AVS 49th International Symposium
    Surface Science Monday Sessions
       Session SS2-MoM

Paper SS2-MoM2
Variable Temperature Scanning Tunneling Microscopy Studies of a Natural Single Crystal @alpha@-Fe@sub 2@O@sub 3@(0001) Sample: Termination and Surface Chemistry with CCl@sub 4@ and Cl@sub 2@

Monday, November 4, 2002, 8:40 am, Room C-112C

Session: Oxide Structure and Surface Chemistry
Presenter: K.T. Rim, Columbia University
Authors: K.T. Rim, Columbia University
T. Müller, Columbia University
J.P. Fitts, Columbia University
K. Adib, Columbia University
N. Camillone III, Brookhaven National Laboratory
R.M. Osgood, Jr., Brookhaven National Laboratory
S.A. Joyce, Los Alamos National Laboratory
G.W. Flynn, Columbia University
Correspondent: Click to Email
Variable Temperature Scanning Tunneling Microscopy (VT STM) has been used to study the reactivity of the reduced surface of a natural single crystal @alpha@-Fe@sub 2@O@sub 3@(0001) sample. STM and LEED measurements reveal that the surface cleaned in ultrahigh vacuum is reduced and composed of a Fe-terminated Fe@sub 3@O@sub 4@ (111) region and an O-terminated Fe@sub 3@O@sub 4@(111) or biphase region. The Fe-terminated Fe@sub 3@O@sub 4@(111) region exhibits reaction with CCl@sub 4@ and Cl@sub 2@, but the O-terminated Fe@sub 3@O@sub 4@(111) (biphase) region does not undergo reaction. Reaction products (Cl) on the Fe- terminated Fe@sub 3@O@sub 4@(111) region were observed with STM at room temperature after the reduced surface was exposed to CCl@sub 4@ and Cl@sub 2@. Chlorines are found to occupy two distinct sites, Fe top sites and O vacancy sites when the surface is exposed to CCl@sub 4@ vapor. However Cl occupies only the top sites when Cl@sub 2@ is dosed on the surface. The O vacancy sites are created only after surface oxygen atoms are abstracted via reaction with CCl@sub 4@ to produce phosgene. The reduced surface was exposed to CCl@sub 4@ at 238K and the surface temperature changed from 238K to 600K in order to identify reaction products and intermediates (chlorine and dichloro-carbene) and to observe oxygen vacancies following oxygen abstraction from the surface. Related TPD, AES, and XPS results will also be presented to support the VT STM observations.