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Измерители относительной влажности и температуры (термогигрометры) Измерители микровлажности газов (гигрометры) Газоанализаторы Измерители скорости воздушного потока (анемометры) Системы пробоподготовки Аэродинамические установки Установки осушки газов Комплексные и индивидуальные решения


IMCS 2012


The properties of nanostructured SiOx films doped with Dawson-type heteropolycompounds at room temperature in clean air and in air containing ammonia were examined. It was studied adsorption activity of the sensors and found that the films formed at the surface of electrodes have a highly developed surface with nano-size pores. It has been shown that heteropolyanion composition and cation type have a significant influence on a sensor behavior of doped films. The study shows that the conditions of the environment affect markedly the sensors characteristics, which can be improved by choosing of the right procedure of forming and processing. Some mechanism of interaction between the sensors’ sensitive layer material and ammonia was proposed.

Motivation and Experimental

Sorption-impedance sensors based on complex composition sorbents hold a special position among the microelectronic gas sensors. This paper examines a gas sensitivity of nanostructured silica films doped with Dawson-type heteropolycompounds (HPCs). Different mechanism may exist to increase a gas sensitivity of activated films depending on additive type and conditions of theirs formation. HPCs are widely used in heterogeneous catalysis and analytical chemistry as catalysts for reduction-oxidation processes [1, 2]. Their redox properties can be varied in wide range. These compounds can act as reversible reagents in the reactions of ligand exchange and redox transformations.

Composite films were deposited to 15.0×5.0 mm test structures with a system of interdigital metal electrodes formed at their surface (Fig.1); active zone of the sensor was 4.0×4.0 mm. Films were prepared by sol-gel method from tetraethoxysilane based solutions. Different composition heteropolycompounds incorporated into the initial solution. The conditions of film formation varied during the tests: solution composition, temperature, and application modes. Standard gas mixtures (MGPZ, Russia), Dräger test gas ampoules (Dräger, Germany) and Environics – 4000 gas-mixture generator (Environics, USA) were used to measure the properties of sensors. Electrical parameters of the sensors have been measured electronically in real-time mode.


Sensor parameters of sensitive layers with various weight compositions of components have been studied. The composition with 30 – 50% of the weight content of doping additive in silica matrix enables to obtain a maximum sensitivity to measured gas. Heteropolyanion composition and cation type have a significant influence on a sensor behavior of doped films (Fig. 2, 3). Some mechanism of interaction between the sensors’ sensitive layer material and gas components being detected has been proposed. Threshold sensitivity to NH3 is 0.5 – 1.0 ppm for SiOx/(NH4)9P2W3Mo15O62 sensors; range of measured concentrations is 1–100 ppm; and response time – 20 s. Important property of the sensors consists in their ability to operate at room temperature, and this provides indisputable advantages for the development and operation of control instruments on their basis.


[1] N. Fay, E. Dempsey, T. Mccormac, Journal of Electroanalytical Chemistry, 574, 2, 359–366 (2005); doi: 10.1016/j.jelechem.2004.07.038

[2] Yu. Cheng, J. Zheng, Z. Wang, L. Liu, Y. Wu, Microchimica Acta, 173, 3–4, 529–535 (2011); doi: 10.1007/s00604-011-0589-0

Fig. 1: Test structure for measurements:

1-interdigitated electrodes; 2-nanostructured film

Fig. 2: Adsorption isotherms of ammonia on doped SiOx films (298 K):

1- (NH4)9P2W3Mo15O62; 2 – H6P2W18O62

Fig. 3: Typical conductivity dependence of doped SiOx films on ammonia content in air.


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