1. Molecular Adsorption on Metallic Nanostructures:
Tailoring Chemisorption by Quantum Confinement of Electrons
Robert A. Bartynski, Department of Physics & Astronomy and Lab. for Surface Modification, Rutgers University
The objective of this research is to determine what aspects of molecular chemisorption are influenced by quantum sized effects in ultrathin metal films. Here we use CO/Cu/fccFe/Cu(100) as a model MQW system. Inverse photoemission spectra show metallic quantum well states crossing Fermi level near a Cu overlayer thickness of 5 ML. IR spectra of the CO stretch vibration shows that the absorption from CO bound to step edges is enhanced at thicknesses where MQW state crosses Fermi level.
CO on terraces
CO at steps
2+ ML Cu/Fe/Cu(100)
5+ ML Cu/Fe/Cu(100) 4 3 2 1
Energy above E F
(eV)
2.5 ML
19ML q Cu
10 ML
Cu/fccFe/Cu(100)
0.5 L CO
Cu thickness
This effect could be associated with an increase in step density for Cu overlayer thicknesses near 5 ML. However STM images show that, if anything, the step density has decreased. We believe that CO-CO coupling is modulated as MQW states cross the Fermi level.