Abstract
Nanocrystalline titanium oxide thin films have been deposited by spin coating technique and then have been analyzed to test their application in NH3 gas-sensing technology. In particular, spectrophotometric and con-ductivity measurements have been performed in order to determine the optical and electrical properties of titanium oxide thin films. The structure and the morphology of such material have been investigated by X ray diffraction, Scanning microscopy, high resolution electron microscopy and selected area electron diffrac-tion. The X-ray diffraction measurements confirmed that the films grown by this technique have good crys-talline tetragonal mixed anatase and rutile phase structure The HRTEM image of TiO2 thin film showed grains of about 50-60 nm in size with aggregation of 10-15 nm crystallites. Selected area electron diffraction pattern shows that the TiO2 films exhibited tetragonal structure. The surface morphology (SEM) of the TiO2 film showed that the nanoparticles are fine The optical band gap of TiO2 film is 3.26 eV. Gas sensing proper-ties showed that TiO2 films were sensitive as well as fast in responding to NH3. A high sensitivity for ammo-nia indicates that the TiO2 films are selective for this gas.
Highlights
It is well known that the electrical conductivities of semiconducting metal oxides change with the composition of the gas atmosphere surrounding them
High resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) pattern were obtained in order to investigate the morphology and structure of titanium oxide thin films
The samples sintered at 400oC and 500oC are relatively less crystalline in nature while the dramatic improvement in the crystallinity with the prominent (101) peak along with (103), (112), (200), (105), (211), (213) and (220) reflection of the anatase TiO2 phase is observed when the samples sintered at 600oC and a mixed anatase and rutile phase is obtained for sample sintered at 700oC (Ti700)
Summary
It is well known that the electrical conductivities of semiconducting metal oxides change with the composition of the gas atmosphere surrounding them. As with several metal oxides, titanium oxide is a polar material of technological importance since it is used as a substrate in catalytical and electrochemical processes [11]. These features make titanium oxide potentially suitable as gas sensing material [6]. For example the deposition parameters can affect the composition, the microstructure and the morphology of metal oxide films and, can have a strong influence on gas sensing properties. X-ray diffraction, high resolution transmission electron microscopy observations, together with spectrophotometric and conductivity measurements, have been considered in order to determine both the microstructure and the optical and electrical properties as a NH3 gas sensor annealed at 700oC
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