Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 152 (2016) 551 – 555
International Conference on Oil and Gas Engineering, OGE-2016
The surface activity forecast implementation of the semiconductor materials ZnTe (AIIIBV) and ZnTe (AIIBIV) for the gas analysis Kirovskaya I.A.a*, Novgorodtseva L.V.a, Kosarev B.A.a, Zverev M.A.a a
Omsk State Technical University, 11 Mira Pr., Omsk 644050, Russian Federation
Abstract Based on the direct investigation results of adsorption properties of semiconductors systems ZnTe – GaSb, ZnTe – ZnS in relation to gases of the different electronic nature (NH3, CO) the predictions of their surface activity to basic and acid gases, expressed on the basis of bulk and acid-base properties are confirmed. Practical recommendations on the use of materials (of certain composition) in the sensor equipment are proposed. © 2016 by Elsevier Ltd.by This is an open © 2016 Published The Authors. Published Elsevier Ltd.access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Omsk State Technical University. Peer-review under responsibility of the Omsk State Technical University
Keywords: semiconductor materials, surface activity, forecasts realization, measuring cells.
1. Inroduction One of the main requirements to create materials for the sensor equipment is the high sensitivity and selectivity of their surface in relation to the analyzed gases of a particular electronic nature. When assessing them it is preferable to determine the adsorption characteristics, and for lack of them, you can use the acid-base ones. But in both cases, the carrying out of varying degrees long-term experiments is needed. Given that the surface properties of the materials cannot influence on their bulk physico-chemical properties, it is reasonable to establish a relation between bulk and surface properties, on which basis it is possible to pre-estimate the surface activity and selectivity (with two or more of the analyzed gases). Confirming periodically by the direct studies the validity of such estimates it is possible to offer a less expensive, financially and in time, searching path of the effective materials for a particular application. The results of the research carried out in this work favour for the mentioned possibilities.
* Corresponding author. Tel.: +7-381-262-86-06; E-mail address:
[email protected]
1877-7058 © 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Omsk State Technical University
doi:10.1016/j.proeng.2016.07.654
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2. Experimental The study subjects were predominantly fine powders such as ZnTe, GaSb, ZnS and their solid solutions (ZnTe)х(GaSb)1-х (х = 0,05; 0,10; 0,15; 0,90; 0,95) и (ZnTe) х(ZnS)1-х (х = 0,91; 0,95; 0,97) obtained by the method of isothermal diffusion at temperatures of 1337 K and 1173K respectively, using a specially designed temperature heat programs [1] and certified mainly by the radiographic studies results. The radiographic analysis was performed on the diffractometer D8 Advance by "Bruker" company (Germany) in CuKα – radiation (λ = 0,15406 nm, Т = 293 К) according to the method of large angle mapping [2-4], using a position-sensitive detector Lynxeye. The decoding of the received x-rays (the diffraction) patterns was performed using the database of powder diffraction ICDDIPDF-2, a refinement of the lattice parameters is performed in the program of 3.0 TOPAS (Bruker) according to the method of least squares. Of acid-base properties the pH of the surface isoelectric state (pHisi) was evaluated, characterizing the average strength of acid sites by hydrolytic adsorption studies with the participation of adsorbents – ampholyte [6]. In the end the pH at which the adsorbent-ampholyte splits an equal (very small) amount of Н+ ions and ОН- was found. The adsorption of gases (NH3, CO) was studied by the piezo-quartz crystal microbalance method [7] the sensitivity of 1.23 10-11 g/cm2 Hz, the temperature of 252 - 393 K and pressure of 1.1 - 10.7 PA). The adsorbates were produced by the known methods [8]. The results reproducibility was tested by the experiments doubling. Calculations and statistical processing of results were performed with the use of computers special programs. 3. Result and discussion As shown by the results of radiographic studies in the systems ZnTe – GaSb, ZnTe – ZnS solid solutions of substitution with a sphalerite cubic structure are formed (at the given composition). This is evidenced by the relative position of the x-ray lines corresponding to the formed solid solutions and of the system binary components, their distribution of intensity, a smooth change with the composition calculated on the basis of the lattice parameter values radiographs (а), interplanar spacings (dhkl), density ((ρr) (Fig. 1).
Fig. 1. Dependences on the lattice parameter values composition α (1, 1'), x-ray density ρr (2, 2') and the interplanar distance d311 (3, 3') of the components of the systems ZnTe – GaSb (1, 2, 3) and ZnTe – ZnS (1', 2', 3').
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According to the results of microscopic studies (see Fig. 2), the components surfaces of the systems ZnTe – GaSb, ZnTe – ZnS are polycrystalline. Components average particle sizes, for example, for the components of the system ZnTe – ZnS are in the range of 1-8 μm, dependences of the particles average number of the most represented particles (nav) on the composition are extreme (i.e. contain minimas) [9].
Fig. 2. The ZnTe powder microscope image.
The isoelectric condition pH values of the initial surfaces (exposed to air) in the series of GaSb → (ZnTe)х(GaSb)1-х → ZnTe; ZnS → (ZnTe)х(ZnS)1-х → ZnTe change in the range of 6.4 to 7.7 and 6.35 to 7.1. That is, with increasing content of zinc telluride in the systems ZnTe – GaSb, ZnTe – ZnS the pHisi growth is observed and, thus, the transition from slightly acidic to slightly alkaline region is observed clearly demonstrating the dependency of pHisi composition, having a smooth character (Fig. 3) and additionally proving the formation of the substitution in the studied solid solutions systems.
Fig. 3. The dependences of the components of the system ZnTe – GaSb (1) and ZnTe – ZnS (2) on the composition of pH – the surface isoelectric state.
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Somewhat different pHisi values of ZnTe can be explained by differences in the dispersion degree and the surface condition of the samples used (with time interval) in the preparation of solid solutions such as (ZnTe)х(GaSb)1-х, (ZnTe)х(ZnS)1-х. The marked trend of the pHisi growth with the increased content of ZnTe in systems correlates reasonably with a similar trend in the change of the x-ray density (ρr): in the series of GaSb → (ZnTe)х(GaSb)1-х → ZnTe и ZnS → (ZnTe)х(ZnS)1-х → ZnTe ρr grows from 5.62 to 5.72 and from 4,066 to 5,668 g/cm3 (Fig. 1, 3). In this case with increasing ρr of the coordination unsaturation of the atoms playing the role of Lewis acidic centers and their relative contribution to the surface acidity decreases (in increasing the Branstad centres relative contribution )for this reason pHisi grows. Accordingly, in these sequences the surfaces activity should increase against acidic gases and decrease in relation to the basic ones. Refer to the direct adsorption studies results (Fig. 4, 5).
Fig. 4. The temperature dependences of the NH3 adsorbtion on GaSb (1) and ZnTe (2) at Pн = 8 PA.
Fig. 5. The temperature dependence of the CO adsorbtion on ZnTe (1) and the solid solution растворе (ZnTe)0,85(GaSb)0,15 (2) at Pн = 8 PA.
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Note: the basic gas adsorption values of NH3 on ZnTe (with large pHisi and ρr) are less than on GaSb (with lower pHisi and ρr), and, on the contrary, the values of adsorption of the relatively more acidic gas such as CO are the greatest on ZnTe and visibly decrease with the GaSb adding. The strength of adsorption bonds is different, as evidenced by the adsorption heat (qα). So, in the temperature range of 313-393K and the adsorption amount of (1.3–5.8).10-4 mol/m2 qαNH3 is: on ZnTe – 1.9–7.6; on GaSb – 2.8–15.9 kJ/mol. And in the same conditions q αСО is: on ZnTe – 4.4–12.8; GaSb – 1.1–10.9 kJ/mol. In other words, on more basic surface the values of acidic CO gas adsorption are higher and the adsorption bonds СО+δ – А-δ are stronger. In contrast of more acidic one: the gas NH3 adsorption values are higher and the bonds NH3+δ – А-δ are more durable. 4. Conclusion Thus, we have the explicit confirmation of forecasts about the semiconductors surfaces activity – components of observed systems in relation to gases of different electronic nature (such as NH3 and CO), expressed on the basis of profound studies (in particular, ρr) and especially acid-base (pHisi) properties. The practical recommendations on the use of the most surface-active materials for the measuring cells fabrication on the micro impurities of NH3 and CO are given. The work is done within the state task project part of the Russian Ministry of Education and Science No 4.2543.2014/К. References [1] I. A. Kirovskaya, Solid solutions of binary and multicomponent semiconductor systems, OmSTU, Omsk, 2010, pp. 287-358 (In Russian). [2] S.S. Gorelik, L. N. Rastorguev, Yu. A. Skakov, Radiography and electronoptical analysis, Metallurgy, Moscow, 1970, pp. 88-107. (In Russian). [3] S. E. Mirkin, Handbook of x-ray diffraction analysis, State. Fiz.-Mat. lit-ry, Moscow, 1961, pp. 524 – 663. (In Russian). [4] Y.N. Parkhomenko, A.A. Shlenskii, V.F. Pavlov, G.V. Shepekina, T.G. Yugova, X-ray diffraction determination of the composition of in xGa1-xSb solid solution, Rus. J. Inorganic Material. 46, No. 14 (2010) 1526-1528. [5] R. E. Clark, K. N. Eberhardt, Microscopic methods of materials research, Technosphere, Moscow, 2007, pp. 250-375. (In Russian). [6] I. A. Kirovskaya, Surface properties of diamond-like semiconductors. The surface chemical composition. Catalysis, Publishing house of ISU, Irkutsk, 1988, pp. 76-120. (In Russian). [7] I. A.Kirovskaya, P. Nor, Adsorption properties of CDS-CDTE system semiconductors, Rus. J. Phys. Chem. 87 (2013) 2077-2081. [8] F. M. Rapoport, A. A. Ilyinskaya, Laboratory methods of obtaining pure gases, Goskhimizdat, Moscow, 1963, pp. 43-168. (In Russian) [9] I.A. Kirovskaya, Gas adsorption at the components of the GAAS-CDS system. Protection of metals and physical chemistry of surfaces, 44 (2008) 184-189.
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