Vanadium oxide films were prepared by chemical coating techniques on glass and ITO coated glass
substrates. Vanadium oxide films were doped with carbon nanotubes and examined their optical band gap
and structures. The effects of carbon nanotubes on visible light absorbance and band gap energies were observed.
Electrochemical, structural and optical studies on vanadium oxide coatings were reported in the
liquid electrolyte. Optical constant such as refractive index, extinction coefficient, and band gap calculation
was done by NKD analyzer. Effect of CNT into vanadium oxide films structural properties were examined
by atomic force microscopy (AFM)
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3500

Karamahmutoglu, N.

Özkan Zayim, E.

Vanadium oxide films were prepared by chemical coating techniques on glass and ITO coated glass substrates. Vanadium oxide films were doped with carbon nanotubes and examined their optical band gap and structures. The effects of carbon nanotubes on visible light absorbance and band gap energies were ob-served. Electrochemical, structural and optical studies on vanadium oxide coatings were reported in the liquid electrolyte. Optical constant such as refractive index, extinction coefficient, and band gap calculation was done by NKD analyzer. Effect of CNT into vanadium oxide films structural properties were examined by atomic force microscopy (AFM

N. Karamahmutoglu

E. Ozkan Zayim

CiteSeerX

Carbon Nanotubes Doped Vanadium Oxide Thin Film

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 1 No 3, 03TF02(3pp) (2012)   2304-1862/2012/1(3)03TF02(3) 03TF02-1  2012 Sumy State University Carbon Nanotubes Doped Vanadium Oxide Thin Film  N. Karamahmutoglu, E. Ozkan Zayim  Istanbul Technical University Faculty of Science and Letters, Physics Department, Istanbul 34469, Turkey,  (Received 18 June; published online16 August 2012)  Vanadium oxide films were prepared by chemical coating techniques on glass and ITO coated glass substrates. Vanadium oxide films were doped with carbon nanotubes and examined their optical band gap and structures. The effects of carbon nanotubes on visible light absorbance and band gap energies were ob-served.  Electrochemical, structural and optical studies on vanadium oxide coatings were reported in the liquid electrolyte. Optical constant such as refractive index, extinction coefficient, and band gap calculation was done by NKD analyzer. Effect of CNT into vanadium oxide films structural properties were examined by atomic force microscopy (AFM)  Keywords: CNT, Vanadium Oxide, Thin Films, Sol-Gel, Electrochromism.   PACS numbers: 61.46.Fg, 68.55. – a   1. INTRODUCTION  Vanadium oxide are widely used in optical and elec-tronic applications. These applications can be classified as thermochromic coatings for windows, high-speed optical and electronic switches, catalytic, electronic information displays, color memory devices, solar ener-gy panels for small, high-capacity Li-ion batteries and thermal sensors as exemplified coatings for the cath-ode. CNT-VO2 composite systems are presently not being taken for these applications including their po-tential use to address environmental problems. VO2 is one of the best candidate materials due to high-speed optical and electronic switches properties, and long-term thermodynamic stability. CNT-VO2 composite system is expected to improve the optical and electrical properties. In this study, it was tried to develop the activation region of vanadium by doping it with CNTs. CNTs have excellent electronic properties, large surface areas and also allow for chemical bonding modifications. In realizing the experiment, two different solutions were prepared: only vanadium oxide solution as the control group and CNT-vanadium oxide solution as the experiment group. Corning glass and ITO glass sub-strates were coated in metal alkoxide precursors by a dip coater. After that, they were undergone some heat treatment. Finally, the samples were characterized via NKD analyzer, AFM  and CV. Vanadium oxide films and CNT doped vanadium oxide films were prepared and characterized separate-ly. Vanadium oxide and carbon nanotubes doped vana-dium oxide films were heated at 100oC. Optical and structural characterization of as-deposited and heat treated films were investigated and compared with each other.   2. EXPERIMENTAL PART  2.1 Preparation of Films  The substrates were cleaned distilled water, ace-tone, methanol and ethanol in turn. The vanadium oxide sol, was prepared by dissolving vanadium oxy-triisopropoxide (2 ml) in isopropanol solution (60 ml) with stirring for 1 h. A small amount of nitric acid was added to the solution as catalyst.  Other solutions in-cluding a desired amount of CNTs (2 ,4, 5 and 6wt% of the produced VO2 in the sol) were also prepared. The CNTs were multi–walled carbon nanotube (MWNT) powders of >95% purity with outer diameter of 20–30 nm and length of 10–30 um. For aging the solution, it was left for 24 hours at the room temperature. The CNT–doped VO2 films were deposited on Corning and ITO glass substrates by a dip-coating method. The substrate immersed in the solution for about 1 minute was pulled at constant speed of 1 mm.s-1 by using the dip coater. After drying the samples at room tempera-ture for 24 hours, they were heat-treated at 100oC in air for 1 hour. Undoped VO2 thin films were also syn-thesized by using the same procedure.   3. RESULT AND DISCUSSION  NKD analyzer with reflection and transmittance in the wavelength range 300-1000 nm measured.  Looking at all the curves in Figure 1 in general, the CNT doped films T value is shifting to longer wave-lengths in UV region . CNT films with the contribution of this behavior show a decrease in band gap as shown in Table 1 and Figure 2. Especially transmittance val-ues of 2%CNT doped VO2 films shift to longer wave-length. T values decrease along the whole spectrum of the CNT doped films (Figure 1). Refractive index curves of the NKD extinction coefficients were calculat-ed using the software program how to change the val-ues of n and k of films.  Table 1 – Band gap values of the films  Samples Band Gap (eV) 0 2.52 2% 2.48 4% 2.49 5% 2.50 6% 2.51  Atomic force microscopy (AFM) was used to study the structure of the all deposited layers in Fig. 3. The images indicate that VO2 films with amorphous structure,   N. KARAMAHMUTOGLU, D. EVECAN, E. OZKAN ZAYIM PROC. NAP 1, 03TF02 (2012)   03TF02-2 1,5 2,0 2,5 3,0 3,50,00,20,40,6  TEnergy (eV) 0 2% 4% 5% 6%  Fig. 1 – Transmittance versus energy curves of all deposited films  1,5 2,0 2,5 3,0 3,5-1,5-1,0-0,50,00,5  dT/dEEnergy (eV) 0 2% 4% 5% 6%  Fig. 2 – dT/dE curves of all deposited films  which has very regular structures include multi-walled CNT structure ensures to become more regular. VO2 films coated with sol-gel method, as expected, has a porous structure. Caused a decrease in the pore struc-ture of the contribution of CNT films and structures has become more rigorous and regular. This result is consistent with the T-  curves. Significant decreases in T levels was observed with the contribution of the CNT. The all as-deposited films were then exposed to electro-chemical and electrochromic investigations using LiClO4 in propylene carbonate as an electrolyte. The CV of va-nadium oxide films are given in Fig. 4-8. The results demonstrated that the CNT cause change on the electro-chemical and structural properties of vanadium oxide films. Vanadium oxide film coated on the ITO electrode carrier of the study, the platinum plate was used as the counter electrode. 1 M LiClO4/PC used as the electro-lyte. With an applied voltage range between -1 V and 10mV / s to 100 mV / s was done at different scan rates. Vanadium oxide becomes transparent while the negative current values applied, and positive current values that the brown-colored state. All coloring is reversible, the increase in scanning rate. Differences have been ob-served CV behavior of CNT doped films. Especially as the amount of CNT has been an increase in CV. CNT films doped with 4-6% CV behavior is similar to the behavior of super-capacitors. It will be studied in more detail in CV curves. This interesting observation may be related to porous structure of these films. This result should be examined in term of super capacitive proper-ties of these films in the further work.  VO2   2%  4% 5% 6%  Fig. 3 – AFM imaged of the films  -1,0 -0,5 0,0 0,5 1,0-1,5-1,0-0,50,00,51,0  Current Density (mA/cm2)Voltage (V) 30mV/s 40mV/s 50mV/s 60mV/s 70mV/s 80mV/sVO2 Fig. 4 – CV curves of vanadium oxide films with various scan rates  CARBON NANOTUBES DOPED VANADIUM OXIDE THIN FILM PROC. NAP 1, 03TF02 (2012)   03TF02-3 -1,0 -0,5 0,0 0,5 1,0-1,5-1,0-0,50,00,51,01,5  Current Density (mA/cm2)Voltage (V) 30 mV/s 40 mV/s 50 mV/s 60 mV/s  2% CNT  Fig. 5 – CV curves of 2% CNT doped vanadium oxide films with various scan rates  -1,0 -0,5 0,0 0,5 1,0-1,5-1,0-0,50,00,51,01,5  Current Density (mA/cm2)Voltage (V) 30 mV/s 40 mV/s 50 mV/s 60 mV/s 70 mV/s 80 mV/s4% CNT  Fig. 6 – CV curves of 4% CNT doped vanadium oxide films with various scan rates -1,0 -0,5 0,0 0,5 1,0-1,5-1,0-0,50,00,51,01,5  Current Density (mA/cm2)Voltage 30mV/s 40mV/s 50mV/s5% CNT  Fig. 7 – CV curves of 5% CNT doped vanadium oxide films with various scan rates  -1,0 -0,5 0,0 0,5 1,0-1,5-1,0-0,50,00,51,0  Current Density (mA/cm2)Voltage (V) 30mV/s 40mV/s 50mV/s6% CNT  Fig. 8 – CV curves of 6% CNT doped vanadium oxide films with various scan rates  AKNOWLEDGEMENTS  Authors are grateful to use NKD for optical analysis to Prof. Fatma Tepehan.   REFERENCES  1. T. Watanabe, Y. Ikeda, T. Ono, M. Hibino, M. Hosoda,  K. Sakai, T. Kudo, Solid State Ionics 151, 313 (2002). 2. Z.J. Lao, K. Konstantinov, Y. Tournaire, S.H. Ng, G.X. Wang, H.K. Liu J. Power Sources 162, 1451 (2006).  3. A. Pana, D. Liua, X. Zhoua, B. Betalla. Garciaa, S. Liangb, Jun Liuc, G. Caoa Journal of Power Sources 195, 3893 (2010). 4. C.D. Lokhande, D.P. Dubal, Oh-Shim Joo, Current Applied Physics 11, 255 (2011).  5. C. Chen, Q. Zhang, M. Yang, C. Huang, Y. Yang, M. Wang Carbon 50 (2012).  

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 1 No 3, 03TF02(3pp) (2012) 
 
 
2304-1862/2012/1(3)03TF02(3) 03TF02-1  2012 Sumy State University 
Carbon Nanotubes Doped Vanadium Oxide Thin Film 
 
N. Karamahmutoglu, E. Ozkan Zayim 
 
Istanbul Technical University Faculty of Science and Letters, Physics Department, Istanbul 34469, Turkey, 
 
(Received 18 June; published online16 August 2012) 
 
Vanadium oxide films were prepared by chemical coating techniques on glass and ITO coated glass 
substrates. Vanadium oxide films were doped with carbon nanotubes and examined their optical band gap 
and structures. The effects of carbon nanotubes on visible light absorbance and band gap energies were ob-
served.  Electrochemical, structural and optical studies on vanadium oxide coatings were reported in the 
liquid electrolyte. Optical constant such as refractive index, extinction coefficient, and band gap calculation 
was done by NKD analyzer. Effect of CNT into vanadium oxide films structural properties were examined 
by atomic force microscopy (AFM) 
 
Keywords: CNT, Vanadium Oxide, Thin Films, Sol-Gel, Electrochromism. 
 
 PACS numbers: 61.46.Fg, 68.55. – a 
 
 
1. INTRODUCTION 
 
Vanadium oxide are widely used in optical and elec-
tronic applications. These applications can be classified 
as thermochromic coatings for windows, high-speed 
optical and electronic switches, catalytic, electronic 
information displays, color memory devices, solar ener-
gy panels for small, high-capacity Li-ion batteries and 
thermal sensors as exemplified coatings for the cath-
ode. CNT-VO2 composite systems are presently not 
being taken for these applications including their po-
tential use to address environmental problems. VO2 is 
one of the best candidate materials due to high-speed 
optical and electronic switches properties, and long-
term thermodynamic stability. CNT-VO2 composite 
system is expected to improve the optical and electrical 
properties. 
In this study, it was tried to develop the activation 
region of vanadium by doping it with CNTs. CNTs have 
excellent electronic properties, large surface areas and 
also allow for chemical bonding modifications. 
In realizing the experiment, two different solutions 
were prepared: only vanadium oxide solution as the 
control group and CNT-vanadium oxide solution as the 
experiment group. Corning glass and ITO glass sub-
strates were coated in metal alkoxide precursors by a 
dip coater. After that, they were undergone some heat 
treatment. Finally, the samples were characterized via 
NKD analyzer, AFM  and CV. 
Vanadium oxide films and CNT doped vanadium 
oxide films were prepared and characterized separate-
ly. Vanadium oxide and carbon nanotubes doped vana-
dium oxide films were heated at 100oC. Optical and 
structural characterization of as-deposited and heat 
treated films were investigated and compared with 
each other.  
 
2. EXPERIMENTAL PART 
 
2.1 Preparation of Films 
 
The substrates were cleaned distilled water, ace-
tone, methanol and ethanol in turn. The vanadium 
oxide sol, was prepared by dissolving vanadium oxy-
triisopropoxide (2 ml) in isopropanol solution (60 ml) 
with stirring for 1 h. A small amount of nitric acid was 
added to the solution as catalyst.  Other solutions in-
cluding a desired amount of CNTs (2 ,4, 5 and 6wt% of 
the produced VO2 in the sol) were also prepared. The 
CNTs were multi–walled carbon nanotube (MWNT) 
powders of >95% purity with outer diameter of 20–30 
nm and length of 10–30 um. For aging the solution, it 
was left for 24 hours at the room temperature. The 
CNT–doped VO2 films were deposited on Corning and 
ITO glass substrates by a dip-coating method. The 
substrate immersed in the solution for about 1 minute 
was pulled at constant speed of 1 mm.s-1 by using the 
dip coater. After drying the samples at room tempera-
ture for 24 hours, they were heat-treated at 100oC in 
air for 1 hour. Undoped VO2 thin films were also syn-
thesized by using the same procedure.  
 
3. RESULT AND DISCUSSION 
 
NKD analyzer with reflection and transmittance in 
the wavelength range 300-1000 nm measured.  
Looking at all the curves in Figure 1 in general, the 
CNT doped films T value is shifting to longer wave-
lengths in UV region . CNT films with the contribution 
of this behavior show a decrease in band gap as shown 
in Table 1 and Figure 2. Especially transmittance val-
ues of 2%CNT doped VO2 films shift to longer wave-
length. T values decrease along the whole spectrum of 
the CNT doped films (Figure 1). Refractive index 
curves of the NKD extinction coefficients were calculat-
ed using the software program how to change the val-
ues of n and k of films. 
 
Table 1 – Band gap values of the films 
 
Samples Band Gap (eV) 
0 2.52 
2% 2.48 
4% 2.49 
5% 2.50 
6% 2.51 
 
Atomic force microscopy (AFM) was used to study the 
structure of the all deposited layers in Fig. 3. The images 
indicate that VO2 films with amorphous structure,  
 N. KARAMAHMUTOGLU, D. EVECAN, E. OZKAN ZAYIM PROC. NAP 1, 03TF02 (2012) 
 
 
03TF02-2 
1,5 2,0 2,5 3,0 3,5
0,0
0,2
0,4
0,6
 
 
T
Energy (eV)
 0
 2%
 4%
 5%
 6%
 
 
Fig. 1 – Transmittance versus energy curves of all deposited films 
 
1,5 2,0 2,5 3,0 3,5
-1,5
-1,0
-0,5
0,0
0,5
 
 
d
T
/d
E
Energy (eV)
 0
 2%
 4%
 5%
 6%
 
 
Fig. 2 – dT/dE curves of all deposited films 
 
which has very regular structures include multi-walled 
CNT structure ensures to become more regular. VO2 
films coated with sol-gel method, as expected, has a 
porous structure. Caused a decrease in the pore struc-
ture of the contribution of CNT films and structures 
has become more rigorous and regular. This result is 
consistent with the T-  curves. Significant decreases in 
T levels was observed with the contribution of the CNT. 
The all as-deposited films were then exposed to electro-
chemical and electrochromic investigations using LiClO4 
in propylene carbonate as an electrolyte. The CV of va-
nadium oxide films are given in Fig. 4-8. The results 
demonstrated that the CNT cause change on the electro-
chemical and structural properties of vanadium oxide 
films. Vanadium oxide film coated on the ITO electrode 
carrier of the study, the platinum plate was used as the 
counter electrode. 1 M LiClO4/PC used as the electro-
lyte. With an applied voltage range between -1 V and 
10mV / s to 100 mV / s was done at different scan rates. 
Vanadium oxide becomes transparent while the negative 
current values applied, and positive current values that 
the brown-colored state. All coloring is reversible, the 
increase in scanning rate. Differences have been ob-
served CV behavior of CNT doped films. Especially as 
the amount of CNT has been an increase in CV. CNT 
films doped with 4-6% CV behavior is similar to the 
behavior of super-capacitors. It will be studied in more 
detail in CV curves. This interesting observation may be 
related to porous structure of these films. This result 
should be examined in term of super capacitive proper-
ties of these films in the further work. 
 
VO2 
 
 
2% 
 
4% 
5% 6% 
 
Fig. 3 – AFM imaged of the films 
 
-1,0 -0,5 0,0 0,5 1,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
 
 
C
u
rr
e
n
t 
D
e
n
s
it
y
 (
m
A
/c
m
2
)
Voltage (V)
 30mV/s
 40mV/s
 50mV/s
 60mV/s
 70mV/s
 80mV/s
VO
2
 
Fig. 4 – CV curves of vanadium oxide films with various scan 
rates 
 CARBON NANOTUBES DOPED VANADIUM OXIDE THIN FILM PROC. NAP 1, 03TF02 (2012) 
 
 
03TF02-3 
-1,0 -0,5 0,0 0,5 1,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
 
 
C
u
rr
e
n
t 
D
e
n
s
it
y
 (
m
A
/c
m
2
)
Voltage (V)
 30 mV/s
 40 mV/s
 50 mV/s
 60 mV/s  
2% CNT
 
 
Fig. 5 – CV curves of 2% CNT doped vanadium oxide films 
with various scan rates 
 
-1,0 -0,5 0,0 0,5 1,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
 
 
C
u
rr
e
n
t 
D
e
n
s
it
y
 (
m
A
/c
m
2
)
Voltage (V)
 30 mV/s
 40 mV/s
 50 mV/s
 60 mV/s
 70 mV/s
 80 mV/s
4% CNT
 
 
Fig. 6 – CV curves of 4% CNT doped vanadium oxide films 
with various scan rates 
-1,0 -0,5 0,0 0,5 1,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
 
 
C
u
rr
e
n
t 
D
e
n
s
it
y
 (
m
A
/c
m
2
)
Voltage
 30mV/s
 40mV/s
 50mV/s
5% CNT
 
 
Fig. 7 – CV curves of 5% CNT doped vanadium oxide films 
with various scan rates 
 
-1,0 -0,5 0,0 0,5 1,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
 
 
C
u
rr
e
n
t 
D
e
n
s
it
y
 (
m
A
/c
m
2
)
Voltage (V)
 30mV/s
 40mV/s
 50mV/s
6% CNT
 
 
Fig. 8 – CV curves of 6% CNT doped vanadium oxide films 
with various scan rates 
 
AKNOWLEDGEMENTS 
 
Authors are grateful to use NKD for optical analysis to Prof. Fatma Tepehan. 
 
 
REFERENCES 
 
1. T. Watanabe, Y. Ikeda, T. Ono, M. Hibino, M. Hosoda,  
K. Sakai, T. Kudo, Solid State Ionics 151, 313 (2002). 
2. Z.J. Lao, K. Konstantinov, Y. Tournaire, S.H. Ng, G.X. 
Wang, H.K. Liu J. Power Sources 162, 1451 (2006).  
3. A. Pana, D. Liua, X. Zhoua, B. Betalla. Garciaa, S. Liangb, 
Jun Liuc, G. Caoa Journal of Power Sources 195, 3893 
(2010). 
4. C.D. Lokhande, D.P. Dubal, Oh-Shim Joo, Current Applied 
Physics 11, 255 (2011).  
5. C. Chen, Q. Zhang, M. Yang, C. Huang, Y. Yang, M. Wang 
Carbon 50 (2012). 
 


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Carbon Nanotubes Doped Vanadium Oxide Thin Film

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