Journal of Alloys and Compounds 487 (2009) 786 789
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Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
MoS2: Preparation and their characterization
K.M. Garadkara,", A.A. Patila, P.P. Hankarea, P.A. Chateb, D.J. Sathea, S.D. Delekarc
a
Department of Chemistry, Material Science Research Laboratory, Shivaji University, Kolhapur 416004, Maharashtra, India
b
Department of Chemistry, J.S.M. College, Alibag, Maharashtra, India
c
Dr. B.A.M. University, P.G. sub- center, Osmanabad, Maharashtra, India.
a r t i c l e i n f o a b s t r a c t
Article history:
Molybdenum disulphide thin films were deposited using chemical bath deposition method on non-
Received 11 April 2009
conducting glass substrate using tartaric acid as a complexing agent at 363 K. The films were characterized
Received in revised form 5 August 2009
by X-ray diffraction, scanning electron microscopy, optical absorption and electrical measurements. X-
Accepted 8 August 2009
ray diffraction pattern shows that polycrystalline with hexagonal structure. The direct optical band gap
Available online 22 August 2009
was found to be 1.8 eV. Electrical measurement suggests that specific conductance was found in the order
of 10-5 to 10-2 ( cm)-1 and showing n-type conduction mechanism.
Keywords:
© 2009 Elsevier B.V. All rights reserved.
Thin films
Optical properties
X-ray diffraction
1. Introduction This communication reports the various preparative parame-
ters such as growth mechanism, structural, morphological, optical,
In the recent years there has been a great deal of interest in the electrical properties that were studied.
study of transition metal dichalcogenides because of their possible
2. Experimental details
applications in lubricants, photoactive material in photoelectro-
All the chemical reagents used for deposition were of analytical grade. It includes
chemical solar energy converters because the main advantage
ammonium molybdate, tartaric acid, hydrazine hydrate, ammonia and thiourea. All
associated with the prevention of electrolyte corrosion [1 5]. The
the solutions were prepared in double distilled water. For deposition of molyb-
crystal structure of such materials is layer of S Mo S interact-
denum disulphide thin film the bath solution was made by vigorous mixing of
ing with each other by weak Van der Waals forces which allow 10 mL (0.1 M) ammonium molybdate solution, 5 mL (0.1 M) tartaric acid, 12 mL (10%)
hydrazine hydrate, and 15 mL ammonia solution in 200 mL beaker. To this, 20 mL
adjacent layer to slide [6]. Molybdenum disulphide includes high
(0.1 M) thiourea solution was added and the total volume of the reaction mixture
density batteries because of its appreciable electrical conductiv-
was made up to 150 mL by adding double distilled water. A reaction vessel was kept
ity and ability to reversibly intercalate lithium [7,8]. It appears to
in oil bath. Glass slides were attached vertically on a specially designed substrate
be a very promising semiconducting material for various appli- holder and rotated in the reaction mixture with a speed of 60 62 rpm. The temper-
ature of the oil bath was then allowed to increase up to 363 K slowly. After 90 min,
cations such as hydrosulphurization catalysts, solid lubricants for
the glass slides were removed from the bath. The films were rinsed with double dis-
tribological applications in high temperature and vacuum environ-
tilled water, dried naturally and preserved in a dessicator over anhydrous calcium
ment where the use of liquid lubricants becomes ineffective [9,10].
chloride.
The spin coating, metal organic chemical vapour deposition, chem-
ical vapour deposition, sputtering technique, sulphurization of
3. Characterization of molybdenum disulphide thin films
metal, laser evaporation, pulsed electrodeposition, and microwave
synthesis are some of the methods used for the deposition of Molyb- Crystallographic studies of molybdenum disulphide thin film
denum disulphide thin films [11 18]. Chemical bath deposition were characterized by using a Phillips PW-1710 X-ray diffrac-
method is an alternative, low cost method that can be operated tometer with Cu K 1 line ( = 1.54056 Å) in 2 range from 10ć%
at low processing temperature and provides large area deposition. to 80ć%. The optical properties were studied by taking absorption
The method consists of complexed metal ion of interest, source spectrum of film using a Hitachi-330 (Japan) double-beam spec-
of chalcogen ions, the stability equilibrium of which provides a trophotometer in the range of 400 800 nm. A substrate absorption
concentration of ions small enough for controlled homogeneous correction was made by placing an identical uncoated glass slides
precipitation of material in the thin film form on substrate [19,20]. in the reference beam. The microstructure was studied by using
JEOL-JSM-6330 Japan, scanning electron microscope. The electrical
conductivity measurements were carried out in the temperature
" range of 303 503 K on a Zintek 502 BC milliohmmeter using the
Corresponding author. Tel.: [phone]; fax: [phone].
E-mail address: [e-mail] (K.M. Garadkar). two-probe method.
0925-8388/$  see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2009.08.069
K.M. Garadkar et al. / Journal of Alloys and Compounds 487 (2009) 786 789 787
4. Results and discussion
4.1. Growth mechanism of MoS2 thin films
Molybdenum disulphide thin films have been deposited by
decomposition of thiourea in aqueous alkaline medium contain-
ing ammonium molybdate as a source of molybdenum and tartaric
acid as complexing agent. Tartaric acid controls the molybdenum
ions concentration in the reaction vessel. Hydrazine hydrate acts
as a reducing agent. A slow increase in temperature decomposes
moderately stable thiourea to yield S2-, while hydrazine hydrate
reduce Mo6+ to Mo4+. The dissociation of Mo A (tartarate) com-
plex at higher temperature liberates bear Mo4+ ions that react with
S2- ion to get molybdenum disulphide thin film. The growth mech-
anism can be described from the following reactions:
Mo6+ + 3A2- [Mo(A)3]
[Mo(A)3] + 2NH2 NH2 + 2OH- Mo4+ + 3A + 2H2O + 2N2Ä™!
Fig. 1. XRD pattern of MoS2 thin film.
CH4N2S + OH- SH- + CH2N2 + H2O
SH- + OH- S2- + H2O
Mo4+ + 2S2- MoS2
The deposition of molybdenum disulphide film occurs when
the ionic product of Mo4+ and S2- exceeds the solubility prod-
uct. At 298 K temperature, supersaturation is low. In the growth
process, no film formation occurs within the first 30 min. This is
the induction period required to form nucleation centers on the
substrates. The presence of induction period suggests ion-by-ion
growth mechanism instead of cluster-by-cluster. Speed of rotation
60 62 rpm was selected to deposit molybdenum disulphide thin
films. The films obtained are uniform, well adherent and yellow in
colour.
4.2. Crystallographic and morphological characterization
The X-ray diffraction (XRD) patterns of MoS2 thin films are Fig. 2. SEM micrographs of MoS2 thin film.
shown in Fig. 1. The presence of sharp peaks is an indication of the
polycrystalline nature of the films. Comparison of observed  d with
almost similar size is observed. Most of the grains are intercon-
standard  d values confirms that chemically deposited film shows
nected to each other. The average grain size of material is reported
hexagonal structure (JCPDS 73-1508). The XRD analysis reveals
in Table 1.
that the obtained films were mono-phase and show prominent
(3 0 0), (3 2 0), (4 1 0), (6 0 0), (6 2 0), and (8 0 1) peaks. The diffused
4.3. Optical properties
background is due to amorphous glass substrate and also to some
amorphous phase present in the MoS2 thin films. The lattice param-
The optical absorption spectrum of MoS2 thin film sample at
Ú Ú
eter was found to be a = 12.30 Á and c = 3.45 Á. The crystallite size of
room temperature was studied by UV vis NIR double-beam spec-
the material was calculated by using Debye Scherrer formula and
trophotometer in the range of 400 800 nm The fundamental edges
Ú
found to be 189 Á. of MoS2 found to be strongly dependent on photon energy, indi-
SEM micrograph of MoS2 thin films at 1000× magnification is cating the presence of more than one transition. Fig. 3 shows the
shown in Fig. 2. The film shows uniform grains and well covers variation of optical absorbance with wavelength. The optical stud-
to glass substrate. The distribution of nodular, spherical grains of ies show that the films are absorptive. The value of absorption
Table 1
Structural and morphological characterization of MoS2 thin film.
Film  d values (Å) hkl planes Grain size (Å) Cell parameter (Å)
Observed Standard XRD SEM
3.5918 3.5507 300
2.4496 2.4437 320 a = 12.30
MoS2 2.3038 2.3244 410
1.8396 1.7753 600 189 193
1.4722 1.4771 620
1.2264 1.2264 801 c = 3.45
788 K.M. Garadkar et al. / Journal of Alloys and Compounds 487 (2009) 786 789
Table 2
Optical and electrical characterization of MoS2 thin film.
Sample Band gap (eV) Activation (eV) energy Specific conductance ( cm)-1
HT LT 303 K 523 K
MoS2 1.8 0.882 0.092 1.3 × 10-5 2.3 × 10-2
Fig. 5. The variations of log (conductivity) with inverse temperature.
close to the characteristic direct band gap value (1.78 eV), which
agrees well with the earlier reported value [22].
Fig. 3. Absorption spectrum of MoS2 thin film.
4.4. Electrical conductivity and thermoelectrical studies
coefficient depends upon radiation energy as well as the com-
The dark electrical conductivity of MoS2 thin film on non-
position of films. The interpretation of experimental results is
conducting glass slide was determined by using a  dc two-probe
most often performed with the help of formula derived for three-
method, in the temperature range of 303 523 K. The specific con-
dimensional crystal model. The band gap  Eg was calculated using
ductance was found to be in the order of 10-2 ( cm)-1 which
the following relation [21]:
agrees well with the earlier reported value [23]. The values of spe-

A cific conductance at 303 and 523 K are reported in Table 2. The
Û = (h - Eg)n
electrical properties of polycrystalline thin films mainly depend
h
upon their structural characteristics and composition [24,25]. It is
where h is the photon energy and A and n are constants. For
observed that the conductivity of the film increases with increase
allowed direct transition n = 1/2, direct forbidden transition n = 3/2
in temperature. This indicates the semiconducting behavior of the
and indirect allowed transition n =2.
thin film. The electrical conductivity variation with temperature
The band gap  Eg was determined from the variation of (Ûh )2
during heating and cooling cycles was found to be different and
with h (Fig. 4). The linear nature of plot indicates the existence of
this shows that the films undergo an irreversible change due to
direct transition. The band gap was determined by extrapolating
annealing out of non-equilibrium defects during first heating.
the straight portion of energy axis at Û = 0. The band gap was found
A plot of log (conductivity) versus absolute temperature for the
to be 1.8 eV for molybdenum disulphide thin film, which is very
cooling curve is shown in Fig. 5. A plot show that electrical conduc-
tivity has two linear regions. The low-temperature extrinsic and
high-temperature intrinsic regions indicate the presence of two
conduction mechanisms. The high-temperature region is due to
grain boundary scattering limited conduction mechanism, while
a low-temperature region is due to variable range hopping con-
duction mechanism. The activation energy is calculated using the
exponential form of Arrhenius equation [26]:

-Ea
= 0exp
KT
where the terms have usual meaning. The activation energies are
0.092 and 0.882 eV for low and high temperature respectively. In
thermoelectric power measurements, the film shows n-type con-
ductivity [27].
5. Conclusion
MoS2 thin films were deposited by using relatively simple chem-
ical bath deposition technique. The X-ray diffractogram reveals that
the films are polycrystalline in nature having hexagonal phase.
Fig. 4. Plots of (Ûh )2 against photon energy.
Optical study shows that band gap energy value 1.8 eV.Temperature
K.M. Garadkar et al. / Journal of Alloys and Compounds 487 (2009) 786 789 789
dependence of electrical conductivity shows that films have semi- [11] C. Amory, J.C. Bernede, N. Hamdadou, Vacuum 72 (2004) 351.
[12] J. Putz, M.A. Aegerter, Thin Solid Films 351 (1999) 119.
conducting in nature.
[13] A. Jäger-Waldau, M. Lux-Steiner, R. Jäger-Waldau, R. Burkhardt, E. Bucher, Thin
Solid Films 189 (1990) 339.
Acknowledgement [14] A.A. van Zomeren, J.H. Koegler, J. Schoonman, P.J. van der Put, Solid State Ionics
333 (1992) 53.
[15] M. Regula, C. Ballif, J.H. Moser, F. Levy, Thin Solid Films 280 (1996) 67.
Authors (AAP) is very thankful to UGC, New Delhi for financial
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support through UGC-SAP Meritorious fellowship. [17] S.M. Delphine, M. Jayachandran, C. Sanjeeviraja, Mater. Res. Bull. 40 (2005)
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[18] J. Ouerfelli, S.K. Srivastava, J.C. Bernede, S. Belgacema, Vacuum 83 (2009)
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