Molecular self-assembly is generally recognized as a powerful biomimetic strategy for the fabrication of nanoscale structures. Among purely synthetic systems, self-assembled monolayers (SAMs) are the prototypical example of two-dimensional molecular organization. The defining characteristic of molecular self-assembly is that molecular interactions lead spontaneously to a well-organized equilibrium structure. Generally, these interactions are "soft" (i.e. non-covalent)  and reversible, because adjustment and molecular motion are necessary to minimize defects and achieve organized assemblies. Thus, by necessity, self-assembly is highly dynamic; it is unlikely that one can design a self-organizing system that is simultaneously well-organized and rigid/static. This suggests that the rational design of stable nanoscale structures requires a understanding of the equilibrium structure and phase behavior of molecular assemblies. 

Self-assembled monolayers form spontaneously at the solution/solid interface as a consequence of molecular adsorption and two-dimensional self-organization.  Our work suggests that the self-organization process can be viewed from the perspective of the nucleation and growth of a dense two-dimensional phase (2D solid) from a less dense phase.  In particular, the nucleation and growth kinetics of solid clusters in coexistence with a 2D “vapor” phase agree quantitatively with models of vapor phase epitaxial growth that predict growth regimes and scaling exponents.  Other growth mechanisms are observed, however, when the adsorbate/substrate interaction is varied.  In fact, one can observe a qualitative change in the growth mechanism for a single system as a function of temperature.  These mechanisms can be classified into three types which can be viewed in a 2D thermodynamic context as occurring (1) below the liquid-vapor triple point, (2) above the liquid-vapor triple point, and (3) above the liquid-“solid” critical point, respectively.