Abstract
One dimensional nanostructure of P-type transparent
conducting oxide is technologically very vital. Nanofibers of CuBO2 were first time successfully
synthesized using the electrospinning
technique. For the fabrication of CuBO2 nanofibers in the first step,
we synthesized CuBO2 material using the sol-gel method, and proper phase formation of CuBO2 was
confirmed using XRD and EDX. In the second step,
we Synthesized CuBO2/PVA Composite Nanofibers with different
solution concentrations of CuBO2 i.e. 0gm, 0.3gm, 0.6gm, 0.9gm,
1.2gm, and 1.5gm with 10wt% PVA solution. The electrospinning technique was used
for the fabrication of Nanofibers and analyzed using FTIR spectroscopy and Scanning
Electron Microscope. The maximum fiber
yield, as well as unidirectional alignment, was achieved at 10wt% PVA+ 1.2gm
CuBO2. For the formation of pure CuBO2 Nanofibers, we annealed
the sample which has maximum fiber yield
and unidirectional alignment i.e. 10wt% PVA+1.2 gm CuBO2 solution
concentration at 200oC, 250oC, and 300oC for 1
hour and analyzed using XRD and FTIR. At 300oC for 1 hour the CuBO2
peak emerged and the morphology of Nanofibers are unaffected. At this optimized
temperature, the
functional group related to PVA is eliminated and absorption peaks related to
CuBO2 are only observed in the FTIR spectroscopy. Preparing aligned CuBO2 Nanofibers rather than randomly
oriented configurations is of great interest for functional devices in the nanoscale.
1. Introduction:
In recent years, 1D nanostructures have had great interest because of their flourishing applications in the field of electronics, Photonics, mechanics, and sensing due to their distinctive properties as compared to bulk material properties.
Significantly in the last decade, a lot
of work has been carried out for the synthesis of oxides-based nanostructures
including nano spikes, Nanorods, nanowires, nanotubes,
nanofibers, and thin-film, etc for their
use in different applications. However, n-type transparent conducting oxides
(TCOs) are extensively used in real-life applications
as compared to p-type transparent
conducting oxides due to their inferior electrical properties. In 1997 first
time Kawazoe
et al. introduce the chemically modulated valence band theory and reported that CuAlO2 has good
conductivity and transparency as compared
to the other existing P-type TCO’s which leads to the discovery of transparent
electronics and invisible electronics. After
the discovery of p-type conductivity in CuAlO2, many Cu(I) based
delafossite including CuScO2, CuYO2, CuInO2,
CuGaO2, and CuCrO2 with transparency and p-type
conductivity have been synthesized and new in this class is the CuBO2.
Among all Cu-based delafossite, CuBO2
is relatively new and is of particular importance
due to its large optical band gap energy (4.5 eV), which is the
highest among all Cu-based delafossite.
2. Experimental details:
CuBO2 Nanofibers were synthesized
using a well-known electrospinning
technique. In the first step, we synthesized the CuBO2
material using precursors Copper acetate, Boric Acid, Citric Acid, and Ethylene glycol by sol-gel
method. In a second step, we prepared an aqueous PVA solution using 30ml of deionized water and dissolved 3 gm PVA beads pinch by pinch in the deionized
water with mechanical as well as magnetic stirring. The temperature of the
solution was maintained at 78oC and continuously stirred the solution
for 2 hours. In this way, a 10 wt% solution of PVA was formed. In the third
step CuBO2 material with different concentrations (0gm, 0.3gm, 0.6gm,
0.9gm, 1.2gm, and 1.5gm) was added to 10 wt% PVA solution and stirred for 3
hours. The prepared solution was transferred to the stainless steel needle
which was associated with the peristaltic
pump with a constant flow rate of 3 mL/h the positive
terminal of the high-voltage power supply
is connected to the needle and the negative terminal was connected to the
collector. The collector was wrapped with aluminum
foil for the collection of Nanofibers.
The distance between the tip of the needle and the collector is 12cm. A high
voltage of 15 kV was applied and the precursor
solution was ejected from the needle. The charged CuBO2/PVA
nanofibers were collected to the counter electrode and the solvent was evaporated.
The compositional analysis and Morphology of the samples were analyzed using
FTIR and SEM. In the last step, we choose one sample which contains 10 wt%
PVA and 1.2 gm CuBO2 and annealed it at different temperatures as well
as different time duration to optimize the parameter at which morphology of the
samples was unaffected and pure CuBO2 fibers were achieved. At 300oC for 1 hour, the pure CuBO2
nanofibers were obtained which was confirmed by the XRD, FTIR, and SEM analysis.
3. Results and Discussion
3.1: XRD of CuBO2:
Structural
analysis of CuBO2 fibers was
carried out using Siemens Cu Kα (1.5406Ao) X-Ray diffractometer. The
spectral profile of CuBO2 material which is used for the synthesis
of CuBO2 nanofibers reveals polycrystalline nature. The profile of
CuBO2 is well-indexed with the JCPDS (00-028-1256) card and no
impurity phase or Nano clustering related to impurity phases was observed in
the detection limit of our XRD.
3.2: Morphological and Compositional
analysis of CuBO2:
The morphological information of the CuBO2
sample was obtained using SEM. the SEM image of CuBO2 reveals
the cluster-like structure. Due to high-temperature
sintering, the material agglomerate and the same nature were observed in the earlier
reported in the literature. The EDX results of CuBO2 samples were used for the synthesis of CuBO2
nanofibers. The EDX results of the CuBO2 sample revealed that all
the constituent elements i.e. Copper, Boron, and oxygen are present.
3.3: SEM of Composite PVA/CuBO2 and pure
CuBO2 Nanofibers:
The SEM micrographs of the fibers as a function of copper boron oxide content. A consistent
increase in the diameters of fibers was
observed with an increasing concentration of copper boron oxide content.
The SEM
micrograph of 10wt% PVA indicates the uniform nanofibers along with the
presence of beads. The formation of the beads is due to the low viscosity of
the solution, which indicates less polymer chain entanglement that results in
unstable jets and forming beads on the fibers.
The SEM image of 10 wt% PVA+0.3gm CuBO2 indicates the
uniformity and the smoothness of the nanofibers increased after adding 0.3
gm of CuBO2.The number of beads reduced as compared to the SEM
micrograph of pure PVA having a diameter ranging from 350nm-1500 nm. The SEM
image of 10 wt% PVA+0.6gm CuBO2 indicates the uniformity and
the smoothness of the nanofibers increased as compared to the SEM micrograph of pure
PVA+0.3gm CuBO2. The beads were totally removed at this concentration of
precursor with the random alignment of fibers having a diameter
in the range of 410 nm-1600 nm. SEM image
of 10wt% PVA + 0.9gm CuBO2 having a diameter
ranging from 630-1650nm and a maximum number
of nanofibers aligned in unidirectional. A maximum
number of fibers have a uniform diameter in this concentration and all
the fibers have a uniform diameter as compared to other micrographs that are under consideration.
SEM
image of 10wt% PVA + 1.2gm CuBO2 having a diameter ranging from 680nm-1790nm and all the nanofibers aligned
in unidirectional. The preparation of
aligned 1D nanostructures rather than randomly oriented configurations is of great interest for functional devices in the nanoscale.
SEM
image of 10wt% PVA + 1.5gm CuBO2 having a diameter ranging from 680nm-5000nm. After increasing the concentration of CuBO2 the
morphology of the fibers deteriorated.
In view of the above
discussion, PVA/CuBO2
composite systems consist of nanofiber and micro-bead structures. All the
micrographs reveal the as-synthesized nanofibers prepared at various precursor
concentrations have a uniform and smooth
surface. As the concentration increases, the diameter of the precursor
increases, and the concentration of microbead
structure considerably decreases with the
enhanced uniformity and alignment of well-defined
nanofibers. These SEM results suggest that the suitable concentration of the
solution for fiber formation is 10 wt%
PVA+ 1.2 gm CuBO2 due to the maximum fiber
yield as well as unidirectional alignment. The higher concentration, on the other hand, can deteriorate the nanofiber
yield because of improper solution viscosity to maintain the fiber morphology
of pure CuBO2 fibers.
In composite nanofibers we select one
fibers sample having a concentration
of the solution is 10wt% PVA+ 1.2gm CuBO2 is sintered at a different temperature and different time
duration. The optimized parameter for
pure CuBO2 fibers was 300oC
temperature for the 1-hour duration.
After sintering the fiber sample, the
average diameter of the fibers was
reduced as well as fibers have a smooth surface.
3.4: FTIR Study of
PVA, CuBO2, PVA/CuBO2 Composite Nanofibers, and CuBO2
Nanofibers:
The FTIR absorption spectra of all the prepared
samples including pure PVA and CuBO2/PVA with different
concentrations of CuBO2 in the wave number range 600-4000 cm1.
The interferogram of the PVA shows several molecular bands. The broadband observed
between 3190 cm-1-3390 cm−1 referred to the intermolecular hydrogen bonding and O-H stretching
vibration. The vibrational band observed between 2889 cm−1-2948 cm−1
is associated with C-H stretching from alkyl groups and the absorption peaks
observed between 1684 cm−1- 1749 cm−1 are due to the
stretching C=O and C-O from the acetate group. The
band centered at 1417-1461cm-1
is designated for stretching the CH-CH group. The band located at 1254 cm-1
is associated with the stretching of the C-O
group. The band positioned at 1084 cm-1 is designated to the C-OH group
and the band centered at 840 cm-1 is associated with the C-C group.
The interferogram of CuBO2 sample was
attributed to several chemical bonds centered at 692cm-1, 863 cm-1,
904 cm-1, 937 cm-1, 985 cm-1, 1032cm-1,
1132 cm-1 and1344 cm-1. The peak centered at 692cm-1 is attributed to the bending vibration
of B-O-B in the BO3 triangle. The
peak located at 863 cm-1, 904 cm-1, 937 cm-1,
and 1032 cm-1 is associated with the BO4 stretching
vibration in various structural collections as well as a peak centered
at 937 cm-1 is the confirmation of Cu2+ attached with the
oxygen. The bond is at 11324 cm-1 assigned to B-O-H bending groups.
In addition to this, peaks 1344 cm-1 are correlated to the B-O stretching
vibration of tetragonal BO3 vibration mode. With the increase of the
concentration of CuBO2, the strong features of PVA were reduced because the CuBO2 was not contained the hydroxyl, carbonate, or
hydro-carbon band. The behavior of the
interferogram of the samples also reveals the bonding of CuBO2 and
PVA. The absorption spectra of CuBO2 Nanofibers. The sample having a concentration of the
solution is 10wt% PVA+ 1.2 gm CuBO2 is sintered at a temperature of 300oC
for 1 hour. When we sintered the sample at 300oC the functional
group related to PVA is eliminated and the absorption peak is only related to CuBO2.
The peak
attributed to 662cm-1 is the B-O-B
bending vibration in the BO3 triangle. The
peak located at 762 cm-1, 1010-1082 cm-1 is associated
with the BO4 stretching vibration in various
structural collections as well as a peak
centered at 909 cm-1 is the
confirmation of Cu2+ attached with the oxygen. The
bond at 1570oC-1607oC
is correlated to the B-O stretching vibration of
tetragonal
BO3 vibration mode.
3.5: Structural Analysis of CuBO2
Nanofibers:
The XRD pattern of CuBO2
nanofibers sample. A sample having a concentration of 10wt% PVA + 1.2gm CuBO2 was sintered at a different temperature and different time
duration. Optimized parameters for pure CuBO2 are 300oC
temperature for a 1-hour time duration.
It
is evident from the figure that as-deposited
Nanofibers on aluminum foil have two
peaks centered at 38.41o
corresponding to the (1 1 1) plane and at 44.74o corresponding to the (2 0
0) plane of Aluminum. After being annealed at different temperatures of 200oC,250oC, and 300oC
for 1 hour the appearance of diffraction peaks related to CuBO2 was
observed along with the peaks related to Aluminum. The peak centered at 33.22o corresponds to the (0 0 6) plane of CuBO2.
4. Conclusion:
CuBO2
material was synthesized using a sol-gel
method. Proper phase formation was confirmed by XRD. Compositional and
structural analysis was carried out by EDX and SEM. CuBO2/ PVA
composite and pure CuBO2 nanofibers were first time synthesized
using an effective as well as versatile Electrospinning technique. A scanning electron microscope was used to study
the morphology of CuBO2/PVA composite and pure CuBO2
Nanofibers. Fourier transform infrared spectroscopy confirmed the bonding of
PVA and CuBO2. For pure CuBO2
nanofibers, optimized parameters were
300oC for 1 hour. At the aforementioned parameters,
the morphology of nanofibers was unaffected and proper phase formation was
confirmed by XRD. FTIR showed the absence of a PVA functional group and only the functional group related to CuBO2 was present.
