Influence of off-cut angle of r-plane sapphire on the crystal quality of nonpolar a-plane AlN by LP-HVPE

The effect of the off-cut angle of an r-plane sapphire substrate has been investigated on the growth of a-plane AlN thick layer by low-pressure hydride vapor phase epitaxy (LP-HVPE). The off-cut angle (θ) was changed from +5.0° (close to c-axis) to −5.0° (close to m-axis). Results show that the crystalline quality and surface morphology are very sensitive to the sign of θ off-angle. The plus θ off-angle is found to be dramatically reduce the full-widths at half-maximum (FWHM) of X-ray rocking curves (XRC), compared with the minus θ off-angle. In-plane FWHM anisotropic feature marked as M- or W-shape dependence on azimuth angle was observed for a-plane AlN. The shape and degree of anisotropy depend on the sign of θ off-angle, while the plus of θ off-angle will leads to the W-shape and the decreased anisotropy. The minimum crystal tilts and twists of the films are observed for the vicinal sapphires with the plus off-angles of +0.2° to +1.0°.     

Angular variation of ESR linewidth in organic ionic radical salt: 1,3'-diethyl-2,2'-quinoselenacyanine-[TCNQ]2

Angular dependence of electron-spin-resonance (ESR) linewidth in 1,3'-diethyl-2,2'-quinoselenacyanine-[TCNQ]₂ single crystal reveals the two-dimensional magnetic nature of the system, where the nearly uniform distribution of magnetic-spins on the TCNQ layers is inferred.     

Stereocontrolled total synthesis of (+)-tutin,a toxic sesquiterpene of picrotoxane-type

The first total synthesis of (+)-tutin (1), a toxic sesquiterpene of picrotoxane-type isolated from the poisonous plants of the $\text{Coriaria}$ species is described.     

Angular variation of ESR linewidth in organic ionic radical salt: 3,3′-diethyl-2,2′-selenacyanine-[TCNQ]2

Angular dependence of ESR linewidth of 3,3′-diethyl-2,2′-selenacyanine-[TCNQ]₂ single crystal reveals the two-dimensional magnetic nature of the system. The dependence is represented well by ΔH(θ)=α(3 cos²θ?1)²+β sin⁴θ where α and β are temperature-dependent parameters.     

Study on titanium carbide field emitters by field-ion microscopy,field-electron emission microscopy,Auger electron spectroscopy,and atom-probe field-ion microscopy

Surface structure, composition, and some field-electron emission properties are examined for thermally annealed titanium carbide emitters. As a result of high temperature heating, low-index planes of {100} and {111} become facetted and are observed as dark areas in field-electron emission patterns. Electrons are emitted predominantly from the {110} planes. The surface composition becomes enriched with carbon when the carbon deficient titanium carbide, TiC_0.71, is heated at high temperatures in vacuum better than 10^?7 Pa. The topmost (110) layer consists of both Ti and C atoms. The instability in the electron emission current of titanium carbide is considered to be due to the local work function change caused by an interaction between vacuum residual gases and chemically active titanium atoms on the emitter surface.     

Thermionic emission properties of hexaborides

Thermionic emission properties of the single crystal hexaborides LaB₆, CeB₆, PrB₆, NdB₆, SmB₆, EuB₆, (La, Sr)B₆, (La, Ba)B₆, (La, Ce)B₆, (La, Pr)B₆, (La, Sm)B₆, and (La, Dy)B₆ are measured in the temperature range between 1250 and 1700°C. Of these, LaB₆ is shown to have the highest emission current density in the temperature range investigated. The LaB₆-based mixed hexaborides, (La, M)B₆, show current densities similar to LaB₆, but a little lower. Analyses by Auger electron spectroscopy indicate that the surface composition of (La, M)B₆ approaches that of LaB₆ at elevated temperatures and that the thickness of the surface layer whose composition is different from that of the bulk is typically several atomic layers. The formation of the surface layer is considered to be caused by a relatively slow evaporation rate of La compared to that of the other metal.     

Synthesis of optically active heterocyclic compounds via deracemization of 1,2-diol monotosylate derivatives bearing a long aliphatic chain by a combination of enzymatic hydrolysis with Mitsunobu inversion

We have succeeded in accomplishing the deracemization of (±)-2-acetoxydecyl and (±)-acetoxy-6-benzyloxyhexyl tosylates, which have a long substituent, via an enzyme-mediated enantioselective hydrolysis with a Mitsunobu inversion using polymer-supported triphenylphosphine to afford the corresponding (S)-enantiomer. Enantiomerically pure (S)- and (R)-γ-dodecalactones, a fruit flavor, were synthesized from (S)-2-acetoxydecyl tosylate as the mutual starting material. The poisonous alkaloid (S)-coniine was also synthesized using enantiomerically pure allyl amine as the key intermediate derived from (S)-acetoxy-6-benzyloxyhexyl tosylate.     

ESR studies on ferromagnetic-spin dynamics in a nearly two-dimensional organic ionic radical salt: 1-methyl-3'-ethyl-2, 2'-quinoselenacy anine-[TCNQ]2

The angular dependence at 77 K of the ESR linewidth of 1-methyl-3'-ethyl-2, 2'-quinoselenacyanine-[TCNQ]₂ single crystal is well expressed by ΔH(θ) = 2.2(3 cos²θ-1)²Oe. The results reveal the two-dimensional ferromagnetic nature of the system.     

A synthesis of (±)-brefeldin A

A macrolide antibiotic, brefeldin A, was synthesized from trans-4-oxocyclopentane-1,2-dicarboxylic acid in a stereoselective manner, the intermediary hydroxy acid being lactonized by the mixed 2,4,6-trichlorobenzoic acid anhydride—4-dimethylaminopyridine method.