Density functional theory calculation of platinum surface segregation energy in Pt3Ni (111) surface doped with a third transition metal

We have used density functional theory method to calculate the Pt surface segregation energy in the Pt₃Ni (111) surface doped with a third transition metal M and thus investigated the influence of component M on the extent of Pt segregation to the outermost layer of these Pt₃Ni/M (111) surface. As a third component in the Pt₃Ni/M (111) surface, V, Fe, Co, Mo, Tc, Ru, W, Re, Os, and Ir were predicted to lead to even more negative Pt surface segregation energies than that in the based Pt₃Ni (111) surface; Ti, Cr, Mn, Cu, Zr, Nb, Rh, Hf, and Ta would still retain the preference of Pt segregation to the surface but with less extent than the replaced Ni, while Pd, Ag, and Au would completely suppress the Pt segregation to the Pt₃Ni/M (111) surfaces. Furthermore, we examined the relation between the Pt surface segregation energy in the Pt₃Ni/M (111) surfaces and the material properties (lattice parameter, heat of solution, and Pt surface segregation energy) of binary alloys Pt₃M. It was found that the surface energy effect, strain effect, and heat of solution effect induced by the doped element M would collectively affect the Pt surface segregation energy in the Pt₃Ni/M (111) surfaces.     

替位杂质对贵金属(111)表面稳定性影响的分子动力学研究

采用嵌入原子方法的原子间相互作用势，通过分子动力学方法研究了过渡族金属Cu，Ag，Au，Ni，Pd，Pt(111)表面的相互替位掺杂对表面稳定性的影响，计算了替位掺杂体系的表面能与表面空位形成能，探讨了影响表面稳定性的因素及其变化规律. 计算表明：替位杂质对表面能变化的影响主要是替位杂质的凝聚能和原子半径，而影响空位形成能变化的原因除凝聚能和原子半径外，合金溶解热具有重要的作用. 此外，通过替位杂质导致的体系表面能变化对合金体系的偏析行为进行了预测，理论预测与实验结果符合很好. 关键词： 替位杂质 贵金属 表面能 表面空位形成能     

A combined XPS/AES study of Cu segregation to the high and low index surfaces of a Cu-Ni alloy

Quantitative information was obtained regarding the equilibrium segregation of Cu to the high index surfaces (cut 5° off the (100) plane in the [001] and [011] directions) and low index surfaces ((100), (111) and (110)) of a Cu: Ni, 5: 95% alloy crystal. Data regarding segregation to the (111) surface of a Cu: Ni, 50: 50% alloy crystal was also obtained. Equilibrium surfaces were obtained by careful annealing in the temperature range 850–920 K to avoid Cu loss by evaporation. The surface composition profile was calculated using data from the combination of the X-ray Photo-electron Spectroscopy and Auger Electron Spectroscopy techniques. Using these techniques, a wide range of electron kinetic energies and associated electron escape depths can be probed, yielding information about the topmost layer concentration and about the concentration profile into the bulk. Extensive Cu segregation was observed for the 5% and 50% Cu alloys. Topmost layer compositions of 85–100% Cu were found for both the high and low index surfaces of the 5% Cu alloy. In the next two or three atomic layers the composition was found to drop swiftly to near bulk Cu levels. For atomic layers deeper than this, some experimental evidence suggested a rise in Cu composition over three or four layers to 8–17% Cu before bulk levels were finally regained. For the 50% Cu alloy sample, a topmost layer composition was found of 95–100% Cu. Bulk levels of Cu were regained in about four atomic layers. These results are discussed in relation to other theoretical and experimental studies of segregation in these Cu-Ni alloys. The significance of the measured composition in relation to an equilibrium surface is also considered.     

Sulfur at nickel-alumina interfaces: Molecular orbital theory

An atom superposition and electron delocalization molecular orbital study has been made of surface atomic layer relaxations in Ni(110) and Ni(111), the binding of p(2 × 2)S to Ni(111), S on Ni(100), and the binding of A1₂O₃ to clean Ni(111) and p(2 × 2)S covered Ni(111). Surface Ni atom relaxations for three-layer thick cluster models are calculated to be close to the experimental results and S heights of 1.68 Å on Ni(111) and 1.40 Å on Ni(100) are also in close agreement with experimental determinations, which indicates cluster models are suitable for determining surface properties. Al³⁺ in the basal plane of Al₂O₃ are predicted to support a low-lying surface state band in the O2p---A13s3p band gap. These orbitals are found to participate in strong Al---Ni bonds and Al---S bonds of intermediate strength at the interfaces with Ni(111) and p(2 × 2) S-covered Ni(111). Should such bonds form, they are expected to be too few in number to lead to strong adhesion. The strongest Al₂O₃---Ni bonding is predicted to occur when the Ni surface is oxidized. In this case, though Ni---O bonds are relatively weak, their number is high. It is concluded from the structure models that are studied that the segregation of impurity S in Ni to the interface will markedly decrease the adhesion of protective Al₂O₃ films that grow on NiAl based alloys.     

杂质对吸附系统O/RhxPt1-x衬底合金(110)表面偏析的影响

构造了考虑吸附与偏析相互作用情况下无序二元合金Rh_xPt_1-x(110)吸附氧表面的原子集团模型,其中O的覆盖度为0.5;构造了考虑杂质Ni,Cu,W对合金可能产生影响的吸附表面原子集团模型,杂质的掺入采用替位式.应用recursion方法计算了合金表面的环境敏感镶嵌能和电子结构.环境敏感镶嵌能计算表明杂质Ni,Ｃu和Ｗ均使O吸附Rh_xPt_1-x(110)合金表面 关键词： 化学吸附 表面偏析 recursion方法 态密度     

Adsorption of SH and OH and coadsorption of S, O and H on Ni(111)

The adsorption of SH and OH radicals on Ni(111) is treated using an ab initio embedding theory. The Ni(111) surface is modeled as a three-layer, 28-atom cluster with the Ni atoms fixed at bulk lattice sites. The Ni(111) energy surface is very flat for SH adsorption if the H tilt angle is allowed to vary. At both atop and bridge sites, the S---H axis is tilted away from the surface normal by 70°, resulting in the sulfur atom being sp³-hybridized and the adsorption energy being 59 kcal mol⁻¹. For SH at the three-fold site, the S---H axis is normal to the surface, the sulfur is sp-hybridized, and the adsorption energy is 58 kcal mol⁻¹. OH is preferentially adsorbed at the three-fold site. The calculated adsorption energy is 90 kcal mol⁻¹ and the O---H axis is perpendicular to the surface. OH adsorption at the atop and bridge sites is 16 and 5 kcal mol⁻¹ less stable than at the three-fold site, respectively. Atomic H, O and S are preferentially adsorbed at the three-fold site. The calculated adsorption energies are 62, 92 and 87 kcal mol⁻¹, for H, O and S, respectively. The calculated adsorbate---Ni bond distances of 1.86 Å for H, 1.86 Å for O and 2.29 Å for S are in good agreement with experimental data. SH and OH bonding to the surface involves a combination of ionic and covalent contributions and substantial mixing with the Ni 3d orbitals. Dipole-moment calculations indicate strong ionic bonding for the atomic O/Ni system and ionic plus covalent character for the atomic S/Ni interactions. Adsorption of S and O at the three-fold site blocks H adsorption at the nearby surface. Moving H away from the S or O adatom reduces the repulsion. The dissociation of SH_ad → S_ad + H_ad is calculated to be exothermic by 5 kcal mol⁻¹ and OH_ad → O_ad + H_ad to be endothermic by 30 kcal mol⁻¹ for infinite separation between S, O and H.     

Corrosion related properties of iron(100) surface in liquid lead and bismuth environments:A first-principles study

The corrosion of steels in liquid metal lead （Pb） and bismuth （Bi） is a critical challenge in the development of accel-erator driven systems （ADS）. Using a first-principles method with a slab model, we theoretically investigate the interaction between the Pb （Bi） atom and the iron （Fe） （100） surface to assess the fundamental corrosion properties. Our investigation demonstrates that both Pb and Bi atoms favorably adsorb on the （100） surface. Such an adsorption decreases the energy required for the dissociation of an Fe atom from the surface, enhancing the dissolution tendency significantly. The seg- regation of six common alloying elements （Cr, A1, Mn, Ni, Nb, and Si） to the surface and their impacts on the corrosion properties are also considered. The present results reveal that Si seems to have a relatively good performance to stabilize the surface and alleviate the dissolving trend caused by Pb and Bi.     

Surface states on random substitutional alloys

We present first principles KKRCPA calculations of the angle-resolved photoemission spectra from CuNi single crystal surfaces. Two surface states have been identified; a Shockley-type state on the (111) surface, and a Tamm-type state on the (100) surface. We determine their dispersion, and investigate their sensitivity to the form of the surface potential. The disorder broadening and the influence of surface segregation are discussed quantitatively.     

The effect of chloride ions on the corroded surface layer of 00Cr22Ni5Mo3N duplex stainless steel under cavitation

The effects of Cl⁻ on the corroded surface layer of 00Cr22Ni5Mo3N duplex stainless steel under cavitation in chloride solutions were investigated using nanoindentation in conjunction with XRD and XPS. The results demonstrate that Cl⁻ had a strong effect on the nano-mechanical properties of the corroded surface layer under cavitation, and there was a threshold Cl⁻ concentration. Furthermore, a close relationship between the nano-mechanical properties and the cavitation corrosion resistance of 00Cr22Ni5Mo3N duplex stainless steel was observed. The degradation of the nano-mechanical properties of the corroded surface layer was accelerated by the synergistic effect between cavitation erosion and corrosion. A key factor was the adsorption of Cl⁻, which caused a preferential dissolution of the ferrous oxides in the passive film layer on the corroded surface layer. Cavitation further promoted the preferential dissolution of the ferrous oxides in the passive film layer. Simultaneously, cavitation accelerated the erosion of the ferrite in the corroded surface layer, resulting in the degradation of the nano-mechanical properties of the corroded surface layer on 00Cr22Ni5Mo3N duplex stainless steel under cavitation.     

Coordination-number dependence of magnetic hyperfine fields at (111)Cd on Ni surfaces

Ferromagnetic Ni surfaces were investigated on an atomic scale using the perturbed angular correlation spectroscopy probe (111)Cd. A comprehensive set of data for magnetic hyperfine fields (B(hf)) at various probe sites is presented. A field variation from -7 T in Ni bulk to the surprisingly large value of 16 T at the adatom position on Ni(111) is observed. A continuous nonlinear dependence is found, correlating the experimental B(hf) values with the number of their nearest Ni neighbors. The data are discussed on the basis of recent calculations on B(hf) values at sp-element impurities on ferromagnetic surfaces.     

A first principle study on the magnetic properties of Cu2O surfaces

Spin-polarized density functional theory calculations were performed to investigate the magnetism of bulk and Cu₂O surfaces. It is found that bulk Cu₂O, Cu/O-terminated Cu₂O(111) and (110) surfaces have no magnetic moment, while, the O-terminated Cu₂O(100) and polar O-terminated Cu₂O(111) surfaces have magnetism. For low index surfaces with cation and anion vacancy, we only found that the Cu vacancy on the Cu₂O(110) Cu/O-terminated surface can induce magnetism. For atomic and molecular oxygen adsorption on the low index surfaces, we found that atomic and molecular oxygen adsorption on the Cu-terminated Cu₂O(110) surface is much stronger than on the Cu/O-terminated Cu₂O(111) and Cu-terminated Cu₂O(100) surfaces. More interesting, O and O₂ adsorption on the surface of Cu/O terminated Cu₂O(111) and O₂ adsorption on the Cu-terminated Cu₂O(110) surface can induce weak ferromagnetism. In addition, we analysis origin of Cu₂O surfaces with magnetism from density of state, the surface ferromagnetism possibly due to the increased 2p–3d hybridization of surface Cu and O atoms. This is radically different from other systems previously known to exhibit point defect ferromagnetism, warranting a closer look at the phenomenon.     

ICP法测定超临界水氧化设备腐蚀液中铜、铬、铝、镍、钛

采用光谱法研究了超临界水氧化设备腐蚀液中Cu,Cr,Al,Ni和Ti元素的含量,分析判断不锈钢设备腐蚀状况及其因素。结果表明,超临界设备不锈钢材料主要成分元素Cr在超临界水中有不同程度的溶解,并且溶解程度随温度和压力升高而增大。     

硫原子在镍基合金825(001)面吸附的第一性原理研究

元素硫在镍基合金表面吸附产生严重的电化学腐蚀,为从原子尺度研究硫腐蚀机理,采用第一性原理方法,构建并优化了镍基合金825的晶胞结构模型,计算分析了S原子在镍基合金825耐蚀性较差面(001)晶面的吸附及电子转移情况.结果表明:Ni原子占据顶角, Cr原子和Fe原子对称占据面心是镍基合金825稳定的晶胞结构;原子S在镍基合金825(001)面上最稳定的吸附位为四重穴位,吸附能为-6.51 eV; S吸附前后的态密度(DOS)和二维电荷差分密度图(DCD)对比发现,镍基合金825中Fe与S之间电荷偏移明显,形成离子键,易生成腐蚀产物Fe_xS_y. S的吸附对镍基合金825中Cr原子的电子分布影响不大,且合金中Cr和Ni抑制了合金中Fe与S之间的相互作用,从而提高了合金耐蚀性.     

Segregation of tin on (111) and (100) surfaces of copper

Surface segregation of Sn in Cu is measured at (111) and (100) surfaces by means of AES and LEED. In the case of at temperature measurements and no cosegregation of impurities occurring, equilibrium segregation is accomplished for Sn bulk concentrations between 40 and 4300 at ppm and temperatures of 800 to 1230 K. The maximum segregation level of Sn corresponds to a (√3 × √3)R30° structure for the (111) surface and a p(2 × 2) structure for the (100) surface. For theoretical analysis, the Langmuir-McLean equation has to be modified. No difference in segregation enthalpies for both surface orientations is found within the experimental error. The mean segregation enthalpy is determined to ΔH = ?(53 ± 5) kJ/g-atom.     

The rate of formation of nickel carbonyl from carbon monoxide and nickel single crystals

We have measured the rate of Ni(CO)_i formation at a total pressure of 1 atm on Ni(100), (110) and (111) single crystals cleaned by argon ion bombardment and UHV annealing. The (111) surface reacts significantly faster than the other two surfaces. The partial pressure dependence of the reaction and the effect of impurities are also discussed.     

Effect of non-metallic X(X=F,N, S) and Cr co-doping on properties of BiFeO3: A first-principles study

In this study, the structural, magnetic, electric and optical properties in X (X=F, N, S) and Cr co-doped BiFeO₃ (BFO) are calculated using the density functional theory. For Cr–X co-doping case, the structure of BFO undergo a phase transition from monoclinic to triclinic structure accompanying net magnetic moments of 5.92 μB, 6.04 μB and 7.80 μB, for Cr–F co-doping, Cr–N co-doping and Cr–S co-doping, respectively. The underlying physical mechanisms are the lattice distortions tunned by doping. The decreased Fe–O–Fe bond angles and Fe–O bond lengths will bring weak antiferromagnetism superexchange interaction. In addition, the band gaps of Cr–X co-doping cases are decreased from 2.20 eV (BFO bulk) to 1.31 eV and 1.80 eV for Cr–F co-doping and Cr–S co-doping, respectively, which are well for photovoltaic applications according to the well-known Shockley-Queisser criterion, suggesting a possible great improvement optical properties in Cr–X co-doped samples.     

无序二元合金（NixCu1－x）不同解理面上O吸附对Cu偏析的影响

应用计算机编程构造出了存在和不存在表面偏析的无序二元合金Ni_xCu_1-x (x=0.4)(１００)表面及(１１０)表面的原子集团模型，然后按覆盖度θ=0.5，构造 出了O吸附后的原子集团模型，应用Recursion方法计算了O在Ni_xCu_{1-x(存在偏析和不存在偏析时)无序二元合金(１００)和(１１０)表面吸附的电子结构.由此 得出：1)O吸附使合金表面态密度峰降低，带宽加宽，并且表面Ni原子的d电子与吸附质O原 子的s，p电子的共价作用比Cu更强烈；2)O吸附在NixCu1-x(x=0.4) (１１０)表面比(１００)表面更稳定；3)O的吸附抑制了Cu在表面富集，且这种作用主要表 现在表面一层. 关键词： 化学吸附 表面偏析 Recursion方法 态密度}     

V(001)表面上(4×1)-O,(2×2)-S两超结构的角分辨光电子谱

用角分辨紫外光电子谱详细研究了V(001)表面上,S和O偏析引起的(4×1)-O,(2×2)-S两超结构,确定了S,O各自引起的吸附态的峰位和对称性;得到了O占据V(001)表面上空位的实验证据。所得实验结果与理论计算相等。 关键词：     

含Nb或Ge的锆合金表面氧吸附行为的第一性原理研究

采用基于密度泛函理论的第一性原理方法, 研究了纯锆表面和含Nb或Ge锆合金表面上氧的吸附性质. 结果表明, Nb和Ge对Zr(0001), (1120)和(1010)表面吸附性质的影响各不相同. 根据计算得到的偏聚能结果, Nb和Ge迁移到Zr(0001)表面比迁移到其他两个表面更容易, 而Nb和Ge 都可以降低Zr(0001)表面对氧原子的吸附能力, 因此这两种元素都能抑制锆合金的初始氧化. 进一步的电子结构分析发现, Nb和Ge改变表面对氧原子的吸附能力是通过改变表面d能带的分布来实现的.     

Effects of oxygen concentration and irradiation defects on the oxidation corrosion of body-centered-cubic iron surfaces: A first-principles study

Oxidation corrosion of steels usually occurs in contact with the oxygen-contained environment, which is accelerated by high oxygen concentration and irradiation. The oxidation mechanism of steels is investigated by the adsorption/solution of oxygen atoms on/under body-centered-cubic (bcc) iron surfaces, and diffusion of oxygen atoms on the surface and in the near-surface region. Energetic results indicate that oxygen atoms prefer to adsorb at hollow and long-bridge positions on the Fe(100) and (110) surfaces, respectively. As the coverage of oxygen atoms increases, oxygen atoms would repel each other and gradually dissolve in the near-surface and bulk region. As vacancies exist, oxygen atoms are attracted by vacancies, especially in the near-surface and bulk region. Dynamic results indicate that the diffusion of O atoms on surfaces is easier than that into near-surface, which is affected by oxygen coverage and vacancies. Moreover, the effects of oxygen concentration and irradiation on oxygen density in the near-surface and bulk region are estimated by the McLean's model with a simple hypothesis.