Influence of the defect density on the ordering of an NHC monolayer on a silicon surface

Abstract

Silicon is the element of choice in semiconductor devices and the functionalization of silicon surfaces is highly desirable for electronic industries. N-Heterocyclic carbenes have been demonstrated to be promising modifiers and anchors for surface functionalization, but so far mainly on metal surfaces. Here, the adsorption behavior of cyclohexyl cyclic (alkyl)(amino)carbene molecules on a silicon surface is investigated using scanning tunneling microscopy. Surprisingly and quite unexpected on semiconductors, we find a self-limited, well ordered growth of a stable monolayer with large domains. The overlayer is characterized by a 3 × 3 periodicity and an upright adsorption geometry of the molecules leading to a strong work function reduction. Moreover, we find that the surface defect density strongly influences the grade of ordering, as the initial adsorption of the molecules takes place on a defect site. Thus, in the studied material system, the defect density of the substrate directly determines the domain sizes.