AVS 51st International Symposium
    Applied Surface Science Tuesday Sessions
       Session AS-TuM

Invited Paper AS-TuM3
Extensions of Photoelectron Spectroscopy to the Study of Nanoscale Systems

Tuesday, November 16, 2004, 9:00 am, Room 210A

Session: Electron Spectroscopies
Presenter: R.L. Opila, University of Delaware
Authors: R.L. Opila, University of Delaware
K. Demirkan, University of Delaware
A. Mathew, University of Delaware
Correspondent: Click to Email
Photoelectron spectroscopy (PES) is a very powerful probe of elemental composition and structure at nanometer length scales. PES of core levels can identify which atoms are present, their relative concentrations, and their chemical bonding. PES of the valence levels yields more insight into the chemical bonding. This technique achieves its surface sensitivity from the charge on the photoelectron and its high probability of inelastic collisions. This complication provides both complications and opportunities. First, the photoelectrons are not collected as a linear function of depth, but approximately by an exponentially decreasing function of depth, where the decay length is given by an average of the emission depth distribution function. Collecting the emitted photoelectrons over several angles changes the sampled range of depths. Several algorithms have been proposed that permit the variation in intensity as a function of collection angle to be converted to elemental concentration as a function of depth. We will discuss a maximum entropy algorithm and show its application to study of high-k dielectrics as gate oxides for transistors. The charge on the photoelectrons also samples the local electronic charges that might be present. Through Coulombic interaction with these charges, their kinetic energy is shifted. It is possible to determine the amount of fixed charge present at a chemical interface by determining the relative shift between the photoelectrons emitted from overlayer and those from the substrate. Examples of interfacial charge, including high-k oxide/Si and Al2O3/Al, will be discussed.