From single-molecule contacts to well-defined molecular ensemble contacts: Influence of intermolecular interactions onto the electronic transport
Organic Molecular Chemistry - Synthesis and Characterisation
Final Report Abstract
In summary, the fabricated CB chips were successfully employed for the electrical characterization of molecular thin films. The relatively high yield of functional junctions in comparison to other fabrication routes, the stability of the junction characteristics over several days, and the observed scaling of the resistance with the junction area, indicate considerable potential for the utilization of embedded CB junctions in Molecular Electronics. However, the spread of conductance traces demands further improvements of the fabrication process. There are different assumptions that might account for this phenomenon which are mostly associated with the variation of the interfacial contact. From the electrical investigations, it is known that the unstable interfacial contact between the molecular film and the top Au contact can significantly influence the electrical performance of the junctions. Although the top contact is deposited by a non-invasive printing process, a minimal variation of the surface topography in the low or even sub-nanometer range can impair the simultaneous conformal contact to bottom and top electrode. Meanwhile, it has been reported that the length, tilt angle and packing density of DAE molecules can slightly vary during the phototransformation between their two states, which may contribute to varying junction characteristics. Future improvements: the manually-controlled printing process could be operated in a more sophisticated manner with a better conformal contact via a so called “air cushion” process similar to nanoimprint lithography, where a gentle vacuum is created between bottom electrode and top electrode stamp before the latter is applied to the chip. The vacuum eliminates entrapped air between top and bottom electrode and the subsequently applied inert gas overpressure leads to an “air cushion press” which distributes equally the forces over the samples and compensates topographical defects. A laterally homogenous conformal contact even on subnanometer scale may reduce the distribution of junction resistances clearly below one order of magnitude, which will facilitate the unambiguous, systematic characterization of photoswitching in large area contacts. Last but not least, it remains an open challenge of how to establish fast as well as reversible photoswitching and how to utilize the accelerated switching kinetics achieved by SPPs. Simply exchanging the electrode material to full carbon or carbon covered top electrode seems not to be a feasible route to achieve this goal as recent publication results indicate. More fundamental experimental as well as theoretical investigations are required on the origin of the photocycloreversion inhibition.
Publications
- (2017) Development of Molecular Area Contacts for Optoelectronic Applications, Konstanz
Volker Schöps
- (2018). Facile, non-destructive characterization of 2d photonic crystals using UV-vis-spectroscopy. Phys. Chem. Chem. Phys. 2018, 20, 4340–4346
Schöps, V., Lenyk, B., Huhn, T., Boneberg, J., Scheer, E., Offenhäusser, A., Mayer, D.
(See online at https://doi.org/10.1039/c7cp07498k) - Stability makes a difference (2019) Nature Nanotechnology 14, 925
Mayer, D., Scheer, E.
(See online at https://doi.org/10.1038/s41565-019-0537-4) - (2020). Surface plasmon enhanced switching kinetics of molecular photochromic films on gold nanohole arrays. Nano Lett. 20, 5243–5250
Lenyk, B., Schöps, V., Boneberg, J., Kabdulov, M., Huhn, T., Scheer, E., Offenhäusser, A., Mayer, D.
(See online at https://doi.org/10.1021/acs.nanolett.0c01569) - Photochem. (2020). Basic enemies of photochromism: irreversible transformation of fluorinated diarylethenes to polyenic enamines and enols. Photobiol. Sci. 2020, 19, 1511– 1516
Sysoiev, D., Huhn, T.
(See online at https://doi.org/10.1039/d0pp00292e)
