New asymmetric vanadium catalyst for highly selective oxidative coupling polymerization

Novel oxovanadium(IV)–bisoxazoline catalysts, such as vanadyl sulfate (VOSO₄)–(R)‐2,2′‐isopropylidenebis(4‐phenyl‐2‐oxazoline) [(R)Phbox], for the asymmetric oxidative coupling polymerization (AOCP) of 2,3‐dihydroxynaphthalene were developed. For example, the AOCP with VOSO₄–(R)Phbox in CH₂Cl₂–MeOH [7/1 (v/v)] at room temperature for 24 h under an O₂ atmosphere, followed by acetylation of the hydroxyl groups, afforded a polymer in a 58% yield with a specific rotation of [α]_D = ?147. The enantioselectivity during the polymerization was estimated to be 80% enantiomeric excess (S), a value much higher than that observed for the polymerizations with the copper(I)‐based catalyst systems and the typical oxovanadium(IV) catalysts reported for the asymmetric oxidative coupling producing the 1,1′‐bi‐2‐naphthol derivatives. © 2005 Wiley Periodicals, Inc., Inc. J Polym Sci Part A: Polym Chem 43: 5872–5878, 2005     

Formation of 10-30 nm SiO2/Si structure with a uniform thickness at ∼120 °C by nitric acid oxidation method

Silicon dioxide (SiO₂) layers with a thickness more than 10 nm can be formed at ∼120 °C by direct Si oxidation with nitric acid (HNO₃). Si is initially immersed in 40 wt.% HNO₃ at the boiling temperature of 108 °C, which forms a ∼1 nm SiO₂ layer, and the immersion is continued after reaching the azeotropic point (i.e., 68 wt.% HNO₃ at 121 °C), resulting in an increase in the SiO₂ thickness. The nitric acid oxidation rates are the same for (1 1 1) and (1 0 0) orientations, and n-type and p-type Si wafers. The oxidation rate is constant at least up to 15 nm SiO₂ thickness (i.e., 1.5 nm/h for single crystalline Si and 3.4 nm/h for polycrystalline Si (poly-Si)), indicating that the interfacial reaction is the rate-determining step. SiO₂ layers with a uniform thickness are formed even on a rough surface of poly-Si thin film.     

NMR studies of the superconducting state of copper oxide superconductors

The authors review and up-date their work on Knight shifts, spin-lattice relaxation, and indirect nuclear spin-spin coupling for YBa₂Cu₃O₇ in the superconducting state. The data are analyzed in particular to show what it may indicate about the orbital and spin pairing of the superconducting state.     

Fluorescence-based temperature sensing using erbium-doped optical fibers with 1.48 μm pumping

Temperature sensing using 1.54 μm fluorescence at the transition between the energy levels⁴I_15/2 (ground state) and⁴I_13/2 generated in an erbium-doped fiber with 1.48 μm pumping is proposed. The fluorescence has a peculiar spectral profile that possesses two peaks around 1.530 μm and 1.552 μm wavelengths. The temperature-dependent fluorescence is investigated in the temperature range between -50°C and 90°C. The power ratio between the two peaks increases with an increase in temperature. The sensitivity of the ratio is 0.007/°C on average in the measured temperature range. The total fluorescence power and the absorption loss at λ = 1480 nm in the fiber decrease as the temperature increases. Optical fiber temperature sensing immune from the fluctuation in pumping power can be performed using the peak power ratio and/or the absorption loss.     

Synthesis and morphology of polyethylene‐block‐poly(methyl methacrylate) through the combination of metallocene catalysis with living radical polymerization

Polyethylene‐block‐poly(methyl methacrylate) (PE‐b‐PMMA) was successfully synthesized through the combination of metallocene catalysis with living radical polymerization. Terminally hydroxylated polyethylene, prepared by ethylene/allyl alcohol copolymerization with a specific zirconium metallocene/methylaluminoxane/triethylaluminum catalyst system, was treated with 2‐bromoisobutyryl bromide to produce terminally esterified polyethylene (PE‐Br). With the resulting PE‐Br as an initiator for transition‐metal‐mediated living radical polymerization, methyl methacrylate polymerization was subsequently performed with CuBr or RuCl₂(PPh₃)₃ as a catalyst. Then, PE‐b‐PMMA block copolymers of different poly(methyl methacrylate) (PMMA) contents were prepared. Transmission electron microscopy of the obtained block copolymers revealed unique morphological features that depended on the content of the PMMA segment. The block copolymer possessing 75 wt % PMMA contained 50–100‐nm spherical polyethylene lamellae uniformly dispersed in the PMMA matrix. Moreover, the PE‐b‐PMMA block copolymers effectively compatibilized homopolyethylene and homo‐PMMA at a nanometer level. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3965–3973, 2003     

An analysis of SEM techniques used to profile chemical etching on the semiconductor Hg1-xCdxTe

Various methods have been used to obtain accurate cross-sectional profiles of Hg_1-xCd_xTe devices after etching. Preliminary measurements from different etching techniques are also presented. Techniques used were scanning electron microscopy with stereo pairs and cleaved cross-sections, topography SEM (multiple detector SEM) and atomic force microscopy.