Engineers want to move from top-down methods of building optical circuits today to a bottom-up approach that would enable a new era of molecular-sized optical circuits, including Harry Potter-like invisibility cloaks.
Engineers want to move from today's top-down methods of
building optical circuits to a bottom-up approach that would enable a new era
of molecular-sized optical circuits including Harry Potter-like invisibility
cloaks.
Applied physicists are creating the building blocks for a
new class of optical circuits inspired by nature and enabling customizable
optical properties at the nanoscale, such as sensors that can identify
individual molecules and invisibility cloaks that divert visible light around
objects.
Today, optical circuitry for communications, sensors and the
"metamaterials" that enable
invisibility cloaks (at radar and infrared frequencies) are fashioned using a
top-down methodology. This method starts with a bulk material and then sculpts
out the needed structures using masking and etching. Now researchers are
experimenting with a bottom-up approach that starts with individual molecules
and then uses self-assembly techniques inspired by nature to fabricate
molecular-scale patterns impossible to achieve from the top down.
The researchers at Harvard University include doctoral
candidate Jonathan Fan working under Harvard physics professors Federico
Capasso and Vinothan Manoharan in collaboration with scientists at Rice
University, the University of Texas at Austin and the University of Houston.
These scientists have taken the first steps toward these tiny optical circuits
by precipitating clusters of nanospheres out of liquid compounds, which exhibit
the customizable properties needed for advanced optical applications.
Materials that operate at optical frequencies, such as
cloaks that divert visible light around objects, have been difficult to
construct using traditional top-down methods. This difficulty arises because
the patterns necessary to divert visible light must be cast at nanoscale sizes
smaller than the wavelength of light being cloaked. Traditional lithographic
techniques cannot reach these resolutions even using the most expensive
fabrication equipment and cleanrooms.
The researchers' technique sidesteps these traditional
constraints by harnessing methods whereby nanoscale structures self-assemble
out of liquid solutions. To form the tiny structures, the researchers coated
tiny particles with polymers, then disolved them in solutions that were placed
on a water-repellent surface. During the evaporation process, the particles
packed together into clusters of the desired shape and size. Using polymer
spacers between these nanoparticles, the researchers were able to demonstrate
repeatable patterns with resolutions as fine as 2 nanometers, a scale
unachievable with traditional top-down approaches.
Schematics of two types of
optical circuits: The three-particle trimer functions as a nanoscale magnet,
while the seven-particle heptamer exhibits almost no scattering for a narrow
range of wavelengths due to interference.
For the current demonstration, the researchers created two
types of patterns: "trimers" and "heptamers." Trimers—three-sided
particles that exhibit a magnetic response—could be used to craft invisibility
cloaks that work in the ordinary visible light wavelengths, unlike top-down
cloaks that only work at radar and microwave frequencies. Heptamers, on the
other hand, could be used to create intense electric fields in nanometer-sized
regions capable of trapping, manipulating and identifying substances from
samples as small as individual molecules.
Next, the researchers want to create a "tool kit"
of techniques for fabricating massive arrays of such materials so that their
nanoscale optical properties can be used at the macroscale—the "holy
grail" of materials science.
A user comment on this articlePosted on: 06-21-10 | By: Roger YI'd seen an aotomotive application recently in R&D that is akin to invisibility cloaking, wondering if it's the same principles applied here. Essentially it was a system that had camera system onboard a car that enables the driver to "see" through the skin of the automobile for full visibility through sheet metal onto the street.
