Towards targeted kinetic trapping of organic-inorganic interfaces: A computational case study

TL;DR

This study uses computational methods to identify conditions under which organic molecules can be kinetically trapped in a specific orientation on a metal surface, enabling targeted interface properties.

Contribution

It introduces a computational framework combining density functional theory and transition state theory to predict kinetic trapping conditions for organic-inorganic interfaces.

Findings

Identified temperature ranges to suppress molecular re-orientation.

Demonstrated the feasibility of kinetically trapping molecules in desired orientations.

Provided insights into controlling interface properties through kinetic control.

Abstract

Properties of inorganic-organic interfaces, such as their interface dipole, strongly depend on the structural arrangements of the organic molecules. A prime example is tetracyanoethylene (TCNE) on Cu(111), which shows two different phases with significantly different work functions. However, the thermodynamically pre-ferred 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 transi-tion state theory to discuss under which conditions such a kinetic trapping might be possible for the model system of TCNE on Cu. Specifically, we want to trap the molecules in the first layer in a flat-lying orientation. This requires temperatures that are sufficiently low to suppress the re-orientation of the molecules, which is thermodynamically more favorable for high dosages, but still high enough to enable ordered growth through diffusion of molecules. Based on the temperature-dependent diffusion and re-orientation rates, we propose a temperature range at which the re-orientation can be successfully suppressed.