Oxygen-Controlled Assembly of Chiral [7]-Helicene on ZnO Surfaces

Abstract

Chiral molecular organization at semiconductor interfaces is vital for advancing quantum and chirality-induced spin-selective (CISS) technologies yet achieving atomic-level control remains challenging. Here, we show that the adsorption and nanoscale assembly of enantiopure [7]-helicene on Zinc Oxide (ZnO) is dictated primarily by the identity of the topmost surface atom rather than by macroscopic surface polarity. Using atomic force microscopy (AFM), circular dichroism (CD), force field molecular dynamics (FFMD), and density functional tight-binding (DFTB), we examine four ZnO terminations and find that polar O-terminated (0001) and both nonpolar surfaces reproducibly host uniform helicene nanoislands with a thickness of about 4 nm, while the polar Zn-terminated (0001) facet largely suppresses adsorption experimentally. FFMD and DFTB analyses provide a picture of the underlying interaction landscape, offering valuable theoretical support for the experimentally observed facet selectivity. The robust formation of oxygen-driven nanoislands identifies surface oxygen as an atomic-scale selector for chiral self-assembly, enabling deterministic patterning of ultrathin 2D chiral domains on oxide semiconductors. These insights establish a design rule for integrating helicene-based chiral architecture into spintronic and quantum devices.