Jahresbericht 2005 - IPHT Jena

68
Fig. 3.7: Alignment of DNA structures (G wires)
following the atomic arrangement in mica crystal
planes. (Top) Overview AFM image (left) with histogram
of orientation of G wire segments (right),
(bottom) orientation of G wires as compared to
the crystal arrangement of the underlying mica
(insets) on air (left) and in buffer (right).
Metal nanoparticles for molecular plasmonics
(A. Steinbrück, A. Csaki, W. Fritzsche)
Utilizing the optical properties of metal nanoparticles
in combination with molecular complexes
represents a promising recent development in
molecular nanotechnology with envisioned applications
especially for bioanalytics but also in
nanophotonic devices. This field is based on the
surface plasmon resonance effect in the particles.
In order to realize complex systems the optical
properties of the nanostructures have to be
tuned and approaches to synthesize designer
Fig. 3.8.: Synthesis of gold-silver core-shell nanoparticles
yields designer particles with adjustable
surface plasmon resonance peak between the
bands of pure gold and pure silver nanoparticles.
The particles were formed using specific silver
deposition onto gold particles using various silver
salt concentrations. All spectra are ensemble
measurements.
MIKROSYSTEME / MICROSYSTEMS
particles with defined optical features are
required. Therefore, core-shell particles consisting
of Ag/Au or Au/Ag were identified as especially
promising systems to tune the resulting plasmon
resonance (see figure 3D on the color
page).
Moreover, optical characterization at both ensemble
and single particle level are needed. The last
year witnessed the set-up of a spectroscopy system
with single particle capabilities in the department
(see figure 3E on the color page). Experiments
demonstrated the ability to yield UV-VIS
spectra of individual nanoparticles, together with
AFM and optical images of this structure.
Photonic nanostructures combined
with metal nanoparticles
(A. Csaki, A. Steinbrück, S. Schröter,
W. Fritzsche)
Photonic nanostructures, such as nanoaperture
arrays, show promising novel effects regarding
e.g. transmission of light. The established experience
with nanoparticle handling and ultramicroscopic
characterization was applied in order to
position metal nanoparticles in nanoapertures.
Comparison of the transmission characteristics
of the apertures with and without particles
showed a higher transmission in the case of particle-modified
openings. This effect seemed even
enhanced when the particle where enlarged
using specific metal deposition.
Fig. 3.9: Light transmission of microfabricated
holes with sub-wavelength dimensions in a
chromium layer in dependence on the presence
of metal nanoparticles. AFM images (top) and
optical images (bottom) of three holes without
particle (left), with an individual particle (center),
and with a particle aggregate (right).