Polymorphism mediated by electric fields: a first principles study on organic/inorganic interfaces

Organic/inorganic interfaces are known to exhibit rich polymorphism, where different polymorphs often possess significantly different properties. Which polymorph forms during an experiment depends strongly on environmental parameters such as deposition temperature and partial pressure of the molecule to be adsorbed. To prepare desired polymorphs these parameters are varied. However, many polymorphs are difficult to access within the experimentally available temperature-pressure ranges. In this contribution, we investigate how electric fields can be used as an additional lever to make certain structures more readily accessible. On the example of tetracyanoethylene (TCNE) on Cu(111), we analyze how electric fields change the energy landscape of interface systems. TCNE on Cu(111) can form either lying or standing polymorphs, which exhibit significantly different work functions. We combine first-principles calculations with a machine-learning based structure search algorithm and ab initio thermodynamics to demonstrate that electric fields can be exploited to shift the temperature of the phase transition between standing and lying polymorphs by up to 100 K.

Automated summary

Organic/inorganic interfaces exhibit different polymorphs with diverse properties, and their formation is influenced by environmental parameters. Electric fields can be used to make certain structures more accessible, as demonstrated by the example of TCNE on Cu(111). By combining first-principles calculations, machine-learning based structure search, and ab initio thermodynamics, it is shown that electric fields can shift the temperature of the phase transition between different polymorphs.