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AZÖRBAYCAN KIMYA JURNALI № 3 2018
ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
UDC 541.13.544.65
INFLUENCE OF VARIOUS FACTORS ON THE COMPOSITION OF ELECTRODEPOSITED THIN FILMS Mo-S
V.A.Majidzade, S.F.Cafarova, A.Sh.Aliyev, D.B.Tagiyev
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
[email protected]. ru Received 22.02.2018
The work is devoted to the study of the influence of various factors - temperature, concentration of components in the electrolyte and current density on the composition of electrodeposited thin semiconductor Mo-S films. Obtained results show that with increasing Na2Mo04 concentration, temperature and current density, the amount of molybdenum in cathode deposits increases. The concentration of Na2S03 influences the amount of molybdenum in the obtained films, respectively. It is established that black, uniform, crystalline, shiny coatings of the alloy Mo-S2 are obtained in 333-338 K temperature range, 7 mA/cm2 current density from electrolyte with the composition of 1.0 M Na2Mo04-2H20 and 0.1 M Na2S03.
Keywords: Mo-S thin films, electrodeposition, semiconductor, aqueous electrolyte.
Recently, metal chalcogenides, due to their physical, optical and electronic properties are widely used in various fields of technology [1-4]. Thin films of molybdenum disulfide (M0S2) are vastly used in microelectronics, as well as in the manufacture of new catalysts in electrochemical processes, such as the reaction evolution of hydrogen from electrochemical decomposition of water [5]. Nanostructures of molybdenum disulfide are of interest for a wide range of nanotechnological applications, ranging from the use of inorganic nanotubes in nanoelectronics and the active use of nanoparti-cles in heterogeneous catalysis [6].
Generally, molybdenum disulfide compounds can be obtained in thin film form by various methods, including magnetron sputtering [7], vapor deposition [5], chemical precipitation [8], electrochemical deposition [9, 10]. Among these methods electrodeposition provides simplicity and economy, control of thickness of the film, uniformity and the possibility of depositing thin films on different supports.
In [9] thin films of molybdenum chalcogenides, in particular selenide (MoSe2) and sulfide (M0S2) were successfully deposited on glass substrates coated with an indium-tin oxide compound (ITO) and stainless steel by electrodeposition. The influence of the deposition time on the growth, the structural and optical properties of the films has been studied. The results of X-ray diffraction confirmed the for-
mation of polycrystalline rhombohedral MoSe2 and hexagonal M0S2. Spectrophotometric measurements showed that the optical band gap of thin films decreases with increasing deposition time and have a value 1.12 to 1.22 eV for MoSe2 and 1.65 to 1.74 eV for thin M0S2 films respectively.
Nanostructured thin films of molybdenum disulfide were deposited from aqueous electrolyte containing molybdate and sulfide ions on various substrates at the constant current [10]. Annealing of deposited thin films at high temperatures within the range of 450-700°C transforms the deposited amorphous films into a nanocrystalline structure. UV-vi-sible spectra confirmed the presence of Mo-S alloys in deposited films.
Amorphous thin M0S2 films were obtained by cathodic electrochemical deposition from aqueous and non-aqueous solutions containing tetrathiomolybdate ions at different temperatures [11, 12]. After annealing at high temperatures, the obtained films became crystallized. A difference in the mechanism of electrodeposition from aqueous and ethylene glycol solutions is also discussed. The thickness of the films was 3-10 nm.
In [13], polycrystalline films are electro-deposited on conductive glass substrates coated with tin oxide (Sn02). X-ray diffraction analysis shows that the deposited films have a hexagonal structure with lattice parameters a=¿ = 3.153 A
and c = 12.279 A. The width of the band gap of M0S2 films is equal to 1.68 eV. The thickness of the films was calculated by the weight method and made up 0.80-0.82 ¡am.
The aim of this work is to study the influence of various factors on the composition of electrodeposited thin semiconductive Mo-S films.
Experimental part
Experimental studies on the electrodepo-sition of thin Mo-S films were carried pelow.
Required concentrations of Na2Mo04 2H20 (pure for analysis) and Na2S03 (pure for analysis) were dissolved in distilled water to prepare the electrolytes of the initial components.
The processes of electrochemical deposition are carried out by the potentiodynamic and galvanostatic methods.
Potentiodynamic experiments were carried out in the IVIUMSTAT Electrochemical Interface potentiostat and an electrochemical triode glass cell was used. As a working electrode served a Ni electrode with an area of 2.0 cm2. The reference electrode was a silver chloride electrode, and an auxiliary electrode was a platinum plate with an area of 4.0 cm2. The universal ultrasonic thermostat UTU-4 was used to regulate the temperature in the cell.
Prior to the Ni experiments, the electrodes were purified in concentrated nitric acid and washed with distilled water. Then, under certain conditions (T = 293-303 K, ; = 0.5 A/dm2, t = 180 s), the Ni electrodes were elec-trochemically polished in mixed solution of sulphuric, phosphoric and citric acids and washed with distilled water.
The composition of cathodic deposits Mo-S was determined in JEOL JSX 3222 Element Analyzer using energy-dispersive X-ray fluorescence (EDXRF), the system (JEOL, Japan).
Results and discussion
The electrochemical co-deposition of molybdenum with sulphur has been studied by potentiodynamic method and the potential fields at which they are deposited, was determined [13]. The influence of various factors (temperature, current density, concentration of initial components) on the composition of the films was studied.
Figure 1 shows the effect of the concentration change of Na2MoC>4 in electrolyte on the mass fraction of molybdenum in the composition of cathode films. The effect of Na2MoC>4 concentration was studied within intervals of 0.1-1.2 M. As can be seen from the Figure, the mass fraction of molybdenum in the composition of cathode films increases due to increasing Na2MoC>4 concentration in the electrolyte. In addition, increasing the concentration improves the quality of the obtained deposits and their adhesion to the surface of the electrode. The increase in the current density also increases the molybdenum content of the obtained thin films. However, after 7 mA/cm2 of current density, adhesion and quality of the films deteriorate and a stoichiometric composition destroys. Therefore, as the optimum option were chosen concentration of Na2MoC>4is 1.0 M and current density is 7 mA/cm2.
Fig. 1. Dependence of molybdenum content in electrodeposited thin films of Mo-S on concentration of Na2Mo04 in the electrolyte. Electrolyte (M): 1.0 Na2Mo04+0.1 Na2S03. Current density (mA/cm2): 1 - 2.8, 2 - 3.2, 3-5, 4-1, 5-9. T=338 K.
0.2 0.4 0.6 0.:
' C№jMo04! M
The effect of composition of electrode-posited thin films on the change of the Na2S03 concentration in electrolyte has been also studied at the constant concentration of Na2Mo04. Figure 2 shows the dependence of the effect of the Na2SC>3 concentration change on the amount of Mo in the composition of thin films. When studying the effect of this factor, it is seen that at different current densities, with increasing its concentration from 0.01 to 0.2 M in the electrolyte, the molybdenum content in the deposits decreases from 91.2 to 7.1%. The experimental results show that thin films of stoichiometric composition are obtained at 0.1 M of Na2SC>3 concentration and 7 mA/cm of current density.
Influence one of the main factors - the temperature on the molybdenum content of the films was studied within the 298-348 K intervals (Figure 3).
As can be seen in the Figure, as the temperature of the electrolyte increases, the molybdenum content of the films increases and the quality of the electrodeposited films also changes. The shiny, uniform, black Mo-S coatings are obtained at a temperature 338 K. With further temperature increase, uneven, loose coatings are obtained at the cathode and their adhesion to the electrode surface deteriorates. Therefore, the optimum temperature to obtain thin Mo-S films by the electrochemical deposition method chosen the temperature interval 333-338 K.
Mo. % 100
0.02 0.06 0.1 0.14 0.18 CNa2S03
Fig. 2. Dependence of Mo content in the electrodeposited thin films on Na2S03 concentration in electrolyte. Electrolyte (M): 1.0 Na2Mo04+Na2S03. Current density (mA/cm2): 1 - 2.8, 2 3.2.3 5.4 7,5-9. 7=338 K.
Fig. 3. Dependence of Mo content in the electrodeposited thin films on temperature for electrolyte 1.0 Na2Mo04 + 0.1 Na2S03 - current density (mA/cm2): 7-5, 2-1.
298 308 318 328 338 348 Т. К
The influence of the current density on the molybdenum content in the obtained cath-
9 .
ode films was studied at the 2.8-9 mA/cm intervals. The studies were carried out at different concentrations of the basis component Na2Mo04.
Mo, 0 b 100 ■
2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 ¿.mA/cm2
Fig. 4. Dependence of Mo content in the elec-trodeposited thin films on current density for the samples electrolyte with different molecular masses (M):
1 - 0.2 Na2Mo04 + 0.1 Na2S03
2 - 0.4 Na2Mo04 + 0.1 Na2S03
3 - 0.6 Na2Mo04 + 0.1 Na2S03
4 - 0.8 Na2Mo04 + 0.1 Na2S03 5-1.0 Na2Mo04 + 0.1 Na2S03
<5-1.2 Na2Mo04 + 0.1 Na2S03. 7=338 K.
Figure 4 shows the effect of current density on the composition of the obtained thin films during the electrodeposition of Mo-S alloys. The results show that thin films of stoichiometric composition are obtained from the electrolyte with the composition of 1.0 Na2MoC>4 + 0.1 Na2SC>3 at 7 mA/cm2 of current density. Since in that case the molybdenum and sulphur contents in cathode sediments are 59.8 and 40.2%, respectively. Despite the increase of molybdenum content in cathode deposits, the further increase of the current density deteriorates their quality and adhesion to the electrode surface.
Conclusions
The process of co-deposition of molybdenum with sulphur on Pt electrodes from aqueous electrolytes was studied by the electrochemical method.
The influence of various factors (the concentration of the initial components, temperature and current density) on the electrochemical deposition of thin Mo-S films on Ni electrodes was determined. The results of all the conducted experiments show that an increase of temperature, current density, and concentration of Na2MoC>4 leads to rise of the molybdenum content in cathode films. Under the influence of the concentration of Na2SC>3 the molybdenum content in the obtained films decreases respectively. With helping of these results, the optimum regimen and composition of the electrolyte were chosen to obtain black, uniform, crystalline, shiny coatings of the stoichiometric composition of the M0S2 compound by the electrochemical method. The electrolyte composition is 1.0 M Na2Mo04 2H20 and 0.1M Na2S03, the electrolyte temperature is 333-338 K, the current density is 7 mA/cm2.
References
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ELEKTROKiMYOVi USULLA COKDURULMU§ Mo-S NAZiK T3B3Q3L3Ril\iN TORKlBiNO
MUXTOLiF AMiLLORlN TOSiM
V.A.Macidzad3, S.F.Cafarova, A.§.01iyev, D.B.Tagiyev
Toqdim olunan is clcktrokimvovi tisulla cokdurulmiis Mo-S varimkccirici nazik toboqolorinin torkibino muxtolif amillorin - temperaturan, clcktrolitdo komponcntlorin qatiliginin, сэгэуап sixligimn tosirinin ovronilmosino liosr edil-misdir. Noticolor gostorir ki, Na2Mo04-un qatiliginin, temperaturan vo сэгэуап sixligimn artmasi ib katod cokiintu-brind9 molibdenin miqdan artir. Na2S03-un qatiliginin artmasi ib iso alinan toboqolordo molibdenin miqdan uygun olaraq azalir. Миэууэп cdilmisdir ki, qara, sotli ii/orindo ЬэгаЬэг paylanmi§, kristallik, panltili MoS2 kimyavi birlos-mosinin ortiikbri 333-338 К temperatur intervalinda, 7 mA/sm2 сэгэуап sixliginda, 1.0 M Na2Mo04-2H20 va 0.1 M Na2S03 brkibli elektrolitd9n alimr.
Agar si'n.br: Mo-S nazik t3b3q3hri, elektrogdkdurulni3, yarimkegirici, su elektroliti.
ВЛИЯНИЕ РАЗЛИЧНЫХ ФАКТОРОВ НА СОСТАВ ЭЛЕКТРОХИМИЧЕСКИ ОСАЖДЕННЫХ ТОНКИХ ПЛЕНОК Mo-S
В.А.Меджидзаде, С.Ф.Джафарова, А.Ш.Алиев, Д.Б.Тагиев
Работа посвящена изучению влияния различных факторов - температуры, концентрации компонентов в электролите, плотности тока на состав электроосажденных тонких полупроводниковых пленок Mo-S. Результаты показывают, что с повышением концентрации Na2Mo04, температуры и плотности тока содержание молибдена в катодных осадках увеличивается. А с повышением концентрации Na2S03 содержание молибдена в полученных пленках уменьшается. Установлено, что черные, равномерные, кристаллические, блестящие покрытия Mo-S2 получаются в интервале температур 333-338 К при плотности тока 7 мА/см2из электролита состава 1.0 М Na2Mo04-2H20 + 0.1М Na2S03.
Ключевые слова: тонкие пленки Mo-S, электроосаждение, полупроводник, водный электролит.
