The role of surface plasmons in the decay of image-potential states on silver surfaces

The combined effect of single-particle and collective surface excitations in the decay of image-potential states on Ag surfaces is investigated, and the origin of the long-standing discrepancy between experimental measurements and previous theoretical predictions for the lifetime of these states is elucidated. Although surface-plasmon excitation had been expected to reduce the image-state lifetime, we demonstrate that the subtle combination of the spatial variation of s-d polarization in Ag and the characteristic non-locality of many-electron interactions near the surface yields surprisingly long image-state lifetimes, in agreement with experiment.Comment: 4 pages, 2 figures, to appear in Phys. Rev. Let

Lifetimes of electrons in the Shockley surface state band of Ag(111)

We present a theoretical many-body analysis of the electron-electron (e-e) inelastic damping rate $\Gamma$ of electron-like excitations in the Shockley surface state band of Ag(111). It takes into account ab-initio band structures for both bulk and surface states. $\Gamma$ is found to increase more rapidly as a function of surface state energy E than previously reported, thus leading to an improved agreement with experimental data

Role of occupied d bands in the dynamics of excited electrons and holes in Ag

The role that occupied d bands play in the inelastic lifetime of bulk and surface states in Ag is investigated from the knowledge of the quasiparticle self-energy. In the case of bulk electrons, sp bands are taken to be free-electron-like. For surface states, the surface band structure of sp states is described with the use of a realistic one-dimensional Hamiltonian. The presence of occupied d states is considered in both cases by introducing a polarizable background. We obtain inelastic lifetimes of bulk electrons that are in good agreement with first-principles band-structure calculations. Our surface-state lifetime calculations indicate that the agreement with measured lifetimes of both crystal-induced and image-potential-induced surface states on Ag(100) and Ag(111) is considerably improved when the screening of d electrons is taken into account

Intermolecular H-bonding for porphyrin molecules on surfaces: experimental evidences and theoretical investigation.

Trabajo presentado a la Conferencia NanoSpain celebrada en Santander (España) del 27 de Febrero al 1 de Marzo de 2012.The study of the chemical bond of adsorbates on and with surfaces is of particular importance for new widespread developments, from healthcare to electronics or environment. In most cases these interactions are weak and they can be considered in the context of supramolecular chemistry, which studies the organization of systems based on weak and reversible noncovalent interactions. Among them, hydrogen bond is one of the most important interactions in chemistry, biology, pharmacology, electronic, etc. In this work, we detect the formation of H bond among porphyrin molecules adsorbed on metal surfaces. Particularly, by the comparison of experimentally observed shifts of the corelevels with first principle calculations, we identify the nature of the interaction of protoporphyrin IX molecules (H2PPIX) evaporated on Cu surfaces at low-temperature and we relate them with the formation of hydrogen bonds, covalent H-N as well as NH ···O-C hydrogen bonding, between the carboxylic group and the pyrrolic ring of adjacent molecules.Peer Reviewe

Role of occupied d bands in the dynamics of excited electrons and holes in Ag

The role that occupied d bands play in the inelastic lifetime of bulk and surface states in Ag is investigated from the knowledge of the quasiparticle self-energy. In the case of bulk electrons, sp bands are taken to be free-electron-like. For surface states, the surface band structure of sp states is described with the use of a realistic one-dimensional Hamiltonian. The presence of occupied d states is considered in both cases by introducing a polarizable background. We obtain inelastic lifetimes of bulk electrons that are in good agreement with first-principles band-structure calculations. Our surface-state lifetime calculations indicate that the agreement with measured lifetimes of both crystal-induced and image-potential-induced surface states on Ag(100) and Ag(111) is considerably improved when the screening of d electrons is taken into account

Novel low-energy collective excitation at metal surfaces

A novel collective excitation is predicted to exist at metal surfaces where a two-dimensional surface state band coexists with the underlying three-dimensional continuum. This is a low-energy acoustic plasmon with linear dispersion at small wave vectors. Since new modern spectroscopies are especially sensitive to surface dynamics near the Fermi level, the existence of surface-state–induced acoustic plasmons is expected to play a key role in a large variety of new phenomena and to create situations with potentially new physics

Coordinated H-bonding between porphyrins on metal surfaces

Using a combination of X-ray photoelectron spectroscopy (XPS) and core level shift first principles calculations, we determine the formation of an unusual intermolecular interaction between porphyrin molecules. We show that protoporphyrin IX molecules (H2PPIX) adsorbed on Cu surfaces at low temperature (LT) form molecular adlayers stabilized by a strong (1.3 eV) tetragonal coordinated H-bond. This unconventional H-bonding involves the four nitrogen atoms in the tetrapyrrole macrocycle of one molecule, four hydrogen atoms, and one of the hydroxyl oxygen atoms from the carboxylic acid groups of an adjacent molecule. The calculations demonstrate that the corresponding fingerprint of this bond is observed in both the nitrogen XPS data, showing a unique peak, and the almost unchanged 1s core level energy of the hydroxyl oxygen atoms. We explain the formation of this bond by a charge rearrangement mechanism that includes proton sharing and migration.We acknowledge funding support from the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-01, MAT2011-26534, MAT2010-21156-C03-01, and -C03-03, PIB2010US-00652), the Basque Government (IT-257-07, IT-366-07), the ETORTEK program funded by the Basque Departamento de Industria and the Diputación Foral de Guipuzcoa. R.G.M. thanks the financial support of DIPC.Peer reviewe

Following the metalation process of protoporphyrin IX with metal substrate atoms at room temperature

6 páginas, 5 figuras.-- et al.We have studied the in situ coordination reaction of porphyrin molecules, particularly protoporphyrin IX (H2PPIX), with copper substrate atoms in ultrahigh vacuum conditions with a combination of X-ray photoelectron spectroscopy and scanning tunneling microscopy. We show that these protoporphyrin IX molecules deposited on Cu surfaces, as Cu(110) and Cu(100), form metalloprotoporphyrin IX (CuPPIX) by incorporation of Cu atoms from the surface already at room temperature. We have followed this reaction as a function of temperature and we have determined intermediate situations at lower temperatures where the physisorbed macrocycle rings present a tendency to establish hydrogen bonding between molecules.We acknowledge funding through Spanish research projects CSD2007-41, MAT2008-1497, PET2008-109, FIS2010-19609- C02-00, and BIO 2007-67523 and intramural project 200960I159. C.S.-S. is grateful to Ministerio de Educación for the AP2005-0433 FPU grant.Peer reviewe