Surface corrugation effects on the adsorption dynamics of xenon on Pt(110)−(1 × 2)

The adsorption probability of xenon on Pt(110)(1 × 2) shows a strong dependence on both the polar (θ_i) and aximuthal angles of incidence. For atoms incident along the (11̄0) direction the adsorption probability increases slowly with increasing angle of incidence, scaling as E_i, cos^0.5θ, whereas along the (100) azimuth it decreases with increasing angle of incidence, exhibiting “negative” energy scaling. The hard cube washboard model does not account quantitatively for these differences with a single consistent set of parameters.     

Ab initio study on the ground states,phase stability,and mechanical properties of the Au–Pt system

For the equilibrium immiscible Au–Pt system, ground states are studied based on the results of the cluster expansion method combined with ab initio calculations. The obtained results show that there is no stable phase for the Au–Pt system at 0 K. The further obtained enthalpies of formation for hypothetical crystalline L1₂, D0₁₉, D0₃ structured Au₃Pt and AuPt₃, as well as L1₀ structured AuPt compounds also have positive values. Moreover, elastic constants are predicted from ab initio for the first time for the metastable L1₂ Au₃Pt, AuPt₃ and L1₀ AuPt compound. Finally, there is an imaginary phonon appearing in the obtained phonon spectra, implying an internal instability of the positions of the nuclear coordinates of the L1₂Au₃Pt compound.     

PAC investigations of Au(110) 1×2-surfaces

Au(110) surfaces with (1×2)-reconstruction have been investigated using perturbed -angular correlation (PAC) spectroscopy. From the two observed electric-field-gradient tensors at¹¹¹In probe atoms, deposited at room temperature in a concentration of about 10^–4 ML, the occupation of substitutional sites in the densely-packed rows along [110]-directions and ninefold coordinated sites within the (111)-oriented microfacets, respectively, can be concluded. Annealing to about 600 K leads to bulk migration of the In atoms, detected by an increase of probe atoms with cubic surroundings. Due to this behaviour the order-disorder transitions of these surfaces occurring atT _c=649 K cannot be detected in our PAC experiments.     

Site-specific core level spectroscopy of CO and NO adsorption on Pt(110)(1×2) and (1×1) surfaces

The adsorption of CO and NO on the (1×2) and (1×1) modifications of the Pt(110) surface was studied by x-ray photoemission spectroscopy, LEED and work-function change measurements. The O(1s) binding energy of adsorbed CO is site-specific and differentiates between on-top and bridge adsorbed species. CO adsorption on Pt(110)(1×2) at 120 K occurred sequentially into on-top and bridge sites yielding an orderedc(8×4) layer at the maximum coverage. At 300 K only on-top bonded CO was present after CO adsorption on the (1×2) surface. CO adsorption on the (1×1) surface at 120 K showed a transient bridge adsorbed CO and on-top CO at saturation, with an ordered (2×1)p1g1 LEED pattern. Heating the (2×1)p1g1 CO layer to 400 K also showed this transient bridge CO species. Work function changes generally correlated with the appearance of different CO species but were complex in detail. The findings for CO adsorption are consistent with the missing row model of the (1×2) surface.Parallel data for NO adsorption on (1×2) and (1×1) surfaces at 120 K were less informative than those for CO because O(1s) spectra showed single broad peaks. Peak contributions due to bridge and on-top bonded NO could be estimated.     

Ab Initio Study on Structures and Vibrational Spectra of M+(H2O)Ar2 (M = Cu,Au)

Previous investigations have shown that it is difficult to acquire the infrared (IR) spectra of M⁺(H₂O) (M?=?Cu, Au) using a single IR photon by attaching an Ar atom to M⁺(H₂O). To explore whether the IR spectra can be obtained using the two Ar atoms tagging method, the geometrical structures, IR spectra and interaction energies are investigated in detail by ab initio electronic structure calculations for M⁺(H₂O)Ar₂ (M?=?Cu, Au) complexes. Two conceivable isomeric structures are found, which result from different binding sites for two Ar atoms. CCSD(T) calculations predict that two Ar atoms are most likely to attach to Cu⁺ for the Cu⁺(H₂O)Ar₂ complex, while the Au⁺(H₂O)Ar₂ complex prefers the isomer in which one Ar atom attaches to an H atom of the H₂O molecule and the other one is bound to Au⁺. Moreover, the calculated binding energies of the second Ar atom are smaller than the IR photon energy, and so it is possible to obtain the IR spectra for both Cu and Au species. The changes in the spectra caused by the attachment of Ar atoms to M⁺(H₂O) are discussed.     

Ab initio study of the (2 × 2) phase of barium on graphene

We present a first-principles density functional theory study on the structural, electronic and dynamical properties of a novel barium doped graphene phase. Low energy electron diffraction of barium doped graphene presents clear evidence of (2 × 2) spots induced by barium adatoms with BaC₈ stoichiometry. First principles calculations reveals that the phase is thermodynamically stable but unstable to segregation towards the competitive BaC₆ monolayer phase. The calculation of phonon spectrum confirms the dynamical stability of the BaC₈ phase indicating its metastability, probably stabilized by doping and strain conditions due to the substrate. Barium induces a relevant doping of the graphene π states and new barium-derived hole Fermi surface at the M-point of the (2 × 2) Brillouin zone. In view of possible superconducting phase induced by foreign dopants in graphene, we studied the electron–phonon coupling of this novel (2 × 2) obtaining λ = 0.26, which excludes the stabilization of a superconducting phase.     

Adsorption of CO and H2 on Pt(110)(1 × 2) studied by photoemission of adsorbed xenon (PAX)

The adsorption of hydrogen and carbon monoxide on Pt(110)(1 × 2) at 97 K has been studied by photoemission of adsorbed xenon (PAX). For both species, it appears that adsorption takes place first in the valleys between the microfacets of this reconstructed surface. Only when these sites are saturated, does adsorption take place on other sites (microfacets or ridges) of the surface.     

Microfacets of the (1 × 2) reconstructed Pt(110) surface seen in the adsorption dynamics of H2

We have detected a strong azimuth dependence of the adsorption dynamics of hydrogen on a Pt(110)(1×2) surface. Adsorption on the (1 ×2) reconstructed surface is found to be governed by the (111) microfacets of the missing row structure. Furthermore we have observed a low temperature α-state in the thermal desorption spectra comparable to the α-states for other fcc (110) surfaces.     

Ethylene adsorption on Co/Pt(110)(1 × 2) surfaces

Ethylene adsorption has been followed by TDS on Pt(110)(1 × 2) surfaces covered with various amounts of cobalt atoms, including the multilayer range. A peculiar behaviour is found below 2.10 × 10¹⁵ cobalt atoms/cm²: partial desorption of ethylene low temperature replaces decomposition. The behaviour of bulk polycristalline cobalt is found above this coverage.     

Atomic Models of the Si(110)-5 × 8 and Ge(110)-c(10 × 8) Surfaces

Journal of Experimental and Theoretical Physics - The atomic models of the Si(110)-5 × 8 and Ge(110)-c(10 × 8) surfaces, which are based on a universal building block for the family of...     

Thermal and Elastic Properties of CexTh1 –xO2 Mixed Oxides: A Self-Consistent Thermodynamic Approach

Technical Physics - A self-consistent thermodynamic model of thorium dioxide and its dilute alloy Ce0.05Th0.95O2, which are of great importance for atomic power engineering, has been constructed...     

Synchrotron-Radiation Photoemission Study of Growth and Stability of Au Clusters on Rutile TiO2(110)-1×1

利用同步辐射高分辨光电子能谱研究了金团簇在部分还原TiO₂-(1×1)表面的生长和稳定性．价带谱实验结果观察到非常少量金团簇的沉积导致了Ti3+的3d峰完全消失,表明金团簇成核在TiO₂-(1×1)表面的氧缺陷位．Au4f芯电子光电子能谱实验结果证明了TiO₂-(1×1)表面氧缺陷位向金团簇转移电荷．还对比研究了化学剂量比和部分还原的TiO₂-(1×1)表面上金团簇的热稳定性．当金团簇尺寸相近时部分还原的TiO₂-(1×1)表面上金团簇要比化学剂量比的TiO₂-(1×1)面上金团簇稳定;在相同的表面上尺寸大的金团簇要比尺寸小的金团簇稳定．     

Similarities in the decomposition and dehydrogenation of cyclohexene on (4 × 4)-CMo(110) and Pt(111)

The decomposition and dehydrogenation of cyclohexene have been used as probing reactions to directly compare the surface reactivities of carbon-modified Mo(110) and Pt(111). By using temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS), we find that the dominant decomposition pathway of cyclohexene can be converted from complete decomposition to atomic carbon and hydrogen on clean Mo(110) to partial dehydrogenation to benzene and hydrogen on (4 × 4)-CMo(110). The latter reaction mechanism is very similar to that observed on Pt(111). Furthermore, in contrast to the near identical catalytic properties that are commonly observed for bulk molybdenum carbide and nitride powder materials, we find that the reactivities of carbon-modified and nitrogen-modified Mo(110) surfaces are qualitatively different.     

The co-induced 1 × 2 ↔ 1 × 1 phase transition of Pt(110) studied by leed and work function measurements

The adsorption of CO on the reconstructed 1 × 2-Pt(110) surface causes a lifting of the reconstruction which has been studied by LEED and work function measurements. The work function initially decreases until at γ = 0.2 the lifting of the reconstruction begins. A comparison with Pt(100) and Pt(111) shows that the similar behaviour of CO-induced work function changes on all three low-index planes of Pt appears to be related with a similar binding geometry of CO adsorbed on top of a (quasi-)hexagonal configuration of Pt atoms. No hysteresis is observed in the adsorption/desorption equilibrium of CO on Pt(110). Although the energetics of the CO-induced phase transition on Pt(110) appear to be analogous to those of the phase transition 1 × 1 ⇹ hex of Pt(100), a number of differences exist between the two surfaces which can be explained by the different structural properties of the various surface phases involved.     

Resonant scattering of He-atoms from missing-row reconstructed Pt(110)1 × 2: comparison of theory and experiment

Close coupled channels calculations concerning the angular dependence of the specular beam were performed on the basis of the He/Pt(110)1 × 2 interaction potential, which we previously derived by analyzing a large number of He-diffraction intensities. The excellent agreement with experimental data obtained for several wavelengths confirms the reliability of the potential form and depth and allows proper assignment of resonant scattering features and thus secure determination of the bound state levels.