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Measurement of the Band Bending and Surface Dipole at Chemically Functionalized Si(111)/Vacuum Interfaces


Gleason-Rohrer, David Charles (2014) Measurement of the Band Bending and Surface Dipole at Chemically Functionalized Si(111)/Vacuum Interfaces. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/PD7F-P488.


The core-level energy shifts observed using X-ray photoelectron spectroscopy (XPS) have been used to determine the band bending at Si(111) surfaces terminated with Si-Br, Si-H, and Si-CH3 groups, respectively. The surface termination influenced the band bending, with the Si 2p3/2 binding energy affected more by the surface chemistry than by the dopant type. The highest binding energies were measured on Si(111)-Br (whose Fermi level was positioned near the conduction band at the surface), followed by Si(111)-H, followed by Si(111)-CH3 (whose Fermi level was positioned near mid-gap at the surface). Si(111)-CH3 surfaces exposed to Br2(g) yielded the lowest binding energies, with the Fermi level positioned between mid-gap and the valence band. The Fermi level position of Br2(g)-exposed Si(111)-CH3 was consistent with the presence of negatively charged bromine-containing ions on such surfaces. The binding energies of all of the species detected on the surface (C, O, Br) shifted with the band bending, illustrating the importance of isolating the effects of band bending when measuring chemical shifts on semiconductor surfaces. The influence of band bending was confirmed by surface photovoltage (SPV) measurements, which showed that the core levels shifted toward their flat-band values upon illumination. Where applicable, the contribution from the X-ray source to the SPV was isolated and quantified. Work functions were measured by ultraviolet photoelectron spectroscopy (UPS), allowing for calculation of the sign and magnitude of the surface dipole in such systems. The values of the surface dipoles were in good agreement with previous measurements as well as with electronegativity considerations. The binding energies of the adventitious carbon signals were affected by band bending as well as by the surface dipole. A model of band bending in which charged surface states are located exterior to the surface dipole is consistent with the XPS and UPS behavior of the chemically functionalized Si(111) surfaces investigated herein.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Fermi level, Work function, Surface states, XPS, UPS
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Lewis, Nathan Saul
Thesis Committee:
  • Gray, Harry B. (chair)
  • Brunschwig, Bruce S.
  • Barton, Jacqueline K.
  • Goddard, William A., III
  • Lewis, Nathan Saul
Defense Date:30 September 2013
Non-Caltech Author Email:gleason.rohrer (AT)
Record Number:CaltechTHESIS:11202013-144350295
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for ch. 2
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8032
Deposited By: David Gleason-Rohrer
Deposited On:14 Jan 2014 17:37
Last Modified:04 Oct 2019 00:03

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