Development + Research


Plasmonic QC laser nanoantennas

Harvard University engineers have demonstrated a plasmonic quantum cascade (QC) laser nanoantenna capable of chemical imaging of materials and biological specimens in unprecedented detail.

The antenna is used to concentrate light to the subwavelength scale. Graduate students Nanfang Yu and Ertugrul Cubukcu worked with Professor Federico Capasso to target the “molecular fingerprint region” of the spectrum. They designed a device with two gold rods separated by a nanometer gap—an optical antenna—built onto the facet of a QC laser that emits at 7µm into the region of the spectrum where most molecules have absorption fingerprints.

“We essentially take a laser and apply a thin, insulating layer of 100nm-thick aluminum oxide to the facet of the laser, because if you put metal directly on the facet of the laser it would electrically short it,” says Capasso. “Next, we apply a thin layer of gold. Then, using a focused ion beam, we sculpt the antenna by taking away the gold and defining it through metallic routes.”

This electron microscope micrograph captures the facet of a QC laser with a built-in nanoantenna. Also shown are an AFM topographic image of the antenna (left) and a near-field scanning optical microscope image showing the localized laser spot in the antenna gap (right).
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The length of the antenna must be along the direction of polarization of the laser because the electric field of the laser radiation makes the electrons of the metal oscillate when it’s directed along the rods. “The length of each arm of the antenna is basically equal to half a wavelength,” Capasso explains. “It’s a resonant antenna that provides a very strong charge oscillation and creates a very strong electric field right where the actual gap is. This near field comes from the surface plasmons, which are the oscillations of electrons within the metal, and you can achieve a large enhancement of the electric field inside the gap to generate very intense laser nanospots about 100x smaller than the laser wavelength at or near the surface of the laser. Then the spot can be scanned across a specimen to provide superior spatial resolution.”

Capasso and his group at Bell Labs invented millimeter-length semiconductor QC lasers in 1994. It may take five to ten years before products using QC laser nanoantenna technology make it to market.

—Sally Cole Johnson

(This article was adapted from Laser Focus World, a sister publication of Small Times.)

Atomic microscopy, 100x faster

Using an existing technique in a novel way, Cornell University physicist Keith Schwab and colleagues at Cornell and Boston University have made the scanning tunneling microscope (STM) at least 100x faster. The simple adaptation, based on a method of measurement currently used in nano-electronics, could also give STMs significant new capabilities—including the ability to sense temperatures in spots as small as a single atom, and to detect changes in position as tiny as 0.00000000000001 meter: a distance 30,000x smaller than the diameter of an atom.

IBM measures nanotube performance in chips

IBM scientists say they have measured the distribution of electrical charges in carbon nanotubes. The team monitored the color of the light scattered from the nanotube (Raman effect) and measured small changes corresponding to changes in the electron density in the nanotube. The technique takes advantage of the interaction between the motion of the atoms and the motion of the electrons, so that electron density changes can be reflected in changes of the frequency of the vibrational motion of the nanotube atoms.

To date, researchers have been able to build carbon nanotube transistors with superior performance, but have been challenged with reproducibility issues.

Vibrations give color to light, allowing local measurement of charges in a nano structure.
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“The success of nanoelectronics will largely depend on the ability to prepare well-characterized and reproducible nano-structures, such as carbon nanotubes,” says Phaedon Avouris, IBM Fellow and lead researcher for IBM’s carbon nanotube efforts. “Using this technique, we are now able to see and understand the local electronic behavior of individual carbon nanotubes.”

ISSYS gets grant for MEMS, electronics integration

Integrated Sensing Systems’ (ISSYS) Phase II Small Business Innovation Research contract from the National Science Foundation, “Wafer-Scale, Hermetic Packaging of MEMS-Based Systems,” is aimed toward development of a novel method that will greatly simplify the packaging of MEMS and their associated electronics.

“This technology is highly enabling for commercialization of viable MEMS products,” says Nader Najafi, president and CEO. “The practical hermetic integration of electronics and MEMS devices allows the commercialization of a variety of MEMS-based products that are currently not possible due to high cost of manufacturing or packaging problems.”

NIST demonstrates industrial-grade nanowire device fabrication

In the growing catalog of nanoscale technologies, nanowires have attracted interest for their potential to build atomic-scale electronics. But before you can buy some at your local Nano Depot, manufacturers will need efficient, reliable methods to build them in quantity. Now researchers at the National Institute of Standards and Technology (NIST) believe they’ve found a way.

Building on earlier work to grow nano-wires horizontally, NIST researchers used conventional semiconductor manufacturing techniques to deposit small amounts of gold in precise locations on a sapphire wafer. In a high-temperature process, the gold deposits bead up into nanodroplets that act as nucleation points for crystals of zinc oxide, a semiconductor. A slight mismatch in the crystal structures of zinc oxide and sapphire induces the semiconductor to grow as a nanowire in one particular direction across the wafer. Because the starting points and the growth direction are known, it is relatively straightforward to add electrical contacts and other features with additional lithography steps.

Metal electrodes are attached to zinc oxide nanowires using NIST’s technique. The dark spots near the center are the gold pads that start nanowire growth; the red arrow shows growth direction.
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As proof of concept, the researchers used this procedure to create more than 600 nanowire-based transistors in a single process. The nanowires typically grew in small bunches of up to eight wires at a time, but finer control over the size of the initial gold deposits should make it possible to select the number of wires in each position. The technique, they say, should allow industrial-scale production of nano-wire-based devices.

MEMS-based artificial kidney

The National Institute of Biomedical Imaging and Bioengineering (NBIB) has awarded Cleveland Clinic researcher Shuvo Roy a $3.2 million, three-year grant to develop a MEMS-based bioartificial kidney that can be used instead of dialysis. Roy and his team are using MEMS technology to create an implantable, self-regulating bioartificial kidney that will filter toxins and absorb necessary salts and water like human kidneys. Roy’s grant is one of four awarded by NIBIB’s Quantum Grants program. Another went to the Baylor College of Medicine (Dr. Karen K. Hirschi is the principal investigator) for Neuro-Vascular Regeneration. The goal of this project is to engineer neuro-vascular regenerative units in a laboratory environment, which can then be implanted into the damaged cortex of stroke patients to provide a source of neural and vascular cells that will continue to develop and differentiate and lead to the repair of stroke-injured tissue.

Ocular nanoparticle drug delivery gets a boost

Charlesson LLC has received several Small Business Innovative Research (SBIR) awards from the National Institutes of Health (NIH), and an award from the Oklahoma Center for the Advancement of Science and Technology (OCAST). The four grants total approximately $2.35 million and will support development of several pharmaceutical drug candidates, as well as nanoparticle-based gene therapies for eye disease.

In contrast to typical gene therapy where viral vectors are used to deliver the gene of interest, Charlesson’s program employs biodegradable nanoparticles for gene delivery. This non-viral approach eliminates many of the safety concerns in eliciting an immune response following gene therapy.

Under a Phase II SBIR award the company will develop CLT-003 for Diabetic Macular Edema (DME), a small-molecule therapeutic with potent effects on reducing vascular leakage and subsequent neovascularization and inflammation that can occur in the eyes of diabetic patients. In addition, the company will develop its gene therapy program to deliver to the retina DNA encoding CLT-001, a naturally occurring peptide. Charlesson has demonstrated that supplementation of this peptide in animal models of diabetes and age-related macular degeneration has profound effects on reducing neovascular and inflammatory events.

Direct, back-of-the-eye delivery methods for macular degeneration medication has long been sought by pharmaceutical companies. Charlesson is seeking commercial partners.