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| Content Provider | IEEE Xplore Digital Library |
|---|---|
| Author | Comini, E. |
| Copyright Year | 2008 |
| Description | Author affiliation: Dept. of Chem. & Phys., Univ. of Brescia, Brescia (Comini, E.) |
| Abstract | Metal oxides are an attractive and heterogeneous class of materials covering the entire range from metals to semiconductors and insulators and almost all aspects of material science and physics in areas including superconductivity and magnetism. As far as chemical sensing is concerned it has been known, from more than five decades, that the electrical conductivity of metal oxides semiconductors varies with the composition of the gas atmosphere surrounding them. The sensing properties of semiconductor metal oxide in form of thin or thick films other than $SnO_{2},$ like $TiO_{2},$ $WO_{3},$ ZnO, $Fe_{2}O_{3}$ and $In_{2}O_{3},$ have been studied for a long time. Due to the huge application range of gas sensors the need of cheap, small, low power consuming and reliable solid state gas sensors, has grown over the years and triggered a huge research worldwide to overcome metal oxide sensor drawbacks, summed up in improving the well known ldquo3Srdquo: Sensitivity, Selectivity and Stability. In 1991 Yamazoe showed that reduction of crystallite size went along with a huge improvement in sensor performance. In a low grain size metal oxide almost all the carriers are trapped in surface states and only a few thermal activated carriers are available for conduction. The challenge became to prepare materials with small crystalline size which were stable when operated at high temperature for long periods. An unexpected step forward has been the successful preparation of stable single crystal quasi-one- dimensional semiconducting oxides nanostructures (so called nano-belts, nano-wires or nano-ribbons) by simply evaporating the desired commercial metal oxide powders at high temperatures. Their crystallinity ensures an improved stability and the nanosized lateral dimension the good sensing properties. Their peculiar characteristics and size effects, make them interesting both for fundamental studies and for potential nano-device applications, leading to a third generation of metal oxide gas sensors. The present work is focused on the preparation of single crystalline metal oxide nanostructures for gas sensing application. We have studied the electrical properties of the different nanostructures focusing our attention on nanowires (NWs) due to their reduced lateral dimensions. The deposition of metal oxide nanostructures has been made by evaporation/condensation technique starting from metal oxide powders. The deposition technique is very simple and cheap, and the size and shape of quasi-ID nanostructures can be controlled by tuning the deposition parameters. The controlled pressure of the inert atmosphere and the gradient of temperature within the furnace allow condensation and nucleation of the nanostructures downstream the gas flow. Such a peculiar thermodynamic condition promotes formation of nanosized 1-D structures, fulfilling the essential requirements for highly sensitive molecular detection. The as-synthesized oxide nanostructures are pure, structurally uniform, and single crystalline. The electrical response towards gases increases with the decrease in lateral dimensions and comparing the performances with the one obtained for thin films the NWs show a remarkable increase in the response. Furthermore the optical properties of ID nanostructures change as a function of the different environments. We have found that the visible photoluminescence of tin and zinc oxide nanowires is quenched by nitrogen dioxide at ppm level in a fast (time scale order of seconds) and reversible way. Besides, the response seems highly selective toward humidity and other polluting species and it is maximum at room temperature. This feature could be interesting for application of nanowires as a selective optical sensor working at room temperature. |
| Starting Page | 13 |
| Ending Page | 15 |
| File Size | 249772 |
| Page Count | 3 |
| File Format | |
| ISBN | 9781424421817 |
| DOI | 10.1109/ICECS.2008.4675126 |
| Language | English |
| Publisher | Institute of Electrical and Electronics Engineers, Inc. (IEEE) |
| Publisher Date | 2008-08-31 |
| Publisher Place | Malta |
| Access Restriction | Subscribed |
| Rights Holder | Institute of Electrical and Electronics Engineers, Inc. (IEEE) |
| Subject Keyword | Nanowires Gas detectors Nanostructures Crystallization Temperature sensors Grain size Metal-insulator structures Magnetic materials Conducting materials Semiconductor materials |
| Content Type | Text |
| Resource Type | Article |
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