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1.
J. Küppers 《Surface science》1973,36(1):53-73
Electron energy loss spectra on a (110) nickel surface exhibit characteristic changes upon adsorption of H2, CO and O2. The clean surface shows only the surface and bulk plasmon losses at 8 eV and 18 eV respectively. Adsorption of CO produces two new loss peaks at 13.5 eV and 5.5 eV. Loss peaks due to hydrogen adsorption at 15 eV and 7.5 eV show a strong correlation with the well known adsorption characteristics of this system. The oxygen induced losses are different for chemisorbed O on Ni and NiO. In any case the chemisorption-induced losses are well established for primary energies below 120eV. In the loss spectra with higher excitation energies only a drastic decrease of the surface plasmon loss peak-height is visible. If the new losses can be attributed to one-electron excitations from molecular orbital levels due to the chemisorption bond, with assumptions of the final state of the excited electron a determination of the postition of these levels can be made. In case of CO and H2 reasonable results are evaluated. 相似文献
2.
We have studied angle-resolved inverse photoemission ( = 9.7 eV) after room temperature adsorption of oxygen on Cu(111) and Cu(110). On Cu(111) exposure to 500 L induces a band (3.0 eV aboveE
F
at) which shows clear dispersion (1.0 eV) to higher energies for off normal incidence. Since no LEED superstructure is seen for that system, our results present strong evidence for the presence of short-range surface order. Two adsorbate bands are identified (2.8 eV and 6.3 eV at) on Cu(110)p(2×1)-O. Our results are in good agreement with a long-bridge adsorption site. 相似文献
3.
We have used uv photoeinission (primarily at a photon energy hv = 40.8 eV) to study chemisorption and decomposition reactions of small oxygen-containing organic molecules on clean polycrystalline Pd surfaces at 120 and 300 K. These molecules include methanol (CH3OH), dimethyl ether (CH3OCH3) formaldehyde (H2CO), acetaldehyde [H(CH3)CO], and acetone [(CH3)2CO]. Chemisorption bonding of these molecules to the Pd surface occurs primarily through the lone-pair orbitais associated with the oxygen atoms, as evidenced by chemical bonding shifts of these orbitais toward larger electron binding energy relative to the other adsorbate valence orbitals. At 300 K all the molecules studied decompose on the surface, resulting in chemisorbed CO. Since chemisorbed (as well as condensed) phases of some of these molecules (CH3OH and H(CH3)CO) are observed at low temperature, the decomposition to CO is a thermally-activated reaction. The observed orbital shifts associated with chemisorption bonding are used to make rough estimates of interaction strengths and chemisorption bond energies (within the framework of Mulliken's theory of electron donor-acceptor complexes as applied to chemisorption by Grimley). The resulting heats of chemisorption are consistent with the observed surface reactions. 相似文献
4.
The bremsstrahlung isochromat (or inverse photoemission) spectrum of CO chemisorbed on a Cu(110) surface has been investigated. An empty level derived from the CO 2 π orbital was found at an energy of 0.9 eV below the vacuum level Evac and to have a halfwidth varying from 1.9 to 2.6 eV as a function of increasing coverage. The energetic position of the empty level is discussed in connection with photoemission data for occupied bands and excitation energies from electron energy loss measurements. 相似文献
5.
We have imaged for the first time individual atoms and small clusters of metal species on a metal substrate at room temperature by means of a scanning tunneling microscope (STM) operated under ultrahigh vacuum conditions. The system we have studied is Fe on W(110), for which a carbon-induced (15×3)-reconstruction of the W(110) substrate has been found to prevent surface diffusion of Fe atoms at 300 K. Upon positioning the STM-tip above individual Fe adsorbates, local tunneling spectra could be obtained. A pronounced empty-state peak at 0.5 eV above the Fermi level has been found, characteristic for individual Fe adsorbates. This peak can serve as a fingerprint for the identification of Fe adsorbate species. 相似文献
6.
The adsorption of benzotriazole (BTAH or C6N3H5) on a Cu(1 1 1) surface is investigated by using first principle density functional theory calculations (VASP). It is found that BTAH can be physisorbed (<0.1 eV) or weakly chemisorbed (∼0.43 eV) onto Cu(1 1 1), and the chemical bond is formed through nitrogen sp2 lone pairs. The weak chemisorption can be stabilized by reaction with neighboring protonphilic radicals, like OH−. Furthermore, the geometries and associated energies of intermolecular hydrogen bonds between adsorbates on Cu(1 1 1) are also calculated. A model of the first layer of BTAH/BTA− on Cu(1 1 1) surface is developed based on a hydrogen bond network structure. 相似文献
7.
A. Nilsson N. Wassdahl M. Weinelt O. Karis T. Wiell P. Bennich J. Hasselström A. Föhlisch J. Stöhr M. Samant 《Applied Physics A: Materials Science & Processing》1997,65(2):147-154
2 and CO on Ni(100), benzene on Ni(100) and Cu(110), and glycine adsorbed on Cu(110). New types of molecular states are observed
which are directly related to the surface chemical bond. The long-accepted Blyholder model which is based on a frontier orbital
concept cannot explain our results for N2 and CO chemisorption. We find it necessary to offer a new picture where changes in the whole molecular orbital framework
have to be considered. We show that both π and σ type interactions are important in describing the bonding in benzene to metal
surfaces. The future prospect is illustrated by the adsorption of the simplest amino acid, glycine, on Cu(110). The adsorbate
has four different atomic centers where X-ray emission spectra are obtained, providing a unique view of the local electronic
structure.
Accepted: 6 March 1997 相似文献
8.
Electron energy-loss spectra of clean and hydrogen-covered Cr(110) surfaces have been investigated in the spectral range of 0–80 eV for primary energies of 60–500 eV. The observed peaks for the clean surface are at the loss energies of 2, 3.5, 5.5, 9.6, 23, 35, 42, 48 and 55 eV. The 3p-excitation spectra for high primary energies (> 250 eV) are in good agreement with the corresponding optical spectrum. The edge at & 42 eV observed for low primary energies is tentatively attributed to the onset of the transition from the 3p subshell to the local 4s-band in the vicinity of the core hole. A characteristic energy-loss at ≈ 15.5 eV is observed after hydrogen adsorption. The 3p-spectrum is not influenced by hydrogen adsorption, indicating that the excitation is of a localized character. 相似文献
9.
本文应用ASED-MO方法,计算研究了Cu在Pt(111),(100),(110)表面的扩散问题。Cu原子在上述三个表面上的扩散激活能的计算结果分别为0.167eV,0.162eV和0.668eV;300K时的扩散系数分别为3.04×1010m2/s,3.69×10-10m2/s和2.42×10-18m2/s。计算结果表明,Cu原子在Pt(111)和(100)面上,扩散激活能很小,极易迁移,而在(110)面上,激活能较大,扩散系数甚小。 相似文献
10.
Mohammad Kemal Agusta Wilson Algerico Diño Melanie David Hiroshi Nakanishi Hideaki Kasai 《Surface science》2011,605(15-16):1347-1353
Hydrazine (N2H4) adsorption on metal surface is important due to its application in the direct hydrazine fuel cell technology. First principles DFT calculations have been carried out to understand the structure and mechanism of hydrazine adsorption on Pt(111). Calculations revealed that configuration with hydrazine adsorbed on its anti-conformation yields the largest adsorption energy suggesting it to be the most stable structure on Pt(111). This result was found to be in disagreement with available XPS results which favor the adsorption on cis-conformation as the most stable configuration. However, by taking into account the energy cost for orbital re-hybridization and internal rotation involves in the adsorption, it was found that the interaction strength between adsorbate and substrate is comparably equal for adsorption on both anti and cis-conformations that indicates the feasibility of the adsorption in cis-conformation to occur. Charge transfers from lone-pair orbitals belong to the highest occupied molecular orbital (HOMO) and second highest occupied molecular orbital (S-HOMO) were found to be important in the formation of the bonding. The π-anti-bonding HOMO lone-pair transfers its charge to the surface which stabilizes the internal structure of the molecule and responsible for the stable anti-conformation adsorption structure. The interaction of the π-bonding S-HOMO lone pair with the surface was found to be dative type and plays an important role in the stabilization of cis-conformation adsorption structure. 相似文献
11.
We have imaged for the first time individual atoms and small clusters of metal species on a metal substrate at room temperature
by means of a scanning tunneling microscope (STM) operated under ultrahigh vacuum conditions. The system we have studied is
Fe on W(110), for which a carbon-induced (15×3)-reconstruction of the W(110) substrate has been found to prevent surface diffusion
of Fe atoms at 300 K. Upon positioning the STM-tip above individual Fe adsorbates, local tunneling spectra could be obtained.
A pronounced empty-state peak at 0.5 eV above the Fermi level has been found, characteristic for individual Fe adsorbates.
This peak can serve as a fingerprint for the identification of Fe adsorbate species. 相似文献
12.
Using the technique of angle-resolved inverse photoemission, we have measured the dispersion of an unoccupied Cu(110) surface state for the clean Cu(110) surface and for the (1 × 2) reconstructed Na/Cu(110) surface along the
symmetry lines. The dispersion of the crystal-induced surface state of clean Cu(110) at 2.05 eV above the Fermi energy at the
point of the SBZ is free-electron-like with an effective mass of (1.0 ± 0.2)me at the
point, which is in good agreement with other experimental results as well as a theoretical calculation. This surface state shifts to 2.5 eV above the Fermi energy for the (1 × 2) phase of Na/Cu(110) with a coverage of 0.25 ML, and the dispersion along the
direction is considerably reduced compared to the clean surface. On the other hand, the dispersion of this state for (1 × 2) Na/Cu(110) (0.25 ML) along the
direction is close to that of clean Cu(110). We account for these results within a missing-row picture of the Na-induced reconstruction. 相似文献
13.
Acetonitrile (CH3CN) coordination to a Pt(111) surface has been studied with electron energy loss vibrational spectroscopy (EELS), XPS, thermal desorption and work function measurements. We compare data for the surface states with known acetonitrile coordination complexes. For CH3CN adsorbed on Pt(111) at 100 K, the molecule is rehybridized and adsorbs with the CN bond parallel or slightly inclined to the surface plane in an η2(C, N) configuration. The ν(CN) frequency is 1615 cm?1 and the C ls and N ls binding energies are 284.6 eV and 397.2 eV respectively. By contrast, weakly adsorbed multilayer acetonitrile exhibits a ν(CN) vibrational frequency of 2270 cm?1, and C ls and N ls binding energies of 286.9 eV and 400.1 eV respectively. Both the EELS and XPS results are consistent with rehybridization of the CN triple bond to a double bond with both C and N atoms of the CN group attached to the surface. In addition to this majority η2(C, N) monolayer state, evidence is found for a second, more strongly bound minority molecular state in thermal desorption spectra. As a result of the low coverage of this state, EELS was unable to spectroscopically identify it and we tentatively assign it as an η4(C, N) species associated with accidental step sites. By contrast to the surface complexes, almost all of the known platinum-nitrile coordination complexes are end-bonded via the N lone-pair orbital. Several cases of side-on bonding are known, however, and we compare the results with the known complex Fe3(η2-NCCH3)(CO)9. The difference in the coordinative properties of a Pt(111) surface versus a single Pt atom must be due to the increased ability of multi-atom arrays to back-donate electrons into the π1 system of acetonitrile. Previously published EELS and XPS results for monolayer acetonitrile on Ni(111) and polycrystalline films are almost identical to the present results on Pt(111). We believe that the monolayer of is also an η2(C, N) species, not an end-bonded species previously proposed by Friend, Muetterties and Gland. 相似文献
14.
In a recent paper, Kojima, Sugihara, Miyazaki and Yasumori concluded that methanol and formaldehyde adsorb molecularly (non-dissociatively) on polycrystalline copper at 300 K. Methanol and methyl formate were also found to produce adsorbed formaldehyde. We demonstrate that the “ formaldehyde” UPS spectrum in their study was incorrectly assigned, and is identical to that of adsorbed formate generated during dissociative exposure of formaldehyde to a Cu(110) surface. We have measured the He II spectra of formaldehyde (120 K) and formate (300 K) on clean Cu(110) and show that they are distinctly different. No evidence is found in the present work for stabilization of molecular formaldehyde, methanol or methyl formate on the Cu(110) surface at 300 K. 相似文献
15.
T. Mandel G. Kaindl K. Horn M. Iwan H.U. Middelmann C. Mariani 《Solid State Communications》1983,46(9):713-716
Photoelectron spectra of the krypton 3d core-levels and MNN Auger spectra of krypton mono- and multilayers on Cu(110) have been recorded with synchrotron radiation. The Kr-3d line is found to shift to higher binding energies by 0.73 eV for first- and second-layer adsorption, respectively. This value is much larger than the work function decrease for Kr mono-layer adsorption, Δø = ?0.29eV. The shift in Auger line energies is found to be about three times larger than the 3d line shift. These observations can be readily explained in terms of image-charge screening of the hole states. 相似文献
16.
E. Bertel 《Applied Physics A: Materials Science & Processing》1991,53(5):356-368
Experimental work on unoccupied electronic states in adsorbate systems on metallic substrates is reviewed with emphasis on recent developments. The first part is devoted to molecular adsorbates. Weakly chemisorbed hydrocarbons are briefly discussed. An exhaustive inverse photoemission (IPE) study of the CO bond to the transition metals Ni, Pb, and Pt is presented. Adsorbed NO is taken as an example to demonstrate the persisting discrepancies in the interpretation of IPE spectra. Atomic adsorbates are discussed in the second part. The quantum well state model is applied to interpret the surface states in reconstructing and non-reconstructing adsorption systems of alkali metals and hydrogen. A recent controversy on the unoccupied electronic states of the Cu(110)/O p(2×1) surface is critically reviewed. The quantum well state model is then compared to tight binding and local-density-functional calculations of the unoccupied bands and the deficiencies of the various approaches are pointed out. Finally, the relation between the surface state model and more chemically oriented models of surface bonding is briefly discussed. 相似文献
17.
Ultraviolet photoemission spectroscopy in ultrahigh vacuum has been used to study the interaction of H2O with argon-ion-bombarded and annealed TiO2(110) and SrTiO3 (100) surfaces. At low exposure, evidence is found for the presence of the OH free radical on both bombarded and annealed TiO2. At high exposure, a spectrum of slightly perturbed adsorbed H2O is observed, with the a1 molecular orbital shifted 0.5–1 eV toward tighter binding. This suggests that H2O binds to the surface of TiO2 via its a1, in-plane O lone-pair orbital. No evidence is found for OH on the surface of SrTiO3. The spectrum of H2O adsorbed on bombarded SrTiO3 shows both the a1 and b2 molecular orbitals shifted 0.4 toward tighter binding, indicating a more complicated bonding to the surface. For SrTiO3 that has been bombarded and then annealed, the spectrum of adsorbed H2O shows no significant bonding effects. 相似文献
18.
Preceding work dealing with the adsorption of methanol on Cu(110) has been extended to include ethanol, n- and iso-propanol and a diol, ethylene glycol. In common with the simplest alcohol, all these molecules are able to form a stable alkoxy species on the surface, that is, the alcohol dissociated at the O-H group. However, in contrast to methanol on the clean surface for which the dissociated methoxy and hydrogen recombined to desorb as methanol, all the higher alcohols reacted further with the surface, dehydrogenating to yield the corresponding aldehyde or ketone in the gas phase. Ethylene glycol reacted to form the most strongly bound intermediate of all, decomposing near 390 K to produce the dialdehyde, glyoxal, with little evidence of monoaldehyde formation or C-C bond breakage. The influence of pre-adsorbed oxygen on these reactions was to generally increase the amount of alkoxy formed on the surface by enhancing the amount of dissociative adsorption (water is formed by the deprotonation of adsorbed alcohol molecules by oxygen atoms). The alkoxide decomposition peaks were shifted to slightly higher temperatures and considerably broadened in such experiments. The decomposition peak temperatures of the different surface alkoxides correlate fairly well with literature values of the αC-H bond strength, which is weaker in iso-propanol than in methanol. XPS showed broad O(1s) spectra for all the molecules adsorbed at 140 K, probably due to hydrogen-bonding effects in the adlayer, with peak emissions at around 533 eV. When the surface was warmed to 250 K, the O(1s) spectra narrowed to close to instrumental linewidths with a concomitant shift to a lower binding energy near 531 eV. C(1s) spectra showed little change between the adsorbed alcohol and alkoxy species. The UPS showed low temperature spectra similar to the gas phase, but the highest occupied orbitals, which are essentially O(2p) orbitals, showed a chemisorption bonding shift of several tenths of an electron volt. UPS for these molecules is shown to have considerable less utility than for the simplest molecule, methanol, due to the masking of possible orbital shifts during chemical changes on the surface by the presence of overlapping emissions in the spectra. 相似文献
19.
The adsorption of L-alanine on Cu(111) surface is studied by means of scanning tunnelling microscopy under ultra-high vacuum conditions. The results show that the adsorbates are chemisorbed on the surface, and can form a two-dimensional gas phase, chain phase and solid phase, depending on deposition rate and amount. The adsorbed molecules can be imaged as individual protrusions and parallel chains in gas and chain phases respectively. It is also found that alanine can form (2 × 2) superstructure on Cu(111) and copper step facet to (110) directions in solid phase. On the basis of our scanning tunnelling microscopic images, a model is proposed for the Cu(111)(2 ×2)-alanine superstructure. In the model, we point out the close link between (110)-direction hydrogen bond chains with the same direction copper step faceting. 相似文献
20.
High energy resolution KL23L23 Auger spectra of polycrystalline Cu and Ni were measured using photon energies up to about 50 eV above the K-absorption edge and down to 5 eV (Cu KLL) and 4 eV (Ni KLL) below threshold. The spectra show strong satellite structures varying considerably as a function of the photon energy. In the sub-threshold region the linear dispersion of the diagram line energy positions and a distortion of the line shape as a function of photon energy, attributable to the Auger resonant Raman process, is clearly observed, indicating the one-step nature of the Auger emission. These changes in the resonant spectra are interpreted using a simple model based on resonant scattering theory in combination with partial density of states obtained from cluster molecular orbital (DV-Xα) calculations. 相似文献