Effective surface passivation of crystalline silicon by rf sputtered aluminum oxide

In recent years, excellent surface passivation has been achieved on both p‐type and n‐type surfaces of silicon wafers and solar cells using aluminum oxide deposited by plasma‐assisted atomic layer deposition. However, alternative deposition methods may offer practical advantages for large‐scale manufacturing of solar cells. In this letter we show that radio‐frequency magnetron sputtering is capable of depositing negatively‐charged aluminum oxide and achieving good surface passivation both on p‐type and n‐type silicon wafers. We thus establish that sputtered aluminum oxide is a very promising method for the surface passivation of high efficiency solar cells. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Excitons in silicon nanocrystallites

Recombination and binding energies of excitons in nanocrystalline silicon quantum dots are calculated within the effective mass approximation including the effects of the induced electrostatic polarization. The calculated exciton recombination energies compare well with other calculations and with the results from photoluminescence measurements in porous silicon. The calculated exciton binding energies are far larger than the bulk exciton binding energy and show substantial dependence on the matrix that surrounds the nanocrystallites. A model is proposed that explains the main orange-red, blue and infrared luminescence peaks of porous silicon within a simple unified framework.     

(1,3‐Diphenyl‐1H‐Pyrazol‐4‐yl)‐Methylamine Analogues as Inhibitors of Dipeptidyl Peptidases

A number of pyrazole compounds reported in literatures elicit anti‐hyperglycemic effects. By modifying the side chain of the heterocyclic skeleton, a new chemical class of DPP‐IV inhibitors structurally derived from the (pyrazol‐4‐yl)‐methylamine scaffold have been discovered and evaluated the biological activities of these inhibitors against DPP‐IV, DPP8, DPP‐II and FAP. The SAR studies showed the (1,3‐diphenyl‐1H‐pyrazol‐4‐yl)‐methylamines with 2,4‐dichloro substituents at the 3‐phenyl ring selectively preferred as DPP‐IV inhibitors, whereas with difluoro substituents at the 3‐phenyl ring selectively preferred as DPP8 inhibitors. The binding mode of representative compound 15h at the active site of DPP‐IV was predicted by computer model. In additional, 15h exhibited the ability to significantly decrease the glucose excursion in mice.     

A dedicated small‐angle X‐ray scattering beamline with a superconducting wiggler source at the NSRRC

At the National Synchrotron Radiation Research Center (NSRRC), which operates a 1.5 GeV storage ring, a dedicated small‐angle X‐ray scattering (SAXS) beamline has been installed with an in‐achromat superconducting wiggler insertion device of peak magnetic field 3.1 T. The vertical beam divergence from the X‐ray source is reduced significantly by a collimating mirror. Subsequently the beam is selectively monochromated by a double Si(111) crystal monochromator with high energy resolution (ΔE/E? 2 × 10^?4) in the energy range 5–23 keV, or by a double Mo/B₄C multilayer monochromator for 10–30 times higher flux (～10¹¹ photons s^?1) in the 6–15 keV range. These two monochromators are incorporated into one rotating cradle for fast exchange. The monochromated beam is focused by a toroidal mirror with 1:1 focusing for a small beam divergence and a beam size of ～0.9 mm × 0.3 mm (horizontal × vertical) at the focus point located 26.5 m from the radiation source. A plane mirror installed after the toroidal mirror is selectively used to deflect the beam downwards for grazing‐incidence SAXS (GISAXS) from liquid surfaces. Two online beam‐position monitors separated by 8 m provide an efficient feedback control for an overall beam‐position stability in the 10 µm range. The beam features measured, including the flux density, energy resolution, size and divergence, are consistent with those calculated using the ray‐tracing program SHADOW. With the deflectable beam of relatively high energy resolution and high flux, the new beamline meets the requirements for a wide range of SAXS applications, including anomalous SAXS for multiphase nanoparticles (e.g. semiconductor core‐shell quantum dots) and GISAXS from liquid surfaces.     

A new mechanism for negative differential conductivity in superlattices

Electrons in a superlattice at high fields are suitably described in terms of localized states related to the potential wells. Conduction is dominated by transitions between adjacent wells if the potential drop over a superlattice period exceeds the width of the lowest miniband. It is shown that the probability of these transitions, and consequently the current as well, decrease with increasing field. This effect originates from decreasing overlap between electron states of neighbouring wells, and it is found for the interaction with acoustic phonons and with impurities as well.     

Numerical approximation of the Oldroyd‐B model by the weighted least‐squares/discontinuous Galerkin method

We consider a numerical method for the Oldroyd‐B model of viscoelastic fluid flows by a combination of the weighted least‐squares (WLS) method and the discontinuous Galerkin (DG) finite element method. The constitutive equation is decoupled from the momentum and continuity equations, and the approximate solution is computed iteratively by solving the Stokes problem and a linearized constitutive equation using WLS and DG, respectively. An a priori error estimate for the WLS/DG method is derived and numerical results supporting the estimate are presented. © 2012 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2013     

Synthesis and properties of flame‐retardant benzoxazines by three approaches

We propose three approaches to obtain flame‐retardant benzoxazines. In the first approach, we synthesize a novel benzoxazine (dopot‐m) from a phosphorus‐containing triphenol (dopotriol), formaldehyde, and methyl amine. Dopot‐m is copolymerized with a commercial benzoxazine [6′,6‐bis(3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazineyl)methane (F‐a)] or diglycidyl ether of bisphenol A (DGEBA). The thermal properties and flame retardancy of the F‐a/dopot‐m copolymers increase with the content of dopot‐m. As for the dopot‐m/DGEBA curing system, the glass‐transition temperature of the dopot‐m/DGEBA copolymer is 252 °C, which is higher than that of poly(dopot‐m). The 5% decomposition temperature of the dopot‐m/DGEBA copolymer increases from 323 to 351 °C because of the higher crosslinking density caused by the reaction of phenolic OH and epoxy. In the second approach, we incorporate the element phosphorus into benzoxazine via the curing reaction of dopotriol and F‐a. After the curing, the thermal properties of the F‐a/dopotriol copolymers are almost the same as those of neat poly(F‐a), and this implies that we can incorporate the flame‐retardant element phosphorus into the polybenzoxazine without sacrificing any thermal properties. In the third approach, we react dopo with electron‐deficient benzoxazine to incorporate the element phosphorus. After the curing, the glass‐transition temperatures of polybenzoxazines decrease slightly with the content of dopo, mainly because of the smaller crosslinking density of the resultant polybenzoxazines. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3454–3468, 2006     

In situ synthesis of hexakis(alkoxy)diquinoxalino[2,3-a:2',3'-c]phenazines: mesogenic phase transition of the electron-deficient discotic compounds

2,3,8,9,14,15-Hexakis(alkoxy)diquinoxalino[2,3-a:2',3'-c]phenazines with alkyl side chains varying from 6 to 12 carbon atoms were readily synthesized by the condensation of hexaketocyclohexane with the respective 1,2-bisalkoxy-4,5-diaminobenzene. Polarization microscopy and DSC studies showed all these compounds to exhibit a very wide mesophase range of over 150 degrees C. An interesting D(hd) to D(rd) transition was observed for the octyl derivative 3b, as determined by X-ray diffraction measurements. The hexyl derivative showed three reduction potentials, suggesting that the HATN core maintained its electron-deficient characteristic and considered suitable as an n-doped discotic-liquid crystalline material. Incorporation of six alkoxy chains did not override the electron deficiency of the HATN core.