Third Day Poster Session, 17 June 2010 - NanoTR-VI

Poster Session, Thursday, June 17
Humidity Sensing Investigation of ZnO Nanostructures Using QCM Technique
Nurdan Asar 1 , Nesli Tekguzel Yagmurcukardes 2 , Ayse Erol 1 , Salih Okur 2 , M. Cetin Arikan 1
1 Istanbul University Faculty of Science Physics Department 34134 Vezneciler, Istanbul, Turkey
2 Izmir Institute of Technology 35430 Urla, Izmir, Turkey
Theme F686 - N1123
Abstract: ZnO nanostructures were synthesized via chemical sol-gel method in two different morphologies. Their humidity sensing properties were investigated by
using Quartz Crystal Microbalance (QCM) technique. It was found that the frequency shift of the ZnO nanostructures coated on QCM increases with increasing relative
humidity between 33-77 % at room temperature. The results show that humidity sensing properties are strongly dependent on morphology of the nanostructures.
ZnO is one of the most important promising metal oxide
semiconductors for gas/vapour/humidity sensing applications and has
pronounced sensitivity to gases such as NH 3 , NO 2 , CO, H 2 , ethanol
and humidity [1-4]. It has been observed that ZnO nanostructures
synthesized in different morphologies compared with its thin film or
bulk counterparts have much more sensitivity due to their high
surface to volume ratio and more chemically active centers [5].
In this study we synthesized ZnO nanostructures by using chemical
sol-gel method. Crystal structure and morphology of ZnO
nanostructures synthesized in different experimental conditions were
characterized by X-Ray Diffraction (XRD) and Scanning Electron
Microscopy (SEM).
(a)
(a)
Samples S2 and S3 were synthesized with different molarities of Zn +2
and OH - solutions. Samples dried in ambient air for 24 hours. As seen
from the Figures 1 (a) and (b), the morphology of S2 is nanoparticle
while the morphology of S3 is nanowire and both structures have
diameter as ~ 20 nm. XRD patterns showed that both samples are
crystallized in hexagonal wurtzite structure.
Humidity sensing investigations of ZnO nanostructures were
carried out using Quartz Crystal Microbalance (QCM) technique.
Samples dispersed in ethanol were dropped on quartz crystal and
exposed to various saturated salt solutions. The frequency responses
of the ZnO nanostructure sensors to relative humidity changing
between 33-77% RH were measured at room temperature. Relative
humidity was recorded by commercial sensor simultaneously.
(b)
Figure 2: Frequency responses of S2 and S3 sensors under 33 – 77% relative humidity
exposure at room temperature.
(c)
(d)
Figure 2 shows response and recovery curves of the sensors. When
%RH was decreased from 77 to 33%, frequencies of the sensors were
backshifted to their initial values. In comparison with nanowires,
nanoparticles showed larger frequency shift.
The experimental results demonstrated that ZnO nanoparticles are
more sensitive to humidity changes compared to nanowires due to
having high surface to volume ratio and much more chemically active
centers.
This work was supported by Scientific Research Projects
Coordination Unit of Istanbul University. Project number 4907.
Figure 1: (a-b) SEM images and (c-d) XRD patterns of samples S2 and S3, respectively.
[1] Hongsith N., Choopun S., Mangkorntong P.,Mangkorntong N., 2005. CMU. J.
Special issue on nanotechnology. vol. 4 No. 1: 15-20.
[2] Sadek A. Z., Choopun S., Wlodarski W., Ippolito S. J., Kalantar Zadeh K., 2007.
IEEE Sensors Journal. Vol. 7, No. 6.
[3] Krishnakumar T., Jayaprakash R., Pinna N., Donato N., Bonavita A., Micali G. and
Neri G., 2009. Sensors & Actuators: B. 143, 198.
[4] Qi Q., Zhang T., Yu Q., Wang R., Zeng Y., Liu L., Yang H., 2008. Sensors and
Actuators B: Chemical. 638-643.
[5] Hongsith N., Viriyaworasakul C., Mangkorntong P. , Mangkorntong N. , Choopun
S., 2008 Ceramics International 34: 823–826.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 698