Avanendra Singh | NISER - Academia.edu (original) (raw)

Papers by Avanendra Singh

Research paper thumbnail of Synthesis of p–n junctions in ZnO nanorods by O+ ion implantation

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Oct 1, 2017

Tandem p-n junctions have been synthesized in ZnO nanorods (NRs) by implantation of 50 and 350 ke... more Tandem p-n junctions have been synthesized in ZnO nanorods (NRs) by implantation of 50 and 350 keV O + ions. Conducting-AFM measurements reveal the formation of Schottky like junctions between AFM tip and NRs. Photoluminescence measurements demonstrate the recovery of near band edge (NBE) emission upon annealing, while an additional dominant deep level emission is also observed. De-convolution analysis shows that these peaks originate from Oxygen interstitials (O i) and may contribute to p-type conductivity in ZnO NRs. Such implanted NRs, may be suitable for green emissions and p-type conductivity.

Research paper thumbnail of Strong Red Luminescent Twin ZnO Nanorods for Nano-thermometry and Phonon Tunnel Device Application

Bulletin of the American Physical Society, Mar 16, 2016

Research paper thumbnail of Enhanced ultraviolet emission from self-assembled ZnO nanorods grown on graphene

Journal of Applied Physics, Dec 18, 2018

We report the intense room temperature ultraviolet photoluminescence (PL) emission from selfassem... more We report the intense room temperature ultraviolet photoluminescence (PL) emission from selfassembled vertically aligned ZnO nanorods grown directly on graphene. The PL intensities from ZnO nanorods grown on other van der Waal bulk solids such as highly oriented pyrolytic graphite and mica under the same experimental condition are also compared. The enhanced PL signal from ZnO nanorods grown on graphene is explained on the basis of lattice matching of ZnO with that of graphene leading to high crystal quality. Furthermore, the role of graphene plasmons on the enhanced PL signal is explored by studying the micro-PL mapping on a single nanorod lying horizontally on the graphene surface. The uniform and high PL intensity distribution is noticed along the central axis of the rod, and the intensity distribution decreases toward either side of the central axis. The occurrence of such intensity distribution is explained by resonant excitation of graphene plasmon near bandgap energy of ZnO, which is modulated by surface corrugation of graphene and followed by its transformation into the propagating photon.

Research paper thumbnail of Second harmonic generation of femtosecond pulses using ZnO nanorods grown by chemical bath deposition with drop casted seed layer

Journal of Nonlinear Optical Physics & Materials, Sep 1, 2016

Using full vector Maxwell simulations we elucidate a fundamental source of temporal splitting of ... more Using full vector Maxwell simulations we elucidate a fundamental source of temporal splitting of the second harmonic field generated by a femtosecond fundamental pulse under phase-mismatched conditions. One component of the generated field propagates at the second harmonic group velocity while the other is driven by the fundamental field and propagates at the fundamental group velocity. We analyze the conditions under which the temporal splitting should be observable.

Research paper thumbnail of Strong Red Luminescent Twin ZnO Nanorods for Nano-thermometry Application

MRS Advances, Feb 24, 2016

ABSTRACTTwo segments of horizontally grown crystalline ZnO nanorods (NRs) connected with an amorp... more ABSTRACTTwo segments of horizontally grown crystalline ZnO nanorods (NRs) connected with an amorphous layer have been successfully and reproducibly synthesized using one-step hydrothermal technique by controlling the growth rate. The confocal photoluminescence (PL) imaging and spectroscopy of twin ZnO NRs at different temperatures shows intense red emission with comparably week UV emission. The strong red emission from the twin NRs is a consequence of structural imperfections. Both UV and red bands showed signatures of strong temperature dependent exciton-phonon scattering. Using the intensity ratio of the UV and red emissions, we show that the individual ZnO NRs can be used as highly sensitive cryogenic temperature sensors below ∼175 K.

Research paper thumbnail of Growth of significantly low dimensional zinc orthotitanate (Zn2TiO4) nanoparticles by solid state reaction method

Science of Sintering

In this work, the ZnO-TiO2 mixed phase nanoparticles were prepared by solid state reaction method... more In this work, the ZnO-TiO2 mixed phase nanoparticles were prepared by solid state reaction method by using ZnO and TiO2 powder as precursors. The X-ray diffraction pattern shows a dominant phase of Zinc Orthotitanate (Zn2TiO4). The average particle size (58?18 nm) calculated by the analysing FESEM data closely matches with the particle size calculated by Scherrer?s equation. The calculated average particle size is significantly smaller than the previously published results of nanoparticles, prepared by same method. In the Brunauer-Emmett-Teller (BET) study the specific surface area of the nanoparticles was found as 8.78 m2/g which is similar to the surface area reported in this material prepared by mechanochemical method. The method which we report is simpler and cost effective unlike the previous reported.

Research paper thumbnail of Modulation of intrinsic defects in vertically grown ZnO nanorods by ion implantation

Physical Chemistry Chemical Physics

Intrinsic defects in vertically grown ZnO nanorods are modulated by inert Xe gas implantation to ... more Intrinsic defects in vertically grown ZnO nanorods are modulated by inert Xe gas implantation to tune the optical bandgap.

Research paper thumbnail of EELS Investigation of the Work Function Reduction in Au decorated ZnO Nanotapers

European Microscopy Congress 2016: Proceedings, 2016

Research paper thumbnail of Tuning field-emission characteristics of ZnO nanorods through defect engineering via O+ ion irradiation

Journal of Applied Physics, 2020

Vertically aligned ZnO nanorods grown by a wet chemical method were implanted with O+ ions with t... more Vertically aligned ZnO nanorods grown by a wet chemical method were implanted with O+ ions with three different ion fluences: (Φ)=5×1014, 5×1015, and 5×1016 ions/cm2. It is observed that the concentration of Oxygen vacancies (OV) introduced by implantation first increases from 25.94% to 54.76% with increasing Φ and decreases beyond Φ=5×1015 ions/cm2. We attribute this to the knocking out of oxygen atoms from the host matrix, which gets saturated due to the presence of an ample amount of O+ ions inside the host matrix beyond Φ=5×1015 ions/cm2 and further confirmed by extended x-ray absorption fine structure measurements. Therefore, the abundant OV becomes more delocalized followed by overlapping with the maxima of valence bands resulting in the narrowing of the bandgap of ∼0.4 eV. The appearance of an additional Raman peak at ∼575cm−1 in Raman spectra further confirmed the presence of impurity states. It is evident that at a fixed J=100 μA/cm2, the turn-on field increases from 3.61 V...

Research paper thumbnail of Femtosecond laser excited second harmonic and multiphoton absorption induced UV luminescence generation behaviour of ZnO nanofibers

Optik, 2018

Femtosecond (fs) laser excited second harmonic (SH) and multiphoton absorption (MPA) induced UV l... more Femtosecond (fs) laser excited second harmonic (SH) and multiphoton absorption (MPA) induced UV luminescence generation behaviour of Zinc oxide (ZnO) nanofibers is reported here. The used nanofibers are grown by seed assisted chemical bath deposition technology over glass substrates and are excited by a near-infrared (NIR) Ti: Sapphire laser emitting pulses of wavelength 812 nm and duration 100 fs. The peak wavelength of SH and MPA induced UV luminescence signals are found to be 406 nm and 398 nm respectively. Due to good optical quality, no defect level related MPA induced visible luminescence is observed in nanofibers. In comparison to this, ZnO nanostructures grown over plane substrate without seed layer shows very less SH and MPA induced UV luminescence. However in this case, the defect level related MPA induced visible luminescence was found to be very high. Applications like ultrafast pulse diagnostics, NIR induced photodynamic therapy etc. require high SH and MPA induced UV luminescence and low defect level related visible luminescence. So the ZnO nanofibers can be a potential candidate for these applications.

Research paper thumbnail of Efficient UV photocatalytic dye decomposition activity with cost effective solid state reaction grown Zinc Orthotitanate (Zn2TiO4) nanoparticles

Journal of Alloys and Compounds, 2018

In this work, detail investigation on UV photocatalytic dye decomposition activity is done with Z... more In this work, detail investigation on UV photocatalytic dye decomposition activity is done with Zinc Orthotitanate (Zn 2 TiO 4) nanoparticles grown by solid state reaction method and shown that these nanoparticles can show 6 times higher activity than standard commercial TiO 2 nanoparticles Degussa P25. This activity is the highest among all the nanoparticles that have been compared with P25 so far. The potential cause for higher activity is explored through absorption spectroscopy. The Zn 2 TiO 4 nanoparticles are prepared from laboratory grade ZnO and TiO 2 powder of extremely low cost. Excellent recycling ability of Zn 2 TiO 4 nanoparticles is shown through their multiple usages.

Research paper thumbnail of Colossal Broad Band Antireflection from Conformally Grown Cu2O on Pyramidally Textured Si and its Photovoltaic Applications

Solar RRL, 2018

In this paper, we show the efficacy of a conformally grown, self‐organized Cu2O overlayer on chem... more In this paper, we show the efficacy of a conformally grown, self‐organized Cu2O overlayer on chemically synthesized, pyramidally textured silicon substrate for a colossal suppression of optical reflection loss. In particular, we demonstrate that p‐Cu2O film deposited on a chemically textured n‐Si substrate shows an ultra‐low average surface reflectance (≈0.25%) over the entire spectral range (300–2400 nm), whereas the same turns out to be ≈25% for the film deposited on an as‐obtained n‐type Si substrate. It is observed that in the former case, Cu2O grows in the form of leaf‐like nanostructures, which is attributed to be responsible for such a low reflectance. In addition, under both configurations, the p‐Cu2O/n‐Si heterostructure shows a non‐linear current–voltage characteristics, clearly suggesting the formation of barrier junctions. Further, it is found that a solar cell fabricated with p‐Cu2O overlayer grown on a pyramidally textured n‐Si substrate shows an eight times higher eff...

Research paper thumbnail of Enhanced ultraviolet emission from self-assembled ZnO nanorods grown on graphene

Journal of Applied Physics, 2018

We report the intense room temperature ultraviolet photoluminescence (PL) emission from self-asse... more We report the intense room temperature ultraviolet photoluminescence (PL) emission from self-assembled vertically aligned ZnO nanorods grown directly on graphene. The PL intensities from ZnO nanorods grown on other van der Waal bulk solids such as highly oriented pyrolytic graphite and mica under the same experimental condition are also compared. The enhanced PL signal from ZnO nanorods grown on graphene is explained on the basis of lattice matching of ZnO with that of graphene leading to high crystal quality. Furthermore, the role of graphene plasmons on the enhanced PL signal is explored by studying the micro-PL mapping on a single nanorod lying horizontally on the graphene surface. The uniform and high PL intensity distribution is noticed along the central axis of the rod, and the intensity distribution decreases toward either side of the central axis. The occurrence of such intensity distribution is explained by resonant excitation of graphene plasmon near bandgap energy of ZnO,...

Research paper thumbnail of Role of work function in field emission enhancement of Au island decorated vertically aligned ZnO nanotapers

Applied Surface Science, 2017

Following are the highlights of the present study: 1. The nanotapers were synthesized using hydro... more Following are the highlights of the present study: 1. The nanotapers were synthesized using hydrothermal technique and the corrugated gold decoration was done using simple evaporation method, both of which are easily scalable techniques for large area applications. 2. A significantly enhanced field emission properties of ZnO nanotapers have been achieved via a corrugated decoration of Au having current densities comparable to the best results in the literature. 3. The metal induced midgap states formed at the ZnO-Au interface are responsible for the observed low turn-on field because, which is related to the reduced the effective work function measured directly using Kelvin probe force microscopy. 4. Tunneling atomic force microscopy measurements revealed a very uniform spatial emission profile in the Au decorated nanotapers, which is a basic requirement for any large scale application. 5. The two most important features of any desirable field emission material viz. low turn-on potential and uniform special emission profile has been observed in one system.

Research paper thumbnail of Synthesis of p–n junctions in ZnO nanorods by O+ ion implantation

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2017

Tandem p-n junctions have been synthesized in ZnO nanorods (NRs) by implantation of 50 and 350 ke... more Tandem p-n junctions have been synthesized in ZnO nanorods (NRs) by implantation of 50 and 350 keV O + ions. Conducting-AFM measurements reveal the formation of Schottky like junctions between AFM tip and NRs. Photoluminescence measurements demonstrate the recovery of near band edge (NBE) emission upon annealing, while an additional dominant deep level emission is also observed. De-convolution analysis shows that these peaks originate from Oxygen interstitials (O i) and may contribute to p-type conductivity in ZnO NRs. Such implanted NRs, may be suitable for green emissions and p-type conductivity.

Research paper thumbnail of Photoluminescent Au-Ge composite nanodots formation on SiO 2 surface by ion induced dewetting

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2017

Medium energy ion irradiation on a bilayer of Au and Ge on SiO 2 is observed to result in gradual... more Medium energy ion irradiation on a bilayer of Au and Ge on SiO 2 is observed to result in gradual morphological evolution from an interconnected network to a nanodot array on the insulator surface. Structural and compositional analyses reveal composite nature of the nanodots, comprising of both Au and Ge. The growing nanostructures are found to be photoluminescent at room temperature where the emission intensity and wavelengths vary with morphology. The growth of such nanostructures can be understood in terms of dewetting of the metal layer under ion irradiation due to ion-induced melting along the ion tracks. The visible PL emission is found to be related with evolution of the Au-Ge nanodots. The study indicates a route towards single step synthesis of metal-semiconductor nanodots on insulator surface.

Research paper thumbnail of Growth of TiO2 thin films on chemically textured Si for solar cell applications as a hole-blocking and antireflection layer

Applied Surface Science, 2017

Growth of TiO2 thin films on chemically textured Si for solar cell applications as a hole-blockin... more Growth of TiO2 thin films on chemically textured Si for solar cell applications as a hole-blocking and antireflection layer, Applied Surface Science http://dx.

Research paper thumbnail of Suppression of near band edge emission in specially engineered ZnO twin nanorods

Physical Chemistry Chemical Physics, 2017

Twin crystalline ZnO nanorods with tunable amorphous joints are synthesized via a hydrothermal ro... more Twin crystalline ZnO nanorods with tunable amorphous joints are synthesized via a hydrothermal route. We find a strong coupling of acoustic phonon modes to free excitons in these structures. As a result, significant non-radiative transfer of carriers from the conduction band to defect bands occurs, leading to a loss of the near band edge emission intensity below ∼180 K.

Research paper thumbnail of Ion-beam-induced nanodots formation from Au/Si thin films on quartz surface

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2016

Abstract We report the synthesis of Si nanodots on quartz surface using ion irradiation. When a b... more Abstract We report the synthesis of Si nanodots on quartz surface using ion irradiation. When a bi-layer of ultrathin Au and Si on quartz surface is irradiated by 500 keV Xe-ion beam, the bi-layer spontaneously transforms into nanodots at a fluence of 5 × 1014 ions cm−2. The spatial density and diameter of the nanodots are reduced with increase in applied ion fluence. The nanostructures exhibit photoluminescence in the visible range at room temperature where the intensity and wavelength depends upon ion fluence. The observed evolution seems to be correlated to ion beam mixing induced silicide formation at Au–Si interface.

Research paper thumbnail of Strong Red Luminescent Twin ZnO Nanorods for Nano-thermometry Application

MRS Advances, 2016

ABSTRACTTwo segments of horizontally grown crystalline ZnO nanorods (NRs) connected with an amorp... more ABSTRACTTwo segments of horizontally grown crystalline ZnO nanorods (NRs) connected with an amorphous layer have been successfully and reproducibly synthesized using one-step hydrothermal technique by controlling the growth rate. The confocal photoluminescence (PL) imaging and spectroscopy of twin ZnO NRs at different temperatures shows intense red emission with comparably week UV emission. The strong red emission from the twin NRs is a consequence of structural imperfections. Both UV and red bands showed signatures of strong temperature dependent exciton-phonon scattering. Using the intensity ratio of the UV and red emissions, we show that the individual ZnO NRs can be used as highly sensitive cryogenic temperature sensors below ∼175 K.

Research paper thumbnail of Synthesis of p–n junctions in ZnO nanorods by O+ ion implantation

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Oct 1, 2017

Tandem p-n junctions have been synthesized in ZnO nanorods (NRs) by implantation of 50 and 350 ke... more Tandem p-n junctions have been synthesized in ZnO nanorods (NRs) by implantation of 50 and 350 keV O + ions. Conducting-AFM measurements reveal the formation of Schottky like junctions between AFM tip and NRs. Photoluminescence measurements demonstrate the recovery of near band edge (NBE) emission upon annealing, while an additional dominant deep level emission is also observed. De-convolution analysis shows that these peaks originate from Oxygen interstitials (O i) and may contribute to p-type conductivity in ZnO NRs. Such implanted NRs, may be suitable for green emissions and p-type conductivity.

Research paper thumbnail of Strong Red Luminescent Twin ZnO Nanorods for Nano-thermometry and Phonon Tunnel Device Application

Bulletin of the American Physical Society, Mar 16, 2016

Research paper thumbnail of Enhanced ultraviolet emission from self-assembled ZnO nanorods grown on graphene

Journal of Applied Physics, Dec 18, 2018

We report the intense room temperature ultraviolet photoluminescence (PL) emission from selfassem... more We report the intense room temperature ultraviolet photoluminescence (PL) emission from selfassembled vertically aligned ZnO nanorods grown directly on graphene. The PL intensities from ZnO nanorods grown on other van der Waal bulk solids such as highly oriented pyrolytic graphite and mica under the same experimental condition are also compared. The enhanced PL signal from ZnO nanorods grown on graphene is explained on the basis of lattice matching of ZnO with that of graphene leading to high crystal quality. Furthermore, the role of graphene plasmons on the enhanced PL signal is explored by studying the micro-PL mapping on a single nanorod lying horizontally on the graphene surface. The uniform and high PL intensity distribution is noticed along the central axis of the rod, and the intensity distribution decreases toward either side of the central axis. The occurrence of such intensity distribution is explained by resonant excitation of graphene plasmon near bandgap energy of ZnO, which is modulated by surface corrugation of graphene and followed by its transformation into the propagating photon.

Research paper thumbnail of Second harmonic generation of femtosecond pulses using ZnO nanorods grown by chemical bath deposition with drop casted seed layer

Journal of Nonlinear Optical Physics & Materials, Sep 1, 2016

Using full vector Maxwell simulations we elucidate a fundamental source of temporal splitting of ... more Using full vector Maxwell simulations we elucidate a fundamental source of temporal splitting of the second harmonic field generated by a femtosecond fundamental pulse under phase-mismatched conditions. One component of the generated field propagates at the second harmonic group velocity while the other is driven by the fundamental field and propagates at the fundamental group velocity. We analyze the conditions under which the temporal splitting should be observable.

Research paper thumbnail of Strong Red Luminescent Twin ZnO Nanorods for Nano-thermometry Application

MRS Advances, Feb 24, 2016

ABSTRACTTwo segments of horizontally grown crystalline ZnO nanorods (NRs) connected with an amorp... more ABSTRACTTwo segments of horizontally grown crystalline ZnO nanorods (NRs) connected with an amorphous layer have been successfully and reproducibly synthesized using one-step hydrothermal technique by controlling the growth rate. The confocal photoluminescence (PL) imaging and spectroscopy of twin ZnO NRs at different temperatures shows intense red emission with comparably week UV emission. The strong red emission from the twin NRs is a consequence of structural imperfections. Both UV and red bands showed signatures of strong temperature dependent exciton-phonon scattering. Using the intensity ratio of the UV and red emissions, we show that the individual ZnO NRs can be used as highly sensitive cryogenic temperature sensors below ∼175 K.

Research paper thumbnail of Growth of significantly low dimensional zinc orthotitanate (Zn2TiO4) nanoparticles by solid state reaction method

Science of Sintering

In this work, the ZnO-TiO2 mixed phase nanoparticles were prepared by solid state reaction method... more In this work, the ZnO-TiO2 mixed phase nanoparticles were prepared by solid state reaction method by using ZnO and TiO2 powder as precursors. The X-ray diffraction pattern shows a dominant phase of Zinc Orthotitanate (Zn2TiO4). The average particle size (58?18 nm) calculated by the analysing FESEM data closely matches with the particle size calculated by Scherrer?s equation. The calculated average particle size is significantly smaller than the previously published results of nanoparticles, prepared by same method. In the Brunauer-Emmett-Teller (BET) study the specific surface area of the nanoparticles was found as 8.78 m2/g which is similar to the surface area reported in this material prepared by mechanochemical method. The method which we report is simpler and cost effective unlike the previous reported.

Research paper thumbnail of Modulation of intrinsic defects in vertically grown ZnO nanorods by ion implantation

Physical Chemistry Chemical Physics

Intrinsic defects in vertically grown ZnO nanorods are modulated by inert Xe gas implantation to ... more Intrinsic defects in vertically grown ZnO nanorods are modulated by inert Xe gas implantation to tune the optical bandgap.

Research paper thumbnail of EELS Investigation of the Work Function Reduction in Au decorated ZnO Nanotapers

European Microscopy Congress 2016: Proceedings, 2016

Research paper thumbnail of Tuning field-emission characteristics of ZnO nanorods through defect engineering via O+ ion irradiation

Journal of Applied Physics, 2020

Vertically aligned ZnO nanorods grown by a wet chemical method were implanted with O+ ions with t... more Vertically aligned ZnO nanorods grown by a wet chemical method were implanted with O+ ions with three different ion fluences: (Φ)=5×1014, 5×1015, and 5×1016 ions/cm2. It is observed that the concentration of Oxygen vacancies (OV) introduced by implantation first increases from 25.94% to 54.76% with increasing Φ and decreases beyond Φ=5×1015 ions/cm2. We attribute this to the knocking out of oxygen atoms from the host matrix, which gets saturated due to the presence of an ample amount of O+ ions inside the host matrix beyond Φ=5×1015 ions/cm2 and further confirmed by extended x-ray absorption fine structure measurements. Therefore, the abundant OV becomes more delocalized followed by overlapping with the maxima of valence bands resulting in the narrowing of the bandgap of ∼0.4 eV. The appearance of an additional Raman peak at ∼575cm−1 in Raman spectra further confirmed the presence of impurity states. It is evident that at a fixed J=100 μA/cm2, the turn-on field increases from 3.61 V...

Research paper thumbnail of Femtosecond laser excited second harmonic and multiphoton absorption induced UV luminescence generation behaviour of ZnO nanofibers

Optik, 2018

Femtosecond (fs) laser excited second harmonic (SH) and multiphoton absorption (MPA) induced UV l... more Femtosecond (fs) laser excited second harmonic (SH) and multiphoton absorption (MPA) induced UV luminescence generation behaviour of Zinc oxide (ZnO) nanofibers is reported here. The used nanofibers are grown by seed assisted chemical bath deposition technology over glass substrates and are excited by a near-infrared (NIR) Ti: Sapphire laser emitting pulses of wavelength 812 nm and duration 100 fs. The peak wavelength of SH and MPA induced UV luminescence signals are found to be 406 nm and 398 nm respectively. Due to good optical quality, no defect level related MPA induced visible luminescence is observed in nanofibers. In comparison to this, ZnO nanostructures grown over plane substrate without seed layer shows very less SH and MPA induced UV luminescence. However in this case, the defect level related MPA induced visible luminescence was found to be very high. Applications like ultrafast pulse diagnostics, NIR induced photodynamic therapy etc. require high SH and MPA induced UV luminescence and low defect level related visible luminescence. So the ZnO nanofibers can be a potential candidate for these applications.

Research paper thumbnail of Efficient UV photocatalytic dye decomposition activity with cost effective solid state reaction grown Zinc Orthotitanate (Zn2TiO4) nanoparticles

Journal of Alloys and Compounds, 2018

In this work, detail investigation on UV photocatalytic dye decomposition activity is done with Z... more In this work, detail investigation on UV photocatalytic dye decomposition activity is done with Zinc Orthotitanate (Zn 2 TiO 4) nanoparticles grown by solid state reaction method and shown that these nanoparticles can show 6 times higher activity than standard commercial TiO 2 nanoparticles Degussa P25. This activity is the highest among all the nanoparticles that have been compared with P25 so far. The potential cause for higher activity is explored through absorption spectroscopy. The Zn 2 TiO 4 nanoparticles are prepared from laboratory grade ZnO and TiO 2 powder of extremely low cost. Excellent recycling ability of Zn 2 TiO 4 nanoparticles is shown through their multiple usages.

Research paper thumbnail of Colossal Broad Band Antireflection from Conformally Grown Cu2O on Pyramidally Textured Si and its Photovoltaic Applications

Solar RRL, 2018

In this paper, we show the efficacy of a conformally grown, self‐organized Cu2O overlayer on chem... more In this paper, we show the efficacy of a conformally grown, self‐organized Cu2O overlayer on chemically synthesized, pyramidally textured silicon substrate for a colossal suppression of optical reflection loss. In particular, we demonstrate that p‐Cu2O film deposited on a chemically textured n‐Si substrate shows an ultra‐low average surface reflectance (≈0.25%) over the entire spectral range (300–2400 nm), whereas the same turns out to be ≈25% for the film deposited on an as‐obtained n‐type Si substrate. It is observed that in the former case, Cu2O grows in the form of leaf‐like nanostructures, which is attributed to be responsible for such a low reflectance. In addition, under both configurations, the p‐Cu2O/n‐Si heterostructure shows a non‐linear current–voltage characteristics, clearly suggesting the formation of barrier junctions. Further, it is found that a solar cell fabricated with p‐Cu2O overlayer grown on a pyramidally textured n‐Si substrate shows an eight times higher eff...

Research paper thumbnail of Enhanced ultraviolet emission from self-assembled ZnO nanorods grown on graphene

Journal of Applied Physics, 2018

We report the intense room temperature ultraviolet photoluminescence (PL) emission from self-asse... more We report the intense room temperature ultraviolet photoluminescence (PL) emission from self-assembled vertically aligned ZnO nanorods grown directly on graphene. The PL intensities from ZnO nanorods grown on other van der Waal bulk solids such as highly oriented pyrolytic graphite and mica under the same experimental condition are also compared. The enhanced PL signal from ZnO nanorods grown on graphene is explained on the basis of lattice matching of ZnO with that of graphene leading to high crystal quality. Furthermore, the role of graphene plasmons on the enhanced PL signal is explored by studying the micro-PL mapping on a single nanorod lying horizontally on the graphene surface. The uniform and high PL intensity distribution is noticed along the central axis of the rod, and the intensity distribution decreases toward either side of the central axis. The occurrence of such intensity distribution is explained by resonant excitation of graphene plasmon near bandgap energy of ZnO,...

Research paper thumbnail of Role of work function in field emission enhancement of Au island decorated vertically aligned ZnO nanotapers

Applied Surface Science, 2017

Following are the highlights of the present study: 1. The nanotapers were synthesized using hydro... more Following are the highlights of the present study: 1. The nanotapers were synthesized using hydrothermal technique and the corrugated gold decoration was done using simple evaporation method, both of which are easily scalable techniques for large area applications. 2. A significantly enhanced field emission properties of ZnO nanotapers have been achieved via a corrugated decoration of Au having current densities comparable to the best results in the literature. 3. The metal induced midgap states formed at the ZnO-Au interface are responsible for the observed low turn-on field because, which is related to the reduced the effective work function measured directly using Kelvin probe force microscopy. 4. Tunneling atomic force microscopy measurements revealed a very uniform spatial emission profile in the Au decorated nanotapers, which is a basic requirement for any large scale application. 5. The two most important features of any desirable field emission material viz. low turn-on potential and uniform special emission profile has been observed in one system.

Research paper thumbnail of Synthesis of p–n junctions in ZnO nanorods by O+ ion implantation

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2017

Tandem p-n junctions have been synthesized in ZnO nanorods (NRs) by implantation of 50 and 350 ke... more Tandem p-n junctions have been synthesized in ZnO nanorods (NRs) by implantation of 50 and 350 keV O + ions. Conducting-AFM measurements reveal the formation of Schottky like junctions between AFM tip and NRs. Photoluminescence measurements demonstrate the recovery of near band edge (NBE) emission upon annealing, while an additional dominant deep level emission is also observed. De-convolution analysis shows that these peaks originate from Oxygen interstitials (O i) and may contribute to p-type conductivity in ZnO NRs. Such implanted NRs, may be suitable for green emissions and p-type conductivity.

Research paper thumbnail of Photoluminescent Au-Ge composite nanodots formation on SiO 2 surface by ion induced dewetting

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2017

Medium energy ion irradiation on a bilayer of Au and Ge on SiO 2 is observed to result in gradual... more Medium energy ion irradiation on a bilayer of Au and Ge on SiO 2 is observed to result in gradual morphological evolution from an interconnected network to a nanodot array on the insulator surface. Structural and compositional analyses reveal composite nature of the nanodots, comprising of both Au and Ge. The growing nanostructures are found to be photoluminescent at room temperature where the emission intensity and wavelengths vary with morphology. The growth of such nanostructures can be understood in terms of dewetting of the metal layer under ion irradiation due to ion-induced melting along the ion tracks. The visible PL emission is found to be related with evolution of the Au-Ge nanodots. The study indicates a route towards single step synthesis of metal-semiconductor nanodots on insulator surface.

Research paper thumbnail of Growth of TiO2 thin films on chemically textured Si for solar cell applications as a hole-blocking and antireflection layer

Applied Surface Science, 2017

Growth of TiO2 thin films on chemically textured Si for solar cell applications as a hole-blockin... more Growth of TiO2 thin films on chemically textured Si for solar cell applications as a hole-blocking and antireflection layer, Applied Surface Science http://dx.

Research paper thumbnail of Suppression of near band edge emission in specially engineered ZnO twin nanorods

Physical Chemistry Chemical Physics, 2017

Twin crystalline ZnO nanorods with tunable amorphous joints are synthesized via a hydrothermal ro... more Twin crystalline ZnO nanorods with tunable amorphous joints are synthesized via a hydrothermal route. We find a strong coupling of acoustic phonon modes to free excitons in these structures. As a result, significant non-radiative transfer of carriers from the conduction band to defect bands occurs, leading to a loss of the near band edge emission intensity below ∼180 K.

Research paper thumbnail of Ion-beam-induced nanodots formation from Au/Si thin films on quartz surface

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2016

Abstract We report the synthesis of Si nanodots on quartz surface using ion irradiation. When a b... more Abstract We report the synthesis of Si nanodots on quartz surface using ion irradiation. When a bi-layer of ultrathin Au and Si on quartz surface is irradiated by 500 keV Xe-ion beam, the bi-layer spontaneously transforms into nanodots at a fluence of 5 × 1014 ions cm−2. The spatial density and diameter of the nanodots are reduced with increase in applied ion fluence. The nanostructures exhibit photoluminescence in the visible range at room temperature where the intensity and wavelength depends upon ion fluence. The observed evolution seems to be correlated to ion beam mixing induced silicide formation at Au–Si interface.

Research paper thumbnail of Strong Red Luminescent Twin ZnO Nanorods for Nano-thermometry Application

MRS Advances, 2016

ABSTRACTTwo segments of horizontally grown crystalline ZnO nanorods (NRs) connected with an amorp... more ABSTRACTTwo segments of horizontally grown crystalline ZnO nanorods (NRs) connected with an amorphous layer have been successfully and reproducibly synthesized using one-step hydrothermal technique by controlling the growth rate. The confocal photoluminescence (PL) imaging and spectroscopy of twin ZnO NRs at different temperatures shows intense red emission with comparably week UV emission. The strong red emission from the twin NRs is a consequence of structural imperfections. Both UV and red bands showed signatures of strong temperature dependent exciton-phonon scattering. Using the intensity ratio of the UV and red emissions, we show that the individual ZnO NRs can be used as highly sensitive cryogenic temperature sensors below ∼175 K.