Surface Chemistry and Photochemistry of Cyclohexane on Rutile TiO_(2)(110)

Cyclohexane is a high-valued chemical receivingsignificant interest in liquid hydrogen storage technology.TiO_(2)-based catalysts show high performance in the photocatalytic dehydrogenation of cyclohexane under mild conditions,but the detailed reaction mechanism is not well understood.With the surface science approaches,we have studied the adsorption and surface chemistry of cyclohexane on rutile TiO_(2)(110).The thermal desorption spectroscopy and X-ray photoelectron spectroscopy results both demonstrate the molecular adsorption of cyclohexane on rutile TiO_(2)(110).Upon the UV Hg light irradiation,photodesorption of cyclohexane occurs from both the chemisorbed monolayer and the multilayer.No decomposition nor dehydrogenation of cyclohexane occurs on rutile TiO_(2)(110).These results deepen the fundamental understanding of the surface chemistry of cyclohexane on the TiO_(2)surface.

Growth mechanism of palladium clusters on rutile TiO_2 (110) surface

Oxide-supported transition metal systems have been the subject of enormous interest due to the improvement of catalytic properties relative to the separate metal.Thus in this paper,we embark on a systematic study for Pd n （n=1-5） clusters adsorbed on TiO2 （110） surface based on DFT-GGA calculations utilizing periodic supercell models.A single Pd adatom on the defect-free surface prefers to adsorb at a hollow site bridging a protruded oxygen and a five-fold titanium atom along the [110] direction,while Pd dimer is located on the channels with the Pd-Pd bond parallel to the surface.According to the transition states （TSs） search,the adsorbed Pd trimer tends to triangular growth mode,rather than linear mode,while the Pd4 and Pd5 clusters prefer three-dimensional （3D） models.However,the oxygen vacancy has almost no influence on the promotion of Pd n cluster nucleation.Additionally,of particular significance is that the Pd-TiO2 interaction is the main driving force at the beginning of Pd nucleation,whereas the Pd-Pd interaction gets down to control the growth process of Pd cluster as the cluster gets larger.It is hoped that our theoretical study would shed light on further designing high-performance TiO2 supported Pd-based catalysts.

Theoretical Study of Cr Doped into TiO_2(110) Surface

The Cr doped into TiO2(110) surface has been studied systematically by using periodic DFT/B3LYP method with slab model. It is found that doping Cr into perfect TiO2 (110) surface can reduce the value of band-gap from 3.13 to 1.16 eV, and then photocatalysis reaction may be achieved in visual light area. The results are in good agreement with the experiments.

In-situ decoration of metallic Bi on BiOBr with exposed(110)facets and surface oxygen vacancy for enhanced solar light photocatalytic degradation of gaseous n-hexane

Photocatalytic degradation of gaseous pollutants on Bi-based semiconductors under solar lightirradiation has attracted significant attention.However,their application in gaseous straight-chainalkane purification is still rare.Here,a series of Bi/BiOBr composites were solvothermally synthe-sized and applied in solar-light-driven photocatalytic degradation of gaseous n-hexane.The charac-terization results revealed that both increasing number of functional groups of alcohol solvent(from methanol and ethylene glycol to glycerol)and solvothermal temperature(from 160 and 180to 200℃)facilitated the in-situ formation of metallic Bi nanospheres on BiOBr nanoplates withexposed(110)facets.Meanwhile,chemical bonding between Bi and BiOBr was observed on theseexposed facets that resulted in the formation of surface oxygen vacancy.Furthermore,the synergis-tic effect of optimum surface oxygen vacancy on exposed(110)facets led to a high visible light re-sponse,narrow band gap,great photocurrent,low recombination rate of the charge carriers,andstrong·O2-and h*formation,all of which resulted in the highest removal efficiency of 97.4%within120 min of 15 ppmv of n-hexane on Bi/BiOBr.Our findings efficiently broaden the application ofBi-based photocatalysis technology in the purification of gaseous straight-chain pollutants emittedby the petrochemical industry.

First-principles study of TiC(110) surface

The structural and electronic properties of TiC（110） surfaces are calculated using the first-principles total-energy plane-wave pseudopotential method based on density functional theory. The calculated results of structural relaxation and surface energy for TiC（110） slab indicate that slab with 7 layers shows bulk-like characteristic interiors, and the changes of slab occur on the outmost three layers, which shows that the relaxation only influences the top three layers. Meanwhile, the strong Ti—C covalent bonding can be found in the distribution of charge density on the （100） plane. The interlayer Ti—C chemical bonds are reinforced and the outermost interlayer distance is reduced as a result of the charge depletion in the vacuum and the charge accumulations in the interlayer region between the first and second layers. The surface energy of TiC（110） is calculated to be 3.53 J/m2.

Evidence for Multiple Underlying Fermi Surface and Isotropic Energy Gap in the Cuprate Parent Compound Ca2CuO2Cl2

The parent compounds of the high-temperature cuprate superconductors are Mott insulators.It has been generally agreed that understanding the physics of the doped Mott insulators is essential to understanding the mechanism of high temperature superconductivity.A natural starting point is to elucidate the basic electronic structure of the parent compound.Here we report comprehensive high resolution angle-resolved photoemission measurements on Ca_2CuO_2Cl_2,a Mott insulator and a prototypical parent compound of the cuprates.Multiple underl.ying Fermi surface sheets are revealed for the first time.The high energy waterfall-like band dispersions exhibit different behaviors near the nodal and antinodal regions.Two distinct energy scales are identified：a d-wave-like low energy peak dispersion and a nearly isotropic lower Hubbard band gap.These observations provide new information of the electronic structure of the cuprate parent compound,which is important for understanding the anomalous physical properties and superconductivity mechanism of the high temperature cuprate superconductors.

Co-adsorption of O_2 and H_2O on α-uranium(110) surface:A density functional theory study

First-principles calculations based on density functional theory corrected by Hubbard parameter U （DFT＋U） are applied to the study on the co-adsorption of O2 and H2O molecules to a-U（110） surface. The calculation results show that DFT＋U method with Ueff = 1.5 eV can yield the experimental results of lattice constant and elastic modulus of a-uranium bulk well. Of all 7 low index surfaces of a-uranium, the （001） surface is the most stable with lowest surface energy while the （110） surface possesses the strongest activity with the highest surface energy. The adsorptions of O2 and H2O molecules are investigated separated. The O2 dissociates spontaneously in all initial configurations. For the adsorption of H2O molecule, both molecular and dissociative adsorptionsoccur. Through calculations of co-adsorption, it can be confirmed that the inhibition effect of O2 on the corrosion of uranium by water vapor originates from the preferential adsorption mechanism, while the consumption of H atoms by O atoms exerted little influence on the corrosion of uranium.

Theoretical Study on the Structural and Electronic Properties of the Reduced SnO_2 (110) Surface

The reduced SnO2（110） surface has been investigated by using first-principles method with a slab model. By examining the vacancy formation energy of three kinds of reduced SnO2（110） surfaces, the most energetically favorable defect surface is confirmed to be the surface with the coexistence of bridging and in-plane oxygen vacancies, which is different with the traditional model by only removing bridging oxygen. The results of band structure calculations indicate that the electronic structure of this defect surface is similar to the SnO surface.

Molecular dynamics simulation of surface melting behaviours of the V(110) plane

The modified analytic embedded-atom method and molecular dynamics simulations are applied to the investigation of the surface premelting and melting behaviours of the V（110） plane by calculating the interlayer relaxation, the layer structure factor and atomic snapshots in this paper. The results obtained indicate that the premelting phenomenon occurs on the V（110） surface at about 1800K and then a liquid-like layer, which approximately keeps the same thickness up to 2020K, emerges on it. We discover that the temperature 2020K the V（110） surface starts to melt and is in a completely disordered state at the temperature of 2140K under the melting point for the bulk vanadium.

Dependence of Atomic-Scale Si(110) Surface Roughness on Hydrogen Introduction Temperature after High-Temperature Ar Annealing

The atomic-scale surface roughness of Si(110) reconstructed via high-temperature Ar annealing is immediately increased by non uniform accidental oxidation during the unloading process (called reflow oxidation) during high-temperature Ar annealing. In particular, for a reconstructed Si(110) surface, characteristic line-shaped oxidation occurs at preferential oxidation sites appearing in pentagonal pairs in the directions of Si[-112] and/or [-11-2]. We previously reported that the roughness increase of reconstructed Si(110) due to reflow oxidation can be restrained by replacing Ar gas with H2 gas at 1000&#176C during the cooling to 100&#176C after high-temperature Ar annealing. It was speculated that preferential oxidation sites on reconstructed Si(110) were eliminated by H2 gas etching and hydrogen termination of dangling bonds. Thus, it is necessary to investigate the effect of H2 gas etching and hydrogen termination behavior on the reconstructed Si(110) surface structure. In this study, we evaluated in detail the relationship between the temperature at which the H2 gas replaces the Ar in high-temperature Ar annealing and the reconstructed Si(110) surface structure. The maximum height of the roughness on the reconstructed surface was the same as if Ar gas was used when the H2 gas introduction temperature was 200&#176C, although the amount of reflow oxidation was decreased to 70% by hydrogen termination. Furthermore, line-shaped oxidation still occurs when H2 gas replaces Ar at this low temperature. Therefore, we conclude that oxidation is caused by slight Si etching at low temperatures, and thus the preferential oxidation sites on the reconstructed structure must be eliminated by hydrogen etching in order to form an atomically smooth Si(110) surface.

Density Functional Theory Study of C_2H_x(x=4～6) Adsorption on the Fe(110) Surface

The density functional theory（DFT） and self-consistent periodic calculation were used to investigate the C2Hx（x = 4～6） species adsorption on the Fe（110） surface. The adsorption energy and equilibrium geometry of the species C2Hx（x = 4～6） on four possible sites（top,hcp,SB and LB） on the Fe（110） surface were predicted and compared. Mulliken charges and density of states analysis of the most stable site have been discussed. It is found that the species of C2H6 and C2H5 are adsorbed strongly on the Fe（110） surface with calculated adsorption energy of -80.24 and -178.89 kJ·mol^-1 at the Fe-LB（long-bridge） ,respectively. However,the C2H4 is adsorbed strongly on the Fe（110） surface with calculated adsorption energies of -114.96 kJ·mol^-1 at the top. The results indicate that the charge transferring process can be completed by chemisorption between Fe（110） surface and the species. Moreover,the chemical bands can be formed by chemisorptions between the Fe（110） surface and the species,too.

GEOMETRIC STRUCTURE OF ETHYLENOXIDE ADSORBED ON Cu(110) SURFACE

The binding energies of ethylene oxide (Et-O) adsorbed on Cu(110) surface for different adsorption sites and orientations are calculated with an atom superposition and electron delocalization molecular orbital (ASED-MO) using cluster models. It shows that the top site of Cu(110) surface is preferable for Et-O adsorption and the orientation of C-C bond of Et-O is parallel to the [110] direction of the substratc. The distance of an oxygen of Et-O to the Cu atom is approximately 1.5817(?). It is different from the supposition of C. Benndorf et al., in which the oxygen was proposed on the short bridge site with C-C bond orientating to [110] direction of Cu(110)

THE PREPARATION OF TITANIUM OXIDE OVERLAYER ON Fe(110) FOR SURFACE SCIENCE STUDIES

The preparation, characterization and properties of titania overlayer on Fe(110) substrate is hereby reported. The TiO_X overlayer was found to form in a layer-by-layer mode with a suboxide of titanium in the form of TiO migrating into the Fe substrate and Fe migrating into the deposited layer of TiO_X simultaneously during the deposition.

First-Principles Study of Pd Single-Atom Catalysis to Hydrogen Desorption Reactions on MgH2（110） Surface

MgH2 is a promising and popular hydrogen storage material.In this work,the hydrogen desorption reactions of a single Pd atom adsorbed MgH2(110)surface are investigated by using first-principles density functional theory calculations.We find that a single Pd atom adsorbed on the MgH2(110)surface can significantly lower the energy barrier of the hydrogen desorption reactions from 1.802 eV for pure MgH2(110)surface to 1.154 eV for Pd adsorbed MgH2(110)surface,indicating a strong Pd single-atom catalytic effect on the hydrogen desorption reactions.Furthermore,the Pd single-atom catalysis significantly reduces the hydrogen desorption temperature from 573K to 367K,which makes the hydrogen desorption reactions occur more easily and quickly on the MgH2(110)surface.We also discuss the microscopic process of the hydrogen desorption reactions through the reverse process of hydrogen spillover mechanism on the MgH2(110)surface.This study shows that Pd/MgH2 thin films can be used as good hydrogen storage materials in future experiments.

Effects of Surface Defects on Adsorption of CO and Methyl Groups on Rutile TiO_(2)(110)

The interaction of reactants with catalysts has always been an important subject for catalytic reactions.As a promising catalyst with versatile applications,titania has been intensively studied for decades.In this work we have investigated the role of bridge bonded oxygen vacancy(O_(v))in methyl groups and carbon monoxide(CO)adsorption on rutile TiO_(2)(110)(R-TiO_(2)(110))with the temperature programmed desorption technique.The results show a clear different tendency of the desorption of methyl groups adsorbed on bridge bonded oxygen(O_(b)),and CO molecules on the five coordinate Ti^(4+)sites(Ti_(5c))as the Ovconcentration changes,suggesting that the surface defects may have crucial influence on the absorption of species on different sites of R-TiO_(2)(110).

The Ab Initio Studies of NO Chemisorption on TiO_2(110) Surface

The studies of NO chemisorption on TiO2(110) surface are the base of research to NO decomposed to N2O on TiO2 surface. In this paper, 12 kinds of possible models of NO adsorbed on TiO2 perfect and defect surface were calculated by use of ab initio cluster method. We carried out optimization of the geometry, calculation of the chemisorption energy and analysis of the Mulliken population to those adsorption models. According to the calculation results, it can be got that the adsorbed decomposition of NO on defect surface is more advantageous and M6 and M12 are the important models to NO chemisorption and decomposition on TiO2 surface.

O_3分子在CuO(110)面吸附的密度泛函理论研究

应用密度泛函理论研究了O3分子在2×1CuO(110)面(S1)和掺杂一个Fe原子的2×1CuO(110)面(S2)的吸附过程和电子特性.计算结果表明,O3分子与表面S1和S2有很强的相互作用,O3分子在表面吸附反应的活化能和反应能均为负值,反应很容易进行.态密度和电荷密度分析结果进一步证实了O3分子在S1上吸附是桥位化学吸附,形成表面臭氧化物,在S2上吸附分解为1个被吸附的表面氧原子和1个自由氧分子.电子特性分析表明,O3分子与S1和S2相互作用的本质是O3分子的价轨道2p与CuO(110)表面杂化轨道的相互作用.

CO和NO在CuO及CU_2O(110)表面吸附选择规律研究

采用离散变分Xα方法分别计算了CO和NO以C（或N）端顶位吸附在CuO（110）及Cu2O（110）表面上的基态势能曲线，结果表明：CO在Cu2O表面上的吸附强，而在CuO表面上的吸附弱；NO则在CuO表面上吸附强，在Cu2O表面上吸附弱．它们的吸附能的大小顺序为：CuO－NO＞Cu2O－CO＞Cu2O－NO＞CuO－CO．对于CuO－NO（或CO）吸附体系，主要是Cu的3d轨道与吸附分子的2π轨道间的相互作用；对于Cu2O－CO（或NO）吸附体系，办主要是吸附质分子的5σ及2π分子轨道与其顶位Cu1的4s及4p轨道和侧位Cu2的3d轨道相互作用．本文通过吸附势能曲线、态密度分析、成键分析及电荷转移量和方向等方面对实验现象做了合理的解释．

Impact of Surface Passivation on the Electronic Structure and Optical Properties of the Si1-xGex Nanowires

The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. The results show that surface passivation influences the characteristics of electronic band structures significantly： the band gap widths and types （direct or indirect） of the Si1-xGe, NWs with different terminators show complex and robust variations, and the effective masses of the electrons in the NWs can be modulated dramatically by the terminators. The study of optical absorption shows that the main peaks of the parallel polarization component of Si1-x Gex NWs passivated with the functional groups exhibit prominent changes both in height and position, and are red-shifted with respect to those of corresponding pure Si NWs, indicating the importance of both the terminators and Ge concentrations. Our results demonstrate that the electronic and optical properties of Si1-xGex NWs can be tuned by utilizing selected functional groups as well as particular Ge concentrations for customizing purposes.

Yield surfaces of fcc crystals with crystallographic slip and mechanical twinning

The mixed yield surfaces of fcc single crystals for slip on{111}〈110〉and mechanical twinning on{111}〈112〉systems have been derived when their critical resolved shear stresses are equal.It has been found that there are 259 stress states that can be classified into 21 groups according to the crystal symmetry.Each group activates 5,6 or 8 slip or/and twinning systems depending on crystallographically non equivalent slip or/and twinning systems groups.Among all those stress states,3 groups activate 8 systems,including 21 stress states;9 groups activate 5 systems,including 70 ones;the remaining 9 groups activate 5 systems,including 168 ones.