Initial Growth\nof the Pentacene Monolayer on a Si(001)‑2\n× 1 Substrate: A Lattice Model View

In this work, we investigate the initial growth of the\npentacene\nmonolayer on the reconstructed Si(001)-2 × 1 surface with a detailed\nlattice gas model. We employ a combination of electron density functional\ntheory (DFT) and tensor renormalization group (TRG) methods to reveal\nthe equilibrium structures of the monolayer and driving forces of\nits self-assembly. The planar adsorption complexes are found to be\npredominant in the pentacene monolayer on the reconstructed Si(001)-2\n× 1 in a wide range of pressure and surface coverages. We found\ntwo equilibrium structures of the monolayer differing in the surface\ncoverage. Both structures of the monolayer consist of a mixture of\nadsorption complexes in which pentacene molecules are oriented either\nalong or perpendicular to the rows of SiSi dimers. The low\ncoverage structure is the network with two-dimensional rectangular\npores. As the pressure increases, this structure transforms into a\ndense phase by filling the pores of the network with extra pentacene\nmolecules. Our TRG calculations demonstrate that self-assembly of\nthe pentacene adsorption monolayer on the Si(001)-2 × 1 surface\nis driven by the subtle interplay between relative stability of different\nadsorption complexes and intermolecular interactions.