Modification of Nitrile-Terminated Biphenylthiol Self-Assembled Monolayers by Electron Irradiation and Related Applications

Abstract

Here we describe the behavior of self-assembled monolayers (SAMs) of 4'-cyanobiphenyl-4-thiol (CBPT) on Au(111) upon electron irradiation. Under such a treatment, the aromatic framework of CBPT SAMs is laterally cross-linked while the nitrile groups, located at the SAM-ambience interface, are reduced to active amine moieties which can be used as docking sites for the coupling of other species. This makes CBPT monolayers as a promising system for conventional and chemical lithography as well as for nanofabrication. Along these lines, we demonstrate the preparation of complex polymer brushes, patterning of the underlying substrate, and fabrication of molecule-thin, free-standing membranes on the basis of CBPT SAMs. The balance between the application-favorable processes and defragmentation in these films is studied in detail, and comparison to the well-established (for the relevant applications) system of 4'-nitrobiphenyl-4-thiols is performed. Taking CBPT SAMs as a model system, the effect of the energy of the primary electrons on the extent of the chemical transformation and cross-linking in substituted aromatic SAMs is investigated.

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

“…56,61,62 Cross-linking was reported for aromatic SAMs under electron irradiation at 10 eV, 24,63 50 eV 8,25,27,28,30,64,65 and higher energies. 29,66 The mechanisms proposed involve primary and secondary electrons that are emitted from the SAM-substrate system, 67 which cause C-H bond breaking within the film. The partially dehydrogenated molecules relax then by forming single and double CC bonds between adjacent phenyl rings, forming a 2D network.…”

Dipole-induced effects on charge transfer and charge transport. Why do molecular electrets matter?

“…106,108 SAMs of rigid molecular moieties, in which the polar groups attached to them or incorporated in them with fixed directions, provide attractive alternatives. [109][110][111] Many of these rigid structures are linked aromatics with extended π-conjugation.…”

Responsive and patterned polymer brushes

“…PS, poly(4‐vinyl pyridine), and PMMA were then subsequently grown from the surface through SIPGP . Increasing brush thickness, regulated by longer polymerization times or higher e‐beam doses, produced films with greater buckling amplitude. The results showed that the brush morphologies were reversibly responsive to external triggers (solvent and pH) and demonstrated buckling and changes in film properties (optical and wetting).…”