This review aims at giving the readers the basic concepts needed to understand two-dimensional bimolecular organizations at the vacuum–solid interface. The first part describes and analyzes molecules–molecules and molecules–substrates interactions. The current limitations and needs in the understanding of these forces are also detailed. Then, a critical analysis of the past and recent advances in the field is presented by discussing most of the key papers describing bicomponents self-assembly on solid surface in an ultrahigh vacuum environment. These sections are organized by considering decreasing molecule–molecule interaction strengths (i.e. starting from strong directional multiple H bonds up to weaker nondirectional bonds taking into account the increasing fundamental role played by the surface). Finally, we conclude with some research directions (predicting self-assembly, multi-components systems, and nonmetallic surfaces) and potential applications (porous networks and organic surfaces).

SummaryThe adsorption on KBr(001) of a specially designed molecule, consisting of a flat aromatic triphenylene core equipped with six flexible propyl chains ending with polar cyano groups, is investigated by using atomic force microscopy in the noncontact mode (NC-AFM) coupled to Kelvin probe force microscopy (KPFM) in ultrahigh vacuum at room temperature. Two types of monolayers are identified, one in which the molecules lie flat on the surface (MLh) and another in which they stand approximately upright (MLv). The Kelvin voltage on these two structures is negatively shifted relative to that of the clean KBr surface, revealing the presence of surface dipoles with a component pointing along the normal to the surface. These findings are interpreted with the help of numerical simulations. It is shown that the surface–molecule interaction is dominated by the electrostatic interaction of the cyano groups with the K+ ions of the substrate. The molecule is strongly adsorbed in the MLh structure with an adsorption energy of 1.8 eV. In the MLv layer, the molecules form π-stacked rows aligned along the polar directions of the KBr surface. In these rows, the molecules are less strongly bound to the substrate, but the structure is stabilized by the strong intermolecular interaction due to π-stacking.