IEEE Robotics & Automation Magazine - June 2013 - 84

nm
100

100608Topography038

50
4

25
2

0
-25

4
nm
(a)

100608Error Signal038

80
6

0
-40

-80
0
0

4
nm
(b)

Figure 3. AFM images made on a cross section of PDMS GNM.
(a) Topography and (b) error signal of the AFM image.

1.0
AuPDMS (GNM)
PDMS

Intensity (a.u.)

0.8
0.6
0.4
0.2
0.0
400

500
600
Wavelength (nm)

700

Figure 4. Experimental UV-visible spectra of the GNM sample
used for the pressure sensor. This, with Figure 3, indicates the
presence of gold micro/nanoparticles.

IEEE ROBOTICS & AUTOMATION MAGAZINE

june 2013

A period of two days is necessary to reach the solid/
elastomeric state of the PDMS without heating. The prototype is obtained by depositing the GNM of a specific
gold concentration. The tapered fiber is a coated silica/
core silica multimode optical fiber (FG-365-LER Thorlabs
fiber) tapered by a controlled system. The system makes it
possible to uniformly pull the fiber by rotating it and
simultaneously by burning the jacket and the cladding for
some seconds (the number of seconds is related to the
intensity and to the distance of the flame). This process
improves a 1 cm of the total tapered profile with about
5 mm of central core region without cladding.
Figure 2(a) and (b) shows the longitudinal section of
the prototype without and with the applied pressure
force, respectively. The piece of GNM behaves as a cap
and covers the remaining upper part of the tapered fiber.
In this way, the contact interface becomes more efficient
for the light coupling between the tapered fiber and
GNM. Figure 2(c) and (d) illustrates the longitudinal section of the optimized prototype without and with the
applied pressure force, respectively: the GNM deposition
is controlled to perfectly cover the upper half of the
tapered fiber, as indicated in the cross section of the core
region of Figure 2(d). The optimized total thickness of
the GNM layer was found to be equal with half diameter
of the fiber. The main physical principle of the sensor is
illustrated in Figure 2(d), where we can observe the
importance of the contact boundary between the fiber
and GNM after the application of the pressure: in this
case, the gold nanoparticles near the contact surface
increase the intensity of light coupling. Two days are adequate to transform the deposited liquid GNM into a solid
elastomeric material. Because of the controlled GNM
PDMS deposition, the contact interface increases the efficiency of the sensor since thewhole tapered region is
totally embedded in GNM.
The atomic force microscopy (AFM) images of the
cross section of the GNM (Figure 3) provide information
about the dimensions of the nanofillers inside the PDMS
nanocomposite material. A nonuniform nanoparticles
dispersion is observed.
Previous studies demonstrate that the use of the PDMS
polymer helps to generate gold nanoparticles by reducing
the gold precursor [24]-[25]. In our study, we establish a
high gold concentration that preserves the elastomeric
properties of the GNM for real-time pressure detection.
In this specific case, we use a chloroauric acid salt as a
gold precursor in water solution [Mw(HAuCl4) =
339.785g/mol; [HAuCl4] = 0.01M] with a concentration
of approximately 10% by weight. The presence of gold
verified in Figure 3 is also proved in Figure 4, representing the experimental ultraviolet (UV)-visible spectra of
the GNM sample used for the pressure sensor prototype;
pure PDMS does not show any absorbance in the visible
region, whereas Au-PDMS (GNM) has an absorbance
centered at m , 530 nm. The full characterization of the

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - June 2013