State of Cd₁₋xZnxTe and Cd₁₋xMnxTe surface depending on treatment type

The morphology and composition of Cd₁₋xZnxTe and Cd₁₋xMnxTe solid solutions surfaces after different types of surface treatment were investigated. Chemical etching of the surfaces and polishing by diamond pastes cause change of surface stoichiometry and ontamination of surface layer by carbon and e...

Ausführliche Beschreibung

Gespeichert in:
Bibliographische Detailangaben
Veröffentlicht in:Semiconductor Physics Quantum Electronics & Optoelectronics
Datum:2004
Hauptverfasser: Dremlyuzhenko, S.G., Zakharuk, Z.I., Rarenko, I.M., Srtebegev, V.M., Voloshchuk, A.G., Yurijchuk, I.M.
Format: Artikel
Sprache:English
Veröffentlicht: Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України 2004
Online Zugang:https://nasplib.isofts.kiev.ua/handle/123456789/118105
Tags: Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
Назва журналу:Digital Library of Periodicals of National Academy of Sciences of Ukraine
Zitieren:State of Cd₁₋xZnxTe and Cd₁₋xMnxTe surface depending on treatment type / S.G. Dremlyuzhenko, Z.I. Zakharuk, I.M. Rarenko, V.M. Srtebegev, A.G. Voloshchuk, I.M. Yurijchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2004. — Т. 7, № 1. — С. 52-55. — Бібліогр.: 9 назв. — англ.

Institution

Digital Library of Periodicals of National Academy of Sciences of Ukraine
id nasplib_isofts_kiev_ua-123456789-118105
record_format dspace
spelling Dremlyuzhenko, S.G.
Zakharuk, Z.I.
Rarenko, I.M.
Srtebegev, V.M.
Voloshchuk, A.G.
Yurijchuk, I.M.
2017-05-28T17:27:45Z
2017-05-28T17:27:45Z
2004
State of Cd₁₋xZnxTe and Cd₁₋xMnxTe surface depending on treatment type / S.G. Dremlyuzhenko, Z.I. Zakharuk, I.M. Rarenko, V.M. Srtebegev, A.G. Voloshchuk, I.M. Yurijchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2004. — Т. 7, № 1. — С. 52-55. — Бібліогр.: 9 назв. — англ.
1560-8034
PACS: 79.20.Rf; 79.60.Bm
https://nasplib.isofts.kiev.ua/handle/123456789/118105
The morphology and composition of Cd₁₋xZnxTe and Cd₁₋xMnxTe solid solutions surfaces after different types of surface treatment were investigated. Chemical etching of the surfaces and polishing by diamond pastes cause change of surface stoichiometry and ontamination of surface layer by carbon and etchant components. Potentiometer studies were carried out to study the processes that take place on the interface "semiconductor-electrolyte". A prediction of phase composition of oxide films on Cd₁₋xZnxTe and Cd₁₋xMnxTe surfaces was made and a mechanism of their dissolution was determined. It was found that chemicomechanical polishing by alkaline colloidal silica compositions is an optimal surface treatment procedure. Chemico-mechanical polishing with this mixture gives a uniform surface without essential change of surface stoichiometry and fouling of the surface layer by etchant components.
The financial support of the Civilian Research and Development Foundation (grant UP2-536) and the Science and Technology Center of Ukraine (grant №1440) is gratefully acknowledged.
en
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
Semiconductor Physics Quantum Electronics & Optoelectronics
State of Cd₁₋xZnxTe and Cd₁₋xMnxTe surface depending on treatment type
Article
published earlier
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
title State of Cd₁₋xZnxTe and Cd₁₋xMnxTe surface depending on treatment type
spellingShingle State of Cd₁₋xZnxTe and Cd₁₋xMnxTe surface depending on treatment type
Dremlyuzhenko, S.G.
Zakharuk, Z.I.
Rarenko, I.M.
Srtebegev, V.M.
Voloshchuk, A.G.
Yurijchuk, I.M.
title_short State of Cd₁₋xZnxTe and Cd₁₋xMnxTe surface depending on treatment type
title_full State of Cd₁₋xZnxTe and Cd₁₋xMnxTe surface depending on treatment type
title_fullStr State of Cd₁₋xZnxTe and Cd₁₋xMnxTe surface depending on treatment type
title_full_unstemmed State of Cd₁₋xZnxTe and Cd₁₋xMnxTe surface depending on treatment type
title_sort state of cd₁₋xznxte and cd₁₋xmnxte surface depending on treatment type
author Dremlyuzhenko, S.G.
Zakharuk, Z.I.
Rarenko, I.M.
Srtebegev, V.M.
Voloshchuk, A.G.
Yurijchuk, I.M.
author_facet Dremlyuzhenko, S.G.
Zakharuk, Z.I.
Rarenko, I.M.
Srtebegev, V.M.
Voloshchuk, A.G.
Yurijchuk, I.M.
publishDate 2004
language English
container_title Semiconductor Physics Quantum Electronics & Optoelectronics
publisher Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
format Article
description The morphology and composition of Cd₁₋xZnxTe and Cd₁₋xMnxTe solid solutions surfaces after different types of surface treatment were investigated. Chemical etching of the surfaces and polishing by diamond pastes cause change of surface stoichiometry and ontamination of surface layer by carbon and etchant components. Potentiometer studies were carried out to study the processes that take place on the interface "semiconductor-electrolyte". A prediction of phase composition of oxide films on Cd₁₋xZnxTe and Cd₁₋xMnxTe surfaces was made and a mechanism of their dissolution was determined. It was found that chemicomechanical polishing by alkaline colloidal silica compositions is an optimal surface treatment procedure. Chemico-mechanical polishing with this mixture gives a uniform surface without essential change of surface stoichiometry and fouling of the surface layer by etchant components.
issn 1560-8034
url https://nasplib.isofts.kiev.ua/handle/123456789/118105
citation_txt State of Cd₁₋xZnxTe and Cd₁₋xMnxTe surface depending on treatment type / S.G. Dremlyuzhenko, Z.I. Zakharuk, I.M. Rarenko, V.M. Srtebegev, A.G. Voloshchuk, I.M. Yurijchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2004. — Т. 7, № 1. — С. 52-55. — Бібліогр.: 9 назв. — англ.
work_keys_str_mv AT dremlyuzhenkosg stateofcd1xznxteandcd1xmnxtesurfacedependingontreatmenttype
AT zakharukzi stateofcd1xznxteandcd1xmnxtesurfacedependingontreatmenttype
AT rarenkoim stateofcd1xznxteandcd1xmnxtesurfacedependingontreatmenttype
AT srtebegevvm stateofcd1xznxteandcd1xmnxtesurfacedependingontreatmenttype
AT voloshchukag stateofcd1xznxteandcd1xmnxtesurfacedependingontreatmenttype
AT yurijchukim stateofcd1xznxteandcd1xmnxtesurfacedependingontreatmenttype
first_indexed 2025-11-24T23:40:09Z
last_indexed 2025-11-24T23:40:09Z
_version_ 1850500693276753920
fulltext Semiconductor Physics, Quantum Electronics & Optoelectronics. 2004. V. 7, N 1. P. 52-55. © 2004, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine52 PACS: 79.20.Rf; 79.60.Bm State of Cd1�xZnxTe and Cd1�xMnxTe surface depending on treatment type S.G. Dremlyuzhenko, Z.I. Zakharuk, I.M. Rarenko, V.M. Srtebegev, A.G. Voloshchuk, I.M. Yurijchuk Chernivtsi National University, 2, Kotsyubynsky str., 58012 Chernivtsi, Ukraine E-mail: microel@chnu.cv.ua, Phone.: +380 (372) 584875 Abstract. The morphology and composition of Cd1�xZnxTe and Cd1�xMnxTe solid solutions surfaces after different types of surface treatment were investigated. Chemical etching of the surfaces and polishing by diamond pastes cause change of surface stoichiometry and con- tamination of surface layer by carbon and etchant components. Potentiometer studies were carried out to study the processes that take place on the interface �semiconductor-electrolyte�. A prediction of phase composition of oxide films on Cd1�xZnxTe and Cd1�xMnxTe surfaces was made and a mechanism of their dissolution was determined. It was found that chemico- mechanical polishing by alkaline colloidal silica compositions is an optimal surface treat- ment procedure. Chemico-mechanical polishing with this mixture gives a uniform surface without essential change of surface stoichiometry and fouling of the surface layer by etchant components. Keywords: Cd1�xZnxTe, Cd1�xMnxTe, semiconductor, surface, morphology, etchant. Paper received 24.11.03; accepted for publication 30.03.04. High-quality structure-perfect semiconductor surfaces which are uniform on chemical composition and purity are very important in production of semiconductor de- vices . Polishing with an etchant is one of the most widely used methods of semiconductor surface treatment. At present the etchants on K2Cr2O7, CrO3 and bromine base give the best results of surface polishing. But chemical etching with K2Cr2O7 and CrO3 etchants results in con- siderable enrichment of cadmium telluride surface by chromium ions, which can be explained by high absorp- tive ability of −2 72OCr ions on cadmium telluride surface [1, 2]. Oxidation mechanisms of these etching processes were not sufficiently studied. The use of the etchants with bromine results in change of surfaces stoichiometry and in enrichment of cadmium telluride surface by bromine ions [3]. A formation of el- ementary tellurium and tellurium dioxide islands was observed in [4, 5]. An etching mechanism of CdTe sur- face by etchants with bromine was studied in [5,6] were the presence of elementary tellurium on the surface was reported. So, the use of these etchants do not give a possi- bility to obtain the surface with minimal contamination with etchant elements. Further studies are needed to work out an optimal surface treatment procedure which causes minimal changes in crystals surface. The purpose of the paper is to determine the etchants composition and an optimal treatment procedure for the Cd1�xZnxTe and Cd1�xMnxTe surfaces. Solution of the problem is possible if only using wide spectra of chemico- physical methods to study the mechanisms and kinetics of the processes that take place at the interface �semicon- ductor-electrolyte�. The studies were carried out on the CdTe, Cd1-xZnxTe (0.02 ≤ x < 0.2) and Cd1�xMnxTe (0.02 ≤ x < 0.55) single crystals grown by the Bridgman technique. Cutting the crystal into wafers was made by tungsten wire (∅ 0.2 mm) with abrasive water suspension of ∅10 µm; mechanical lapping � with free abrasives of ∅10 µm and ∅5 µm; me- chanic polishing � with diamond pastes with grain size less than 1 µm. The depth of structure changes has been controlled using two-crystal X-ray spectrometer by sub- sequent etching the wafers surface [7]. Local distribution of structure defects of thin surface layers was studied by X-ray method with the use of skew asymmetric diffrac- tion geometry with a small critical angle of total internal reflection [8]. The morphology and element composition of the surfaces were studied by an electron raster micro- scope and X-ray microanalyzer Camscan 4DV. The studies were carried out after different types of surface treatment: polishing with abrasive pastes; etch- S.G. Dremlyuzhenko et al.: State of Cd1�xZnxTe and Cd1�xMnxTe surface depending ... 53SQO, 7(1), 2004 ing in etchant 1 (HNO3:H2O:K2Cr2O7) and etchant 2 (Br (8 %): methanol); chemico-mechanical polishing. The studies of the Cd1�xZnxTe and Cd1�xMnxTe surface com- position after different treatments reveal the presence of carbon and oxygen on the surface. The presence of car- bon on the Cd1�xZnxTe and Cd1�xMnxTe surfaces can be caused by: the contamination of the material by pirolytic coating of quarts container in which the crystal was grown; the chafing of carbon while cutting the samples by corun- dum abrasive; the contamination while lapping and pol- ishing with abrasive pastes; the contamination of the sur- face while etching with chemical solutions and washing in organic solvents. The removal of damaged layer after mechanical polishing was achieved by long-term chemi- cal treatment of the surface with polishing etchants. The use of rather long etching time results in breakdown of plainness and emergence of a relief (Fig. 1a, b). Besides, in these samples the local micro inhomogeneities (<100 µm) were revealed by the X-ray method. In topograms, as a rule, they are surrounded by bright back- ground, which testifies about the existence of tensions around them. Using skew asymmetric X-ray topography we have found that one part of these inhomogeneities are humps and the other are pits. The roughness of the sur- face is caused by different etching velocity of the matrix and inclusions. The dimension of the inclusions is of 10÷50 µm (Fig. 1c). The studies of the element composi- tion of the humps by X-ray microanalyzer have shown that most of the humps have considerable content of tel- lurium (Table 1). The presence of silicon, aluminium, oxygen, iron, sulphur and others was also detected. Quan- titative analysis of the matrix (beyond the inclusions) de- tects the presence of non-uniformly distributed impurity elements which concentration is up to 1 at. %. The pres- ence of the impurities in the matrix changes the composi- tion of the solid solution. Chemical etching of the Cd1�xZnxTe and Cd1�xMnxTe surfaces with bromine-methanol etchants enriches the sur- face layer by bromine and oxygen into the depth of 13� 15 nm, so as in the case of cadmium telluride surface [3]. In order to determine an optimal composition of the etchant it is necessary to study the processes that take place in the system �CdTe�etchant�. Electro-potentio- meter method is an effective tool for studying the proces- ses on the interface �semiconductor�electrolyte� (�semi- conductor�etchant�). One of the possible ways to carry out electro-potentiometer investigation is to determine the dependencies of equilibrium potential on pH (Pour- baix diagram). An analysis of the Pourbaix diagram give a possibility to make a reliable prediction of the phase composition of oxide films on semiconductors surface and to find out a mechanism of their solubility. The analysis of the ϕ�pH diagram for the CdTe�H2O system shows that region of thermodynamic stability of cadmium telluride in solid phase spreads through whole studied pH interval. A mechanism of corrosion processes in the CdTe�H2O system and chemical forms of corrosion prod- ucts are defined by the values of the oxidative potential of the medium and pH [9]. Proposed procedure for ther- modynamic prediction of possible redox reactions in the CdTe�H2O system may also be used for an analysis of more complex �semiconductor-electrolyte� systems. Zinc component doesn�t considerably change (from thermodynamic point of view) the possible oxidative pro- cesses in the CdTe�H2O system, because cadmium and zinc are chemically similar elements. More higher zinc activity somewhat restrict the pH interval in which Cd1�xZnxTe single crystal surface can be in active state. In the �Cd1�xZnxTe�aqueous solution� system a forma- tion of insoluble Zn(OH)2 phase, which passivate a semi- conductor surface, is possible at pH = 6.13, whereas a formation of Cd(OH)2 � at pH = 6.9. Zinc hydroxide is thermodynamically stable in 6.13�12.37 pH interval and dissolve at higher values of pH forming − 2HZnO and −2 2ZnO ions. Thermodynamic analysis of redox processes in the Cd1�xMnxTe�H2O system is more complicated as com- pared to the CdTe�H2O system. It is caused by the pres- ence of manganese, which can be oxidized to Mn2+, Mn3+, Mn4+, Mn6+ and Mn7+ forming soluble and in- soluble in water compounds. Analysis of the literature reveals more than 30 reactions by which manganese and its components can be oxidized in aqueous solutions. Calculations of the ϕ = f(pH) dependencies define the Pourbaix diagram for the Mn�H2O system. Comparing �equilibrium potential � pH� diagrams for the Mn�H2O and the CdTe�H2O systems the prediction of thermody- namic possible reactions in the Cd1�xMnxTe�H2O sys- tems is given and an estimate of the chemical state of the semiconductors surface in aqueous solutions with diffe- rent pH is made. In the high acidic medium (pH < � 0.37), all the com- ponents (Cd, Mn, Te) dissolve and pass into the solution in the form of Cd2+, Mn2+, Te4+ ions. It indicates on uniform dissolution of the semiconductor and gives a pos- sibility to predict (introducing special agents into the so- lution) the possible effect of the Cd1�xMnxTe single crys- tal surface etching. Mineral or organic acid substances, which form stable complex compounds with above men- tioned ions, can be used as a special agents. It is worth to note that unlike the Mn2+/Mn and the Cd2+/Cd systems the Te4+/Te system has a positive value of the standard electrode potential ϕ° =0.568 V. So, taking into account the high concentration of free surface electrons, the re- duction of the Te4+ ions and the formation of the elemen- tary tellurium phase on the Cd1�xMnxTe single crystals surface is expected. In the pH interval 0.37�5.45, the mechanism of cad- mium and manganese components dissolution does not change, and tellurium oxidizes forming dissoluble + 2HTeO . However a small increase of the oxidizing potential of the medium (for example, due to the dissolved O2) pro- duces a conditions for extraction of low soluble H2TeO4 phase on the Cd1�xMnxTe surface. An increase of Te4+ and + 2HTeO ions concentrations in the Cd1�xMnxTe�H2O system also makes for this process. In low-acidic, neutral and low-alkaline solutions (pH 5.45�10.45) the Cd1�xMnxTe surface is passivated. It is 54 SQO, 7(1), 2004 S.G. Dremlyuzhenko et al.: State of Cd1�xZnxTe and Cd1�xMnxTe surface depending ... caused by the formation of the oxide and hydroxide com- pounds on the semiconductor surface. Calculated Gibbs free energies of possible Cd1�xMnxTe oxidation products have negative values and decrease in the row: CdO→ →TeO2→Cd(OH)2→Mn(OH)2. Taking into account the ability of the CdO, TeO2, Cd(OH)2 to dissolve in alka- line medium, it is possible to predict an enrichment of the passivating films by Mn(OH)2 phase, which transforms into Mn3O4 and Mn2O3 with an increase of the oxidative potential. Further increase of pH activates dissolution processes of the film: TeO2 completely dissolves at pH ≥ ≥ 10.45; Cd(OH)2 � at pH ≥ 11.17; Mn(OH)2 � at pH ≥ ≥ 11.45. Therefore, one can expect that in high-alkaline medium (pH ≥ 11.45) the Cd1�xMnxTe surface is free from oxides and hydroxides. Calculations show that cadmium, manganese and tellurium oxidation is possible in this conditions. In the result the soluble in water − 2HCdO , − 2HMnO and −2 3TeO ionic forms are produced. The analysis of the Pourbaix diagram allows us to conclude: � dominant action of Te is caused by the fact that the oxidation potential of the reactions, that take place in �semiconductor-electrolyte� system with tellurium com- ponent, is greater than the oxidation potentials of cad- mium, manganese and zinc; � according to the thermodynamic analysis a uni- form dissolution from the surface takes place in acidic mediums. Polishing etching is possible in the systems which oxidation potential is not less than 0.416 V. The most effective systems are etchants which contain the sol- vent HNO3 as an oxidizer; Fig. 1. Scanning electron microscope image of the Cd0.55Mn0.45Te surface: a) after mechanical lapping; b) after etching with bromine methanol solutions; c) inclusions on the surface after etching with bromine methanol solutions; d) after chemico-mechanical polishing with SiO2 colloidal solution. a b c d S.G. Dremlyuzhenko et al.: State of Cd1�xZnxTe and Cd1�xMnxTe surface depending ... 55SQO, 7(1), 2004 � in highly alkaline mediums the substances which electrode potential doesn�t exceed the potential of the reaction Te + 6OH� = −2 3TeO + 6H+ + 4e (ϕ° = �0.57 V) can serve as an oxidizer. There are many substances that meet this condition, but the use of H2O2, taking into ac- count the specificity of the medium (pH ≥ 11.45), is more preferred because its decomposition products are reduced in alkaline medium at potentials greater than �0.267 V. These conclusions confirm the right choice of the chemico-mechanical polishing with a solution which con- sists of fine-dispersed SiO2, H2O2, NaOH, glycerin and monoethanolamin [3] as a final treatment. This is due to the fact that the SiO2 colloidal powder with 2�20 nm size as an abrasive material doesn�t cause essential structural distortion and its hydrophilic character allows to put easily it into water medium and to obtain stable water dispersions. The products of polishing are eliminated from the surface due to high absorption ability of the etchant, caused by large SiO2 colloidal powder surface with active hydroxo-(OH) and amino-(NH2) groups. Be- sides, in order to transfer an etching process into the dif- fusive region and to remove roughness of the working surface the glycerine is added to the solution. Glycerine addition leads to a decrease of etching velocity and gives a possibility to control and regulate effectively an etch- ing process. Monoethanolamin fixes the dissolution prod- ucts in the etchants volume. Hence, chemico-mechanical polishing by colloidal silica compositions does not contaminate the surface layer with etchants components. Besides, this method causes a minimal change of the Cd1�xZnxTe and Cd1-xMnxTe sur- face stoichiometry as compared with chemical etching, that was confirmed by investigation of the surface com- position. An advantage of this method is also a possibil- ity to obtain a surface free from local micro-inhomoge- neities, that are formed on chemical etching (Fig. 1d). Moreover, the chemico-mechanical polishing does not brake down the plane-parallelism of the surface. Thus, the use of the chemico-mechanical polishing with colloi- dal silica compositions allows to obtain a surface, which mostly satisfies the demands, which are required to the optical devices surface. Table 1. Composition of the matrix and inclusions (in at.%) of Cd1�xZnxTe (0,02 ≤≤≤≤≤ x < 0,2) and Cd1�xMnxTe surfaces after etching with K2Cr2O7 solution (M � matrix; I � inclusions). N Sample Cd Te Zn Mn Si Al Fe Cr Cl S Na O 1 CdZnTe (M) 44.8 49.5 4.97 0.69 2 CdZnTe (M) 44.6 49.6 5.03 0.41 0.11 0.24 3 CdMnTe (M) 45.9 50.2 3.01 0.18 0.32 0.13 0.22 4 CdMnTe (M) 46.7 49.7 2.88 0.34 0.19 0.22 5 CdZnTe (I) 19.0 38.7 1.25 35.3 2.49 2.8 0.38 6 CdZnTe (I) 8.66 34.0 0.48 37.1 12.7 0.12 3.48 1.24 0.24 7 CdMnTe (I) 12.8 15.1 1.5 17.0 7.16 0.92 19.1 15.3 11.0 8 CdMnTe (I) 34.4 35.6 3.58 12.2 2.8 2.65 8.67 Acknowledgements The financial support of the Civilian Research and De- velopment Foundation (grant UP2-536) and the Science and Technology Center of Ukraine (grant ¹1440) is gratefully acknowledged. Reference 1. R.N. Fesh, P.I. Feichuk, O.E. Panchuk, L.P. Shcherbak, Che- mical etching of cadmium telluride single crystals // Izvestiya AN SSSR, Neorganicheskie Materialy, 17(6), pp. 1118-(1981). 2. V.N. Tomachshyk, Î.Î. Panchuk, Z.F. Tomachshyk, Chemi- cal etching of CdTe with sulphate solution of bichromate potassium // Neorganicheskie Materialy, 31(8), pp.1023-1026 (1995). 3. Z.I. Zakharuk, I.M. Rarenko, O.N. Krylyuk, S.G. Dremlu- zhenko, Yu.P. Stetsko State of cadmium telluride surface after different treatment, // Ukrainskiy Chimischeskiy Zhurnal, 66(12), pp.97-99 (2000). 4. A.K. Gutakovsky, V.M. Eliseev, R.I. Lyubinskaya, N.V. Lyach, A.S. Mardezhov, I.P. Petrenko, L.D. Pokrovsky, I.V. Sabini- na, Yu.G.Sidorov, V.A.Schvets, Study of CdTe sufrace state // Poverkhnost. Fizika. Chimiya. Mechanika, N9, pp.80-87 (1988). 5. M.Sh. Komisarchik, L.M. Prokator, Yu.F. Orlov, The mecha- nism of cadmium selenide etching in alcoholic solution of bromine // Izvestiya AN SSSR, Neorganicheskie Materialy, 20(1), pp.24-27 (1984). 6. I.M. Kotina, L.M. Tukhkonen, G.V. Patsekina, A.V. Shchu- karev, G.M.Gusinskii, Study of CdTe etching process in al- coholic solution of bromine // Semicond. Sci. Technol., 13, pp. 890-894 (1998). 7. V.V. Ratnikov, V.N. Sorokin, V.I. Ivanov-Omskiy, K.E. Miro- nov, I.A. Gerko, V.K. Erganov, V.M. Merinov, X-ray studies of cadmium telluride single crystals structure perfection // Pis�ma v JTF, 14, pp.1410-1413 (1988). 8. C.A.Kshevetskiy, Yu.P.Stetsko, I.M. Fodchuk, I.V. Melni- chuk, V.S. Polyanko, Non-symmetric X-ray topography of single crystals surface layers // Ukrainskiy Fizicheskiy Zhurnal, 35(3), p.444-447 (1990). 9. A.G. Voloshchuk, N.I. Tsypyshchuk, Dependence of equi- librium reaction potentials on pH for CdTe-H2O system // Neorganicheskie Materialy, 38(11), pp.1320-1323 (2002).