Scanning tunneling microscopy studies of organometallic molecules on Au(111): Mixed valence states and quasicrystalline ordering

Doctoral Dissertation
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Abstract

Scanning tunneling microscopy (STM) is used to study large, organometallic complexes with multiple metal centers. These complexes are capable of forming stable mixed-valence (MV) states and are typically characterized using ensemble measurements according to the Robin-Day classification. Neutral and MV molecules are studied with the STM after pulse deposition onto an Au(111) substrate in ultra-high-vacuum and low-temperature conditions. Pulse deposition of molecules on a substrate removes bulk solvent and the charge-transfer properties of the molecules of interest can be studied. The STM tip is a sensitive probe for the visualization of the electronic properties of both neutral and MV molecules. Generally, neutral molecules show a symmetric electronic charge distribution whereas MV molecules show an asymmetric charge distribution in STM images. Factors such as geometry of the metal centers and molecule-surface interactions also play a role in charge transfer capabilities within a molecule. Electronic structure calculations from density functional theory (DFT) and constrained density functional theory (CDFT) are also used to study MV characteristics of molecules.

STM was also used to study self-assembly of carboxylic acid monolayers. In most cases, the formation of two strong hydrogen bonds results in dimer formation; in some others, linear catemer chains are formed. Observation of a five-membered catemer ring, stabilized by additional CH$cdots$O interactions available in the cyclic structure is reported. The existence of CH$cdots$O hydrogen bonding is confirmed with DFT calculations and by observing the disappearance of pentamers when molecules without suitable CH donors are used. Long range assembly of pentamers results in a two-dimensional quasicrystalline lattice, the first observation of such structure from small-molecule self assembly.

Attributes

Attribute NameValues
URN
  • etd-04102014-131405

Author Natalie Anna Wasio
Advisor S. Alex Kandel
Contributor S. Alex Kandel, Committee Chair
Contributor Zachary Scultz, Committee Member
Contributor Franklin Tao, Committee Member
Contributor Steven Corcelli, Committee Member
Degree Level Doctoral Dissertation
Degree Discipline Chemistry and Biochemistry
Degree Name PhD
Defense Date
  • 2014-04-04

Submission Date 2014-04-10
Country
  • United States of America

Subject
  • organometallic

  • STM

  • mixed valence

  • oxidation

Publisher
  • University of Notre Dame

Language
  • English

Record Visibility and Access Public
Content License
  • All rights reserved

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