Assembly and spectroscopy of monatomic Cu/Cu(111) quantum wires

Starting from single Cu atoms adsorbed on a Cu(111) surface, one-atom-wide close-packed chains can be assembled by means of STM-based atom manipulation. We find that the electronic states confined to the atom chain are quantized. The formation of these quantum states, which determine the overall physical properties of the nanostructure, can be understood within the Hückel scheme – a simple theoretical approach well known from physical chemistry textbooks to describe molecular orbitals. Spatial mapping of the differential tunneling conductance dI/dV allows us to measure the squared wave function of the respective eigenstates. Complementary density functional calculations verify the existence of unoccupied electronic states delocalized along the chain which derive from the coupling between sp_z hybrid orbitals associated with the discrete Cu/Cu(111) adatom.

Figure:

STM images of a single Cu adatom, a dimer, and chains containing three to seven atoms (A), corresponding dI/dV spectra revealing the existence of unoccupied quantum levels (B), dI/dV maps showing the state densities of the quantum states of a Cu₉ chain (C), and DFT-calculated wave function of the chain-localized state (D).

Related publications:

S. Fölsch, P. Hyldgaard, R. Koch and K. H. Ploog, Quantum confinement in monatomic Cu chains on Cu(111), Phys. Rev. Lett. 92, 056803-1/056803-4  (2004)

F. E. Olsson, M. Persson, A. G. Borisov, J.-P. Gauyacq, J. Lagoute and S. Fölsch, Localization of the Cu(111) surface state by single Cu adatoms, Phys. Rev. Lett. 93, 206803-1/206803-4 (2004)

J. Lagoute, X. Liu and S. Fölsch, Electronic properties of straight, kinked and branched Cu/Cu(111) quantum wires: A low-temperature scanning tunneling microscopy and spectroscopy study, Phys. Rev. B 74, 250410-1/250410-8  (2006)

S. Díaz-Tendero, S. Fölsch, F. E. Olsson, A. G. Borisov and J.-P. Gauyacq, Electron propagation along Cu nanowires supported on a Cu(111) surface, Nano Lett. 8, 2712-2717 (2008)