Highly efficient flexible piezoelectric nanogenerator and femtosecond two-photon absorption properties of nonlinear lithium niobate nanowires Manoj Kumar Gupta, Janardhanakurup Aneesh, Rajesh Yadav, K. V. Adarsh, and Sang-Woo Kim Citation: Journal of Applied Physics 121, 175103 (2017); doi: 10.1063/1.4982668 View online: http://dx.doi.org/10.1063/1.4982668 View Table of Contents: http://aip.scitation.org/toc/jap/121/17 Published by the American Institute of Physics Articles you may be interested in Optical damage assessment and recovery investigation of hydrogen-ion and deuterium-ion plasma-irradiated bulk ZnO single crystals Journal of Applied Physics 121, 175102175102 (2017); 10.1063/1.4982346 Determination of the complex refractive index and optical bandgap of CH3NH3PbI3 thin films Journal of Applied Physics 121, 173104173104 (2017); 10.1063/1.4982894 Magnetic order and noncollinear spin transport of domain walls based on zigzag graphene nanoribbons Journal of Applied Physics 121, 174303174303 (2017); 10.1063/1.4982892 Identifying phase transition behavior in Bi1/2Na1/2TiO3-BaTiO3 single crystals by piezoresponse force microscopy Journal of Applied Physics 121, 174103174103 (2017); 10.1063/1.4982910 Ultrafast response of dielectric properties of monolayer phosphorene to femtosecond laser Journal of Applied Physics 121, 173105173105 (2017); 10.1063/1.4982072 Ferroelectric, pyroelectric, and piezoelectric properties of a photovoltaic perovskite oxide Journal of Applied Physics 110, 063903063903 (2017); 10.1063/1.4974735
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Highly efficient flexible piezoelectric nanogenerator and femtosecond two-photonabsorption properties of nonlinear lithium niobate nanowiresManoj Kumar Gupta, Janardhanakurup Aneesh, Rajesh Yadav, K. V. Adarsh, and Sang-Woo Kim
Citation: Journal of Applied Physics 121, 175103 (2017); doi: 10.1063/1.4982668View online: http://dx.doi.org/10.1063/1.4982668View Table of Contents: http://aip.scitation.org/toc/jap/121/17Published by the American Institute of Physics
Articles you may be interested in Optical damage assessment and recovery investigation of hydrogen-ion and deuterium-ion plasma-irradiatedbulk ZnO single crystalsJournal of Applied Physics 121, 175102175102 (2017); 10.1063/1.4982346
Determination of the complex refractive index and optical bandgap of CH3NH3PbI3 thin filmsJournal of Applied Physics 121, 173104173104 (2017); 10.1063/1.4982894
Magnetic order and noncollinear spin transport of domain walls based on zigzag graphene nanoribbonsJournal of Applied Physics 121, 174303174303 (2017); 10.1063/1.4982892
Identifying phase transition behavior in Bi1/2Na1/2TiO3-BaTiO3 single crystals by piezoresponse forcemicroscopyJournal of Applied Physics 121, 174103174103 (2017); 10.1063/1.4982910
Ultrafast response of dielectric properties of monolayer phosphorene to femtosecond laserJournal of Applied Physics 121, 173105173105 (2017); 10.1063/1.4982072
Ferroelectric, pyroelectric, and piezoelectric properties of a photovoltaic perovskite oxideJournal of Applied Physics 110, 063903063903 (2017); 10.1063/1.4974735
Highly efficient flexible piezoelectric nanogenerator and femtosecondtwo-photon absorption properties of nonlinear lithium niobate nanowires
Manoj Kumar Gupta,1,a) Janardhanakurup Aneesh,1 Rajesh Yadav,1 K. V. Adarsh,1
and Sang-Woo Kim2
1Department of Physics, Indian Institute of Science Education and Research, Bhopal, Bhopal Bypass Road,Bhauri, Bhopal, Madhya Pradesh 462066, India2School of Advanced Materials Science and Engineering, SKKU Advanced Institute of Nanotechnology(SAINT), Center for Human Interface Nanotechnology (HINT), and IBS Center for Integrated NanostructurePhysics, Institute for Basic Science (IBS), Sungkyunkwan University (SKKU), Suwon 440-746, South Korea
(Received 7 March 2017; accepted 15 April 2017; published online 3 May 2017)
We present a high performance flexible piezoelectric nanogenerator (NG) device based on the
from open aperture z-scan measurement at two different
wavelengths are shown in Fig. 3(a). The measurements were
carried out with an on-axis peak intensity of 78 GW cm�2. It
can be seen that for 800 nm photon light, LiNbO3 NWs do not
show any significant non-linear absorption, whereas for
560 nm, it exhibits non-linear absorption. Further, a decrease
in transmittance as a function of input intensity is also
observed, which clearly indicates the presence of non-linear
absorption in the LiNbO3 NWs for 560 nm photons (Fig.
3(b)). This behavior of NLA in LiNbO3 NWs under two dif-
ferent excitation wavelengths can be easily understood in
terms of the band gap of LiNbO3 as shown in the schematic
diagram of Fig. S2. It is obvious that in the case of the 800 nm
laser beam, the photon energy (1.55 eV) is below the band
gap of LiNbO3. Therefore, transition of electrons from the
valence band to the conduction band is not possible for
800 nm photons, which results in no nonlinear absorption.
Interestingly, although the photon energy of 560 nm (2.21 eV)
is still less than the band gap of LiNbO3, the two photon
energy was sufficient to induce electron transitions from
the valence band to the conduction band in LiNbO3 NWs
as confirmed in the obtained result. Moreover, at the lower
intensity side, there is no significant absorption for 560 nm.
Nevertheless, at the higher intensity side, a significant reduc-
tion in transmittance is measured, which is due to the increase
in the density of photons that increases the probability of
simultaneous absorption of two photons (usually known as a
two photon absorption (TPA) process).
In the case of two photon absorption (TPA), the normal-
ized light transmittance for a laser pulse having both tempo-
ral and spatial Gaussian profiles is given by48
T ¼ 1
Q zð Þffiffiffippð1�1
ln 1þ Q zð Þx2� �
dx; (1)
where
Q zð Þ ¼bI0Lef f
1þ z
zr
� �2:
b is the two photon absorption coefficient, I0 is the peak
intensity at focus in the absence of the sample, Zr is the
Rayleigh length for the focusing lens, z is the sample posi-
tion with respect to the focus (z¼ 0), and Lef f ¼ 1�e�aLð Þa is
the effective length for a sample having thickness L, where ais the linear absorption coefficient.
The nonlinear absorption coefficient b was obtained by
curve fitting of Equation (1) for the experimental z-scan dataFIG. 2. UV-Vis spectrum of the LiNbO3 NWs.
FIG. 1. Scanning electron microscopy
(SEM) image (a) of the LiNbO3 NWs
with an average diameter of 300 nm
and a length in the range of 10–15 lm.
(b) Transmission electron microscopy
image. (c) The lattice fringe image
for (012) and (116) with its (d) FFT
transformation.
175103-3 Gupta et al. J. Appl. Phys. 121, 175103 (2017)
of the excitation wavelength at 560 nm. The two photon
absorption coefficient b is found to be 0.13 6 0.02 mm
GW�1. This value is slightly smaller as compared to the pre-
viously reported bulk form of LiNbO3.49 The decrease in the
b is due to the nanocrystalline size of LiNbO3, which is con-
sistent with the recent studies.50 However, in order to estab-
lish the relationship of the optical nonlinearity with crystallite
size, extensive work on varying sizes is required. The optical
limiting property of the LiNbO3 NWs was also investigated.
Fig. 3(c) shows the output intensity through the sample as a
function of input intensity. It can be seen that at the lower
intensity side, the output intensity is linearly proportional to
the input intensity; however, as the input intensity increases
up to a certain value, it starts deviating from its linear behav-
ior. The results indicate that LiNbO3 NWs are well suitable
for optical limiting applications such as protection of human
eyes and sensors from intense laser radiations, in which
blocking or limiting the high-intensity beams is required.
Further, owing to its well-known piezoelectric property
of LiNbO3, we demonstrated alternative-current (AC) power
generation from piezoelectric NGs as a potential application
of these LiNbO3 NWs. A robust flexible NG device was
designed to harvest mechanical energy from the living
environment. A composite type flexible NG was fabricated
using a device structure of the ITO coated PET substrate/
(LiNbO3:PDMS) with an aluminum (Al) top electrode as
shown in Fig. 4. An ITO coated PET substrate was used as
the bottom electrode and as a flexible substrate. The sche-
matic diagram of device fabrication is shown in Fig. S3.
Initially, a mixture of the LiNbO3 NW and PDMS polymer
with a volume ratio of 40:60 was prepared and then spin
coated on the ITO/PET substrate at 1000 rpm for 15 s. In
order to prepare the top electrode, a thin layer of Al was
deposited on the Cr coated flexible polyethylene-naphthalate
(PEN) substrate and then carefully mechanically integrated
with the top of the composite layer to form a complete NG
device. A schematic diagram and original photo image of the
practical device are shown in Figs. 4(a) and 4(b), respec-
tively. The FE-SEM analysis of the LiNbO3:PDMS sample
was carried out, to gain insights into the NW distribution
behavior, as shown in Figs. 4(c) and 4(d). The low and high
magnified SEM images confirmed that LiNbO3 NWs are
FIG. 3. Open aperture z-scan curve for LiNbO3 NWs dispersed in ethanol: (a) the variation of normalized transmitted intensity as a function of position, (b)
input intensity (solid line represents the theoretical fit), and (c) optical limiting curve showing the deviation from linear behaviour for higher input intensity.
FIG. 4. (a) Schematic diagrams of the
flexible PDMS assisted LiNbO3NW
based piezoelectric NG, (b) original
photo image of the flexible NG on the
transparent ITO/PET substrate and the
top view of the composite (inset), and
(c) low and (d) high magnified-SEM
images of the LiNbO3: PDMS composite.
175103-4 Gupta et al. J. Appl. Phys. 121, 175103 (2017)
randomly distributed inside the PDMS polymer. From the
cross-sectional FE-SEM images shown in Fig. S4, the thick-
ness of the composite layer was estimated to be about 350 lm.
Fourier transform infrared spectroscopy (FT-IR) spectra were
also measured in order to obtain physical insights into the
chemical bonding and phase formation in the PDMS:LiNbO3
composite (Fig. S5). The result of FT-IR is discussed in the
supplementary material.
The piezoelectric output voltage and current generated
from a composite LiNbO3:PDMS based hybrid NG were
obtained under periodic vertical pushing and releasing condi-
tions using the computer interface force simulator. An output
voltage of about 4.0 V and a current density of about 1.5 lA
cm�2 were obtained under a vertical compression of 1 kgf
at a frequency of 4 Hz (sinusoidal vibration) as shown in
Figs. 5(a)–5(d) and 6, respectively. The device was electri-
cally poled before the piezoelectric signal measurement with
a dc electric field of about 90 kV/cm at room temperature.
It is noteworthy that the electric dipoles can be easily ori-
ented or switched in a particular direction after applying a
suitable electric field due to the ferroelectric property of the
LiNbO3 NW.6,7
To confirm that the measured signal was from the
NG rather than the instruments, we performed “switching-
polarity” tests. As predicated, when the voltage meter/
current meter was forward connected to the NG (i.e., positive
and negative probes were connected to the positive and nega-
tive electrodes, respectively), positive pulses were recorded
during the pushing and when the voltage meter/current meter
was connected in reverse, the output pulses were also
reversed as shown for output voltage (Figs. 5(a) and 5(c))
and output current (Figs. 6(a) and 6(b)). Enlarged views of
one cycle of output voltage (Figures 5(b) and 5(d)) and out-
put current (Figs. S6 and S7 of supplementary material) were
given for further verification of the piezoelectric reversible
signal under pushing and releasing conditions. It is notewor-
thy that generated output voltage from the device was almost
10 times and output current was almost 150 times higher
than the previously reported LiNbO3 based NG (0.46 V,
9.11 nA).51 This drastic enhancement of output voltage and
FIG. 5. (a) Piezoelectric output voltage
generated from the LiNbO3 NW:PDMS
based NG under compressive force
(forward connection), (b) enlarged view
of one cycle of output voltage under
forward connection, (c) output voltage
under reverse connection (switching-
polarity test), and (d) enlarged view of
one cycle of output voltage under
reverse connection.
FIG. 6. (a) Piezoelectric output voltage
generated from the LiNbO3 NW:PDMS
based NG under compressive force (for-
ward connection) and (b) output current
under reverse connection (switching-
polarity test).
175103-5 Gupta et al. J. Appl. Phys. 121, 175103 (2017)
current may be due to the comparatively large band gap. It is
expected that due to the large band gap and therefore com-
paratively small free charge carriers in LiNbO3 NWs, the
piezoelectric screening effect reduces, which results in high
piezoelectric output performance. A comparison of output
performance of other reported composite type piezoelectric
NGs is given in the supplementary material (Table S1).
Further, it was also reported that the formation of the second-
ary phase such as LiNb3O8 (niobium-rich grain boundaries)
in the lithium niobate phase decreases the piezoelectric
charge coefficient, which indicates that the piezoelectric out-
put voltage/current can be further reduced.52 Interestingly, in
contrast to expectation, piezoelectric output voltage/current
from the as-grown LiNbO3 sample based NG (which con-
tains a small amount of the LiNb3O8 phase) was much higher
than the previously reported LiNbO3 based NG. Therefore,
we proposed that enhancement of piezoelectric output volt-
age and current from the NG device is mainly due to the dra-
matic increase in the band gap and reduction of screening of
piezoelectric polarisation charges by free carriers. It is worth
to point out that no significant output voltage was observed
from only the PDMS based NG under the same compressive
force.
The working principle of the piezoelectric NG device for
generating the electrical signal is presented in Fig. 7. In the
absence of any external pressure (and/or electric field), no
piezo-induced electric charge is generated due to zero net
dipole moment, and therefore, no electric signal is detected
(Fig. 7(a)). However, when an external pushing force is verti-
cally applied to the top electrode of the electric poled NG
device, the electric dipoles of LiNbO3 presented in the matrix
are strongly aligned due to the poling effect. Consequently, a
piezoelectric potential is created due to mechanical deforma-
tion of the device. As a result, overall polarization across the
electrodes changes and a significant piezoelectric potential
across the external electrodes is produced during pushing
(positive pulse). Further, when the vertical compressive force
is released, the piezoelectric effect is disappeared, and the
accumulated charges at the bottom electrode side move back
to the opposite direction and an electric signal in the reverse
direction is obtained (Fig. 7(b)).
CONCLUSIONS
In summary, we demonstrated the growth of large scale
synthesis of LiNbO3 NWs using the low-cost hydrothermal
solution technique. Nonlinear optical analysis and optical
limiting properties of LiNbO3 were investigated via the two
photon absorption technique using femtosecond laser pulses.
The flexible piezoelectric NG device was fabricated using
the composite of the PDMS polymer and lead-free LiNbO3
NWs. Under vertical periodic compressive force, a large out-
put voltage about 4.0 V and a very large current density of
about 1.5 lA cm�2 were obtained under the cyclic compres-
sive force. The output current was 150 times higher than the
previously reported LiNbO3 based NG. To align the electric
dipoles of ferroelectric/piezoelectric LiNbO3 inside the poly-
mer matrix, the electric poling method was employed. To
understand the enhancement of output performance, UV-ViS
and femtosecond laser studies were also carried out. We
have shown that large piezoelectric output voltage/current
from the composite NG is strongly affected by the large
band gap and nonlinear properties of LiNbO3. Such a result
can be exploited for harvesting mechanical energy and for
piezoelectronics and piezo-phototronic applications due to
their multifunctional properties.
SUPPLEMENTARY MATERIAL
See supplementary material for the XRD pattern of
LiNbO3 NWs, experimental details of two-photon absorp-
tion, the schematic image of two photon induced transition,
schematic diagrams of the piezoelectric nanogenerator
device fabrication process, the cross-sectional FE-SEM
image of the LiNbO3:PDMS composite, FT-IR spectra of the
LiNbO3:PDMS composite, the enlarged view of one cycle of
output current under forward and reverse connections under
mechanical stress, and a table showing the comparison of
output performance of the NG present here with other
reported composite type NGs.
ACKNOWLEDGMENTS
M.K.G. is grateful to the Department of Science &
Technology, Government of India, for awarding the DST-
INSPIRE Faculty Fellowship [IFA-13 PH-81].
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