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UDC 541.13.544.65
AZERBAIJAN CHEMICAL JOURNAL No 1 2020
ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
CO-ELECTRODEPOSITION OF THIN Mo-S FILMS
S.F.Jafarova
M.Nagiyev Institute of Catalysis and Inorganic Chemistry NAS of Azerbaijan
Received 03.06.2019 Accepted 04.11.2019
The co-electrodeposition process of Mo with S from aqueous electrolytes was investigated. It has been determined the range of potentials of co-electrodeposition of Mo with S by plotting the cyclic polarization curves on a Pt-electrode. When studying the obtained thin films by the methods of the X-ray phase and Raman spectroscopic (Raman scattering) analyses, it was found that the peaks on the curve correspond to the formed MoS2 compound.
Keywords: MoS2, polarization, thin films, electrodeposition, semiconductors.
doi.org/10.32737/0005-2531-2020-1-16-19
Thin films are widely used as various functional coatings to increase strength, corrosion resistance, improve the magnetic and electrical properties of materials applied in aviation and space technology, mechanical engineering, medicine, energetics, and digital microelectronics. Recently, studies on the getting thin films by the electrochemical method from various electrolytes have been intensively tested. The use of thin-film materials reduces the material consumption of devices for various purposes. Thin-film semiconductors with sulfur are of great interest for the photoelectrochemical and photochemical conversion of solar energy.
Dichalcogenides of transition metals are layered materials with strong in-plane and weak out-of-plane interactions, allowing them to exfoliate into two-dimensional thin sheets. Although they have been studied for decades, recent advances in the characterization of na-noscale materials and device manufacturing have opened up new possibilities for them in nano- and optoelectronics.
The authors of the work [1] have electro-chemically deposited MoS2 films using ionic liquids. This technique is especially useful for the inexpensive, environmentally friendly synthesis of molybdenum chalcogenides and mixed metal chalcogenides. The electrodeposited low-layer MoS2 showed characteristic fluorescence properties, demonstrating that these materials have optoelectronic properties of ultra-thin MoS2 film, preferably, for applications such as
photodetectors and light-emitting devices. In addition, this method allows an optional setting of the film thickness and demonstrates high photoluminescent activity during decreasing the number of layers.
MoS2 can be electrodeposited from different media - from molten salts, ionic liquids, non-aqueous and aqueous solutions [2]. The magnitude of the potential at which MoS2 is deposited depends on the medium from which the deposition occurs. Deposits obtained at more negative potentials are rich in molybdenum, and therefore essentially metallic. The authors of [2] found that the temperature of the electrolyte significantly affects the growth of deposits since a higher temperature leads to faster growth rates of crystals, as well as to adhesion of the films. At high values of pH, the deposition rate is relatively low, while at lower pH values, mixed - phase films of MoS2 are obtained. It was also found that the electrodeposi-tion of MoS2 from high-temperature molten salt permits to obtain clearly defined crystals. The photoelectrochemical behavior of MoS2 electrodes in neutral and alkaline electrolytes showed that the MoS2 semiconductor reacts with water, which leads to its decomposition into metal ions and molecular sulfur.
Nanostructured thin films of molybdenum disulfide have been deposited on various substrates in the electrolyzer at a constant current from an aqueous electrolyte containing molyb-date and sulfide ions by the authors of [3]. An-
nealing the deposited thin films at higher temperatures in the range of 450-7000C, turns the deposited amorphous films into a nanocrystalline structure. UV and visible spectra confirmed the presence of Mo-S in the deposited films.
In studies [4, 5], thin films of molybdenum sulfide (MoSx) have been obtained on substrates of indium-tin-oxide/polyethylene naphthalate (ITO/PEN) by a pulse electrochemical deposition method. The results showed that thin MoSx films are uniformly deposited on flexible ITO/PEN substrates and are active catalysts for triiodide reduction. MoSx thin films are obtained at room-temperature and atmospheric-pressure in a simple and quick way. This is an important practical contribution to the production of flexible, inexpensive thin-film solar cells based on plastic substrates.
According to the literature, of the electrochemical deposition of molybdenum with sulfur have been studied differently. To obtain accurate results in this area, the aim of this work is to study the kinetics of the co-electrodeposition process of molybdenum with sulfur from an aqueous solution and to determine the range of potentials in which they are deposited. As you know, to obtain thin films of semiconductor materials by co-deposition, the first need to do is to study the kinetics and mechanism of the electro-reduction process of the components separately. This was investigated by us in [6, 7].
Experimental part
The process of electrochemical deposition of molybdenum with sulfur from aqueous electrolytes was carried out as follows. Solutions containing molybdenum and sulfur are
prepared separately. The molybdenum solution contains 1M Na2MoO42H2O, and sulfur solution 0.1 M Na2SO3.
Polarization curves were plotted using an IVIUMSTAT Electrochemical Interface poten-tiostat. An electrochemical three-electrode glass cell was used. A Pt-electrode with an area of 0.4 cm2 was used as a working electrode. The silver chloride electrode served as the reference electrode, and the platinum plate with an area of 4 cm2 served as the auxiliary electrode.
The phase composition of the obtained thin layers was determined in the "D2 Phazer" X-ray phase analyzer of Bruker Company (CuKa-radiation Ni filter).
Raman scattering of Mo-S samples (Raman spectroscopy) was studied using Niodim YAG laser beams in a device of 3D Confocal Raman System, Micro-NanoScale Microspec-troscopy, Nanofinder 30 (Tokyo Instr., Japan) at X = 532 nm.
Results and their discussion
The electrochemical reduction processes of molybdenum [6] and sulfur [7] were studied separately to determine the potential region, deep reduction, and the nature of polarization for carrying out joint electrochemical deposition, as described above.
As is seen from the figure, the electrochemical reduction process of molybdate ions carries out within 0.2-(-0.7)V potential interval (Figure 1, curve 1), while of sulphit ions in the range of 0.4-(-0.3)V potential (Figure.1, curve 2) it was determined that the electrochemical reduction of both ions is accompanied by electrochemical polarization.
Potential
Fig.l. Cathodic polarization curves of electrodeposition process of molybdate ions (/) and sulphit ions (2) from aqueous electrolytes on the Pt electrode. Electrolyte (M): 1 - 1 Na2MoO4-2H2O; 2 - 0.1 Na2SO3; T = 298 K, Ev=0.02 V/s.
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S.F.JAFAROVA
Fig.2. Cyclic polarization curve of electrodeposi-tion process of molybdenum with sulfur from aqueous electrolytes on Pt electrode. Electrolyte (M): 1Na2MoO4-2H2O + O.lNazSOs; T = 298 K, EV=0.02 V/s.
Figure 2 shows the cyclic polarization curve of the electrochemical co-deposition of molybdenum with sulfur. As can be seen from the figure, the electrochemical deposition occurs in stages within potential intervals of 0.3-(-0.65) V on the Pt-electrode according to the following reaction:
Mo4+ + 2S2"^MoS2.
(1)
Starting from the 0.3V potential, on the electrode surface, the electrodeposition of sulfur
occurs till -0.3 V. Then, in the range of potentials -0.3 - (-0.65) V, the co-electrodeposition of molybdenum with sulfur begins reaction (1). In this case, the surface of the electrode is covered with a black layer. The continuation of the process is presented on the anode branch of the cyclic curve. The peak obtained at the potential of -0.3 V pertains to the dissolution of the obtained molybdenum compound with sulfur, but after 0.2 to 1.0 V, it relates to the dissolution of sulfur [8, 9]. The studying electrodeposition process up to -0.7V is related to observing the release of hydrogen after this potential value.
Thin films obtained on the surface of a platinum electrode were studied using various analysis methods. Figure 3 shows the X-ray diffraction pattern of the deposited Mo-S films. As can be seen from the figure, in the X-ray diffraction pattern, there are peaks corresponding to the MoS2 compound. This is also confirmed by Raman scattering. Since the active shift of Raman scattering for molybdenum disulfide is recorded in the range of 350-450 cm-1. Here, the peaks located on the surface at 350 and 380 cm-1 correspond to sulfur atoms fluctuating in one direction, and the peak located at 420 cm-1 is related to the molybdenum atom.
Fig. 3. X-ray diffraction pattern for MoS2 compound. Electrolyte (M): 1 Na2MoO42H2O + 0.1Na2SO3; T = 298 K, EV=0,02 V/s.
Conclusions
The voltammetric method was used to study the process of co-deposition of Mo-S on Pt-electrodes from aqueous electrolytes. It was determined that co-deposition occurs in the potential region of -0.3-(-0.65) V. Also, using X-ray phase analysis and Raman scattering, it was found that noticeable peaks confirm the codeposition process and the obtaining the MoS2 compound resulting from this co-deposition.
References
1. Murugesan S., Akkineni A., Chou B.P., Glaz M.S., Vanden Bout D.A., Stevenson K.J. Room Temperature Electrodeposition of Molybdenum Sulphide for Catalytic and Photoluminescence Applications. ACS Nano. 2013. V. 7. No 9. P. 8199-8205. doi:10.1021/nn4036624
2. Aliyev A.Sh., Elrouby M., Cafarova S.F. Electrochemical synthesis of molybdenum sulphide semiconductor. Materials Science in Semiconductor Processing. 2015. V. 32. P. 31-39.
3. Ghosh S.K., Srivastava C., Nath S., Celis J.P. Simple Formation of Nanostructured Molybdenum Disulfide Thin Films by Electrodeposition. International Journal of Electrochemistry. 2013. V. 2013. Article ID 138419, 7 pages, http://dx.doi.org/10.1155/2013/138419
4. Cheng C.K., Hsieh C.K. Electrochemical deposition of molybdenum sulphide thin films on conductive plastic substrates as platinum-free flexible counter electrodes for dye-sensitized solar cells. Thin Solid Films. 2015. V. 584. P. 52-60
5. Lin C.-H., Tsai C.-H., Tseng F.-G., Ma C.-C. M., Wu H.-C., Hsieh C.-K. Three-dimensional vertically aligned hybrid nanoarchitecture of two-dimensional molybdenum disulphide nanosheets anchored on directly grown one-dimensional carbon nanotubes for use as a counter electrode in dye-sensitized solar cells. J. Alloys and Compounds. 2017. V. 692. P. 941-949. doi.org/10.1016/ j.jallcom.2016.09.149.
6. Cafarova S.F., Aliyev A.Sh., Elrouby M., Soltanova N.Sh., Tagiyev D.B. Studying the electrochemical deposition process of molybdenum from aqueous solution of molybdate ions. J. Elec-trochem. Sci. Eng. 2015. V. 5. No 4. P. 231-235; doi: 10.5599/jese.219.
7. Cafarova S.F., Macidzada V.A., Oliyev A.§. Tio-sulfat ionlarinin molibden elektrodda elektrore-duksiya prosesinin tadqiqi. Chemical Problems. 2017. № 1. S. 72-76.
8. Majidzade V.A., Cafarova S.F., Aliyev A.Sh., Nu-riyev Y.A., Farhatova N.B., Tagiyev D.B. Electrochemical deposition of thin semiconductive Mo-S films. Azerb. Chem. Journ. 2019. № 1. P. 63-13.
9. Majidzade V.A., Cafarova S.F., Aliyev A.Sh., Tagiyev D.B. Influence of various factorson the composition of electrodeposited thin films Mo-S. Azerb. Chem. Journ. 2018. No 3. P. 6-10.
Mo-S NAZIK TOBaQOLORININ BIRGO ELEKTROCOKDURULMOSI
S.F.Cafarova
Taqdim edilan i§da elektrolitlarin suda mahlullarindan molibden va kükürdün birga elektrokimyavi Qókma prosesi oyranilmi§dir. Pt elektrodu üzarinda tsiklik polyarizasiya ayrilarinin gakilmasi ila Mo va S-ün birga elektrokimyavi Qókma prosesi ügün potensial sahasi tayin edilmi§dir. Alinan nazik tabaqalarin müxtalif müasir metodlarla oyranilmasi zamani, müayyan edilmi§dir ki, rentgen faza va Raman sapalanmasi (kombinassion sapalanma) analizlari naticasinda alda olunan piklar MoS2 birla§masina uygundur.
Agar sozlar: MoS2, polyarizasiya, nazik tabaqalar, elektrokimyavi gókdürülma, yarimkegirici.
СОВМЕСТНОЕ ЭЛЕКТРООСАЖДЕНИЕ ТОНКИХ ПЛЕНОК Mo-S
С.Ф.Джафарова
В данной работе изучено совместное электроосаждение молибдена с серой из водных электролитов. Снятием циклических поляризационных кривых на Pt-электроде определена область потенциалов совместного электроосаждения Mo с S. При исследовании полученных тонких пленок различными современными методами установлено, что пики, полученные в результате рентгенофазовых и Раман спектроскопических (комбинационное рассеяние) анализах соответствуют получению соединения MoS2.
Ключевые слова: MoS2, поляризация, тонкие пленки, электроосаждение, полупроводники.
