The Gas Sensitive And Light Sensitive Performance Of Titanium Dioxide Nanocrystal Material

TiO₂ nano-material is a star in lots of nano-materials. Its characteristics are investigated and applied in many domains for example photocatalysis, sensor, photocell and so on. At present doing research on TiO₂ nano-material is very popular in nano-material domains. In this article we aim at researching TiO₂ nano-material's application potentiality at the aspect of sensor. TiO₂ is not only a wonderful gas sensitive material, but also a photosensitive material because of its absorption to UV and photovoltaic effect. In my article, I research the two kinds of characteristics of TiO₂ and make preparation in laboratory for developing sensing devise further.Two types of nanocrystalline TiO₂ materials were synthesized by stearicacid-gel methods and characterized by XRD, DTA-TG, TEM, XPS and others. The indirect-heating sensor devices were fabricated by these nanocrystalline TiO₂. A series of tests showed that nanocrystalline TiO₂ materials exhibited high response to TMA prepared in my lab with anatase having higher response than rutile. It was also found that proper doping in nanocrystalline TiO₂ could increase the TMA response, reduce its resistance and enhance the selectivity against disturbing gases. The nanocrystalline materials doped with AgBr shows the best performance among some other metal ions.The sensor device improved the TMA response and recovery times but the longtime stability is under improvement. I also discuss the conduction mechanism and sensitivity mechanism utilizing surface chemistry and absorption chemistry. The gas sensor device is of great value to develop the sensor to detect the freshness of seafood.The TiO₂ thin films were prepared on different substrates (glass, ITO, quartz and Si) by sol-gel method. In the article the influence of sol preparation, coating method, substrate material, sintering temperature and membranous layers on TiO₂ thin film's quality, crystal and characteristics are researched detailedly. The film forming mechanism is discussed. The thin film's characteristics, ultraviolet absorption and photoelectric response are tested in the articles. We found that TiO₂ thin film combines substrate so compactly that could hardly be broken away. The ball-shaped nanocrystalline TiO₂ grains are piled up compactly and arrayed trimly whose average diameters are nearly uniform, about 30nm-40nm. At 600℃TiO₂ thin film is anatase phase. After 800℃anatase TiO₂ begins to be transformed into rutile TiO₂. At 1000℃rutile TiO₂ is formed completely. It should be noticed that crystal formation temperature of TiO₂ thin film is much higher than TiO₂ power. TiO₂ thin film can absorb UV-light great. Compare the UV-absorption of the two kinds of crystals, anatase TiO₂ has strong UV absorption ability. Anatase TiO₂ has stronger ability to absorb UV light than rutile TiO₂, but the rutile TiO₂ has a broader absorption region. Anatase TiO₂ has good photo-volt effect. The UV absorption rule from 360nm to 280nm and photocurrent signal change rule are identical. When TiO₂ thin film absorb UV light, we can detect the signal it produceNiO thin film was prepared by sol-gel method, their characteristics and performance were tested. NiO grains are almost global, whose diameters are from 20nm to 70nm. The surface of NiO thin film is not flat. There are lots of small ravines and cavities. We also find NiO grains aggregated slightly.TiO₂ is an N type semiconductor oxide, NiO is a P type semiconductor oxide. I have prepared TiO₂/NiO composite thin film successfully and observe its structure by SEM. It can be seen obviously that the combination between NiO and TiO₂ thin film is compact. The boundary between the two films is distinct. Their thickness is uniform. From the UV spectra test of TiO₂ thin film, NiO thin film and TiO₂/NiO composite thin film, we found both TiO₂ and NiO thin film have absorption in UV region; composite thin film's absorption intensity is stronger than both of the two film. Because the composite thin film is prepared by P type and N type semiconductor, it exhibits obvious P-N junction commutation characteristic and has formed a P-N junction. The composite thin film's photoelectricity response is much stronger than that of TiO₂ and NiO thin film, and its range of response is wider than TiO₂ thin film. I believe that it is just because of the PN junction that the surface photovoltage increases. The kind of composite thin film P-N junction has great value in investigating high-power light-sensitive device. The kind of composite thin film has wonderful photovoltaic effect and will has great value in photocatalysis, UV photo detector, gas sensor, solar cell for research and applications.