2
0
D.P. Dubal et al. / Journal of Physics and Chemistry of Solids 73 (2012) 18–24
seen in the micrograph (Fig. 4a), the worm like architecture is
clearly observed for MnO thin film, the approximate size of
which is about 10–20 nm. For 0.5 at% Fe (Fig. 4b) doping this
worm like architecture gets converted into interconnected web
Δ − Stainless steel
Δ
Δ
2
4
.0at% Fe
.0at% Fe
2
like network. Here the surface of MnO
crystalline, whereas as Fe doping concentration increases to 1 at%
Fig. 4c), the surface of MnO becomes slightly compact and
spongy. Further as the Fe concentration in the plating solution
continuously increased to 2.0 at%, the spongy surface of MnO
was converted into more nanocrystalline oxides (Fig. 4d). Due to
Fe addition, the surface of the MnO electrode becomes nanocrystal-
2
becomes slightly nano-
1
.0at% Fe
.5at% Fe
Undoped
(
2
0
2
2
line. However, as can be confirmed from Fig. 4e, the nanocrystalli-
nity began to decrease as the Fe addition in the plating solution
is further increased. The surface became compact and is even
1
0
20
30
40
50
60
70
80
90 100
2
θ (Degree)
Fig. 2. XRD patterns of MnO
2
and Fe: MnO thin films prepared with respect to
2
smoother than the plain MnO
to 2 at% the Fe addition modifies the surface of the MnO
2
. Thus the results indicated that up
electrode.
different Fe concentrations onto SS substrate.
2
This type of amorphous and nanocrystalline structure is expected to
produce high supercapacitance values.
(
a)
b)
Fig. 5(a and b) shows typical EDAX patterns for MnO
2
and Fe:
MnO thin films on ITO substrate. The elemental analyses were
2
(
carried out for Mn and Fe. Here elements like Si and Sn were
detected due to glass substrate and ITO conduction layer, respec-
tively. The strong peaks of Mn were found in both the spectra
(Fig. 5(a and b)), and in Fig. 5(b) there are few elemental peaks
due to Fe. Thus the existence of Fe was confirmed from the EDAX
spectrum. The average atomic percentage of Mn: Fe is listed
in Table 1. Thus the elemental composition analyses showed
that for 2 at% Fe doping in plating bath, only 0.69 at% Fe has
1
121 cm-1
resulted into MnO
reported by Chang et al. [25] for viologen doped MnO
2
sample. A similar type of behavior has been
thin films
4
000 3500 3000 2500 2000 1500 1000
500
2
-
1
Wave number (cm
)
using potentiodynamic and potentiostatic modes of electro-
deposition.
Fig. 3. FTIR spectra of (a) MnO and (b) 2 at% Fe: MnO
2
2
films.
Fig. 6(a, b and c) shows transmission electron micrograph,
corresponding SAED pattern and high resolution transmission
Ni doped MnO
2
thin films by solid state reaction route and
2
electron micrograph of MnO film. Fig. 6(a) shows that the growth
reported a similar kind of amorphous behavior. Thus, the earlier
reports suggest that the amorphous oxides are very useful for
high energy density applications [18,19].
has taken place ‘cluster by cluster’ and randomly oriented
nanocrystals are formed with amorphous matrix. The crystallites
are grown together to form clusters where the crystallites are
indistinguishable. Fig. 6(b) shows corresponding selected area
3.3. FTIR studies
electron diffraction (SAED) pattern of worm like MnO
2
. The
blurred bright electron diffraction rings show that the MnO
2
Fig. 3(a and b) shows the FTIR spectra of MnO
2
and Fe: MnO
2
film is amorphous or poorly crystalline, supporting the X-ray
diffraction results. The high resolution transmission electron
(
2 at%) samples, respectively. Samples showed several small
ꢀ
1
peaks in the range of 1400–1650 cm and a broad peak at about
micrograph (Fig. 6(b)) indicates that the worm like MnO
amorphous nature.
2
has
ꢀ
1
3
416 cm
[20,21]. These peaks are associated with the trace of
surface-adsorbed moisture in the sample. It can be obviously
observed that the stretching peak of –OH groups is much more
intensified because the manganese oxide sample is synthesized in
the aqueous solution, which may form the tunnel structure
3.5. Surface wettability test
Wettability test is carried out to investigate the interaction
between the electrolyte and MnO and Fe: MnO electrode. If the
wettability is high, contact angle is small and the surface is
hydrophilic. On the contrary, if the wettability is low, is large
and the surface is hydrophobic. Fig. 7 shows the water contact
angles of MnO and Fe: MnO films for different Fe concentra-
tions. For the MnO thin film, the water lies slightly flat on the
worm-like structure at a contact angle of 451. As the Fe doping
concentration increases, the water contact angles of MnO thin
during the reaction process; thus a small amount of H
2
O mole-
2
2
cules is intercalated in the tunnel. Several small absorption peaks
y
ꢀ
1
at around 1000–1500 cm
are normally attributed to the bend-
y
ing vibrations of O–H bonds connected with Mn atoms. The
ꢀ
1
absorption peaks situated at 619 and 520 cm , as shown in
Fig. 3(a and b), are attributed to the vibrations of Mn–O bonds
2
2
2
ꢀ
1
[
22]. The FTIR peaks in the range of 400–1000 cm could reveal
the existence of octahedral MnO [23]. The peaks associated with
6
2
the vibrations of Mn–O bonds are slightly shifted towards lower
wavenumbers after Fe doping. Thus the presence of Mn–O bond
and hydroxyl groups was confirmed from the FTIR spectrum of
manganese oxide sample [24].
films decrease. The contact angles of 381, 241 and 151 for 0.5,
1.0 and 2.0 at% Fe doping concentrations, respectively, were
observed. Thus the result indicates that the contact angle
decreases as the Fe doping concentration increases and finally
the film surface becomes more hydrophilic. Hydrophilicity is
attributed to amorphous nature [26]. From the SEM images, it is
confirmed that the surface becomes porous due to Fe doping.
Thus, water placed on the surface of the film goes inside the pores
due to which the contact angle decreases with increase in
3.4. Surface morphological and compositional analyses:
The scanning electron micrographs of MnO
2
thin films doped
with different Fe concentrations are displayed in Fig. 4(a–e). As