Tunable Two-Dimensional Patterning of a Semiconducting and Nanometer-Thin C₆₀ Fullerene Film Using a Spatial Light Modulator

Abstract

The photochemical coupling of fullerene molecules into covalently connected oligomeric or polymeric structures can result in drastically lowered solubility in common solvents with retained semiconductor properties. Here, we exploit this combination of properties for the utilization of fullerenes as a negative photoresist material with electronic functionality. Specifically, we develop an easily tunable exposure system, essentially comprising a laser and a computer-controlled spatial light modulator (SLM) featuring >8 million independently controlled pixels, for the spatially selective photochemical transformation of nanometer-thin C60 fullerene films. With a carefully designed laser-SLM-exposure/solvent-development cycle, we are able to realize well-resolved two-dimensional hexagonal or square patterns of circular C60 microdots with a center-to-center distance of 1–5 μm and a maximum thickness of 20–35 nm over several square-millimeter-sized areas on a substrate. The functionality of such a hexagonal C60 pattern was demonstrated by its inclusion in between the transparent electrode and the active material in a light-emitting electrochemical cell, which featured an enhanced light output by >50% in comparison to a reference device void of the patterned C60 layer.

Configurable laterally stacked 2D layered fullerene C60-graphene system with precise spatialization

“…As shown, at the center of the line pattern graphitization and carbonization [36] is formed where the power density is highest (1.26 mW/ µm 2 ). Near the edge of the channel, distinct contrast (boundary) is observed due to C 60 photopolymerization [34], here the power density is a little lower than the center (0.79 mW/µm 2 ). The irradiation power near the outer part of the channel is lower (0.20 mW/µm 2 ) and the contrast image is observed to be lower, indicating that only a solid polymer structure is formed.…”

“…This phenomenon is analogous to the formation of C 60 from naphthalene via direct thermal pyrolysis [32]. Following that, photopolymerization of C 60 occurs, in which each cluster tends to form a covalent bond with each other and produces polymeric layered 2D C 60 at the near high energy laser region [34]. Photo-assisted bond cleavage and ring opening of 2D C 60 occur via the photolysis process in the high-energy region of the laser beam (center spot).…”

“…The corresponding precursor can be "zipped" to the target fullerene by the simultaneous intramolecular Aryl-Aryl coupling. Additionally, the latest study on the photopolymerization of C 60 monomers shows that C 60 -C 60 crosslinking results in the formation of polymeric C 60 nanometer thin lms [34]. The interaction of UV photons with carbonaceous species occurs in photodissociation regions, which are where this type of photolysis and photocoupling phenomena have actually been seen in the space/universe [33].…”