AVS 50th International Symposium
    Surface Science Wednesday Sessions
       Session SS+NS-WeA

Paper SS+NS-WeA8
Quantum Size Effect Induced Modification of CO Chemisorption on Cu/fccFe/Cu(100)

Wednesday, November 5, 2003, 4:20 pm, Room 328

Session: Perspectives and New Opportunities
Presenter: A.G. Danese, Rutgers University
Authors: A.G. Danese, 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 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. We have studied the role of MQW states in the chemisorption of CO on n ML Cu/fccFe/Cu(100) where ~2 < n < ~14 using inverse photoemission (IPE) and temperature programmed desorption (TPD). IPE results show the unoccupied MQW states in the Cu overlayer increasing in energy as a function of increasing Cu thickness with MQW states crossing the Fermi energy (E@sub F@) at 5 ML Cu and 11 ML Cu in both the bare and CO covered system. Accordingly the IPE intensity at E@sub F@ oscillates as a function of Cu well thickness and temperature programmed desorption (TPD) performed on the CO covered Cu films exhibits modulations in the CO peak desorption temperature (T@sub des@) which are correlated with these IPE modulations. The MQW states are quasi 2 dimensional (2-d) and we attribute this chemisorption QSE to the bottom of a 2-d subband that crosses E@sub F@ every time a MQW is observed to cross E@sub F@. This increases the density of states at E@sub F@ available for the CO-Cu bond, thus strengthing the bond as observed by two T@sub des@ maxima at 5 ML Cu and 11 ML Cu. Between these E@sub F@ crossings, the DOS as measured by IPE intensity decreases and we observe that the two quantities oscillate together.