Atomic force microscope microcantilevers used as humidity sensors

Atomic force microscope microcantilevers used as sensors
for monitoring humidity
C. Steffens a,b,⇑
, A. Manzoli b
, F.L. Leite a,c
, O. Fatibello a,d
, P.S.P. Herrmann a,b
a
Department of Biotechnology, Federal University de São Carlos (UFSCar), SP 13565-905, Brazil
b
National Nanotechnology Laboratory for Agribusiness, Embrapa Instrumentation, São Carlos, SP 13560-970, Brazil
c
Department of Physics Mathematics and Chemistry (DFMQ), Federal University of São Carlos (UFSCar), Sorocaba, SP 18052-780, Brazil
d
Department of Chemistry, Federal University of São Carlos (UFSCar), São Carlos, SP 13565-905, Brazil
a r t i c l e i n f o
Article history:
Received 20 January 2013
Received in revised form 8 July 2013
Accepted 23 July 2013
Available online 2 August 2013
Keywords:
Microcantilever sensor
Humidity
Polyaniline
Sensitivity
a b s t r a c t
A microcantilever sensor is presented. Functionalization of the cantilever with a polyaniline (PANI) sen-
sitive layer and its use as a humidity sensor were investigated. Polyaniline was produced by interfacial
synthesis and the sensitive layer was deposited on the microcantilever surface by the spin-coating
method. The microcantilever deflection at various levels of relative humidity (RH) was read by means
of the optical lever of an atomic force microscope (AFM Veeco Dimension V). A range of RH from 20%
to 70% was introduced into the AFM chamber by mixing streams of dry and wet nitrogen. The sensitivity
and reversibility of the sensors were assessed at various RH and temperatures (10, 20 and 30 °C). A large
deflection was observed in the coated microcantilever sensors, with faster response time at 10 °C and bet-
ter sensitivity and reversibility at 30 °C. These results demonstrate that the spin-coated microcantilever
can be used as a sensor to detect relative humidity at various different temperatures.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
The development of microelectromechanical systems (MEMs)
has motivated the construction of new miniature sensing systems
of high selectivity and sensitivity [1]. In this context, the cantilever
sensors used in atomic force microscopy (AFM) have emerged as
very sensitive and selective miniature devices [2–4]. The working
principle of microcantilever sensors is based on the adsorption of
analytes on a sensitive surface, which usually induces a surface
stress and an increase in microcantilever mass [5–7]. These sensors
have several advantages, compared to conventional analytical
techniques, such as small analyte volume (lL), high sensitivity,
low cost, simple and non-hazardous procedures and fast response
[3,8]. The sensitivity of these microcantilever sensors depends on
the sensitive layer, which reacts with the target molecules [9–11].
Microcantilever sensors used to measure humidity need to
show good sensitivity over a wide humidity range, low hysteresis,
good reproducibility and durability. A way of potentially satisfying
these requirements is to use a thin layer of conductive polymer as
the sensitive layer [12,13]. Conducting polymers suffer many
changes when exposed to an analyte, such as modifications of
the backbone conformation, solvation effects on the polymer chain
and the attraction of dopant counter ions or transfer of electrons.
Thus, changing the electron mobility of charge carriers and on
swelling of the polymer matrix are converted into electrical and/
or mechanical signals [14]. The conducting polymer that is most
promising as a sensitive layer is polyaniline (PANI) [15–17].
The great interest in PANI is due to its low cost, ease of synthesis
and doping in aqueous solution, environmental stability, electronic
properties and moderately high conductivity relative to other con-
ducting polymers. PANI is the only conducting polymer whose con-
ductivity is controlled by the doping level [15]. In the undoped
reduced state, the conductivity is very low but can be increase by
ten orders of magnitude or more by exposure to doping acids. This
doping process can be reversed during dedoping by exposure to
bases [18]. PANI exhibits the fastest adsorption/desorption of va-
pors among the tested polymeric materials [19,20], and is a suit-
able material to be investigated as a sensitive layer to detect
water molecules [21].
Several techniques have been reported for the functionalization
of the surface of a microcantilever with polymers. Lahav et al. [12]
used an electrochemical method to deposit PANI on the cantilever
and detected a deflection on electrochemical oxidation/reduction
of the PANI film. Fig. 1 schematically represents the mechanical
deflection of the cantilever and the vertical displacement (Dz) of
the tip during the redox reactions occurring when exposed to var-
ious stimuli. However, this method of deposition is not as simple as
the spin-coating technique, in which the conducting polymer
0167-9317/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.mee.2013.07.015
⇑ Corresponding author at: Department of Biotechnology, Federal University de
São Carlos (UFSCar), SP 13565-905, Brazil. Tel.: +55 5435209000; fax: +55
5435209090.
E-mail addresses: clarices@uricer.edu.br, claristeffens@yahoo.com.br (C. Stef-
fens).
Microelectronic Engineering 113 (2014) 80–85
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solution is spread on a rotating substrate. Spin-coating can some-
times produce nonuniform layers, which impair the sensor re-
sponse, affecting the reproducibility and suitability of the sensor
system for a particular application. Several studies in the literature
[22,23] also reported the use of the spin coating technique for sen-
sors coatings with promising results and suggest that achieving
uniform coatings on cantilevers using spin-coating procedures
was challenging.
However, there are contradictory reports. Even so, there are no
published studies in which this simple technique was used to func-
tionalize the microcantilever with PANI.
Thus, the innovatory part of the present study was to develop a
microcantilever sensor functionalized with PANI by a spin-coating
technique, whose deflection response to humidity was monitored
optically, using an atomic force microscope (AFM). The PANI was
produced by interfacial synthesis and was characterized by FTIR,
XRD and contact angle measurements. The deflection of microcan-
tilevers with and without the PANI coating at various relative
humidities (RH) was recorded at these temperatures (10, 20 and
30 °C).
2. Experimental
Rectangular silicon microcantilevers were purchased (NT-MDT),
with resonance frequency 4–17 (±13) kHz, spring constant 0.03–
0.13 N/m and length 350 lm, width 30 lm and thickness 0.5–
1.5 lm. The silicon microcantilevers were immersed in Piranha
solution, 4:1 (H2SO4/H2O2) for 30 min to remove all impurities,
then rinsed with distilled water several times, dried in an oven
at 50 °C for 10 h and stored in a vacuum desiccator.
2.1. Interfacial syntheses and polyaniline film characterization
All reagents used for chemical synthesis were of analytical
grade and used as received. For interfacial polymerization, the
monomer (aniline) was dissolved in dichloroethane and the oxi-
dant (ammonium persulfate) in 1 M HCl dopant acid solution.
Next, the oxidant solution was poured carefully on to the monomer
solution, in order to avoid mixing the phases; the interfacial reac-
tion ran for 2 h in a sealed bottle at room temperature. The solid
product of this reaction was filtered (Millipore 25 lm filter paper)
and rinsed with methanol and Milli-Q water in abundance. It was
then dried for 12 h in a vacuum desiccator at room temperature
and the resulting powder was stored in amber vials to protect it
from light and oxygen.
The chemical composition of the PANI (doped and dedoped)
was identified by FTIR (Fourier transform infrared) spectroscopy,
with a Perkin-Elmer Spectrum 1000 spectrophotometer. All mea-
surements were performed in the range 4000–600 cmÀ1
, scanned
16 times in steps of 2 cmÀ1
, on a KBr pellet containing about
1.0% by weight of the sample.
The hydrophobicity and hydrophilicity of the surface of the sil-
icon microcantilever, with and without a PANI film, were deter-
mined by measuring the contact angle of a water drop (Milli-QÒ
,
surface tension 72.7 mJ/m2
), using a contact-angle meter (KSV
Instruments). The measurements were performed in triplicate, at
25 °C and 45% R.H., after depositing around 4.0 lL water with a
Hamilton syringe.
X-ray diffractograms (XRD) were collected in a Shimadzu XRD
6000 X-ray diffractometer with a CuKa radiation source. Powder
samples of both doped and dedoped PANI produced by interfacial
synthesis were scanned. Scans were executed from 5° to 35° (2h)
at a speed of 2 minÀ1
.
The morphology and roughness of the PANI films deposited on
the microcantilever surfaces were analyzed with a Dimension V
(Veeco) atomic force microscope (AFM), using a silicon nitride tip
attached to a cantilever with a spring constant of 42 N/m and res-
onance frequency of 285 kHz. All images were obtained in tap-
ping™ mode at a scan rate of 1 Hz. The images were processed
with the aid of GwydionÓ 2.1 data analysis software.
2.2. Microcantilever functionalization
The microcantilevers were coated with a sensitive layer of PANI
by the spin-coating method. The HCl-doped PANI solution em-
ployed was previously prepared from the powder obtained in the
synthesis described above. The dedoped PANI was prepared by
stirring the doped PANI in ammonium hydroxide (0.1 M NH4OH)
for 12 h and then filtering (filter paper) and washing the precipi-
tate with Milli-Q water. The films were cast on the surface of the
microcantilever with a spinner. After the microcantilever was spun
at 500 rpm for 8 s, 3.0 lL of PANI solution was deposited on its sur-
face; the spinning rate was then increased to 1000 rpm for 10 s and
finally to 3000 rpm for 1 min. The experiments were performed at
room temperature 25 ± 2 °C and relative humidity (RH). After-
wards, the coated microcantilever sensors were dried in a vacuum
desiccator for 12 h at room temperature.
2.3. Deflection measurement in microcantilevers
The spring constants were measured in the force curve module
of the Veeco Dimension V AFM, at room temperature. The voltage
of the microcantilever sensor was measured by monitoring the po-
sition of a laser beam focused on its tip and reflected to a four-
quadrant photodiode, in the static mode. The voltage generated
in the photodiode was converted into motion of the light beam
in nanometers, which was transformed into deflection of the tip.
The microcantilever sensor deflection was measured at various
RH in a closed chamber in the static mode. The humidity in the
chamber was controlled by passing dry nitrogen Analog flow mass
controller at a fixed flow rate of 0.1 L/min through a gas bubbler
tube containing water.
The influence of the temperature (10, 20 and 30 °C) on the re-
sponse of these microcantilever sensors to humidity was assessed.
Fig. 1. Sketch of cantilever mechanical deflection during redox reaction between environmental stimuli and the sensitive layer (upper surface of the microcantilever coated
with polyaniline). Reprinted with permission [12].
C. Steffens et al. / Microelectronic Engineering 113 (2014) 80–85 81

The experiment was maintained at a constant temperature
(±0.2 °C) by performing it in an ultrathermostatic bath (Nova Ética,
521/2D).
The sensitivity (S) to humidity and reversibility (g) of the micro-
cantilever sensors were calculated from Eqs. (1) and (2) [24]:
S ¼
D À D0
D
Ã 100 ð1Þ
g ¼
D À Df
D À D0
Ã 100 ð2Þ
where D0 is the initial deflection of the microcantilever sensor, D
the deflection after exposure to a flow of dry nitrogen and Df the
minimum deflection after the exposure to wet nitrogen from a
water bubbler.
3. Results and discussion
3.1. PANI characterization
The characterization of the sensitive layer is very important for
adjusting its doping, crystallinity and hydrophilicity/hydrophobic-
ity in the process of functionalizing mechanical sensors aimed at
the detection of humidity.
FTIR analysis allows the identification of chemical groups and
the investigation of polymer composition; thus the spectrum of
PANI deposited by interfacial synthesis is shown in Fig. 2. The band
located at 1100 cmÀ1
, which indicates the vibrational mode of pro-
tonated amines, indicates that the imine nitrogens of the PANI
doped with HCl are protonated. There is a significant rise in this
band in the FTIR spectrum for doped PANI, which according to Ping
et al. [25] is due to the effect of the positive charge on the polymer
chain, inducing a dipole moment. The absorption bands at 3450
and 3250 cmÀ1
are attributed to symmetric deformation of the
groups N–H and C–H, respectively. The absorption peaks at 1590
and 1500 cmÀ1
are related to the symmetric deformation of the
C@C bonds of the quinoid and benzenoid aromatic rings, respec-
tively. Around 3250 cmÀ1
, two extended bands of differing intensi-
ties are present, which are attributed to the H bonding and the
N–H2 asymmetric stretching vibration, also observed in a study
performed by Paschoalin et al. [26]. According to Angelopoulos
et al. [27,28] the interchain H-bonds between amine and imine
groups, in the emeraldine basic form of the polymer result in a
molecular conformation showing a torsion of the adjacent rings,
so that the benzoid and quinoid rings of the PANI are no longer
coplanar. The peaks at 1350 and 1256 cmÀ1
, the latter resembling
a broad band, are attributed to symmetrical deformation of (C–N)+
secondary amine linked to aromatic groups and to the –NH+
groups, indicating that the PANI is in the doped salt state.
X-ray diffraction was used to evaluate the fine structure, crys-
tallinity and orientation of the polymer. Fig. 3 shows the diffraction
patterns of the PANI emeraldine oxidation states (salt and base)
produced by interfacial synthesis. The diffractograms of dedoped
PANI show a pattern characteristic of an amorphous polymer,
whereas these of doped PANI show the presence of four shoulders
located at 2h = 9°, 15°, 21° and 25°. These experimental peaks are
identical those reported in other work by Chen & Lee [29] and Ste-
jskal & Gilbert [30], indicating an increase in the crystallinity of
PANI when doped with HCl.
In Fig. 3 it can be seen that an improvement has occurred in the
definition of the peaks in the doped polymer, whose area has in-
creased especially at the peak around 25°, suggesting that crystal-
lization was promoted in the doped layer. As the interfacial
reaction used to synthesize the PANI is characterized by the forma-
tion of nanofibers [31], a narrow and intense peak was observed at
6.5°, which indicated the presence of these nanofibers. Yin et al.
[32], also observed the presence of the peak around 6.5°, in sam-
ples of PANI nanofibers. In the same study, the authors found that
the peak at 2h = 21° should be due to periodicity parallel to the
polymer chain, while the peak 2h = 19° was related to the PANI
nanofibers, also observed in the present study.
The contact angle measurements can be used to show quantita-
tively the modifications to the surface that define the wetting and
adhesion properties. Contact angle was measured on a drop of
water deposited on coated and uncoated surfaces, and the angle
was calculated from the outline tangent of a drop deposited on a
surface, giving 64° and 79° (± degrees), respectively. Thus, a de-
crease was found in the contact angle on the coated surfaces, indi-
cating a rise in hydrophilicity, as a consequence of increased
surface porosity.
The deposition of PANI films by spin-coating on the surface of
the AFM microcantilever can alter considerably its surface rough-
ness. To illustrate the change in roughness on the cantilever sur-
face, Fig. 4 displays 2D AFM images of (a) a base microcantilever
surface and (b) the microcantilever surface functionalized with a
spin-coated film of PANI. The uncoated surface (Fig. 4(a)) had a
roughness of 2.02 (±0.30) nm and the PANI-coated surface a rough-
ness of 79.43 (±7.80) nm, over a surface area of 100.0 lm2
. These
average values of roughness were based on 3 images. Thus, the in-
crease in the hydrophilicity and roughness of the surface coated
with PANI leads to a much larger surface area available for adsorp-
tion of water vapor, making the PANI-coated microcantilever appli-
cable as a humidity sensor.
4000 3500 3000 2500 2000 1500 1000 500
Doped
Dedoped
Wavenumber (cm
-1
)
Fig. 2. FTIR spectra of polyaniline layer produced in the emeraldine oxidation state
by interfacial synthesis, doped with HCl (salt) and dedoped with NH4OH (base).
0 5 10 15 20 25 30 35 40
*
*
*
*
*
*
*
Dedoped
Doped
* polyaniline
Intesity(a.u.)
Two theta (degree)
Fig. 3. X-ray diffractograms of the doped and dedoped polyaniline obtained by
interfacial synthesis.
82 C. Steffens et al. / Microelectronic Engineering 113 (2014) 80–85

3.2. Deflection response of microcantilever sensors to humidity
The measurement of deflection of the microcantilever sensors
under varying humidity was performed in triplicate, the microcan-
tilever bending being read by the optical lever principle, after 9 h of
stabilization. The influence of various temperatures (10, 20 and
30 °C) on the response time, sensitivity and reversibility of the
microcantilever humidity sensors was assessed (Fig. 5). This exper-
iment was performed inside a closed chamber by exposing the
microcantilever sensor to three cyclic variations of RH from 70%
to 20% and from 17% to 70% RH. The RH inside the chamber was
varied by combining flows of dry and wet nitrogen at a flow rate
of 0.1 L/min. The temperature and humidity were monitored inside
the chamber with a commercial sensor (Sensirium, with a resolu-
tion of ±0.3 °C and ±1.8% humidity).
In Fig. 5, a stable and repeatable response of deflection (nm)
versus time (min) can be seen, with no change in the baseline.
The fastest response was shown by the sensor at a temperature
of 10 °C. In the static mode, the cantilever bending changes in re-
sponse to differential surface stress due to molecular adsorption,
temperature change [33] and also partly to the ‘‘biomaterial’’ ef-
fect. According to Finot et al. [34], the double-layer microcantile-
vers are extremely sensitive to variations in temperature because
of the bimaterial effect related to the difference between the ther-
mal expansion coefficients of the two materials. A possible expla-
nation for the long response time in Fig. 5 may be the
experimental conditions, especially the large volume of the cham-
ber, which precluded a rapid gas exchange.
The sensitivity and reversibility were calculated from Eqs. (1)
and (2) respectively, and the results were good at all temperatures,
the best values being obtained at 30 °C (Fig. 6). The excellent sen-
sitivity shown by the proposed microcantilever sensors can be re-
lated to the fact that the PANI sensitive layer is able to undergo
physical and structural changes in the presence of humidity, due
to changes in its oxidation state, which augment the deflection
due to absorption/desorption of water. Thus, it is observed in
Fig. 5 that the microcantilever sensor deflected many nanometers
when exposed to humidity, probably because of the stress transfer
ability of the sensitive polymer layer.
Larsen et al. [35] studied the response of silicon-rich nitride
cantilevers, coated with SU-8 by spin-coating to humidity in the
air. The cantilevers showed an increased deflection as the
Fig. 4. 2D AFM images of (a) uncoated microcantilever and (b) microcantilever functionalized with spin-coated film of PANI.
0 10 20 30 40 50 60
0
1000
2000
3000
4000
5000
6000
Wet gas
Drygas
Deflection(nm)
Time (min)
10 °C
20 °C
30 °C
Fig. 5. Deflection of microcantilever sensors in response to humidity at 3 different
temperatures (10, 20 and 30 °C).
(a)
10 20 30
97
98
99
100
101
Reversibility(%)
Temperature (°C)
(b)
10 20 30
2000
2500
3000
3500
4000
4500
Sensitivity(%)
Temperature (°C)
Fig. 6. (a) reversibility and (b) sensitivity of the microcantilever sensors to
humidity at various temperatures (10, 20 and 30 °C).

temperature was raised from 20 to 35 °C, which then decreased
from 35 to 50 °C. This behavior was also observed with our sensors,
in the range from 20 to 30 °C.
3.2.1. Humidity sensitivity
The sensitivity of the humidity measurement of the proposed
system at the different temperatures (10, 20 and 30 °C (±0.2))
was determined from the deflection response of the coated and ref-
erence uncoated microcantilevers (nm) to the variation of relative
humidity (Fig. 7). The system sensitivity was determined by vary-
ing the humidity over a large range (RH = 50%, from 20% to 70%).
The deflection exhibited good linearity with humidity over certain
ranges, with a regression coefficient of R2
> 0.990. The sensitivities
calculated in the linear ranges of relative humidity variation are
shown in Table 1. It can also be observed in Fig. 7 that, in the linear
ranges, greater sensitivity was achieved by microcantilever sensors
at 20 and 30 °C than 10 °C. The uncoated reference cantilever
exhibited no sensitivity to humidity, confirming that the sensor
sensitivity is due to the sensitive layer. The sensitivity in the linear
ranges (RH $ 20%) of the microcantilever sensor, at all 3 tempera-
tures studied, was higher than 125 nm/% RH. This may be com-
pared with results reported by Singamaneni et al. [36] for a
humidity microcantilever coated with methacrylonitrile polymer
by the spin-coating technique, with a sensitivity of 110 nm/1%
RH. When the microcantilever sensors are exposed to humidity cy-
cles, there is a change in surface tension resulting in a reversible
nanomechanical bending of the sensors, which is related to the
absorption/desorption of water molecules by the polymeric film
(Fig. 5). These results corroborate those found by Lin et al. [37],
in which the deflection of a three-layered ceramic–metal–polymer
microcantilever versus temperature was linear, reversible, and
repetitive.
Nonlinear bending behavior was observed in the range of 30% to
45% RH. One reason for this nonlinearity in the cantilever sensor
response is the transduction mechanism, which is based on
mechanical movements or deformations of the beam when it is
subjected to varying humidity. Also, we used the static mode,
and this mode is sensitive to surface stress changes, which can
be referred to the Stoney equation [38].
This assumes a uniform curvature for the whole deflected struc-
ture, which is too ideal for the nonlinear analysis of a large deflec-
tion in the film [38,39]. In work performed by Jungchul et al. [40],
the authors observed that the cantilever electrical resistivity is a
highly nonlinear function of temperature, corroborating the results
found in our work.
It can be observed in Fig. 8 that when the sensors were exposed
to the lower range of RH, the surface tension caused the microcan-
tilever to curve upwards, due to the repulsion of polymer chains
and shrinkage of the polymer as the water vapor desorbed from
the sensitive layer. At higher RH, the microcantilever bent down-
wards, due to swelling of the polymer layer. This behavior is con-
sistent with the results reported by Lahav et al. [12], who found
less sensitive deflection in sensors at high RH (downward bend),
whereas at low RH the deflection sensitivity increased (upward
bend).
3.2.2. Humidity hysteresis of microcantilever sensor at three
temperatures
The humidity hysteresis of microcantilever sensor was analyzed
at three temperatures (10, 20 and 30 °C (±0.3)). The humidity was
decreased from 70% to 20% (by introducing dry nitrogen into
chamber) and increased from 20% to 70% (wetting nitrogen by
passing through water at the same rate of 0.1 L/min) (Fig. 8). The
hysteresis was calculated as the difference between the mean mea-
sured values during the drying and wetting stages. The deflection
of the microcantilever humidity sensor during 8 consecutive cycles
of wetting and drying showed 1.53% hysteresis at 10 °C, 1.86% at
20 °C and 4.18% at 30 °C. Thus, the hysteresis of the proposed
microcantilever humidity sensors increased with increasing tem-
perature. According to Singamaneni et al. [36], hysteresis values
lower than 2% are considered modest values, which qualifies the
microcantilever sensors tested at temperatures of 10 and 20 °C as
adequate humidity sensors. Wachter & Thundat [41] also found
hysteresis in this range (linear response R2
= 0.998), for a silicon
cantilever coated with gelatin exposed to varying relative
humidity.
20 25 30 35 40 45 50 55 60 65 70 75
0
1000
2000
3000
4000
5000
Deflection(nm)
Humidity (%)
10°C
20°C
30°C
Uncoated
Fig. 7. Effects of temperature and PANI coating on humidity sensitivity of the
microcantilever sensor.
Table 1
Linearity of the humidity sensitivity at three temperatures (10, 20 and 30 °C) of the
coated and uncoated microcantilever sensors.
Temperatures R2
Sensitivity (nm/% RH) Linear range of % RH
Coated 10 °C 0.999 125.494 (±1.984) 20–40
0.999 84.289 (±0.152) 50–70
Coated 20 °C 0.994 177.583 (±6.116) 20–40
0.990 65.158 (±3.365) 40–65
Coated 30 °C 0.999 153.543 (±1.546) 20–40
0.995 39.372 (±1.775) 45–68
Uncoated 20 °C 0.960 0.7062 (±0.0592) 20–70
20 30 40 50 60 70
0
1000
2000
3000
4000
5000
20 °C
10 °C
30 °C
Deflection(nm)
Relative Humidity (%)
Humidity drop
Humidity rise
Fig. 8. Humidity hysteresis curves for the microcantilever sensors at 10, 20 and
30 °C.
84 C. Steffens et al. / Microelectronic Engineering 113 (2014) 80–85

4. Conclusions
The characterization of the PANI sensitive layer with FTIR, XRD
and contact angle techniques showed that the polymer was depos-
ited on the silicon microcantilever as a doped hydrophilic layer,
with properties essential for a microcantilever functionalized with
polyaniline to be used as a humidity sensor.
The microcantilever sensor was tested with respect to its re-
sponse, sensitivity and reversibility by measuring its deflection in
response to humidity variation, at three different temperatures.
The new microcantilever sensor showed a large response to
humidity within the range investigated, faster at 10 °C, but with
better sensitivity and reversibility at 30 °C. The system sensitivity
was estimated with respect to a large change in humidity, showing
greatest sensitivity of the sensor at 20 °C. The hysteresis of the
microcantilever sensor was lower than 2% at the temperatures of
10 and 20 °C. The characterization of the sensitive layer and micro-
cantilever sensors indicated a good possibility of using the device
as a humidity microcantilever sensor.
Acknowledgements
The authors would like to thank Embrapa Instrumentation,
responsible for the National Nanotechnology Laboratory for Agri-
business, for the infrastructure and facilities, and FAPESP (2009/
08244-0) and INCT-NAMITEC (CNPq 573738/2008-4) for financial
support for this research.
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