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71.
Abstract In 1989, Chandani et al. showed that the tristable switching, already observed by themselves and by others in 4-(1-methylheptyloxycarbonyl) phenyl 4′-octyloxybiphenyl-4-carboxylate (MHPOBC). 相似文献
72.
We have investigated the Si(111)-√21 × √21-(Ag, Cs) superstructure using reflection high-energy positron diffraction. Rocking curve analysis based on the dynamical diffraction theory reveals that Cs atoms are located at a height of 3.04 Å above the underlying √3 × √3-Ag structure and that they form a triangular structure with a side length of 10.12 Å. The structure of the Si(111)-√21 × √21-(Ag, Cs) surface is significantly different from those of the Si(111)-√21 × √21-Ag and Si(111)-√21 × √21-(Ag, Au) surfaces, probably because of the different electronic structures of the alkali and noble metal atoms. 相似文献
73.
Yuki Yamaguchi Yukari Emoto Tohru Kineri Masakatsu Fujimoto Hideo Mae Atsuo Yasumori Keishi Nishio 《Ionics》2012,18(5):449-453
A well-known gasochromic material is Pt particle-dispersed tungsten trioxide (Pt/WO3). Its optical properties could make it effective as a hydrogen gas sensor. In this study, Pt nanoparticle-dispersed WO3 thin films were prepared using the sol–gel process, and their optical and electrical properties dependent on the working
environment (i.e., temperature, hydrogen gas concentration, oxygen partial pressure, etc.) were investigated. The Pt/WO3 thin films prepared at 400 °C showed the largest change in optical transmittance and electrical conductivity when exposed
to hydrogen gas compared with the films prepared at other temperatures. The optical absorbance and electrical conductivity
were found to be dependent on the hydrogen and oxygen gas concentration in the atmosphere because generation and disappearance
of W5+ in the thin films depend on the equilibrium reaction between injection and rejection of H+ into and from the thin films. In addition, the equilibrium reaction depends on the hydrogen and oxygen gas concentrations. 相似文献
74.
D. Wang Z.Q. Chen F. Zhou W. Lu M. Maekawa A. Kawasuso 《Applied Surface Science》2009,255(23):9371-9375
Fe ions were implanted into ZnO single crystals with multiple energies between 50 and 380 keV up to a total fluence of 12.5×1017 cm−2. The crystal quality of Fe+ implanted ZnO was investigated by X-ray diffraction 2θ scans and ω-rocking curve measurements. The appearance of Fe related diffraction peaks after C annealing of the implanted sample indicates possibly formation of Fe nanoparticles. Superconducting quantum interference device measurements revealed ferromagnetic behavior below 250 K for both the as-implanted and post-annealed ZnO. Photoluminescence and Raman scattering as well as X-ray rocking curve measurements all indicate introduction of structural defects after Fe implantation. Some of the defects act as nonradiative recombination centers, and suppress the visible and ultraviolet (UV) emission in ZnO. These defects also break the Raman selection rule, and lead to the activation of some silent phonon modes. Annealing of the implanted sample at C causes partial recovery of the defects, however, the X-ray diffraction results of the anneal ZnO show even an improvement of the crystal quality compared with the un-implanted one. This could be attributed to the recovery of the grown-in defects in ZnO. 相似文献
75.
Herein, we describe the first total synthesis of fomitellic acid B (2), a potent inhibitor of DNA polymerases α and β. There are two key features in this synthesis: (i) the AB ring system, with all requisite chiral centers, is stereoselectively constructed by means of titanium(III)-mediated radical cascade cyclization of epoxypolyene; and (ii) an enone moiety in the B-ring is generated by isomerization of an olefin followed by allylic oxidation. 相似文献
76.
Eu-doped pyrochlores, La2M2O7 (M=Zr, Hf, Sn), were synthesized by solid-state reaction at a temperature range of 1473 and 1673 K, and their structures and optical properties were characterized by X-ray Rietveld analysis, field emission scanning electron microscope (FE-SEM), and photoluminescent spectroscopy. The Rietveld analysis indicated that the distortion of the (EuO8)n− scalenohedra increased with decreasing ionic radii of the M4+ ion, and the crystallinity increased with the sintering temperature. The splitting width of 5D0-7F1 transition of Eu3+ ions increased with the distortion of the (EuO8)n− scalenohedra. The luminescent intensity ratio of magnetic dipole transitions to electronic dipole transitions decreased with the crystallinity, and the chromaticity changed from deep-red to orange-red. The relationship between the chromaticity of phosphors and the crystallinity was clarified, and the control of crystallinity is an important factor that provides phosphors with required chromaticity. 相似文献
77.
We have developed a positron microbeam using magnetic lenses based on the commercial scanning electron microscope (SEM). A slow positron beam was generated using a handmade source with 22Na and a solid neon moderator. The beam diameter was 3.9 μm on a target. Two-dimensional image of S parameter was successfully obtained. By introducing a beam pulsing section, positron lifetime measurement beam is also available. 相似文献
78.
Masayuki Yamane Hiroshi Kawazoe Atsuo Yasumori Toshikazu Takahashi 《Journal of Non》1988,100(1-3):506-510
A glass rod of the PbO---K2O---B2O3---SiO2 system having a radial gradient of refractive index has been prepared by the sol-gel process using aqueous solutions of lead acetate and potassium nitrate as the sources for index-modifying cations. A gel prepared by gelatinizing a sol from the mixture of tetramethoxysilane, tetraethoxysilane, and the aqueous solutions of boric acid and lead acetate was placed in an aqueous solution of potassium nitrate to form the concentration gradient of modifier cations by diffusion through the micropores of the gel. The glass rod of about 7 mm in diameter obtained by drying and sintering the gel had a refractive index of parabolic profile changing from the center toward the perimeter with a maximum difference of about 0.04. 相似文献
79.
80.
Regio-isomers, 6A6B, 6A6C, and 6A6D-ditosylates of β-cyclodextrin prepared by the reaction of β-cyclodextrin with tosyl chloride were easily and effectively separated through reversed phase column chromatography and assigned. 相似文献