AVS 62nd International Symposium & Exhibition
    Nanometer-scale Science and Technology Tuesday Sessions
       Session NS-TuP

Paper NS-TuP2
Understanding the “Click Chemistry” Approach to Achieve High-Coverage, High-Precision Nanostructures Deposited on Solid Surfaces

Tuesday, October 20, 2015, 6:30 pm, Room Hall 3

Session: Nanometer-scale Science and Technology Poster Session
Presenter: Mackenzie G. Williams, University of Delaware
Authors: M.G. Williams, University of Delaware
A.V. Teplyakov, University of Delaware
Correspondent: Click to Email
The use of layered nanostructures as a platform for surface reactions requires the ability to maintain precise control over the architectural structure and surface chemistry. The use of a copper(I)-catalyzed cycloaddition between azide and alkyne moieties to build such structures has been amply reported. This “click reaction” allows selective covalent attachment but the development of a layered structure in which each layer consists of a single layer with a coverage close to 100% has yet to be reported. In the present work, gold substrates were functionalized with terminal azide groups and silica nanoparticles of different sizes were functionalized with either alkyne or azide groups. This approach allows for a simple verification of a full monolayer deposition via microscopy. In a sonication-assisted “click reaction”, a monolayer of the alkyne-terminated nanoparticles was attached to the substrate. The formation of the monolayer was confirmed by scanning electron microscopy (SEM) and the calculated surface coverage, close to 95% compared to the absolute maximum, was much higher than those reported in literature for similar systems. Atomic force microscopy (AFM) was used to verify that a single layer of nanoparticles was produced instead of a well-ordered stack of multiple layers. A focused ion beam (FIB) was used to cut into the sample and confirm the nanoparticle layer height by SEM. Subsequent “click reactions” with alternating alkyne- and azide-modified silica particles formed high-coverage multilayer structures. In a separate set of experiments, iron oxide nanoparticles were modified with alkyne groups and were “clicked” onto a gold substrate. The chemical attachment was followed by attenuated total reflectance infrared (ATR IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) and compared to predicted spectra obtained through density functional theory (DFT) calculations to confirm completion of the “click reaction”. The improved control and surface coverage over previously-reported systems is thought to result in part from the sonication-assisted attachment, in contrast to typical procedures that include stirring or dip-coating to promote attachment. The mechanism of attachment, specifically the catalyst intermediate, is also thought to play a role in the nanoparticle attachment density. DFT investigations into the stability of the intermediate were used to determine how the functionalization scheme of the starting materials may affect surface coverage. This work outlines modifications to a commonly-practiced attachment procedure that provide unparalleled surface coverage and control over individual layers of the nanostructures produced.