Jahresbericht 2005 - IPHT Jena

into the Ta 2O 5 layers. Unlike for porous layers the
samples of compact material had to be heated
up to 150 °C for optimal results.
An example of a triangular grating in nanoporous
Ta 2O 5 is shown in Fig. E3.
Fig. E3: Triangular grating with a period of
620 nm and an average hole diameter of about
230 nm at the top etched 150 nm into a 600 nm
thick layer of porous Ta 2O 5 imaged at 0° and
60°.
The polarisation independent transmission spectra
for normal incident light for the case of a dry
and wet environment are displayed in Fig. E4.
The pronounced transmission minima at λ >
830 nm are caused by resonant diffraction
effects.
Fig. E4: Spectral shift of the transmission minima
between dry and wet samples (∆λ min = 10.4 and
13.5 nm for the first and second resonance wavelength,
respectively).
By simulating the transmission behaviour with a
rigorous coupled wave method, a sufficient
agreement with the experiment was obtained for
150 nm deep cylindrical holes with a diameter of
210 nm, see Fig. E5.
A change of the refractive index from 1.97 to 2.01
yields ∆λ min = 13 and 15 nm for the first and second
transmission minimum, respectively, and all
wavelengths of the transmission minima differ
from the experimental values by less than 1.5 nm.
INNOVATIONSPROJEKT / INNOVATION PROJECT
Fig. E5: Simulated transmission properties of a
grating with the parameters given in Fig. E3,
assuming cylindrical holes with a diameter of
210 nm.
A variety of different devices which include the
square lattices of holes have been fabricated in
compact and humidity sensitive Ta 2O 5 layers and
are currently under detailed investigation.
The nanoporous tantalum pentoxide samples
were provided by the Fraunhofer IOF in Jena and
investigated here mainly because it could be possible
selectively to measure the moisture content
of other than water vapour analytes.
The filling of the holes of two-dimensional gratings
with metallic nanoparticles provides an
opportunity for the biosensing of e.g. DNA molecules
immobilised on gold nanoparticles. This
method utilises the special plasmon scattering
properties of the ordered arrays.
Chemically activated samples with 2D-gratings
were placed at an angle into preheated (80 °C)
colloidal nanoparticle solutions (30 nm in diameter)
with a concentration of 2 · 10 11 particles/ml.
During the drying process the receding meniscus
causes an influx of the metal nanoparticles into
the holes, see Fig. E6.
Fig. E6: Transmission mode optical micrograph of
a 2D grating in Ta 2O 5 (square array with a period
of 620 nm) when the holes are partially filled with
gold particles.
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