Interface originated modification of electron-vibration coupling in resonant photoelectron spectroscopy

Abstract

We present a comprehensive study of the photon-energy (hν)-dependent line-shape evolution of molecular orbital signals of large π -conjugated molecules by resonant photoelectron spectroscopy (RPES). A comparison to RPES data on small molecules suggests that the excitation into different vibrational levels on the intermediate-state potential energy surface of the electronic excitation is responsible for the observed effect. In this simplified picture of electron-vibration coupling the character of the potential energy surfaces involved in the RPES process determines the line shape of the molecular orbital signal for a particular hν. We use the sensitivity of this effect to probe the influence of different interfaces on the electron-vibration coupling in the investigated systems. The magnitude of the variation in line shape throughout the particular hν region allows us to reveal significant differences within the physisorptive regime.

Island shape and electronic structure in diindenoperylene thin films deposited on Au(110) single crystals

“…18 In the region around the p* NEXAFS resonance at 285.4 eV the line presents a characteristic pointed shape that becomes again broader above 285.7 eV. The RPES line shape is influenced by the charge-vibration coupling, 79,[81][82][83] and it reflects the dynamics of the core states. 84,85 The symmetry of the spectroscopic line at 285.4 eV indicates that the transitions involve vibrational levels having the same quantum numbers, and thus, very close energy giving rise to a narrow peak.…”

Observation of a molecule–metal interface charge transfer related feature by resonant photoelectron spectroscopy

“…Interestingly, a comparison to the corresponding data of the clean Ag(111) substrate (open symbols infigure 2(b)) demonstrates the absence of the low E B feature for the bare Ag(111) surface. Such a feature is furthermore not observed in the corresponding PES data of a coronene multilayer film[30] 3 . This leads to the conclusion that the low E B feature in figure 2(a) originates from the metal-organic interface and hence a particluar interaction of the Ag(111) substrate with the coronene adsorbate film must be present.…”

“…This 1D spectrum is equal (within the chosen ν h increment) to the partial electron yield near edge x-ray absorption fine structure spectroscopy (NEXAFS) spectrum and can be used for the identification of the NEXAFS resonances. Since the measurement of a constant E K window is referred to as constant final state (CFS) spectroscopy we call the obtained 1D spectrum CFS NEXAFS in the following (for further details see [30]). In the ν h region of the two most intense NEXAFS resonances A and B we further observe a substantial intensity enhancement of the HOMO signal which is located at slightly lower E B than the rising edge of the Ag4d bands.…”

“…Here not only the intensity enhancement of the HOMO signal but also its line-shape variation as a function of ν h becomes obvious. This effect is due to a difference in the vibronic progression of the HOMO signal which is a consequence of the particular vibronic excitations within the photon absorption [32] and hence a function of ν h (for a detailed discussion see [30]). Here we focus on the additional feature centered at ≈ E 0.5 B eV which becomes clearly visible after the intensity of the PES detail map is multiplied by a factor of 10.…”

“…Note that in contrast to figure 2(c) in[30] the 2nd order C1s signal has been subtracted from the 0.8 ML data so a contribution by this signal can be excluded.…”