Tuning organic/inorganic interfaces via kinetic trapping, a case study

Properties of inorganic-organic interfaces, such as their interface dipole, strongly depend on the structural arrangements of the organic molecules. A prime example is TCNE on Cu(111), which shows two different phases with a significant work function difference. However, the thermodynamically preferred phase is not always the one that is best suited for a given application. Rather, it may be desirable to selectively grow a kinetically trapped structure. In this work, we employ density functional theory and transition state theory to predict under which conditions such a kinetic trapping is possible for the model system of TCNE on Cu. In detail, we want to trap the molecules in the first layer in a flat-lying orientation. This requires suppressing the re-orientation to upright-standing TCNE that becomes thermodynamically more favorable for high dosages, while still enabling ordered growth. Based on the temperature-dependent diffusion and re-orientation rates,we propose a temperature range at which the re-orientation can be successfully suppressed.