Gold-C28 molecular junction gas sensor: A simulation study

The research and development of recent years on molecular electronic systems, in which the properties of devices are dictated by a molecule, has brought to the creation of a variety of structures. Thanks to the intrinsic characteristics of molecules, devices with a small footprint, and therefore portable and ready to be used, may be realized. Furthermore, the great tunability simply provided by a different choice of the employed molecule allows to build systems according to needs. As a consequence, an interesting area of study in molecular electronics is represented by gas sensors, where the possibility of having devices showing high selectivity with respect to desired targets is the main goal. In this viewpoint, the present work comes with the purpose of providing an in-depth characterization of a sensor employing the C28 fullerene as the sensing region. In particular, the resulting system is a molecular junction with gold contacts. Starting from the description of the molecule, of which two isomeric forms are taken into account, a detailed study of possible configurations for the sensor is performed to find the most stable ones and that are hence expected to be obtained experimentally with an higher probability. The chosen structure is then analyzed in the presence of species naturally found in the atmosphere, both in equilibrium and out of equilibrium conditions, to verify the sensing ability of the device. Equilibrium studies are also exploited for the comparison, in results, of more precise density functional theory based models and semi-empirical ones, like extended Hückel theory and Slater-Koster. Next, considering the purpose of a sensor being the detection of a desired target, possible pollutants are introduced in the neighboring region of the channel to find species for which the sensor may show a good selectivity. Finally, exploiting the results of these analysis, a discussion on why specific variations in the properties of the system occurred is provided to present a theoretical justification for the observed modifications.