Structure and electronic properties of end states of self-assembled 1D covalent molecular chains on Au(111)

One-dimensional structures offer a rich ecosystem for realizing quantum states with potential application for advanced information technologies. Surface confined molecular self-assembly is one avenue for creating 1d systems, where the extant structure is controlled by the precursor shape, and functional group interlinking chemistry. Here we study self-assembled 1d chains of zwitterionic molecule bis-bidentate ditopic (DABQDI) on Au(111) in ultrahigh vacuum, measured at 5K using combined scanning tunneling and non-contact atomic force microscopies (STM/ nc-AFM). Submolecular resolution achieved with a CO- functionalized tip offers detailed structural information, specifically regarding the unusual hydrogen bonds linking the precursor units. In-gap electronic states near the Fermi energy are observed via scanning tunneling spectroscopy (STS), strongly localized to the chain ends. We present our latest efforts to understand and simulate the observed structures via density functional theory (DFT) and nc-AFM simulations, and rationalize the observed electronic properties via modelling inspired by the Su, Schrieffer, Heeger (SSH) one-dimensional tight binding model.