An ordered organic radical adsorbed on a Cu-doped Au(111) surface

Abstract

The tri-para-carboxylic polychlorotriphenylmethyl radical adsorption on a Cu/Au(111) surface has been investigated in ultra-high vacuum environment. The presence of copper favours the formation of metal-organic assemblies, which are analysed using scanning tunnelling microscopy (STM) and high resolution electron energy loss spectroscopy (HREELS). DFT methods indicate that the unpaired electron survives after adsorption, thus creating systems which could be regarded as potential candidates for spintronics applications.

Structure and Reactivity of Cu-doped Au(111) Surfaces

“…As revealed by combined STM and vibrational spectroscopy measurements, the balance between the affinity of chlorine atoms for gold [55] and the formation of hydrogen bonds, typical of carboxylic groups, steers molecular assembly to a flat-lying geometry on Au(111), whereby PTMTC radicals are characterized by intermolecular hydrogen bonding and interact with the gold surface through the chlorine atoms [56]. On copper doped Au(111) surfaces PTMTC was found to adopt an upright geometry [8], as a result of the deprotonation of one of the carboxylic acid groups followed by coordination with copper adatoms, and repulsive interaction between the Cl-substituted benzene rings. The change in geometry has important consequences regarding the preservation of the unpaired electron, as highlighted when comparing the calculated spin-projected density of states (SP-DOS) of the gas-phase free radical with those of the adsorbed species (Fig.…”

“…5(c)] [8]. However, a more thorough characterization of the flat-lying species, especially of those in contact with the substrate, is still required, in order to determine unambiguously whether the open shell structure is retained [8,56,57], and characterize the spin polarization [8,56].…”

“…Tris-p-carboxylicpolychlorotriphenylmethyl radical (PTMTC) is a perchlorinated trityl radical derivative with an open shell electronic configuration stable and persistent at ambient conditions [54], with the unpaired electron mostly localized in the central carbon atom, C * [8]. As revealed by combined STM and vibrational spectroscopy measurements, the balance between the affinity of chlorine atoms for gold [55] and the formation of hydrogen bonds, typical of carboxylic groups, steers molecular assembly to a flat-lying geometry on Au(111), whereby PTMTC radicals are characterized by intermolecular hydrogen bonding and interact with the gold surface through the chlorine atoms [56].…”

“…Nucleation of guest metals on Au(111) generally occurs via the place-exchange mechanism [5], which was initially ruled out for the adsorption of copper; however, it was later reported that the onset of copper adsorption does occur via a place-exchange mechanism, at specific sites identified as the narrowed regions within the highly reactive elbows of the Au(111)-(22× √ 3), irrespective of hcp or fcc stacking [1]. Other than for copper [6][7][8], this is also the case for other transition metals such as nickel [9][10][11][12], iron [13,14], and chromium [15,16], to name a few. Added clusters are regarded as a source of reactive metal atoms, over a surface commonly considered as a 2D inert support, opening up the possibility of modifying the reactivity of the Au(111) surface itself, via the formation of surface alloys, whereby both the added metal and gold are present in the top layer.…”

Role of Hydrogen Bonding in the Formation of Adenine Chains on Cu(110) Surfaces

“…Molecular self-assembly on solid surfaces is a research topic of extensive experimental [1,2,3,4,5,6,7,8,9] and theoretical studies [10,11], owing to the promising applications in future organic-based nanoelectronics [1,12,13]. Organic molecules, including DNA and RNA bases, are capable of forming a range of nanostructures from well-ordered, two-dimensional (2D) molecular networks to one-dimensional rows upon deposition on a surface [1,2].…”