Page 297 - Mechanical design of microresonators _ modeling and applications

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Microcantilever and Microbridge Systems for Mass Detection

296 Chapter Six
microcantilevers whose deflections can be as small as 1 nm (Britton
2
3
et al. or Baselt et al. ).
Resonant nano- and microcantilevers are the main tool of choice in
conducting resonant mass detection, and the modeling approach
comprises resonant frequency evaluation (of both the original system
and the altered system), systems sensitivity, and evaluation of the
5
4
deposited mass quantity (Dufour and Fadel ). Garcia et al. proposed a
shape optimization method for microcantilevers that can be utilized in
mass detection and atomic force microscopy applications. Examples of
mass detection through resonant methods are quite numerous, and
the following sample inevitably mentions just a few. Brown et al. 6
presented the cantilever-in-cantilever microresonator which was
utilized to monitor the levels of external (viscous) damping through
changes in air pressure by means of magnetic actuation and piezo-
7
resistive detection. Kawakatsu et al. studied the design and per-
formance of nanometric oscillators built as head-and-neck structures
that can operate in the 0.5-GHz domain and can be implemented in
8
scanning probe microscopy. Rogers et al. used microcantilevers with
integrated piezoelectric film for both actuation and sensing to detect
mercury vapors that were adsorbed onto a gold layer with concen-
trations as low as 93 parts per billion (ppb). Pinnaduwage et al. 9
reported the use of silicon microcantilevers with gold surface and a self-
assembled monolayer acid to capture the presence of plastic explosive
substances in the range of 10 to 30 parts per trillion (ppt).
10
Ilic et al. designed and studied the resonant response of an array of
silicon nitride cantilevers that were capable of detecting the attachment
of 16 cells (the equivalent of 6 × 10 –12 g of mass) of Eschericia coli cells
on antibody layer under ambient conditions. Similar cantilevers were
11
reported by Ilic et al. in applications that captured the presence of
heat-killed E. coli cells attaching to a reactive E. coli antibody substance
coated on the microcantilevers. The experiment enabled detection of a
single cell (a mass of 665 fg was calculated from the resonant frequency
shift, which was consistent with other cell mass evaluations). Sekaric
12
et al. studied the performance of thin-film crystalline-diamond
nanoresonators that operated in the 640-MHz range due to the elevated
sound velocity of the diamond and the very small cantilever dimensions
(lengths in the micrometer range and thickness of 80 nm). Paddle
13
nanostructures were utilized by Sekaric et al. in an experimental
design which used laser-light pumping to diminish the viscous damping
losses in air and therefore to substantially improve the quality factors.
Constant rectangular cross-section and paddle microcantilevers with
14
thicknesses of 50 to 100 nm were analyzed by Lavrik and Datskos to
detect chemisorption of thiol molecules at the femtogram level by using

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