BN(110)弛豫表面电子结构的理论研究

本文利用形式散射理论的格林函数方法 ,采用考虑最紧邻的sp3s 模型描述体带 ,计算了BN(110 )面的电子结构 .分别给出了理想表面和驰豫表面的投影带结构和波矢分辨的层态密度 ,并进行了较详细的讨论 .结果表明 :BN(110 )面的电子结构与大多数Ⅲ Ⅴ族和Ⅱ Ⅵ族半导体的 (110 )面的电子结构定性上是类似的 .但在各表面态的能级位置、色散特性和轨道特性等方面均有较大的差别 .

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.

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).

Ga N,Al N和 BN(110 )表面反常弛豫的电子结构计算

在紧束缚模型框架下采用形式散射理论方法计算了具有闪锌矿结构的化合物半导体 Ga N,Al N和 BN(110 )反常弛豫表面的表面电子结构 ,讨论了表面弛豫对表面电子结构的影响 ,并将结果同 Ga As(110 )表面的表面电子结构作了比较 .

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.

TiO_2(110)面的弛豫结构及吸附O_2的密度泛函研究

采用DFT/B3LYP方法研究了TiO2 ( 110 )的完整和氧缺陷表面的弛豫构型 ,并对O2 在氧缺陷表面的三种可能吸附构型进行了优化 ,计算了它们的吸附能、振动频率和重叠布居 .分析并预测了吸附后可能产生的物种 .本文的计算结果与XPS 。

具有{110}面的锐钛矿TiO_(2)单晶的可控合成与光催化性能

采用水热法合成了同时具有最高表面能{110}和{001}晶面的锐钛矿TiO2单晶,通过X射线衍射、扫描电镜和激光拉曼光谱等手段对样品的形貌和结构进行了表征,并系统考察了过氧化氢、氢氟酸和反应温度等关键因素对所得样品中{110}面比例的影响,实现了持续提高{110}面比例的过程.在光催化降解亚甲基蓝反应中,具有{110}面的锐钛矿TiO_(2)单晶的光催化活性显著高于无{110}面的单晶.

Mn掺杂ZnS(110)表面的电子结构和磁性

采用基于密度泛函理论的第一性原理方法,研究Mn掺杂ZnS(110)表面的电子结构和磁性.计算分析不同掺杂组态的几何参数、形成能、磁矩、电子态密度以及电荷密度.结果表明:单个Mn原子掺杂,替位于表面第二层的Zn原子时体系形成能最低,说明该层是最稳定的掺杂位置.对于两个Mn原子的掺杂,当Mn与Mn之间呈反铁磁耦合时体系最稳定.体系的总磁矩和自由Mn原子的磁矩差别很小,但是Mn原子的局域磁矩却依赖于Mn原子的3d态和近邻S原子的3p态的杂化作用,即受周围S原子环境的变化影响较大.此外,分析电荷密度图得出Mn原子替换Zn原子后与S原子形成了更强的共价键.

AlN粉末特性对AlN-BN复合陶瓷致密化的影响

以比表面积分别为4．26和17．4m^2／g两种A1N粉末为原料，添加5％Y2O3作为烧结助剂制备AIN15BN陶瓷（质量分数，％），研究了A1N粉末特性对复合陶瓷致密化过程的影响。结果表明，A1N粉末比表面积对复合陶瓷致密化有重要影响，比表面积高的AIN粉末所制备的复合陶瓷致密化过程主要发生在1500-1650℃，1650℃烧结3h后，复合材料的相对密度达95．6％，继续升高温度，对材料的密度影响不大；而低比表面积的A1N粉末所制备的复合陶瓷的致密化过程主要发生在1650～1850℃，1850℃烧结3h，复合陶瓷的相对密度为86．4％。即高比表面积的AIN粉末有利于获得相对密度高的A1N—BN复合材料。