为什么水在金属表面的吸附构型是倾斜的——水在铜、铝表面吸附的量子化学计算

用量子化学从头算方法,分别以原子簇Ｃｕ５、Ａｌ４、Ａｌ１０模拟Ｃｕ（１００）和Ａｌ（１１１）表面,在不同基组水平上,计算了水在两种金属表面上倾斜吸附的热能面,结果表明：当计算基组中不含氧原子的ｄ轨道时,得到水分子在金属垂直吸附的构型,这与实验结果不符;当水中氧原子加极化函数时,水分子倾斜吸附时能量较低,得到与实验相符的吸附构型。这说明水中氧原子ｄ轨道在计算中起着关键作用,在成键过程中有着重要影响。     

Interfacial reaction kinetics

We study irreversible A-B reaction kinetics at a fixed interface separating two immiscible bulk phases, A and B. Coupled equations are derived for the hierarchy of many-body correlation functions. Postulating physically motivated bounds, closed equations result without the need for ad hoc decoupling approximations. We consider general dynamical exponent z, where is the rms diffusion distance after time t. At short times the number of reactions per unit area, , is 2nd order in the far-field reactant densities . For spatial dimensions dabove a critical value , simple mean field (MF) kinetics pertain, where Q_b is the local reactivity. For low dimensions , this MF regime is followed by 2nd order diffusion controlled (DC) kinetics, , provided . Logarithmic corrections arise in marginal cases. At long times, a cross-over to 1st order DC kinetics occurs: . A density depletion hole grows on the more dilute A side. In the symmetric case (), when the long time decay of the interfacial reactant density, , is determined by fluctuations in the initial reactant distribution, giving . Correspondingly, A-rich and B-rich regions develop at the interface analogously to the segregation effects established by other authors for the bulk reaction . For fluctuations are unimportant: local mean field theory applies at the interface (joint density distribution approximating the product of A and B densities) and . We apply our results to simple molecules (Fickian diffusion, z=2) and to several models of short-time polymer diffusion (z>2). Received 8 June 1998 and Received in final form 10 September 1999     

Surface reactions of monoethylgermane on Si(100)-(2×1)

The adsorption and decomposition of monoethylgermane (GeH₃Et) on the Si(100)-(2×1) surface was investigated with the intent of elucidating the surface processes leading to the deposition of germanium. The low-temperature adsorption of the molecule was explored, as well as its thermal decomposition. H₂ and C₂H₄ are observed as the desorption products in temperature-programmed desorption experiments. The ethylene is produced by a hydride elimination reaction within the adsorbed ethyl groups. The amount of Ge which can be deposited in a reaction cycle is correlated with the number of sites occupied by the ethyl groups upon the dissociation of GeH₃Et.     

密度泛函理论研究草甘膦在纯的, 金属原子掺杂石墨烯表面的吸附机理

本研究采用密度泛函理论方法详细讨论了纯的石墨烯及Ti, Fe, Al, Ca原子掺杂石墨烯吸附草甘膦的机理.通过它们之间的吸附能,差分电荷密度,布居电荷,态密度分析发现草甘膦可以被纯的石墨烯及金属原子掺杂石墨烯不同程度地吸附.纯的石墨烯对草甘膦的吸附作用远不及掺杂石墨烯,其中,草甘膦在Ca掺杂石墨烯表面有最强相互作用.这是因为草甘膦与纯的石墨烯之间主要形成了-P=O…π,-COOH…π和-OH…π非共价的相互作用,而与掺杂石墨烯之间主要形成了Metal-O“单齿”和O-Metal-O“双齿”共价相互作用.本研究结果希冀为石墨烯在环境保护方面的应用提供有价值的理论指导.     

Kr/Xe气体在塑料闪烁体表面的吸附与扩散行为研究

采用基于Compass力场的分子动力学(MD)方法,研究了惰性气体氙(Xe)和氪(Kr)在塑料闪烁体(聚乙烯基对甲苯)的平整和粗糙表面的吸附和扩散行为.由惰性气体吸附曲线的均方根位移(MSD),得到了Xe/Kr气体在聚乙烯基对甲苯表面的扩散系数.研究结果表明,Kr/Xe气体均被稳定地吸附在塑料闪烁体表面,其稳定性随着温度的升高而增加,Xe分子的吸附性强于Kr分子. Kr/Xe气体在聚乙烯基对甲苯表面具有较强的扩散性能,扩散深度随着温度与厚度的增加而增加,最大为22.865?,Kr分子扩散能力强于Xe分子.基底粗糙表面增加了两种惰性气体分子的吸附和扩散.     

Investigation on densification of Al2O3/B4C ceramic by ab initio calculation and experiment

Compared to experiment, the adsorption energies, bonding properties, and electronic structure of two different Al₂O₃/B₄C bridge sites with seven different Al₂O₃ surfaces are investigated by ab initio periodic density functional theory. The Al₂O₃/B₄C ceramic sintered in Ar is synthesized and measured by XRD and TEM. The calculated results reveal that the densification of O_bridge site of Al₂O₃/B₄C surface is better than that of Al_bridge. The Al₂O₃ (1 1 3)/B₄C with O_bridge is the most favorable and stable. The electronic structure shows that the electron hybridization exists between Al, O atoms and C, B atoms. The results indicate that the calculated results are in good agreement with the experiment.     

Fibrinogen adsorption onto 316L stainless steel, Nitinol and titanium

Fibrinogen adsorption onto mechanically polished biomedical grade 316L stainless steel (316LSS), nickel titanium alloy (Nitinol) and commercially pure titanium (CpTi) surfaces were studied by measurements of adsorption isotherms and adsorption kinetics using an ex-situ wavelength dispersive spectroscopy technique (WDS). Surface composition, roughness and wettability of these materials were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle (WCA) measurements. Adsorption isotherm results showed that surface protein concentration on these materials increased with increasing concentration of fibrinogen in phosphate buffer solution. The fibrinogen adsorption isotherms were modeled by both the monolayer Langmuir isotherm and the multilayer Brunauer-Emmett-Teller (BET) isotherm. The results strongly suggest that fibrinogen forms multilayer structures on these materials when the concentration in solution is high. Complementary measurements on the absorbed fibrinogen films by spectroscopic ellipsometry (SE) support this view.     

One-dimensional defects in iodine adlayers on Pt(1 0 0)

One-dimensional defect structures of closed-packed adlayers of iodine on Pt(1 0 0) were studied with scanning tunneling microscopy (STM). On the terraces of the Pt(1 0 0) surface we observed rotational domains with line defects running in [0 1 0] directions, in coexistence with nearly defect-free domains. In addition to these prevailing line defects (A-defects) with a local coverage lower than that of a defect-free surface, we report on much less frequently observed line defects with higher local coverages (B- and C-defects). The strong dependence of the concentration of these defects on the adsorption temperature is governed by the decrease of the overall iodine coverage with increasing temperature. Iodine adsorption at ∼1100 K leads to self-organization of A-defects in quasi-periodic arrangements. The relevance of these defects as important structural elements of commensurate superstructures of iodine on Pt(1 0 0) is stressed.     

Phase behavior and fluid-solid surface tension of argon in slit pores and carbon nanotubes

Phase behaviors of argon in several types of cylindrical and slit pores are examined by grand-canonical Monte Carlo simulations. Condensation processes in single- and multi-walled carbon nanotubes along with those in hard-wall tubes are compared. Effects of the pore size on pressure-tensor components, the fluid-wall surface tension, and the adsorption are also compared for the different fluid-pore interactions. The chemical potential at which the fluid begins to condense in the single-walled nanotube is greater than that in the multi-walled nanotube by an amount nearly equal to the difference in the potential-well depth of the fluid-pore interaction, and the adsorption isotherms overlap each other almost completely for narrow pores and partially for wider pores. Similar analyses are performed for slit pores of two different hydrocarbon models.     

亚甲基蓝在胶体银表面的吸附——表面增强拉曼光谱和密度泛函理论计算

获得了不同浓度下亚甲基蓝(methylene blue,MB)溶液在银溶胶中的表面增强拉曼光谱。结果表明： 亚甲基蓝分子与银纳米粒子高浓度下物理吸附为主,低浓度下化学吸附为主;不同浓度下存在不同的吸附取向,即高浓度下为“直立”取向,低浓度为“平躺”取向。通过观察低浓度下MB在银胶中吸附时间对谱图的影响,得知低浓度下吸附取向不随时间发生变化。应用密度泛函(DFT)方法在B3LYP/6-31+G*和LANL2DZ基组水平上对亚甲基蓝阳离子(MB+)及MB+与Ag原子形成的不同构型体系进行了结构优化和频率计算。实验与理论计算结果表明,MB+有可能通过N—Ag和S—Ag与Ag原子形成两种较强的吸附构型。电荷布居分析表明,与S原子相比,芳香环上的N原子更易与Ag发生相互作用。还对实验观察到的部分谱峰及它们的振动模式作出了初步归属和讨论。