共查询到20条相似文献,搜索用时 46 毫秒
1.
The faceting of Pd/W(111) surfaces has been studied using a Scanning tunneling microscope (STM). Three-sided pyramidal facets having {211} faces with dimensions ranging from 3 to 15 nm can be induced by ultrathin Pd films (≥ 1 monolayer), upon annealing to 700 K or higher. From atomic-resolution STM-images of these surfaces, we obtain direct confirmation of the {211} structure on individual facets of the 3-sided pyramids. In addition, the atomic structure of the facet edges indicates that edge energy may play a role in faceting. When the as-deposited coverage of Pd is greater than the critical value ( 1 monolayer) for inducing faceting, the extra Pd atoms diffuse to form 3-dimensional clusters, some with discernible crystalline structures, upon annealing. 相似文献
2.
应用密度泛函理论,系统研究了Al原子在Pt(111),Ir(111)和Au(111)表面的桥位、顶位、三重面心立方(fcc)洞位和六角密排(hcp)洞位这四个典型位置的吸附情况. 主要计算了三吸附体系的几何结构、平均结合能和差分电荷密度,并系统讨论了相关原子的密立根电荷布居数和投影态密度.研究发现,对于Pt(111)和Ir(111)表面,Al原子在hcp洞位最稳定,但是对于Au(111)表面,Al原子在fcc洞位最稳定.
关键词:
吸附
密度泛函理论
结合能
电子结构 相似文献
3.
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. 相似文献
4.
Calculation of the surface energy of fcc metals with modified embedded-atom method 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The surface energies for 38 surfaces of fcc metals Cu, Ag, Au, Ni, Pd, Pt, A1, Pb, Rh and Ir have been calculated by using the modified embedded-atom method. The results show that, for Cu, Ag, Ni, A1, Pb and Ir, the average values of the surface energies are very close to the polycrystalline experimental data. For all fcc metals, as predicted, the close-packed (111) surface has the lowest surface energy. The surface energies for the other surfaces increase linearly with increasing angle between the surfaces (hkl) and (111). This can be used to estimate the relative values of the surface energy. 相似文献
5.
Giordano L Pacchioni G Goniakowski J Nilius N Rienks ED Freund HJ 《Physical review letters》2008,101(2):026102
We present a combined experimental (STM/scanning tunneling spectroscopy) and theoretical (density functional theory) study on the deposition of Au and Pd metal atoms on FeO/Pt(111) ultrathin films. We show that while the Pd atoms are only slightly oxidized, the Au atoms form positive ions upon deposition, at variance to a charge transfer into the Au atoms as observed for MgO/Ag(100). The modulation of the adsorption properties within the surface Moiré cell and the charging induce the formation a self-assembled array of gold adatoms on FeO/Pt(111), whereas Pd atoms are randomly distributed. 相似文献
6.
Ab initio calculations of the atomic and electronic structures of Me(111)/α-Al2O3(0001) interfaces (Me = V, Cr, Nb, Mo, Ta, W) in the framework of density functional theory are reported. The energies of
separation of metal films from oxide surfaces have been calculated. The structural and electronic factors responsible for
the strong adhesion of bcc metal films on the oxygen termination of the surface of aluminum oxide have been analyzed. 相似文献
7.
8.
本文将元素变量(φ*和nWS)和MAEAM相结合,从原子尺度上对10种fcc金属Cu,Ag,Au,Ni,Pd,Pt,Rh,Al,Ir和Pb的38个不同晶面的表面能进行模拟计算及各向异性分析. 结果表明,fcc金属的密排面(111)的表面能最小,则该晶粒取向优先生长,与实验结果和第一原理的LMTO-ASA计算结果一致;各个晶面的表面能均随着其他晶面与(111)晶面的夹角cosθ(hkl)的增长而呈线性
关键词:
FCC金属
MAEAM
表面能
表面偏析 相似文献
9.
B. Heinrich J. F. Cochran A. S. Arrott S. T. Purcell K. B. Urquhart J. R. Dutcher W. F. Egelhoff Jr. 《Applied Physics A: Materials Science & Processing》1989,49(5):473-490
Ultrathin films, bcc Fe(001) on Ag(001), fcc Fe(001) on Cu(001) and Fe/Ni(001) bilayers on Ag, were grown by molecular beam epitaxy. A wide range of surface science tools were employed to establish the quality of epitaxial growth. Ferromagnetic resonance and Brillouin light scattering were used to extract the magnetic properties. Emphasis was placed on the study of magnetic anisotropies. Large uniaxial anisotropies with easy axis perpendicular to the film surface were observed in all ultrathin structures studied. These anisotropies were particularly strong in fcc Fe and bcc Fe films. In sufficiently thin samples the saturation magnetization was oriented perpendicularly to the film surface in the absence of an applied field. It has been demonstrated that in bcc Fe films the uniaxial perpendicular anisotropy originates at the film interfaces. In situ measurements indentified the strength of the uniaxial perpendicular anisotropy constant at the Fe/vacuum, Fe/Ag and Fe/Au interfaces asK
us = 0.96, 0.63, and 0.3 ergs/cm2 respectively. The surface anisotropies deduced for [bulk Fe/noble metal] interfaces are in good agreement with the values obtained from ultrathin films. Hence the perpendicular surface ansiotropies originate in the broken symmetry at abrupt interfaces. An observed decrease in the cubic anisotropy in bcc Fe ultrathin films has been explained by the presence of a weak 4th order in-plane surface anisotropy,K
1S=0.012 ergs/cm2. Fe/Ni bilayers were also investigated. Ni grew in the pure bcc structure for the first 3–6 ML and then transformed to a new structure which exhibited unique magnetic properties. Transformed ultrathin bilayers possessed large inplane 4th order anisotropies far surpassing those observed in bulk Fe and Ni. The large 4th order anisotropies originate in crystallographic defects formed during the Ni lattice transformation. 相似文献
10.
Field-ion microscopy has been previously used [1–4] to determine the surface energy anisotropy of tungsten and iridium. Drechsler and Nicholas [5] have used field emission patterns of equilibrium shapes of emitters to determine the surface energy anisotropies for a number of fcc and bcc metals including α-iron. The purpose of the present paper is to report some observations by field-ion microscopy on the vacuum faceting of α-iron and the surface energy anisotropy at about half the absolute melting point. Qualitative results on the effect of hydrogen on the surface energy anisotropy are also presented. 相似文献
11.
Pd and Pt monolayers on the (011) surface of bcc metals (Nb,Ta,Mo,W) resemble in many respects the faces of noble metals. We show that this behaviour can be reproduced in a simple tight-binding s-d electron model without invoking any additional mechanism. 相似文献
12.
Molecular dynamics simulations with a classical many-body potential are used to study the high-temperature stability of stepped non-melting metal surfaces. We have studied in particular the Au(111) vicinal surfaces in the (M + 1,M− 1,M) family and the Au(100) vicinals in the (M,1,1) family. Some vicinal orientations close to the non-melting Au(111) surface become unstable close to the bulk melting temperature and facet into a mixture of crystalline (111) regions and localized surface-melted regions. On the contrary, we do not find high-temperature faceting for vicinals close to Au(100), also a non-melting surface. These (100) vicinal surfaces gradually disorder with disappearance of individual steps well below the bulk melting temperature. We have also studied the high-temperature stability of ledges formed by pairs of monatomic steps of opposite sign on the Au(111) surface. It is found that these ledges attract each other, so that several of them merge into one larger ledge, whose edge steps then act as a nucleation site for surface melting. 相似文献
13.
Voicescu Mariana Angelescu Daniel G. Ionescu Sorana Teodorescu Valentin S. 《Journal of nanoparticle research》2013,15(4):1-10
Metallic nanoparticles (NPs) supported on oxides thin films are commonly used as model catalysts for studies of heterogeneous catalysis. Several 4d and 5d metal NPs (for example, Pd, Pt and Au) grown on alumina, ceria and titania have shown strong metal support interaction (SMSI), for instance the encapsulation of the NPs by the oxide. The SMSI plays an important role in catalysis and is very dependent on the support oxide used. The present work investigates the growth mechanism and atomic structure of Rh NPs supported on epitaxial magnetite Fe3O4(111) ultrathin films prepared on Pd(111) using the Molecular Beam Epitaxy (MBE) technique. The iron oxide and the Rh NPs were characterized using X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction and photoelectron diffraction (PED). The combined XPS and PED results indicate that Rh NPs are metallic, cover approximately 20 % of the iron oxide surface and show height distribution ranging 3–5 ML (monolayers) with essentially a bulk fcc structure. 相似文献
14.
We have studied the dynamics of atom motion at face centered metal (111) surfaces. The interactions between atoms are modelled with central forces and angle bending forces. Results for frequencies and polarizations of surface modes are presented for the following metals: Ag, Al, Au, Cu, Ni, Pd and Pt. In addition, the results obtained for phonon spectral densities are presented for nickel. 相似文献
15.
B. Borca O. Fruchart E. Kritsikis F. Cheynis A. Rousseau Ph. David C. Meyer J.C. Toussaint 《Journal of magnetism and magnetic materials》2010,322(2):257-264
We report a detailed magnetic study of a new type of self-organized nanowires discussed briefly previously [B. Borca et al., Appl. Phys. Lett. 90 (2007) 142507]. The templates, prepared on sapphire wafers in a kinetically limited regime, consist of uniaxially grooved W(1 1 0) surfaces, with a lateral period here tuned to 15 nm. Fe deposition leads to the formation of (1 1 0) 7 nm-wide wires located at the bottom of the grooves. The effect of capping layers (Mo, Pd, Au, Al) and underlayers (Mo, W) on the magnetic anisotropy of the wires was studied. Significant discrepancies with figures known for thin flat films are evidenced and discussed in terms of step anisotropy and strain-dependent surface anisotropy. Demagnetizing coefficients of cylinders with a triangular isosceles cross-section have also been calculated, to estimate the contribution of dipolar anisotropy. Finally, the dependence of magnetic anisotropy with the interface element was used to tune the blocking temperature of the wires, here from 50 to 200 K. 相似文献
16.
We investigated the electronic structure, adsorption energies, magnetic properties, dipole moment and work function of metal adatoms (Mg, Cr, Mo, Pd, Pt, and Au) adsorption on a blue phosphorene monolayer. For Mg, Pt and Au metals, the most stable state was found in hollow site while for Cr, Mo and Pd metals we found an adsorption in valley site. We suggest that the Pd and Pt atoms prefer 2D growth mode while the Mg, Cr, Mo and Au atoms prefer 3D island growth mode on monolayer phosphorene. The electronic band structures and magnetic properties were dependent on the doping site and dopant materials. For instance, the semiconducting features were preserved in Mg, Pd, Pt, and Au doped systems. However, the Cr and Mo doped systems displayed half-metallic band structures. The total magnetic moment of 4.05, 2.0 and atom were obtained in Cr, Mo and Au doped systems whereas the Mg, Pd and Pt doped systems remained nonmagnetic. We also investigated the magnetic interaction between two transition metal impurities. We observed ferromagnetic coupling between two transition metal impurities in Cr and Mo doped systems while the Au doped system displayed almost degenerated magnetic state. For Mg, Cr, and Mo adsorptions, we found relatively large values of dipole moments compared to those in the Pd, Pt and Au adsorptions. This resulted in a significant suppression of the work function in Mg, Cr and Mo adsorptions. Overall, adsorption can tune the physical and magnetic properties of phosphorene monolayer. 相似文献
17.
P. Bak 《Solid State Communications》1979,32(7):581-583
The reconstruction transitions on certain clean metal surfaces are shown to be isomorphous with two-dimensional models of phase transitions. Specifically, the Pt, Ir, and Au(110) transitions correspond to the 2d-Ising model, the W(100) transition to the 2d?XY model with cubic anisotropy. The Mo (100) reconstruction is described in terms of the Kosterlitz-Thouless picture of the 2d-XY model. Experiments (LEED or He diffraction) are suggested to check theories of 2d systems. 相似文献
18.
We examine via molecular simulation the dependence of the crystal-melt interfacial free energy gamma on molecular interaction and crystal structure (fcc vs bcc) for systems interacting with inverse-power repulsive potentials, u(r)=epsilon(sigma/r)(n), 6< or =n< or =100. Both the magnitude and anisotropy of gamma are found to increase as the range of the potential increases. Also we find that gamma(bcc)相似文献
19.
20.
H. Hofsäss K. Zhang A. Pape O. Bobes M. Brötzmann 《Applied Physics A: Materials Science & Processing》2013,111(2):653-664
We investigate the ripple pattern formation on Si surfaces at room temperature during normal incidence ion beam erosion under simultaneous deposition of different metallic co-deposited surfactant atoms. The co-deposition of small amounts of metallic atoms, in particular Fe and Mo, is known to have a tremendous impact on the evolution of nanoscale surface patterns on Si. In previous work on ion erosion of Si during co-deposition of Fe atoms, we proposed that chemical interactions between Fe and Si atoms of the steady-state mixed Fe x Si surface layer formed during ion beam erosion is a dominant driving force for self-organized pattern formation. In particular, we provided experimental evidence for the formation of amorphous iron disilicide. To confirm and generalize such chemical effects on the pattern formation, in particular the tendency for phase separation, we have now irradiated Si surfaces with normal incidence 5 keV Xe ions under simultaneous gracing incidence co-deposition of Fe, Ni, Cu, Mo, W, Pt, and Au surfactant atoms. The selected metals in the two groups (Fe, Ni, Cu) and (W, Pt, Au) are very similar regarding their collision cascade behavior, but strongly differ regarding their tendency to silicide formation. We find pronounced ripple pattern formation only for those co deposited metals (Fe, Mo, Ni, W, and Pt), which are prone to the formation of mono and disilicides. In contrast, for Cu and Au co-deposition the surface remains very flat, even after irradiation at high ion fluence. Because of the very different behavior of Cu compared to Fe, Ni and Au compared to W, Pt, phase separation toward amorphous metal silicide phases is seen as the relevant process for the pattern formation on Si in the case of Fe, Mo, Ni, W, and Pt co-deposition. 相似文献