Tuning of 1D Plasmon properties in Au-induced quantum wires on Si(hhk) surfaces

Gold-induced atomic wires on Si(hhk) surfaces possess intriguing properties of collective electron excitations, which are strongly responsive to the electronic state and also to structural motifs. The modification and control of plasmonic excitations in metallic nanowires are of particular interest due to their fundamental and technological importance. In this work, the effect of O₂ and H₂ adsorption on the plasmons in arrays of single [Si(557)-Au] and double chains of gold [Si(553)-Au] have been experimentally examined by an EELS with high resolution both in energy and momentum. Theoretical results show that oxygen and hydrogen atoms bind preferably not to the Au chains directly, but to adjacent Si-honeycomb chains (Si-HC) and Si-adatom rows (The latter exist only in Si(557)-Au). The Si-HC turns out to be mostly responsible for the plasmonic changes. While atomic H reduces the plasmon frequency on Si(553)-Au, as predicted theoretically, adsorbed oxygen leaves it unchanged. On the Si(557)-Au, however, a frequency increase is found to be induced by oxygen, indicating a change in band structure. Comparing the oxygen adsorption on Si(553)-Au and Si(557)-Au, both the structural motifs, as well as electronic distributions across the terraces play a role in plasmonic excitations.