AVS 53rd International Symposium
    Surface Science Wednesday Sessions
       Session SS1-WeM

Paper SS1-WeM3
CO Adsorption on a Transition Metal Quantum Well System: fcc Co/Cu(100)*

Wednesday, November 15, 2006, 8:40 am, Room 2002

Session: Reactions on Metal & Bimetallic Surfaces
Presenter: L. Tskipuri, Rutgers University
Authors: L. Tskipuri, Rutgers University
H. Yao, Rutgers University
R.A. Bartynski, Rutgers University
Correspondent: Click to Email
Nanoscale metal thin films can exhibit quantum size effects (QSE) whereby their electronic, structural, magnetic and chemical properties may differ greatly from those of the bulk. The quantum confinement of electrons forms so-called metallic quantum well (MQW) states which give rise to many of these interesting phenomena. In previous studies we found that MQW states the strength of CO boding to Cu MQW overlayers on the pseudomorphic fcc-Co/Cu(100) and fcc-Fe/Cu(100) systems. Here we report on the adsorption properties of the pseudomorphic transition metal layers themselves. These systems have partially filled d-bands may be grown in a metastable structure. We have examined the unoccupied electronic structure and CO bonding strength on the n-ML fccCo/Cu(100) system using inverse photoemission (IPE) and temperature programmed desorption (TPD), respectively. As-grown Co films exhibit well-defined MQW states that disperse upward with increasing film thickness, but are less pronounce than on other similar systems owing to partial overlap of exchange spit states. Upon CO adsorption a well-defined structure centered about 3.8 eV above the Fermi level appears and is assigned to the unoccupied CO 2@pi@* orbital. CO adsorbs molecularly at room temperature and in TPD measurements we find a desorption temperature of approximately 375 K, which is about 30 K lower than what is observed for CO adsorbed on the hcp Co surfaces. When Co films are dosed at low temperatures (~ 120K), we find a second CO desorption peak around 230 K, once again similar to what is seen for hcp Co, but as a markedly lower temperature. We have observed similar desorption peak temperature shifts when CO desorption from the Ni/Cu(100) system is compared to single crystal Ni(100). The CO desorption temperature varies with Co layer thickness and the possible role of quantum size effects on the molecule-surface bond will be discussed. @FootnoteText@ * funded by the Petroleum Research Fund.