Two-Dimensional Functionalized Ultrathin Semi-Insulating CaF2 Layer on the Si(100) Surface at a Low Temperature for Molecular Electronic Decoupling

International audienceOur ability to precisely control the electronic coupling/decoupling of adsorbates from surfaces is an essential goal. It is not only important for fundamental studies in surface science, but also in several applied domains including for example miniaturized molecular electronic or for the development of various devices such as nanoscale bio-sensors or photovoltaic cells. Here, we provide atomic scale experimental and theoretical investigations of a semi-insulating layer grown on a silicon surface via its epitaxy with CaF2. We show that, following the formation of a wetting layer, the ensuing organized unit-cells are coupled to additional physisorbed CaF2 molecules, periodically located in their surroundings. This configuration shapes the formation of ribbons of stripes that functionalize the semiconductor surface. The obtained assembly, having a monolayer thickness, reveals a surface gap energy of ~ 3.2 eV. The adsorption of iron-tetraphenylporphyrin molecules on the ribbons of stripes is used to estimate the electronic insulating properties of this structure via differential conductance measurements. Density functional theory (DFT) including several levels of complexity (annealing, DFT+U and non-local van der Waals functionals) are employed to reproduce our experimental observations. Our findings offer a unique and robust template that brings an alternative solution to electronic semi-insulating layer on metal surfaces such as NaCl. Hence, CaF2/Si(100) ribbon of stripes structures, which lengths can reach more than 100 nm, can be used as a versatile surface platform for various atomic scale study of molecular devices