American Ceramic Society Bulletin

advances in nanomaterials
Perovskite-based tunable superlens developed
The DOE’s Lawrence Berkeley
National Lab says its staffers have
developed a novel mode of fabricating
a superlens for the infrared spectrum
using, for the first time, perovskitebased
oxides. The lab says a group led
by Ramamoorthy Ramesh has reported
on its “Near-field examination of
perovskite-based superlenses and superlens-enhanced
probe-object coupling”
in Nature Communications (doi:10.1038/
ncomms1249).
The innovation is an alternative to
super resolution imaging approaches
that are based on metamaterials. In
brief, metamaterials are difficult to
make and absorb a lot of precious light
energy.
According to the lab’s release, “The
perovskite-based oxides on the other
hand are simpler and easier to fabricate
and are ideal for capturing light in the
mid-infrared range. This 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.”
The group says it is able to achieve
an imaging resolution of λ/14 at the
superlensing wavelength.
One of the biggest challenges for
the researchers according to the report
was finding the right combination of
perovskites that would make an effective
superlens. What they landed on
was a layer of bismuth ferrite and a
layer of strontium titanate with thicknesses
of 200 and 400 nanometers,
respectively. These thin films were
grown by pulsed-laser deposition.
In the lab’s release, Susanne
Kehr, now with the University of St.
Andrews (Scotland) and Yongmin Liu,
a metamaterials expert at Berkeley’s
NSF Nanoscale Science and Engineering
Center, provide additional
information about the advantages of
perovskites. “The bismuth ferrite and
strontium titanate material feature a
American Ceramic Society Bulletin, Vol. 90, No. 4
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,” they say. “This combination
of low absorption and scattering
losses significantly improves the
imaging resolution of the superlens.”
This research was conducted by an
international collaboration of scientists,
including ACerS member Lane Martin
at the University of Illinois, Champaign-Urbana.
Because of thickness and related
wavelength issues, these investigators
sought and found a way to gain detailed
control over the superlens, selective
tuning sections or toggling the effect
via an external electric field.
“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,”
(Credit: Kehr, et. al.)
▲ Experimental setup shows an IR freeelectron
laser light source and perovskite
superlens consisting of BiFeO 3 and SrTiO 3
layers. Imaged objects are SrRuO 3 patterns
(orange) on a SrTiO 3 substrate. The near-field
probe is shown in blue and the evanescent
waves in red.
▲ AFM image of subwavelength strontium ruthenate rectangles imaged with perovskitebased
superlens using incident IR light of 14.6 micrometer wavelengths.
Kehr says. “This is the concept of datastorage,
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.
“Compared with optical wavelengths,
there are significant limitations
in the basic components available today
for biophotonic delivery in the midinfrared.
Our superlens has the potentials
to eliminate these limitations.”
Liu suggests the world is full of
opportunities for these materials, saying,
“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
nonvolatile memory, microsensors and
microactuators, as well as applications
in nanoelectronics.”
Visit: www.lbl.gov n
(Credit: Kehr, et. al.)
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