Yasuhiro Maeda

Observation of single- and double-stranded DNA using non-contact atomic force microscopy

Non-contact atomic force microscopy (NC-AFM) has been applied to observe single- and double-stranded DNA. For the wet processes used to prepare the sample, a strong adhesion force at the surface is observed even in vacuum conditions. Despite the presence of this adhesion force, single- and double-stranded DNA images can be obtained by NC-AFM. Because of the high sensitivity of the tip-sample interaction, NC-AFM images provide stronger contrast than tapping mode (TM)-AFM images. NC-AFM images reveal detailed structures of single- and double-stranded DNA which are not revealed by TM-AFM. In addition, several NC-AFM images show contrast artifacts, which might provide information on the detailed structure of DNA.

Ultraviolet electroluminescence from colloidal ZnO quantum dots in an all-inorganic multilayer light-emitting device

We report ultraviolet (UV) electroluminescence (EL) at 3.30 eV of colloidal ZnO quantum dots (QDs) in an inorganic multilayer thin-film EL device. The EL spectrum was identical to the photoluminescence spectrum of the source solution of ZnO QDs, and the emission is attributable to quantum confined electron hole pair recombination. The UV emission was successful when the ZnO QD layer was sandwiched by thin MgO layers, while only a defect-related visible emission appeared without MgO layers. The type-I quantum well structure of MgO/ZnO/MgO and surface passivation of ZnO QDs by MgO must be important for the UV EL emission.

Dynamic behaviour of excited charge transfer systems in polar solvents

Abstract Dynamic behaviour of some excited charge transfer systems have been investigated by the nanosecond laser photolysis method. Associated with the quenching of the excited state due to the electron transfer, ionic dissociation, relaxation to the triplet state and proton transfer etc, are observed, depending upon the chemical property of donor-acceptor pairs. On the basis of the present results, it has been pointed out that a kind of exciplex formed immediately after charge transfer has an important role in determining the primary processes. In the case of aromatic hydrocarbon-nitrile systems, detailed studies on ionic dissociation mechanism as well as degradation process to the ground state are given.

Laser photolysis studies on intramolecular exciplex systems of benzophenone and N,N-dimethylaniline

Abstract Photoprimary processes of intramolecular exciplex systems of benzophenone and N,N-dimethylaniline were studied by means of laser spectroscopy. Electron transfer in acetonitrile and hydrogen abstraction in benzene occur quite rapidly almost independent of the number of methylene chain connecting both moieties, which indicates that a definite and restricted structure is not necessary for both processes.

UV luminescent organic-capped ZnO quantum dots synthesized by alkoxide hydrolysis with dilute water

A novel synthesis route to organic-capped and colloidal ZnO quantum dots (QDs) has been developed. Specifically, zinc-di-t-butoxide and zinc-di-n-butoxide are hydrolyzed by very dilute water (400-600 mass ppm) in hydrophilic benzylamine and polymerized to ZnO by dehydration and/or a butanol elimination reaction. Growth of the ZnO QDs and exchange of the surface capping ligand from the hydroxyl groups and/or benzylamine to the oleylamine occur by heating the colloidal solution after addition of the oleylamine at 100-180°C. The final ZnO QDs with diameters in the range of 3-7 nm are highly dispersible in various organic solvents. The ZnO QDs exhibit the quantum size effect upon UV emission; it was controlled between 3.39 and 3.54 eV in the present study. The defect-related Vis emission decreased and the UV emission becomes dominant when zinc-di-n-butoxide with a 99.99% zinc purity is used as the starting material. The intensity of the photoluminescence UV emission is 1.5 times higher than that of the Vis emission.

Low temperature adsorption of hydrogen on Si(111) and (100) surfaces studied by elastic recoil detection analysis

Abstract Hydrogen adsorption on clean Si(111)-7×7 and Si(100)-2×1 surfaces at low temperatures (100 K) has been investigated by a combined use of high-energy ion-beam and LEED techniques. The effect of substrate temperatures on the absolute amount of adsorbed hydrogen atoms has been measured. When hydrogen is adsorbed at room temperature, the hydrogen coverage saturates at about 1.5 monolayer (ML) for Si(111)-7×7 and at about 2.0 ML for Si(100)-2×1, respectively. However, when the substrate temperature is kept at about 100 K during adsorption, such a saturation could not be observed. The hydrogen coverage gradually increases with the increase in hydrogen exposure. After 6000 langmuir (L) exposure, the coverage is 2 or 3 times larger than those at room temperature for Si(100) and Si(111) surfaces, respectively. LEED observation shows no ordered surface structure after hydrogen adsorption.

A new method for the detection of native oxide on Si with combined use of 16O(α,α)16O resonance and channeling

Abstract Native oxide on Si and very thin SiO2 films (less than 300 A) formed on Si have been investigated with the combined use of 16O(α,α)16O 3.045 MeV resonant backscattering and channeling. Usually, oxygen surface peak in the channeling non-resonant Rutherford backscattering mode was used to estimate the SiO2 film thickness and Si atom distortions at the interface. But the method is insufficient to obtain information for native oxide on Si because of the low sensitivity to thin layers. We present a more sensitive method, a combination of 16O(α,α)16O resonant backscattering and channeling techniques. A clear oxygen signal for native oxide films was detected by this method. We have shown that the combined use of resonant backscattering and channeling is five times more sensitive when compared to a normal channeling method. Native oxide films with different fabrication conditions were investigated. Advantage and disadvantage of this method are also discussed.

Photoexcited Carrier Effect on Imaging of Organic Molecules On Si(100)2×l Surfaces

Photocurrent images of zinc-phthalocyanine (ZnPc) and coronene molecules adsorbed on Si(100)2×1 surface have been obtained by scanning tunneling microscopy. The ZnPc molecules are observed as bright images indicating large local density of state (LDOS) at the bias voltage. However, coronene molecules show wide variety of contrast in their images. This difference is the result of variations of LDOS on molecules which are attribute to the difference of energy gap between highest occupied and lowest unoccupied molecular orbitals