Functionalized Surfaces
Members: Jun-Hyun Kim, Owen Compton, Ehow Chen
Silicon Surface Chemistry
For the first time, the formation of well-defined, coherent organic monolayers on hydrogen-passivated Si(111) surfaces
via UV (ultraviolet, 254 nm wavelength) treatment was demonstrated for several styrenyl derivatives having different
conjugation lengths. These organic monolayers possess terminal Br functionalities that can be further functionalized with
other types of molecules (e.g., biological entities). In addition, they have conjugated carbon chains connecting directly to
Si(111) surface via Si-C bond that can facilitate electron transfer to the underlying semiconducting substrate. Such
functionally well-defined covalently attached organic monolayers on Si(111) surfaces are highly attractive as a platform for
deploying electronic applications or for interfacing with biologically important molecules. This work is in collaboration
with the Hersam Group.
less ordered
‘partially’
conjugated
conjugated
Si(111)
H H H H H
Si(111)
UV
more ordered
semi-conductor
‘fully’
conjugated
conjugated
Si(111)
Scheme 1. ’Partially’ and ‘fully’ conjugated monolayers on semiconducting silicon surface
Polymer-Inorganic Nanocomposites
We developed reliable methods for the preparation of discrete nanomaterials composed of functional norbornenebased polymer shells with various inorganic (SiO2, gold, and/or Fe2O3) cores.
These nanocomposites are composed of external stimuli responsive polymer layers on inorganic cores and can serve as
environmental responsive materials for coatings, electrical, optical, and biological carriers
Scheme 2: SEM images of the changes in morphology of polymer-coated SiO2 particles as a function of pH
Graphene Sheets and Nanocomposites
Graphene sheets, the basic structural units of graphite and carbon nanotubes, are predicted to posess outstanding
mechanical, electrical and thermal properties. It is for this reason that they have been targeted for many potential
applications. While individual single-walled carbon nanotubes represent a source of graphene sheets, they are still
comparatively expensive for large scale applications. On the other hand, the inexpensive and abundant material graphite can
serve as a starting material for large scale production of graphene sheets, provided it can be completely exfoliated.
In our approach, graphite oxide, an oxidation product of graphite, is used as a source of graphene sheets. Current research
focuses on the synthesis of graphene sheets by solution-phase exfoliation of graphite oxide, and their chemical
derivatization to both achieve their comatibilization with various organic and inorganic matrices, and to fine-tune their
properties, for preparation of novel composite materials.
Scheme 3: Graphene/Polymer Nanocomposites
Modeling Environmental Interfaces
Geochemical and biologically relevant models can be simulated by functionalizing glucose on silica surfaces. For example,
the transport of metals may be hindered by the cellulose content of soil. This glucose-functionalized system may also be
used to model glycoproteins and imitate binding events in biological systems. Click chemistry is specific, high yielding,
and has no side products. These characteristics are advantageous for surface chemistry, which requires high-yielding
processes for effective surface coverage and analysis. Nonlinear optical processes play a significant role in studying the
functionalized interface. For example, broadband vibrational sum frequency generation (SFG) spectroscopy is used to study
the presence of organic functional groups at the air-solid interface. Additionally, second harmonic generation (SHG) is used
to track pollutant binding (such as nitrates and heavy metals) at the liquid-solid interface. This work is in collaboration with
the Gieger Group.
Scheme 4: 1,3-dipolar cycloaddition of azide attached to the anomeric carbon of D-glucose with an acetylenefunctionalized silica surface. The “wavy bond” indicates the possibility of a carbon chain beyond a single covalent bond.