157-nm coherent light source as an inspection tool for F(2) laser lithography

We have developed a 157-nm coherent light source by two-photon resonant four-wave mixing in Xe, with two tunable single-mode 1-kHz Ti:sapphire laser systems at 768 and 681 nm. This light source has been developed to determine the instrumental function of a vacuum ultraviolet spectrometer and to evaluate optical designs for ultra-line-narrowed F(2) laser lithography. The spectral linewidth of the source was less than 0.008 pm (FWHM), with an average power of 0.6 mW.     

Attaining 186-nm light generation in cooled beta-BaB(2)O(4) crystal

The transparency range of beta-BaB(2)O(4) (BBO) was expanded by means of cooling, and the resulting absorption coefficient at 193.4 nm was reduced to 0.29cm(-1) at 91 K from 1.39cm(-1) at 295 K. Further, generation of light at 186.0 nm (the measurement limit in air) by type I sum-frequency generation (SFG) based on fundamental (744-nm) and third-harmonic (248-nm) light from a Ti:sapphire laser was confirmed for cooled BBO. Calculations based on observed data for SFG wavelengths and phase-matching angles indicate a potential for cooled BBO to generate wavelengths as low as 181.7 nm.     

Pressure induced self-oxidation of Fe(OH)2

M?ssbauer spectroscopy, x-ray diffraction, and electrical resistance [R(P,T)] studies in Fe(OH)(2) to 40 GPa revealed an unforeseen process by which a gradual Fe2+ oxidation takes place, starting at approximately 8 GPa reaching 70% Fe3+ abundance at 40 GPa. The nonreversible process Fe2+-->Fe3++e(-) occurs with no structural transition. The "ejected" electrons form a deep band within the high-pressure electronic manifold becoming weakly localized at P>50 GPa. This process is attributed to an effective ionization potential created by the pressure induced orientationally deformed (OH) dipoles and the unusual small binding energy of the valence electron in Fe2+(OH)(2).     

Molecular orientation dependence of ortho-para H2 conversion on Fe(OH)3 cluster induced by hyperfine contact interaction

We investigate the molecular orientation dependence of the (o)rtho-(p)ara H₂ conversion on Fe(OH)₃ cluster. Taking Fermi's contact interaction as perturbation, we find that the o-p H₂ conversion yield for the molecular orientation angle θ= 10^○ with respect to the surface normal is larger than that for θ= 70^○.     

The tautomerization of H2NCH2C(OH)NH to H2NCH2CONH2 in the interstellar medium

The tautomerization of H2NCH2C(OH)NH to H2NCH2CONH2 is an important step by way of Strecker synthesis for the production of glycine in the interstellar medium (ISM) with respect to the origin of amino acids on the early Earth.Our work indicates two mechanisms for the tautomerization to occur.k CVT/SCT (rate constant) is 45.6s-1 at 50 K,obtained with the small curvature tunneling (SCT) approximation and canonical variational transition state theory (CVT),to support one mechanism assisted by quantum tunneling...     

(SiO2)nO2H4的红外振动光谱的理论研究

运用密度泛函理论,在6-31G(d)基组水平上,计算了纳米尺度的(SiO2)nO2H4链状、环状、笼状三种不同构型的红外振动光谱.对准一维的链状和环状结构,红外振动较强峰的频率随着长度的增加单调变化,显示了较强的尺寸依赖性;沿纳米线(环)轴向和垂直于轴向的振动模式,频率对尺寸的依赖关系相反,揭示了纳米材料的振动性质的各向异性.笼状结构由于构型的复杂性而使得其不具备准一维的特性,同时结构的对称性降低,红外振动模式数目增加.三种构型中二元环和硅羟基的振动以及笼状构型中硅氧四面体骨架的振动与实验上所观测到的振动峰相吻合.红外光谱方面的理论计算结果对实验合成的SiO2纳米材料的表征具有指导意义.     

Raman microscopy of haidingerite Ca(AsO3OH)·H2O and brassite Mg(AsO3OH)·4H2O

Raman spectroscopy has been used to study the arsenate minerals haidingerite Ca(AsO₃OH)·H₂O and brassite Mg(AsO₃OH)·4H₂O. Intense Raman bands in the haidingerite spectrum observed at 745 and 855 cm⁻¹ are assigned to the (AsO₃OH)²⁻ν₃ antisymmetric stretching and ν₁ symmetric stretching vibrational modes. For brassite, two similarly assigned intense bands are found at 809 and 862 cm⁻¹. The observation of multiple Raman bands in the (AsO₃OH)²⁻ stretching and bending regions suggests that the arsenate tetrahedrons in the crystal structures of both minerals studied are strongly distorted. Broad Raman bands observed at 2842 cm⁻¹ for haidingerite and 3035 cm⁻¹ for brassite indicate strong hydrogen bonding of water molecules in the structure of these minerals. OH···O hydrogen‐bond lengths were calculated from the Raman spectra based on empirical relations. Copyright © 2009 John Wiley & Sons, Ltd.     

Hydrogen bonding in mixed OH+H2O overlayers on Pt(111)

The stability of OH on Pt(111) has been investigated to determine the role of hydrogen bonding in stabilizing the overlayer. We find that the optimal structure is a mixed (OH+H2O) phase, confirming recent density-functional theory predictions. The reaction O+3H(2)O forms a hexagonal (sqrt[3]xsqrt[3])R30 degrees -(OH+H2O) lattice with a weak (3x3) superstructure, caused by ordering of the hydrogen bonds. The mixed overlayer can accommodate a range of H(2)O/OH compositions but becomes less stable as the H2O content is reduced, causing defects in the hydrogen-bonding network that lift the (3 x 3) superstructure and destabilize the overlayer.     

Bragg gratings in ternary SiO(2):SnO(2):Na(2)O optical glass fibers

Bragg gratings have been written in an optical fiber with a core made from ternary SiO(2): SnO(2): Na(2)O glass and a SiO(2) cladding. The presence of Na(2)O allows for higher concentrations of SnO>(2) , which are believed to be responsible for the photorefractive response of this composition. In these preliminary experiments significant refractive-index modulations, up to 6.2x10(-4) , have been achieved with a 248-nm excimer laser and a phase mask to write gratings for reflectivity at ~1.5microm . The induced refractive-index changes show enhanced temperature stability, and there is no sign of any erasure up to temperatures exceeding 600 degrees C.     

Structural modifications induced by the second discharge process in the Ni(OH)2/NiOOH redox system

Electrochemical behavior and related structural modifications of the nickel hydroxide/oxyhydroxide electrode are investigated as a function of the reduction state achieved on discharge. Reduction proceeds at two successive potential steps, with recovering of the initial structural properties only after the second discharge process. Active material cycled in the positive potential range (vs. Hg/HgO), including only the first discharge step, is non-stoichiometric and characterized by high lattice defect content. Whatever the oxidation state, the presence of Ni³⁺ defects and protonic delocalization are observed. The 2nd discharge process restores O-H covalent bonds and a better defined Ni(II) state, similar to the precursor nickel hydroxide chemically obtained. Electrochemical cycling in the positive potential range is characterized by the retention of the same nanocrystallite dimension and a high fragmented morphology, while the 2nd discharge induces crystallite agglomeration. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Ni2(OCH3)2/SiO2催化剂上CO2和CH3OH的吸附和反应性能

采用表面改性和离子交换相结合的方法制备了Ni2 (OCH3 ) 2 /SiO2 负载型双核金属甲氧基配合物催化剂 ,利用红外光谱 (IR)、程序升温脱附 (TPD)、程序升温表面反应 (TPSR)和微反技术考察了催化剂的表面结构以及CO2 和CH3 OH的化学吸附和反应性能 .结果表明 :Ni2 (OCH3 ) 2 /SiO2 中Ni2 + 与载体SiO2 表面O2 -以双齿配位形式键合 ,甲氧基以桥基形式联结双金属离子形成双核物种Ni2 (OCH3 ) 2 ;CO2 在催化剂表面存在甲氧碳酸酯基物种和桥式两种吸附态 ,CH3 OH则只有一种分子吸附态 ;在 10 0～ 2 0 0℃条件下 ,CO2 和CH3 OH在催化剂上的反应产物主要是DMC和H2 O ;根据反应结果 ,讨论了催化反应机理 .     

Insertion and abstraction pathways in the reaction O(1D2) + H2-->OH+H

Rigorous quantum dynamical calculations have been performed on the ground 1 1A' and first excited 1 1A" electronic states of the title reaction, employing the most accurate potential energy surfaces available. Product rovibrational quantum state populations and rotational angular momentum alignment parameters are reported, and are compared with new experimental, and quasiclassical trajectory calculated results. The quantum calculations agree quantitatively with experiment, and reveal unequivocally that the 1 1A" excited state participates in the reaction.     

Electronic structure of oxygen dangling bond in glassy SiO2: the role of hyperconjugation

The electronic structure and the nature of optical transitions in oxygen dangling bond in silica glass, the nonbridging oxygen hole center (NBOHC), were calculated. The calculation reproduced well the peak positions and oscillator strengths of the well-known optical absorption bands at 2.0 and 4.8 eV, and of the recently discovered absorption band at 6.8 eV. The 2.0 eV band was attributed to transition from the sigma bond between Si and dangling oxygen to nonbonding pi orbital on the dangling oxygen. The uniquely small electron-phonon coupling associated with the 2.0 eV transition is explained by stabilization of Si-O bond in the excited state by hyperconjugation effects.     

SiO2脊形条波导热极化引起的电光效应

通过理论模拟对具有上覆盖层的SiO2脊形条波导结构进行了优化,在此基础上利用微电子工艺制作了SiO2脊形波导Mach-Zehnder 型电光调制器,并进行热极化引起的电光和非线性效应的研究.热极化过程大幅增强了样品的电光及非线性效应,二次电光系数由热极化前的1.56×10-22(m/V)2提高到热极化后的8.50×10-22(m/V)2,极化后得到了0.093pm/V的线性电光系数,对热极化的物理机理进行了理论分析.     

Preparation of SiO2 overlayers on oxide substrates by chemical vapor deposition of Si(OC2H5)4

The deposition of SiO₂ onto ZrO₂, TiO₂, MgO, SiO₂ and Al₂O₃ by chemical vapor deposition (CVD) of Si(OC₂H₅)₄ was studied by temperature programmed desorption (TPD) and Auger electron spectroscopy (AES). TPD showed that Si(OC₂H₅)₄, adsorbed at 300 K, decomposed on ZrO₂, TiO₂, MgO and Al₂O₃ to give ethene and H₂O during the TPD. SiO₂ did not adsorb Si(OC₂H₅)₄ at 300 K. The decomposition of Si(OC₂H₅)₄ on ZrO₂ decreased as the amount of SiO₂ grew. The Zr AES signals attenuated strongly while that of Si increased. We conclude that a SiO₂ thin film about 10 Å thick forms on ZrO₂. This thin film was stable in vacuum up to 723 K but, at 823 K, either rearranged into small clusters or formed a solid solution with the surface of ZrO₂. The decomposition activity of TiO₂ for Si(OC₂H₅)₄ did not decrease strongly as SiO₂ deposition proceeded. This is accounted for if SiO₂ clusters are produced leaving TiO₂ sites exposed. Over both ZrO₂ and TiO₂ adsorption of CO₂ was suppressed by the deposition of SiO₂. There is no significant carbon buildup during deposition on ZrO₂ but on all the other oxides its accumulation is important.     

Raman spectroscopy of hydrogen‐arsenate group (AsO3OH) in solid‐state compounds: cobalt mineral phase burgessite Co2(H2O)4[AsO3OH]2·H2O

Raman spectrum of burgessite, Co₂(H₂O)₄[AsO₃OH]₂· H₂O, was studied, interpreted and compared with its infrared spectrum. The stretching and bending vibrations of (AsO₃) and As‐OH units, as well as the stretching, bending and libration modes of water molecules and hydroxyl ions were assigned. The range of O H···O hydrogen bond lengths was inferred from the Raman and infrared spectra of burgessite. The presence of (AsO₃OH)²⁻ units in the crystal structure of burgessite was proved, which is in agreement with its recently solved crystal structure. Raman and infrared spectra of erythrite inferred from the RRUFF database are used for comparison. Copyright © 2010 John Wiley & Sons, Ltd.     

Role of mobile interstitial oxygen atoms in defect processes in oxides: interconversion between oxygen-associated defects in SiO(2) glass

The role of mobile interstitial oxygen atoms (O(0)) in defect processes in oxides is demonstrated by interconversion between the oxygen dangling bond and the peroxy radical (POR) in SiO2 glass. Superstoichiometric O(0) was created by F2 laser photolysis of the interstitial O2. On annealing above 300 degrees C, O(0) migrated and converted the oxygen dangling bond to POR. Exposure to 5.0 eV light converted POR back to a pair of the oxygen dangling bond and O(0) (quantum yield: approximately 0.1). These findings suggest that various defect processes typically occurring in SiO2 glass at approximately 300-500 degrees C are related to migration of O(0), which exists in the glass network in the peroxy linkage form.