brittle materials come apart in large uncontrolled
chunks or they simply fracture completely. The researchers
are trying to control the machining process so that
well-defined, accurate, microscopic patterns can be
created in brittle materials.
Demands for smaller channels
in glass for micro fluids, dimples to create tiny
chemical reservoirs and MEMs – microelectromechanical
systems, fuel the need to find quick, inexpensive
ways to create these tiny devices.
Marsh; Chris J. Morgan, graduate
student at University of Kentucky, and R. Ryan Vallance,
assistant professor, George Washington University,
begin with polycrystalline diamond on Carborundum
-- a commercially available product -- to create miniature
drills and end mills using microelectro discharge
machining. EDM removes parts of the millimeter diamond
surface by sputtering them off to fashion the tool.
They use this noncontact method because the tools
are tiny and fragile. The Carborundum base becomes
the shaft of the drill or mill end.
The researchers describe how
the tools are created and used in an online edition
of the Journal of Micromechanics and Microengineering,
which will be available in hard copy on Dec. 10. The
engineers take advantage of the uneven surface created
by diamond removal at the microscopic level and use
the rough surface for cutting.
The tools spin exceptionally
fast to remove material to create dimples or channels.
The fast spinning, however, does not mean that the
carving takes place rapidly. The tools are so small
and so fragile that only very slight pressure, about
as much as a paperclip exerts, sculpts the surface.
It can take as long as an hour to produce one dimple
a half millimeter in diameter.
Slow as that may be, the process
would be faster than the current process which employs
photolithography. Tiny tools can be designed and manufactured
in less than a day and used to create the desired
surface immediately. Photolithography requires many
more steps and much longer lead-time.
While photolithography is typically
only used on silicon chips or wafers, the tiny tools
will work on glass, emeralds, sapphires, ceramics
of all kinds and calcium fluorite. There are applications
in optics, DNA analysis and biocomputers on a chip.
Tiny tools can also create
shapes that photolithography cannot. In photolithography,
surface shapes have to be built up by layer after
layer of material creating a stair-step surface. Tiny
tools grind and shape smooth surfaces although they
cannot yet achieve the nano-size structures available
"This really is a way
to get shapes that we cannot get any other way,"
Currently, the researchers
are using existing machines designed for larger equipment
to operate the tools, but they hope to develop a tabletop
appliance. Equipment donations from Professional Instruments
and Lion Precision in Minnesota and Panasonic supported
this work. The National Science Foundation funded
Contact: A'ndrea Elyse Messer