The metallic bond for monolayer transition metal layers on transition metal surfaces (original) (raw)
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Transition metal compound surfaces
Progress in Surface Science, 1979
Studies of transition metal compound surfaces using modern surface science techniques are reviewed. Studies of the surface structure and composition of model transition metal compound surfaces are emphasized. The growth of the transition metal compound surface from a chemisorbed layer is used as an introduction to investigations of the surface properties of macroscopic single crystals of transition metal compounds. Examples of both binary and tenary compound systems are examined in relation to chemisorbed layer studies. Although only a few systems are chosen to illustrate work in this field, extensive references to other studies and other systems are included.
Interaction of metals with semiconductor surfaces* 1
Applications of surface science, 1982
Metal films on semiconductor surfaces produce strong atom and charge rearrangement at their microscopic interface which can be characterized on an atomic scale by soft X-ray photoemission spectroscopy (SXPS). For compound semiconductors, the presence of a metal film induces a substrate dissociation and diffusion of cation and anion into the metal. SXPS reveals that the magnitude and stoichiometry of this semiconductor outdiffusion depends systematically on the strength and nature of interface chemical bonding and that metal indiffusion also takes place. In addition, we have used monolayer thicknesses of reactive metal "interlayers" at metal film-semiconductor substrate interfaces to modulate the chemical and electronic structure of the extended metal-semiconductor interface.
Interaction of metals with semiconductor surfaces
Applications of Surface Science
Metal films on semiconductor surfaces produce strong atom and charge rearrangement at their microscopic interface which can be characterized on an atomic scale by soft X-ray photoemission spectroscopy (SXPS). For compound semiconductors, the presence of a metal film induces a substrate dissociation and diffusion of cation and anion into the metal. SXPS reveals that the magnitude and stoichiometry of this semiconductor outdiffusion depends systematically on the strength and nature of interface chemical bonding and that metal indiffusion also takes place. In addition, we have used monolayer thicknesses of reactive metal "interlayers" at metal film-semiconductor substrate interfaces to modulate the chemical and electronic structure of the extended metal-semiconductor interface.
Physical and chemical properties of bimetallic surfaces
Surface Science Reports, 1996
Recent studies dealing with the structural, electronic, chemical and catalytic properties of well-defined bimetallic surfaces are reviewed. LEED and STM show that two metals interacting on a surface can form compounds with structures not seen in bulk alloys. Many novel phenomena related to the kinetics of growth of metals on metals have been discovered. The knowledge gathered in this area provides a solid basis for the synthesis of new materials with applications in areas of catalysis, electro-chemistry and microelectronics. In many cases, the formation of a surface bimetallic bond induces large changes in the band structure of the metals. For surfaces that contain transition or s,p metals, the strongest metal-metal interactions occur in systems that combine a metal with a valence band almost fully occupied and a metal in which the valence band is almost empty. A very good correlation is found between the electronic perturbations in a bimetallic system and its cohesive energy. Bimetallic bonds that display a large stability usually involve a significant redistribution of charge around the metal centers. The electronic perturbations affect the reactivity of the bonded metals toward small molecules (CO, NO, Hz, Ca, S2, CzH4, CH3OH, etc.). For supported monolayers of Ni, I'd, Pt and Cu a correlation is observed between the shifts in surface core-level binding energies and changes in the desorption temperature of CO from the metal adlayers. Examples are provided which demonstrate the utility of single-crystal studies for understanding the role of "ensemble" and "ligand" effects in bimetallic catalysts.
Charged and metallic molecular monolayers through surface-induced aromatic stabilization
Nature Chemistry, 2013
Large p-conjugated molecules, when in contact with a metal surface, usually retain a finite electronic gap and, in this sense, stay semiconducting. In some cases, however, the metallic character of the underlying substrate is seen to extend onto the first molecular layer. Here, we develop a chemical rationale for this intriguing phenomenon. In many reported instances, we find that the conjugation length of the organic semiconductors increases significantly through the bonding of specific substituents to the metal surface and through the concomitant rehybridization of the entire backbone structure. The molecules at the interface are thus converted into different chemical species with a strongly reduced electronic gap. This mechanism of surface-induced aromatic stabilization helps molecules to overcome competing phenomena that tend to keep the metal Fermi level between their frontier orbitals. Our findings aid in the design of stable precursors for metallic molecular monolayers, and thus enable new routes for the chemical engineering of metal surfaces.
Effect of metal film thickness on surface-atom coupling
Optics Communications
Metal film thickness is found to be an important parameter in the nonradiative coupling of atoms to metal surlhces. Silver, sodium, and potasium fihns in the thickness range 8-120 nm are evaporated onto a 40 K substrate in ultra high vacuum. At ! ! K, layers of N2 in the thickness range 3-300 nm are condensed onto the metal films. Low ener~ electrons excite the N, 2D--, 4S (o~) electronic transition. The lifetime of o~ is measured as a function of nitrogen thickness and metal film thickness. Results are found to be in good agreement with classical theory based on nonradiative coupling of perpendicular dipoles to surface plasmons of the metal surface.
9587-9600 9587 L.; BlBser, D.; Boese, R.; Vollhardt, K. P. C., manuscript in preparation.) These results agree well with our predictions. We thank Prof. Vollhardt for providing us with access to this data. Supplementary Material Available: Tables of bond lengths and bond angles and torsions (2 pages). Ordering information is given on any current masthead page. thank the SDSC for a grant of computer time. Note Added in Roof* As we received the proofs Of this manuscript , we also received a manuscript from Prof. K. P. C. Vollhardt on the structure of 6. The low-temperature X-ray structure of 6 reveals an exo bond length of 1.390 A and an endo bond length of 1.413 A (6 = 2.3 pm) (Haley M. M.; Mohler, D. Abstract: The concepts of both Fermi surface nesting and local chemical bonding were employed to analyze the electronic origin of the structural modulations of layered transition-metal dichalcogenides 1 T-MX2 and 2H-MX2. Analogies between the two concepts and their complementary nature were examined. The concept of hidden Fermi surface nesting was used to explain the d-electron-count dependence of the structural modulations of the 1T-MX, layers containing d413, d2, and d3 ions on the basis of their hidden one-dimensional Fermi surfaces. The latter are derived from the observations that these layers are made up of three different sets of edge-sharing octahedral chains and that strong u-bonding interactions between the t2g orbitals occur along each chain direction. From the viewpoint of local chemical bonding, the driving force for the diamond-chain formation in the d3 systems and the zigzag-chain formation in the d2 systems is two-center, two-electron a-bonding, but that for the ribbon-chain formation in the d413 systems is three-center, two-electron o-bonding. Several structural modulations of IT-MX2 and 2H-MX2 layers, difficult to understand in terms of Fermi surface nesting, were examined by performing molecular orbital and tight-binding band electronic structure calculations. The d l 3 X d l 3 modulation of a d1 1T-MX2 layer is described as a superposition of linear, multicenter u-bonding interactions which occur in three different directions around metal atoms. The 2 X 2 modulation of 1T-TiSe2 results from a second-order Jahn-Teller instability of the TiSe6 octahedra with do ions. The 3 X 3 modulation of a d' 2H-MX2 layer occurs to enhance the extent of the metal-metal bonding interactions between adjacent MX, trigonal prisms. Structural modulations arising from Fermi surface nesting in low-dimensional metals are equivalent in nature to first-order Jahn-Teller distortions of molecules. Structural modulations of low-dimensional metals do not always originate from Fermi surface nesting, just as not all molecular distortions are caused by first-order Jahn-Teller distortions.
Physical Review Letters, 2004
Periodic density functional calculations are used to illustrate how the combination of strain and ligand effects modify the electronic and surface chemical properties of Ni, Pd, and Pt monolayers supported on other transition metals. Strain and the ligand effects are shown to change the width of the surface d band, which subsequently moves up or down in energy to maintain a constant band filling. Chemical properties such as the dissociative adsorption energy of hydrogen are controlled by changes induced in the average energy of the d band by modification of the d-band width.
Physical Review B, 2002
The stability of metal vicinal surfaces with respect to faceting is investigated using pair potentials, semiempirical potentials, and tight-binding electronic structure calculations for several domains of orientations. It is proven that pair potentials are not precise enough to determine the stability of these surfaces. The answer obtained with semi-empirical potentials is shown to be quite sensitive to the cutoff distance chosen for the interactions and may be too schematic. The results derived from electronic structure calculations open up the possibility of a larger diversity of behaviors due to the existence of electronic step-step interactions. Finally it is shown that the effects of temperature are quite small, at least up to room temperature.