The adsorption of CO on Cu-Ni alloy surfaces has been studied at 300 and 120 K using LEED, AES, TDS, and work function measurement. The alloys have been prepared as thin (111) epitaxial films evaporated on mica, and as poly crystalline foils. At 300 K the alloy surfaces show an adsorption behavior similar to that of pure Ni: the work function increases to a saturation value which is higher for Ni-rich surfaces than for Cu-rich. The isosteric heat of adsorption (106 kJ/mole) is nearly as high as with pure Ni. At 120 K the alloys exhibit a more Cu-like adsorption behavior: the work function passes through a minimum which becomes deeper at higher Cu surface concentration. The isosteric heat of adsorption at low temperatures (50 kJ/mole) is nearly as low as for pure Cu. From TDS it can be shown, that the binding energy of the highest (Ni-like) adsorption states increases with increasing Ni surface concentration. At the (111) alloy surfaces no LEED superstructures due to CO adsorption could be observed. 相似文献
Using electron stimulated desorption (ESD) and electron stimulated desorption ion angular distribution (ESDIAD) techniques, we have determined that coadsorbed potassium systematically quenches the O+ ion yield from CO on the Ni(111) surface for 1000 eV electron excitation energies. The quenching appears to be a short range K-CO interaction; 3 or 4 CO molecules are affected for each K atom adsorbed on the surface. The quenching effect of K on CO indicates that a significant electronic perturbation of CO is caused by its local interaction with K. This effect prevents ESDIAD observation of the K-quenched CO species. In addition, the CO molecules that are not quenched at a potassium coverage of 0.02 K/Ni exhibit a normally oriented C-O bond similar to that found for CO adsorbed on a K-free Ni(111) surface. 相似文献
The secondary alkali ion yield vs. the work function change (Δφ) of Na, K and Cs/Si(100) and Si(111) was measured to discuss the details of secondary ion emission processes. In the case of alkali/metal systems, the secondary ion emission is explained by the electron tunneling model. In this model, the ionization of the ejected atom occurs as a result of electron resonant tunneling through the potential barrier separating an atom and a metal, and the secondary ion yield depends on exponentially the work function change of metal surface. For alkali/Si(100) systems, the secondary ion emission processes are explained in terms of the electron tunneling model since the secondary alkali ion yield vs. the work function change (Δφ) follows the exponential manner. However, it is not easy to apply the simple electron tunneling model to our experimental results for alkali/Si(111) systems. There is the essential difference in surface structures between Si(100) and Si(111). Therefore, it is suggested that the local electronic environment around the adsorbates might be taken into consideration for alkali/Si(111) systems. 相似文献
The presence of a buried, ultra-thin amorphous interlayer in the interface of room temperature deposited Ni film with a crystalline
Si(100) substrate has been observed using cross sectional transmission electron microscopy (XTEM). The electron density of
the interlayer silicide is found to be 2.02 e/?3 by specular X-ray reflectivity (XRR) measurements. X-ray diffraction (XRD) is used to investigate the growth of deposited
Ni film on the buried ultra-thin silicide layer. The Ni film is found to be highly textured in an Ni(111) plane. The enthalpy
of formation of the Ni/Si system is calculated using Miedema’s model to explain the role of amorphous interlayer silicide
on the growth of textured Ni film. The local temperature of the interlayer silicide is calculated using enthalpy of formation
and the average heat capacity of Ni and Si. The local temperature is around 1042 K if the interlayer compound is Ni3Si and the local temperature is 1389 K if the interlayer compound is Ni2Si. The surface mobility of the further deposited Ni atoms is enhanced due to the local temperature rise of the amorphous
interlayer and produced highly textured Ni film.
Received: 2 March 2000 / Accepted: 28 March 2000 / Published online: 11 May 2000 相似文献
The scattering of CO+ and CO+2 at grazing incidence from Ni(111)+K and clean Ni(111), Ni(110) surfaces produces CO, CO2 and dissociated species. The observation of negative species O− and CO−2 is strongly dependent on the K coverage or work function of the surface. The dissociation of CO+ (CO) is weakly changed by the presence of K, whereas in the CO+2 (CO2) case dissociation via CO−2 → CO + O− is strongly increasing with K coverage. 相似文献
Overlayers formed by the adsorption of Ni(CO)4 in CO on the Ni(111) surface at 100 K were characterized using high resolution electron energy loss spectroscopy and thermal desorption spectroscopy. At temperatures below 135 K, molecular nickel carbonyl adsorbs on the CO saturated Ni(111) surface as suggested by several observations. Vibrational transitions characteristic of molecular Ni(CO)4 are dominant. The energy dependence of both the elastic and inelastic electron scattering cross sections are dramatically altered by Ni(CO)4 adsorption. All of the mass spectrometer ionization fragments typical of molecular Ni(CO)4 are observed in the narrow thermal desorption peak at 150 K. The inelastic scattering cross sections for both adsorbed nickel carbonyl and adsorbed CO on the Ni(111) surface suggest that a nonresonant dipole scattering mechanism is dominant. 相似文献
We report the electronic structure of the Au-intercalated graphene/Ni(111) surface using angle-resolved photoemission spectroscopy and low energy electron diffraction. The graphene/Ni(111) shows no Dirac cone near the Fermi level and a relatively broad C 1s core level spectrum probably due to the broken sublattice symmetry in the graphene on the Ni(111) substrate. When Au atoms are intercalated between them, the characteristic Dirac cone is completely recovered near the Fermi level and the C 1s spectrum becomes sharper with the appearance of a 10?×?10 superstructure. The fully Au-intercalated graphene/Ni(111) surface shows a p-type character with a hole pocket of ~0.034?Å?1 diameter at the Fermi level. When the surface is doped with Na and K, a clear energy gap of ~0.4?eV is visible irrespective of alkali metal. 相似文献
Adsorption of K on Fe(110), (100) and (111) surfaces was studied by means of LEED, AES, thermal desorption and work function measurements. The monolayer capacity is about 5.5 × 1014 K-atoms/cm2 in all three cases. With Fe(111) an ordered 3 × 3 overlayer was found at fairly low coverages. The work function decreases to a minimum and the initial dipole moments were determined to μ0 = 7.0 Debye for Fe(110), μ0 = 4.4 Debye for K/Fe(100) and μ0 = 3.9 Debye for K/Fe(111). The heat of adsorption decreases from its initial value (Fe(110): 57; Fe(100): 54; Fe(111): 52 kcal/mole) continuously with increasing coverage which parallels the continuous decrease of the dipole moment of the adsorbate complex. 相似文献
The hyperfine field andthe electric field gradient on Cd probe atoms at Ni(100) and Ni(111) surfaces are calculated self-consistently within the local density molecular/cluster approach. 相似文献
Photoelectron spectroscopy (UPS), thermal desorption spectroscopy (TDS), isotope exchange experiments, work function change (δφ) and LEED were used to study the adsorption and dissociation behavior of H2O on a clean and oxygen precovered stepped Ni(s)[12(111) × (111)] surface. On the clean Ni(111) terraces fractional monolayers of H2O are adsorbed weakly in a single adsorption state with a desorption peak temperature of 180 K, just above that of the ice multilayer desorption peak (Tm = 155 K). In the angular resolved UPS spectra three H2O induced emission maxima at 6.2, 8.5 and 12.3 eV below EF were found for θ ≈ 0.5. Angular and polarization dependent UPS measurements show that the C2v symmetry of the H2O gas-phase molecule is not conserved for H2O(ad) on Ni(s)(111). Although the Δφ suggest a bonding of H2O to Ni via the negative end of the H2O dipole, the O atom, no hints for a preferred orientation of the H2O molecular axes were found in the UPS, neither for the existence of water dimers nor for a long range ordered H2O bilayer. These results give evidence that the molecular H2O axis is more or less inclined with respect to the surface normal with an azimuthally random distribution. H2O adsorption at step sites of the Ni(s)(111) surface leads in TDS to a desorption maximum at Tm = 225 K; the binding energy of H2O to Ni is enhanced by about 30% compared to H2O adsorbed on the terraces. Oxygen precoverage causes a significant increase of the H2O desorption energy from the Ni(111) terraces by about 50%, suggesting a strong interaction between H2O and O(ad). Work function measurements for H2O+O demonstrate an increase of the effective H2O dipole moment which suggests a reorientation of the H2O dipole in the presence of O(ad), from inclined to a more perpendicular position. Although TDS and Δφ suggest a significant lateral interaction between H2O+O(ad), no changes in the molecular binding energies in UPS and no “isotope exchange” between 18O(ad) and H216O(ad) could be observed. Also, dissociation of H2O could neither be detected on the oxygen precovered Ni(s)(111) nor on the clean terraces. 相似文献
The interaction of ethylenediamine with a Ni(111) surface was investigated in the temperature range 170–420 K by means of X-ray photoelectron spectroscopy. Molecularly absorbed species were predominant below 290 K giving the C1s and the N 1s peaks at 286.4 and 399.9 eV (at 250 K) and at 286.0 and 399.7 eV (at 290 K), respectively. The amount dehydrogenated species increased during heating up to 420 K resulting in a variation of the N 1s binding energy as 399.7 → 397.7 → 397.5 → 397.7 eV. The variation was correlated with successive dehydrogenation reactions such as The interaction of acetic acid with molecularly absorbed ethylenediamine below 200 K brought about the appearance of the N 1s peak at 401.9 eV assignable to the ammonium form of nitrogen at the expense of the N 1s peak at 400.1 eV. The remaining N 1s peak is located at 399.6 eV. Ethylenediamine absorbed at 290 K, showing the N 1s peak at 399.7 eV, gave no ammonium form even after interaction with acetic acid at 220 K. These results indicate that a part of ethylenediamine was unidentate and the rest was bidentate (chelating) on the Ni(111) surface at 250 K and all of the molecules were bidentate at 290 K. When acetic acid was adsorbed on a clean Ni(111) surface at 165 K, formation of an acetyl group was indicated besides acetate. 相似文献
By means of first principles simulations we demonstrate that tiny deviations from stoichiometry in the bulk composition of the NiPt-L1(0) ordered alloy have a great impact on the atomic configuration of the (111) surface. We predict that at T=600 K the (111) surface of the Ni51Pt49 and Ni50Pt50 alloys corresponds to the (111) truncation of the bulk L1(0) ordered structure. However, the (111) surface of the nickel deficient Ni49Pt51 alloy is strongly enriched by Pt and should exhibit the pattern of the 2x2 structure. Such a drastic change in the segregation behavior is due to the presence of different antisite defects in the Ni- and Pt-rich alloys and is a manifestation of the so-called off-stoichiometric effect. 相似文献
Using density-functional calculations, we studied the interactions between interstitial impurities (H, O, N, S, and P) and Ni (111) surfaces doped, or not, with Cr, and studied the effect of Cr doping on the dissolution corrosion resistance of Ni(111) surfaces. The aim of this work was to study, at the atomic scale, the effects of Cr on the segregation behaviors of impurities and the synergetic effects between co-doped atoms on the resistance to dissolution corrosion of Ni (111) surfaces. The results indicate that impurities S, P, O, and H prefer to be trapped at near-surface sites, that Cr was uniformly distributed in the Ni crystal and can affect the segregation behavior of impurities S and P to move toward the surface, and it affects impurities N and O such that they shift from the surface to the subsurface. The formation of near-surface Cr nitrides (speculated to be Cr2N based on the results obtained for particular co-doped surfaces) was also noted. Introducing Cr enhances the structural stability of the Ni (111) surface and protects it from being corroded when impurities are present. The elementary processes studied afforded microscopic insights into the formation of a Cr-depleted zone, a phenomenon that leads to local corrosion of the Ni alloy surface. The results of our theoretical calculations explain some of the experimental results previously observed at the atomic scale. 相似文献
The ESDIAD method (electron stimulated desorption ion angular distributions) has been combined with LEED (low energy electron diffraction) in a study of the adsorption of NO on Ni(111). For adsorption at 80 K, NO appears to be bonded with its molecular axis perpendicular to the Ni(111) surface at all coverages. Heating the 80 K layer leads to a striking structural change which we interpret as the formation of inclined or bent NO in the range 120 ? T ? 250 K. Upon adsorption at 150 K, only the bent form of NO is present at low coverages; at higher coverages at 150 K, the perpendicular form appears, in agreement with recent electron energy loss spectroscopy (EELS) data of Lehwald, Yates, and Ibach. When NO is coadsorbed with p(2 × 2) oxygen, the perpendicular form of NO dominates at all coverages and temperatures studied. Dissociated NO adsorbed at steps and defect sites on Ni(111) produces a welldefined hexagonal ESDIAD pattern. 相似文献
Ultraviolet photoelectron spectroscopy (UPS) has been used to study the chemisorption of CO, O2, and H2 on platinum. Three single crystal surfaces ((111), 6(111) × (100), and 6(111) × (111)) and two polycrystalline surfaces were studied. These studies yielded three important results. First, the most dominant change in the Pt valence band upon gas adsorption was a decrease in the height of the peak immediately below the Fermi level. This decrease was nearly identical for all three gases studied. Second, CO adsorption resulted in the formation of a resonance state ~8 eV below the Fermi level which was attributed to CO molecular orbitals. In contrast, no dominant resonance states were observed for adsorbed O or H. The lack of an O resonance state on platinum is in contrast to the results observed for O adsorbed on Fe and Ni and suggests important differences between the OPt chemisorption bond and the OFe and ONi chemisorption bonds. Finally, adsorption of CO at steps or defects led to a decrease in work function while its adsorption on terraces led to an increase in work function. For H, adsorption at steps led to an increase in work function while adsorption on terraces led to a decrease in work function. The adsorption of O led to an increase in work function on all of the surfaces studied. 相似文献