Thermodynamics of the Segregation of a Kinetically Trapped Two-Dimensional Amorphous Metal-Organic Network
Surface-confined self-assembled molecular networks are commonly described as crystalline structures with short- and long-range order. Few exceptions to this trend are found in the literature reporting on amorphous and glassy networks and, discussing the origins of their disordered nature at the atomic, scale. Here, we show that an amorphous two component metal-organic network can be synthesized on a crystalline metal surface at room temperature by vapor deposition of organic molecules and metal atoms. Scanning tunneling microscopy reveals the transformation of a crystalline close packed organic layer into a disordered porous layer formed through the self-assembly of an organic semiconductor functionalized with two cyano groups upon introduction of iron atoms on Ag(111). In contrast to the commonly observed preference for trigonal crystal symmetry in 2D systems that form, glassy networks, our metal organic network favors rhombic or square tessellation of the surface. Statistical analysis of the network's morphology reveals that entropy plays a critical part in its stabilization. Phase segregation of the binary mixture of monodisperse metal atoms and organic molecules into spatially separate homogeneously crystalline domains of molecules and metal atoms upon thermal annealing and subsequent cooling is observed. This suggests that the amorphous network is kinetically trapped at room temperature during the preparation process.