Masayoshi Ichimiya

Multicolor Cathodoluminescence Microscopy for Biological Imaging with Nanophosphors

We report the first demonstration of a multicolor high-spatial-resolution imaging technique for observation of biological cells using cathodoluminescence from nanophosphors. Three kinds of rare-earth-doped nanophosphors were injected into J744A.1 macrophages, and the spatial distribution of nanophosphors was visualized by using a scanning electron microscope cathodoluminescence (SEM-CL) system. The spectral bandwidth of the phosphors was narrow enough to distinguish the types of the phosphors. CL images of the nanophosphors on Si substrates were obtained with high resolution comparable to that of SEM images. These nanophosphors will be candidates to image more than two kinds of biological molecules at high resolution.

Y2O3:Tm,Yb nanophosphors for correlative upconversion luminescence and cathodoluminescence imaging.

We present a phosphor nanoparticle that shows both upconversion luminescence (UCL) and cathodoluminescence (CL). With this particle, low-autofluorescence, deep-tissue and wide-field fluorescence imaging can be achieved with nanometer-order high-spatial-resolution imaging. We synthesized Y2O3:Tm,Yb nanophosphors that emit visible and near-infrared UCL under 980 nm irradiation and blue CL via electron beam excitation. The phosphors were applied to fluorescent imaging of HeLa cells. The photostability of the phosphors was superior to that of a conventional organic dye. We show that after uptake by HeLa cells, the particles can be imaged with SEM and CL contrast in a cellular section. This indicates that correlative UCL and CL imaging of biological samples could be realized.

High-resolution microscopy for biological specimens via cathodoluminescence of Eu- and Zn-doped Y 2 O 3 nanophosphors

High-resolution microscopy for biological specimens was performed using cathodoluminescence (CL) of Y(2)O(3):Eu, Zn nanophosphors, which have high CL intensity due to the incorporation of Zn. The intensity of Y(2)O(3):Eu nanophosphors at low acceleration voltage (3 kV) was increased by adding Zn. The CL intensity was high enough for imaging even with a phosphor size as small as about 30 nm. The results show the possibility of using CL microscopy for biological specimens at single-protein-scale resolution. CL imaging of HeLa cells containing laser-ablated Y(2)O(3):Eu, Zn nanophosphors achieved a spatial resolution of a few tens of nanometers. Y(2)O(3):Eu, Zn nanophosphors in HeLa cells were also imaged with 254 nm ultraviolet light excitation. The results suggest that correlative microscopy using CL, secondary electrons and fluorescence imaging could enable multi-scale investigation of molecular localization from the nanoscale to the microscale.

ZnO Nanobox Luminescent Source Fabricated by Three-Dimensional Nanotemplate Pulsed-Laser Deposition

A novel nanofabrication technique for metal oxide has been developed by combining inclined pulsed laser deposition with a three-dimensional (3D) nanotemplate prepared by nanoimprint lithography. ZnO nanobox structures with a tunable wall width of 20 to 100 nm can be successfully fabricated by controlling their alignment on a large scale. Cathodoluminescence measurements at 300 K showed an intense luminescence peak at around 380 nm corresponding to near-band-edge emission from even a single ZnO nanobox. The architecturally designed 3D ZnO nanostructures with an excellent wide-gap luminescent character should be good candidates for nanoscale device applications as a luminescent source.

Synthesis of Y 2 O 3 nanophosphors by homogeneous precipitation method using excessive urea for cathodoluminescence and upconversion luminescence bioimaging

Yttrium oxide-based nanophosphors that emit both upconversion luminescence (UPL) and cathodoluminescence (CL) were synthesized by a precipitation method using excessive urea. Precursors of Y2O3 nanophosphors were synthesized with size control to less than 50 nm and a chemical yield greater than 90%. Concentrations of rare-earth co-dopants in nanophosphors were controlled with optimal molar ratios. Co-dopants Tm, Yb/Er, Yb enabled NPs to emit UPL at wavelengths around 810/660 nm and CL at wavelengths around 450/660 nm via excitation with 980 nm NIR light and an electron beam. Synthesized NPs were imaged by NIR and CL microscopy.

Photoelectron spectroscopic study on the electronic structures of the dental gold alloys and their interaction with L-cysteine

The valence electronic structures of the dental gold alloys, type 1, type 3, and K14, and their interaction with L-cysteine have been studied by ultraviolet photoelectron spectroscopy with synchrotron radiation. It was found that the electronic structures of the type-1 and type-3 dental alloys are similar to that of polycrystalline Au, while that of the K14 dental alloy is much affected by Cu. The peak shift and the change in shape due to alloying are observed in all the dental alloys. It is suggested that the new peak observed around 2 eV for the L-cysteine thin films on all the dental alloys may be due to the bonding of S 3sp orbitals with the dental alloy surfaces, and the Cu–S bond, as well as the Au–S and Au–O bonds, may cause the change in the electronic structure of the L-cysteine on the alloys.

Identification of Giant Mott Phase Transition of Single Electric Nanodomain in Manganite Nanowall Wire

In the scaling down of electronic devices, functional oxides with strongly correlated electron system provide advantages to conventional semiconductors, namely, huge switching owing to their phase transition and high carrier density, which guarantee their rich functionalities even at the 10 nm scale. However, understanding how their functionalities behave at a scale of 10 nm order is still a challenging issue. Here, we report the construction of the well-defined (La,Pr,Ca)MnO3 epitaxial oxide nanowall wire by combination of nanolithography and subsequent thin-film growth, which allows the direct investigation of its insulator-metal transition (IMT) at the single domain scale. We show that the width of a (La,Pr,Ca)MnO3 nanowall sample can be reduced to 50 nm, which is smaller than the observed 70-200 nm-size electronic domains, and that a single electronic nanodomain in (La,Pr,Ca)MnO3 exhibited an intrinsic first-order IMT with an unusually steep single-step change in its magnetoresistance and temperature-induced resistance due to the domains arrangement in series. A simple model of the first-order transition for single electric domains satisfactorily illustrates the IMT behavior from macroscale down to the nanoscale.

Undoped ZnO phosphor with high luminescence efficiency grown by thermal oxidation

Various ZnO morphologies with hexagonal cross sections were fabricated by a thermal oxidation method. Depending on the growth temperature, the lateral lengths of the hexagonal cross section varied from several hundred nanometers to the micrometer order. Comparing the cathodoluminescence (CL) of the synthesized ZnO to that of commercial ZnO:Zn phosphor revealed that a strong luminescence can be realized in undoped ZnO by fabricating one-dimensional structures. Specifically, in the micropyramid and towerlike structures, the CL intensity is locally concentrated near the hexagonal boundary. The enhanced green emission in these structures can be qualitatively explained by whispering gallery resonance modes produced in the hexagonal microcavity.

Effects of c/a Anisotropy and Local Crystal Structure on Superconductivity in AFe2(As1−xPx)2 (A = Ba1−ySry, Sr1−yCay and Eu)

We investigated the effects of c/a anisotropy and local crystal structure on superconductivity (SC) in As/P solid solution systems, AFe2(As1−xPx)2 (A122P) with various A ions. With decreasing A site atomic size from A = Ba to Eu, the structural anisotropy decreases, and the rate of decreasing with x also increases. The rapid narrowing of the region of antiferromagnetic composition (x) can be considered to be a result of this anisotropy change due mainly to the change in the Fermi surface (FS) nesting condition. By contrast, although the structural anisotropy systematically changes, the maximum Tc values are almost the same in all A122P systems except for Eu122P. These results indicate that the modification of the FS topology via the structural anisotropy does not affect SC. However local structural parameters, such as pnictogen height, are crucial for Tc.

Molecular-Chain Formation Induced by Infrared-Laser Light Observed in L-Cysteine and Potassium Dihydrogenphosphate

Each of amino acids and phosphate group is capable of forming a chain through repeating dehydration condensation reaction. We have observed Raman scattering spectra of L-cysteine (HSCH2CH(NH2)COOH) and potassium dihydrogenphosphate (KH2PO4 or KDP) before and after irradiation of one pulse of an erbium-doped yttrium aluminum garnet (Er:YAG) laser with its wavelength of 2.94 µm, duration of 0.2 ms, and peak power density of 0.4 MW/cm2. Extra peaks are observed in the spectra after the irradiation, which are not seen in the spectra before the laser irradiation. Comparison of the experimentally obtained spectra with the calculated ones of the chain compounds suggests that the laser light does induce such reactions.