Synthesis and structural characterization of rutile SnO 2 nanocrystals
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Synthesis and structural characterization of rutile SnO2 nanocrystals Zhiwen Chen,a) J.K.L. Lai, C.H. Shek, and Haydn Chen Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong, People’s Republic of China (Received 20 January 2003; accepted 26 February 2003)
Nanocrystalline tin dioxide (SnO2) thin films were prepared on glass substrate by pulse laser deposition for the first time. The thin films were characterized for their composition, morphology, and crystalline structure by x-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. It was found that the thin films consisted only of the tetragonal phase SnO2 with no structural change, and they were well crystallized during deposition. In most cases, SnO2 particles were overlapped, predominantly grown on preferred (101) plane, and connected with two or three neighbors through necks. The average grain size of the as-prepared thin films was about 12 nm. These facts are of great importance for sensor characteristics, since smaller grains and preferred orientation properties provide higher gas sensitivity to the whole thin films. Our findings indicate that the n-type wide-band-gas semiconductor nanocrystalline thin films can be manipulated by using pulse laser deposition techniques, offering new opportunities to control material fabrication.
Research on tin dioxide (SnO2) attracts a lot of interest because it has been widely used in many applications, such as transparent electrodes, far-infrared detectors, and high-efficiency solar cells.1–5 More recently, much attention has been focused to their potential use as gas sensors.6 Tin dioxide is an n-type wide-band-gas semiconductor material (Eg ⳱ 3.6 eV) where inherent oxygen vacancies act as an n-type dopant.7,8 Extensive studies have been conducted on this material in the form of thin film due to its useful electrical and optical properties.9–11 SnO2 thin films are used as sensors of various purposes, such as monitoring ecological conditions, toxic and explosive gases in the air, breath alcohol content (drunken driver test), and tobacco smoke in ventilation systems. The basis for these sensors is a reaction between the semiconductor and the ambient gas, producing a change in the conductivity of the semiconductor.12 a)
Present address: Department of Physics and Materials Science, on leave from the Structure Research Laboratory, University of Science and Technology of China, Hefei 230026, Anhui, People’s Republic of China. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 6, Jun 2003
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The most important form of naturally occurring SnO2 is cassiterite, a SnO2 phase with the tetragonal rutile structure. One of the important factors affecting the sensing properties of semiconductor gas sensors is the microstructure of the polycrystalline thin film. In general, the crystallite of semiconductor oxide has an electrondepleted surface layer (space-charge
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