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Functionalization of Si(111) Surfaces and the Formation of Mixed Monolayers for the Covalent Attachment of Molecular Catalysts in Photoelectrochemical Devices


Lattimer, Judith Rebecca Cabelli (2014) Functionalization of Si(111) Surfaces and the Formation of Mixed Monolayers for the Covalent Attachment of Molecular Catalysts in Photoelectrochemical Devices. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/5EJQ-5134.


The functionalization of silicon surfaces with molecular catalysts for proton reduction is an important part of the development of a solar-powered, water-splitting device for solar fuel formation. The covalent attachment of these catalysts to silicon without damaging the underlying electronic properties of silicon that make it a good photocathode has proven difficult. We report the formation of mixed monolayer-functionalized surfaces that incor- porate both methyl and vinylferrocenyl or vinylbipyridyl (vbpy) moieties. The silicon was functionalized using reaction conditions analogous to those of hydrosilylation, but instead of a H-terminated Si surface, a chlorine-terminated Si precursor surface was used to produce the linked vinyl-modified functional group. The functionalized surfaces were characterized by time-resolved photoconductivity decay, X-ray photoelectron spectroscopy (XPS), electro- chemical, and photoelectrochemical measurements. The functionalized Si surfaces were well passivated, exhibited high surface coverage and few remaining reactive Si atop sites, had a very low surface recombination velocity, and displayed little initial surface oxidation. The surfaces were stable toward atmospheric and electrochemical oxidation. The surface coverage of ferrocene or bipyridine was controllably varied from 0 up to 30% of a monolayer without loss of the underlying electronic properties of the silicon. Interfacial charge transfer to the attached ferrocene group was relatively rapid, and a photovoltage of 0.4 V was generated upon illumination of functionalized n-type silicon surfaces in CH3CN. The immobilized bipyridine ligands bound transition metal ions, and thus enabled the assembly of metal complexes on the silicon surface. XPS studies demonstrated that [Cp∗Rh(vbpy)Cl]Cl, [Cp∗Ir(vbpy)Cl]Cl, and Ru(acac)2vbpy were assembled on the surface. For the surface prepared with iridium, x-ray absorption spectroscopy at the Ir LIII edge showed an edge energy and post-edge features virtually identical to a powder sample of [Cp∗Ir(bipy)Cl]Cl (bipy is 2,2 ́-bipyridyl). Electrochemical studies on these surfaces confirmed that the assembled complexes were electrochemically active.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:silicon, surfaces, functionalization, hydrosilylation, ferrocene, passivation
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Gray, Harry B.
Thesis Committee:
  • Okumura, Mitchio (chair)
  • Gray, Harry B.
  • Lewis, Nathan Saul
  • Agapie, Theodor
  • Brunschwig, Bruce S.
Defense Date:21 April 2014
Non-Caltech Author Email:jlattimer (AT)
Funding AgencyGrant Number
National Science FoundationCHE-1305124
Record Number:CaltechTHESIS:05022014-101347718
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8209
Deposited By: Judith Lattimer
Deposited On:03 Jun 2014 19:30
Last Modified:24 Oct 2020 00:12

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