High‐Resolution Scanning Near‐Field Optical Lithography of Conjugated Polymers

Abstract

The fabrication of high‐resolution nanostructures in both poly(p‐phenylene vinylene), PPV, and a crosslinkable derivative of poly(9,9′‐dioctylfluorene), F8, using scanning near‐field optical lithography, is reported. The ability to draw complex, reproducible structures with 65000 pixels and lateral resolution below 60 nm (< λ/5) is demonstrated over areas up to 20 μm × 20 μm. Patterning on length‐scales of this order is desirable for realizing applications both in organic nanoelectronics and nanophotonics. The technique is based on the site‐selective insolubilization of a precursor polymer under exposure to the confined optical field present at the tip of an apertured near‐field optical fiber probe. In the case of PPV, a leaving‐group reaction is utilized to achieve insolubilization, whereas the polyfluorene is insolubilized using a photoacid initiator to create a crosslinked network in situ. For PPV, resolubilization of the features is observed at high exposure energies. This is not seen for the crosslinked F8 derivative, r‐F8Ox, allowing us to pattern structures up to 200 nm in height.

Efficient light confinement with nanostructured optical microfiber tips

“…One consists in directly "writing" the photoresist layer [56,57]. This technique of direct writing and a fiberized sub-wavelength light confinement source can be conceived like a "pen".…”

“…Yet, SNOM probes have very low transmission efficiencies, e.g. 10 -3 ~10 -6 [26,30], as they require small apertures and small tapering angles, which results in a strong decay in the evanescent field intensity. Also, they usually can only stand relatively small powers, typically of the order of 1 mW.…”

Polymer Nanostructures Made by Scanning Probe Lithography: Recent Progress in Material Applications

“…Polymeric carriers for functional materials agarose, [ 32 ] PEG, [ 33 , 34 ] PEOblock -P2VP, [ 36 ] photocurable photoresist [ 38 ] PEDOT:PSS, [ 39 ] polypyrrole, [ 40a ] polyaniline, [ 40b ] nanoscratching physical: mechanical scratching of the surface 100 nm, [ 39 ] 15 nm [ 40b ] single tip PPV [ 41 , 42 ] [ 42 ] single tip crosslinkable F8 derivatives [ 42 ] SNOL chemical: photocrosslinking 60 nm single tip water-soluble conjugated polymers, [ 43 ] PVDF-TrFE [ 45 ] DPN, physical: physisorption 130 nm for conjugated polymers, [ 43a ] 19 nm for PVDF-TrFE [ 45 ] single tip PDDT [ 44 ] thermal DPN physical: melting of polymers and physisorption…”

“…[ 41a ] SNOL has also been demonstrated to spur the localized formation of PPV from its salt precursor, as well as the site-selective photo-crosslinking of a poly(9,9 ′ -dioctylfl uorene) (F8) derivative, producing patterns with resolution below 60 nm. [ 42 ] DPN is also capable of patterning some conjugated polymers. However, only very thin nanostructures of conjugated polymers have been fabricated in previous reports [ 43 ] because of the ineffi cient transport of the polymers.…”

Pure optical nano-writing on light- switchable spiropyrans/merocyanine thin film

“…The use of conjugated polymers in different applications, such as multicolored displays [1], integrated plastic circuits [2] and non-conventional light sources [3] requires patterned thin film technology [4]. To match the needs of recent developments in nano-electronics and photonics, lithography techniques have been pushed down to the nanometric scale [5]. However, the spatial resolution achievable by optical lithography by classical methods is diffraction limited and non-conventional methods are required for sub-micron scale resolution.…”