AVS 59th Annual International Symposium and Exhibition
    Applied Surface Science Thursday Sessions
       Session AS-ThA

Paper AS-ThA6
Non-Destructive Depth Profiling using VKE-XPS and Maximum Entropy Regularization

Thursday, November 1, 2012, 3:40 pm, Room 20

Session: Applications of Large Cluster Ion Beams - Part 2 (2:00-3:20 pm)/ Surface Analysis using Synchrotron Techniques (3:40-5:40 pm)
Presenter: C. Weiland, National Institute of Standards and Technology
Authors: C. Weiland, National Institute of Standards and Technology
J.C. Woicik, National Institute of Standards and Technology
Correspondent: Click to Email
X-ray photoelectron spectroscopy (XPS) is an excellent tool for semi-quantitative analysis of the chemical structure of solid material systems. However, the in-depth distribution of elements in a solid is known to affect the intensity of the measured photoelectron peaks and can thus lead to errors in quantification. The depth distribution itself can be interesting for deposited thin-film systems and buried interfaces. Typically, depth dependent measurements are made by sputtering layers of the material off the surface, but complications can arise due to knock-on effects, differential sputtering rates and implantation of the sputtering ions. Angle-resolved XPS (ARXPS) coupled with maximum entropy regularization can provide non-destructive depth sensitive information, but analysis is typically performed using a lab-based X-ray source, limiting the ultimate probe depth to tens of Angstroms. Here, we adapt the maximum entropy analysis method used for ARXPS to variable kinetic energy XPS (VKE-XPS) using hard X-rays. Using VKE-XPS with beam energies ranging between 2.1 and 6 keV, we can vary the photoelectron inelastic mean free path to adjust the effective analysis depth to technologically relevant thicknesses. Conversion from intensity vs. beam energy to depth profile can be accomplished using a regularization routine. Development of the routines will be discussed, followed by results of VKE-XPS analysis of plasma-enhanced chemical vapor deposited TiO2 films on Si performed at NIST beamline X24A at the National Synchrotron Light Source.