探测空气中甲烷的小型气体敏感器

一种新研制成功便携式以室温半导体激光器为基础的中红外气体敏感器用于测量空气中甲烷浓度。这种气体敏感器由波长为８１０ｎｍ的单极性半导体激光器和波长为１０８３ｎｍ的分布反馈式半导体激光器作为泵浦光并通过周期性极化的磷酸锂晶体产生了在３３μｍ连续差频光。通过调谐单极性半导体激光器使差频光调谐在３０４５～３１７０波数之间。外场测量空气中的甲烷得到的灵敏度为１８ｐｐｂｍ／Ｈｚ１／２，探测灵敏度主要受激光强度噪声所限制。

Gas concentration monitoring system for small and medium-sized coal mines based on gas-sensing detection and single-chip control

This paper is aimed at the actual conditions of disaster caused by gas in small and medium-sized coal mines. A new gas concentration monitoring system for coal mines is developed on the basis of gas-sensing detection and single-chip control. The monitoring system uses the tin oxide as the main material of N-type semiconductor gas sensors, be- cause it has good sensitive characteristics for the flammable and explosive gas （ such as methane, carbon monoxide）. The QM-N5-semiconductor gas sensor is adopted to detect the output values of the resistance under the different gas con- centrations. The system, designedly, takes the AT89C51 digital chip as the core of the circuit processing hardware structure to analyze and judge the input values of the resistance, and then achieve the control and alarm for going beyond the limit of gas concentration. The gas concentration monitoring system has man）, advantages including simple in struc- ture, fast response time, stable performance and low cost. Thus, it can be widely used to monitor gas concentration and provide early wamings in small and medium-sized coal mines.

High performance room temperature gas sensor based on novel morphology of zinc oxide nanostructures

Zinc oxide uniform nanostructures with novel morphologies were synthesized through simple and fast ammonia based controlled precipitation method in aqueous media and in the absence of any additive. Selected batches of the synthesized solids were characterized by SEM, XRD, FTIR and TG/DTA. FTIR analysis revealed that the morphology of nanostructures had little effect on their IR spectral profile of the synthesized material. The as-prepared, calcined and commercial ZnO nanostructures (ZnO-AP, ZnO-Cal and ZnO-Com) were then employed as gas sensors for the detection of ammonia, acetone and ethanol. ZnO-AP and ZnO-Cal based sensors showed superior and reproducible performance towards 1×10^-6 ammonia with gas response of 63.79% and 66.87% and response/recovery time of 13 and 3 s, respectively, at room temperature (29℃). This was attributed to the unique morphology and remarkable uniformity in shape and size of the synthesized nanostructures. In contrast, the ZnO-Com based sensor did not respond to ammonia concentration less than 200×10^-6. In addition, ZnO-Cal showed high selectivity to ammonia as compared to acetone and ethanol at room temperature. Moreover, the lowest detection limit was 1×10^-6, which demonstrates excellent ammonia sensing characteristics of the synthesized ZnO.

Neck-controlled sensitivity study on nano-grain SnO_2 gas sensors

The electrical potential inside a cylinder with a space charge layer is used to express the neck potential barrier of nano-SnO2 gas elements, and the neck-controlled sensitivity and the grain size effect are studied. It is shown that the sensing properties are influenced by the microstructural features, such as the grain size, the geometry and connectivity between grains, and that the neck controlled sensitivity alone is higher than the neck-grain controlled sensitivity and the difference between the neck controlled sensitivity and the neck-grain controlled sensitivity is large in the high sensitivity range for nano-SnO2 gas elements, which suggests a possible approach to the improvement of the sensitivity of a sensor by decreasing the number of necks of a nano-grain SnO2 gas element.

Structure and Oxygen Sensing Properties of TiO_2 Porous Semiconductor Thin Films

Semiconductor-type TiO2 oxygen sensing thin films were synthesized using tetrabutyl titanate （Ti （OBu）4） as precursor and diethanolamine （DEA） as complexing agent by the sol-get process. The porous and oxygen sensing TiO2 films were obtained by the addition of polyethylene glycol （PEG）. The micrographs of scanning electron microscope （SEM） show that the pores of the sample about 400-600 nm in size with PEG（2 000 g/mol） are larger than those about 300 nm in size with PEG（ 1 000 g/mol）, while the density of pores is lower. The results also indicate that increasing the content of PEG properly is beneficial to the formation of porous structure. With the increasing content of PEG from 0 g to 2.5 g, the oxygen sensitivity increases from 330 to more than 1 000 at 800 ℃, from 170 to more than 1 000 at 900℃, and the response time to O2 and H2 are about 1.5 s and less than 1s, respectively.

Fabrication of single-walled carbon nanotube-based highly sensitive gas sensors

A highly sensitive single-walled carbon nanotube(SWCNT)-based ammonia(NH3) gas detector is manufactured by orderly assembling SWCNT using the dielectrophoretical(DEP) technology.Atom force microscopy(AFM) and scanning electron microscopy(SEM) images revealed that SWCNTs were assembled between the microelectrodes.SWCNTs were affected by the electrophoretic force which was carried out by the related theoretical analysis in a nonuniform electric field.The SWCNT field effect transistors geometry was obtained.The electrical performance of NH3 gas sensor with the SWCNT field effect transistors geometry was tested before and after the adoption of NH3 at room temperature.Experimental results indicated that the efficient assembly of SWCNT was obtained by the applied alternating current voltage with frequency of 2 MHz and amplitude of 10 V.The SWCNTs-based gas sensor had high sensitivity to NH3,and the electrical conductance of NH3 gas sensor reduced two times after interaction with NH3.The SWCNTs surface gas molecules were removed by means of ultraviolet ray irradiation for 10 min.Hence,the fabricated NH3 gas sensor could be reversible.There is a clear evidence that the adsorption of NH3 on the SWCNT channel is easy to be realized.Our theoretical results are consistent with recent experiments.