A SPALEED structural study of cesium adsorption on stepped copper surfaces Cu(211) and Cu(511)

The adsorption of cesium on stepped copper surfaces Cu(211) and Cu(511) at temperatures ranging from 130 to 300 K was studied using SPALEED. The two Cu substrates differ mainly in the low index orientation of the relatively short terraces and permit a comparison of the effect of orientation on the adsorption behaviour. For coverages between 0.6 and 1.8 ML on Cu(211) within the whole temperature range Cs forms quasihexagonal layers corresponding to rows of Cs atoms running along the step edges of the substrate. A strong 15% compression of the distance between Cs atoms along the step edge direction was found. Similar structures were found on Cu(511) where in addition at crystal temperatures in excess of 250 K and coverage of 1 monolayer, the Cs atoms induce a double step reconstruction of the substrate.     

The adsorption of oxygen on Cu(210)

The system Cu(210)-O₂ has been examined using LEED and AES, combined with optical simulation of diffraction patterns to investigate the detailed structure of the adsorbed layer. Exposure at 300 K and 5 × 10^?9 Torr resulted in LEED patterns showing pronounced streaks. The corresponding structures are believed to require an adsorption mechanism in which O₂ dissociation can occur only at a limited number of surface sites and in which O atoms after dissociation diffuse over quite large distances (?10 nm) before becoming chemisorbed. Heating these structures to 500–600 K produced a sharp (2 × 1) pattern; this step is thought to involve equilibration of the adsorbed layer. Further combinations of exposure (?1 × 10^?6Torr) and heating (up to 500 K) resulted in a series of (2 × 1) and (3 × 1) patterns, while heating to 800 K at any stage of the oxygen interaction regenerated the clean surface.     

乙烯在Ru( )表面价带电子特性研究

在200K以下乙烯（C2H4）可以在Ru（1010^-）表面上以分子状态稳定吸附,200K以上乙烯发生了脱氢分解反应生成乙炔（C2H2）。乙烯分解生成乙炔后,σCC和σCH 分子轨道能级向高结合 能方向分别移动了0.5和1.1eV。偏振角分辨紫外光电子谱（ARUPS）结果表明：在Ru(10106-)表面上,乙烯和脱氢反应后生成的乙炔分子在C－C键轴都不平行 于表面,而是沿表面<0001>晶向倾斜。     

Site-selective adsorption of xenon on a stepped Ru(0001) surface

The adsorption of xenon has been studied with UV photoemission (UPS), flash desorption (TDS) and work function measurements on differently conditioned Ru(0001) surfaces at 100 K and at pressures up to 3 × 10^?5 Torr. Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) served to ascertain the surface perfectness. On a perfect Ru(0001) surface only one Xe adsorption state is observed, which is characterized by$\text{Xe}\text{5}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$,$\text{1}\text{2}$ electron binding energies of 5.40 and 6.65 eV, an adsorption energy of E_ad≈ 5 kcal/mole and dipole moment of μ'_T ≈ 0.25 D. On a stepped-kinked Ru(0001) surface, the terrace-width, the step-height and step-orientation of which are well characterized with LEED, however, two coexisting xenon adsorption states are distinguishable by an unprecedented separation in$\text{Xe}\text{5}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$,$\text{1}\text{2}$ electron binding energies of 800 meV, by their different UPS intensities and line shapes, by their difference in adsorption energy ofΔE_ad ≈ 3 kcal/mole and finally by their strongly deviating dipole moments of μ_S = 1.0 D and μ_T = 0.34 D. The two xenon states (which are also observed on a slightly sputtered surface) are identified as corresponding to xenon atoms being adsorbed at step and terrace sites, respectively. Their relative concentrations as deduced from the UPS intensities quantitatively correlate with the abundance of step and terrace sites of the ideal TLK surface structure model as derived from LEED. Furthermore, ledge-sites and kink-sites are distinguishable via E_ad. The E_ad heterogeneity on the stepped-kinked Ru(0001) surface is interpreted in terms of different coordination and/or different charge-transfer-bonding at the various surface sites. The enormous increase in Xe 5p electron binding energy of 0.8 eV for Xe atoms at step sites is interpreted as a pure surface dipole potential shift. —The observed effects suggest selective xenon adsorption as a tool for local surface structure determination.     

The adsorption kinetics of C2H2, and C2H4 on W(110) at 1100 K

The adsorption kinetics of C₂H₂ and C₂H₄ gases on W(110) have been studied using Auger electron spectroscopy and qualitative LEED. Below 1100 K, adsorption of either C₂H₂; or C₂H₄ does not follow any simple kinetic model to saturation. At 1100 K adsorption is identical for both gases and follows first order monolayer kinetics with unity sticking coefficient and a carbon-to-tungsten atomic ratio of 0.64 ± 0.05. This carbon is present as a surface carbide which starts to in-diffuse about 1500 K and has completely dissolved after a few seconds at 2400 K.     

团簇ConAgm (n +m =13)表面吸附C2H4的第一性原理研究

基于密度泛函理论的第一性原理计算方法,本文对ConAgm(n+m=13)团簇的几何结构进行优化后,研究了C2H4分子在这类团簇的表面吸附行为,讨论了团簇的平均结合能、二阶能量差分、稳定性、DOS以及吸附前后键长的变化情况。结果表明,C2H4在团簇top位的吸附主要为物理吸附,而在face位和bridge位的吸附主要为化学吸附。吸附后,C2H4@Ag13的稳定性高于C2H4@Co13,且在face位吸附时C2H4@Co2Ag11的结构最为稳定。随着Co原子数的增加,团簇中原子间成键能力减弱,而d电子轨道则呈现出较强的相互作用,并导致其向能量相对高处发生转移     

The crystal structure of copper dipyridine dibromide Cu(C5H5N)2Br2

The X-ray structural analysis of copper dipyridine dibromide was carried out. The substance is monoclinic, its space group isP2₁/n, having the lattice constantsa=8.30 kXU,b=17.72 kXU,c=4.04 kXU,=96°,Z=2. The localization of the heavy atoms was carried out by means of the projections of the Patterson functionsP(u, v) andP(v, w), which provided the bases for determining the signs of the majority of structure factors. The projections of the electron density(x, y) and(y, z) were calculated on the basis of these data. The positions of the atoms were refined three times by methods of differential syntheses and by geometrical analysis. The structure of CuPy₂Br₂ is very close to that of CuPy₂Cl₂ [1], [2], differing from it primarily in the orientation of the symmetry elements with respect to the crystallographic axes. In both structures the copper atom is octahedrally coordinated with four halogen and two nitrogen atoms. The nitrogen atoms and two bromine atoms are bound to the copper covalently in the structure of the bromine derivative, as follows from the length of the bonds (Cu-N 1.99 kXU, Cu-Br, 2.46 kXU), while the remaining two bromine atoms are bound to the copper by weaker bonds and mediate the chain formation of molecules in the direction of thec axis.

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Cu(C₅H₅N)₂Br₂

. , 2₁/ ==8,30 kX,b=17,72 kX,=4,04 kX,=96°,z=2. (, v) P(v, w), . (, ) (, z). . CuPy₂Br₂ u₂1₂, . . , (-N 1,99 kX, u-r 2,46 kX), .

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The authors thank M. Serátor for supplying the crystal samples and for initiating the work, the management of the Institute of Technical Physics, Czechoslovak Academy of Sciences, in Prague and especially Dr. A. Línek for making it possible to calculate some of the Fourier maps on the special computer Elika and finally A. lechtová for carefully calculating the Fourier maps and structure factors.

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The first stage of this work was reported on at the 3rd State Conference on Inorganic Chemistry, held in Bratislava from June 29th to July 4th, 1959.     

Effects of surface corrugation on the molecular rotational dependence of H2 dissociative adsorption dynamics on Cu(100)

We investigate and discuss how surface corrugation affects the molecular rotational dependence of H₂ dissociative adsorption dynamics on Cu(100) by performing six-dimensional (6D) quantum dynamics calculations. We calculate the dissociative adsorption probability as a function of the initial rotational state J and the normal energy E_norm of incident molecules, and compare with the dissociative adsorption results obtained by four-dimensional (4D) quantum dynamics calculations where the surface is treated as flat. In our calculation, for the case of normal incidence, the increase in dissociative adsorption probability with increasing E_norm and the non-monotonic behavior of dissociative adsorption probability with respect to J are suppressed on a corrugated surface as compared to that on a flat surface.     

One- and two-dimensional S=12 Heisenberg antiferromagnetism in Cu(C5H5NO)6 (ClO4)2 and Cu(C5H5NO)6 (BF4)2, respectively

Specific-heat data on CuL₆(ClO₄)₂ and CuL₆(BF₄)₂ in the temperature range 0.05 < T < 20 K are presented (L ≡ C₅H₅NO). The magnetic contributions are found to have the form of broad maxima, occurring near 1 K. Small χ-type anomalies are observed at T_c = 0.62 ± 0.01 K and 0.142 ± 0.002 K for CuL₆(BF₄)₂ and CuL₆(ClO₄)₂, respectively. The analyses show the magnetic structure to be an assembly of weakly coupled antiferromagnetic chains or layers for CuL₆(ClO₄)₂ and CuL₆(BF₄)₂, respectively. For CuL₆(ClO₄)₂ the intrachain exchange constant is J/K = -1.02 ± 0.02 K, for CuL₆(BF₄)₂ the intralayer exchange constant is J/K = -1.10 ± 0.02 K. Additional evidence for the lower-dimensional magnetic structures is obtained from the temperature dependences of the antiferromagnetic susceptibilities. The data on CuL₆(BF₄)₂ clearly indicate the absence of a divergence in the specific heat for the quadratic-layer Heisenberg antiferromagnet, and provide an estimate for the specific heat for this model. A comparison is made with the corresponding result for the ferromagnetic Heisenberg layer.     

Oxygen adsorption on stepped Pd(100) surfaces

We use scanning tunneling microscopy (STM) and high-resolution core-level spectroscopy (XPS) measurements to study the initial oxidation of vicinal Pd(100) surfaces exhibiting close-packed (111) steps. The XPS data analysis is supported by detailed surface-core level shift calculations based on density-functional theory. Both STM images and the XPS spectra are found to be perfectly consistent with a characteristic zigzag O decoration of the Pd steps predicted by a preceding cluster-expansion based theoretical study [Y. Zhang and K. Reuter, Chem. Phys. Lett. 465, 303 (2008)]. Continued oxygen uptake leads to the additional stabilization of a p(2 × 2)-O overlayer on the Pd(100) terraces, and ultimately to step bunching with the resulting large Pd(100) terraces covered by the PdO(101) surface oxide.     

Fe,Co,Ni掺杂石墨烯表面吸附C_2H_4的第一性原理研究

基于密度泛函理论(DFT)的广义梯度近似(GGA),本文对本征石墨烯以及掺杂Fe,Co,Ni石墨烯的几何结构和电子性质进行了优化计算,并计算了C_2H_4在本征石墨烯以及掺杂石墨烯表面的吸附过程,讨论了体系的吸附能、稳定性、DOS及掺杂对键长的影响.结果表明C_2H_4在本征石墨烯B位的吸附和掺杂石墨烯的吸附为化学吸附,在本征石墨烯T和H位的吸附为物理吸附;掺杂后石墨烯的比表面积增大,与本征石墨烯相比,掺杂使费米能级附近的态密度积分显著提高,表明掺杂石墨烯的电导性会发生变化,从而影响对C_2H_4的气敏度..C_2H_4在Fe、Co、Ni分别掺石墨烯的最佳吸附位为T位、H位和B位;掺杂Fe,Ni后体系的吸附能力显著提高,且掺杂Ni时体系的吸附能力最好.     

C2H4 adsorption on the Ni(111) face at room temperature: Vibrations of surface complexes studied by electron energy loss spectroscopy

Ethylene adsorption at room temperature on the Ni(111) surface has been followed by vibrational high resolution electron energy loss spectroscopy coupled with LEED, work function changes and thermodesorption measurements. The vibrational spectra of adsorbed species exhibit loss peaks at 365, 151, 85, 60 and 39 meV (274, 147, 79 and 39 meV with C₂D₄). The similarity of these spectra with those obtained after short exposure to acetylene suggests a dehydrogenating adsorption well confirmed by thermodesorption data: C₂H_{4 gas}→ C₂H_2ads + 2 H_ads. From the observed v_C-C frequencies (151 and 147 meV for the respective C₂H₂ and C₂D₂ adsorbed species) one can deduce a residual force constant ƒ_C-C ≅ 5.25 mdyn/Å. By comparison to gaseous molecules, this value suggests a near sp³ hybridization state of the C atoms confirmed by the position of the v_C-H stretching mode (365 meV). Taking in account these results, a triangular surface chemisorption site for the C₂H₂ species with two σ bonds and one π bond to three Ni atoms is suggested. Frequency analysis of this model allows to fit the experimental loss energies for reasonable force constant values, the C₂H₂ residue lying flat on the triangular site with a bent H-C-C-H arrangement (C-C-H angle ≅ 155°).     

Iodine adsorption on a platinum stepped surface: Pt(s)[6(111) × (111)]

I₂ adsorption on Pt(s)[6(111) × (111)] surfaces under vacuum and atmospheric pressure conditions was studied by LEED, AES and thermal desorption. In contrast to smooth Pt(111), the surface structures were composed of multiple phase domains having (3 × 3) or ($\text{3}\text{×}\text{3}$)R30° local geometry and structural coincidence of the adjacent terraces. No special stability or instability of iodine adsorption at steps was observed.