AVS 52nd International Symposium
    Applied Surface Science Thursday Sessions
       Session AS+TF-ThA

Paper AS+TF-ThA6
Scanning Auger Microscopy of Alkylated Crystalline Silicon(111) Surfaces

Thursday, November 3, 2005, 3:40 pm, Room 206

Session: Thin Film Characterization II
Presenter: H.M. Meyer III, Oak Ridge National Laboratory
Authors: H.M. Meyer III, Oak Ridge National Laboratory
L.J. Webb, California Institute of Technology
D.F. Paul, Physical Electronics
N.S. Lewis, California Institute of Technology
Correspondent: Click to Email
Silicon materials used in solar energy conversion devices must be prepared to a high degree of purity in order to prevent recombination of the photoexcited electron-hole pair. Recently, a wet chemical alkylation technique has been shown to result in an atomically-flat surface covered with bound alkyl groups preventing complete formation of silicon oxides at the surface even after exposure to oxidizing environments over long time periods. Surface charge carrier recombination velocities remain remarkably low, indicating that silicon oxides forming do not result in charge carrier trap states as previously observed on un-passivated, hydrogen-terminated Si(111). These results indicate that any detectible oxide is not growing in a uniform manner, but rather in small patches leaving large portions of the alkylated surface free of any oxide. Extensive x-ray photoelectron spectroscopic evidence on the chemical structure and reactions of these passivated surfaces has been collected over large areas of the surface. Scanning Auger microanalysis was used to map the oxidation of alkylated Si surfaces to determine if it was proceeding uniformly or in discrete areas. Preliminary results using a PHI 680 Scanning Auger Nanoprobe showed distinct patches of oxide less than 100 nm in width. The orientation of the oxide patches suggested that growth was occurring along step edges between flat terraces, leaving the terraces themselves chemically unaltered. Comparison of these early results were made with data obtained using PHI 700 Field Emission Scanning Auger Nanoprobe, a higher performance Auger Electron Spectroscopy (AES) system. The PHI 700 Schottky field emission optics offer Auger spatial resolution of less than 8nm and made it possible to image the oxide features more clearly. Further, the PHI 700 was able to image areas with comparable resolution as the PHI 680, but with less current and therefore less alteration of the oxide due to electron beam reduction.