Page 298 - Mechanical design of microresonators _ modeling and applications

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Microcantilever and Microbridge Systems for Mass Detection

Microcantilever and Microbridge Systems for Mass Detection 297

Figure 6.1 Scanning electron microscope (SEM) imaging of randomly dispersed
molecules on microcantilevers. (Courtesy of Dr. Ilic, the Cornell NanoScale Facility.)

photothermal excitation and interferometric readout. Ilic, Yang, and
15
Craighead reported the use of paddle nanocantilever arrays that were
coated with antibody agents in order to detect baculoviruses in solution
with mass sensitivities of 10 í19 g/Hz. The designs and associated
experimental characterization enabled detection of the mass of a single
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virus which is 3 × 10 í15 g approximately. Ilic et al. designed and char-
acterized paddle cantilever and bridge designs that were fabricated of
polycrystalline silicon and silicon nitride. These structures were cov-
ered with gold dots as small as 50 nm in diameter, which enabled
localized mass detection of a thiol monolayer.
An important performance metric factor of nanoresonators is the
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quality factor, which quantifies losses. Evoy et al. analyzed the dis-
sipation by temperature-dependent internal friction in paddle bridge
nanoresonators operating in the megahertz range, by investigating the
shifts in both the flexural and torsional resonant frequencies. Yasumara
18
et al. performed Q measurements that reached levels of 30,000 for
170-Å-thick, 5-“m-wide, and 80-“m-long microcantilevers. Yang, Ono,
19
and Esashi analyzed the losses and associated Q factors of water
adsorption by means of 60 to 170-nm-thick cantilevers. Tamayo
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et al. proposed a Q control method for liquid biosensing applications
where magnetic excitation and photodetection were applied in experi-
ments that were capable of recording quality factors 3 orders of mag-
nitude higher than the regular ones.
Figures 6.1 through 6.7 are pictures of various resonant microdevices
(one also shows the corresponding resonant response) that have been
designed and experimentally tested for mass deposition detection by
Dr. Rob Ilic and coworkers at the Cornell NanoScale Facility.
This chapter briefly analyzes the main traits of detecting mass
deposition by using the static approach, but mainly focuses on the
resonant shift method of detecting mass addition. Constant rectangular
and variable-cross-section microcantilevers and microbridges are
studied in conjunction with their abilities to capture the effects of added
mass that can be immobilized in either pointlike or layerlike manner.

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