Hydroxylation-induced modifications of the Al2O3/NiAl(0 0 1) surface at low water vapour pressure

STM, STS, LEED and XPS data for crystalline θ-Al₂O₃ and non-crystalline Al₂O₃ ultra-thin films grown on NiAl(0 0 1) at 1025 K and exposed to water vapour at low pressure (1 × 10⁻⁷-1 × 10⁻⁵ mbar) and room temperature are reported. Water dissociation is observed at low pressure. This reactivity is assigned to the presence of a high density of coordinatively unsaturated cationic sites at the surface of the oxide film. The hydroxyl/hydroxide groups cannot be directly identify by their XPS binding energy, which is interpreted as resulting from the high BE positions of the oxide anions (O_1s signal at 532.5-532.8 eV). However the XPS intensities give evidence of an uptake of oxygen accompanied by an increase of the surface coverage by Al³⁺ cations, and a decrease of the concentration in metallic Al at the alloy interface. A value of ∼2 for the oxygen to aluminium ions surface concentration ratio indicates the formation of an oxy-hydroxide (AlO_xOH_y with x + y ∼ 2) hydroxylation product. STM and LEED show the amorphisation and roughening of the oxide film. At P(H₂O) = 1 × 10⁻⁷ mbar, only the surface of the oxide film is modified, with formation of nodules of ∼2 nm lateral size covering homogeneously the surface. STS shows that essentially the valence band is modified with an increase of the density of states at the band edge. With increasing pressure, hydroxylation is amplified, leading to an increased coverage of the alloy by oxy-hydroxide products and to the formation of larger nodules (∼7 nm) of amorphous oxy-hydroxide. Roughening and loss of the nanostructure indicate a propagation of the reaction that modifies the bulk structure of the oxide film. Amorphisation can be reverted to crystallization by annealing under UHV at 1025 K when the surface of the oxide film has been modified, but not when the bulk structure has been modified.     

提高微波功率源性能的一种新型控制系统

本控制系统用于抑制大功率速调管输出微波功率宏脉冲平顶波纹,改善电子直线加速器输出束流的品质.控制方法采用微分线性逼近和矩阵算法对系统的输入和输出进行分析,求出代表系统响应的传输矩阵,从而将复杂的激励一响应计算转化为简单的代数运算.实验结果显示出宏脉冲平项波纹得到了有效抑制,说明采用自适应前馈控制来获得平坦的宏脉冲平顶是切实可行的.     

Heat-treatment studies of molybdenum oxide-monohydrate

The dehydration of molybdic acid, MoO₃---H₂O, was studied by thermal analysis, X-ray diffractometry and FTIR spectroscopy. The results show that an intermediate phase, MoO₃-2/3H₂O is formed at 216 °C and the monoclinic form of MoO₃ is grown above 350 °C. The mechanism of dehydration and structural rearrangement were confirmed by the features of the infrared spectra showing formation of corner-shared MoO₆ octahedra.     

Complementary spectroscopic techniques to model the association of contaminant uranium with structural surfaces

Contaminant uranium poses unique problems for decontamination of former weapons processing and nuclear power facilities, as well as chemical plants, waste storage sites and former mining facilities. In addition, dealing with the possibility of intentional (i.e., a terrorist act) or accidental release of radioactive material in a populated area requires an accurate understanding of the nature of the association of such material with structural surfaces. These surfaces must also be considered in the context of repeated contamination, and the importance of atmospheric exposure, interaction with other possible contaminants, and corrosion or surface degradation due to such exposure must be taken into account. Complementary spectroscopic techniques, especially surface spectroscopies, are essential in developing models for the interaction of contaminants with surfaces and interfaces. In this review (which also presents new data on uranium association with corroding steel surfaces), we collect models of this association as determined by spectroscopic techniques, assess the important considerations in the development of more accurate models, and address some of the questions which remain.     

A Tin(IV) Porphyrin with Two Axial Organometallic NCN‐Pincer Platinum Units

A tin(IV) porphyrin was combined with two axial NCN‐pincer platinum(II) fragments by utilizing the oxophilicity of the apical positions on the tin atom and the acidic nature of the NCN‐pincer platinum derived benzoic acid. The solid‐state structure determined by X‐ray crystallography revealed some close contacts between the pincer complexes and the meso‐p‐tolyl subsitutents of the porphyrin. It was shown by ¹H NMR spectroscopy that these close contacts were not present in solution and that this compound can potentially act as a novel building block for supramolecular architectures.     

Lorentz-Compton佯谬与一个双赢判决性散射实验设计

通过对“可见光区域是否存在Compton效应”的讨论而进一步深化到经典条件下“光的量子理论能否包含光的经典电磁理论”的实验验证,发现了Lorentz-Compton佯谬,并基于逆Compton散射设计了一个敏感而又可行的双赢判决性散射实验来解决此佯谬。     

Magnetic Properties of Metallic Multilayered Systems

Hyperfine Interactions - The giant magnetoresistance (GMR) effect was an epoch-making discovery in the field of magnetic materials research. In this article, studies on magnetic multilayered...     

高功率微波高斯馈源口面场分析

 用波导本征模展开方法对用于高功率微波发射系统的方角锥高斯馈源口面场进行分析，提出结合馈源远场辐射特性和避免高功率击穿折衷选定相应的高斯模注腰半径，进而确定多个波导模幅值，从而为运用模匹配或耦合波理论设计高斯馈源提供依据。     

Synthesis and structures of nitroxyalkyl methylphosphonates

The reactions of ethylene glycol mononitrate and glycerol 1,3-dinitrate with methylphosphonic dichloride afforded new nitroxyalkyl methylphosphonates.