Journal of Alloys and Compounds 487 (2009) 786–789

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Journal of Alloys and Compounds

j o u r n a l h o m e p a g e :

w w w . e l s e v i e r . c o m / l o c a t e / j a l l c o m

MoS

2

: Preparation and their characterization

K.M. Garadkar

a

,

∗

, A.A. Patil

a

, P.P. Hankare

a

, P.A. Chate

b

, D.J. Sathe

a

, S.D. Delekar

c

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

Article history:
Received 11 April 2009
Received in revised form 5 August 2009
Accepted 8 August 2009
Available online 22 August 2009

Keywords:
Thin films
Optical properties
X-ray diffraction

a b s t r a c t

Molybdenum disulphide thin films were deposited using chemical bath deposition method on non-
conducting glass substrate using tartaric acid as a complexing agent at 363 K. The films were characterized
by X-ray diffraction, scanning electron microscopy, optical absorption and electrical measurements. X-
ray diffraction pattern shows that polycrystalline with hexagonal structure. The direct optical band gap
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.

© 2009 Elsevier B.V. All rights reserved.

1. Introduction

In the recent years there has been a great deal of interest in the

study of transition metal dichalcogenides because of their possible
applications in lubricants, photoactive material in photoelectro-
chemical solar energy converters because the main advantage
associated with the prevention of electrolyte corrosion

[1–5]

. The

crystal structure of such materials is layer of S–Mo–S interact-
ing with each other by weak Van der Waals forces which allow
adjacent layer to slide

[6]

. Molybdenum disulphide includes high

density batteries because of its appreciable electrical conductiv-
ity and ability to reversibly intercalate lithium

[7,8]

. It appears to

be a very promising semiconducting material for various appli-
cations such as hydrosulphurization catalysts, solid lubricants for
tribological applications in high temperature and vacuum environ-
ment where the use of liquid lubricants becomes ineffective

[9,10]

.

The spin coating, metal organic chemical vapour deposition, chem-
ical vapour deposition, sputtering technique, sulphurization of
metal, laser evaporation, pulsed electrodeposition, and microwave
synthesis are some of the methods used for the deposition of Molyb-
denum disulphide thin films

[11–18]

. Chemical bath deposition

method is an alternative, low cost method that can be operated
at low processing temperature and provides large area deposition.
The method consists of complexed metal ion of interest, source
of chalcogen ions, the stability equilibrium of which provides a
concentration of ions small enough for controlled homogeneous
precipitation of material in the thin film form on substrate

[19,20]

.

∗ Corresponding author. Tel.: [phone]; fax: [phone].

E-mail address:

[e-mail]

(K.M. Garadkar).

This communication reports the various preparative parame-

ters such as growth mechanism, structural, morphological, optical,
electrical properties that were studied.

2. Experimental details

All the chemical reagents used for deposition were of analytical grade. It includes

ammonium molybdate, tartaric acid, hydrazine hydrate, ammonia and thiourea. All
the solutions were prepared in double distilled water. For deposition of molyb-
denum disulphide thin film the bath solution was made by vigorous mixing of
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
(0.1 M) thiourea solution was added and the total volume of the reaction mixture
was made up to 150 mL by adding double distilled water. A reaction vessel was kept
in oil bath. Glass slides were attached vertically on a specially designed substrate
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,
the glass slides were removed from the bath. The films were rinsed with double dis-
tilled water, dried naturally and preserved in a dessicator over anhydrous calcium
chloride.

3. Characterization of molybdenum disulphide thin films

Crystallographic studies of molybdenum disulphide thin film

were characterized by using a Phillips PW-1710 X-ray diffrac-
tometer with Cu K

␣

1

line (

 = 1.54056 Å) in 2 range from 10

◦

to 80

◦

. The optical properties were studied by taking absorption

spectrum of film using a Hitachi-330 (Japan) double-beam spec-
trophotometer in the range of 400–800 nm. A substrate absorption
correction was made by placing an identical uncoated glass slides
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
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 MoS

2

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 S

2

−

, while hydrazine hydrate

reduce Mo

6+

to Mo

4+

. The dissociation of Mo–A (tartarate) com-

plex at higher temperature liberates bear Mo

4+

ions that react with

S

2

−

ion to get molybdenum disulphide thin film. The growth mech-

anism can be described from the following reactions:

Mo

6

+

+ 3A

2

−

→ [Mo(A)

3

]

[Mo(A)

3

]

+ 2NH

2

–NH

2

+ 2OH

−

→ Mo

4

+

+ 3A + 2H

2

O

+ 2N

2

↑

CH

4

N

2

S

+ OH

−

→ SH

−

+ CH

2

N

2

+ H

2

O

SH

−

+ OH

−

→ S

2

−

+ H

2

O

Mo

4

+

+ 2S

2

−

→ MoS

2

The deposition of molybdenum disulphide film occurs when

the ionic product of Mo

4+

and S

2

−

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 MoS

2

thin films are

shown in

Fig. 1

. The presence of sharp peaks is an indication of the

polycrystalline nature of the films. Comparison of observed ‘d’ with
standard ‘d’ values confirms that chemically deposited film shows
hexagonal structure (JCPDS 73-1508). The XRD analysis reveals
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
background is due to amorphous glass substrate and also to some
amorphous phase present in the MoS

2

thin films. The lattice param-

eter was found to be a = 12.30 ´˚A and c = 3.45 ´˚A. The crystallite size of
the material was calculated by using Debye–Scherrer formula and

found to be 189 ´˚A.

SEM micrograph of MoS

2

thin films at 1000

× magnification is

shown in

Fig. 2

. The film shows uniform grains and well covers

to glass substrate. The distribution of nodular, spherical grains of

Fig. 1. XRD pattern of MoS

2

thin film.

Fig. 2. SEM micrographs of MoS

2

thin film.

almost similar size is observed. Most of the grains are intercon-
nected to each other. The average grain size of material is reported
in

Table 1

.

4.3. Optical properties

The optical absorption spectrum of MoS

2

thin film sample at

room temperature was studied by UV–vis–NIR double-beam spec-
trophotometer in the range of 400–800 nm The fundamental edges
of MoS

2

found to be strongly dependent on photon energy, indi-

cating the presence of more than one transition.

Fig. 3

shows the

variation of optical absorbance with wavelength. The optical stud-
ies show that the films are absorptive. The value of absorption

Table 1
Structural and morphological characterization of MoS

2

thin film.

Film

’d’ values (Å)

h k l planes

Grain size (Å)

Cell parameter (Å)

Observed

Standard

XRD

SEM

3.5918

3.5507

300

2.4496

2.4437

320

a = 12.30

MoS

2

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 MoS

2

thin film.

Sample

Band gap (eV)

Activation (eV) energy

Specific conductance (

 cm)

−1

HT

LT

303 K

523 K

MoS

2

1.8

0.882

0.092

1.3

× 10

−5

2.3

× 10

−2

Fig. 3. Absorption spectrum of MoS

2

thin film.

coefficient depends upon radiation energy as well as the com-
position of films. The interpretation of experimental results is
most often performed with the help of formula derived for three-
dimensional crystal model. The band gap ‘Eg’ was calculated using
the following relation

[21]

:

˛ =



A

h



(

h − Eg)

n

where h

 is the photon energy and A and n are constants. For

allowed direct transition n = 1/2, direct forbidden transition n = 3/2
and indirect allowed transition n = 2.

The band gap ‘Eg’ was determined from the variation of (

˛h)

2

with h

 (

Fig. 4

). The linear nature of plot indicates the existence of

direct transition. The band gap was determined by extrapolating
the straight portion of energy axis at

˛ = 0. The band gap was found

to be 1.8 eV for molybdenum disulphide thin film, which is very

Fig. 4. Plots of (

˛h)

2

against photon energy.

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]

.

4.4. Electrical conductivity and thermoelectrical studies

The dark electrical conductivity of MoS

2

thin film on non-

conducting glass slide was determined by using a ‘dc’ two-probe
method, in the temperature range of 303–523 K. The specific con-
ductance was found to be in the order of 10

−2

(

 cm)

−1

which

agrees well with the earlier reported value

[23]

. The values of spe-

cific conductance at 303 and 523 K are reported in

Table 2

. The

electrical properties of polycrystalline thin films mainly depend
upon their structural characteristics and composition

[24,25]

. It is

observed that the conductivity of the film increases with increase
in temperature. This indicates the semiconducting behavior of the
thin film. The electrical conductivity variation with temperature
during heating and cooling cycles was found to be different and
this shows that the films undergo an irreversible change due to
annealing out of non-equilibrium defects during first heating.

A plot of log (conductivity) versus absolute temperature for the

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]

:

 = 

0

exp



−E

a

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

MoS

2

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.
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-
conducting in nature.

Acknowledgement

Authors (AAP) is very thankful to UGC, New Delhi for financial

support through UGC-SAP Meritorious fellowship.

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