12CaO·Al2O3 (C12A7) crystal is a constituent of alumina cements and an electrical insulator with a large band gap of ∼7 eV. It is possible to replace almost all the O2− ions in its crystallographic cages with electrons by reduction treatments. As a result, C12A7 is converted to a metallic conductor C12A7:e− with a low work function of ∼2.4 eV via an insulator-metal transition. We have developed a technique to prepare C12A7:e− thin films. The electrical and optical properties, and also an application to an electron injection layer for an organic light emitting device are reviewed.
We have observed the quantum Hall-effect (QHE) of ZnO/MgxZn1−xO bilayers grown on ScAlMgO4 substrates by using pulsed-laser deposition. Two-dimensional electron gas was spontaneously formed in the interface due to the polarization mismatch between the layers. In order to obtain high electron mobility, we first developed a high-temperature annealed buffer layer, and then carefully investigated the growth temperature dependences of surface morphologies and electrical properties. As the result, electron mobility was recorded to be 440 cm2/Vs at room temperature and 5500 cm2/Vs at 1 K. The observation of QHE allows to access direct determination of the electronic structure of the heterointerface.
We have investigated the effects of dopants (Ti, Zr, H, Sn) and growth processes for In2O3 transparent oxide films in terms of their electrical and optical properties. Ti- and Zr-doped In2O3 showed higher mobility than conventional Sn-doped In2O3 in epitaxial and polycrystalline films fabricated by vapor-phase-crystal growth. On the other hand, we have found that polycrystalline H-doped In2O3 films fabricated by crystallization of the amorphous phase at 200oC show larger mobility (130 cm2/Vs) with resistivity of 2.7×10−4 Ωcm and improved near infrared transparency. Analysis of temperature dependence of Hall mobility reveals that the high mobility in the H-doped In2O3 films is ascribable to suppression of multicharged and neutral impurities as well as grain boundary defects. Relationship between the values of room temperature Hall mobility and carrier concentration further supports our conclusion.
Recent developments of Nb-doed anatase TiO2 (TNO) transparent conductors are reported. We have successfully fabricated highly conductive (resistivity : 9.5×10−4 Ωcm) and visibly transparent (transmittance : 60−80%) TNO polycrystalline films by annealing a sputter-deposited amorphous phase. This is the first step toward the practical use of this material. Transport properties of the annealed films were found to strongly depend on the sputter conditions for growing amorphous ones. Low temperature deposition of reduced amorphous phases seems to be a key for fabricating highly conductive TNO in polycrystalline thin films.
We have performed local ferroelectric field effect experiments using an epitaxial heterostructure composed of ferroelectric Pb (Zr0.2Ti0.8)O3 and superconducting Nb doped SrTiO3, fabricated on an (100)SrTiO3 substrate by off-axis radio frequency magnetron sputtering and pulsed laser deposition. By switching the polarization field of the 50 nm thick Pb(Zr0.2Ti0.8)O3 layer, we induced a large change in resistivity and a shift of Tc in the 26 nm thick epitaxial Nb doped SrTiO3 layer. At 270 mK, superconducting on-off switch is realized. Ferroelectric domain array was poled in submicron scale by AFM (Atomic Force Microscope) tip to make a low Tc array in a high Tc superconducting path. A stepwise magnetoresistance was clearly observed in the array device around the Tc. This behavior suggests that 2D superconducting fluctuation induces phase slips and the low Tc array stabilizes them.
We have newly developed a retarding-type Mott spin detector for spin- and angle-resolved photoelectron (SARPE) spectroscopy. Detection of scattered electrons at the Au target in an appropriate energy-loss window with a large opening angle has helped us to increase the efficiency of the spin polarimeter. The SARPE spectroscopy equipped with the developed spin detector has been applied to the study of surface and bulk electronic structures of fcc Co thin films grown on Cu(001) surface. The improved efficiency has enabled us to obtain the spin-resolved spectra while the surface is kept clean. As a result, we have successfully resolved a negatively spin-polarized surface resonance state of fcc Co/Cu(001) at Γ− of the surface Brillouin zone. It has also been clarified that the surface resonance state is markedly influenced by a spin-orbit coupling.
The ISO/TC202 was established in 1991 as the first Chinese ISO/TC (Technical Committee) secretariat. Its scope is the standardization in the field of microbeam analysis (measurement, parameters, methods and reference materials) that uses electrons as an incident beam with electrons and photons as the detection signal. The purpose is to analyze the compositional and structural characteristics of solid materials. The volume of analysis will generally involve a depth of up to 10 micrometers and a surface area less than 100 square micrometers. In the future, consideration of other techniques may be included as these techniques mature and further standards are required. At present the instruments which are included in this scope are EPMA (Electron Probe Microanalysis), AEM (Analytical Electron Microscopy), SEM (Scanning Electron Microscopy), EDS (Energy Dispersive Spectrometry) and EBSD (Electron Backscattered Diffraction). The international standards that have been established since theTC202 was founded in 1991 and also those that are still under establishment are shown here.
Study of STM-excited light emission (STML) from organic films is significant for the potential applications to organic photoelectronics devices in nanometer scale. In this note, practical tips for measurements are given, focusing on how to detect very weak light signals efficiently. The mechanism of STML from molecules is described, and the technique of surface-plasmons enhanced molecular fluorescence is utilized for observation of intense light emission at far field regions. Provided are experimental results of STML from spin cast organic films of porphyrin series such as H2TBPP, H2TPP and PhTPP and conjugate polymer MEH-PPV under atmospheric conditions as well as in UHV as the examples.