Photodesorption of physisorbed molecules from a Ag(111) surface: The low photon energy threshold and the low translational temperature of desorbed molecules (original) (raw)
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Nonclassical behavior of energy transfer from molecules to metal surfaces: Biacetyl(3nπ*)/Ag(111)
The Journal of Chemical Physics, 1985
The distance dependent lifetime of biacetyl separated from a Ag(111) crystal by NH3 spacer layers ranging in thickness from 28 to 457 Å has been measured. We extended previous work, where the molecular emission was resonant with the silver interband/plasmon transition, to the case where the emission is below the interband transition. The modulation of the radiative rate is described inadequately by the classical theory for our experimental geometry. At short distances where nonradiative energy transfer to the metal is important, the classical prediction deviates from the data as well. These observations are consistent with a model in which energy is transferred to electrons localized at the metal surface but might also be explained by an inability of the classical theory to model the radiative rate properly.
Adsorbate effects on photoemission from Ag Adsorbate effects on photoemission from Ag
The underlayer influence on photoemission and thermal desorption of xenon adsorbed on Ag(111) We have used pyridine and a number of related molecules to lower the workfunction of thin Ag films so as to compare the effects of various molecular properties on the photoemission process and on surface electronic modes. We find that a nitrogen lone pair electronic orbital is essential for a large threshold shift. Other molecular properties, such as dipole moment and polarizability have a very small effect. The films are rough, therefore we see strong photoyields at the energy of the surface plasma mode, 3.6 eV. There is also a peak in the photoyield at 3.85 eV, the energy of the bulk plasmon.
The Journal of Chemical Physics, 1982
The phosphorescence lifetime of pyrazine above a Ag (111) surface has been measured as a function of molecule–metal separation between 10 and 420 Å. The distance dependence of lifetime is in accord with the predictions of the classical point dipole theory over this range of distances. Using this classical model, the decay of electronically excited pyrazine is separated into contributions from radiative decay, resonant surface plasmon excitation, and lossy surface wave damping. The relative importance of these decay channels is calculated for silver and nickel in the near UV, and the dominant mechanism for energy transfer to these two metals in this distance regime is interpreted in terms of the electronic structure of the metal.
Physical Review B, 2007
We have measured angle-dependent photoemission spectra for one-photon and two-photon excitation from Ag͑111͒. The observed dispersion of the sp-band transition of Ag͑111͒ can be reproduced using a nearly-freeelectron model for the initial and final states involved. The observed dispersion agrees with the known band structure. We illustrate how the strong refraction of low-energy electrons becomes a limiting factor to obtain quantitative band-structure information. Conversely, low-energy electrons of a well-defined direct optical interband transition can provide a sensitive probe of the inner potential. We observe asymmetric two-photon photoelectron intensity distributions with respect to detection along the surface normal. These intensity distributions can be well described by a phenomenological model which employs the Fresnel equations to calculate the electric field components of the incident radiation inside the sample. Very good agreement is found using tabulated optical constants and a momentum matrix element, which is oriented along the surface normal. In contrast, the observed intensity distribution for one-photon photoemission from Ag͑111͒ does not fit the simple Fresnel model. We interpret this as the influence of surface photoemission. By comparison to Cu͑001͒, we show that the expected intensity distributions of the Fresnel model for one-photon photoemission and twophoton photoemission are valid for an orientation of the momentum matrix element along the surface normal if the influence of additional effects like surface photoemission can be neglected.
Direct transition in the system Ag (111) studied by one-and two-photon photoemission
Structures in two-photon photoemision (2PPE) spectra are usually related to initial and intermediate states by the peak shifts with an incident photon energy. Based on the direct sp-transitions in thin silver films evaporated on Cu(100), we demonstrate that the linear shift in the 2PPE spectra is a strict requirement but not a sufficient criterion for assigning the feature to an intermediate state.
Adsorbate effects on photoemission from Ag
The Journal of Chemical Physics, 1991
We have used pyridine and a number of related molecules to lower the workfunction of thin Ag films so as to compare the effects of various molecular properties on the photoemission process and on surface electronic modes. We find that a nitrogen lone pair electronic orbital is essential for a large threshold shift. Other molecular properties, such as dipole moment and polarizability have a very small effect. The films are rough, therefore we see strong photoyields at the energy of the surface plasma mode, 3.6 eV. There is also a peak in the photoyield at 3.85 eV, the energy of the bulk plasmon.
Simulation of two-photon photoemission from the bulksp-bands of Ag(111)
Physical Review B, 2005
Theoretical and experimental studies on the two-photon photoemission excited by femtosecond laser pulses from the sp-band of Ag͑111͒ in normal direction are reported. At low temperatures, the two-photon photoemission spectrum is found to consist mainly of nonresonant direct transitions from the lower to the upper sp-band across the L-projected band gap involving the upper sp-band as virtual intermediate states. This direct photoemission signal is calculated from the Ag band structure using optical Bloch equations and dipole moments derived from the nearly free electron approximation. For finite temperatures, a minor additional temperature-dependent, continuous contribution to the two-photon photoemission spectrum is experimentally determined. This background due to the secondary electrons is theoretically modeled combining the Debye model and Fermi Liquid Theory to account for electron relaxation effects during the two-photon photoemission process.
Enhanced near-threshold photoemission from adsorbate-covered Au and Ag films
Surface Science, 1986
We report here the first observation of enhanced photoyields at the surface plasma resonance in silver using molecular adsorbates. Monolayer and sub-monolayer coverings of polar and nonpolar molecules were found to be sufficient to reduce the work function below the energy of the surface plasmon. Different yields were obtained on continuous than on quasi-continuous metal films. Enhancements by factors up to 10 2 were obtained. Cesium was used as an adsorbate for comparison.
Temperature dependence of the dynamics of the first image-potential state on Ag(111)
Physical Review B, 2012
The temperature dependence of the dynamics of electrons in the n = 1 image potential state on the Ag(111) surface has been investigated by means of time-resolved two-photon photoemission spectroscopy and many-body calculations. We show that the decay rate of electrons in this state grows linearly with temperature. The thermal shortening of the lifetime is caused by the increase of the electron-electron scattering rate, due to deeper penetration of the image state wave function into the bulk metal at higher temperature. The electron-phonon scattering in this state is found to be small.
Scattering of Nitrogen Atoms off Ag(111) Surfaces: A Theoretical Study
The Journal of Physical Chemistry C, 2013
The study of the reflection of N atoms on a Ag(111) surface is performed by means of classical molecular dynamics and using an accurate three-dimensional potential energy surface, built from density functional theory calculations. The influence of energy loss channels is analyzed by including phonon and electron−hole pair excitations in the simulations. Our calculations show good agreement with recent experimental results. The broadness of the experimental angular distributions is due to the corrugation of the potential energy surface and is well reproduced by our model. Regarding the energy loss distributions, we show that the simulation of an effusive beam coupled to phonon excitations is required to obtain satisfactory results. This is due to dynamic effects that make the reflection process very dependent on the initial energy of N atoms.