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

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.

Spectroscopic properties of poly(9,9‐dioctylfluorene) thin films possessing varied fractions of β‐phase chain segments: enhanced photoluminescence efficiency via conformation structuring

“…The recently demonstrated spatial patterning of the β‐phase conformation in thin films of PFO 15 and PFO derivatives on length scales ≤500 nm has been proposed as an attractive approach to the design and fabrication of novel nanophotonic elements . A versatile imaging method is therefore needed to determine the spatial distribution of β‐phase fraction within such samples to optimize and control the simultaneously induced local change in refractive index .…”

“…), are likely to be problematic in the case of complex device architectures involving electrodes and opaque substrates or due to the presence of strong interference effects. PL microscopy, especially when carried out in a confocal geometry with spectrally filtered detection, may provide a potentially high‐resolution alternative; however, the occurrence of excitation energy transfer prevents straightforward estimation of the β‐phase fraction and its spatial distribution (cf. Table and discussion above).…”

“…When processed from solutions in good solvents (Hildebrand solubility parameter δ ≈ 9.2 cal 1/2 cm −3/2 as for, e.g., chloroform or tetrahydrofuran) that also allow for sufficiently rapid solvent evaporation during film deposition (e.g., toluene heated to 100 °C), in‐plane isotropic, “glassy” PFO films are obtained . In such films the PFO chains adopt a range of disordered wormlike conformations, collectively also termed “glassy,” featuring a broad distribution of intermonomer torsion angles .…”

“…A detailed method of measuring PLQE is presented, with the results expected to allow the performance of β‐phase PFO‐based light‐emitting devices to be further optimized. Second, following the recent demonstration of sub‐micrometer‐scale spatial patterning of the β‐phase, and therewith refractive index , in PFO films using dip‐pen nanolithography we investigate Raman spectroscopy as an alternative means (to optical absorption) for quantifying the β‐phase fraction in PFO films, as well as for spatially resolved imaging of β‐phase patterns. Raman spectroscopy offers the key advantage of being suitable for probing PFO films within device structures for which conventional optical transmission measurements may be problematic due to opaque substrates, the presence of electrodes or strong optical interference effects.…”

Tissue engineering of retina and Bruch’s membrane: a review of cells, materials and processes

“…With the development of alternative microfabrication techniques, membranes can be patterned to simulate the natural BM–ECM patterns. These techniques include microcontact printing47 and dip-pen nanolithography patterning 48. The resulting pattern is then used to control adsorption of biomolecules, such as proteins, to the surface, which subsequently interacts with the cells to promote site-specific anchorage to the surface 47…”