Structural relaxation of adlayers in the presence of adsorbate-induced reconstruction:C60/Cu(111)

Abstract

We revisit submonolayer growth of ${\mathrm{C}}_{60}$ on Cu(111) by scanning tunneling microscopy (STM), with emphasis on the formation of higher-order commensurate metastable states. These phases show concomitant interfacial reconstruction, adlayer buckling, and adlayer rotation in order to match as closely as possible the 10.0 \AA{} ${\mathrm{C}}_{60}$ nearest neighbor (NN) distance. Most interestingly, a clear correlation between the adlayer rotation angle and molecular contrast patterns is demonstrated. This is caused by the ${\mathrm{C}}_{60}$-induced reconstruction at preferred binding sites and adlayer buckling in adjustment to strain. Four contrast patterns, i.e., ``disordered maze,'' ``linear-wall maze,'' $``p(\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7}),''$ and $``p(2\ifmmode\times\else\texttimes\fi{}2),''$ with increasing ${\mathrm{C}}_{60}$ NN distances are categorized. In the most compressed phase, buckling is favored and it is analogous to the ground state of a strongly-coupled antiferromagnetic system on a triangular lattice with alike adlayer buckling and interfacial corrugation. In contrast, the molecular orderings in the other structures are mostly dictated by lateral displacements of ${\mathrm{C}}_{60}$ toward preferred reconstructive binding sites. These metastable phases thus illustrate structural relaxation of a molecular layer on an adsorbate-induced reconstructed substrate in different adsorbate-adsorbate and adsorbate-substrate interaction limits.