Chemistry, Technology and Application of Substances Vol. 3, No. 1, 2020 M. A. Sozanskyi, V. E. Stadnik, P. Yo. Shapoval, O. P. Kurylo, R. R. Guminilovych Lviv Polytechnic National University, Department of Physical, Analytical and General Chemistry [email protected] QUANTUM-CHEMICAL MODELING OF THE CHEMISTRY PROCESS OF THE ZINC SULFIDE AND ZINC SELENIDE FILMS SYNTHESIS https://doi.org/ The quantum-chemical modeling of the synthesis process chemistry of ZnS and ZnSe in aqueos solutions was carried out.For modeling the simulation of ZnS synthesis was made through the formation of Zn(II) complex forms with the trisodium citrate, sodium hydroxide and the pair of ammonium hydroxide with hydrazine hydrate. For the synthesis of ZnSe was used only sodium hydroxide.It was established that this process passes through several intermediate stages with the transitional reactive complexes formation. On the basis of obtained data, the energy stages diagrams are constructed and the comparison of ZnS and ZnSe synthesis processes with various complexing agents is presented.The ZnS and ZnSe filmswere obtained by chemical synthesis method from an aqueous solution of zinc salt, complexing and chalcogenizing agents. X-ray phase analysis confirmed the formation of desired compounds, as well as the formation of ZnO in the case of ammonium hydroxide – hydrazine hydrate usage at the synthesis of ZnS films. Key words: zinc sulfide, zinc selenide, thin films, quantum-chemical modeling, semiempirical methods, semiconductors. Introduction which occur between the liquid and solid phases Semi-empirical method of quantum chemistry (newly formed the reaction product and substrate) at is one of the modeling reactions methods between a short distance from the latter. molecules and substances by quantum-chemical cal- For the some metals ions (Me = Pb2+, Cu2+, culations [1–3]. In Refs. [4–6], the theoretical basis Cd2+, Hg2+), the formation of complexes with 2+ of metal sulfides films formation from aqueous thiourea of [Me((NH2)2CS)4] type was established solution were described. Among the main factors [4, 7]. From the reference data [4], the value of the affecting the course of the reaction, the following stability constant of such zinc complex is very small can be distinguished: (often absent in reference books),which does not 1. Concentration of initial reagents of the apply to the mentioned above metals. So it is logical solution from which depositionismade and the phy- to assume the formation of intermediate complexes sical parameters of the process (temperature, syn- of [Ln∙∙∙Zn∙∙∙(NH2)2CS] type, where zinc is coor- thesis duration, etc.); dinated on the one hand by ligands of the comp- 2. Nature of complexing and chalcogenizing lexing agent, and on the other by thiourea. The reagents that surround the metal ion and generate decomposition process of such intermediate comp- chalcogen ions during the synthesis, respectively; lexes, as a rule, involves the formation of molecular 3. Nature of the substrate surface on which the forms, and then monomolecular layers of zinc films are formed. chalcogenide. To reduce the formation of by-pro- It was noted [4] that during the synthesis ducts, it is necessary to create conditions in which process, the formation of transitional molecular the supply of zinc- and chalcogen-containing agents reactive complexes (TMRC), associates, cluster and will be the same. It is also worth noting that some colloidal forms were possible in the working solution complexing agents perform only one function – the due to cooperation and fluctuation phenomena, formation of a complex with metal. In this case, it is 1414 Quantum-chemical modeling of the chemistry process of the zinc sulfide and zinc selenide films synthesis necessary to add an additional pH regulator to ensure Results and discussion the stability and reactivity of the complex. Other The results of quantum chemical modeling of complexing agents are able tofulfill two functions at the ZnS and ZnSe films synthesis chemistry in the same time – to coordinate the metal ion and aqueous solutions with various complexing agents by create the required hydrogen index of the solution. semi-empirical methods are presented in table 1. The geometry of starting zinc complexes are illustratedin Aim of the work Fig. 1–3. The aims of the present study are the follo- Quantum-chemicalmodelingof ZnS synthesis wing: 1. Implementationofquantum-chemical mode- chemistry with Na3C6H5O7. ling of the ZnS and ZnSe synthesis processes Initially, when mixing solutions of zinc salt – withtheuseof PM7 method in MOPAC 2012 and trisodium citrate, a soluble [Zn(C6H5O7)] software package. This could be made on the basis of complex is formed (Fig. 1), where citrate ion plays the hypothesis about the possibility of formation of the role of a ligand. transient reactive complexes, associates, clusters, As can be seen from the conducted quantum- structures of colloidal nature, which are structural chemical modeling(table. 1, no. 1, stages 1–3) that units during the synthesis of zinc chalcogenide films after adding thiourea and a small amount of pH due to the effects of co-operation and fluctuation in regulator to the solution, the 3– the working solution. 2. Comparison of the obtained [(NH2)2CS∙∙∙Zn(OH)2(C6H5O7)] TMRC is formed results of ZnS and ZnSe simulations with the in the early stages of deposition. In the TMRC the investigated properties of respective films. 3. Feasi- Zn atom is coordinated with the S atom (Fig. 4). This bility and efficiency evaluation of the synthesis in process is accompanied by a slight endoeffect, that observed systems. is, energy absorption. Next, starting from stage 3 to stage 6, the Materials and research methods formed complex undergoes rearrangement of two Modeling and calculations of the system hydrogen atoms of (NH2)2CS with two hydroxyl energy change (ΔE) for the synthesis stages of zinc groups and detaching of two water molecules. As a 3– sulfide and zinc selenide were carried out by the result, [(N2H2СS∙∙∙Zn(C6H5O7)] TMRC is formed. semi-empirical method PM7 [8] with the use of The result of these stages is a decrease in total MOPAC 2012 software package [9] and the energy of the system. Winmostar graphical interface [10]. At the last stage, which is the most energy- The synthesis of ZnS films was carried out intensive, the newly formed intermediate complex from a working solution prepared by mixing aqueous decomposed with the formation of zinc sulfide, solutions of zinc chloride (ZnCl2), complexing agent, citrate ion and cyanamide (stages 6–7). thiourea ((NH ) CS) and, if necessary, the pH regu- 2 2 During deposition process, the citrate ion lator. Solutions of trisodium citrate (Na C H O ), 3 6 5 7 (C H O 3–) does not change its structure and sodium hydroxide (NaOH), and a pair of ammonium 6 5 7 performs only a ligand role. hydroxide (NH4OH) with hydrazine hydrate (N2H4·H2O) were used as complexing agents. The Quantum-chemicalmodelingof ZnS synthesis exact synthesis parameters of ZnS films are given in chemistry with NaOH. ref. [11]. In the case of mixing of a zinc salt solution The synthesis of ZnSe films was carried out with an excess of sodium hydroxide solution, which from a working solution prepared by mixing aqueous is a complexing agent and pH regulator at the same solutions of zinc chloride (ZnCl2), sodium hydroxide time, a soluble complex of tetratrahydroxozincate and elemental selenium (Se) dissolved therein with 2– ([Zn(OH)4] ) is formed (Fig. 2). the presence of hydrazine hydrate. The exact synthe- As can be seen from the performed modeling sis parameters of ZnS films are given in ref. [12, 13]. The X-ray diffraction patterns of deposited (table 1, no. 2, stages 1–2) that TMRC 2– ZnS and ZnSe films samples were performedwith the [(NH2)2CS∙∙∙Zn(OH)4] is formed at the beginning use of DRON-3.0 diffractometer (Cu Kα–radiation). of the deposition, after the addition of thiourea in the The primary treatment of films diffractogram for the working solution (Fig. 5). InthisTMRC, the zinc identification of phases was carried outby using atom is coordinated with the sulfur atom of the Powder Cell program [14]. thiourea, with a slight increase in system energy. 15 M. A. Sozanskyi, V. E. Stadnik, P. Yo. Shapoval, O. P. Kurylo, R. R. Guminilovych Table 1 Modeled stages of ZnS and ZnSe films synthesis and energy stages diagrams Complexing No. Film Energy stages diagrams Modeled stages agent -3000 Stages 1→3: ZnS (Na3C6H5O7) – – -3050 [Zn(C6H5O7)] + 2OH + (NH2)2CS → 3– → [(NH2)2CS∙∙∙Zn(OH)2(C6H5O7)] ; -3100 Stages 3→6: 3– 1. ZnS Na3C6H5O7 E, kJ/mol -3150 [(NH2)2CS∙∙∙Zn(OH)2(C6H5O7)] → 3– → [(N2H2СS∙∙∙∙∙Zn(C6H5O7)] + 2H2O ; -3200 Stages 6→7: 3– -3250 [(N2H2СS∙∙∙Zn(C6H5O7)] → ZnS↓ + 1 2 3 4 5 6 7 3– + C6H5O7 + CH2N2 . Stage number Stages 1→2: 2– -1550 [Zn(OH)4] + (NH2)2CS → 2– ZnS (NaOH) → [(NH2)2CS∙∙∙Zn(OH)4] ; -1600 Stages2→5: -1650 2– [(NH2)2CS∙∙∙Zn(OH)4] → 2– -1700 → [(N2H2СS∙∙ Zn(OH)2] + 2H2O ; 2. ZnS NaOH E, kJ/mol -1750 Stages5→6: [(N H СS∙∙ Zn(OH) ]2– → -1800 2 2 2 2– [S∙∙∙Zn(OH)2] + CH2N2 ; -1850 1 2 3 4 5 6 7 Stages 6→7: Stage number 2– – [S∙∙∙Zn(OH)2] → ZnS↓ + 2OH . Stages 1→2: -350 2+ – [Zn(NH3)4] + 2OH → Zn(OH)2 + ZnS (NH4OH + N2H4H2O) -400 4NH3↑; -450 Stages 2→3: Zn(OH)2 + (NH2)2CS → NH4OH + -500 3. ZnS E, kJ/mol → [(NH2)2CS∙∙∙Zn(OH)2] ; N2H4·H2O -550 Stages 3→7: -600 [(NH2)2CS∙∙∙Zn(OH)2] → -650 → ZnS↓ + CH2N2 + 2H2O ; 1 2 3 4 5 6 7 Stage number By-process: Zn(OH)2→ZnO+ H2O . -2300 ZnSe (NaOH) -2400 Stages 1→2: 2- 2- 4– [Zn(OH)4] + Se → [Se∙∙∙Zn(OH)4] ; -2500 4.