苯在Si(111)-7×7表面化学吸附的理论研究

采用两种大小不同的原子簇模型Si_(30)H_(28)和Si_(13)H_(16)，分别用两层 ONIOM方法（对较大原子簇）和普通量子化学方法（对较小原子族）考察了苯分子 在Si(111)-7 * 7表面的化学吸附。对三种可能的吸附物种分别用DFT或HF方法进行 了计算。通过大小原子簇吸附物种的吸附能以及几何构型优化参数的比较发现，对 于稳定的吸附物种，较小的原子簇基本上可以代替较大的原子簇进行计算，而对于 不太稳定的吸附物种，就不得不考虑周边原子的影响。计算结果表明苯在Si(111)- 7 * 7表面的主要吸附种是双σ成键的1，4加成产物，不稳定的单吸附物种可能是 1，4加成物种的前驱态。     

苯在CuCl（111）表面吸附的密度泛函理论研究

采用量子化学的密度泛函理论方法,探讨了苯分子在CuCl(111)表面上不同覆盖度下不同吸附位上的平行吸附行为. 计算结果表明,随覆盖度的减小,吸附作用增强, Cl位上的吸附是稳定的吸附模式,在低覆盖度下吸附能约为74 kJ/mol, 在顶位和穴位上的吸附属于较弱的物理吸附. 同时对吸附前后的电子布居和态密度进行了分析. 吸附过程中,苯分子的π电子向底物转移,同时Cu的 3d轨道的电子反馈给苯的反键π轨道.     

苯在Rh(111)表面化学吸附的DV-Xα研究

The chemisorption of benzene on the Rh(111) surface is calculated using DVX_a method. The electronic structure, the ground states valence levels, Mulliken overlap populations, and the density of states (LDOS and TDOS) of the adsorption system C_6H_6/Rh_6(111) are obtained. The results of DV-X_a calculations indicate that the adsorbed benzene structure is unpertured from its stable gas-phase structure, is π-bonded to the Rh surface with ring plane parallel to the metal plane, and has a C_(3ν)(σ_d) bonding symmetry. We also discuss the charge transfer between adsorbate and substrate. The π electrons of benzene transfer to the empty d orbitals of Rh, so is resonance stability decreases and is easy to be hydrogenated. The results of TDOS are in agreement with UPS, supporting the LEED structural analysis. From figure 3, it can be found that the two peaks at 5—6 eV and 7—9 eV under Fermi level (E_F) move to left by about 0.5 eV in the process of adsorption, which are mainly contributed by the 2π and 1π orbiatls of benzene respectively and are widened, and the peaks at 2 eV and 4 eV over Fermi level also move to left, which are contributed by the empty d orbitals of Rh.     

ZrC(111)弛豫表面电子结构及其吸附氢的理论研究

采用第一性原理的方法对ZrC（111）清洁和氢吸附表面的电子结构进行了研究 。构型优化结果表明，从表面深入到体相一定深度，层间距存在交替“收缩”和“ 扩张”的现象，其紧邻E_F以下的DOS峰对应于活性表面态，主要成分为表面Zr原子 4d_(xz)/d_(yz)轨道；与理想表面相比，表面弛豫对该表面态影响不大。对于氢吸 附表面，计算结果表明氢原子倾向于吸附在表面孔洞上方位置（正对着第三层Zr原 子），此时H的1s态从体相的电子态中分离出来。此外，本文中H/ZrC（111）和 H/NbC（111）体系的H 1s诱导态变化进行了解释，并对清洁的吸附表面的芯能级位 移以及功函的变化进行了探讨。     

甲硫醇在Cu(111)表面的解离吸附: 密度泛函理论研究

采用基于密度泛函理论的第一性原理方法和平板模型研究了CH₃SH分子在Cu(111)表面的吸附反应.系统地计算了S原子在不同位置以不同方式吸附的一系列构型, 第一次得到未解离的CH₃SH分子在Cu(111)表面顶位上的稳定吸附构型,该构型吸附属于弱的化学吸附, 吸附能为0.39 eV. 计算同时发现在热力学上解离结构比未解离结构更加稳定. 解离的CH₃S吸附在桥位和中空位之间, 吸附能为0.75-0.77 eV. 计算分析了未解离吸附到解离吸附的两条反应路径, 最小能量路径的能垒为0.57 eV. 计算结果还表明S―H键断裂后的H原子并不是以H₂分子的形式从表面解吸附而是以与表面成键的形式存在. 通过比较S原子在独立的CH₃SH分子和吸附状态下的局域态密度, 发现S―H键断裂后S原子和表面的键合强于未断裂时S原子和表面的键合.     

(RXNR)_4(X=B，Al，Ga)簇合物的结构与化学键性质

用自洽场理论（HF）和密度泛函理论（DFT）的B3LYP方法，在6-311G~*水平上 ，首次从理论上研究了(RXNR)_4 (R = B，Al，Ga；R = H，CH_3，NH_2，OH)簇合 物及其先驱化合物（RXNR）_2的几何构型、电子结构和化学键性质，并与其异构体 及其等电子化合物进行了比较。结果表明，(RBNR)_4为环状骨架结构，(RAlNR)_4 和(RGaNR)_4为建立骨架结构。     

苯在Ag(100)表面吸附的周期性密度泛函理论研究

 采用量子化学中的密度泛函理论结合平板周期模型方法,研究了苯在Ag(100)面上的吸附方式和相对稳定性. 通过对不同吸附位置的吸附能和几何构型参数的比较发现,苯在Ag(100)表面的吸附属于较强的化学作用,穴位吸附的稳定性优于桥位,顶位吸附最不稳定. 吸附的苯分子的平衡构型发生扭曲, C-C键有较大程度的伸长; C-H键的键长基本不变,但是偏离苯环平面,并背离Ag(100)表面. 在吸附过程中,电子由苯向表面银原子转移. 本文给出了详细的轨道示意图和电荷布居分析,并且与相关的实验和理论研究结果进行了比较.     

噻吩在Ni(111)表面吸附的密度泛函理论研究

采用密度泛函理论方法,运用平板模型对噻吩分子在Ni(111)表面的水平吸附进行了结构优化和能量计算.结果表明,hcpA位的吸附最稳定,以bridgeB吸附最不稳定;噻吩吸附在表面上时,S原子向上翘起,4个C原子与边面Ni原子的作用更紧密,表面原子与噻吩的匹配程度决定了吸附的强度和吸附后S—C键的活泼性;噻吩以bridgeA吸附时分子与表面之间的电子给予与反馈最多,分子最活泼,而hcpA位吸附后噻吩分子轨道上电子的能量变稳定,分子并不活泼.     

Cux (x=1-4)团簇在CeO2(111)表面的吸附

用基于密度泛函理论的第一性原理方法研究了Cu团簇(Cu_x, x=1-4)在CeO₂(111)表面的吸附. 研究发现当团簇比较小时(x=2, 3), 倾向于平铺表面; 当x=4时, Cu团簇在CeO₂(111)表面以三维的四面体结构吸附较为稳定, 从Cu 3d到Ce 4f的电荷转移使Cu团簇带正电荷. 由二维的菱形结构到三维的四面体结构的转变势垒为1.05 eV, 并且其中一个Cu原子直接迁移到另外三个Cu原子的空位顶部的转变路径比较有利. 在Cu团簇与CeO₂的相互作用过程中, Cu-O和Cu-Cu相互作用的竞争最终决定了Cu团簇在CeO₂上的形貌. 这种CeO₂(111)负载的带正电的三维Cu团簇将对水分解, 进而对水煤气反应具有高的催化活性.     

Ion-Stimulated Chemisorption of Nitrogen on the Si(111) Surface

Russian Journal of Physical Chemistry A - Nitriding of a silicon surface with a beam of low-energy (100–700 eV) nitrogen ions from a source with electronic excitation was studied. The density...     

高氧化态(II-IV)三核金属簇合物构型分布的模式识别对应分析

本文采用模式识别方法, 对高氧化态(II-IV)三核簇合物的构型分布进行了对应分析, 找出了一组分类关系式, 为预报未知簇合物构型提供了定量的判据, 并初步讨论了构型分布和结构规律。     

硅表面纳米银团簇的氧助迁移行为

 采用原位扫描隧道显微镜研究了Si（111）－7×7表面蒸镀纳米银团簇的迁移行为以及氧气氛的促进作用．在覆盖度较低的情况下，蒸镀的银原子在Si（111）－7×7表面形成具有规整三角形结构单元的有序银团簇，它们主要占据在Si（111）－7×7表面有位错的半单胞内．在氧的存在下，形成的结构单元在硅表面发生迁移，并逐渐团聚成无明显结构特征的大粒子．原位观察结果表明，在连续扫描过程中，团聚后的大粒子在氧覆盖的硅表面也会发生迁移，最后稳定在硅表面原子氧吸附位周围．进一步的观察发现，硅表面银团簇的存在对随后氧的吸附状态具有明显的影响．这些结果为解释纳米银团簇在SiO2表面具有独特的催化性能提供了依据．     

Dissociation of N2 on a Si(111)-7x7 Surface at Room Temperature

We demonstrate that the strong N₂ bond can be efficiently dissociated at low pressure and ambient temperature on a Si(111)-7x7 surface. The reaction was experimentally investigated by scanning tunnelling microscopy and X-ray photoemission spectroscopy. Experimental and density functional theory results suggest that relatively low thermal energy collision of N₂ with the surface can facilitate electron transfer from the Si(111)-7x7 surface to the π*-antibonding orbitals of N₂ that significantly weaken the N₂ bond. This activated N₂ triple bond dissociation on the surface leads to the formation of a Si₃N interface.     

Binding of glycine and L-cysteine on Si(111)-7 x 7

The adsorption of glycine and l-cysteine on Si(111)-7 x 7 was investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). The observation of the characteristic vibrational modes and electronic structures of NH3+ and COO- groups for physisorbed glycine (l-cysteine) demonstrates the formation of zwitterionic species in multilayers. For chemisorbed molecules, the appearance of nu(Si-H), nu(Si-O), and nu(C=Omicron) and the absence of nu(O-H) clearly indicate that glycine and l-cysteine dissociate to produce monodentate carboxylate adducts on Si(111)-7 x 7. XPS results further verified the coexistence of two chemisorption states for each amino acid, corresponding to a Si-NH-CH2-COO-Si [Si-NHCH(CH2SH)COO-Si] species with new sigma-linkages of Si-N and Si-O, and a NH2-CH2-COO-Si [NH2CH(CH2SH)COO-Si] product through the cleavage of the O-H bond, respectively. Glycine/Si(111)-7 x 7 and l-cysteine/Si(111)-7 x 7 can be viewed as model systems for further modification of Si surfaces with biological molecules.     

Surface chemistry of five-membered aromatic ring molecules containing two different heteroatoms on Si(111)-7 x 7

The surface chemistry of three representative aromatic molecules containing two different heteroatoms isoxazole, oxazole, and thiazole on Si(111)-7 x 7 was studied. These molecules exhibit different competition and selectivity for multiple reaction channels with this surface, determined by a combination of molecular electronic and structural factors. Isoxazole is chemically attached to Si(111)-7 x 7 through both dative-bond addition and [4 + 2]-like cycloaddition. Oxazole chemisorbs on Si(111)-7 x 7 through both dative-bond addition and [2 + 2]-like cycloaddition. The kinetically favored [2 + 2]-like cycloadduct at low temperature is thermally converted into the thermodynamically preferred [4 + 2]-like cycloadduct at a temperature higher than 300 K. Thiazole is chemically bound to this surface only through formation of a Si...N dative bond at low temperature. This dative-bonded molecule is thermally converted into a [4 + 2]-like cycloadduct. The reaction channels of the three five-membered aromatic molecules containing two different heteroatoms (isoxazole, oxazole, and thiazole) and of the aromatic molecules containing only one heteroatom (pyridine, pyrrole, furan, and thiophene) are compared and analyzed for a thorough understanding of the reaction mechanisms of various heterocyclic aromatic molecules on this surface. The intrinsic connection between surface reaction mechanism and molecular electronic structure is demonstrated. This includes the distribution of electron density on the molecular ring determined by the geometric arrangement of the heteroatoms, the electronegativity of the heteroatoms, and the electronic contribution of the heteroatoms to formation of aromatic pi conjugation, as well as the molecular polarity.     

金属离子在多孔硅表面和吸附与电镀过程中金属在多孔硅表面的淀积

刚制备的多孔硅与金属盐溶液接触会产生金属离子在多孔硅表面和吸附现象。实验显示这一现象只发生在新鲜的多孔硅表面, 而存放一月以后的样品不具备此性质。文中把这一现象归因于新鲜的多孔硅表面电子的富集, 溶液中金属离子从多孔硅表面获得电子而附着。多孔硅表面电镀金属过程中, 一定电压下电镀电流密度在起始阶段逐渐下降, 可以用一个指数关系式较好地描述, 在本文中有一个唯象模型予以解释。