AVS 52nd International Symposium
    Surface Science Monday Sessions
       Session SS-MoP

Paper SS-MoP8
Electrochemical Formation of a Semiconducting Metal Oxide observed by In Situ Tunneling Spectroscopy

Monday, October 31, 2005, 5:00 pm, Room Exhibit Hall C&D

Session: Surface Science Poster Session
Presenter: I. Diez-Perez, University of Barcelona, Spain
Authors: I. Diez-Perez, University of Barcelona, Spain
A. Guell, University of Barcelona, Spain
P. Gorostiza, University of California, Berkeley
F. Sanz, University of Barcelona, Spain
Correspondent: Click to Email
Obtaining tunneling spectroscopic data in electrolytic solutions is fundamental to understand electrode reactivity.Electrochemical scanning tunneling spectroscopy(ECTS) represents a powerful method for the in situ elucidation of the electronic structure on solid-electrolyte interfaces.Its experimental realization has been reported only in a few instances with some limitations.@footnote 1@ We present tunneling spectra of an Fe electrode immersed in a borate buffer electrolyte while it is reversibly oxidized to different potentials within the three oxidation ranges:Fe(0),Fe(II) and Fe(III).@footnote 2@ Complete series of ECTSpectra within the entire Fe passivation range allow us the representation of oxide surface conductograms by plotting the e- energy level on the Y-axis(tip potential),the electrode oxidation state on the X-axis(sample potential) and surface conductance represented by the Z gray scale.Our spectra span up to 2.2V using high tip potential scan rates(up to 15V/s).We have developed a new method to prepare and isolate Pt/Ir tips specially for in situ STS applications.@footnote 3@ Under conditions where the passive film is chemically stable in the working buffer,we found that the different redox transitions at the iron surface result from the availability of free charge carriers controlled by electron energy barriers at the oxide/solution interface.The passivity of iron results from the build-up of an energy barrier in n-Fe(III) and the absence of states available for charge exchange within almost 1.5eV below the CB edge.Increasing the sample potential in the passive plateau results mostly in increasing the band bending inside the oxide and decreasing the electron concentration. @FootnoteText@ @footnote 1@E.Tomita,N.Matsuda,K.Itaya,J.Vac.Sci.Technol.,A8(1)534(1990).@footnote 2@I.Diez-Perez,P.Gorostiza,F.Sanz.J.Electrochem.Soc.,150:B348(2003).@footnote 3@A.G.Guell,I.Diez-Perez,P.Gorostiza,F.Sanz, Anal Chem.,76,5218.(2004).