David Kirkpatrick

September 3, 2010

Cool nanotech image — a 2-water molecule thick ice crystal

Researchers used graphene to trap the room-temperature ice on a mica surface.

Atomic force micrograph of ~1 micrometer wide × 1.5 micrometers (millionths of a meter) tall area. The ice crystals (lightest blue) are 0.37 nanometers (billionths of a meter) high, which is the height of a 2-water molecule thick ice crystal. A one-atom thick sheet of graphene is used to conformally coat and trap water that has adsorbed onto a mica surface, permitting it to be imaged and characterized by atomic force microscopy. Detailed analysis of such images reveals that this (first layer) of water is ice, even at room temperature. At high humidity levels, a second layer of water will coat the first layer, also as ice. At very high humidity levels, additional layers of water will coat the surface as droplets. Credit: Heath group/Caltech

Hit the link for the full story on this image.

April 22, 2010

New negative-index metamaterial for invisibility cloaks and more

Here’s news on a new artificial optical material with applications for invisibility cloaking tech and more.

From the first link:

Caltech-led team designs novel negative-index metamaterial that responds to visible light

Uniquely versatile material could be used for more efficient light collection in solar cells

IMAGE: Arrays of coupled plasmonic coaxial waveguides offer a new approach by which to realize negative-index metamaterials that are remarkably insensitive to angle of incidence and polarization in the visible range….

Click here for more information.

PASADENA, Calif.—A group of scientists led by researchers from the California Institute of Technology (Caltech) has engineered a type of artificial optical material—a metamaterial—with a particular three-dimensional structure such that light exhibits a negative index of refraction upon entering the material. In other words, this material bends light in the “wrong” direction from what normally would be expected, irrespective of the angle of the approaching light.

This new type of negative-index metamaterial (NIM), described in an advance online publication in the journal Nature Materials, is simpler than previous NIMs—requiring only a single functional layer—and yet more versatile, in that it can handle light with any polarization over a broad range of incident angles. And it can do all of this in the blue part of the visible spectrum, making it “the first negative index metamaterial to operate at visible frequencies,” says graduate student Stanley Burgos, a researcher at the Light-Material Interactions in Energy Conversion Energy Frontier Research Center at Caltech and the paper’s first author.

“By engineering a metamaterial with such properties, we are opening the door to such unusual—but potentially useful—phenomena as superlensing (high-resolution imaging past the diffraction limit), invisibility cloaking, and the synthesis of materials index-matched to air, for potential enhancement of light collection in solar cells,” says Harry Atwater, Howard Hughes Professor and professor of applied physics and materials science, director of Caltech’s Resnick Institute, founding member of the Kavli Nanoscience Institute, and leader of the research team

What makes this NIM unique, says Burgos, is its engineering. “The source of the negative-index response is fundamentally different from that of previous NIM designs,” he explains. Those previous efforts used multiple layers of “resonant elements” to refract the light in this unusual way, while this version is composed of a single layer of silver permeated with “coupled plasmonic waveguide elements.”

Surface plasmons are light waves coupled to waves of electrons at the interface between a metal and a dielectric (a non-conducting material like air). Plasmonic waveguide elements route these coupled waves through the material. Not only is this material more feasible to fabricate than those previously used, Burgos says, it also allows for simple “tuning” of the negative-index response; by changing the materials used, or the geometry of the waveguide, the NIM can be tuned to respond to a different wavelength of light coming from nearly any angle with any polarization. “By carefully engineering the coupling between such waveguide elements, it was possible to develop a material with a nearly isotopic refractive index tuned to operate at visible frequencies.”

This sort of functional flexibility is critical if the material is to be used in a wide variety of ways, says Atwater. “For practical applications, it is very important for a material’s response to be insensitive to both incidence angle and polarization,” he says. “Take eyeglasses, for example. In order for them to properly focus light reflected off an object on the back of your eye, they must be able to accept and focus light coming from a broad range of angles, independent of polarization. Said another way, their response must be nearly isotropic. Our metamaterial has the same capabilities in terms of its response to incident light.”

This means the new metamaterial is particularly well suited to use in solar cells, Atwater adds. “The fact that our NIM design is tunable means we could potentially tune its index response to better match the solar spectrum, allowing for the development of broadband wide-angle metamaterials that could enhance light collection in solar cells,” he explains. “And the fact that the metamaterial has a wide-angle response is important because it means that it can ‘accept’ light from a broad range of angles. In the case of solar cells, this means more light collection and less reflected or ‘wasted’ light.”

“This work stands out because, through careful engineering, greater simplicity has been achieved,” says Ares Rosakis, chair of the Division of Engineering and Applied Science at Caltech and Theodore von Kármán Professor of Aeronautics and Mechanical Engineering.


In addition to Burgos and Atwater, the other authors on the Nature Materials paper, “A single-layer wide-angle negative index metamaterial at visible frequencies,” are Rene de Waele and Albert Polman from the Foundation for Fundamental Research on Matter Institute for Atomic and Molecular Physics in Amsterdam. Their work was supported by the Energy Frontier Research Centers program of the Office of Science of the Department of Energy, the National Science Foundation, the Nederlandse Organisatie voor Wetenschappelijk Onderzoek, and “NanoNed,” a nanotechnology program funded by the Dutch Ministry of Economic Affairs.

Visit the Caltech Media Relations website at http://media.caltech.edu.

November 27, 2009

Beautiful nature image — triangular snowflakes

I didn’t know snowflakes come in all sorts of geometric shapes.

From the link:

The beautiful six-fold symmetry of snowflakes is the result of the hydrogen bonds that water molecules form when they freeze.

But snowflakes can form other shapes too when the growth of the crystal is perturbed on one side. In theory, diamonds, trapezoids and other irregular shapes can all occur. And yet the one most commonly observed (after hexagons) is the triangle. The puzzle for is why? What process causes deformed snowflakes to become triangles rather than say squares or rectangles?

August 16, 2009

DNA scaffolding and circuit boards

A release red hot from the inbox:

IBM Scientists Use DNA Scaffolding To Build Tiny Circuit Boards

Nanotechnology advancement could lead to smaller, faster, more energy efficient computer chips

SAN JOSE, Calif., Aug. 17 /PRNewswire-FirstCall/ — Today, scientists at IBM Research (NYSE:IBM) and the California Institute of Technology announced a scientific advancement that could be a major breakthrough in enabling the semiconductor industry to pack more power and speed into tiny computer chips, while making them more energy efficient and less expensive to manufacture.

  (Photo:  http://www.newscom.com/cgi-bin/prnh/20090817/NY62155-a )
  (Photo:  http://www.newscom.com/cgi-bin/prnh/20090817/NY62155-b )
  (Logo:  http://www.newscom.com/cgi-bin/prnh/20090416/IBMLOGO )

IBM Researchers and collaborator Paul W.K. Rothemund, of the California Institute of Technology, have made an advancement in combining lithographic patterning with self assembly – a method to arrange DNA origami structures on surfaces compatible with today’s semiconductor manufacturing equipment.

Today, the semiconductor industry is faced with the challenges of developing lithographic technology for feature sizes smaller than 22 nm and exploring new classes of transistors that employ carbon nanotubes or silicon nanowires. IBM’s approach of using DNA molecules as scaffolding — where millions of carbon nanotubes could be deposited and self-assembled into precise patterns by sticking to the DNA molecules – may provide a way to reach sub-22 nm lithography.

The utility of this approach lies in the fact that the positioned DNA nanostructures can serve as scaffolds, or miniature circuit boards, for the precise assembly of components – such as carbon nanotubes, nanowires and nanoparticles – at dimensions significantly smaller than possible with conventional semiconductor fabrication techniques. This opens up the possibility of creating functional devices that can be integrated into larger structures, as well as enabling studies of arrays of nanostructures with known coordinates.

“The cost involved in shrinking features to improve performance is a limiting factor in keeping pace with Moore’s Law and a concern across the semiconductor industry,” said Spike Narayan, manager, Science & Technology, IBM Research – Almaden. “The combination of this directed self-assembly with today’s fabrication technology eventually could lead to substantial savings in the most expensive and challenging part of the chip-making process.”

The techniques for preparing DNA origami, developed at Caltech, cause single DNA molecules to self assemble in solution via a reaction between a long single strand of viral DNA and a mixture of different short synthetic oligonucleotide strands. These short segments act as staples – effectively folding the viral DNA into the desired 2D shape through complementary base pair binding. The short staples can be modified to provide attachment sites for nanoscale components at resolutions (separation between sites) as small as 6 nanometers (nm). In this way, DNA nanostructures such as squares, triangles and stars can be prepared with dimensions of 100 – 150 nm on an edge and a thickness of the width of the DNA double helix.

IBM uses traditional semiconductor techniques, the same used to make the chips found in today’s computers, to etch out patterns, creating the lithographic templates for this new approach. Either electron beam or optical lithography are used to create arrays of binding sites of the proper size and shape to match those of individual origami structures. The template materials are chosen to have high selectivity so that origami binds only to the patterns of “sticky patches” and nowhere else.

The paper on this work, “Placement and orientation of DNA nanostructures on lithographically patterned surfaces,” by scientists at IBM Research and the California Institute of Technology will be published in the September issue of Nature Nanotechnology and is currently available at: http://www.nature.com/nnano/journal/vaop/ncurrent/abs/nnano.2009.220.html.

For more information about IBM Research, please visit http://www.research.ibm.com/.

To view and download DNA scaffolding images, in high or low resolution, please go to: http://www.thenewsmarket.com/ibm.

Photo:  http://www.newscom.com/cgi-bin/prnh/20090416/IBMLOGO
PRN Photo Desk, photodesk@prnewswire.com
Source: IBM

Web Site:  http://www.research.ibm.com/

June 4, 2009

Nanoscale zipper cavities

More nanotech news.

The release:

Caltech scientists create nanoscale zipper cavity that responds to single photons of light

Device could be used for highly sensitive force detection, optical communications and more

IMAGE: Scanning electron microscope image of an array of “zipper ” optomechanical cavities. The scale and sensitivity of the device is set by its physical mass (40 picograms/40 trillionths of a gram)…

Click here for more information. 

PASADENA, Calif.—Physicists at the California Institute of Technology (Caltech) have developed a nanoscale device that can be used for force detection, optical communication, and more. The device exploits the mechanical properties of light to create an optomechanical cavity in which interactions between light and motion are greatly strengthened and enhanced. These interactions, notes Oskar Painter, associate professor of applied physics at Caltech, and the principal investigator on the research, are the largest demonstrated to date.

The device and the work that led to it are described in a recent issue of the journal Nature.

The fact that photons of light, despite having no mass, nonetheless carry momentum and can interact with mechanical objects is an idea that dates back to Kepler and Newton. The mechanical properties of light are also known to limit the precision with which one can measure an object’s position, since simply by using light to do the measurement, you apply a force and disturb the object.

It was important to consider these so-called back-action effects in the design of devices to measure weak, classical forces. Such considerations were part of the development of gravity-wave detectors like the Laser Interferometer Gravitational-Wave Observatory (LIGO). These sorts of interferometer-based detectors have also been used at much smaller scales, in scanning probe instruments used to detect or image atomic surfaces or even single electron spins.

To get an idea of how these systems work, consider a mirror attached to a floppy cantilever, or spring. The cantilever is designed to respond to a particular force—say, a magnetic field. Light shining down on the mirror will be deflected when the force is detected—i.e., when the cantilever moves—resulting in a variation in the light beam’s intensity that can then be detected and recorded.

“LIGO is a huge multikilometer-scale interferometer,” notes Painter. “What we did was to take that and scale it all the way down to the size of the wavelength of light itself, creating a nanoscale device.”

They did this, he explains, because as these interferometer-based detectors are scaled down, the mechanical properties of light become more pronounced, and interesting interactions between light and mechanics can be explored.

“To this end, we made our cantilevers many, many times smaller, and made the optical interaction many, many times larger,” explains Painter.

They call this nanoscale device a zipper cavity because of the way its dual cantilevers—or nanobeams, as Painter calls them—move together and apart when the device is in use. “If you look at it, it actually looks like a zipper,” Painter notes.

“Zipper structures break new ground on coupling photonics with micromechanics, and can impact the way we measure motion, even into the quantum realm,” adds Kerry Vahala, Caltech’s Ted and Ginger Jenkins Professor of Information Science and Technology and professor of applied physics, and one of the paper’s authors. “The method embodied in the zipper design also suggests new microfabrication design pathways that can speed advances in the subject of cavity optomechanics as a whole.”

To create their zipper cavity device, the researchers made two nanobeams from a silicon chip, poking holes through the beams to form an effective optical mirror. Instead of training a light down onto the nanobeams, the researchers used optical fibers to send the light “in plane down the length of the beams,” says Painter. The holes in the nanobeams intercept some of the photons, circulating them through the cavity between the beams rather than allowing them to travel straight through the device.

Or, to be more precise, the circulating photons actually create the cavity between the beams. As Painter puts it: “The mechanical rigidity of the structure and the changes in its optical response are predominantly governed by the internal light field itself.”

Such an interaction is possible, he adds, because the structure is precisely designed to maximize the transfer of momentum from the input laser’s photons to the mechanical nanobeams. Indeed, a single photon of laser light zipping through this structure produces a force equivalent to 10 times that of Earth’s gravity. With the addition of several thousand photons to the cavity, the nanobeams are effectively suspended by the laser light.

Changes in the intensity and other properties of the light as it moves along the beams to the far end of the chip can be detected and recorded, just as with any large-scale interferometer.

The potential uses for this sort of optomechanical zipper cavity are myriad. It could be used as a sensor in biology by coating it with a solution that would bind to, say, a specific protein molecule that might be found in a sample. The binding of the protein molecule to the device would add mass to the nanobeams, and thus change the properties of the light traveling through them, signaling that such a molecule had been detected. Similarly, it could be used to detect other ultrasmall physical forces, Painter adds.

Zipper cavities could also be used in optical communications, where circuits route information via optical beams of different colors, i.e., wavelengths. “You could control and manipulate what the optical beams of light are doing,” notes Painter. “As the optical signals moved around in a circuit, their direction or color could be manipulated via other control light fields.” This would create tunable photonics, “optical circuits that can be tuned with light.”

Additionally, the zipper cavity could lead to applications in RF-over-optical communications and microwave photonics as well, where a laser source is modulated at microwave frequencies, allowing the signals to travel for kilometers along optical fibers. In such systems, the high-frequency mechanical vibrations of the zipper cavity could be used to filter and recover the RF or microwave signal riding on the optical wave.




Other authors on the Nature paper, “A picogram- and nanometre-scale photonic-crystal optomechanical cavity,” include graduate students Matt Eichenfield (the paper’s first author) and Jasper Chan, and postdoctoral scholar Ryan Camacho.

Their research was supported by a Defense Advanced Research Projects Agency seeding effort, and an Emerging Models and Technologies grant from the National Science Foundation.

January 23, 2009

Nanoscale lasers and whispering galleries

Big breakthrough in tiny lasers — the apps here include lightening quick communications and data handling (photonics) and optical microchips.

The release:

Plasmonic whispering gallery microcavity paves the way to future nanolasers

The principle behind whispering galleries – where words spoken softly beneath a domed ceiling or in a vault can be clearly heard on the opposite side of the chamber – has been used to achieve what could prove to be a significant breakthrough in the miniaturization of lasers. Ultrasmall lasers, i.e., nanoscale, promise a wide variety of intriguing applications, including superfast communications and data handling (photonics), and optical microchips for instant and detailed chemical analyses.


Researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the California Institute of Technology have developed a “whispering gallery microcavity” based on plasmons – electromagnetic waves that race across the surfaces of metals. Such a plasmon wave has very small wavelength compared with the light, enabling the scaling down optical devices beyond diffraction limit of the light. Cavities are the confined spaces in lasers where light amplification takes place and this new micro-sized metallic cavity for plasmons improves on the quality of current plasmonic cavities by better than an order of magnitude.

“We have shown for the first time that metallic microcavities based on surface plasmons can have a large quality factor and can thereby enable ultra-small device fabrication and strong enhancement of the light,” said Xiang Zhang, a mechanical engineer who holds a joint appointment with Berkeley Lab’s Materials Sciences Division and the University of California (UC) Berkeley where he directs the NSF Nano-scale Science and Engineering Center.

“Plasmonic microcavities have uniquely different physical properties when compared to dielectric cavities and can extend microcavity research in entirely new ways, particularly at nanoscale dimensions,” said Kerry Vahala, a physics professor at Cal Tech and authority on photonic devices. “Our work shows that the full potential of this new class of device can be realized with careful design and material control.”

Zhang and Vahala led this collaborative research which is reported in the January 22, 2009 edition of the journal Nature. The paper is entitled: “High-Q surface-plasmon-polariton whispering-gallery microcavity.” In addition to Zhang and Vahala, other authors of the paper were Bumki Min, Eric Ostby, Volker Sorger, Erick Ulin-Avila and Lan Yang.


Surface Plasmons and Whispering Galleries

Just as the energy in waves of light is carried through space in discrete or quantized particle-like units called photons, so, too, is the energy in waves of charged gas (plasma) carried in quantized particle-like packets called plasmons, as they travel along metallic surfaces. When photons excite the collective electron oscillations at the interfaces between metal and dielectric (insulator) materials, they can form yet another quasi-particle called a surface plasmon polariton(SPP). Such polaritons play an important role in the optical properties of metals and can be used to manipulate light on a nanoscale.

“Metal-dielectric materials, also known as plasmonics, can be used to confine an optical field to a very small scale, much smaller than conventional insulators,” said Min, lead author on the Nature paper and former postdoctoral researcher in Zhang’s Lab, now an assistant professor at the Korea Advanced Institute of Science and Technology (KAIST). “This capability, often termed as breaking the light diffraction, is unobtainable with dielectric materials alone.”

The main obstacle to working with plasmonic materials for creating nanoscale lasers has been a low quality or “Q” factor, which is a measure of power loss in the lasing cavity – a laser cavity with a high-Q factor has a low power loss. Enter the whispering gallery phenomenon, which Cal Tech’s Vahala has used to boost the Q factor of dielectric microcavities. Whispering galleries are found in circular or elliptically shaped buildings, such as St. Paul’s Cathedral in London, where the phenomenon was first made famous, or Statuary Hall in the U.S. Capitol building.

The prevailing theory behind why whispering galleries work (first proposed in 1871 by British astronomer George Airy to explain St. Paul’s cathedral) is that sound originating at one point along the circumference of an enclosed sphere is reflected to another point along the circumference opposite the source. Vahala and his group applied this idea to dielectric microcavities, and Zhang and Min along with Ostby, Sorger and Ulin-Avila applied the idea to plasmonic microcavities.


“In these sphere-shaped microcavities, optical waves propagate in a similar way that sound waves propagate in a whispering gallery,” said Zhang. “They continue to circle around the edge of the cavity sphere and smoothness of the edge enhances or boosts the cavity’s Q factor.”

In this study, Zhang and his collaborators created a high-Q SPP whispering gallery microcavity by coating the surface of a high-Q silica microcavity with a thin layer of silver.


Explained Zhang, “Whenever light propagates in a metal it experiences some loss of power and this obviously reduces the performance of a device. Silver is the metal with the lowest loss, that is available.”


Whereas previous plasmonic microcavities achieved a best Q factor below 100, the whispering gallery plasmonic microcavity allows Q factors of 1,376 in the near infrared for SPP modes at room temperature.


“This nearly ideal value, which is close to the theoretical metal-loss-limited Q factor, is attributed to the suppression and minimization of radiation and scattering losses that are made possible by the geometrical structure and the fabrication method,” said Min, who believes that there is still room for plasmonic Q-factor improvement by geometrical and material optimizations.

Min said one of the first applications of the whispering gallery plasmonic microcavity is likely to be the development of a plasmonic nanolaser.

“To build a working laser, it is essential to have both the laser cavity (or resonator) and the gain media,” Min said.  “Therefore, we need a good, high-Q plasmonic microcavity to make a plasmonic nanolaser. Our work paves the way to accomplish the demonstration of a real plasmonic nanolaser.  In addition, fundamental research can also be pursued with this plasmonic cavity, such as the interaction of a single light emitter with plasmons.”

This work was supported by the U.S. Air Force Office of Scientific Research MURI program, and by the NSF Nanoscale Science and Engineering Center.


Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Visit our website at http://www.lbl.gov.

November 21, 2008

News from the galaxy

This is some crazy research.

The release:

Crash Test-Iconic Rings and Flares of Galaxies Created by Violent, Intergalactic Collisions, Research by Pitt and Partners Finds

Findings published in “The Astrophysical Journal” challenge existing theory about the formation of such galaxies as the Milky Way

PITTSBURGH-The bright pinwheels and broad star sweeps iconic of disk galaxies such as the Milky Way might all be the shrapnel from massive, violent collisions with other galaxies and galaxy-size chunks of dark matter, according to a multi-institutional project involving the University of Pittsburgh. Published in the Nov. 20 edition of “The Astrophysical Journal,” the findings challenge the longstanding theory that the bright extensions and rings surrounding galaxies are the remnants of smaller star clusters that struck a larger, primary galaxy then fragmented.

The study’s team consisted of Andrew Zentner, a professor of physics and astronomy in Pitt’s School of Arts and Sciences; James Bullock, a physics and astronomy professor at the University of California at Irvine; Stelios Kazantzidis, a postdoctoral researcher at Ohio State University; Andrey Kravtsov, a professor of astronomy and astrophysics at the University of Chicago; and Leonidas Moustakas, a researcher at the NASA Jet Propulsion Laboratory, California Institute of Technology.

The team’s computer simulations of galaxy formation suggests that disk galaxies most likely began as flat, centralized star clusters. Smaller galaxies collided with and tore through these disks billions of years ago, casting disk stars outward into the wild extensions present now; the bright center is the original formation. In addition, vast bodies of dark matter-a low-density, high-gravity invisible mass thought to occupy nearly one-quarter of the Universe-swept through these disks and further pulled stars from the main disk.

The researchers’ scenario largely applies to the formation of the rings and long flares of stars that surround such galaxies as the Milky Way, Zentner said. But the model also presents a possible solution to how star spirals-the arcs of stars that radiate from the center of some disk galaxies-maintain their shape. Spirals form as a result of any disturbance to the star disk, Zentner said. However, the prolonged disturbance of a galaxy and dark matter expanse passing through a disk explains why the spirals seem to never recede.

“Our model suggests that a violent collision throws stars everywhere and continues moving through the disk, disturbing its structure,” Zentner said. “It also has been known for some time that for star spirals to develop and maintain their well-known form, there must be a prolonged disturbance. We show that large masses moving through a galaxy could provide that disturbance.”

The team’s findings were serendipitous, Zentner explained. They were modeling disk galaxies for an unrelated astrological survey when they inadvertently discovered that stars in the main disk scattered when satellite galaxies-smaller galaxies surrounding larger ones-passed through. They shared their results with colleagues a year ago, and the results have since been replicated, Zentner said.

“One of the major advantages of these results is that we didn’t set out to find them,” he said. “They happened as we simulated existing galaxies.”

The paper is available on Pitt’s Web site at http://www.pitt.edu/news2008/zentner_paper.pdf


Related links:

The Astrophysical Journal

September 22, 2008

Nanopencil offers terabit of data storage

Pretty amazing bit of nanotech.

From the PhysOrg link:

The probe’s tip can write bit sizes with radii as small as 6.8 nanometers, allowing for a nonvolatile memory density of 1 Tbit/in2. With improvements, such technology has been predicted to realize storage density of 10 Tbits/in2.

This isn’t the first time that carbon nanotubes have been used as scanning probes for writing and reading data. However, the researchers, consisting of a team from Intel Corporation in Santa Clara, California, and the California Institute of Technology in Pasadena, California, made some improvements to enhance the performance and lifetime of the device.

While carbon nanotubes have strong mechanical and wear-resistant properties, one of the biggest challenges of using nanotubes as data storage read-and-write devices is that they’re still prone to bending and buckling after significant use. By coating the carbon nanotube with a 65-nm-thick layer of silicon-oxide, the researchers discovered that they could greatly increase the probe’s mechanical strength. In a sense, the improvement is the equivalent of putting wood around a long, thin stick of graphite in a regular pencil. After depositing the protective silicon-oxide sheath, the researchers used a diamond to “sharpen” the nanopencil to expose the carbon nanotube electrode.

Noureddine Tayebi, et al.

Image of the 870-nm-long nanopencil taken with a transmission electron microscope. The inset shows the carbon nanotube electrode protruding from the silicon-oxide sheath. Credit: Noureddine Tayebi, et al.

Noureddine Tayebi, et al.
Ferroelectric domain patterns written by a nanopencil probe with 6V pulses. Credit: Noureddine Tayebi, et al.