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1.
We describe a method for determining the interaction potential between a helium atom and a metal surface from diffraction data. Results are presented for He/Ni(110) and He/Cu(110). For He/Cu(110) the potential 3s in good agreement with a first principles calculation but this is not true for He/Ni(110). We also show that a surface relaxation of 10% produces measurable changes in intensities. 相似文献
2.
《Surface science》1986,167(1):L203-L209
We evaluate the proportionality constant β for neon in the Esbjerg-Nørskov potential VR(r) = βϱ(r) from experimental data on Ni(110), Ni(113), Cu(110) and Pd(110). Our calculations using overlapping atomic charge densities require that β be material and surface-dependent. Although Ne diffraction is more sensitive to details of corrugation shapes than He, we found it to be insensitive to normal relaxations of the topmost layers. 相似文献
3.
The adsorption of O2 and CO on the (110) face of a Cu/Ni alloy (55 at% Cu) has been studied by means of low energy electron diffraction (LEED), Auger electron spectroscopy, work function measurements, and flash desorption. A comparison with the behavior of Cu(110) and Ni(110) is made. It is shown that the height of an Auger peak is proportional to the surface concentration of the corresponding species and that the surface composition of the alloy is identical with the composition of the bulk. Adsorption of oxygen leads to the formation of an ordered 2 × 1 structure, as is the case for Cu(110) and Ni(110). Further exposure causes disordered adsorption in contrast to the pure components where c6 × 2 respectively 3 × 1 structures are formed. Oxygen increases the work function of Cu and Cu/Ni by about 0.25 eV whereas for Ni the increase is > 1 eV. CO is not irreversibly adsorbed on Cu at 25°C, but forms a stable 1 × 1 structure on Ni(110). With the alloy two ordered phases (2 × 1 and 2 × 2) are observed. The flash desorption spectrum shows three maxima which are similar to the binding states of CO on Ni(110) and Ni(100). The results are discussed in view of the electronic structure of Cu/Ni alloys and the parameters influencing the configuration of adsorbed particles. 相似文献
4.
J.P. Muscat 《Surface science》1981,110(1):85-110
The interaction between H adatoms on a surface is calculated within the embedded cluster model of chemisorption. The model is first applied to the case of two H atoms on a free electron surface. The interaction energy is found to be an oscillatory function of the H-H separation Rab. Application of the free electron model to the problem of chemisorption on transition metal surfaces leads to unphysical results with the prediction of formation of ordered H overlayers which are not observed in LEED experiments. We next include the l = 2 TM muffin tins. Results for H adsorption on the low index faces of Ni and Pd substrates are presented. Graphitic structures are predicted for the (111) faces of both Ni and Pd with the H atoms occupying both types of three-fold hollow sites on the surface. This agrees with the results of LEED experiments for H/Ni(111). Comparison with experiment is not possible in the case of H/Pd(111) owing to the lack of low temperature studies for that system. Zig-zag chains with the H atoms adsorbed in sites of three-fold coordination on alternate sides of the TM(110) rows are predicted for both Ni and Pd. This is in agreement with the results of He diffraction experiments for H/Ni(110). No structure determination has been done for H/Pd(110). Adsorption in the four-fold centre sites for H on the (100) faces of Ni and Pd is found to be unfavourable. The H atoms are expected to adsorb in sites of three-fold symmetry below the (100) surface for H on Pd with formation of a c(2 × 2) structure in agreement with the LEED observations. For H/Ni(100) the H atoms are believed to adsorb above the surface, away from the centre site and to bond to two surface Ni atoms. No short-range ordered structures are predicted in this case. 相似文献
5.
H+ desorption induced by the impact of metastable helium atoms has been found for H(2)O/Na/Ni(110) coadsorption systems. The measurements were carried out using a time-of-flight technique and a pulsed-discharge type metastable helium atom ( He(*)) source. It is concluded that the H+ desorption by He(*) is induced by a hole created on the valence levels via the Auger deexcitation of He(*). The H+ desorption by He(*) may be understood within the framework of the Menzel-Gomer-Readhead model. 相似文献
6.
7.
The adsorption of oxygen on clean Ni(110) has been studied at room temperature and at 475 K by Rutherford backscattering, using the effects of channeling and blocking, and lowenergy electron diffraction. At both temperatures successive LEED structures are formed at low oxygen coverage (?0.5 monolayer). With increasing oxygen content stoichiometric NiO is formed on top of the Ni(110) surface, at room temperature as an amorphous layer and at 475 K as patches of crystalline oxide, oriented with the NiO(100) planes parallel to the Ni(110) surface plane. At 475 K the nickel atoms in the interface region between oxide and substrate are displaced over a thickness of less than 2 monolayers. Based on the measurement of the oxide composition as function of coverage we suggest a modification of the island growth model as proposed by Holloway and Hudson for the Ni(100) and (111) surfaces. 相似文献
8.
Peters KF Walker CJ Steadman P Robach O Isern H Ferrer S 《Physical review letters》2001,86(23):5325-5328
The crystallographic structure of CO adsorbed on Ni(110) has been investigated with x-ray diffraction at ambient pressures of CO ranging from 2.3 to 10(-10) bars. At room temperature, the high pressure and vacuum structures are identical. Above room temperature ( approximately 130 degrees C), the high pressure of CO induces a restructuring of the Ni substrate that develops strained (111) microfacets. 相似文献
9.
S.B. Vojvodić 《Physics letters. A》1983,97(5):210-212
Resonant charge exchange between slow atomic particles and a partially coated metal surface, in the presence of a homogeneous electric field, is considered. The survival probabilities are calculated for H- ions, emerging from Cs-coated W and K-coated Ni(110) in fields of strengths 10-4, 10-5 and 0 au. 相似文献
10.
The interaction of water vapour with clean as well as with oxygen precovered Ni(110) surfaces was studied at 150 and 273 K, using UPS, ΔΦ, TDS, and ELS. The He(I) (He(II)) excited UPS indicate a molecular adsorption of H2O on Ni(110) at 150 K, showing three water-induced peaks at 6.5, 9.5 and 12.2 eV below EF (6.8, 9.4 and 12.7 eV below EF). The dramatic decrease of the Ni d-band intensity at higher exposures, as well as the course of the work function change, demonstrates the formation of H2O multilayers (ice). The observed energy shift of all water-induced UPS peaks relative to the Fermi level (ΔEmax = 1.5 eVat 200 L) with increasing coverage is related to extra-atomic relaxation effects. The activation energies of desorption were estimated as 14.9 and 17.3 kcal/mole. From the ELS measurements we conclude a great sensitivity of H2O for electron beam induced dissociation. At 273 K water adsorbs on Ni(110) only in the presence of oxygen, with two peaks at 5.7 and 9.3 eV below EF (He(II)), being interpreted as due to hydroxyl species (OH)δ? on the surface. A kinetic model for the H2O adsorption on oxygen precovered Ni(110) surfaces is proposed, and verified by a simple Monte Carlo calculation leading to the same dependence of the maximum amount of adsorbed H2O on the oxygen precoverage as revealed by work function measurements. On heating, some of the (OH)δ? recombines and desorbs as H2O at ? 320 K, leaving behind an oxygen covered Ni surface. 相似文献
11.
12.
Meyerheim HL Sander D Popescu R Kirschner J Robach O Ferrer S 《Physical review letters》2004,93(15):156105
The correlation between an ad-layer-induced spin reorientation transition (SRT) and the ad-layer-induced structural relaxation is investigated by combined in situ surface x-ray diffraction and magneto-optical Kerr-effect experiments on Ni/Fe/Ni(111) layers on W(110). The Fe-induced SRT from in-plane to out-of-plane, and the SRT back to in-plane upon subsequent coverage by Ni, are each accompanied by a small lattice relaxation of at most 0.002 A. Such a small strain variation excludes a magnetoelasticity driven SRT, and we suggest the interface anisotropy as a possible driving force. 相似文献
13.
Puzzling trends in surface stress have been reported experimentally for Ni/W(110) as a function of Ni coverage. In order to explain this behavior, we have performed a density-functional-theory study of the surface stress and atomic structure of the pseudomorphic and several different possible 1 × 7 configurations for this system. For the 1 × 7 phase, we predict a different, more regular atomic structure than previously proposed based on surface x-ray diffraction. At the same time, we reproduce the unexpected experimental change of surface stress between the pseudomorphic and 1 × 7 configuration along the crystallographic surface direction which does not undergo density changes. We show that the observed behavior in the surface stress is dominated by the effect of a change in Ni adsorption/coordination sites on the W(110) surface. 相似文献
14.
R. Koch M. Borbonus O. Haase K. H. Rieder 《Applied Physics A: Materials Science & Processing》1992,55(5):417-429
The fcc(110) surfaces are well known for their strong tendency to missing-row (MR) type reconstructions either in the clean state (Au, Pt) or driven by adsorbates (Ni, Cu, Pd, Ag). The present knowledge on the different reconstruction behaviour of flat (110) surfaces is reviewed. The survey focuses on recent scanning tunneling microscopy (STM) studies, which for the first time also elucidate the dynamics of the reconstruction process for the various systems. An overview of our recent STM and low energy electron diffraction studies on vicinal Au(110) and Ni(110) surfaces is given, aiming for a deeper understanding of the influence of steps on reconstruction behaviour of fcc(110) surfaces on the one hand, and on the stability of reconstructing vicinal surfaces on the other. Finally, we report on the reconstruction behaviour of Ir(110), which stabilizes in the clean state by formation of mesoscopic (331) facets and dereconstructs to the (1×1) phase upon oxygen adsorption at 700–900 K. 相似文献
15.
Ni thin films are prepared on GaAs(100) single-crystal substrates at room temperature by using an ultra-high vacuum radio-frequency magnetron sputtering system. The growth behavior and the crystallographic properties are studied by in-situ refection highenergy electron diffraction and pole-figure X-ray diffraction. In an early stage of film growth, a metastable bcc Ni(100) single-crystal film is formed on GaAs(100) substrate, where the bcc structure is stabilized through hetero-epitaxial growth. With increasing the film thickness, fcc crystals coexist with the bcc(100) crystal. High-resolution cross-sectional transmission electron microscopy shows that the film consists of a mixture of bcc and fcc crystals and that a large number of planar faults exist parallel to the fcc(111) close-packed plane. The results indicate that the bcc structure starts to transform into fcc structure through atomic displacement parallel to the bcc{110} close-packed planes. 相似文献
16.
The well-known classical path approximation is applied to a calculation of diffraction intensities in the scattering of atoms from a rigid crystal with a soft interaction potential. A general expression is derived for the diffraction intensities which can be applied to potentials with several higher-order terms in the Fourier series. For an uncorrugated Morse potential with a first-order exponential corrugation term an analytic solution is obtained which is compared with the infinite order suddent (IOS) approximation calculations for Ne/W(110) and He/LiF(100). Both approximations are very accurate for the weakly corrugated Ne/W system. For He/LiF the present approximation is more accurate than the sudden (IOS) approximation and has the added advantage of providing an analytic solution. Several improvements are suggested. 相似文献
17.
The formation of doubly excited states of He atoms during collisions of He2+ ions with projectile energies between 74 eV and 124 eV with an Fe(110) and a Ni(110) surface is studied via Auger electron spectroscopy. We observe that the electron spectra from autoionization of doubly excited states of 2s2, 2s2p, 2p2 configurations show a pronounced dependence on the coverage with oxygen for both surfaces. For a controlled O2 adsorption on the Fe(110) and Ni(110) surfaces we can explain the resulting changes in the electron spectra by the modification of the measured work functions of the target surfaces. In terms of thermal desorption and dissolution into the bulk of surface contaminations at elevated temperatures, we present an alternative interpretation of similar previous studies by another group, where the local electron spin polarization of Fe(110) and Ni(110) surfaces was deduced from changes in the electron spectra as function of target temperature. 相似文献
18.
PING Feilin JIANG Gang ZHANG Lin & ZHU Zhenghe . Institute of Atomic Molecular Physics Sichuan University Chengdu China . Research Center of Laser Fusion Mianyang China 《中国科学G辑(英文版)》2005,48(6)
1 Introduction LaNi5 intermetallic compounds, used in storage, separation and purification of hydro- gen and hydrogen isotopes, are known for a high-density storage, easy activation, low pressure, and rapid and reversible absorption and desorption[1-15]. Tritium as an impor- tant material in the nuclear industry is radioactively decaying into 3He with a half-life of 12.3 years. With time, there are many changes in the electronic and physical properties of the tritide for the deposition of 3He… 相似文献
19.
M. Nishijima S. Masuda M. Jo M. Onchi 《Journal of Electron Spectroscopy and Related Phenomena》1983,29(1):273-278
High-resolution electron energy loss spectra of hydrogen-covered Ni(110) surfaces both at 100 and 300 K are presented. The adsorbed sites of hydrogen atoms are discussed.High-resolution electron energy loss spectra of hydrogen covered Ni(110) surfaces have been studied. Tentative models for the adsorbed sites of hydrogen atoms are as follows: (1) For the (2 × 1)-H surface, hydrogen is adsorbed in the three-coordinated sites of the rudimentary (111) face of the unreconstructed Ni(110) substrate. (2) For the low-temperature (1 × 2)-H surface, hydrogen is adsorbed in the three-coordinated sites and, probably, in the two-fold hollow sites of the distorted Ni(110) substrate. (3) For the room-temperature (1 × 2)-H surface, hydrogen is disorderedly adsorbed in the three-coordinated, two-fold hollow and short-bridge sites and, possibly, in the octahedral sites of the distorted Ni(110) substrate. Some of the unresolved problems in the above assignments are summarized: (1) Strictly, the three-coordinated sites above are somewhat different from those discussed in the molecular-beam diffraction study [5]. (2) For the low-temperature (1 × 2)-H surface, the loss associated with hydrogen in the two-fold hollow sites is apparently not observed. (3) Intensity changes of the three losses for the room-temperature (1 × 2)-H surface with increasing hydrogen pressure (Fig. 2) are not well understood. 相似文献
20.
采用分子动力学方法研究了Pb液滴在Ni(100)晶面、(110)晶面和(111)晶面的铺展润湿行为. 结果表明: Pb液滴在Ni(100)及(111)基底上的润湿铺展现象呈各向同性, 而在Ni(110)基底上的润湿铺展现象呈明显的各向异性, 且这种各向异性源于Ni(110)晶面点阵结构上Pb原子沿不同晶向的扩散机制及速度的明显差异; Pb液滴在Ni(111)晶面上铺展时, 未发生表面合金化, 液滴铺展动力学描述近似满足 R2 ∝ t, 而液滴在(100)晶面和(110)晶面上铺展时表面产生合金化现象, 铺展动力学关系近似满足 R4 ∝ t, 且液滴在(100)晶面上的铺展速度高于(110)晶面上的铺展速度.
关键词:
分子动力学
润湿各向异性
铺展膜
扩散机制 相似文献