Alexander J. C. Kuehne

Hybrid inorganic/organic microstructured light-emitting diodes produced using photocurable polymer blends

Light-emitting diodes (LEDs) in the form of a one-dimensional array of microstripes emitting at 370nm were fabricated from AlInGaN inorganic semiconductor. These microlight sources were then used to “directly write” microstructures in photocurable blends of organic light-emitting polymers (LEPs) spin coated onto the LED surface. In this way, thin microstripes of LEP as narrow as 50μm have been fabricated and integrated with the micro-LEDs. These “self-aligned” polymer microstripes serve as wavelength downconverters under further excitation by the UV micro-LEDs, producing hybrid inorganic/organic microstructured LEDs.

Novel polymer systems for deep UV microlens arrays

We report for the first time a UV curable polymer with effective optical transmission below 300 nm. Through careful control of kinetics, various viscosities can be generated to optimize the film forming properties via spin coating. The transmission of the monomers and films is investigated over a spectral range which spans the 240–370 nm output of ultraviolet AlInGaN light-emitting diodes. The refractive index of the polymer has been measured by ellipsometry to give a value of 1.57 at 280 nm. Using standard lithography techniques with reactive ion etching, arrays of microlenses have been fabricated in this polymer with diameters of 30 µm and below and are characterized by atomic force microscopy and confocal microscopy.

Self-Correction Strategy for Precise, Massive, and Parallel Macroscopic Supramolecular Assembly

Macroscopic supramolecular assembly (MSA) represents a new advancement in supramolecular chemistry involving building blocks with sizes beyond tens of micrometers associating through noncovalent interactions. MSA is established as a unique method to fabricate supramolecularly assembled materials by shortening the length scale between bulk materials and building blocks. However, improving the precise alignment during assembly to form orderly assembled structures remains a challenge. Although the pretreatment of building blocks can ameliorate order to a certain degree, defects or mismatching still exists, which limits the practical applications of MSA. Therefore, an iterative poststrategy is proposed, where self-correction based on dynamic assembly/disassembly is applied to achieve precise, massive, and parallel assembly. The self-correction process consists of two key steps: the identification of poorly ordered structures and the selective correction of these structures. This study develops a diffusion-kinetics-dependent disassembly to well identify the poorly aligned structures and correct these structures through iterations of disassembly/reassembly in a programmed fashion. Finally, a massive and parallel assembly of 100 precise dimers over eight iteration cycles is achieved, thus providing a powerful solution to the problem of processing insensitivity to errors in self-assembly-related methods.

Light emitting polymer blends and diffractive optical elements in high-speed direct laser writing of microstructures

In this paper, we describe a series of improvements that have been made to our direct laser writing waveguide/microfluidic fabrication technology. We demonstrate significant increases in the writing speed (measured in micrometres of written structure per second) by both the use of customized photopolymers containing light emitting polymer and the inclusion of a diffractive optical element to enable the writing of multiple channels in a single pass.

Controlled micro-patterning of highly-fluorescent truxene-oligofluorene nanostructured blends

Truxene-oligofluorene nanostructured blends have been controllably patterned with feature size to below 6 mum using inkjet printing and laser direct-writing. Our blending approach provides an attractive method of handling fluorescent macromolecules for optoelectronic applications.

Energy up-conversion in dilute polyfluorene solutions

Poly(9,9-dioctylfluorene) (PFO) shows highly efficient blue emission with photo excitation occurring between 340–400 nm. Here we show that PFO can in dilute solution emit at a wavelength well below that at which it is being exited. This, we propose is related to an energy transfer from conjugated parts of the polymer chain into more localised states which then emit at a lower wavelength. These localised states can be considered as defects in the conjugation of the polymer or as chain ends. These may produce quasi monomer or quasi dimer species within the chain, which will have a HOMO-LUMO gap of higher energy than the conjugated polymer. These then fluoresce at the lower wavelength; essentially causing, by energy transfer, a process of energy up-conversion.