GAS SENSING PROPERTIES OF NANOSTRUCTURED 1-D ZnO OBTAINED BY GAS SENSING PROPERTIES OF NANOSTRUCTURED 1-D ZnO OBTAINED BY HYDROTHERMAL PROCESSHYDROTHERMAL PROCESS

GG. Telipan1, L. Pislaru-Danescu1, V. Marinescu1, P. Prioteasa1, G. Zarnescu1. Telipan1, L. Pislaru-Danescu1, V. Marinescu1, P. Prioteasa1, G. Zarnescu11National Institute for Electrical Engineering ICPE-CA, Splaiul Unirii 313, sector 3, Bucharest1National Institute for Electrical Engineering ICPE-CA, Splaiul Unirii 313, sector 3, Bucharest, ROMANIA, ROMANIA

Correspondent author: Gabriela Telipan, e-mail: Correspondent author: Gabriela Telipan, e-mail: gtelipan@icpe-ca.rogtelipan@icpe-ca.ro

Zinc oxide is one of the earliest discovered oxide for gas sensing Zinc oxide is one of the earliest discovered oxide for gas sensing semiconductor materials. ZnO is a n type semiconductor oxide of semiconductor materials. ZnO is a n type semiconductor oxide of wurtzite structure with a wide bandgap of 3.37 eV and large wurtzite structure with a wide bandgap of 3.37 eV and large excitation binding energy of 60 mV at room temperature [1-2]. excitation binding energy of 60 mV at room temperature [1-2]. ZnO is a material with great potential for a variety of practical ZnO is a material with great potential for a variety of practical applications, such as piezoelectric tranduscers, optical applications, such as piezoelectric tranduscers, optical waveguides, transparent conductive oxides, chemical sensors [3].waveguides, transparent conductive oxides, chemical sensors [3].

1-D ZnO Synthesis1-D ZnO Synthesis

ZnO was obtained by hydrothermal process using ZnO was obtained by hydrothermal process using Zn(CHZn(CH33COO)COO)22x2Hx2H22O 98% like precursor and cationic surfactant O 98% like precursor and cationic surfactant

tetra-n-buthylammonium bromide-TBAB.The molar ratio tetra-n-buthylammonium bromide-TBAB.The molar ratio surfactant/Zn precursor was 0.6. The solution of zinc acetate surfactant/Zn precursor was 0.6. The solution of zinc acetate dihydrate was acidified with HCl 1:1 to pH 2, was added in dihydrate was acidified with HCl 1:1 to pH 2, was added in drops to the surfactant solution and was stirring for 1 hour at the drops to the surfactant solution and was stirring for 1 hour at the room temperature.The pH was adjusted to 9 using NHroom temperature.The pH was adjusted to 9 using NH44OH OH

aqueous solution. The gel obtained was stirring for 24 hours and aqueous solution. The gel obtained was stirring for 24 hours and transferred to an autoclave for 3 days at the 100transferred to an autoclave for 3 days at the 100oo C. The obtained C. The obtained materials were filtered, washed and dried at 100materials were filtered, washed and dried at 100oo C calcined at C calcined at 500500ooC and pressed in the disc form with the dimensions C and pressed in the disc form with the dimensions 6x1 6x1

mm at 2 tone force.mm at 2 tone force. ► Structural Characterization of 1-D Structural Characterization of 1-D

Nanostructured ZnONanostructured ZnO► X-Ray diffractionX-Ray diffraction► X-ray diffraction was effected on the uncalcined and calcined X-ray diffraction was effected on the uncalcined and calcined

powder with the Brucker D08 Advance X-ray diffractometer powder with the Brucker D08 Advance X-ray diffractometer wavelength wavelength =1.5405982 Å with CuK=1.5405982 Å with CuK radiation.For radiation.For uncalcined powder was obtained a amorphous structure and for uncalcined powder was obtained a amorphous structure and for calcined powder was obtained calcined powder was obtained a cristaline structure type a cristaline structure type hexagonal wurtzite with lattice constants a=0.324982 nm and hexagonal wurtzite with lattice constants a=0.324982 nm and c=0.520661 nm,.-Figure 1. The average crystal domain size is c=0.520661 nm,.-Figure 1. The average crystal domain size is estimated to be 48.9 nm using Debye-Scherrer equation based estimated to be 48.9 nm using Debye-Scherrer equation based on the XRD (101) peak. on the XRD (101) peak.

Figure Figure 33. 3D images for ZnO disc. 3D images for ZnO disc

Figure 1. X-ray diffraction of ZnO powder

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

Figure 2. SEM images for ZnO (a) uncalcined; (b). calcined at 500 oC (b).

Light interferometry analysisZnO 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.

Figure 6. The profilograme of ZnO disc

The gas sensing propertiesThe 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.

Scanning electron microscopy

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Figure5. The histogram for the CO2 detection REFERENCES[1]. Pai-Chun Chang, Zhiyyong Fan, Dawei Wang, Wei-Yu Tseng, Wen-An Chiou, Juan Hong, Jia G. Lu, „ ZnO nanowires synthesized by vapor trapping CVD method“, Chem. Mater. 2004, 16, 5133-5137.[2]. Y. Chen, D. Bagnall, T. Yao, “ ZnO as a novel photonic material for the UV region”, Mater. Sci. Eng. B, (2000), 75, 190-198.[3]. L. Vayssieres, K. Keis, A. Hagfeldt, S.E. Lindquist, “ Three-dimensional array of highly oriented crystalline ZnO microtubes”, Chem. Mater, (2001), 13, 4395-4401.