PORTLAND, Ore. IBM Research has created what it claims is the world's first 3D magneto-optical crystal, complete with embedded quantum dots with optical properties.
The work underscores IBM's strategy for nanoscale metamaterials that feature tunable properties not found in naturesuch as magnetic crystals. By gradually melding metamaterials with traditional silicon technologies, IBM envisions a mix-and-match cookbook of metamaterials.
The first metamaterial exhibits long-sought magneto-optical coupling. This was achieved by carefully packing magnetic- and optical-nanoparticles into a common crystaline superlattice, thereby coupling their properties. It also enabled a magnetic field to modulate an optical transmission.
"We want to have a family of metamaterials coming out of this workmaterials that take advantage of the multicomponent self-assembly methods we are pioneering," said Christopher Murray, manager of nanoscale materials and devices at IBM Research (Yorktown Heights, N.Y.).
"We want to have metamaterials in the pipeline now, so that when our engineers need new technological opportunities, they can draw upon the self-assembly techniques we are developing now. We have begun filling that pipeline," said Murray who worked with Stephen O'Brien of Columbia University, Franz Redl, a researcher affiliated with both Columbia and IBM, and Kyung Sang Cho, a researcher affiliated with IBM and supported by the University of New Orleans.
Metamaterials can act in a fashion opposite that of natural materials, creating a class of complementary, designer materials that can handle whatever needs to be controlled. So far, such metamaterials have only been demonstrated to exhibit a "left-handed" index-of-refraction at microwave wavelengths. By downsizing to the nanoscale, IBM said it can accomplish the same goal at optical wavelengths.
"We were inspired by a lot of the work done on left-handed materials at microwave frequencies," said Murray, adding that some funding was provided by the Defense Advanced Research Projects Agency's metamaterials program.
IBM began by coupling a magnetic nanoparticle with a semiconducting nanoparticle called a quantum dot, thereby enabling a magnetic field to modulate an optical transmission.
"We were interested in magneto-optical propertiescoupling up novel quantum optical properties with the magnetic tunability of iron oxide particles," said Murray.
IBM claimed success at self-assembling optical semiconducting
nanoparticles (quantum dots) into a superlattice with separately brewed magnetic nanoparticles, creating a composite metamaterial that it has not fully characterized yet. The hope is that such "designer metamaterials" will enable a magnetic field to modulate the optical properties of the quantum dots.
IBM synthesized the crystal after analyzing self-organizing growth techniques for 3D synthetic opals, and shrinking them to the nanoscale. The metamaterial included lead selenide, a semiconductor with applications in infrared detectors and
thermal imaging, and magnetic iron oxide like that used in magnetic recording media. Both were chosen because of their tunable infrared regions in communications bands between 1.3- and 1.5-micron.
The researchers settled on 60,000-atom iron oxide particles
measuring 11 nanometers in diameter and 3,000-atom
lead selenide particles measuring six nanometers in diameter. IBM confirmed experimentally that the sized particles will
self-assemble, under the right conditions, into a common crystalline superlattice with coupled optical and magnetic properties. IBM is now fully characterizing the metamaterial.
"What we would like to see on the ten-year time horizon is the
integration of nanoscale metamaterials with lithography," said Murray. "What's really liberating about this technique is the modular assembly. You can grab fascinating physics from what had been distinct fields of nanotechnology, and bring them together into such close proximity that they begin to couple together and influence each other."
IBM said it is targeting applications that take advantage
of nanoscale coupling in building blocks.
By virtue of its modularized building-block methodology, IBM plans to fill its cookbook with new composites made using "wet chemistry" methods it downsized to the nanoscale from synthetic opal technologies.
"We have this mix-and-match opportunity to bring materials together. We will begin by selecting combinations of materials that we feel will be enabling for magneto-optic applications," said Murray.
IBM is now cataloging the possibilities, synthesizing new
metamaterials and characterizing their performanceat least a two-year job, according to Murray.
IBM is currently characterizing a range of other metamaterials using all the possible combinations of known nanoparticle
candidateseach matched for like regions of operation and
characterized for how parameter changes affect relevant performance metrics. This will be IBM's cookbook for future metamaterial integration with its existing silicon chips.
"The precise and energy-efficient self-assembly of matter into
material structures with properties that cannot be achieved otherwise is an important goal for nanotechnology," said Mihail Roco, the National Science Foundation's senior advisor for nanotechnology and chair of the National Science and Technology Council's Subcommittee on Nanoscale Science and Engineering.
"This is just one way that nanotechnology will help foster the next industrial revolution."