Low-energy electron induced resonant loss of aromaticity: consequences on cross-linking in terphenylthiol SAMs

L. Amiaud (1) , J. Houplin (1) , M. Bourdier , V. Humblot (2) , R. Azria (1) , C.-M. Pradier (2) , A. Lafosse (1)

1 ISMO - Institut des Sciences Moléculaires d'Orsay
2 LRS - Laboratoire de Réactivité de Surface

Aromatic self-assembled monolayers (SAMs) can be used as negative tone electron resists in functional surface lithographic fabrication. A dense and resistant molecular network is obtained under electron irradiation through the formation of a cross-linked network. The elementary processes and possible mechanisms involved were investigated through the response of a model aromatic SAM, p-terphenylthiol SAM, to low-energy electron (0-10 eV) irradiation. Energy loss spectra as well as vibrational excitation functions were measured using High Resolution Electron Energy Loss Spectroscopy (HREELS). A resonant electron attachment process was identified around 6 eV through associated enhanced excitation probability of the CH stretching modes ν(CH)(ph) at 378 meV. Electron irradiation at 6 eV was observed to induce a peak around 367 meV in the energy loss spectra, attributed to the formation of sp(3)-hybridized CHx groups within the SAM. This partial loss of aromaticity is interpreted to be the result of resonance formation, which relaxes by reorganization and/or CH bond dissociation mechanisms followed by radical chain reactions. These processes may also account for cross-linking induced by electron irradiation of aromatic SAMs in general.

Domaines: Chimie

L. Amiaud, J. Houplin, M. Bourdier, V. Humblot, R. Azria, et al.. Low-energy electron induced resonant loss of aromaticity: consequences on cross-linking in terphenylthiol SAMs. ChemPhysChem, 2014, 16 (3), pp.1050-9. ⟨10.1039/c3cp53023j⟩. ⟨hal-01121193⟩