CMDITR Review of Undergraduate Research - Pluto - University of ...

Crystallization. We attempted to crystallize
the sample using two different methods. Our
most common method involved placing the
sample in a cavity formed by two microslides
separated by a 20 micron Mylar film gasket. The
microslides were cleaned thoroughly with soap,
water, and ethanol before being rinsed with high
purity water and dried in a stream of air. The
microslides were then placed in a plasma cleaner
to remove organic contamination and make the
slides hydrophilic. The Mylar films underwent
similar cleaning but without ethanol or plasma
treatment. The Au@SiO 2 spherical colloids were
forced to enter the packing cell via capillary
action, concentrated at all edges of the gasket
through solvent removal, and crystallized into a
long-range ordered lattice under continuous
sonicating. We also attempted to crystallize the
sample by a process developed by Colvin. 2 For
this procedure the sample was redispersed in
ethanol and placed in a vial with a clean vertical
glass substrate where capillary forces selfassemble
the colloids on the substrate.
Analysis
We imaged our samples with a field
emission electron microscope (FEI Sirion) set to
backscattering with an accelerating voltage of
10-15kV. Reflectance spectra were obtained with
an Ocean Optics S2000 fiber optic spectrometer.
Results/Conclusion
Figure 1 shows the SEM micrograph of
gold-silica core-shell colloids with shells of
~40nm thickness. By changing the
concentrations of TEOS, ammonium hydroxide,
water, and gold nanoparticles, and by adjusting
reaction times it was possible to modify the shell
thickness and monodispersity. By using the
glass-cell self-assembly method we were able to
crystallize an Au@SiO 2 sample and obtain the
reflectance spectrum shown in Figure 2. Future
work will involve continued modification of
experimental conditions and procedures to
maximize colloid monodispersity and yield as
well as study of the linear and non-linear
properties of Au@SiO 2 photonic crystals.
References
1. Cao, G. 2004. Nanostructures & Materials –
Synthesis, Properties, & Applications.
Imperial College Press; London. 409-411.
2. Jiang, P., J. F. Bertone, K. S.Hwang, and V.
L. Colvin. 1999. Chem. Mater. 11:2132-
2140.
3. Lu, Y., Y.Yin, Z. Li, Y. Xia, 2002. Nano
Lett. 2:785-788.
4. Wright, J.D. and N. Sommerdijk. 2001. Sol-
Gel Materials Chemistry and Applications.
Philips, D., P. O’Brien, S. Roberts, Eds.
Advanced Chemistry Texts Volume 4.
Gordon and Breach Science Publishers,
Amsterdam. 4:4-5.
5. Ouellette, J. 2001. The Industry Physicist.
December 2001/January 2002, 14.
Figure 1. Scanning electron
microscope (SEM) image of
50nm gold particles coated with
amorphous silica shells of
~40nm in thickness.
Figure 2. Visible reflectance spectrum of a Au@SiO 2
colloidal crystal, self-assembled from particles with an
average diameter of ~170nm (50nm Au cores and ~
65nm-thick SiO 2 shells). Note that one third of the
particles in this sample did not contain gold cores.
CMDITR Review of Undergraduate Research Vol. 1 No. 1 Summer 2004 35