Pb液滴在Ni基底润湿铺展行为的分子动力学模拟

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     

Mass and lattice effects in trapping: Ar, Kr, and Xe on Pt(1 1 1), Pd(1 1 1), and Ni(1 1 1)

The trapping probabilities of argon, krypton, and xenon on Pd(1 1 1) and Ni(1 1 1) have been investigated using supersonic molecular beam techniques. The trapping probability of argon exhibits normal incident energy in a similar fashion on both Pd(1 1 1) and Pt(1 1 1) because the mass of argon is significantly less than the surface mass of either Pd or Pt. In contrast, dynamic corrugation in the gas-surface potential is observed for krypton trapping on Pt(1 1 1) and Pd(1 1 1), resulting in a decreased angular dependence of the trapping probability compared to argon. For xenon trapping on Pd significant lattice deformation during the gas-surface collision appears to give rise to total energy scaling. The trapping probability of xenon on Pd(1 1 1) remains high at unusually high incident kinetic energies due to the overall enhanced energy transfer from the incident atom to the lattice. Trapping probabilities of Ar, Kr, and Xe are significantly lower on Ni(1 1 1) than on either Pt(1 1 1) or Pd(1 1 1) despite the lower surface mass of the Ni atoms. This result is attributed to the lower binding energy of the rare gases on Ni(1 1 1) and the higher Debye temperature of Ni. The energy scaling of Ar trapping on Ni(1 1 1) is determined by static corrugation, but the energy scaling for Kr and Xe on Ni(1 1 1) may involve the effects of dynamic corrugation. In the latter cases, the greater stiffness of the nickel lattice decreases the dynamic corrugation relative to Pt(1 1 1) and Pd(1 1 1).     

Phonon spectra of clean and Ni-terminated diamond (111) surfaces: An ab-initio study

The phonon densities of states (ph-DOSs) of clean and Ni-terminated C(111) surfaces with 1 × 1 and 2 × 1 surface structures were investigated using ab-initio density functional perturbation theory. The ph-DOSs showed vibrational spectra associated with the surface structures of C(111) and Ni/C(111). Further analyses of various surface phonon modes were performed to identify vibrational features involving the surface atoms of C(111) and Ni/C(111). These features provide important information for experimentally verifying the formation of a diamond bulk-like structure at Ni/C(111), as suggested in a previous study.     

The interplay between geometry,electronic structure,and reactivity of Cu-Ni bimetallic (111) surfaces

The mutual influence of surface geometry (e.g. lattice parameters, morphology) and electronic structure is discussed for Cu-Ni bimetallic (111) surfaces. It is found that on flat surfaces the electronic d-states of the adlayer experience very little influence from the substrate electronic structure which is due to their large separation in binding energies and the close match of Cu and Ni lattice constants. Using carbon monoxide and benzene as probe molecules, it is found that in most cases the reactivity of Cu or Ni adlayers is very similar to the corresponding (111) single crystal surfaces. Exceptions are the adsorption of CO on submonolayers of Cu on Ni(111) and the dissociation of benzene on Ni/Cu(111) which is very different from Ni(111). These differences are related to geometric factors influencing the adsorption on these surfaces. Received: 26 August 2002 / Accepted: 4 September 2002 / Published online: 5 February 2003 RID="*" ID="*"Corresponding author. Fax: +44-1223/76-2829, E-mail: gh10009@cam.ac.uk [+1pt] Present address: University of Cambridge, Lensfield Road, Department of Chemistry, Cambridge CB2 1EW, UK     

Direct graphene growth on Co3O4(111) by molecular beam epitaxy

Direct growth of graphene on Co(3)O(4)(111) at 1000 K was achieved by molecular beam epitaxy from a graphite source. Auger spectroscopy shows a characteristic sp(2) carbon lineshape, at average carbon coverages from 0.4 to 3 ML. Low energy electron diffraction (LEED) indicates (111) ordering of the sp(2) carbon film with a lattice constant of 2.5(±0.1) ? characteristic of graphene. Sixfold symmetry of the graphene diffraction spots is observed at 0.4, 1 and 3 ML. The LEED data also indicate an average domain size of ~1800 ?, and show an incommensurate interface with the Co(3)O(4)(111) substrate, where the latter exhibits a lattice constant of 2.8(±0.1) ?. Core level photoemission shows a characteristically asymmetric C(1s) feature, with the expected π to π* satellite feature, but with a binding energy for the 3 ML film of 284.9(±0.1) eV, indicative of substantial graphene-to-oxide charge transfer. Spectroscopic ellipsometry data demonstrate broad similarity with graphene samples physically transferred to SiO(2) or grown on SiC substrates, but with the π to π* absorption blue-shifted, consistent with charge transfer to the substrate. The ability to grow graphene directly on magnetically and electrically polarizable substrates opens new opportunities for industrial scale development of charge- and spin-based devices.     

Observation of eta'c production in gammagamma fusion at CLEO

We report on the observation of the eta(')(c)(2(1)S0), the radial excitation of the eta(c)(1(1)S0) ground state of charmonium, in the two-photon fusion reaction gammagamma-->eta(')(c)-->K(0)(S)K+/-pi(-/+) in 13.6 fb(-1) of CLEO II/II.V data and 13.1 fb(-1) of CLEO III data. We obtain M(eta(')(c))=3642.9+/-3.1(stat)+/-1.5(syst) MeV and M(eta(c))=2981.8+/-1.3(stat)+/-1.5(syst) MeV. The corresponding values of hyperfine splittings between 1S0 and 3S1 states are DeltaM(hf)(1S)=115.1+/-2.0 MeV and DeltaM(hf)(2S)=43.1+/-3.4 MeV. Assuming that the eta(c) and eta(')(c) have equal branching fractions to K(S)Kpi, we obtain Gamma(gammagamma)(eta(')(c))=1.3+/-0.6 keV.     

Effect of Ni, Pd and Ni-Pd nano-islands on morphology and structure of multi-wall carbon nanotubes

In this research, the effect of Ni, Pd and Ni-Pd catalysts have studied on morphology and structure of synthesized multi-wall carbon nanotubes (MWCNTs). Initially, thin films of Ni (with two thicknesses of 10 and 20 nm), Pd/Ni (5/10 nm) and Pd (10 nm) were deposited as catalysts on SiO₂ (60 nm)/Si(1 0 0) substrates, using dc magnetron sputtering technique. The deposited films were annealed at 900 °C in ammonia environment for 45 min, in order to obtain nano-structured catalyst on the surface. Using scanning electron microscopy (SEM), the average size of Ni nano-islands (synthesized by the 10 and 20 nm Ni films), Pd and Ni-Pd nano-islands were measured about 55, 110, 45 and 50 nm, respectively. According to X-ray photoelectron spectroscopy analysis (XPS), the ratio of Ni/Pd on the surface was about 3 for the bilayer sample. The CNTs were synthesized on the nano-island catalysts at 940 °C in CH₄ ambient using a thermal chemical vapor deposition method. The results revealed that average diameter of the CNTs were about 70, 110, 120 nm for Ni, Ni-Pd and Pd catalysts, respectively. Raman spectra of the MWCNTs showed that intensity ratio of two main peaks located in the range of 1550-1600 and 1250-1450 cm⁻¹ (as a quality factor for the CNTs) for Ni, Pd and Ni-Pd catalysts were 1.42, 0.91 and 0.85, respectively. Therefore, based on our data analysis, although addition of Pd to Ni catalyst caused a considerable reduction in the quality of the grown MWCNTs as compared to the pure Ni catalyst, but it resulted in an enhancement in the methane decomposition rate. For the pure Pd catalyst samples, both a slow methane decomposition rate as compared with Ni-Pd catalyst samples and a poor quality of CNTs were observed as compared with the Ni catalyst, under similar experimental conditions.     

Growth and photoluminescence properties of inclined ZnO and ZnCoO thin films on SrTiO₃（110） substrates

ZnO thin film growth prefers different orientations on the etched and unetched SrTiO 3(STO)(110) substrates.Inclined ZnO and cobalt-doped ZnO(ZnCoO) thin films are grown on unetched STO(110) substrates using oxygen plasma assisted molecular beam epitaxy,with the c-axis 42 inclined from the normal STO(110) surface.The growth geometries are ZnCoO[100]//STO[110] and ZnCoO[111]//STO[001].The low temperature photoluminescence spectra of the inclined ZnO and ZnCoO films are dominated by D 0 X emissions associated with A 0 X emissions,and the characteristic emissions for the 2 E(2G)→ 4A2(4F) transition of Co 2+ dopants and the relevant phonon-participated emissions are observed in the ZnCoO film,indicating the incorporation of Co 2+ ions at the lattice positions of the Zn 2+ ions.The c-axis inclined ZnCoO film shows ferromagnetic properties at room temperature     

C_2H_x(x=4～6)在Ni(111)表面吸附的DFT研究

采用密度泛函理论与周期平板模型相结合的方法,对物种C_2H_x(x=4～6)在Ni(111)表面的top,fcc,hcp和bridge位的吸附模型进行了结构优化、能量计算,得到了各物种较有利的吸附位;并对最佳吸附位进行密立根电荷和总态密度分析.结果表明:C_2H_6和C_2H_4在Ni(111)表面的最稳定吸附位都是top位,吸附能分别是-36.41和-48.62 kJ·mol~(-1),物种与金属表面吸附较弱;而C_2H_5在Ni(111)表面的最稳定吸附位hcp的吸附能是-100.21 kJ·mol~(-1),物种与金属表面较强;三物种与金属表面之间都有电荷转移,属于化学吸附.     

Graphene domain boundaries on Pt(111) as nucleation sites for Pt nanocluster formation

The growth of Pt nanoclusters on a graphene layer on Pt(111) was studied with ultra high vacuum scanning tunneling microscopy. Different periodicities in the moiré patterns of the graphene layer are observed corresponding to different orientations with respect to the Pt(111) lattice. Various graphene orientations are possible because of a relatively weak graphene–Pt interaction. Following Pt deposition onto the graphene-covered surface, small Pt nanoclusters are observed to preferentially form along the moiré domain boundaries. The weak interaction of graphene with Pt(111) leads to a weak corrugation in the superlattice compared to other transition metals, such as Ru, but it is found even this weak corrugation is sufficient to serve as a template for the formation of mono-dispersed one-dimensional Pt nanocluster chains. These Pt nanoclusters are relatively stable and only undergo agglomeration at annealing temperatures above 600 K.     

Chlorine chemisorption on Cu(0 0 1) by surface X-ray diffraction: Geometry and substrate relaxation

We report on the precise location of Cl atoms chemisorbed on a Cu(0 0 1) surface and the interlayer relaxations of the metal surface. Previous studies have shown that chlorine dissociates on Cu(0 0 1) to form a c(2 × 2) chemisorbed layer with Cl atoms occupying four-fold hollow sites. A Cu-Cl interlayer spacing of 1.60 Å and a slightly expanded Cu-Cu first interlayer spacing of 1.85 Å (1.807 Å for bulk Cu) was determined by LEED. The resulting Cu-Cl bond length, 2.41 Å, is very similar to the SEXAFS value of 2.37 Å. Contradictory results were obtained by angle-resolved photoemission extended fine structure: while confirming the Cu-Cl interlayer spacing of 1.60 Å, no first Cu-Cu interlayer relaxation has been observed. On the other hand, a small corrugation of the second Cu layer was pointed out. We carried out a detailed structural determination of the Cu(0 0 1)-c(2 × 2)-Cl system using surface X-ray diffraction technique with synchrotron radiation. We find a Cu-Cl interlayer spacing of 1.584(5) Å and confirm the expansion of the first Cu-Cu interlayer, with an average spacing of 1.840(5) Å. In addition, we observe a small corrugation of the second Cu layer, with Cu atoms just below Cl atoms more tightly bound to the surface layer, and even a second Cu-Cu interlayer expansion.     

Pressure induced friction collapse of rare gas boundary layers sliding over metal surfaces

In this Letter we show that friction of anticorrugating systems can be dramatically decreased by applying an external load. The counterintuitive behavior that deviates from the macroscopic Amonton law is dictated by quantum mechanical effects that induce a transformation from anticorrugation to corrugation in the near-surface region. We describe the load-driven modifications occurring in the potential energy surface of different rare gas-metal adsorbate systems, namely, Ar, Kr, Xe on Cu(111), and Xe on Ag(111), and we calculate the consequent friction drop for the commensurate Xe/Cu system by means of combined ab initio and classical molecular dynamics simulations.     

Thermal decomposition of CO on a stepped Ni surface

The adsorption-desorption behaviour of CO on the stepped Ni(S) [5(111) × (11̄0)] and the smooth Ni(111) plane are compared by using LEED, thermal flash desorption and AES. Above room temperature flash desorption from the Ni(111) face yields a single α peak characteristic of molecularly adsorbed CO whereas from the stepped surface in addition to the a peak α second desorption peak (β2) appears around 550°C which is assigned to associative CO desorption. If carbon and oxygen are separately chemisorbed on Ni(111) associative desorption of CO leads to a desorption peak around 350° C. It is concluded that steps lower the activation energy for CO decomposition but increase the activation energy for associative desorption.     

Density functional theory calculation of platinum surface segregation energy in Pt3Ni (111) surface doped with a third transition metal

We have used density functional theory method to calculate the Pt surface segregation energy in the Pt₃Ni (111) surface doped with a third transition metal M and thus investigated the influence of component M on the extent of Pt segregation to the outermost layer of these Pt₃Ni/M (111) surface. As a third component in the Pt₃Ni/M (111) surface, V, Fe, Co, Mo, Tc, Ru, W, Re, Os, and Ir were predicted to lead to even more negative Pt surface segregation energies than that in the based Pt₃Ni (111) surface; Ti, Cr, Mn, Cu, Zr, Nb, Rh, Hf, and Ta would still retain the preference of Pt segregation to the surface but with less extent than the replaced Ni, while Pd, Ag, and Au would completely suppress the Pt segregation to the Pt₃Ni/M (111) surfaces. Furthermore, we examined the relation between the Pt surface segregation energy in the Pt₃Ni/M (111) surfaces and the material properties (lattice parameter, heat of solution, and Pt surface segregation energy) of binary alloys Pt₃M. It was found that the surface energy effect, strain effect, and heat of solution effect induced by the doped element M would collectively affect the Pt surface segregation energy in the Pt₃Ni/M (111) surfaces.     

Epitaxial growth of graphene on transition metal surfaces: chemical vapor deposition versus liquid phase deposition

The epitaxial growth of graphene on transition metal surfaces by ex situ deposition of liquid precursors (LPD, liquid phase deposition) is compared to the standard method of chemical vapor deposition (CVD). The performance of LPD strongly depends on the particular transition metal surface. For Pt(111), Ir(111) and Rh(111), the formation of a graphene monolayer is hardly affected by the way the precursor is provided. In the case of Ni(111), the growth of graphene strongly depends on the applied synthesis method. For CVD of propene on Ni(111), a 1 × 1 structure as expected from the vanishing lattice mismatch is observed. However, in spite of the nearly perfect lattice match, a multi-domain structure with 1 × 1 and two additional rotated domains is obtained when an oxygen-containing precursor (acetone) is provided ex situ.     

Corrugated single layer templates for molecules: From h-BN nanomesh to graphene based quantum dot arrays

Functional nano-templates enable self-assembly of otherwise impossible arrangements of molecules. A particular class of such templates is that of sp² hybridized single layers of hexagonal boron nitride or carbon (graphene) on metal supports. If the substrate and the single layer have a lattice mismatch, superstructures are formed. On substrates like rhodium or ruthenium these superstructures have unit cells with ~3-nm lattice constant. They are corrugated and contain sub-units, which behave like traps for molecules or quantum dots, which are small enough to become operational at room temperature. For graphene on Rh(111) we emphasize a new structural element of small extra hills within the corrugation landscape. For the case of molecules like water it is shown that new phases assemble on such templates, and that they can be used as “nano-laboratories” where many individual processes are studied in parallel. Furthermore, it is shown that the h-BN/Rh(111) nanomesh displays a strong scanning tunneling microscopy-induced luminescence contrast within the 3 nm unit cell which is a way to address trapped molecules and/or quantum dots.     

Frictional and atomic-scale study of C60 thin films by scanning force microscopy

Scanning force microscopy (SFM) was employed to characterize C₆₀ island films in an ultra-high vacuum (UHV). The initial growth stage of C₆₀ on NaCl cleavage faces and nanotribological properties of this solid lubricant are investigated. In comparison to the NaCl(001) face, higher friction is measured on the C₆₀ islands, resulting in a ratio of friction of 13 for NaClC₆₀. The friction coefficient of the (111) oriented C₆₀ island is determined to be 0.15±0.05. High-resolution SFM images reveal the hexagonal lattice of the unreconstructed (111) top surfaces and the overgrowth relationships of the C₆₀ islands.     

Scattering of N2 from Ni(111)

A cold (T_rot<10 K) beam of N₂ with an initial translational energy of 0.40 eV strikes an Ni(111) surface at surface temperatures from 300 to 873 K at several incident angles from 15 to 60°. The rotational energy and angular distributions of the scattered molecules are probed using (2+1) resonance-enhanced multiphoton ionization. Molecules scattered in the specular direction have mean rotational energies that are independent of surface temperature, whereas those scattered at angles far from the specular show a dependence on surface temperature, caused likely by multiple collisions with the surface before escape. A rotational rainbow, seen in systems such as CO–Ni(111) and N₂–Ag(111), is not seen in this system. For molecules that scatter close to the specular direction, approximately 10% of the initial translational energy is converted into rotational energy of the scattered N₂. For surface temperatures above room temperature, the angular distributions indicate that molecules that scatter into low-J states also tend to exit in a broad peak (10–20° FWHM) near the specular, and this peak is broadened with increasing incident angle. The molecules that scatter into high-J states have a much broader distribution, indicating that they are trapped rotationally during the initial collision and suffer multiple collisions before leaving the surface.     

Sulfur at nickel-alumina interfaces: Molecular orbital theory

An atom superposition and electron delocalization molecular orbital study has been made of surface atomic layer relaxations in Ni(110) and Ni(111), the binding of p(2 × 2)S to Ni(111), S on Ni(100), and the binding of A1₂O₃ to clean Ni(111) and p(2 × 2)S covered Ni(111). Surface Ni atom relaxations for three-layer thick cluster models are calculated to be close to the experimental results and S heights of 1.68 Å on Ni(111) and 1.40 Å on Ni(100) are also in close agreement with experimental determinations, which indicates cluster models are suitable for determining surface properties. Al³⁺ in the basal plane of Al₂O₃ are predicted to support a low-lying surface state band in the O2p---A13s3p band gap. These orbitals are found to participate in strong Al---Ni bonds and Al---S bonds of intermediate strength at the interfaces with Ni(111) and p(2 × 2) S-covered Ni(111). Should such bonds form, they are expected to be too few in number to lead to strong adhesion. The strongest Al₂O₃---Ni bonding is predicted to occur when the Ni surface is oxidized. In this case, though Ni---O bonds are relatively weak, their number is high. It is concluded from the structure models that are studied that the segregation of impurity S in Ni to the interface will markedly decrease the adhesion of protective Al₂O₃ films that grow on NiAl based alloys.     

Comparative study of the nature of chemical bonding of corrugated graphene on Ru(0001) and Rh(111) by electronic structure calculations

Recently, atomic resolved scanning tunneling microscopy investigations revealed that, depending on the substrate (Ni(111), Ru(0001), Ir(111), Pt(111), Rh(111)), graphene overlayer might present regular corrugation patterns, with periodically repeated units of a few nanometers. Variations of the interactions at the interface and the modulation of the local electronic properties are associated with the exact atomic arrangement of the carbon pairs with respect to the metal atoms of the substrate. Better understanding of the atomic structure and of the chemical bonding between graphene and the underlying transition metal is motivated by the fundamental scientific relevance of such systems, but it is also crucial in the perspective of possible applications. With the present work, we propose model systems for the two interfaces showing the most pronounced corrugation patterns, i.e. graphene/Ru(0001) and graphene/Rh(111). Our goal is to understand the nature of the interactions by means of electronic structure calculations based on Density Functional Theory. Our simulations qualitatively reproduce very well experimental results such as the STM topographies and the electrostatic potential maps, and quantitatively provide the closest agreement that has been published so far. The detailed analysis of the electronic structure at the interface highlights similarities and differences by changing the supporting transition metal. Our results point to a fundamental role of the hybridization between the π orbitals of graphene with the d band of the metal in determining the specific corrugation of the adsorbed monolayer. It is shown that differences in the response of the graphene electronic structure to the interaction with the metal can hinder the hybridization and lead to substantially different structures.