Toward Targeted Kinetic Trapping of Organic–Inorganic Interfaces: A Computational Case Study

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 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 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 reorientation of the molecules, which is thermodynamically more favorable for high dosages, but still high enough to enable ordered growth through diffusion of molecules. On the basis of the temperature-dependent diffusion and reorientation rates, we propose a temperature range at which the reorientation can be successfully suppressed.

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

“…This interface system is ideal for our study because its surface chemistry (in the absence of electric elds) is fairly well characterized, both experimentally [40][41][42] and through simulations. [42][43][44][45] Different polymorphs of TCNE on Cu(111) have been shown to exhibit substantially different properties such as the work function, which varies by up to 3 eV between polymorphs. 45 TCNE is known to bond to the surface through a Blyholder-like interaction, 46 comprising charge-donation from the metal into the molecular LUMO and back-donation from the molecular s-system to the surface.…”

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

“…This interface system is ideal for our study because its surface chemistry is fairly well characterized (in absence of electric fields), both experimentally [40][41][42] and through simulations. [42][43][44][45] Different polymorphs of TCNE on Cu(111) have been shown to exhibit substantially different properties such as the work function, which varies by up to 3 eV between polymorphs. [45] TCNE is known to bond to the surface through a Blyholder-like interaction, [46] comprising charge-donation from the metal into the molecular LUMO and back-donation from the molecular π-system to the surface.…”

“…In these relaxations, and throughout this work, the substrate is kept fixed. While relaxation of the substrate is expected to change the relative stability of adsorption geometries somewhat [44] this change is hardly affected by the electric field as we discuss in the Supporting Information. For the sake of simplicity, it is, therefore, neglected in the following discussion.…”

Controlling the polymorphism of organic/inorganic interfaces with electric fields

“…68,[70][71][72]74 Conversely, the vibrations of the molecules on the substrate can differ substantially from the molecules in the gas phase, especially when charge-transfer at the interface occurs. 73 For the special case of TCNE/Cu(111), it was shown in previous work 43,44 the zero-point energy of the adsorption geometries differs only very little when there is no field applied.…”

“…This interface system is ideal for our study because its surface chemistry is fairly well characterized (in absence of electric fields), both experimentally 39-41 and through simulations. [41][42][43][44] Different polymorphs of TCNE on Cu(111) have been shown to exhibit substantially different properties such as the work function, which varies by up to 3 eV between polymorphs. 44 TCNE is known to bond to the surface through a Blyholder-like interaction, 45 comprising charge-donation from the metal into the molecular LUMO and back-donation from the molecular system to the surface.…”