Interplay between structure and electronic states in step arrays explored with curved surfaces

Abstract

Atomic staircases in noble metal surfaces are model one-dimensional superlattices, where free-electron-like surface states transform into superlattice bands with sizeable quantum size shifts and gaps. At critical step spacings d = n × (λF /2), such superlattice gaps lie at the Fermi energy, affecting the electronic energy, and hence the structural stability of the step lattice, which is held by weak elastic interactions. We use Cu, Ag, and Au curved crystals to smoothly tune the superlattice constant d in Angle Resolved Photoemission (ARPES) and Scanning Tunneling Microscopy (STM) experiments. With ARPES we accurately quantify terrace size effects and determine the superlattice potential, which increases from Ag to Cu and to Au. With STM we analyze the d-dependent terrace width distribution for Cu and Ag, and observe non-linear variations in Cu. On the grounds of simple electronic and elastic models, we conclude that terrace width distribution instabilities and electronic energy variations at d = n×(λF /2) have the same order of magnitude for Cu. In contrast, the weak superlattice potential in Ag, i.e., its smoother band structure modulation is not sufficient to alter the step lattice.

Lateral confinement effects of M¯-point Tamm state in vicinal Cu(100) surfaces

“…The barrier strength for Cu(100) vicinals is similar as the barrier found for Ag(111) steps [39] and it increases slightly for smaller d terraces, as also found for Au and Cu(111) vicinal systems. Changes in the elastic stress at steps as a function of terrace width or the interaction between line dipoles of neighboring steps could in fact slightly modify the potential barrier.…”

Long-range surface faceting induced by chemisorption of PTCDA on stepped Ag(111) surfaces

“…Such "manipulations" can induce changes of sticking probability, chemical bonding, or orientation of molecular adsorbates, or can lead to potentially drastic changes of surface reactivity and catalytic efficiency. They can also be used to create regular patterns or superstructures on a surface [1,2], the properties of which can then be investigated [3] or taken as (nanostructured) template for the further growth of molecules with tailored properties [4][5][6][7] or as tailored interface in a metal-organic device.…”

“…The archetype system PTCDA (3,4,9,10 perylene-tetracarboxilicdianhydride) on (stepped) Ag(111) surfaces was chosen as model system, because much knowledge from various surface science methods is already available. In particular it was clear from previous studies that PTCDA molecules chemisorb on different Ag surfaces [8][9][10][11][12][13][14][15] and form highly ordered monolayers, i.e.…”

Determination of the photoelectron reference plane in nanostructured surfaces

“…But before describing our system electronically, it is convenient to briefly review the effects of regular step arrays on the Cu(111) Shockley state. The problem of the scattering of surface states at step arrays on noble metal surfaces has recently been revisited using cylindrical crystals [27]. The most characteristic observation is the size effect, namely the surface state shift toward the Fermi energy as the terrace width decreases, which reflects the repulsive character of the scattering potential of the steps [18,27,28].…”