- Email: [email protected]
The Effect of the Anionic Component on the Surface Properties of the Binary Semiconductors-analogues and their Solid Substitution Solutions
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 113 (2015) 461 – 465
International Conference on Oil and Gas Engineering, OGE-2015
The effect of the anionic component on the surface properties of the binary semiconductors-analogues and their solid substitution solutions Kirovskaya I.A.a*, Nor P.E.a, Bukashkina T.L.a, Mironova E.V.a a
Omsk State Technical University, 11, Mira Pr., Omsk 644050, Russian Federation
Abstract New materials were obtained by the developed technique, namely, solid substitution solutions based on the CdBV binary semiconductors-analogues (CdTe, CdSe, CdS). The surface physicochemical properties (acid-base, adsorption, electrophysical) were investigated. The mechanisms and laws of atomic (acid-base, adsorption) and electrical surface interactions were specified, as well as their correlation with the basic bulk physicochemical properties. The state diagrams "property - composition" were constructed and used to find the most active adsorbents, the primary transducer materials of the sensors for CO micro-impurities. © 2015Published The Authors. Published by Elsevier Ltd. © 2015 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. Peer-review under responsibility of the Omsk State Technical University Keywords: Semi-conductors; solid solutions; nanofilms; acid-base, adsorption, electrophysical properties; mechanism; laws; sensors
1. Introduction To find new materials for modern technologies, including nano- and sensor technologies [1], the present work studies acid-base, adsorption and electrophysical properties of the binary semiconductors-analogues CdTe, CdSe, and CdS and their solid solutions (CdTe)x(CdSe)1-x and (CdTe)x(CdS)1-x. The results of these investigations are discussed in terms of the basic bulk physicochemical properties. The aim of this work was to obtain the unknown new materials by the developed technique. The materials were to be obtained on the base of relatively investigated binary semiconductors (CdTe, CdSe, CdS). The other aims included the determination of the mechanisms and interrelated laws of the acid-base, adsorption and electronic
* Corresponding author. Tel.: +7-904-071-4039. E-mail address: [email protected]
1877-7058 © 2015 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.2015.07.336
462
I.A. Kirovskaya et al. / Procedia Engineering 113 (2015) 461 – 465
surface interactions and finding application opportunities for the obtained materials to produce sensors for environmental purposes. 2. Experimental The study subjects were the powders (Ssp = 0.405–0.91 m2/g) and nanofilms (d = 20–100 nm) of CdTe, CdSe, and CdS and their solid solutions (CdTe)x(CdSe)1-x (х = 0.85; 0.75; 0.5; 0.25; 0.15 mol.) and (CdTe)x(CdS)1-x (х = 0.84; 0.76; 0.5; 0.4 mol.). The techniques for obtaining the mentioned materials and the investigation of their acid-base, adsorption and electrophysical properties and the used modern equipment are described in [1–5]. 3. Results and discussion The study of the surface acid-base properties allowed to determine the nature, strength and acid sites consentration in changing the composition of the semiconductors-analogues and under impact of the gases (NH3, CO). The surface coordinatively unsaturated atoms, adsorbed water molecules and OH-groups are responsible for the acid sites. The strength of acid sites is proved by the slightly acid nature of the studied binary and ternary semiconductors surfaces (pHiso is within 5.84-6.81), this slightly acid nature suggesting the increased adsorptive activity towards the basic gases. The expected increased absorptive activity of such surfaces towards the basic gases is proved by the alkalescency (increased pHiso) in ammonia treatment. The calculated total concentration of the acidic sites (Сa) passes through maximum at CdTe – CdSe and CdTe – CdS systems composition changes (Fig. 1). At carbon oxide treatment (II), Cf decreases which is consistent with the earlier proposed [1,4] and herein discussed adsorption mechanism mainly resulting from the electronic structure and the molecules dual function.
Fig. 1. The dependence of total concentration of the acidic sites of the CdTe–CdS system components exposed to air (1) and in CO medium (2) on the composition.
Absorption isobar (mostly CO) appearance (Fig. 2) allows to make the preliminary conclusion that physical adsorption proceeds at the temperatures lower than 303-323 K and the chemically activated adsorption does at the
I.A. Kirovskaya et al. / Procedia Engineering 113 (2015) 461 – 465
463
higher temperatures. This conclusion is proved by the analysis results of the balanced and kinetic isotherms, activation energy and adsorption heat calculations, and electrical conductivity measurements (Fig. 3,4). The conclusion on the mainly donor-acceptor mechanism of CO adsorption [1,4] is made based on the investigation results of the adsorption, acid-base, electrophysical properties of the named compounds surfaces.
Fig. 2 Adsorption isobars of СО on CdS (2), СdTe (3), CdSe (5) and solid solutions (CdTe)0.84(CdS)0.16 (1), (CdTe)0.85(CdS)0.15 (4) at Рн = 13-18 Pa.
The observed change of the electrical conductivity during adsorption process and, consequently, the surface charging indicate the dependence of the adsorbate molecules adsorbing property not only on the local factor (molecules and active site chemical properties) but on the collective (electronic) factor as well, the latter being determined by the Fermi level position and the surface energy spectrum nature [3,6,7,8]. Gas adsorption selectivity, however, is subject to the surface local properties [1,3].
464
I.A. Kirovskaya et al. / Procedia Engineering 113 (2015) 461 – 465
Fig. 3. The dependence of the adsorption values (1), activation energy (2), heat (3) of CO adsorption on CdTe–CdS system composition
Fig. 4. The kinetic isotherms of р-CdTe monocrystal electrical conductivity change in СО adsorption (1) and mixture of СО:О2 = 1 : 2 (2) at Т = 360 К, Рн = 10 Pa.
4. Conclusion In complex examining of the conducted research results, the following facts and laws, scientifically and practically noteworthy, were specified. The most CO active binary semiconductor under adsorption conditions is cadmium telluride, and the solid solutions of the compositions (CdTe)0.85(CdSe)0.15 and (CdTe)0.84 (CdS)0.16 are among multi-component semiconductors. A mention should be made of the similar content of cadmium telluride in the named most active solid solutions (0.85; 0.84 mol.) and their almost identical pHiso values (6.13; 6.1). At the same time one can notice the same sequences in the binary semiconductors pHiso changes (рНisoCdTe<рНisoCdS<рНisoCdSe), CO adsorption values (under the similar conditions of αCO/CdTe>αCO/CdS>αCO/CdSe) and in the relative positioning of adsorption isobars (Fig.
I.A. Kirovskaya et al. / Procedia Engineering 113 (2015) 461 – 465
465
2). These laws are closely connected to the basic bulk physicochemical properties changing laws such as electronegativity differences, fraction of ionic bonds, forbidden bandgap and others. As a result the most active CO adsorbents, CdTe – CdSe and CdTe–CdS systems components, were predicted based on the "acid-base property - composition" dependence and were found on the basis of the "adsorption property - composition" dependence. These adsorbents served as the materials for developing the relevant sensors. Acknowledgements This research was conducted as the part of the state assignment № 4.2543.2014/К of the Ministry of Education and Science. References [1] I. Kirovskaya and E. Mironova, Preparation and identification of substitutional solid solutions of the InSb-CdTe system, Russ. J. Inorg. Chem.. 51 (2006) 645-648. DOI: 10.1134/S0036023606040243 [2] I.A. Kirovskaya and T.N. Filatova, Bulk physicochemical properties of solid solutions and binary components of the InSb-CdS system, J. of Phys. Chem. 86 (2012) 325–329. DOI: 10.1134/S0036024412020161 [3] I.A. Kirovskaya and P.E. Nor, Adsorption properties of CdS-CdTe system semiconductors, J. of Phys. Chem. 87 (2013) 2077–2081. DOI:10.1134/S003602441312011X [4] I. Kirovskaya, E. Mironova, E. Bykova, O. Timoshenko and T. Filatova, Adsorption and electrophysical studies of the sensitivity and selectivity of the surface of the INSB-CDTE system with respect to toxic gases. J. of Phys. Chem. 82 (2008) 830-834. DOI: 10.1134/S0036024408050233 [5] I. Kirovskaya, Gas adsorption at the components of the GaAS-CdS system, Prot. Met. 44 (2008) 184-189. DOI: 10.1007/s11124-008-2013-7 [6] V.F. Kiselev and G.S. Plotnikov, Photoinduced electron and proton processes on a semiconductor surface// Opt. Spectrosc. 44 (1997) 516– 519. [7] E.E. Gutman, V.F. Kiselev and G.S.Plotnikov, Vibronic Effects As A Clue To The Solution Of The Selectivity Problem Of Semiconductor Gas Sensors, Sens. Actuators. 44 (1997) 468–473. [8] V.F. Kiselev, S.N. Kozlov and N.I. Levshin On The Mechanism Of Dissipation Of Charge Carriers To Adsorptive Slow States Of Semiconductor, Phys. Status Solidi. 66 (1981) 93-98.
ScienceDirect Procedia Engineering 113 (2015) 461 – 465
International Conference on Oil and Gas Engineering, OGE-2015
The effect of the anionic component on the surface properties of the binary semiconductors-analogues and their solid substitution solutions Kirovskaya I.A.a*, Nor P.E.a, Bukashkina T.L.a, Mironova E.V.a a
Omsk State Technical University, 11, Mira Pr., Omsk 644050, Russian Federation
Abstract New materials were obtained by the developed technique, namely, solid substitution solutions based on the CdBV binary semiconductors-analogues (CdTe, CdSe, CdS). The surface physicochemical properties (acid-base, adsorption, electrophysical) were investigated. The mechanisms and laws of atomic (acid-base, adsorption) and electrical surface interactions were specified, as well as their correlation with the basic bulk physicochemical properties. The state diagrams "property - composition" were constructed and used to find the most active adsorbents, the primary transducer materials of the sensors for CO micro-impurities. © 2015Published The Authors. Published by Elsevier Ltd. © 2015 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. Peer-review under responsibility of the Omsk State Technical University Keywords: Semi-conductors; solid solutions; nanofilms; acid-base, adsorption, electrophysical properties; mechanism; laws; sensors
1. Introduction To find new materials for modern technologies, including nano- and sensor technologies [1], the present work studies acid-base, adsorption and electrophysical properties of the binary semiconductors-analogues CdTe, CdSe, and CdS and their solid solutions (CdTe)x(CdSe)1-x and (CdTe)x(CdS)1-x. The results of these investigations are discussed in terms of the basic bulk physicochemical properties. The aim of this work was to obtain the unknown new materials by the developed technique. The materials were to be obtained on the base of relatively investigated binary semiconductors (CdTe, CdSe, CdS). The other aims included the determination of the mechanisms and interrelated laws of the acid-base, adsorption and electronic
* Corresponding author. Tel.: +7-904-071-4039. E-mail address: [email protected]
1877-7058 © 2015 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.2015.07.336
462
I.A. Kirovskaya et al. / Procedia Engineering 113 (2015) 461 – 465
surface interactions and finding application opportunities for the obtained materials to produce sensors for environmental purposes. 2. Experimental The study subjects were the powders (Ssp = 0.405–0.91 m2/g) and nanofilms (d = 20–100 nm) of CdTe, CdSe, and CdS and their solid solutions (CdTe)x(CdSe)1-x (х = 0.85; 0.75; 0.5; 0.25; 0.15 mol.) and (CdTe)x(CdS)1-x (х = 0.84; 0.76; 0.5; 0.4 mol.). The techniques for obtaining the mentioned materials and the investigation of their acid-base, adsorption and electrophysical properties and the used modern equipment are described in [1–5]. 3. Results and discussion The study of the surface acid-base properties allowed to determine the nature, strength and acid sites consentration in changing the composition of the semiconductors-analogues and under impact of the gases (NH3, CO). The surface coordinatively unsaturated atoms, adsorbed water molecules and OH-groups are responsible for the acid sites. The strength of acid sites is proved by the slightly acid nature of the studied binary and ternary semiconductors surfaces (pHiso is within 5.84-6.81), this slightly acid nature suggesting the increased adsorptive activity towards the basic gases. The expected increased absorptive activity of such surfaces towards the basic gases is proved by the alkalescency (increased pHiso) in ammonia treatment. The calculated total concentration of the acidic sites (Сa) passes through maximum at CdTe – CdSe and CdTe – CdS systems composition changes (Fig. 1). At carbon oxide treatment (II), Cf decreases which is consistent with the earlier proposed [1,4] and herein discussed adsorption mechanism mainly resulting from the electronic structure and the molecules dual function.
Fig. 1. The dependence of total concentration of the acidic sites of the CdTe–CdS system components exposed to air (1) and in CO medium (2) on the composition.
Absorption isobar (mostly CO) appearance (Fig. 2) allows to make the preliminary conclusion that physical adsorption proceeds at the temperatures lower than 303-323 K and the chemically activated adsorption does at the
I.A. Kirovskaya et al. / Procedia Engineering 113 (2015) 461 – 465
463
higher temperatures. This conclusion is proved by the analysis results of the balanced and kinetic isotherms, activation energy and adsorption heat calculations, and electrical conductivity measurements (Fig. 3,4). The conclusion on the mainly donor-acceptor mechanism of CO adsorption [1,4] is made based on the investigation results of the adsorption, acid-base, electrophysical properties of the named compounds surfaces.
Fig. 2 Adsorption isobars of СО on CdS (2), СdTe (3), CdSe (5) and solid solutions (CdTe)0.84(CdS)0.16 (1), (CdTe)0.85(CdS)0.15 (4) at Рн = 13-18 Pa.
The observed change of the electrical conductivity during adsorption process and, consequently, the surface charging indicate the dependence of the adsorbate molecules adsorbing property not only on the local factor (molecules and active site chemical properties) but on the collective (electronic) factor as well, the latter being determined by the Fermi level position and the surface energy spectrum nature [3,6,7,8]. Gas adsorption selectivity, however, is subject to the surface local properties [1,3].
464
I.A. Kirovskaya et al. / Procedia Engineering 113 (2015) 461 – 465
Fig. 3. The dependence of the adsorption values (1), activation energy (2), heat (3) of CO adsorption on CdTe–CdS system composition
Fig. 4. The kinetic isotherms of р-CdTe monocrystal electrical conductivity change in СО adsorption (1) and mixture of СО:О2 = 1 : 2 (2) at Т = 360 К, Рн = 10 Pa.
4. Conclusion In complex examining of the conducted research results, the following facts and laws, scientifically and practically noteworthy, were specified. The most CO active binary semiconductor under adsorption conditions is cadmium telluride, and the solid solutions of the compositions (CdTe)0.85(CdSe)0.15 and (CdTe)0.84 (CdS)0.16 are among multi-component semiconductors. A mention should be made of the similar content of cadmium telluride in the named most active solid solutions (0.85; 0.84 mol.) and their almost identical pHiso values (6.13; 6.1). At the same time one can notice the same sequences in the binary semiconductors pHiso changes (рНisoCdTe<рНisoCdS<рНisoCdSe), CO adsorption values (under the similar conditions of αCO/CdTe>αCO/CdS>αCO/CdSe) and in the relative positioning of adsorption isobars (Fig.
I.A. Kirovskaya et al. / Procedia Engineering 113 (2015) 461 – 465
465
2). These laws are closely connected to the basic bulk physicochemical properties changing laws such as electronegativity differences, fraction of ionic bonds, forbidden bandgap and others. As a result the most active CO adsorbents, CdTe – CdSe and CdTe–CdS systems components, were predicted based on the "acid-base property - composition" dependence and were found on the basis of the "adsorption property - composition" dependence. These adsorbents served as the materials for developing the relevant sensors. Acknowledgements This research was conducted as the part of the state assignment № 4.2543.2014/К of the Ministry of Education and Science. References [1] I. Kirovskaya and E. Mironova, Preparation and identification of substitutional solid solutions of the InSb-CdTe system, Russ. J. Inorg. Chem.. 51 (2006) 645-648. DOI: 10.1134/S0036023606040243 [2] I.A. Kirovskaya and T.N. Filatova, Bulk physicochemical properties of solid solutions and binary components of the InSb-CdS system, J. of Phys. Chem. 86 (2012) 325–329. DOI: 10.1134/S0036024412020161 [3] I.A. Kirovskaya and P.E. Nor, Adsorption properties of CdS-CdTe system semiconductors, J. of Phys. Chem. 87 (2013) 2077–2081. DOI:10.1134/S003602441312011X [4] I. Kirovskaya, E. Mironova, E. Bykova, O. Timoshenko and T. Filatova, Adsorption and electrophysical studies of the sensitivity and selectivity of the surface of the INSB-CDTE system with respect to toxic gases. J. of Phys. Chem. 82 (2008) 830-834. DOI: 10.1134/S0036024408050233 [5] I. Kirovskaya, Gas adsorption at the components of the GaAS-CdS system, Prot. Met. 44 (2008) 184-189. DOI: 10.1007/s11124-008-2013-7 [6] V.F. Kiselev and G.S. Plotnikov, Photoinduced electron and proton processes on a semiconductor surface// Opt. Spectrosc. 44 (1997) 516– 519. [7] E.E. Gutman, V.F. Kiselev and G.S.Plotnikov, Vibronic Effects As A Clue To The Solution Of The Selectivity Problem Of Semiconductor Gas Sensors, Sens. Actuators. 44 (1997) 468–473. [8] V.F. Kiselev, S.N. Kozlov and N.I. Levshin On The Mechanism Of Dissipation Of Charge Carriers To Adsorptive Slow States Of Semiconductor, Phys. Status Solidi. 66 (1981) 93-98.