RU2697920C1 - Semiconductor nitrogen dioxide sensor - Google Patents

Abstract

FIELD: gas analysis.SUBSTANCE: invention relates to gas analysis and can be used for environmental monitoring tasks. Disclosed is a semiconductor sensor of nitrogen dioxide, consisting of a semiconductor base made in form of a polycrystalline film of zinc selenide (ZnSe), which is deposited on a non-conductive substrate.EFFECT: sensor according to the invention with considerable simplification of its manufacturing technology enables to determine content of nitrogen dioxide with sensitivity several times higher than that of known sensors.1 cl, 2 dwg

Description

The invention relates to the field of gas analysis, in particular to detection devices used for recording and measuring the content of trace elements of nitrogen dioxide (NO2). The invention can be used to solve environmental control problems.

A known sensor (detector) for thermal conductivity, the action of which is based on the difference between the thermal conductivity of the vapor of the substance and the carrier gas (Vyakhirev D.A., Shushukova A.F. Guide to gas chromatography. M .: Higher school, 1987. - 287 p. ) However, the sensitivity of such a sensor (detector) is limited to substances with thermal conductivity close to the thermal conductivity of the carrier gas. For example, when using this sensor for analysis of nitrogen dioxide, the accuracy of determination is low.

Also known is a sensor (sensor) of nitrogen dioxide, consisting of a substrate made of polycrystalline Al2O3, a sensitive layer in the form of a thin film of nanocrystalline tin dioxide, in which nanoparticles of nickel oxide and gold, and platinum electrodes are additionally introduced (Patent RU No. 2464554 M. cl G01N 27/12, published on October 20, 2012). Gas sensor for indicating nitrogen dioxide / A.M. Gaskov, M.N. Rumyantseva, 2012), which allows determining the content of nitrogen dioxide with greater sensitivity, but having a number of disadvantages.

The disadvantages of the known device are low selectivity with respect to NO ₂ (exhibits sensitivity to CO), design complexity, relatively high (compared to room temperature) working temperature (125-200 ° C), the use of precious metals (Au, Pt), duration and the complexity (complexity) of its manufacture: the formation of the film of the sensitive element occurs in several stages, including the production of tin acid gel, washing and drying, modifying the surface of tin dioxide with gold and nickel oxide, drying and subsequent temperature calcination: 80 ° С - 24 hours, 120 ° С - 10 hours, 160 ° С - 10 hours, 200 ° С - 10 hours, 300 ° С - 10 hours and 350 ° С - 24 h., the application of platinum electrodes. The implementation of this method of manufacturing a gas sensor, characterized by multi-stage technological operations, is associated with large time costs.

The closest technical solution to the invention (prototype) (patent RU No. 2437087, publ. 20.12.2011) is a gas sensor consisting of a semiconductor base made of a polycrystalline film of indium antimonide doped with cadmium sulfide and a substrate, which serves as the electrode pad of a piezoelectric crystal .

The disadvantages of this device is its lack of sensitivity in the control of trace amounts of nitrogen dioxide. In addition, the design of the device provides for the development of a special technology, mode, temperature control program and the process of doping indium antimonide in its manufacturing process; deposition of metal electrodes and direct adsorption measurements.

The technical result of the invention is the creation of a sensor characterized by increased sensitivity and manufacturability of its manufacture.

The specified technical result is achieved by the fact that in the known gas sensor containing a semiconductor base deposited on an electrode pad of a piezoelectric crystal according to the invention, the semiconductor base is made in the form of a polycrystalline film of zinc selenide deposited on a non-conductive substrate.

The invention is illustrated in the drawing and table, which presents:

in FIG. 1 - design of the inventive sensor;

in FIG. 2 - calibration curve of the change in the pH of the isoelectric state of the surface (∆pH _iso ) of the semiconductor base during adsorption at room temperature on the initial pressure NO ₂ (P _NO2 );

in the table - data on the effect of nitrogen dioxide on the pH of the isoelectric state of the surface (∆pH _iso ) of zinc selenide.

The table shows the noticeable effect of nitrogen dioxide on the pH of the surface of a semiconductor base - a polycrystalline film of zinc selenide, and the calibration curve clearly indicates the high sensitivity of the semiconductor base to nitrogen dioxide.

The sensor consists of a semiconductor base 1, made in the form of a polycrystalline ZnSe film, and a non-conductive substrate 2 (figure 1).

The principle of operation of such a sensor is based on adsorption-desorption processes that occur on a semiconductor film deposited on a non-conductive substrate, and cause a change in the pH of the isoelectric state and, accordingly, the strength of the active centers of its surface.

The operation of the sensor is as follows.

The sensor is placed in a chamber at room temperature (it can be an ordinary glass tube) through which the gas analyzed for nitrogen dioxide is passed (or in which it is held). Upon contact of the transmitted gas with the surface of the ZnSe semiconductor film, selective adsorption of NO ₂ molecules and a change in the pH of the isoelectric state of the surface occur. Using calibration curves, you can determine the content of nitrogen dioxide in the test medium.

From the analysis of FIG. 2. typical calibration curve obtained using the inventive sensor and expressing _iso dependence ΔpH of nitrogen dioxide (P _NO2), it follows that the claimed sensor with a substantial simplification of its manufacturing technology allows to determine the content of nitrogen dioxide with a sensitivity higher than in the known sensitivity several times sensors. A significant simplification of the manufacturing technology of the sensor is due to the exception of the development of a special technology, mode, temperature control program, the process of doping the semiconductor base itself, as well as the exception of the operations of applying metal electrodes to the semiconductor base and laborious adsorption measurements.

Small dimensions of the device (working volume less than 0.2 cm ³ ) in combination with a small mass of the film - adsorbent can reduce the sensor constant in time to 10-20 ms.

The design of the inventive sensor can also improve other characteristics: speed, regenerability, the ability to work not only in static but also in dynamic mode.

Table

PH values of the isoelectric state of the surface of zinc selenide during various surface treatments

Table

PH values of the isoelectric state (pH _iso ) of the surface of selenide
zinc Air exposure Argon treatment Nitrogen dioxide exposure 8.20 7.95 4,50

Claims (1)

A semiconductor nitrogen dioxide sensor containing a semiconductor base deposited on a non-conductive substrate, characterized in that the semiconductor base is made of a polycrystalline film of zinc selenide.

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