Oxygen as a site specific probe of the structure of water and oxide materials

The method of oxygen isotope substitution in neutron diffraction is introduced as a site specific structural probe. It is employed to measure the structure of light versus heavy water, thus circumventing the assumption of isomorphism between H and D as used in more traditional neutron diffraction methods. The intramolecular and intermolecular O-H and O-D pair correlations are in excellent agreement with path integral molecular dynamics simulations, both techniques showing a difference of ?0.5% between the O-H and O-D intramolecular bond distances. The results support the validity of a competing quantum effects model for water in which its structural and dynamical properties are governed by an offset between intramolecular and intermolecular quantum contributions.     

Adsorption bond length for H2O on TiO2(110): a key parameter for theoretical understanding

Scanned-energy mode photoelectron diffraction results show the adsorption site of molecular water on TiO2(110) to be atop under-coordinated surface Ti atoms, confirming the results of total energy calculations and STM imaging. However, the Ti-O(water) bond length is 2.21 +/- 0.02 A, much longer than Ti-O bond lengths in strongly chemisorbed species on this surface, but significantly shorter than found in most total energy calculations. The need for theory to describe this weak bond effectively may be a key factor in the controversial problem of understanding this important surface reaction system.     

Isotope effects in water as investigated by neutron diffraction and path integral molecular dynamics

The structures of heavy and light water at 300?K were investigated by using a joint approach in which the method of neutron diffraction with oxygen isotope substitution was complemented by path integral molecular dynamics simulations. The diffraction results, which give intra-molecular O-D and O-H bond distances of 0.985(5) and 0.990(5)??, were found to be in best agreement with those obtained by using the flexible anharmonic TTM3-F water model. Both techniques show a difference of ??0.5% between the O-D and O-H intra-molecular bond lengths, and the results support a competing quantum effects model for water in which its structural and dynamical properties are governed by an offset between intra-molecular and inter-molecular quantum contributions. Further consideration of the O-O correlations is needed in order to improve agreement with experiment.     

高压液态重水的拉曼光谱研究

应用金刚石压腔结合拉曼光谱技术研究了重水在291 K,0.1～800 MPa条件下的拉曼谱图。结果表明：压力增大的过程中,重水的拉曼伸缩振动光谱向低频方向移动,并且频移和压力基本呈线性相关。频移没有突变,没有发生相的转变。将重水的拉曼谱峰分解为代表分子内O—D振动的高频峰和代表分子间氢键振动的低频峰。研究这两种不同类型谱峰的性质,发现代表分子间氢键的低频峰峰面积在不同的压力范围内呈现出不同的变化特征,压力对分子间氢键的影响并不是持续不变的。拉曼峰的峰面积反映的是产生这种拉曼峰的振动的数目,峰面积的变化反映了特征振动数目的变化。由于分子间氢键的强相互作用,水分子总是倾向于形成对称的空间五分子四面体结构,因此最大峰面积代表了最稳定的五分子团簇结构。     

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.     

D2EHPA萃取稀土的有机相红外光谱及添加DMHPA的影响

本文研究了部分皂化的二（２－乙基己基）磷酸（Ｄ２ＥＨＰＡ）－正庚烷体系萃取稀土离子Ｙ＾３＋，Ｐｒ＾３＋，Ｎｄ＾３＋，Ｅｕ＾３＋后有机的傅里叶变换红外光谱（ＦＴ－ＩＲ）。发现不同稀土离子与萃取剂的配位能力有差异，并且皂化度对萃取有机相中的Ｐ＝Ｏ谱带的频率和吸收强度皆有影响，在Ｄ２ＥＨＰＡ中加入二（１－甲基庚基）磷酸（ＤＭＨＰＡ）导致Ｐ＝Ｏ谱带形状和吸收强度发生变化。     

Deuterium isotope effects on iron core formation in ferritin

We present comparative Mössbauer investigations of nanosized FeOOH and FeOOD biomineral phases nucleated within the 7-nm diameter cavity of horse-spleen apoferritin in order to assess deuterium isotopic effects on nanoscale, bioinorganic lattice structures with extended hydrogen bond networks. Differences in magnetic anisotropy energy, packing density and degree of crystallinity in the resulting iron oxo-hydroxide nanophases obtained via D₂O (heavy water) vs. H₂O (light water) solution chemistry are noted. These observations point to the possibility of stabilizing new thermodynamic states in the solid-state by utilizing isotope effects, with important implications for new synthetic pathways to novel nano materials.     

Association of rhodamine 6G in light and heavy water solutions

The absorption characteristics of rhodamine 6G molecules in light and heavy water solutions are studied. The association efficiencies of dye molecules and the structure and the binding energy of complexes formed are determined in relation to the solvent composition. The structure of H₂O +D₂O solutions is studied using correlation and low-frequency Raman spectroscopy. The distribution of dissolved complex molecules in the water matrix is shown to have inhomogeneities, which are responsible for a high association efficiency. The characteristic size of these inhomogeneities is estimated. The fractal dimension of the structural formations of light and heavy water molecules is determined as a function of their concentration.     

A photoelectron diffraction investigation of vanadyl phthalocyanine on Au(1 1 1)

Scanned-energy mode photoelectron diffraction using the O 1s and V 2p emission perpendicular to the surface has been used to investigate the orientation and internal conformation of vanadyl phthalocyanine (VOPc) adsorbed on Au(1 1 1). The results confirm earlier indications from scanning tunnelling microscopy that the VO vanadyl bond points out of, and not into, the surface. The VO bondlength is 1.60 ± 0.04 Å, not significantly different from its value in bulk crystalline VOPc. However, the V atom in the adsorbed molecule is almost coplanar with the surrounding N atoms and is thus pulled down into the approximately planar region defined by the N and C atoms by 0.52 (+0.14/−0.10) Å, relative to its location in crystalline VOPc. This change must be attributed to the bonding interaction between the molecule and the underlying metal surface.     

Inelasticity corrections for time-of-flight and fixed wavelength neutron diffraction experiments

Time-of-flight neutron diffraction methods are widely used to study the structure of liquids and glasses. The scattering nuclei in these experiments suffer nuclear recoil in the course of the neutron scattering process, which gives rise to distortions to both the self and distinct structure factors extracted from the data. These distortions are in general difficult to evaluate quantitatively, especially when the mass of the nucleus is similar to that of the neutron, such as when hydrogen is present in the material being studied. Traditional treatments of this effect generally assume the neutron energy is lower than the excitation energy of an atom, but for time-of-flight diffraction this is never the case, and the experiments typically sample a wide range of energy transfers from sub-meV to tens of eV. In addition, by attempting to produce an analytical correction, such methods invariably make a long list of approximations which can be difficult to justify in particular cases. Here, a model for the scattering kernal is developed based on the well known harmonic oscillator model [A.C. Zemach and R.J. Glauber, Phys. Rev. 101, 118 (1956)]. This is shown to have the correct first and second moments of the scattering kernal for both the self and distinct scattering, and is used to estimate the self and distinct scattering from a diatomic ‘dumbell’ molecule. The model gives a realistic account of the single atom scattering from light and heavy water over a wide range of incident neutron energies, but is not yet accurate enough to perform quantitative corrections. In lieu of a quantitative approach, a ‘top hat’ convolution method is developed to perform the subtraction of self scattering from real data, and to allow data from multiple detector banks to be merged into a single structure factor. The harmonic oscillator model is also used to address the question of inelasticity effects on the interference scattering. For the intramolecular correlations at least at low scattering angles up to ～40° it is found that the effect of inelasticity is rather small – around 0.6% on the estimated OH bond length for H₂O. Although the emphasis here is on time-of-flight diffraction, the model is quite general and can just as easily be applied to the case of fixed wavelength neutron diffraction where it also gives accurate results.     

Temperature dependence of structure and density for D?O confined in MCM-41-S

Using neutron diffraction, we have tracked the temperature dependence of structural properties for heavy water confined in the nanoporous silica matrix MCM-41-S. By observing the correlation peak corresponding to the pore-pore distance, which is determined by the scattering contrast between the silica and the water, we monitored the density of the confined water. Concurrently, we studied the prominent first diffraction peak of D(2)O at ≈ 1.8 ?(-1), which furnishes information on the microscopic arrangement of the water molecules. The data show the presence of a density maximum at ≈ 275 K (± 10 K), a property similar to bulk water, and the occurrence of a density minimum at ≈ 180 K (± 10 K). The prominent diffraction peak of D(2)O is found to shift and sharpen over a wide T range from 200 to 270 K, reflecting structural changes that are strongly correlated with the changes in density. We also observe the continuous formation of external ice, arising from water expelled from the pores while expansion takes place within the pores. An efficient method for monitoring the density of the confined D(2)O using a triple-axis spectrometer is demonstrated.     

酸根离子及其水溶液对镎酰离子结构性质的影响

利用B3LYP杂化密度泛函方法,在相对论有效芯势模型下,优化得到了NpO22+离子及其配合物在气相和水溶液中的几何结构和电子结构, 研究了NO3-、SO42-和CO32-离子及其水溶液对NpO22+离子的结构和性质的影响.结果表明,NpO22+离子结合各种酸根离子后其Np=O键的键长都有明显增长、Np和O原子的价电子轨道能均有升高,而考虑溶剂化效应后酸根离子的影响将减小.电荷分析发现,结合酸根离子后,NpO22+中Np和O原子间形成的共价键的强度减弱、键长增长.对NpO22+离子与三种酸根离子的理论结合能的比较显示,NpO2CO3分子最为稳定.     

酸根离子及其水溶液对镎酰离子结构性质的影响

利用B3LYP杂化密度泛函方法,在相对论有效芯势模型下,优化得到了NpO_2~(2+)离子及其配合物在气相和水溶液中的几何结构和电子结构,研究了NO-3、SO2-4和CO2-3离子及其水溶液对NpO_2~(2+)离子的结构和性质的影响.结果表明,NpO_2~(2+)离子结合各种酸根离子后其Np=O键的键长都有明显增长、Np和O原子的价电子轨道能均有升高,而考虑溶剂化效应后酸根离子的影响将减小.电荷分析发现,结合酸根离子后,NpO_2~(2+)中Np和O原子间形成的共价键的强度减弱、键长增长.对NpO_2~(2+)离子与三种酸根离子的理论结合能的比较显示,Np O2CO3分子最为稳定.     

Observation of depolarized ZnO(0001) monolayers: formation of unreconstructed planar sheets

A novel nonpolar structure of 2 monolayer (ML) thick ZnO(0001) films grown on Ag(111) has been revealed, using surface x-ray diffraction and scanning tunneling microscopy. Zn and O atoms are arranged in planar sheets like in the hexagonal boron-nitride prototype structure. The observed depolarization is accompanied by a significant lateral 1.6% expansion of the lattice parameter and a 3% reduced Zn-O bond length within the sheets. The nonpolar structure stabilizes an atomically flat surface morphology unseen for ZnO surfaces thus far. The transition to the bulk wurtzite structure occurs in the 3-4 ML coverage range, connected to considerable roughening.     

Light scanner based on a viscoelastic stretchable grating

We present a new technique for light scanning by use of viscoelastic-based deformable phase diffraction gratings. Mechanical stretching of the grating permits control of its spatial period, and thus the orders of diffraction can be spatially deflected. In the experiments the viscoelastic gratings with triangular and rectangular profiles have been characterized at lambda = 633 nm. It is demonstrated that the reversible elongation can exceed 20% of the initial length. For the triangular profile grating, the diffraction angle of the first order changed from 6.6 degrees to 5.4 degrees while the diffraction efficiency remained almost constant at approximately 17%. Dynamic scanning of a laser beam at frequencies of approximately 1 kHz is demonstrated by use of electromechanically driven viscoelastic gratings.     

Dynamical scaling of the structure factor of some non-Euclidean systems

Predictions of nonlinear theories on dynamics of new phase formation have been examined for the hydration of calcium silicates with light water and heavy water. In the case of hydration with light water, reasonable agreement has been observed with dynamical scaling hypothesis with a new measure of the characteristic length. The characteristic length does not follow a power law relation with time. Hydrating mass is found to be mass fractal throughout hydration, with mass fractal dimension increasing with time. But, in the case of hydration with heavy water, no agreement has been observed with the scaling hypothesis. Hydrating mass undergoes transition from mass fractal to surface fractal and finally again to mass fractal. The qualitative features of the kinetics of hydration, as measured in small-angle scattering experiments, are strikingly different for hydration with light water and heavy water.     

Local structure of OH adsorbed on the Ge(0 0 1)(2 × 1) surface using scanned-energy mode photoelectron diffraction

The local geometry of OH fragments adsorbed on the Ge(0 0 1)(2 × 1) surface has been examined using O 1s scanned energy mode photoelectron diffraction. These fragments were obtained by the dissociative reaction of the clean surface with H₂O. The Ge–O bond length is found to be 1.76 ± 0.02 Å and the Ge–O bond angle to be 15° ± 2° relative to the surface normal. Some information about the positions of the Ge dimer atoms has also been obtained.     

ZnO/Cu_2O异质结纳米阵列制备及光催化性能

利用湿化学法在FTO玻璃基底上制备了高度规整的ZnO纳米棒阵列(ZnO NRAs),以此为衬底,采用磁控溅射法在ZnO NRAs表面沉积Cu_2O薄膜。分别用X射线衍射仪、X射线光电子能谱、扫描电镜、光致光谱、紫外可见分光光度计和电化学工作站对样品的物相、形貌、吸收光谱、光电性能进行了表征,用甲基橙(MO)模拟有机物废水研究复合材料的光催化性能。结果表明:ZnO纳米棒为六方纤锌矿结构,其直径约为80~100 nm,长约2~3μm,棒间距约100~120 nm。立方晶系的Cu_2O颗粒直径约为100~300 nm,形成致密膜层并紧密覆盖在ZnO NRAs表面上,构成ZnO/Cu_2O异质结纳米阵列(ZnO/Cu_2O HNRAs)结构。与纯ZnO NRAs和Cu_2O相比,ZnO/Cu_2O HNRAs在可见光范围内的吸收显著增强,吸收波长向可见光方向偏移。ZnO/Cu_2O HNRAs的载流子传递界面的电荷转移速度快,有效促进了光生电子和空穴的分离。在紫外-可见光照射65 min后,ZnO/Cu_2O HNRAs的降解效率为94%,分别是纯ZnO NRAs和Cu_2O的18倍和1.7倍。     

大气中Pd-H(D)系中H(D)的释放及其表面附近H的分布

将经过950℃热处理后缓慢冷却及淬火处理的Pd样品,分别作为阴极在重水(D₂O)和轻水(H₂O)中进行150h电解,以引入H和D。用X射线衍射方法测量Pd-H(D)系存放于大气中经过不同时间后的衍射图及β相晶格常数的变化,并用¹H(¹⁹F,αγ)¹⁶O核反应测量H在各Pd-H(D)系表面层中的分布。淬火Pd与退火Pd相对比,在电解吸H(D)后,前者初始含H(D)百分比较高而H(D)的释放速度较快。H的浓度在Pd-H合金的表面处达到极大值而在离表面深度为数百埃处达到极小值。 关键词：     

Fabrication of high-efficiency diffraction gratings in glass

We investigated a microfabrication process for optical gratings with periods of micrometer order that use ultrafast laser pulses in semiconductor-doped glass. ZnS- or PbS-doped SiO2-A12O3-B2O3-CaO-ZnO-Na2O-K2O glass was prepared by a melting method. Glass transmission diffraction gratings with a high refractive-index difference were fabricated with femtosecond laser pulses. The first-order diffraction efficiencies of these gratings were approximately 80%, and the first-order diffraction angles of these gratings were 8 degrees at telecommunication wavelengths.