2004 Fiscal Year Final Research Report Summary
Development of semiconductor gas sensor ultra-sensitive in ppb level
Grant-in-Aid for Scientific Research (B)
|Allocation Type||Single-year Grants |
Functional materials chemistry
|Research Institution||KYUSHU UNIVERSITY |
SHIMANOE Kengo Kyushu University, Faculty of Engineering Sciences, Professor -> 九州大学, 大学院・総合理工学研究院, 教授 (10274531)
|Project Period (FY)
2003 – 2004
|Keywords||Higher order structure / Structure controlled / Hydrothermal treatment / Thin oxide / Sol / Grain size / Fine structure / Utility factor|
In order to develop gas sensors for very high sensitivity, three key factors have been recognized to control the sensitivity (sensor response) of the sensors of this type, i.e., receptor function, transducer function and utility factor. The importance of the last factor is made obvious when one considers that the target gas (reducing gas) reacts with the oxide surface on its way of diffusion into the sensor device. In this study, we have been investigating new ways of processing for sensing materials from the viewpoint of the above three factors.
The thin films derived from the neat sols of SnO_2 appeared to have pores rather small in size. It was then tried to modify the pore structure by dispersing various amounts of poly ethylene glycol (PEG) into the SnO_2 sol prior to spin-coating. It was observed that, under the same spin-coating conditions, the responses of the resulting thin films to H_2 increased with increasing PEG content, in parallel with the increase of pore size, although
film thickness increased correspondingly in this case. Obviously larger pore sizes are favorable for increasing utility factor.
We have tried to grow the size of SnO_2 crystallites in the sols and succeeded in it by adjusting the conditions of hydrothermal treatments. Now the sols of mono-dispersed SnO_2 with a crystallite size up to about 16 nm are available. We have shown that the thin films derived tend to increase sensor response to H_2 rather sharply as the crystallite size increases and the pore size increases accordingly. In addition, more strong dependence on the crystallite size and film thickness was disclosed for the sensor response to H_2S. This gas has larger molecular weight than H_2 and at the same time it is more reactive on the oxide surface as well. These features make this gas more sensitive to microstructure of the films.
We have investigated sensor responses of thick films derived from Co_3O_4 (typically 0.5 wt%)-SnO_2 composite powders, which were prepared by mixing the component oxides thoroughly in a planet ball mill. What is of interest here was that the response, especially to CO, increased rather drastically with an increase in ball-milling time. It turned out that the promotion of response was almost in parallel with an increase in pore size. It follows that enlarged pores would make it more favorable for CO molecules to diffuse through the films, leading to the extremely large responses. The sensor responses to various concentrations of CO are compared among several SnO_2 based devices so far reported. The outstandingly large responses of the present film appear to assure the relevance of sensor response with microstructure.
We investigated also gas sensors for detecting other gases. Less
Research Products (40 results)