Electronic relaxation effects in condensed polyacenes: A high-resolution photoemission study

Abstract

We present a high-resolution photoelectron spectroscopy investigation of condensed films of benzene, naphthalene, anthracene, tetracene, and pentacene. High spectroscopic resolution and a systematic variation of the molecular size allow a detailed analysis of the fine structures. The line shapes of the C 1s main lines are analyzed with respect to the different contributions of inhomogeneous broadening, vibronic coupling, and chemical shifts. The shake-up satellite spectra reveal trends, which give insight into the charge redistribution within the molecule upon photoexcitation. In particular, the shake-up between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) increases in intensity and moves closer toward the C 1s main line if the size of the aromatic system is increased. An explanation is given on the basis of the delocalization of the aromatic system and its capability in screening the photogenerated core hole. A comparison of the HOMO-LUMO shake-up position to the optical band gap gives additional insight into the reorganization of the electronic system upon photoexcitation.

Transport band gap opening at metal–organic interfaces

“…10 This was observed for several molecules, see, e.g., Ref. 31. The distance between the shake-up satellite and the main peak is smaller compared to the transport band gap of the molecule due to final state screening of the core hole and to an optimized redistribution of charge within the molecule upon photoexcitation.…”

“…The distance between the shake-up satellite and the main peak is smaller compared to the transport band gap of the molecule due to final state screening of the core hole and to an optimized redistribution of charge within the molecule upon photoexcitation. 31 All these results bring us to raise the questions: what is the reason for the peak shifts with film thickness and why is there a difference in the core level and valence band spectra between CuPc on Au and on Co substrates? Regarding the first question we already answered it in the previous paragraphs.…”

“…The most likely transition is the one from HOMO to LUMO state; thus, the satellite to main peak distance is associated to be equal with the transport band gap (E t ). [29][30][31] Figure 4(a) summarizes the peak positions versus the CuPc film thickness determined from the spectra of Figs. 3(a)-3(c).…”

Seleno groups control the energy-level alignment between conjugated organic molecules and metals

“…Note that φ for TSeT deposited on Au(111) is comparable to that induced by many physisorbed molecules, such as the prototypical organic semiconductor pentacene, 49,50 which also compares well to TSeT in terms of IE and molecular structure, 51,87,88 or, e.g., benzene. 4 However, the φ induced by pentacene is due to the push-back effect, whereas XPS clearly showed chemisorption of TSeT on Au(111).…”

Fingerprint of Fractional Charge Transfer at the Metal/Organic Interface

“…With increase of the nominal thickness, the C1s main line is shifted toward higher binding energy by ~1 eV. A widely spread satellite structure which is typical for acenes [28] is also visible at higher binding To investigate the origin of this non-rigid shift, we perform UPS measurements. The He I UPS spectra (Figure 1c) do not show any evidence for band gap states.…”