Project summary: The goal of the project is to develop novel types of organic thin-film transistors (OTFT) containing a functionalized interfacial layers between the gate dielectric and the active layer to control the device-characteristics. In particular, we will focus on chemically reactive layers, which are suitable for chemical sensing, translating the presence of an analyte into a strong modification of threshold voltage and source-drain current of the transistor. This will allow the demonstration of new concepts for chemical or photochemical probes (to measure the total exposure of the device utilizing irreversible reactions) and sensors (to determine the current level of the analyte using reversible reactions). In preliminary tests, we have already realized devices with a covalently bound silane-based interfacial layer, in which exposure to NH3 shifts the threshold-voltage by up to 70V !
The main task of the project will be the realization of OTFT based sensors, and, most importantly, to understand the physical and chemical details of the involved processes. To achieve the latter, we will apply a multitude of analytical techniques: In addition to an in depth electrical characterisation of the devices, these include numerous surface-sensitive techniques to investigate layer thickness, structure, and morphology as well as the chemical composition of the layers. To complement the experiments, we will also perform standard quantum-mechanical calculations on suitable model systems. As interfacial layers, we will apply
(i) covalently bound functional molecules having suitable docking groups (trichlorosilane or trialkoxysilane) groups to link to the substrate (i.e., the SiOx dielectric) and bearing also chemically reactive or photosensitive end groups; for these layers we have gathered significant experience during the past months, especially regarding their application in OTFTs.
(ii) Spin-cast polymers (as an additional insulating layer of the dielectric on top of SiOx) bearing the same functional sensing units as the molecules mentioned above. Here, the sensing functionality will be either included directly during synthesis (by our partners), or added a posteriori through surface reactions on the spin-cast films.
(iii) Langmuir-Blodgett (LB) type mono- and multilayers of analogous materials; the main potential of these materials is that they allow for well controlled self-assembly processes and a full control over the layer thickness (enabling, e.g., the fabrication of well defined multilayer structures).
As reactive functional groups, we will apply analyte-docking groups like (e.g., sulfochloride, crown-ethers and non-protic bases) or photo-isomerisable/cleavable units.
The proposed project aims at forming a bridge between the two big national research clusters on organic materials currently under way in Austria: The ISOTEC project of the Austrian Nanotechnology Initiative and the NFN Interface controlled and functionalized organic films. With a thematic position between the two clusters (interface controlled organic sensors), this project will help linking those activities to generate additional synergetic effects and simultaneously strongly benefit from numerous collaborations.