Title: GAS SENSING PROPERTIES OF NANOSTRUCTURED 1-D ZnO OBTAINED BY HYDROTHERMAL PROCESS G. Telipan1, L. Pislaru-Danescu1, V. Marinescu1, P. Prioteasa1, G. Zarnescu1 1National Institute for Electrical Engineering ICPE-CA, Splaiul Unirii 313, sector 3,
1GAS SENSING PROPERTIES OF NANOSTRUCTURED 1-D ZnO
OBTAINED BY HYDROTHERMAL PROCESSG. Telipan1, L.
Pislaru-Danescu1, V. Marinescu1, P. Prioteasa1,
G. Zarnescu11National Institute for Electrical
Engineering ICPE-CA, Splaiul Unirii 313, sector
3, Bucharest, ROMANIACorrespondent author
Gabriela Telipan, e-mail gtelipan_at_icpe-ca.ro
- Zinc oxide is one of the earliest
discovered oxide for gas sensing semiconductor
materials. ZnO is a n type semiconductor oxide of
wurtzite structure with a wide bandgap of 3.37 eV
and large excitation binding energy of 60 mV at
room temperature 1-2. ZnO is a material with
great potential for a variety of practical
applications, such as piezoelectric tranduscers,
optical waveguides, transparent conductive
oxides, chemical sensors 3. - 1-D ZnO Synthesis
- ZnO was obtained by hydrothermal
process using Zn(CH3COO)2x2H2O 98 like precursor
and cationic surfactant tetra-n-buthylammonium
bromide-TBAB.The molar ratio surfactant/Zn
precursor was 0.6. The solution of zinc acetate
dihydrate was acidified with HCl 11 to pH 2,
was added in drops to the surfactant solution and
was stirring for 1 hour at the room
temperature.The pH was adjusted to 9 using NH4OH
aqueous solution. The gel obtained was stirring
for 24 hours and transferred to an autoclave for
3 days at the 100o C. The obtained materials were
filtered, washed and dried at 100o C calcined at
500oC and pressed in the disc form with the
dimensions ?6x1 mm at 2 tone force.
Figure 2. SEM images for ZnO (a) uncalcined (b).
calcined at 500 oC (b).
Light interferometry analysis ZnO probe was
scanned using white light interferometry
technique with VEECO Interferometry
microscope-USA ZnO probe surface was analyzed in
three different zones, covering an area of 255 µm
length (X axis) and 191 µm width (Y axis) for
each focusing. Each profile gives complete
information about roughness and height variation
for X axis and Y axis. In accord with the
profilogram the maximum surface peaks are around
27 µm and maximum valleys dimensions are also 24
µm. The average roughness that exists on all
selected areas is 2 µm. Figure 3 and 4.
- Structural Characterization of 1-D Nanostructured
ZnO - X-Ray diffraction
- X-ray diffraction was effected on the uncalcined
and calcined powder with the Brucker D08 Advance
X-ray diffractometer wavelength ?1.5405982 Å
with CuK? radiation.For uncalcined powder was
obtained a amorphous structure and for calcined
powder was obtained a cristaline structure type
hexagonal wurtzite with lattice constants
a0.324982 nm and c0.520661 nm,.-Figure 1. The
average crystal domain size is estimated to be
48.9 nm using Debye-Scherrer equation based on
the XRD (101) peak.
- Figure 3. 3D images for ZnO disc
Figure 6. The profilograme of ZnO disc
The gas sensing properties The sensor was tested
in dynamic regime in the conditions the flow of
300 cm3/min CO2 at the 25, 50 and 70oC gas
testing chamber temperature and was measured the
voltage values function of the time. The maximum
voltage values obtained were 320 mV, 430 mV and
245 mV corresponding for 25, 50 and 70oC
respectively, after 6, 4 and 5 minutes gas
exposure-Figure 5.
Figure 1. X-ray diffraction of ZnO powder
Figure5. The histogram for the CO2 detection
Scanning electron microscopy
The SEM images performed with a Quanta 200
microscope, confirm the structure of ZnO obtained
by X-ray diffraction . For the material
uncalcined was obtained a amorphous phase-Figure
2a and for ZnO calcined was obtained a
crystalline phase- Figure 2
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