اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدInfluence of step structure on preferred orientation relationships of Ag deposited on Ni(111)
79
0
0.0
(
0
)
تأليف
Dominique Chatain
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Previous studies have shown that the orientation relationships which develop in hetero-epitaxy are strongly influenced by the alignment of steps in the deposit with the pre-existing steps of the substrate. In this paper we use a combination of experiments with computer simulations to identify the important influence of substrate step structure on the eventual orientation relationships that develop in the deposit. We have made use of Ag deposited on Ni as it has been used extensively as a model system for the study of hetero-epitaxy. This system displays a large lattice mismatch of 16%. It is shown that on any surface vicinal to Ni(111), which has two possible kinds of <110> steps (A-steps with {100} ledges and B-steps with {111} ledges), a Ag deposit adopts a single orientation relationship because only A-steps remain stable in the presence of Ag.
قيم البحث
اقرأ أيضاً
Angle-resolved photoemission spectroscopy and Auger electron spectroscopy have been applied to study the intercalation process of silver underneath a monolayer of graphite (MG) on Ni(111). The room-temperature deposition of silver on top of MG/Ni(111
) system leads to the islands-like growth of Ag on top of the MG. Annealing of the as-deposited system at temperature of 350-450 C results in the intercalation of about 1-2 ML of Ag underneath MG on Ni(111) independently of the thickness of pre-deposited Ag film (3-100 A). The intercalation of Ag is followed by a shift of the graphite-derived valence band states towards energies which are slightly larger than ones characteristic for pristine graphite. This observation is understood in terms of a weakening of chemical bonding between the MG and the substrate in the MG/Ag/Ni(111) system with a small MG/Ni(111) covalent contribution to this interaction.
We examine the adsorption of a single Ni atom on a monolayer of MgO on a Ag substrate using DFT and DFT+U computational approaches. We find that the electronic and magnetic properties vary considerably across the three binding sites of the surface. T
wo of the binding sites are competitive in energy, and the preferred site depends on the strength of the on-site Coulomb interaction U. These results can be understood in terms of the competition between bonding and magnetism for surface adsorbed transition metal atoms. Comparisons are made with a recent experimental and theoretical study of Co on MgO/Ag, and implications for scanning tunneling microscopy experiments on the Ni system are discussed.
The effects of a step defect and a random array of point defects (such as vacancies or substitutional impurities) on the force of friction acting on a xenon monolayer film as it slides on a silver (111) substrate are studied by molecular dynamic simu
lations and compared with the results of lowest order perturbation theory in the substrate corrugation potential. For the case of a step, the magnitude and velocity dependence of the friction force are strongly dependent on the direction of sliding respect to the step and the corrugation strength. When the applied force F is perpendicular to the step, the film is pinned forF less than a critical force Fc. Motion of the film along the step, however, is not pinned. Fluctuations in the sliding velocity in time provide evidence of both stick-slip motion and thermally activated creep. Simulations done with a substrate containing a 5 percent concentration of random point defects for various directions of the applied force show that the film is pinned for the force below a critical value. The critical force, however, is still much lower than the effective inertial force exerted on the film by the oscillations of the substrate in experiments done with a quartz crystal microbalance (QCM). Lowest order perturbation theory in the substrate potential is shown to give results consistent with the simulations, and it is used to give a physical picture of what could be expected for real surfaces which contain many defects.
Size-selected silver clusters on Ag(111) were fabricated with the tip of a scanning tunneling microscope. Unoccupied electron resonances give rise to image contrast and spectral features which shift toward the Fermi level with increasing cluster size
. Linear assemblies exhibit higher resonance energies than equally sized compact assemblies. Density functional theory calculations reproduce the observed energies and enable an assignment of the resonances to hybridized atomic 5s and 5p orbitals with silver substrate states.
The evolution of titanyl-phthalocyanine (TiOPc) thin films on Ag(111) has been investigated using IRAS, SPA-LEED and STM. In the (sub)monolayer regime various phases are observed that can be assigned to a 2D gas, a commensurate and a point-on-line ph
ase. In all three phases the non-planar TiOPc molecule is adsorbed on Ag(111) in an oxygen-up configuration with the molecular pi-conjugated backbone oriented parallel to the surface. The commensurate phase reveals a high packing density, containing two molecules at inequivalent adsorption sites within the unit cell. Both molecules assume different azimuthal orientations which is ascribed to preferred sites and azimuthal orientations with respect to the Ag(111) substrate and, to a lesser extent, to a minimization of repulsive Pauli interactions between adjacent molecules at short distances. At full saturation of the monolayer the latter interaction becomes dominant and the commensurate long range order is lost. DFT calculations have been used to study different adsorption geometries of TiOPc on Ag(111). The most stable configurations among those with pointing up oxygen atoms (bridge+, bridgex, topx) seem to correspond to those identified experimentally. The calculated dependence of the electronic structure and molecular dipole on the adsorption site and configuration is found to be rather small.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
