providing not only the oxygen potential but also information on the gas species. The
integration of many sensor chips on one substrate (as shown in Figure 2.19b) opens
the gate for further far-reaching possibilities, especially if the individual sensing
elements are coated with a second material of varying thickness [8,9] or if the
sensing elements are maintained at different temperatures [10,9]. A typical example
of the influence of a coating at the surface of the sensor is shown in Figure 2.20,
where the sensor signal is plotted against the concentration of the gas to be
determined (in this case, benzene and propane). Owing to the different sizes of
these two molecules, the coating has an individual influence on the signal, and the
subsequent use of some mathematics allows the gas species and its concentration to
be determined. However, this approach is clearly valid only for those species where
the calibration curves already exist.
2.2.4
Scaling of Vibrations
Looking at mechanical properties of nanorods and nanotubes gives important
insights of phenomena related to the reduction of the dimensions. Not only
electrical properties, the transition from diffusive electrical conductivity to ballistic
conductivity (see Chapter 10), are influenced, but also the mechanical behavior. In
this case, just the reduction of the dimensions is sufficient to result in interesting
phenomena, leading, possibly, to new applications.
The frequency of the basic bending vibration mode n 1 of a cylindrical rod, fixed on
one end, is given by:
n 1 ¼
p
32
d
l
2
E
r
1
2 ¼
p
32
a
1
l
E
r
1
2
ð2:5Þ
Figure 2.20 Calibration curves for bare and
10-nm SiO 2 -coated gas sensors using SnO 2 to
prepare the sensing nanoparticles. As the
influence of the coating is dependent on the gas
species, the nature, concentrations, and/or
relative proportions of the two species can be
determined [8].
20j 2 Nanomaterials and Nanocomposites
integration of many sensor chips on one substrate (as shown in Figure 2.19b) opens
the gate for further far-reaching possibilities, especially if the individual sensing
elements are coated with a second material of varying thickness [8,9] or if the
sensing elements are maintained at different temperatures [10,9]. A typical example
of the influence of a coating at the surface of the sensor is shown in Figure 2.20,
where the sensor signal is plotted against the concentration of the gas to be
determined (in this case, benzene and propane). Owing to the different sizes of
these two molecules, the coating has an individual influence on the signal, and the
subsequent use of some mathematics allows the gas species and its concentration to
be determined. However, this approach is clearly valid only for those species where
the calibration curves already exist.
2.2.4
Scaling of Vibrations
Looking at mechanical properties of nanorods and nanotubes gives important
insights of phenomena related to the reduction of the dimensions. Not only
electrical properties, the transition from diffusive electrical conductivity to ballistic
conductivity (see Chapter 10), are influenced, but also the mechanical behavior. In
this case, just the reduction of the dimensions is sufficient to result in interesting
phenomena, leading, possibly, to new applications.
The frequency of the basic bending vibration mode n 1 of a cylindrical rod, fixed on
one end, is given by:
n 1 ¼
p
32
d
l
2
E
r
1
2 ¼
p
32
a
1
l
E
r
1
2
ð2:5Þ
Figure 2.20 Calibration curves for bare and
10-nm SiO 2 -coated gas sensors using SnO 2 to
prepare the sensing nanoparticles. As the
influence of the coating is dependent on the gas
species, the nature, concentrations, and/or
relative proportions of the two species can be
determined [8].
20j 2 Nanomaterials and Nanocomposites