High Frequency Cantilevers
as a tool in Nanotechnology
E. Farnault*, M. Hoummady, E. Rochat, and H.
Fujita
Institute
of Industrial Science, University of Tokyo
This is an abstract
for a poster to be presented at the
Fifth
Foresight Conference on Molecular Nanotechnology.
There will be a link from here to the full article when it is
available on the web.
Scanning force microscopy is now a common tool for imaging,
modifying, and manipulating samples with nanometer-scale
resolution. Despite dynamic modes, including non-contact and
intermittent-contact modes, avoid to damage soft surfaces such as
organic materials, near-atomic resolution is not reproducible
with any kind of samples. In order to combine local and highly
sensitive detection, we are developing high frequency
microfabricated mechanical oscillators. Some of their advantages
are the following:
- lower minimum detectable force gradient
- lower settling time
- lower thermal motion
Small mass cantilevers hold good enough compromise between low
stiffness and high frequency. Separate item fabrication
techniques often used expansive microelectronics equipment, such
as focused-ion-beam or electron-beam systems. In our previous
work, we developed an original method based on local
electrochemical etching of a tungsten wire. Fabrication of
cylindrical nanomechanical oscillator consisting of a ball
supported by a neck has been achieved. According to
nanocantilever dimensional parameters (neck radius: 25 nm, neck
length: 200 nm, ball diameter: 1 micron), the estimated resonant
frequency was roughly 300 MHz, which is high enough to foresee
applications in molecular nanotechnology.
Regarding batch-processed microsensors, higher harmonics of
conventional single crystal silicon cantilevers have been used to
operate at higher frequencies. For instance, a 300
kHz-fundamental frequency cantilever is able to vibrate in air at
14 MHz on its 6th flexural mode. For each eigenmode, cantilever
dynamics was analyzed at different tip-sample spacing by sweeping
the frequency through the cantilever free resonance. Regarding
tip-sample interactions, first results showed force gradient
detection sensitivity 7-fold increased using the second harmonic.
Moreover, measurements using higher flexural modes induce weaker
hydrodynamic damping that occurs during relative motion between
cantilever and sample. Thus the method overcomes energy
dissipation effect that often prevents measurements at the
molecular scale in an aqueous environment. The technique
described here takes things step by step in order to perfect non
conventional optical detection system and control electronics in
the frequency range 1 MHz - 100 MHz.
*Corresponding Address:
Etienne Farnault, Laboratory for Integrated Micro-Mechatronic
Systems (LIMMS), Institute
of Industrial Science, the University of Tokyo, 7-22-1
Roppongi, Minato-ku, Tokyo 106, JAPAN, ph: +81-3-3402-9568, fax:
+81-3-3402-9568, e-mail: [email protected]
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