Because of the rate of production, the
MCA is not cost-competitive with current
lighting options, but since Congress mandated that incandescent lights be phased
out in 2014, the research team believes
that there will be a much greater acceptance of MCA technology in the future.
It is suitable for light production and is
ideal for on-chip special chemistries. By
using the linear microchannel design, as
employed in an MCA lighting panel, a
large number of parallel receptors can be
placed within a small area to perform a
variety of sensory activities, depending
upon the chemical composition within the
Blocked holes boost light on the nanoscale
PRINCETON, N.J. – Capping a hole
should block light transmission through
that hole, right? Not on the nanoscale. In
fact, placing a metal cap over a small hole
in a metal film does not stop light from
passing through the hole, but rather enhances its transmission.
This finding by scientists at Princeton
University could have significant implications and various uses, particularly in optical instrumentation.
In an example of the “twists” in physics
that can occur at very small scales, electrical engineer Stephen Chou and his colleagues made an array of tiny holes in a
thin metal film, then blocked each hole
with an opaque metal cap. When they
shined light into the holes, they found that
as much as 70 percent more light came
through when the holes were blocked than
when they were open.
Chou said that the result might require
scientists and engineers to rethink techniques they use to block all light transmission. In very sensitive optical instruments
– for example, spectrometers, telescopes,
microscopes and other optical detectors –
it is common to coat a metal film onto
glass with the intention of blocking light.
Dust particles, which are unavoidable in
metal film deposition, inevitably create
tiny holes in the metal film, but these holes
have been assumed to be harmless because
the dust particles become capped and surrounded by metal, which was thought to
block the light completely.
Chou said that this assumption is not
correct; rather, the plug greatly enhances
the leakage. He explained that in his own
field of nanotechnology, light often is used
to carve ultrasmall patterns in silicon or
other materials. Thin metal film patterns
on a glass plate serve as a mask, directing
light through certain locations and blocking others. Given the new finding, engineers ought to examine whether the mask
blocks the light as expected, Chou said.
These electron microscope images show an experiment demonstrating that blocking a hole in a thin
metal film could cause more light to pass through
the hole than leaving it unblocked does. The top
image shows an array of holes with gold caps, each
of which is 40 percent bigger than the hole on
which it sits. The bottom image shows a cross-section view of one hole with the cap sitting on top.
Surprisingly, a hole covered with the cap allows
more light to be transmitted through the film than a
hole without the cap. Courtesy of Stephen
Chou said the metal disk acts as a sort
of antenna that picks up and radiates electromagnetic waves. In this case, the disks
pick up light from one side of the hole and
radiate it to the opposite side. The waves
travel along the surface of the metal and
leap from the hole to the cap or vice versa,
depending upon which way the light is
The findings were published in Optics
Express ( http://dx.doi.org/10.1364/OE.
The research group is investigating how
the effect could be applied to enhancing
the performance of ultrasensitive detectors.