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8Hydrogen detectors
HYDROGEN INFLUENCE ON ELECTRICAL PROPERTIES OF METAL OXIDE FILMS ALLOYED WITH SILICON
A. L. Gusev1, I. V. Zolotukhin, Yu. E. Kalinin, L. N. Korotkov, O. I. Samokhina, A. V. Sitnikov, B. A. Spiridonov
Voronezh State Technical University, 14 Moskovsky pr., Voronezh, 394026, Russia Phone: (0732) 46-66-47, fax: (0732) 46-32-77, e-mail: kalinin@ns1.vstu.ac.ru 1Russian Federal Nuclear Centre — All-Russian Research Institute of Experimental Physics, 37 Mira pr., Sarov, Nizhniy Novgorod Region, 607188, Russia
In order to obtain composite nanostructures of tin oxide stabilised by silicon, the ion beam sputtering method was used. The samples obtained as a result of sputtering were films with the thickness of 0.15-1.5 mm with an amorphous structure. The chemical ion beam method of palladium deposition on the surface of tin oxide films alloyed by silicon was used for the deposition of catalytic palladium.
The structure obtained as a result of thermal annealing has a fine-grained pattern. The biggest grains of ~ 100 nm are observed in an alloy with the minimal silicon content. As the silicon content grows as a result of crystallisation of the amorphous phase, the grain size will decrease up to d <5 nm.
In the initial amorphous state, the Sn27 6Si3 9O68 5 films have very high electrical resistance values. Heating in an argon atmosphere leads to exponential reduction of the specific electrical resistance, which is followed by a sharp drop at the crystallisation temperature. After crystallisation, the value of electrical resistance of films is reduced by several orders.
The reduction of the concentration of the alloying silicon impurity leads to reduction of the crystallisation temperature for Sn30 2Si2 5O67 5 films up to Tx = 500 0C and Sn32 6Si06O 67 4 films up to T = 425 0C, i. e. the introduction of silicon into thin tin oxide films contributes to the thermal stability of the amorphous state and the crystallisation temperature growth. The introduction of silicon atoms contributes to the growth of the value of specific electrical resistance of films in the crystalline state.
As the crystallisation temperature of all films under investigation was below 600 0C, the isothermal annealing of samples at T = 600 0C during 60 minutes in the open air was used for its transfer into the crystalline state and the structure stabilisation.
The investigations of the sensitivity of films in respect to hydrogen have shown that silicon, raising the thermal stability of the amorphous structure of the film, at the same time slows down the processes of hydrogen reaction with the sample, thus reducing the sensitivity in respect to gas.
For studying the catalyst influence on the thermal and gas sensitivity of tin dioxide films, the Sn31Sit 5O67 5 films have been chosen having the optimal concentration of the alloying silicon impurity. As the surface palladium energy is very high, the fine-dispersed islands
of Pd of the size from 0.5 to 2 mm chaotically distributed on the film surface were being formed on the alloyed tin oxide surface. The application of palladium has not changed the value of specific electrical resistance of amorphous films of Sn31Si15O67 5 at the room temperature, however it has increased the crystallisation temperature up to 600 0C. Moreover, after a short-term annealing at 600 0C during 5 minutes and film crystallisation, the value of specific electrical resistance rises almost by an order as compared with the initial state.
The introduction of hydrogen into the argon medium leads to a jump-wise growth of electrical resistance approximately by 3%, and the electrical resistance will be maintained at the constant level for 10 minutes. In case of pumping out of Ar+H2 , the electrical resistance will sharply (for 1 minute) be reduced up to the values being typical for vacuum (~ 10-4 Torr) and then, at the over-supply of argon, a slow growth of the by 2.5% during 10 minutes is observed, which is followed by a quick rise of the electrical resistance with the addition of hydrogen to argon. Thus the electrical resistance of the Sn31Si15O67 5 film with palladium islands on the surface, which structure is in quasi-amorphous state, is characterised in vacuum of ~ 10-4 Torr by a relatively high value of electrical resistance, which than is sufficiently slowly grows in the argon medium and very quickly rises at the addition of molecular hydrogen with the partial pressure of ~ 7.6 Torr to argon.
Completely different relations of the electrical resistance behaviour are observed in the case when the Sn31Si15O67 5 film becomes nanocrystalline. In this case, the replacement of vacuum with the argon gaseous medium will also be accompanied by a rise of electrical resistance approximately by 10% for 15 minutes, and the addition of hydrogen into the argon medium will be accompanied by a sharp (for 1 minute) reduction of electrical resistance by 25%. The removal of hydrogen and the addition of argon and holding in the argon medium during 10 minutes will increase the electrical resistance up to the initial value. The introduction of hydrogen into argon will again lead to a jump-wise change of electrical resistance by 22.5%. The change of electrical resistance occurred in approximately 1 minute.
The work has been executed with the support by ISTC (Project No. 1580).
ISJAEE Special issue (2003)
