter of 100 nm. The observations proved that the microscope has a spatial resolution higher than the diffraction limits.

Formation of ZnO luminescent films on SiN films for light source of high-resolution optical microscope

We fabricated ZnO/SiN films for use as a light source of a high-resolution optical microscope and characterized the properties of the films, and demonstrated images obtained with the microscope using the fabricated ZnO/SiN films. A 100-nm-thick ZnO film deposited on a SiN film showed a much higher CL intensity than the SiN film, and it was enhanced by high-temperature annealing of the ZnO film. Electron beam excitation assisted optical microscope images of gold particles of 200 nm diameter taken using the ZnO/SiN film and SiN indicated that the ZnO/SiN films can provide a higher signal-to-noise (S/N) ratio and a higher frame rate than the SiN film. It was shown that the dynamic observation of living cells becomes possible using the high-resolution optical microscope with a bright light source. Moreover, this fact promises that such optical microscope can contribute to progress in the medical and biological fields.

Thermal Neutron Detection by CdTe Detector

Thermal neutron detector is developed by using Cadmium telluride (CdTe) semiconductor, due to large thermal neutron capture cross section of Cd. The developed detector demonstrated the occurrence of the 96 keV gamma ray emissions from 113Cd(n, γ) 114Cd reaction.

Development of phosphor thin films on SiN substrate for electron beam excitation assisted optical microscope

We prepared ZnO thin films on SiN substrate as a phosphor thin film of EXA microscope. ZnO films were crystallized with high c-axis orientation and crystallinity of films was improved as annealing temperature increased. UV and visible emissions were observed in the annealed ZnO films. Blue-green emission was enhanced by annealing in H2 atmosphere and suppressed by annealing in O2 atmosphere.

Evaluation of characteristics of CdTe detector by laser pulses

Pulse laser was due to investigate characteristics of Schottky-diode type CdTe detector. The pulse laser was irritated to cleaved surface of the CdTe detector to control incident position and time accurately. Even though one-photon energy of the plse laser is different from that of γ-ray mainly detected by the CdTe detectors, amount of pulse energy of the laser can be adjustable to the γ-ray energy by controlling incident power and pulse duration time. Incident position dependence of electric signal through preamplifier was measured and the dependence was changed by charging bias voltage applied to the CdTe detector. This dependence can be explained by distribution of depletion layer at the Schottky interface.