Electronic Properties and Morphology of Beam‐Oligomerized 3‐Hexylthiophene

Abstract

A novel means of lithographically forming fluorescent oligothiophene patterns is demonstrated. MgKa x-ray and low energy electron irradiation of 3-hexylthiophene (3HT) monomer condensed on a cold metal surface result in the formation of photoluminescent films as thick as several microns. The excitation maxima for the x-ray-and electron-formed samples are 350 and 405 nm, respectively, with corresponding emission maxima of 430 and 525 nm, indicating that the films are oligomeric rather than polymeric. Ultraviolet photoelectron spectra (UPS) of 3HT monomer and beam-formed films have been compared with theoretically simulated density-of-states spectra of 3HT, thiophene, bithiophene, terthiophene, and quaterthiophene. The radiation-induced changes in the 3HT UPS valence spectra are explained by delocalization of electrons along the oligomer backbone. Comparison of the experimental UPS and simulated spectra suggests that the average conjugation length of the beam-formed films is less than six. This is consistent with the photoluminescence results. Fluorescence and atomic force microscopies of electron-formed samples show the presence of oligomerized 3HT islands residing on a less fluorescent organic background. Electrical conductivity of the beam-formed samples is low, on the order of 10 À9 cm À1 ohm À1 , consistent with the formation of islands of conjugated material surrounded by a less electronically delocalized,

Photoemission Studies of Polythiophene and Polyphenyl Films Produced via Surface Polymerization by Ion-Assisted Deposition

“…C. UPS of 3T SPIAD and Evaporated 6T Films. UPS of the 6T evaporated, 3T SPIAD, and 3T evaporated films in Figure display their lowest binding energy peaks below 3 eV which are assigned as π* antibonding orbitals. − These π* antibonding orbitals are of greatest interest to conducting polymer electronic structure and those of the 3T SPIAD film display a continuous band from 1.3 to 1.7 eV binding energy, intermediate between those bands observed for 3T and 6T. All three films display UPS peaks near 4 eV, which are assigned to n nonbonding orbitals, while the groups of peaks from 6 to 10 eV are assigned to π bonding orbitals.…”

Electron Beam Patterning of Metal–Organic Frameworks

“…Despite the demonstrations of e-beam and scanning probe microscopy tools to directly write polymeric, oxide, metallic, or other patterns with nm resolution, understanding of e-beam-driven reactions with organic and metal–organic precursors remains incomplete. − Therefore, here, only a preliminary discussion of possible reactions involved in the MOF patterning process is attempted.…”

One-step nanopatterning of conjugated polymers by electron-beam-assisted electropolymerization

“…The absorption peak appears ∼470 nm and photoluminescence peak appears ∼600 nm when the film was excited by the light ranging from 450 to 490 nm, indicating that the film is composed of conjugated compound. As compared with the spectra of oligomers [ 26 ] and polymers of 3HT [ 29 ], the peak position of the film is similar to those of polymers. Taking the results of FT-IR, visible absorption and photoluminescence spectroscopies into considerations, the film formed by the electron beam irradiation was P3HT.…”

“…Although the reaction mechanism of the conjugated monomers under electron beam irradiation has not been fully clarified, it is thought that the reaction mechanism of the electron-beam-assisted electropolymerization is similar to that of conventional electropolymerization based on anodic oxidation [ 26 , 33 ]. To investigate the versatility and formation mechanism of our polymerization method, an electropolymerizable monomer used for cathodic reduction, poly( p -phenylene vinylene), was also examined.…”

“…Because the resist film must be placed in a specimen chamber under high vacuum in this method, it is difficult to use liquid monomers of conjugated polymers as precursors in conventional electron-beam lithography. Recently, Ahn et al [ 26 ] used X-rays and electron beams to solidify 3-hexylthiophene (3HT), which was condensed on a cryogenically cooled substrate, to generate a film of 3HT oligomer on a micrometer scale. They assumed that the reaction mechanism was similar to that of conventional electropolymerization.…”