Hello everyone, my name is Diego.
I'm going to talk a little bit about my research in inverse opals.
So, just a little bit a quick outline of this
presentation I'm going to give a brief background on the topic of photonic
crystals then we're going to go to objectives and the experimental results
we have obtained, and finally move on to conclusions and future work
So photonic crystals are periodically ordered micro structures. They're built from
dielectric materials and the periodicity of this materials is in the range of the
visible wavelength. So diffraction and interference caused by the
periodic condition of the structure generates a band
gap in the photonic structure, similar to the electronic band gap in
semiconductors and this results in a bright angle dependent coloration of the
material that comes from the structure itself and not from a dye absorber and a
light absorbing molecule like a dye which is the most common kind of coloration.
In nature we can find several examples of structural color
such as the opal gemstone, which is a close packed array of silica spheres
We also have a very beautiful examples in insects such as the Japanese
jewel beetle, that has a multi-layer structure in it's shell which results in
this very bright green color. One of the most common known examples is the
Blue Morpho butterfly which has this Christmas tree like structure in it's
wing scales and that gives this very bright beautiful blue color.
So, the color of these materials or the optical properties of the materials have to do
with some physical parameters of the structure, such as the lattice spacing
the size of the periodic structure, the refractive index contrast
between the two phases, and also the grade of
symmetry and the grade of order that we have in the structure
The objective of this project is to design and assemble composite photonic
crystals in order to study the optical properties and looking on to
how to tune these optical properties. Experimentally we can obtain photonic
crystals in the form of opals by self-assembly of polymer collids in
solution by vertical deposition. We can also obtain the inverse structure the
inverse opal by making this assembly in a solution containing a precursor of
silica, for example, or any other dielectric ceramic and then when we
dry and calcinate it we get rid of the polymer template and we are only left
with our inverse opal structure. So the resulting species, as expected, exhibit
angle dependent coloration which is characteristic of these structures
They have a face centered cubic structure, particularly with the 1 1 1 plane lined
up with the surface of the of the material. The optical properties can be
tuned by changing the polymer-colloid size used for
templating the structure, so here we we work with a range between 240 up to
1000 nanometers, and additionally it was found that when we spotted coat metallic
layer on top of these structures, for example a silver layer,
we see a very important change in the optical properties of the materials
probably because of new effects being induced such as plasmonic resonance in
the metallic layer.
In terms of color tuning, we were able to obtain a change
in coloration, for example this sample is a 240 nano meter inverse opal
sputter-coated with silver, and when we infiltrate this
structure with ethanol we are basically changing the refractive index contrast
between the two phases and that results in a change in coloration from a bright
orange when the structure is infilled with air, to a deep
blue when its infilled with ethanol and we can see that in the
spectra as a drop in the 600 nanometers reflectance.
So, to conclude, we have been able to fabricate these photonic structures
by self-assembly in a vertical deposition method.
The samples, or the structures, present angle dependent coloration characteristic of photonic
structures, and future work will be based around working with smart
materials in order to try to actively tune the photonic structure and the
optical properties of these materials, looking forward to maybe using these
materials for applications such as sensing, and color display devices
Thank you very much. If anyone have any questions...
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