(524b) Layer-by-Layer Silica Reactive Assembly On Nanoscale Chemical Templates

Layer-by-Layer Silica
Reactive Assembly on Nanoscale Chemical Templates

Juan Pablo Hinestrosa^*
& Scott Retterer^*,µ

^*Center for Nanophase
Material Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37834

^µBiosciences Division, Oak
Ridge National Laboratory, Oak Ridge, TN 37834

Reactive
assembly of silica onto nano- and micro-scale organic templates was achieved using
a combination of chemical lift-off and solution chemistry performed under mild
conditions of pH and temperature. Well-defined gratings, honeycomb-lattices,
and dot arrays were created by electron beam lithography and used as templates
for the generation of silica nanostructures. Initially, an amine-silane
monolayer was vapor deposited onto the patterned substrates.  They were
subsequently reacted with silicic acid solutions made in buffers of varying pH
and salt content at room temperature. The process of vapor treatment followed
by the reactive assembly of silica in solution could be repeated multiple times
to perform layer-by-layer deposition while keeping the nanoscale organic
templates intact, as seen in the Figure.  It was observed that the conditions
for the silicic acid deposition, namely pH, salts and solution age, had a
strong effect on thickness of each layer and the morphology of the amorphous
silica formed.

Following
silica reactive assembly, the templates can be easily removed by sonication in
acetone leaving only the silica nanostructures on the substrates. ?Defects' in
the arrays of silica nanostructures were relatively minor (~ 10% after three
depositions) and do not affect the overall organization of the layers.  These
defects were attributed to difficulties associated with completely removing the
PMMA mask from underneath the deposited silica.  The number of defects
increased with the addition of each silica layer. The biomimetic method described
here allows for the generation of well-defined, complex nanostructures starting
from small molecules under mild conditions; thus, we believe it provides a
robust platform for high-throughput reactive assembly process and growth of
organic-inorganic hybrid nanostructures.

Figure. SEM images of silica gratings, honeycomb
lattices and dot arrays after reactive assembly from silicic acid solution.