Finite size effects in surface states of stepped Cu nanostripes

J E Ortega,M Ruiz-Osés,J Kuntze

doi:10.1103/physrevb.72.195416

Abstract

Cu nanostripes with finite arrays of monatomic steps are self-assembled by Ag-induced faceting of vicinal Cu(111) surfaces. By varying the amount of Ag in the submonolayer range one can tune the internal step spacing $d$ of Cu stripes, while decreasing its total width ${w}_{\mathrm{Cu}}$. We can observe, by means of angle-resolved photoemission, a progressive transition from two-dimensional surface bands to one-dimensional quantum well states as ${w}_{\mathrm{Cu}}$ decreases. A direct comparison between surface states of infinite vicinals and nanostripes with the same $d$ indicates a small upwards energy shift in the latter, which is well explained by assuming electron confinement in an infinite quantum well of size ${w}_{\mathrm{Cu}}$. Nanostripe finite size effects are more straightforwardly observed in Fermi surfaces, which are asymmetrically broadened in the perpendicular direction. This effect is quantitatively analyzed and explained as due to the characteristic spectral broadening observed in photoemission from ${w}_{\mathrm{Cu}}$-wide one-dimensional quantum wells.

Highlights

Lateral nanostructures grown at surfaces, like quantum dots, stripes or atomic wires, are matters of intensive research due to their potential in different areas of nanotechnology
A direct comparison between surface states of infinite vicinals and nanostripes with the same d indicates a small upwards energy shift in the latter, which is well explained by assuming electron confinement in an infinite quantum well of size wCu
Nanostripe finite size effects are more straightforwardly observed in Fermi surfaces, which are asymmetrically broadened in the perpendicular direction

Summary

INTRODUCTION

Lateral nanostructures grown at surfaces, like quantum dots, stripes or atomic wires, are matters of intensive research due to their potential in different areas of nanotechnology. Vicinal111͒ noble metal surfaces are suitable to investigate surface electron scattering by ARPES.2–7 They usually display regular arrays of straight steps, such that the vicinal surface can be viewed as a 1D step superlattice, where the step-to-step distance d is the 1D lattice constant. Shockley-type surface states with changing dimensionality have been observed in 1D stepped Cu stripes, i.e., step arrays with a finite number of steps.6 Such nanostripes are self-assembled during Ag-induced periodic faceting of vicinal Cu111͒ surfaces.. As a function of Ag coverage⌰͒, Ag stripes become wider and Cu stripes narrower, i.e., the system smoothly evolves from very wide Cu stripes with a large number of steps and short step spacing d, to Cu stripes defined by a relatively wided ϳ 36 Å, single111͒ terrace.9 In such a two-phase system surface states split into distinct Ag-like statesabove EF, and Cu-like statesbelow EF. The quantitative analysis indicates that this k-vector spreading is the one expected in photoemission from QW’s of size wCu.

EXPERIMENT

COVERAGE-DEPENDENT STEP SPACING AND

SURFACE STATE CONFINEMENT WITHIN NANOSTRIPES

SURFACE STATE BROADENING IN K-SPACE

SUMMARY