Biomedical Engineering Reference
In-Depth Information
Penza
. [36] demonstrated vertically aligned MWCNTs layers
RF-PECVD synthesized on Fe-coated alumina substrates as
et al
forest-
like
nanostructure. A miniaturized CNT-based gas sensor array was
developed for monitoring landfill gas (LFG) at a temperature of
150°C. The sensor array was composed of four sensing elements with
unmodified CNT, and CNT loaded with 5 nm nominally thick sputtered
clusters of Pt, Ru, and Ag. Chemical analysis of the multicomponent
gas mixtures constituted of CO
was
performed by array sensor responses and pattern recognition based
on Principal Component Analysis (PCA). PCA results demonstrated
that the metal-decorated and vertically aligned CNT sensor array
is able to discriminate the NO
, CH
, H
, NH
, CO, and NO
2
4
2
3
2
presence in the multicomponent
mixture LFG. The size of metal clusters decorating CNT top-surface
varied in the range of 5-50 nm. Functional characterization based on
electrical charge transfer sensing mechanisms in the metal-modified
CNT chemoresistors array demonstrated high sensitivity providing
minimal sub-ppm level detection down up to 100 ppb NO
2
, at
2
150°C.
9.5.2
FETs
FET devices based on semiconducting CNTs as conductive channel
between two electrodes (source
S
and drain
D
) with chemical gating
modulated by a third back-gate (
) electrode have been designed,
modeled and fabricated for molecular electronics [268-271] and
biochemical sensing applications [33, 34, 93, 143, 151, 154, 203, 204,
207, 210, 211, 242, 272-278, 280-282]. Avouris [268] and Dekker
et al.
G
[269] first reported the fabrication of a CNTFET in 1998. These
CNTFETs are composed of individual [268, 269] or random networks
[271] of CNTs between source (
S
) and drain (
D
) electrodes with a
Si back-gate (
G
) separated by a insulating layer (e.g., SiO
). Under a
2
constant
bias voltage, the conductance of the semiconducting
CNTs can be modulated by applying an electrical potential to the gate
electrode. The transport properties of the random CNT networks
[271] of SWCNTs integrated into a FET structure are typically, at
low nanotube densities (
S
-
D
−2
~
1
µ
m
),
p
-type semiconductor with a
2
field-effect mobility of about 10 cm
/V s; while at higher densities
~
µ
−2
2
(
/V s. In this
case, the CNTFET behaves as a semiconductor with a high current
density. Studies on the modeling of CNTFET have been reported as
well [279].
10
m
), the field-effect mobility can exceed 100 cm
