posted on 2022-01-17, 10:43authored byTeng Zhang, Pamela H. W. Svensson, Iulia Emilia Brumboiu, Valeria Lanzilotto, Cesare Grazioli, Ambra Guarnaccio, Fredrik O. L. Johansson, Klára Beranová, Marcello Coreno, Monica de Simone, Luca Floreano, Albano Cossaro, Barbara Brena, Carla Puglia
In this article,
we analyze the electronic structure modifications
of triphenylamine (TPA), a well-known electron donor molecule widely
used in photovoltaics and optoelectronics, upon deposition on Au(111)
at a monolayer coverage. A detailed study was carried out by synchrotron
radiation-based photoelectron spectroscopy, near-edge X-ray absorption
fine structure (NEXAFS) spectroscopy, scanning tunneling microscopy
(STM), and ab initio calculations. We detect a new feature in the
pre-edge energy region of the N K-edge NEXAFS spectrum that extends
over 3 eV, which we assign to transitions involving new electronic
states. According to our calculations, upon adsorption, a number of
new unoccupied electronic states fill the energy region between the
highest occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO) of the free TPA molecule and give rise to
the new feature in the pre-edge region of the NEXAFS spectrum. This
finding highlights the occurrence of a considerable modification of
the electronic structure of TPA. The appearance of new states in the
HOMO–LUMO gap of TPA when adsorbed on Au(111) has crucial implications
for the design of molecular nanoelectronic devices based on similar
donor systems.