In this photo, carbon and silicon sharpened to a nano-sized tip are integrated on the end of a silicon microcantilever for use in atomic force microscopy. The tip is heated to approximately 800 C, making it glow in this photo. |
Scientists
at the University of Pennsylvania, the University of Wisconsin-Madison
and IBM Research—Zurich have fabricated an ultrasharp silicon carbide
tip possessing such high strength that it is thousands of times more
wear-resistant at the nanoscale than previous designs. The new tip,
which is 100,000 times smaller than the tip of a pencil, represents an
important step towards nanomanufacturing for applications, including bio
sensors for healthcare and the environment.
The
search for hard materials to extend the working life of sharp tools is
an age-old problem that started with the first chisels used in stone
carving. Eventually iron was discovered and steel tools revolutionized
the era. Today, the challenge remains the same, but on a much smaller
scale—the need for a nano-sized tip that is both ultrasharp, yet still
physically robust, particularly under extreme temperatures and harsh
chemical environments.
“The
dream tip material for thermomechanical nanofabrication should have a
high hardness, temperature stability, chemical inertness, and high
thermal conductivity,” said Dr. Mark Lantz, manager in storage research
at IBM Research—Zurich. “With this novel tip we continue to deliver on
IBM’s vision of a smarter, instrumented world with microscopic sensors
monitoring everything from water pollution to patient care.”
Extending
their previous successful collaboration, scientists at the University
of Pennsylvania, the University of Wisconsin-Madison and IBM
Research—Zurich have developed a new, resistant nano-sized tip that
wears away at the rate of less than one atom per millimeter of sliding
on a substrate of silicon dioxide. This is much lower than the wear rate
of conventional silicon tips and its hardness is 100 times greater than
that of the previously state-of-the-art silicon oxide-doped
diamond-like carbon tips developed by the same collaboration last year.
“Compared
to our previous work in silicon, the new carbide tip can slide on a
silicon dioxide surface about 10,000 times farther before the same wear
volume is reached and 300 times farther than our previous diamond-like
carbon tip. This is a significant achievement that will make
nanomanufacturing both practical and affordable,” said Prof. Robert W.
Carpick, University of Pennsylvania.
To
create the new tip, scientists developed a process whereby the surfaces
of nanoscale silicon tips are exposed to carbon ions and then annealed
so that a strong silicon carbide layer is formed, but the nanoscale
sharpness of the original silicon tip is maintained. Although silicon
carbide has long been known as an ideal candidate material for such
tips, the unique carbon implantation and annealing process made it
possible to harden the surface while maintaining the original shape and
ensuring strong adhesion between the hardened surface of the tip and the
underlying material—similar to how steel is tempered to make it harder.
Consisting
primarily of carbon and silicon, the tip is sharpened to a nano-sized
apex and integrated on the end of a silicon microcantilever for use in
atomic force microscopy. The importance of the development lies not only
in its ability to maintain the sharpness of the tip and its resistance
to wear, but also in its endurance when sliding against a hard substrate
such as silicon dioxide. Because silicon—used in almost all integrated
circuit devices—oxidizes in the atmosphere, forming a thin layer of its
oxide, this system is among the most relevant for emerging applications
in nanolithography and nanomanufacturing applications.
More
specifically, scientists hope that the new tip can be used to fabricate
bio sensors, for example for managing glucose levels in diabetic
patients or monitoring pollution levels in water.
Within this vacuum chamber IBM scientists fabricated an ultra sharp, silicon carbide tip possessing such high strength that it is thousands of times more wear-resistant at the nanoscale than previous designs. The new tip, which is 100,000 times smaller than the tip of a pencil, represents an important step towards nanomanufacturing for applications, including bio sensors for healthcare and the environment. |
Probe-based
technologies are expected to play a predominant role in many such
technologies. However, poor wear performance of the tip materials used
so far, especially when slid against silicon oxide, have previously
limited their usefulness for experimental applications.
The next step for scientists is to begin testing the new tip for use in applications, starting with nanomanufacturing.
This
research was partially funded by the Nano/Bio Interface Center of the
University of Pennsylvania through the National Science Foundation under
grant CMMI-0826076.
Wear-Resistant Nanoscale Silicon Carbide Tips for Scanning Probe Applications