Dissertation/Thesis Abstract

Robust, physisorbed self -assembled monolayers on graphite and their applications in nanoscience
by Wei, Xiaoliang, Ph.D., Brown University, 2010, 277; 3430226
Abstract (Summary)

This dissertation work focuses on preparations and applications of robust, physisorbed SAMs on HOPG. The molecules contain an anthracene derivative core and two - CH2OC6H12OC22H 45 side chains. Robustness of the SAMs is examined through solvent rinse experiments. Cold tetradecane (6°C), EtOH and pentane afford “normal” SAMs, and are used to expose the SAMs.

Two applications of robust SAMs are investigated. The first is templated AuNP capture and patterning. Acquisition of patterned AuNPs depends on strong SAM-HOPG and SAM-AuNP interactions. Three strategies adopting different SAM-AuNP interactions are explored: (i) direct place-exchange on DMAP-AuNPs using carboxylic acid SAMs; (ii) Cu2+ ion bridges using carboxylic acid-functionalized AuNPs and SAMs; and (iii) Grubbs coupling between norbornene-functionalized AuNPs and SAMs. Factors affecting AuNP capture and patterning are investigated, including AuNP concentration, incubation time, surface density of gold-binding functional groups in SAMs, and/or number of SAM-binding functional groups on AuNPs. The Cu2+ bridge strategy offers the best control over AuNP capture and patterning. However, AuNP surface aggregates are commonly observed in all three strategies, indicating the controls are limited.

Surface polymerization adds inter-molecular covalent bonds within pre-formed SAMs, affording higher SAMs' physisorptions to HOPG. The SAM Molecules containing two isothiocyanates are cross-linked through reactions with 1,4-diaminobutane. The surface reaction products are characterized by MALDI-TOF MS. Optimization of reaction conditions using n-butylamine establishes 20mM diamine and 2 hours are suitable for surface polymerization. The surface polymerization produces the monomer, dimer and trimer of the diisothiocyanate. The time dependence of surface polymerization is measured.

Molecular conformer rectifiers (MCRs) form robust SAMs on HOPG. Rectification that originates from bias-induced molecular conformational changes are investigated using STM and STS. STM imaging indicates that introduction of a “chemical marker” such as S may be crucial to measure the rectification in mixed SAMs. STS studies provide encouraging results, showing remarkable asymmetry in i-V curves. However, the i-V curves are not constant due to thermal drift.

Indexing (document details)
Advisor: Zimmt, Matthew B.
School: Brown University
School Location: United States -- Rhode Island
Source: DAI-B 71/11, Dissertation Abstracts International
Subjects: Inorganic chemistry, Organic chemistry, Physical chemistry
Keywords: Gold nanoparticles, Graphite, Molecular diodes, Self-assembled monolayers, Surface polymerization
Publication Number: 3430226
ISBN: 978-1-124-30157-0
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