Full Picture of Valence Band Structure of Rubrene Single Crystals Probed by Angle-Resolved and Excitation-Energy-Dependent Photoelectron Spectroscopy

Abstract

The valence band structure of rubrene single crystals was experimentally determined by high-resolution angle-resolved and excitation-energy-dependent photoelectron spectroscopy at room temperature. The energy position of the peak derived from the highest occupied molecular orbital did not depend on the excitation energy, reflecting an absence of energy dispersion along the surface normal direction. A two-dimensional valence band dispersion relation over the surface Brillouin zone obtained by angle-resolved photoemission to three critical points was reproduced excellently by a two-dimensional tight binding approximation. Highly anisotropic values of intermolecular transfer integrals to four adjacent molecules were obtained from the present results.

Molecular Semiconductors for Logic Operations: Dead‐End or Bright Future?

“…Results of Gao et al corroborate the anisotropic behavior in the a–b plane with a width of W ≈ 230 and 250 meV for the two HOMO‐derived bands along the shortest axis and a nearly negligible dispersion along the longest axis. A more recent study at room temperature validates previous experimental and theoretical results . A bandwidth of W ≈ 410––470 meV was recorded and transfer integrals, i.e., J a = −5 ± 3 meV, J b = 108 ± 4 meV, J d = 10 ± 15 meV were deduced ( Figure ).…”

“…Schematic illustration of the packing of rubrene molecules with unit a and b cell parameter and transfer integrals. Phenyl rings have been omitted for clarity …”

Electronic Structures of a Well-Defined Organic Hetero-Interface: C₆₀on Pentacene Single Crystal

“…After production, the crystals were bounded onto gold-coated Si plates with silver paste in air for XPS and UPS experiments, while they were fixed by a tiny piece of conductive carbon tape onto bare Si substrates for PYS. Detailed description on the sample preparation scheme can be found elsewhere [22,23]. It should be noted that the Pen-SC samples were used without any surface treatment and thus the surface may not be the "clean surface" but a few percent of oxidized species existed at the surface [10].…”

Determination of the highest occupied molecular orbital energy of pentacene single crystals by ultraviolet photoelectron and photoelectron yield spectroscopies

“…Details of this techniques can be found elsewhere. 18,19) All the UPS spectra presented in this work were obtained in the spatiallyresolving electron lens mode (so called ''Transmission mode'') of the electron analyzer in the normal emission geometry. In this measurement condition, since photoelectrons emitted in a wide angular range (³10°) are collected unselectively, the resultant spectra have to be regarded as angular-averaged ones.…”