Structural Studies of n-CdO with
p-PEDOT: PSS Heterojunction Films Synthesized by Low-cost Method
N. B. Sonawane
Karm. A. M. Patil Arts, Comm.
& Kai. Annasaheb N. K. Patil. Sicence Sr.College, Pimpalner, Sakri (Dhule)
[M. S.] India
Abstract
The
commercially available poly (3, 4 ethylenedioxytheophene: poly (styrene
sulfonic acid)) (PEDOT:PSS) was deposited by using dip coating technique onto
n-CdO necklace type nanostructures synthesized by simple chemical route to get
high surface area heterojunction network. The structural properties of the
films were measured by using Fourier transform
infrared (FTIR) technique whereas surface morphology was viewed by high
resolution Field emission scanning electron microscopy (FE-SEM, JEOL 6360A), attached
with energy‐dispersive X‐ray
spectrometer (EDAX). The surface morphology of
necklace like nanostructure CdO film under different magnifications
Keywords: n-CdO/p-PEDOT:PSS; chemical route;
nanoheterojunction.
1. Introduction
A
nanostructure such as nanowires, nanotubes, nanorods etc. has an importance in
basic the scientific research and its potential in technological applications.
Wide efforts have been taken for the synthesis of the semiconducting nanomaterial
with different nanoforms such as nanorods [1-3], nanowires [4] and nanotubes
[5] etc. The nanoheterojunction can be synthesized by the deposition of p-type
semiconducting inorganic or organic material on n-type semiconducting material
synthesized in the form of nanowires or nanotubes or nanorods etc. In recent
years, the conducting polymers have been widely investigated as effective
materials for room temperature chemical sensors. PEDOT:PSS is commonly accepted
to be more environmentally stable than other conducting polymers such as
polypyrrole and polyaniline. These features make PEDOT:PSS and its derivatives appealing
for gas sensing applications [6]. The Cadmium oxide (CdO), a II-VI group, is an
important n-type semiconducting material with direct band gap of 2.5 eV and
indirect band gap 1.98 eV [7]. CdO is most promising semiconducting material
for different applications such as in solar cells, phototransisters, catalysts
and gas sensors [8].
In the present investigation, effort has been taken for the
synthesis of necklace like nanostructure of inorganic n-type semiconducting
material CdO and formation of a nanoheterojuction by deposition of organic p-PEDOT:
PSS on n-CdO. The very low cost and room temperature chemical route was used
for the synthesis of the nanoheterojunction films on fluorine doped tin oxide
(FTO) coated glass substrates. Energy-dispersive
X-ray spectrum of CdO nanonecklace and CdO/PEDOT: PSS on FTO is investigated. The
intensity of generated X-ray is related to the concentration fraction of each
element present in the target material. Comparing
elemental spectrum of bare CdO with PEDOT: PSS coated CdO nanonecklace,
existence of Cd and O peak are observed which confirms the formation CdO. The
carbon content in the PEDOT: PSS coated CdO nanostructure gives rough
confirmation towards the existence of PEDOT: PSS layer on CdO.
2.
Experimental details
2.1 Synthesis of CdO necklace type
nanostructure
Initially,
Cd(OH)2 nanowires were synthesized at room temperature by using chemical
method reported earlier [9]. Specifically, 0.1 M/L (50 mL) CdCl2 was
complexed by drop wise addition of ammonia (10 mL) to the solution. The pH of
the complexed bath was maintained at 12. The solution was stirred for few
seconds and gently immersed the well cleaned FTO coated glass substrates
vertically in a solution along the wall of the beaker at room temperature [27 oC].
After 21 h, the white Cd(OH)2 film was deposited on the substrate
surface. Then, substrate was taken out from the solution, rinsed with double
distilled water and dried in dry air [10]. CdO
necklace like nanostructure film was obtained by annealing Cd(OH)2
film at optimized temperature of 290 OC in contact with air for two
hours.
2.2
Deposition PEDOT:PSS on CdO necklace type
nanostructure
The
deposition of PEDOT: PSS on CdO nanostructure was performed by using simple
dipping technique. Commercially available PEDOT: PSS solution from Baytron (HC
Starck’s Clevios PH1000) was used to form the shell. Different ratios of PEDOT:
PSS::H2O was used and the ratio 1:4 was found to be optimal. For
this, PEDOT: PSS containing 80% water was coated on FTO/CdO film by using dip
coating technique. At each time, each volume of PEDOT: PSS::H2O was
ultrasonicated for 1 h. For single dip, FTO/CdO film was dipped vertically into
PEDOT: PSS: H2O solution for 2-3 seconds and taken out vertically.
After 4 to 5 such a dips in the intervals of few seconds, a very thin,
homogeneous layer of PEDOT: PSS was coated on CdO. The dip coated film of FTO/CdO/PEDOT:PSS
was heated at 100 oC for 10 min in air. The PEDOT: PSS::H2O
ratio, ultrasonication, dipping and heating times were optimized with respect
to get uniform and thin layer coating of PEDOT: PSS on CdO necklace type
nanostructure towards better gas sensing performance.
2.3
Characterizations
The structural
properties of the films were measured by using Fourier
transform infrared (FTIR) technique where as surface morphology was
viewed by high resolution Field emission scanning electron microscopy (FE-SEM, JEOL
6360A), attached with energy‐dispersive X‐ray
spectrometer (EDAX). The gas sensing properties of n-CdO/p-PEDOT:PSS
were studied on the home made gas sensor unit, under forward biased current density–voltage (J–V) characteristics
between 0 and 2 V.
3.
Result and discussion
3.1
Surface morphological studies and elemental analysis
The surface morphology of necklace like nanostructure CdO film under
different magnifications are as shown fig.1 (a) and (b) for 1 µm and 500 nm respectively
whereas fig 1 (c) and (d) for PEDOT:PSS coated CdO necklace like nanostructure with
magnifications of 1 µm and 500 nm, respectively. From fig.1(a), it
clearly shows the string of small beads to form necklace like nanostructures. With higher magnification (500 nm), the random
distribution of CdO nanonecklace spread on FTO substrate with enough porous
surface area is observed (fig.1 (b)). It is quite difficult to observe coating
of PEDOT:PSS on CdO, rather blurred image gives prediction about the coating of
polymer. The lower magnification image clearly depicts the formation of blurred
CdO necklace like nanostructure confirming uniform coating of PEDOT: PSS over
the CdO necklace nanostructure (fig.1(c)). At higher magnification, it is
observed that PEDOT: PSS slurry was uniformly coated on CdO to form
nanoheterojunction (fig.1 (d)). At the junction between necklaces, PEDOT:PSS
stacked to form the bigger particles due to agglomeration of PEDOT:PSS which
clearly visualized in lower as well as higher magnification images. The uniform
growth of p-type polymer on the n-type necklace nanostructure results into the
formation of high surface area p–n junction at the nano level and hence, the
formation of nanoheterojunction.
Figure 1.
Field Effect Scanning Electron Microscopic Images of CdO and CdO + PEDOT: PSS
thin films a) CdO thin film with 1mm scale b) CdO thin films with
500 nm scale, c) CdO + PEDOT: PSS thin film with 1mm scale, and
d) CdO + PEDOT: PSS thin film with 500 nm scale,
Energy-dispersive X-ray spectrum of CdO
nanonecklace and CdO/PEDOT: PSS on FTO is as shown in fig.2. The intensity of
generated X-ray is related to the concentration fraction of each element
present in the target material. Comparing
elemental spectrum of bare CdO (fig.2 (a)) with PEDOT: PSS coated CdO
nanonecklace (fig.2 (b)), existence of Cd and O peak are observed which confirms
the formation CdO. The carbon content in the PEDOT: PSS coated CdO
nanostructure gives rough confirmation towards the existence of PEDOT: PSS
layer on CdO. The appearance of Sn in CdO is contribution from FTO coated glass
substrate. The intensity of Sn peak diminished in PEDOT: PSS coated CdO
nanostructure, which shows coating of polymer layer on CdO.
 |
Figure 2: Energy
dispersive X-ray (EDX) spectrum of a) bare CdO and b) with PEDOT: PSS coated CdO nanonecklace
thin films.
3.2 Fourier transform infrared (FTIR) studies of CdO and PEDOT:PSS
deposited CdO
Fig.3 (a) shows the FT-IR spectrum of CdO necklace type
nanostructure. The peak at 1437 cm-1 attributed to C-C
stretching of aromatics. The peaks at 854 cm-1 and 640 cm-1
may be attributed to C-Cl and C-Br stretching of alkyl halides respectively.
Inclusion of Cl-group is from used cadmium chloride as a source material. The FT-IR spectrum of PEDOT: PSS coated on CdO
nanostructure is as shown in fig.3 (b). The aromatic band due to extended
resonance the of polar characteristic related C=C double bond stretching at
about 1641.28 cm-1 in five member vinyl ether group assigned to
thiophene ring. The band at 1199 cm-1 occurs due to the C-O
stretching. The small peak at 1043 cm-1 may be due to symmetric
stretching of S=O [11, 12].
Fig.3. FT-IR absorption spectrum of (a) CdO and (b) PEDOT:PSS
coated CdO
4. Conclusions
In
present work, we have successfully synthesized necklace like nanostructure of
n-CdO onto FTO coated glass substrates by simple and low cost chemical method
followed by deposition of p-PEDOT:PSS on n-CdO by simple dipping technique. Formation
of such a novel morphology of n-CdO/p-PEDOT:PSS necklace type
nanoheterojunction with high surface area leads to demonstrate a gas sensors and
phototransistors.
Acknowledgement
Author is thankful to Prof.
Dr. B. R. Sankapal, Head of Department of Physics, for his guidance and
constant encouragement. Prin. Dr. L. B.
Pawar, Karm.A.M.Patil
Arts,Comm. & Kai.Annasaheb N.K.Patil. Sicence Sr.College, Pimpalner for his
support to experimental work.
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