114 research outputs found
Angle-Resolved Photoelectron Spectroscopy of C60
Angle-resolved photoelectron spectra of gaseous C60 were recorded in the photon energy regions from 21 to 108 eV and from 295 to 320 eV. Partial cross sections σ and the angular distribution anisotropy parameter β vary significantly with photon energy, particularly in the near-threshold region of the valence and the core ionization regimes. Some of these effects may be attributed to scattering of the outgoing photoelectron by the atoms of the ionized C60 molecule. Our results indicate that the observed satellites of the C(1s) main line are most likely of shake-up character. Low-energy electrons emitted below the shake-off threshold indicate the occurrence of K-shell vacancy filling double Auger decay
Band dispersion in the deep 1s core level of graphene
Chemical bonding in molecules and solids arises from the overlap of valence
electron wave functions, forming extended molecular orbitals and dispersing
Bloch states, respectively. Core electrons with high binding energies, on the
other hand, are localized to their respective atoms and their wave functions do
not overlap significantly. Here we report the observation of band formation and
considerable dispersion (up to 60 meV) in the core level of the carbon
atoms forming graphene, despite the high C binding energy of 284
eV. Due to a Young's double slit-like interference effect, a situation arises
in which only the bonding or only the anti-bonding states is observed for a
given photoemission geometry.Comment: 12 pages, 3 figures, including supplementary materia
\AA ngstrom depth resolution with chemical specificity at the liquid-vapor interface
The determination of depth profiles across interfaces is of primary
importance in many scientific and technological areas. Photoemission
spectroscopy is in principle well suited for this purpose, yet a quantitative
implementation for investigations of liquid-vapor interfaces is hindered by the
lack of understanding of electron-scattering processes in liquids. Previous
studies have shown, however, that core-level photoelectron angular
distributions (PADs) are altered by depth-dependent elastic electron scattering
and can, thus, reveal information on the depth distribution of species across
the interface. Here, we explore this concept further and show that the
anisotropy parameter characterizing the PAD scales linearly with the average
distance of atoms along the surface normal. This behavior can be accounted for
in the low-collision-number regime. We also show that results for different
atomic species can be compared on the same length scale. We demonstrate that
atoms separated by about 1~\AA~along the surface normal can be clearly
distinguished with this method, achieving excellent depth resolution.Comment: Submitted to Phys. Rev. Let
Observation of electron transfer mediated decay in aqueous solution
Photoionization is at the heart of X ray photoelectron spectroscopy XPS , which gives access to important information on a sample s local chemical environment. Local and non local electronic decay after photoionization in which the refilling of core holes results in electron emission from either the initially ionized species or a neighbour, respectively have been well studied. However, electron transfer mediated decay ETMD , which involves the refilling of a core hole by an electron from a neighbouring species, has not yet been observed in condensed phase. Here we report the experimental observation of ETMD in an aqueous LiCl solution by detecting characteristic secondary low energy electrons using liquid microjet soft XPS. Experimental results are interpreted using molecular dynamics and high level ab initio calculations. We show that both solvent molecules and counterions participate in the ETMD processes, and different ion associations have distinctive spectral fingerprints. Furthermore, ETMD spectra are sensitive to coordination numbers, ion solvent distances and solvent arrangemen
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