Ill. --- The first practical fountain pen was invented
in 1884 by Lewis Waterman. Although pens with self-contained
ink reservoirs had existed for more than a hundred
years before his invention, they suffered from ink
leaks and other troubles. Waterman solved these problems
by inventing the capillary feed which produced even
ink flow. Now fountain pen history is repeating itself
in the tiny world of nanoscale writing.
Researchers at Northwestern University have demonstrated
writing at the sub-100 nanometer molecular scale
in fountain-pen fashion. They developed a novel atomic
force microscope (AFM) probe chip with an integrated
microfluidic system for capillary feeding of molecular
ink. Their results are published online by Small,
a new journal dedicated to breakthroughs in nanoscience
( http://dx.doi.org/10.1002/smll.200500027 ).
Dip-pen nanolithography (DPN) has been well-known
for its capability of high-resolution direct writing
as a bottom-up nanofabrication technique. The DPN
technique exploits controlled deposition of molecules
from an AFM tip to a surface. However, the need of
replenishing ink whenever exhausted has been a limiting
feature. Various attempts have been reported to overcome
such a drawback, but none of them reached molecular
patterns with features smaller than 100 nanometers.
The Nanofountain Probe (NFP) developed by Horacio
D. Espinosa, professor of mechanical engineering,
and his colleagues employs a volcano-like dispensing
tip and capillary fed solutions to enable sub-100
nanometer molecular writing. The NFP was microfabricated
on a chip to be mounted on commercially available
AFMs. The device consists of an on-chip reservoir,
microchannels and a volcano-like dispensing tip.
The microchannels are embedded in the AFM cantilevers
of the chip and the volcano dispensing tip has an
annular aperture to guide ink dispensing. The ink
on the reservoir is driven through the microchannel
via capillary action to reach the dispensing tip.
At present, the smallest feature width achieved with
the device is 40 nanometers.
The standard microfabrication techniques used for
the NFP chip -- an important feature of this development
-- provides scalability to massively parallel arrays
of probes and reservoirs for high throughput patterning
with multiple molecular inks.
"The writing capability of such NFP arrays with
chemical and bimolecular inks in fountain-pen mode
is unique," said Espinosa. "We believe the technology
will likely lead to many high-impact applications
in the field of nanosensors, biotechnology and pharmaceuticals."
In addition to Espinosa, other authors on the Small paper
are graduate student Keun-Ho Kim and research assistant
professor of mechanical engineering Nicolaie A. Moldovan,
both from Northwestern.
was supported by the Nanoscale Science and Engineering
Initiative of the National Science Foundation under
NSF Award Number EEC-011802.