Understanding the nucleation and growth kinetics of thin films is a prerequisite for their large-scale utilization in devices. For self-assembled molecular phases near thermodynamic equilibrium the nucleation-growth kinetic models are still not developed. Here, we employ real-time low-energy electron microscopy (LEEM) to visualize a phase transformation induced by the carboxylation of 4,4'-biphenyl dicarboxylic acid on Ag(001) under ultra-high-vacuum conditions. The initial (α) and transformed (β) molecular phases are characterized in detail by X-ray photoemission spectroscopy, single-domain low-energy electron diffraction, room-temperature scanning tunneling microscopy, noncontact atomic force microscopy, and density functional theory calculations. The phase transformation is shown to exhibit a rich variety of phenomena, including Ostwald ripening of the α domains, burst nucleation of the β domains outside the α phase, remote dissolution of the α domains by nearby β domains, and a structural change from disorder to order. We show that all phenomena are well described by a general growth-conversion-growth (GCG) model. Here, the two-dimensional gas of admolecules has a dual role: it mediates mass transport between the molecular islands and hosts a slow deprotonation reaction. Further, we conclude that burst nucleation is consistent with a combination of rather weak intermolecular bonding and the onset of an additional weak many-body attractive interaction when a molecule is surrounded by its nearest neighbors. In addition, we conclude that Ostwald ripening and remote dissolution are essentially the same phenomenon, where a more stable structure grows at the expense of a kinetically formed, less stable entity via transport through the 2D gas. The proposed GCG model is validated through kinetic Monte Carlo (kMC) simulations.

CEITEC Central European Institute of Technology Brno University of Technology Purkyňova 123 612 00 Brno Czech Republic

Centro de Física de Materiales CFM Materials Physics Center MPC Centro Mixto CSIC UPV EHU Manuel Lardizabal 5 20018 Donostia San Sebastián Spain

Department of Materials Physics Faculty of Chemistry University of the Basque Country UPV EHU Manuel Lardizabal 3 20018 Donostia San Sebastián Spain

Donostia International Physics Center Manuel Lardizabal 4 20018 Donostia San Sebastián Spain

Faculty of Mathematics and Physics Charles University 5 Holešovičkách 2 180 00 Prague Czech Republic

Institute of Physical Engineering Brno University of Technology Technická 2896 2 616 69 Brno Czech Republic

Institute of Physics of the Czech Academy of Sciences Cukrovarnická 10 16200 Prague 6 Czech Republic

Regional Centre of Advanced Technologies and Materials Department of Physical Chemistry Faculty of Science Palacký University Šlechtitelů 27 78371 Olomouc Czech Republic

References provided by Crossref.org

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