A new class of flavonoids bearing cyclic polyethers involving a phenyl ring was conveniently provided by the intramolecular photochemical dimerization of 2-chromonecarboxylic esters. Irradiation of 2-chromonecarboxylate with a polyether tethered at both ends promoted intramolecular [2 + 2] cyclobutane formation leading to 14- to 27-membered cyclic polyethers. The efficiency depended on the substituted position of the phenyl ring, with ortho- and meta-substituted derivatives giving cycloadducts in good chemical yields and quantum efficiencies, whereas the para-derivatives were inert toward photolysis. X-ray crystallographic analysis revealed that the stereochemistry of the macrocyclic cycloadducts exhibited C2-symmetry. 相似文献
This article describes a method for silica coating of Co–Pt alloy nanoparticles prepared in the presence of poly(vinylpyrrolidone)
(PVP) as a stabilizer. The Co–Pt nanoparticles were prepared in an aqueous solution at 25–80 °C from CoCl2 (3.0 × 10−4 M), H2PtCl6 (3.0 × 10−4 M), PVP (0–10 g/L), and NaBH4 (4.8 × 10−3–2.4 × 10−2 M). The silica coating was performed for the Co–Pt nanoparticle colloid containing the PVP ([Co] = [Pt] = 3.0 × 10−5 M) at 25 °C in (1/4) (v/v) water/ethanol solution with tetraethoxyorthosilicate (TEOS) (7.2 × 10−5–7.2 × 10−3 M) and ammonia (0.1–1.0 M). Silica particles, which had an average size of 43 nm and contained multiple cores of Co–Pt nanoparticles
with a size of ca. 8 nm, were produced at 1.4 × 10−3 M TEOS and 0.5 M ammonia after the preparation of Co–Pt nanoparticles at 80 °C, 5 g/L PVP, and 2.4 × 10−2 M NaBH4. Their core particles were fcc Co–Pt alloy crystallites. Their saturation magnetization was 2.0-emu/g sample, and their coercive
field was 12 Oe. 相似文献
Semi-polar (1 1 2¯ 2) GaN layers were selectively grown by metal organic chemical vapor phase epitaxy on patterned Si (3 1 1) substrates without SiO2 amorphous mask. The (1 1 2¯ 2) GaN layers could be selectively grown only on Si (1 1 1) facets when the stripe mask width was narrower than 1 μm even without SiO2. Inhomogeneous spatial distribution of donor bound exciton (DBE) peak in low-temperature cathodoluminescence (CL) spectra was explained by the difference of growth mode before and after the coalescence of stripes. It was found that the emission intensity related crystal defects is drastically decreased in case of selective growth without SiO2 masks as compared to that obtained with SiO2 masks. 相似文献
Adopting anisotropy etching method, a (1 1 1) facet of Si is obtained on a Si substrate and selective area growth (SAG) of GaN is performed with metal-organic vapor phase epitaxy on the facet. The epitaxial lateral overgrowth of (1 1¯ 0 1), (1 1 2¯ 2) GaN is investigated on (0 0 1) and (1 1 3) Si substrate, respectively, and the incorporation properties of Si, C, and Mg elements are discussed in relation to the atomic configuration on the surface. Analyzing the optical and electrical properties of C-doped (1 1¯ 0 1) GaN layer, it is shown that carbon creates a shallow acceptor level. On the thus prepared (1 1¯ 0 1) GaN layer, a light emitting diode (LED) with a C-doped p-type layer is fabricated. 相似文献
The authors describe an organic complementary inverter with N,N′‐ditridecyl‐3,4,9,10‐perylenetetracarboxylic diimide as an n‐type semiconductor and pentacene as a p‐type semiconductor. Each transistor of the inverter exhibited high carrier mobility: 1.62 cm2/Vs for an n‐type drive transistor and 0.57 cm2/Vs for a p‐type switch transistor. The gain of the inverter reached 125. Another inverter using Ta2O5 as a high κ gate dielectric performed well with a gain of 500 and an operation voltage of only 5 V.
We review our nuclear-magnetic resonance (NMR) and nuclear-quadrupole-resonance (NQR) studies in superconducting Sr2RuO4, which have been performed in order to investigate the gap structure and the pairing symmetry in the superconducting state and magnetic fluctuations in the normal state. The spin-lattice relaxation rate (1/T1) of a high-quality sample with shows a sharp decrease without a coherence peak just below Tc, followed by a T3 behavior down to 0.15 K. This result indicates that the superconducting gap in pure Sr2RuO4 is a highly anisotropic character with a line-node gap. The Knight shift, which is related to the spin susceptibility, is unchanged in the superconducting state irrespective of the direction of the applied fields and various magnitude of the field. This result strongly suggests that the superconducting pairs are in the spin-triplet state, and the spin direction of the triplet pairs is considered to be changed by small fields of several hundred Oe. 相似文献
Microstructure variation of FePt thin film upon annealing at elevated temperatures was investigated by transmission electron microscopy (TEM). A special shape aperture was employed to observe the ordered L10 phase in the dark-field TEM images. With increasing the annealing temperature, crystal grains formed clusters with gathering of neighboring grains, and crystal grain growth proceeded within the cluster. L10 ordered crystal grains were preferentially formed near the grain boundaries, and their sizes grew with increasing the annealing temperature. 相似文献
We demonstrate atomic-column imaging by scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). The silicon atomic-columns of a β-Si3N4 (0 0 1) specimen are clearly resolved. The atomic-site dependence and the energy-loss dependence of the spatial resolution are elucidated on the basis of the experimental results and multislice calculations. We describe two decisive factors for realizing atomic-column imaging in terms of localization in elastic and inelastic scattering. One is the channeling of the incident probe due to dynamical diffraction, which has atomic-site dependence. The other is the localization in inelastic scattering; in addition to the energy-loss dependence of delocalization, we point out its dependence on the offset energy from the ionization energy, i.e., an additional localization factor concerning the Bethe surface. The present atomic-column observation of the Si-L core-loss image indicates that the local approximation, which can be interpreted intuitively, is achievable under appropriate experimental conditions, such as high-energy-loss, a small convergence angle and a large collection angle (e.g., 400 eV, 15 and 30 mrad, respectively). 相似文献