 At top (A) is the higher resolution image of the word NANO created with a silver superlens. Below that (B) is an image created during a control experiment in which the superlens is replaced by spacer layer. The averaged line width is 60 nanometers in image A with the superlens, and 321 nanometer in image B without the superlens. The scale bar in both images is 2 micrometers. (Image by Cheng Sun, UC Berkeley)
The
team of scientists produced images of holes in a gold film that were
smaller than a wavelength of light, about 500 nanometers in diameter,
by equipping a near-field scanning optical microscope with a newly
fabricated superlens.
"Though the idea of a superlens was
invented in 2000, it has been unclear how, or if, a superlens could be
integrated into an imaging system," says Gennady Shvets, associate
professor of physics at The University of Texas at Austin. "Nor has it
been demonstrated that ultra-small two-dimensional objects, such as
holes or nanodiscs, can be imaged by a superlens.
"We were able to image a two-dimensional object--holes in a surface. Such imaging would be impossible without the superlens."
The
resolution of conventional optical microscopes is limited to about half
the wavelength of the light used to illuminate an object. The superlens
was invented by Sir John Pendry in 2000 to overcome that limit and make
images of very tiny objects.
The new superlens was
fabricated at The University of Texas at Austin using specialized
equipment at the Center for Nano and Molecular Science and Technology
and the J.J. Pickle research campus. The lens was made of a thin film
of silicon carbide and was sandwiched between two layers of silicon
oxide. A layer of gold only 60 nanometers thick pocked with holes of
various sizes was attached to the bottom of the lens.
Researchers
Thomas Taubner and Rainer Hillenbrand at MPI then used the Texas
superlens with a near-field scanning optical microscope to create an
image of the holes in the gold layer beneath the surface of the lens.
Near-field
scanning optical microscopy (NSOM) works by passing a tiny probe across
the surface of a specimen, producing an image of the surface line by
line. While the resolution attained by NSOM is very good, it can record
only the surface of a nanoscale object. The action of the scanning
probe in contact with the surface also makes it difficult to visualize
fragile specimens, such as living cells.
Adding the
superlens to NSOM not only increases the resolution of the image, but
also provides a barrier between the scanning probe and the object.
"This
is the first attempt to integrate a superlens into a scanning optical
microscope, something that could be very useful in industrial
applications," says Shvets. "One new possible application could be the
imaging of biological objects in their natural environment, separated
by a superlens from the probing tip."
Shvets says another
application of the superlens could be the non-destructive probing of
metallic interconnects buried under a layer of glass, as is commonly
used in semiconductor devices.
Shvets cautions there is much
work to be done before applying the technique widely. His group at The
University of Texas at Austin aims to make thinner silicon carbide
films (50-100 nanometers thick) that will provide even higher
resolution images.
Related Links:
Taubner et al., "Near-Field Microscopy Through a SiC Superlens", Science 15 September 2006:
Vol. 313. no. 5793, p. 1595
DOI: 10.1126/science.1131025
"Superlens microscope gets up close" at PhysicsWeb.org
"Superlens breakthrough" at PhysicsWeb.org
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Experimental Methods & Techiques 
