Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Berkeley Lab researchers make first perovskite-based superlens for the infrared

Superlenses earned their superlative by being able to capture the "evanescent" light waves that blossom close to an illuminated surface and never travel far enough to be "seen" by a conventional lens.

Superlenses hold enormous potential in a range of applications, depending upon the form of light they capture, but their use has been limited because most have been made from elaborate artificial constructs known as metamaterials.

The unique optical properties of metamaterials, which include the ability to bend light backwards - a property known as negative refraction - arise from their structure rather than their chemical composition. However, metamaterials can be difficult to fabricate and tend to absorb a relatively high percentage of photons that would otherwise be available for imaging.

Now, researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have fabricated a superlens from perovskite oxides that are simpler and easier to fabricate than metamaterials, and are ideal for capturing light in the mid-infrared range, which opens the door to highly sensitive biomedical detection and imaging. It is also possible that the superlensing effect can be selectively turned on/off, which would open the door to highly dense data writing and storage.

"We have demonstrated a superlens for electric evanescent fields with low absorption losses using perovskites in the mid-infrared regime," says Ramamoorthy Ramesh, a materials scientist with Berkeley Lab's Materials Sciences Division, who led this research. "Spectral studies of the lateral and vertical distributions of evanescent waves around the image plane of our lens show that we have achieved an imaging resolution of one micrometer, about one-fourteenth of the working wavelength."

Ramesh, who also holds appointments with the University of California Berkeley's Department of Materials Science and Engineering and the Department of Physics, is the senior author of a paper in the journal Nature Communications titled "Near-field examination of perovskite-based superlenses and superlens-enhanced probe-object coupling."

Conventional lenses create images by capturing the propagating light waves emitted by an object under illumination and then bending these captured light waves into focus. No matter how perfect a conventional lens is, the smallest image it can ever resolve is about half the wavelength of the illuminating (incident) light - a restriction known as the "diffraction limit." Superlenses overcome the diffraction limit by capturing the evanescent light waves, which carry detailed information about features on an object that are significantly smaller than the wavelengths of incident light. Because evanescent waves dissipate or "vanish" after traveling a very short distance, conventional lenses seldom ever see them.

"A superlens made out of a metamaterial focuses propagating waves and reconstructs evanescent waves arising from the illuminated objects in the same plane to produce an image with sub-wavelength resolution," says Susanne Kehr, a former member of Ramesh's Berkeley research group and now with the University of Saint Andrews in the United Kingdom. "Our perovskite-based superlens doesn't focus propagating waves, but instead reconstructs evanescent fields only. These fields generate the sub-wavelength images that we study with near-field infrared microscopy."

Kehr is one of two leading authors of the Nature Communications paper, along with Yongmin Liu, a metamaterials expert in the research group of Xiang Zhang, who also worked on this study. In 2005, Zhang, who holds joint appointments with Berkeley Lab and the University of California, Berkeley, led the first experimental demonstration of a superlens at optical frequencies.

Kehr and Liu say that perovskites hold a number of advantages over metamaterials for superlensing. The perovskites they used to make their superlens, bismuth ferrite and strontium titan¬ate, feature a low rate of photon absorption and can be grown as epitaxial multilayers whose highly crystalline quality reduces interface roughness so there are few photons lost to scattering. This combination of low absorption and scattering losses significantly improves the imaging resolution of the superlens.

"In addition, perovskites display a wide range of fascinating properties, such as ferroelectricity and piezoelectricity, superconductivity and enormous magnetoresistance that might inspire new functionalities of perovskite-based superlenses, such as non-volatile memory, microsensors and microactu¬ators, as well as applications in nanoelectronics," says Liu. "Bismuth ferrite, in particular, is multiferroic, meaning it simultaneously displays both ferroelectric and ferromagnetic properties, and therefore is a good candidate to allow for electric and magnetic tunability."

This research represents the first application of perovskite materials to superlensing. One of the biggest challenges was to find the right combination of perovskites that would make an effective superlens. The perovskite thin films they fabricated were grown by pulsed-laser deposition and found to be single phase and fully epitaxial. However, this too was a challenge, as Kehr explains.

"Our superlenses consisted of a layer of bismuth ferrite and a layer of strontium titan¬ate with thicknesses of 200 and 400 nanometers, respectively, which is rather thick for epitaxial growth with pulsed laser deposition," she says. "At these thicknesses, accurate thickness and flat interfaces become a problem."

A combination of near-field infrared microscopy with a tunable free-electron laser provided a first of its kind highly detailed study of the spatial and spectral near-field responses of the superlens. This study led to the observation of an enhanced coupling between the illuminated objects – rectangles of strontium ruthenate on a strontium titanate substrate - and a near-field scattering probe - a metal-coated atomic-force microscope tip with a typical radius of 50 nanometers.

"At certain distances between the probe and the surface of the object, we observed a maximum number of evanescent fields," Ramesh says. "Comparisons with numerical simulations indicate that this maximum originates from an enhanced coupling between probe and object, which might be applicable for multifunctional circuits, infrared spectroscopy and thermal sensors."

In their Nature Communications paper, Ramesh and his co-authors say that the multiferroic bismuth ferrite layer should make their superlens tunable through the application of an external electric field. This tunability could be used to change the superlensing wavelength or sharpen the final image, but even more importantly, might be used to turn the superlensing effect on and off.

"The ability to switch superlensing on and off for a certain wavelength with an external electric field would make it possible to activate and deactivate certain local areas of the lens," Kehr says. "This is the concept of data-storage, with writing by electric fields and optical read-outs."

Liu says that the mid-infrared spectral region at which their superlens functions is prized for biomedical applications.

"Most biomolecules have specific absorption and radiation features in this range that depend on their chemical composition and therefore yield a fingerprint in the spectra," he says. "However, compared with optical wavelengths, there are significant limitations in the basic components available today for biophotonic delivery in the mid-infrared. Our superlens has the potentials to eliminate these limitations."

This research was carried out by an international collaboration of scientists. In addition to Kehr, Liu and Ramesh, other co-authors of the paper "Near-field examination of perovskite-based superlenses and superlens-enhanced probe-object coupling," were Lane Martin, Pu Yu, Martin Gajek, Seung-Yeul Yang, Chan-Ho Yang, Marc Wenzel, Rainer Jacob, Hans-Georg von Ribbeck, Manfred Helm, Xiang Zhang and Lukas Eng.

The broad range of expertise represented by these co-authors was critical to the success of the research, as Kehr explains.

"Our perovskite oxide superlens was designed and grown in Ramesh's group, but the idea for a perovskite superlens originated with Lukas Eng at the University of Technology in Dresden," she says. "A collaboration at Dresden between Eng and Manfred Helm provided the expertise for combining near-field infrared microscopy and free-electron laser technologies, and Yongmin and Xiang Zhang provided the expertise in optics for interpreting our results."

Support for this research came primarily from DOE's Office of Science.

Lawrence Berkeley National Laboratory is a U.S. Department of Energy (DOE) national laboratory managed by the University of California for the DOE Office of Science. Berkeley Lab provides solutions to the world's most urgent scientific challenges including sustainable energy, climate change, human health, and a better understanding of matter and force in the universe. It is a world leader in improving our lives through team science, advanced computing, and innovative technology. Visit our Website at

Lynn Yarris | EurekAlert!
Further information:

More articles from Materials Sciences:

nachricht New material for digital memories of the future
19.10.2017 | Linköping University

nachricht Electrode materials from the microwave oven
19.10.2017 | Technical University of Munich (TUM)

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>



Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

Latest News

Electrode materials from the microwave oven

19.10.2017 | Materials Sciences

New material for digital memories of the future

19.10.2017 | Materials Sciences

Physics boosts artificial intelligence methods

19.10.2017 | Physics and Astronomy

More VideoLinks >>>