氮在含氧Mo(100)面上的吸附与反应

 用HREELS, AES, LEED和TDS考察了氮在含氧Mo(100)上的吸附和热脱附. 120 K下氮在含氧Mo(100)上吸附时存在着N—N伸缩振动频率2150和1600 cm-1, 分别对应于线式(γ态)和侧位(α态)两种分子吸附态. 升温引起γ态氮的脱附和α态氮的解离. 其中γ态氮的脱附峰温位于155 K, 遵循一级脱附动力学; 由α态解离生成的N原子占据Mo(100)的四重空位(即β态), 并在高于1?150 K的温度重新化合形成氮而脱附. 120 K时,氮的吸附是无序的; 吸附了氮的表面经1100 K退火后生成了有序的c(2×2)-N表面结构.     

XPS,AFM, ATR and TPD evidence for terraced,dihydrogen terminated, 1×1 (100) silicon

Heating (100) silicon at high temperature (say, higher than 850 °C) in H₂, cooling to 670–700 °C in the same ambient, and quenching to room temperature in N₂ results in environmentally robust, terraced 1 × 1 (100) SiH₂. Evidence for this conclusion is based on angle‐resolved x‐ray photoelectron spectroscopy, atomic force microscopy, infrared absorption spectroscopy in the attenuated total reflection mode, thermal programmed desorption, and reflection high‐energy electron diffraction. Copyright © 2005 John Wiley & Sons, Ltd.     

Bonding and correlation analysis of various Si2CO isomers on the potential energy surface

At various levels of theory, singlet and triplet potential energy surfaces (PESs) of Si₂CO, which has been studied using matrix isolation infrared spectroscopy, are investigated in detail. A total of 30 isomers and 38 interconversion transition states are obtained at the B3LYP/6‐311G(d) level. At the higher CCSD(T)/6‐311+G(2d)//QCISD/6‐311G(2d)+ZPVE level, the global minimum ¹1 (0.0 kcal/mol) corresponds to a three‐membered ring singlet O‐cCSiSi (¹A′). On the singlet PES, the species ¹2 (0.2 kcal/mol) is a bent SiCSiO structure with a ¹A′ electronic state, followed by a three‐membered ring isomer Si‐cCSiO (¹A′) ¹3 (23.1 kcal/mol) and a linear SiCOSi ¹4 (¹Σ⁺) (38.6 kcal/mol). The isomers ¹1, ¹2, ¹3 , and ¹4 possess not only high thermodynamic stabilities, but also high kinetic stabilities. On the triplet PES, two isomers ³1 (³B₂) (18.8 kcal/mol) and ³7 (³A″) (23.3 kcal/mol) also have high thermodynamic and kinetic stabilities. The bonding natures of the relevant species are analyzed. The similarities and differences between C₃O, C₃S, SiC₂O, and SiC₂S are discussed. The present results are also expected to be useful for understanding the initial growing step of the CO‐doped Si vaporization processes. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Si 2p XPS spectrum of the hydrogen‐terminated (100) surface of device‐quality silicon

An experimental study of the Si 2p XPS spectrum at different take‐off angles of atomically flat, hydrogen‐terminated 1 × 1 Si(100) is reported. The observed spectrum can be described accurately by considering three additional contributions to the spectrum of elemental silicon. Each contribution is attributed to a chemical state of silicon on the basis of its chemical shift with respect to elemental silicon and the depth of the region where it was originated. Copyright © 2003 John Wiley & Sons, Ltd.     

Molecular orbital study for Na, Mg, and Al adsorption on the Si (111) surface

We investigated the interactions between the Si(111) surface and the Na, Mg, and Al atoms using cluster model calculations. Calculations were performed at levels of complete-active-space self-consistent-field (CASSCF) and multi-reference singly and doubly excited configuration interaction (MRSDCI) calculations using the model core potential method. Our calculations revealed that the most favorable sites of Na, Mg, and Al adsorption on Si(111) are on top (T₁), bridge (B₂), and 3-fold filled (T₄) sites, respectively. The nature of chemical bonds between these metal atoms and the dangling bonds of the surface Si atoms are found to be essentially covalent.     

Interaction of CO and NO with the spinel CuCr2O4 (100) surface: A DFT study

The characteristics of CO and NO molecules at Cu²⁺ and Cr³⁺ ion sites on the CuCr₂O₄ (100) surface have been studied by first principles calculations based on spin‐polarized density functional theory (DFT). The calculated results show that adsorption energies for X‐down(C, N) adsorption vary in the order: Cu²⁺‐CO>Cr³⁺‐NO≈Cr³⁺‐CO>Cu²⁺‐NO. CO molecules are preferentially adsorbed at Cu sites, whereas NO molecules adsorb favorably at Cu²⁺ and Cr³⁺ ion sites. The C‐O and N‐O stretching frequencies are red‐shifted upon adsorption. Combining the analysis of frontier molecular orbitals and Mulliken charge, for CO and NO X‐down adsorption systems, the 5σ orbitals donate electrons and the 2π^* orbitals obtain back‐donated electrons. Although for NO with O‐down adsorption systems, the NO‐2π^* orbitals obtain back‐donated electrons from substrates without 5σ‐donation. Coadsorption calculations show the CO/NO mixture adsorb selectively at the Cu²⁺ion site but simultaneously at the Cr³⁺ ion site, respectively. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

A Model Calculation for the Isomerization and Decomposition of Chemisorbed HCN on the Si(100)-2×1 Surface

Ab initio molecular orbital and hybrid density functional theory calculations have been performed to study the adsorption, isomerization, and decomposition of HCN on Si(100)-2×1 using the Si₉H₁₂ cluster model of the surface. The results of our calculations indicate that the HCN can adsorb molecularly without a barrier onto the surface with both end-on (LM1) and side-on (LM2) positions. LM1 can isomerize to LM2 with a small barrier of 8 kcal/mol. The isomerization of LM2 by H-migration from C to the N atom, requires 76 kcal/mol activation energy (c.f. 47.5 kcal/mol in the gas phase) because of surface stabilization. Both HCN(a) and HNC(a) end-on adsorbates were found to dissociate readily, as concluded in our earlier experiment, to produce H and CN adspecies. The computed vibrational frequencies of HCN, CN, and also HCNH adspecies agree reasonably well with those observed experimentally. HCNH was found to be stable, with either the C or the N attaching to the surface.     

Adsorption and migration growth of the Ce,O, and F adatoms on the CeO2 (111) surface: A density functional theory study

In order to investigate the microscopic behavior of the crystal surface growth of the fluorinated cerium dioxide polishing powder, the adsorption and migration of the Ce, O, and F atoms on the CeO₂ (111) surface were studied by using density functional theory with Hubbard correction +U. The adsorption energies of three single atoms at five high-symmetry sites and the migration activation energies along the migration pathway on the CeO₂ (111) surface were calculated. Results show that the most stable adsorption sites of the Ce, O, and F atoms were the O_h, Ce_bri, and Ce_t sites, respectively. The Ce atom migrated from the O_h to the O_t site. The O atom migrated from the Ce_bri to the O_bri site. The F atom migrated from the Ce_t to the O_h site. The migration activation energies of the Ce, O, and F atoms along the migration pathways were 1.526, 0.597, and 0.263 eV, respectively. The F adatom does not change the spatial configuration of the Ce and the O atoms. When the O vacancy occurs on the CeO₂ (111) surface, the F adatom can make up for the O vacancy defect.     

Theoretical study on AlnO2 (n = 1–10) clusters and O2 adsorption on the Al(111) surface

The structural properties of neutral and ionic Al_nO₂ (n = 1–10) clusters have been systematically investigated using the density functional method B3LYP with a standard 6‐311+G(d) basis set. The calculated results show that in the Al_nO, Al_nO₂, and Al_nO (n ≥ 3) clusters, O atoms tend to penetrate into the aluminum clusters with some Al atoms moving outward. The binding energies and natural charges populations indicate that the oxygen‐etching is generally stronger in the order Al < Al_n < Al for n < 3, and Al > Al_n > Al for n ≥ 3. To further understand the mechanism of interaction between Al and O₂, the adsorption of O₂ on the Al(111) surface was studied using the density functional theory with plane wave pseudopotential method. The calculated results are consistent with the experimental observation that the O₂ molecule would dissociate on the Al(111) surface and be adsorbed in adjacent hollow sites, forming a local structure of Al₃O–Al₃O. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

The adsorption of CO2, H2CO3, HCO3− and CO32− on Cu2O (111) surface: First‐principles study

The adsorption of CO₂, and its derivatives, H₂CO₃, HCO, and CO, on Cu₂O (111) surface has been investigated by first‐principles calculations based on the density functional theory at B3LYP hybrid functional level. The Cu₂O (111) surface has been modeled using an embedded cluster method,in which the quantum clusters plus some ab initio ion model potentials were inserted in an array of point charges. On the surface, H₂CO₃ was dissociated into an H⁺ and an HCO ion. Among the CO₂ species, HCO was the only activated species on the surface. The results suggest that the reduction of CO₂ on Cu₂O (111) surface can start from the form of HCO. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

5-(Pyridylmethylidene)-substituted 2-thiohydantoins and their complexes with CuII, NiII, and CoII: Synthesis, electrochemical study, and adsorption on the cystamine-modified gold surface

A series of Cu^II, Ni^II, and Co^II complexes with 5-(pyridylmethylidene)-substituted 2-thiohydantoins (L) were synthesized by the reactions of the corresponding organic ligands with MCl₂·nH₂O. The resulting complexes have the composition LMCl₂ (M = Cu or Ni) or L₂MCl₂ (M = Co). The reactions with N(3)-unsubstituted thiohydantoins afford complexes containing four-membered metallacycles, in which the metal ion is coordinated by the S and N(3) atoms of the thiohydantoin ligand. The reactions of N(3)-substituted thiohydantoins give complexes in which the S and N(1) atoms are involved in coordination. Study by IR spectroscopy demonstrated that the pyridine nitrogen atom is not involved in coordination. Based on the results of electrochemical study of the ligands and complexes by cyclic voltammetry and calculation of their frontier orbitals by the PM3(tm) method, the mechanism of oxidation and reduction of these compounds was proposed. In the first reduction and oxidation steps, the metal atom in the copper and nickel complexes remains, apparently, intact, and these processes occur with the involvement of the ligand fragments, viz., the coordinated thiohydantoin ligand and chloride anion, respectively. In the cobalt complexes, the first reduction step occurs at the ligand; the first oxidation state, at the metal atom. Measurements of the contact angle of aqueous wetting and electrochemical study demonstrated that carboxy-containing 2-thiohydantoins and their complexes can be adsorbed on the cystamine-modified gold surface. The structures of the complexes on the surface differ from the structures of these complexes in solution. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 978–990, June, 2006.     

Vibrational spectroscopy for glycine adsorbed on silicon clusters: Harmonic and anharmonic calculations for models of the Si(1 0 0)-2 × 1 surface

The vibrational spectroscopy of a glycine molecule adsorbed on a silicon surface is studied computationally, using different clusters as models for the surface. Harmonic frequencies are computed using density functional theory (DFT) with the B3LYP functional. Anharmonic frequency calculations are carried out using vibrational self-consistent field (VSCF) algorithms on an improved PM3 potential energy surface. The results are compared with experiments on Glycine@Si(1 0 0)-2 × 1.

The main findings are: (1) Agreement of the computed frequencies with experiment improves with cluster size. (2) The anharmonic calculations are generally in better agreement with experiment than the harmonic ones. The improvements due to anharmonicity are most significant for hydrogenic stretching. (3) An important part of the anharmonic effects is due to anharmonic coupling between different normal modes of the system. (4) The anharmonic coupling between glycine vibrational modes is much larger than the anharmonic coupling between glycine and “phonon” (cluster) modes.

Implications of the results for surface vibrational spectroscopy are discussed.