Powder Pattern Hyperfine Spectroscopy of Shallow- Donor Muonium Centres

The hyperfine spectroscopy of muonium in II–VI semiconductors is reviewed, suggesting that whereas hydrogen is a deep-level defect in ZnS, ZnSe and ZnTe, it constitutes a shallow donor in ZnO, CdS, CdSe and CdTe. Shallow and deep states coexist in CdTe. Using new data for ZnO, it is shown that the principal values of the muonium hyperfine tensor may be obtained with equal facility from measurements in longitudinal or in transverse magnetic field, and from samples that are polycrystalline powders or single crystals. Spin density on the central muon in the shallow states correlates with the electron binding energy or donor depth. This revised version was published online in September 2006 with corrections to the Cover Date.     

稳定同位素方法研究正构烷烃与四氢萘二元体系的反应

以正构烷烃作为模型化合物的热反应、临氢反应、临氢催化反应中,添加供氢剂抑制正构烷烃所裂化;气相氢和供氢剂的供氢参与饱和烯烃,两者是性质不同的氢源,前者加速裂化,后者抑制裂化。供氢剂供氢行为依赖于反应体系自由基的多少和温度以及反应过程,反应体系较多的自由基和较高的反应温度有利于供氢行为。稳定同位素方法研究模型化合物的裂化反应表明,供氢剂的作用是通过脱氢湮灭自由基来抑制裂化反应,同时发现H12－四氢萘和D12－四氢萘的供氢（氘）率上存在着动力学同位素效应,在临氢及临氢催化体系中尤其是临氢催化体系中,动力学同位素效应变得不再明显。     

Revisiting the Limiting Factors for Overall Water‐Splitting on Organic Photocatalysts

In pursuit of inexpensive and earth abundant photocatalysts for solar hydrogen production from water, conjugated polymers have shown potential to be a viable alternative to widely used inorganic counterparts. The photocatalytic performance of polymeric photocatalysts, however, is very poor in comparison to that of inorganic photocatalysts. Most of the organic photocatalysts are active in hydrogen production only when a sacrificial electron donor (SED) is added into the solution, and their high performances often rely on presence of noble metal co‐catalyst (e.g. Pt). For pursuing a carbon neutral and cost‐effective green hydrogen production, unassisted hydrogen production solely from water is one of the critical requirements to translate a mere bench‐top research interest into the real world applications. Although this is a generic problem for both inorganic and organic types of photocatalysts, organic photocatalysts are mostly investigated in the half‐reaction, and have so far shown limited success in hydrogen production from overall water‐splitting. To make progress, this article exclusively discusses critical factors that are limiting the overall water‐splitting in organic photocatalysts. Additionally, we also have extended the discussion to issues related to stability, accurate reporting of the hydrogen production as well as challenges to be resolved to reach 10 % STH (solar‐to‐hydrogen) conversion efficiency.     

Revisiting the Limiting Factors for Overall Water-Splitting on Organic Photocatalysts

In pursuit of inexpensive and earth abundant photocatalysts for solar hydrogen production from water, conjugated polymers have shown potential to be a viable alternative to widely used inorganic counterparts. The photocatalytic performance of polymeric photocatalysts, however, is very poor in comparison to that of inorganic photocatalysts. Most of the organic photocatalysts are active in hydrogen production only when a sacrificial electron donor (SED) is added into the solution, and their high performances often rely on presence of noble metal co-catalyst (e.g. Pt). For pursuing a carbon neutral and cost-effective green hydrogen production, unassisted hydrogen production solely from water is one of the critical requirements to translate a mere bench-top research interest into the real world applications. Although this is a generic problem for both inorganic and organic types of photocatalysts, organic photocatalysts are mostly investigated in the half-reaction, and have so far shown limited success in hydrogen production from overall water-splitting. To make progress, this article exclusively discusses critical factors that are limiting the overall water-splitting in organic photocatalysts. Additionally, we also have extended the discussion to issues related to stability, accurate reporting of the hydrogen production as well as challenges to be resolved to reach 10 % STH (solar-to-hydrogen) conversion efficiency.     

In Situ Tracking of Dynamic NO Capture through a Crystal-to-Crystal Transformation from a Gate-Open-Type Chain Porous Coordination Polymer to a NO-Adducted Discrete Isomer

Optimal control of gas adsorption properties in metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) remains a great challenge in the field of materials science. An efficient strategy to capture electron-acceptor-type gas molecules such as nitrogen monooxide (NO) is to use host–guest interactions by utilizing electron-donor-type MOFs/PCPs as host frameworks. Herein, we focus on a highly electron-donating chain compound by using the paddlewheel-type [Ru₂^II,II] complex [Ru₂(2,4,5-Me₃PhCO₂)₄] (2,4,5-Me₃PhCO₂⁻=2,4,5-trimethylbenzoate) with the phenazine (phz) linker: [Ru₂(2,4,5-Me₃PhCO₂)₄(phz)] ( 1 ). Compound 1 exhibited a specific gated adsorption for NO under gas pressures greater than 60 kPa at 121 K, which finally resulted in approximately seven molar equivalents being taken up at 100 kPa followed by four molar equivalents remaining under vacuum at 121 K; its Rh isomorph ( 2 ) with weaker donation ability was inactive for NO. When the sample of 1 ⊃4 NO was heated to room temperature, the compound underwent a crystal-to-crystal phase transition to give [Ru₂(2,4,5-Me₃PhCO₂)₄(NO)₂](phz) ( 1 -NO), involving a post-synthetic nitrosylation on the [Ru₂] unit, accompanied by an eventful site-exchange with phz. This drastic event, which is dependent on the NO pressure, temperature, and time, was coherently monitored by using several different in situ techniques, revealing that the stabilization of NO molecules in nanosized pores dynamically and stepwisely occurred with the support of strong electronic/magnetic host–guest interactions.     

Methyltrioxorhenium catalyzed domino epoxidation-nucleophilic ring opening of glycals

The use of catalytic methylrhenium trioxide (MTO) and urea hydrogen peroxide in room temperature ionic liquid for the hydroxyglycosylation with glycals in a domino fashion is reported. Excellent conversions and good selectivities for the epoxidation reaction were observed. Application to the synthesis of glycosylphosphates, good glycosyl donors, has been studied.     

High sensitivity detection of trace impurities in the presence of other impurity species: The shallow thermal donors in Cz-Silicon

The combination of the techniques of Fourier transform spectroscopy (FTS) with the highly sensitive method of photothermal ionization spectroscopy (PTIS) opens up new possibilities for the investigation of trace impurities in semiconductors. The interpretation of the PTIS spectra when many donor species contribute to the photoconductivity is discussed with reference to the case of the shallow thermal donors in silicon.     

Submillimeter wave photoconductivity observation of shallow donors in In0.53Ga0.47As

The hydrogen like 1s 2p (m=–1,0,+1) transitions of two donors have been observed in high intensity magnetic fields up to 8.5T. The m=–1 transitions ocurred between 2 cm^–1 and 25 cm^–1. The signature curves for donors in ternary semiconductor In_0.53Ga_0.47As have now been established.Work supported by the U.s. Air Force Office of Scientific Research under Contract # AFOSR-78-3708-DSupported by the National Science Foundation     

Synthesis and Characterization of the Zinc Amides: [EtZnL]2 and [ZnL2] (L = N,N‐dimethyl(N′‐trimethylsilyl)ethane‐1,2‐diaminate)

The ligand N,N‐dimethyl(N′‐trimethylsilyl)ethane‐1,2‐diamine (HL) was treated with ZnEt₂ in varying stoichiometric ratios to synthesize [EtZnL]₂ and [ZnL₂] complexes. Crystal data: [EtZnL]₂, monoclinic, P2₁/n, a = 10.0149(5) Å, b = 8.0296(3) Å, c = 16.1689(8) Å, β = 91.715(2)°. [ZnL₂], monoclinic, P2₁/n, a = 8.8457(3) Å, b = 15.4249(6) Å, c = 16.0121(7) Å, β = 92.656(1)°. The former complex is an amido nitrogen bridged dimer with distorted tetrahedral stereochemistry of the zinc atom and the latter is a distorted tetrahedral monomer based on amide/amine chelation.     

New 3 D Tubular Porous Structure of an Organic–Zincophosphite Framework with Interesting Gas Adsorption and Luminescence Properties

A new 3D tubular zinc phosphite, Zn₂(C₂₂H₂₂N₈)_0.5(HPO₃)₂?H₂O ( 1 ), incorporating a tetradentate organic ligand was synthesized under hydro(solvo)thermal conditions and structurally characterized by single‐crystal X‐ray diffraction. Compound 1 is the first example of inorganic zincophosphite chains being interlinked through 1,2,4,5‐tetrakis(imidazol‐1‐ylmethyl)benzene to form a tubular porous framework with unusual organic–inorganic hybrid channels. The thermal and chemical stabilities, high capacity for CO₂ adsorption compared to that for N₂ adsorption, and interesting optical properties of LED devices fabricated using this compound were also studied.