Chemisorption

About: Chemisorption is a research topic. Over the lifetime, 16298 publications have been published within this topic receiving 554989 citations.

DFT Study of Cysteine Adsorption on Au(111)

Abstract: The adsorption of the cysteine amino acid (H−SCβH2−CαH−NH2−COOH) on the (111) surface of gold is studied by means of periodic density functional calculations. Results for different adsorption sites and molecular configurations show that chemisorption involving S(thiolate)−Au bonds on Au(111) is favored by starting with either cysteine or cystine gas-phase molecular precursors. In the most stable adsorption configuration, the sulfur headgroup sits at the bridge site between two surface Au atoms, and the S−Cβ bond is tilted by 57° with respect to the surface normal, whereas the in-plane orientation of the molecular backbone plays a secondary role. The analysis of the electronic properties shows that the hybridization of the p-like S states with the d-like Au states produces both bonding and antibonding occupied orbitals, and the process is well described by a model for the interaction of localized orbitals with narrow-band dispersive electron states. The bonding orbitals well below the Fermi level contribut...

Molecular orbital cluster model study of bonding and vibrations of CO adsorbed on MgO surface

Abstract: The interaction of CO with the MgO(100) surface has been investigated by means of all electron cluster model calculations. The CO molecule is bound on the Mg2+ site of MgO with a chemisorption energy of about 0.2 eV. The binding mechanism is electrostatic in nature and arises almost entirely from the interaction of the weak electric field generated by the ionic surface and the CO charge distribution, with negligible contributions from chemical effects as the CO σ donation. When CO is bound through carbon, its vibrational frequency increases with respect to the gas-phase value. This shift, Δ, has been analyzed and decomposed into the sum of different contributions. It is found that the positive Δω does not arise entirely from the field–dipole interaction but is due, in part, to the increase in Pauli repulsion occurring when the CO molecule vibrates in the presence of the surface “wall.” A stronger electrostatic interaction, bringing the CO adsorbate closer to the surface, increases this wall effect and results in a more pronounced positive ω shift. It is also found that the two CO orientations exhibit opposite shifts in ωe, thus, the two orientations can be distinguished, in principle, by IR spectroscopy. The analysis of our ab initio cluster wave functions gives a very different picture than the standard view of the metal–CO bond as arising from σ donation and π back donation.

Formation of multilayers by self-assembly

Abstract: Monolayer and multilayer films were formed by self-assembly of methyl 23-(trichlorosilyl)tricosanoate (1) from organic solution. In agreement with published results, this compound was found to form good quality, close-packed monolayers on silicon surfaces. We have, however, found that films significantly thicker than the three monolayers previously obtained can be formed from continued chemisorption of monolayers of this compound followed by reduction of the surface ester with LiAlH4 in THF to form an “alcohol surface”. The quality of monolayer formation in the multilayer films was monitored in detail by ellipsometry, contact angle, and FTIR measurements, and, although generally increasing disorder can be detected, films of up to 25 discrete monolayers can be successfully made. These results indicate that self-assembly is a viable alternative to the Langmuir-Blodgett transfer technique for the construction of relatively thick (0.1-hm scale), ordered, multilayer films. In recent years organized molecular systems have attracted growing attention. The techniques which are presently available for the construction of such systems include both Langmuir-Blodgett (LB)’ and self-assembly methods, by which ordered, monomolecular layers can be formed on hydrophilic surfaces. These systems are believed to have technological potential in both optical and molecular e1ectronics.l They allow the chemist to potentially design new organic materials at a molecular level by incorporating useful functional groups into such systems and controlling such variables as the spacing of these groups within and between monomolecular layers. Although the LB method has been studied intermittently for many years and has been found successful for the formation of an extremely wide variety of monolayer and multilayer films (including relatively thick films of even several hundred layers), the SA method offers important advantages for future applications in such areas as molecular electronics and optical applications. The use of derivatives of alkyltrichlorosilanes (e.g., octadecyltrichlorosilane, OTS) results in monomolecular layers which are durable, thermally stable! and resistant to degradation by a variety of strong reagents.%l6 The trichlorosilyl head group forms covalent bonds to the hydrophilic surface as well as cross-links to adjacent molecules via Si-0 bonds created upon hydrolysis with trace water. This method can be adapted to the formation of multilayers by designing monolayers containing terminal functional groups that can be treated with various reagents to unmask a fresh, hydrophilic surface upon which a succeeding monolayer can be adsorbed.’J’