One-dimensional organic nanowires provide a valuable platform for understanding the emergent electronic phenomena in organic semiconductor materials. We have prepared a class of organic nanowires consisting of stacked pi-conjugated building blocks covalently attached to a solubilizing backbone. We have formed self-assembled monolayers from nanowires of various lengths and sequence contexts on gold substrates and characterized their properties with a range of techniques, including xray photoelectron spectroscopy (XPS), near-edge x-ray absorption fine structure spectroscopy (NEXAFS), and resonant photoemission spectroscopy (RPES). These studies have elucidated the nanowires’ electronic structure and charge carrier dynamics, geometric orientation at solid substrates, and interaction with the surrounding environment. Our experiments may offer improved insight into the design of pi-conjugated materials for organic electronic applications.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 2797156Charge transfer rates at metal/organic interfaces affect the efficiencies of devices for organic based electronics and photovoltaics. Here we report our results on the measurements of ultrafast charge transfer rates across the pyridine/Au(111) interface, using X-ray resonant photoemission spectroscopy and the core-hole clock method. Careful control of the molecular orientation on the metal by adjusting the molecular coverage allowed us to study its effect on the charge transfer rates. Furthermore, we demonstrate that a bi-directional charge transfer across the molecule/metal interface occurs following the creation of a core exciton on the molecule, with a rate strongly depending on the molecular adsorption angle.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 2966884The charge transport properties of a vertically stacked organic hetero-junction, based on the aminocarboxylic (A-C) hydrogen bond coupling scheme, are investigated by means of X-ray Resonant Photoemission and the Core-Hole Clock method. We demonstrate that hydrogen bonding in molecular bi-layers of benzoic acid/cysteamine (BA/CA) with an A-C coupling scheme opens a site selective pathway for ultrafast charge transport through the junction. Whereas charge transport from single BA layer directly coupled to the Au(111) is very fast and it is mediated by the phenyl group, the interposition of an anchoring layer of CA selectively hinders the delocalization of electrons from the BA phenyl group, but opens a fast charge delocalization path through the BA orbitals close to the A-C bond. This evidences that the amino-carboxylic functionalization of a hetero-organic interface can be exploited to tailor the charge transport properties of the system.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 2967396The controlled growth of 2D arrays of molecules on surfaces is an exciting challenge and a mandatory step for the design of efficient organic nano-devices. For this purpose, guest-host approach has been widely exploited, where an organic framework templates the surface and hosts the guest molecules. We present here an alternative guest-host strategy, based on the chemical affinity between template and guest molecules. In particular, as a template, we employ self-assembled monolayer of a carboxyl terminated tetraphenylporphyrin. In a second step, an aminomethyl-terminated molecule, namely 2-(aminomethyl)-15-crown-5, is deposited on top of the template. The natural amino-carboxylic recognition between the molecular terminations drives the intercalation and thus the ordering of the aminomethyl-terminated molecules in 2D arrays.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 2967140We have investigated bidirectional femtosecond charge transfer dynamics using the core–hole clock implementation of resonant photoemission spectroscopy from 4,4'-bipyridine molecular layers on different surfaces: Au(111) and epitaxial graphene on Ni(111). We showed that the lowest unoccupied molecular orbital (LUMO) of the molecule drops partially below the Fermi level upon core–hole creation in all systems, opening an additional decay channel for the core–hole, involving electron donation from substrate to the molecule. Using the core–hole clock method, we find that the bidirectional charge transfer time between the substrate and the molecule is 2 fs on Au(111), and around 4 fs for epitaxial graphene.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 2789988