Asymmetric relief of surface stress induced by a chiral adsorbate: Alaninate adsorption on Cu(110)

Abstract

Using first-principles calculations, we explore symmetry breaking in the surface stress tensor induced upon adsorption of chiral species on an achiral metallic substrate, namely, alaninate on Cu(110). The stress sensitivity to coverage and adsorption geometry is studied in the known $(2\ifmmode\times\else\texttimes\fi{}3)$ phase and other related reconstructions. We find that alaninate relieves stress in the Cu(110) surface by electron transfer from the substrate to the molecule. In a low coverage regime, $\ensuremath{\Theta}=1/6$, the principal stresses are found to deviate in opposite directions by an angle $\ensuremath{\alpha}\ensuremath{\sim}15\ifmmode^\circ\else\textdegree\fi{}$ from the substrate mirror plane directions, $[1\overline{1}0]$, depending on the chirality of the alaninate adsorption footprint. In medium-high coverage regimes, $\ensuremath{\Theta}\ensuremath{\ge}0.3$, the observed asymmetries are weaker, consistent with the presence of H bonds lying close to $[1\overline{1}0]$. The studied $\ensuremath{\Theta}=1/3$ enantiopure models show the same asymmetry orientation with $\ensuremath{\alpha}\ensuremath{\sim}5\ifmmode^\circ\else\textdegree\fi{}$. Thus, stress relief anisotropy is diagnostic of the molecular chirality in this case. We also find that the substrate intrinsic tensile stress is relieved at $\ensuremath{\Theta}\ensuremath{\gtrsim}0.25$, when the adsorbates form the onset of a H-bound network. At higher coverages, the system is under net compressive stress.