Dip-pen patterning of poly(9,9-dioctylfluorene) chain-conformation-based nano-photonic elements.

Aleksandr Perevedentsev,Donal D C Bradley,Paul N Stavrinou,Yannick Sonnefraud,Anthony E G Cass,Colin R Belton,Ji-Seon Kim,Stefan A Maier,Sanjiv Sharma

doi:10.1038/ncomms6977

Aleksandr Perevedentsev, Donal D C Bradley + Show 7 more

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https://doi.org/10.1038/ncomms6977

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Abstract

Metamaterials are a promising new class of materials, in which sub-wavelength physical structures, rather than variations in chemical composition, can be used to modify the nature of their interaction with electromagnetic radiation. Here we show that a metamaterials approach, using a discrete physical geometry (conformation) of the segments of a polymer chain as the vector for a substantial refractive index change, can be used to enable visible wavelength, conjugated polymer photonic elements. In particular, we demonstrate that a novel form of dip-pen nanolithography provides an effective means to pattern the so-called β-phase conformation in poly(9,9-dioctylfluorene) thin films. This can be done on length scales ≤500 nm, as required to fabricate a variety of such elements, two of which are theoretically modelled using complex photonic dispersion calculations.

Highlights

Metamaterials are a promising new class of materials, in which sub-wavelength physical structures, rather than variations in chemical composition, can be used to modify the nature of their interaction with electromagnetic radiation
Typical embodiments use molecular assembly to generate a template to guide metal particle array formation or the attachment of molecular units to metal nanoparticles that enables their assembly into hierarchical structures. In the former category, interesting recent work includes metal-organic framework structures[2] and in the latter, bio-enabled assembly strategies[3]. These approaches do not use the optical properties of the molecular component to define the interaction with electromagnetic radiation; that interaction is still based on metals
We have previously introduced the concept of conformational metamaterials in which the physical geometry of a molecule acts as a vector for refractive index change

Summary

Introduction

Metamaterials are a promising new class of materials, in which sub-wavelength physical structures, rather than variations in chemical composition, can be used to modify the nature of their interaction with electromagnetic radiation. We demonstrate that a novel form of dip-pen nanolithography provides an effective means to pattern the so-called b-phase conformation in poly(9,9-dioctylfluorene) thin films This can be done on length scales r500 nm, as required to fabricate a variety of such elements, two of which are theoretically modelled using complex photonic dispersion calculations. The bottom-up, molecular approach to structure formation offers interesting opportunities for metamaterials fabrication without the need for conventional optical or electron beam lithography, an important consideration where visible wavelength metamaterials, requiring nano-structuring, are concerned. We demonstrate the formation of spatial patterns of the b-phase conformation in poly(9,9-dioctylfluorene) (PFO) on length scales r500 nm using a novel dip-pen nanolithography (DPN) method, in which a liquid solvent is used as ink. Further reductions in length scale are anticipated, offering the prospect of a versatile approach to visible wavelength, conformationbased, conjugated polymer photonic elements

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