AVS 51st International Symposium
    Surface Science Friday Sessions
       Session SS2-FrM

Paper SS2-FrM8
Chemisorption and Quantum Size Effects on Pseudomorphic fcc-Co and fcc-Fe Films Grown on Cu(100)

Friday, November 19, 2004, 10:40 am, Room 210C

Session: Bimetallic Surface Chemistry and Structure
Presenter: H. Yao, Rutgers University
Authors: H. Yao, Rutgers University
A.G. Danese, Rutgers University
C.J. Bosco, Seton Hall University
F.G. Curti, Seton Hall University
R. 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 due to high reflectivity scattering at the film's interfaces forms so-called metallic quantum well (MQW) states which give rise to many of these interesting phenomena. In previous studies we have examined the role of MQW states in the chemisorption of CO on Cu MQW overlayers on pseudomorphic fcc-Co and fcc-Fe films grown on Cu(100). In the current work, we report on the adsorption properties of the pseudomorphic transition metal layers themselves. In addition to the fact that the pseudomorphic films represent metastable structures, these systems have partially filled d-bands that change significantly as a function of film thickness. For a Co film with an approximate coverage of 5 monolayers of Co we find that a saturation dosage of CO leads to the formation of a c(2x2) structure as observed in low energy electron diffraction. Inverse photoemission spectra of this system exhibits a two peaked structure centered at 3.8 eV above the Fermi level and is assigned to the unoccupied CO 2@pi@* orbital. CO is found to adsorb molecularly at room temperature and in TPD measurements we find a desorption temperature of approximately 400 K, a temperature in the range previously seen for CO adsorbed on hcp Co surfaces. For saturation doses carried out at lower temperatures we find a second lower temperature desorption peak around 270 K in the desorption spectra. These results, and those from fcc-Fe, are compared to the parent single crystal systems.