Electron Microscopy of Self-Assembled Superparamagnetic Plasmon Resonant Colloidal Nanostructures
Klupp Taylor R (2002)
Publication Type: Conference contribution, Conference Contribution
Publication year: 2002
Conference Proceedings Title: Proceedings of the 15th International Congress on Electron Microscopy
Event location: Durban
ISBN: 0620292946
Abstract
The development of techniques to form identical nanostructures in solution is of great
importance to many applications. In recent years there has been a departure from the
most simple of requirements – to produce identical pure nanoparticles. It is clear that
such pure particles, whilst often displaying interesting and potentially useful properties
have other drawbacks such as chemical and colloidal instability or undesirable surface
properties. It is therefore becoming increasingly common to engineer such pure particles
into identical nanostuctures, which retain or enhance the favourable properties whilst
passivating against the unfavourable. As the toolkit of possible particle engineering
strategies becomes more elaborate, it is clear that multi-functional structures also
become possible. This means the combination of properties which would traditionally be
mutually exclusive in pure materials or composites using traditional formation
techniques, e.g. ceramic processing.
This work aims to combine two classes of quite strongly functional nanoparticulate
materials, namely those with magnetic and plasmon resonant properties. It is well known
that below a certain size particles of ferro- or ferrimagnetic material can only support a
single magnetic domain and that for very small particles thermally-activated rotation of
the magnetisation gives rise to superparamagnetic behaviour at ambient conditions. A
simple method for the formation of such small particles comprising of iron oxide
(magnetite or maghemite) has been known for some time [1] . A controlled agglomeration
of these nanoparticles onto larger monodisperse cores would retain the
superparamagnetic behaviour whilst increasing the effective dipole per particle. Gold
sols have long been known for their deep colours which are due to a collective optical
frequency oscillation of conduction electrons. Furthermore, it has recently been
confirmed that the formation of a thin gold shell around a dielectric core results in a
similar resonance but with a far greater tunability, namely in the core diameter to shell
thickness ratio [2]. The formation of nanostructures combining these components would
allow for the magnetic modulation of optical properties and also provide individual
building blocks for subsequent magnetic directed self-assembly of nanochains. These
nanochains are expected to behave like tiny transmission lines, with particles connected
through the near-field of their shell plasmon resonances.
We have made use of a JEOL 4000EX transmission electron microscope to evaluate the various stages of nanostructure fabrication. The growth of superparamagnetic plasmon resonant nanostructures followed the general scheme:
(i) Monodisperse 250nm silica spheres were produced by the well-known Stoeber process [3].
(ii) Iron oxide (maghemite) nanocrystals with an approximate size of 8nm were attached to the cores by the layer-by-layer (LbL) process [4].
(iii) A barrier layer of silica was then grown by a modified Stoeber process.
(iv) A gold shell was finally grown around the structures using a successive gold colloid attachment gold reduction process
This manufacturing process therefore is an example of how three distinct strategies
(LbL, sol-gel and seeded growth) can be utilised on the same nanoscale workpiece.
Figure 1(b) shows the result of magnetic directed assembly of the particles in
Fig.1(a)(iv).
Electron microscopy was essential to the optimisation of the silica barrier layer and to
monitor attachment of the seed gold colloid. In the former case, a thin or broken silica
layer would adversely effect the attachment of seed colloid whereas a thick layer would
effectively shield the interparticle magnetic interaction which could ultimately be useful
when performing magnetic directed assembly. Microscopy was also utilised to estimate
the decrease in surface roughness as the silica thickness.
In this contribution we will present recent work on the self-assembly of multi-functional
colloidal nanostructures, making note particularly of the microscopical features of our
analysis.
References
1. Massart, R. (1981) IEEE Trans. Magn. (1981) 17, 1247.
2. Oldenburg S.J. et al. (1998) Chem. Phys. Lett. 288, 243.
3. Stober, W., Fink, A., Bohn, E. (1968) J. Colloid Interface Sci., 26, 62.
4. Caruso F. et al. (1999) Adv. Mater. 11(11), 950.
Authors with CRIS profile
How to cite
APA:
Klupp Taylor, R. (2002). Electron Microscopy of Self-Assembled Superparamagnetic Plasmon Resonant Colloidal Nanostructures. In Proceedings of the 15th International Congress on Electron Microscopy. Durban, ZA.
MLA:
Klupp Taylor, Robin. "Electron Microscopy of Self-Assembled Superparamagnetic Plasmon Resonant Colloidal Nanostructures." Proceedings of the 15th International Congress on Electron Microscopy, Durban 2002.
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