Integration of Nanoimprinted Layers in Organic Semiconductor Chemical Sensors and Lasers

Organic semiconductors are attractive materials for additive manufacture of optoelectronic and photonic devices by solution or vapour deposition. They can also be combined with nanoimprint techniques to add functionality to films and devices by patterning them at the nanoscale. In this presentation we will discuss approaches for nanoimprinting thin-film chemical sensors and lasers both at the sub-wavelength and molecular scales.

Nanoimprint lithography offers a simple and scalable process to pattern polymer films on length scales of 10s to 100s of nanometres. We have previously applied these techniques both in UV-photocurable polymer layers and directly to pattern the organic semiconductor using solvent immersion imprint lithography. We will present processes for reliable replication of photonic crystal and distributed feedback structures in layers that can be additively integrated with organic semiconductor waveguides as an optical cavity for very low threshold visible lasers.

Organic semiconductor sensors, which exploit luminescence quenching in the presence of certain target analyte molecules, offer an attractive approach for extremely sensitive detection of trace levels of hazardous environmental chemicals. These sensors operate by absorbing analyte molecules into the organic film from the vapour or solution surrounding the sensor. The absorbed molecules can interrupt the light emission process through a photoexcited electron transfer from the light emitting material to the (electronegative) analyte molecule. We have shown that the speed and sensitivity of the sensor response can be improved by configuring the sensor film as a nanopattered organic laser. A major challenge in these sensors, however, is how to increase their specificity to be able to discriminate a target molecule from potential distractant chemicals. We will also present an approach to imprint a molecular recognition layer above the organic semiconductor film using molecular imprinting in a porous solgel. The shape-imprinted channels in this layer can allow accumulation of the target analyte molecule in the sensing layer, while significantly suppressing quenching by other similar molecules from the headspace above the sensor. We will also present progress and potential in developing applications of these sensors for detection of explosives, pharmaceuticals and environmental pollutants in water or in vapour phase.