Research

Our research interests are to study fundamental properties of functional nanostructures, nanocomposites, semiconducting, magnetic and superconductor materials and explore its novel applications.

v Effect of Intrinsic Strain/defects in the Nanostructures Materials

One of theme of research is to explore the effect of presence of intrinsic stress/strain in nanostructured materials/films on magnetic and optical properties. we have demonstrated that by controlling the intrinsic stress magnetic/optical properties of CoFe₂O₄ and optical properties of semiconducting nanoparticles can be tuned.

CoFe₂O₄ nanoparticles

(a) Variation of crystalline size and strain with synthesis temperature of the CFO nanoparticles (b) Variation of M_s with particles size diameters of the CFO nanoparticles (Solid lines are simulated curves). The variation of magnetic coercivity and optical band gap of CFO nanoparticles with intrinsic strain is shown in (c) and (d) respectively.
(https://doi.org/10.1016/j.apsusc.2015.12.205)

Cu₂ZnSnS₄ nanoparticles:

The crystallite size of the as deposited and heated ?lms was remain similar but the intrinsic strain varies and optical band gaps of the CZTS ?lms decerase with the increase of the heating temperature. The observed red shift in the band gap of the CZTS nanostructured ?lms was not due to the size e?ect and has been attributed to intrinsic stain present in the CZTS nanostructured films.

The Variation ofΔE_Strain  with the intrinsic strain in CZTS nanostructures films heated at different temperature.
(https://doi.org/10.1016/j.tsf.2018.05.003)

ZnO nanostructures films:

We have demonstrated that by controlling Al doping in ZnO nanostructured films, the stress in the film can be tuned, which result in the variation of the optical band gap and Photoluminance properties of the films.

(a) Variation of stress as a function of different wt% of Al doping in ZnO nanostructured films (b) Optical absorption spectra of ZnO and AZO films (c) Normalized PL spectra of ZnO and AZO films. Inset (a) shows the blow-up part of UV emission and inset shows the blow-up part of defect peaks for AZO films. (d) plot of (αhν)² versus photon energy (hν) for ZnO and AZO films. Inset shows the variation of band gap of ZnO films with different Al concentrations.
(https://doi.org/10.1088/0022-3727/43/46/465402)

v Resistive Switching

 Valence Change Bipolar Resistive Switching Accompanied With Magnetization Switching in CoFe2O4 Thin Film.

Resistive Switching in oxides has offered new opportunities for developing resistive random access memory (ReRAM) devices. Here we demonstrated bipolar Resistive Switching along with magnetization switching of cobalt ferrite (CFO) thin film using Al/CFO/FTO sandwich structure. Nearly constant resistance values in LRS and HRS confirm the stability and non-volatile nature of the device. The device shows different conduction mechanisms in the HRS and LRS i.e. Schottky, Poole Frenkel and Ohmic. Magnetization of the device is also modulated by applied electric field which has been attributed to the oxygen vacancies formed/annihilated during the voltage sweep and indicates the presence of valence change mechanism (VCM) in our device.

Tuning of optical bandgap and magnetization of CoFe₂O₄ thin films.
(https://doi.org/10.1063/1.4890863)

We demonstrated that the optical bandgap and the saturation magnetization of CFO films can be modified by controlling the annealing temperature of CFO films and by controlled doping if Zn in CFO. We have correlated these changes in the optical and magnetic properties of the post annealed films at different temperatures and Zn doped CFO films with the redistribution of Co2+ among tetrahedral and octahedral sites and explained it quantitatively using the Raman peak intensity ratio which is a novel approach.

Tuning of optical bandgap and magnetization of CoFe₂O₄ thin films through controlled annealing

Tailoring the optical bandgap and magnetization of cobalt ferrite thin films through controlled zinc doping.(https://doi.org/10.1063/1.4960989)

v Magnetically Tunable Band pass And Band stop Microwave Filters

  Bandpass microwave filter with CFO thin film in the flip-chip geometry and Transmission characteristic of microwave filter.
(https://doi.org/10.1016/j.ssc.2016.01.014)

  Spur-line based bandstop filter with ferrite thin films in the flip-chip geometry and Transmission characteristic of microwave filter.

v Tunability of 7-8% for a small magnetic field of ~ 250 Oe has been demonstrated.(https://doi.org/10.1063/1.4982592)

Spur-line bandstop filter with CFO NRs in the flip-chip geometry and Transmission characteristic of bandstop filter

v Clean Energy and Environment

Thermoelectrics:

      Nanostructures, nanocomposites and thin films for harvesting thermal energy

Our research approach is to develop nanocomposite materials by combining nanostructure semiconducting materials with CNT/2D material and polymer to enhance figure of merit. The combination of semiconducting nanostructures with 2D/CNT is expected to enhance electrical conductivity and cut down to thermal conductivity due to enhanced phonon scattering at the interfaces. We are exploring properties of various nanocomposites such as Bi₂Te₃-MWCNT, Bi₂Te₃-RGO, Sb₂Te₃-RGO, Bi₂Te₃-CFO etc. with the objective to develop efficienct thermoelectric generator.(https://doi.org/10.1016/j.ceramint.2017.08.017)

Nanogenerator for harvesting mechanical energy

We are designing and synthesizing flexible nanogenerators based on Piezoelectric and Triboelectric effect for energy harvesting applications. By combining piezoelectric/ferroelectric nanostructures and RGO material with PVDF, we demonstrated that flexible nanogenarator with enhanced performance can be obtained. This smart device can be productively used for driving small scale electronic devices at any environmental conditions.
(https://doi.org/10.1002/pat.4096) (https://doi.org/10.1016/j.compscitech.2017.06.013)

Free standing flexible nanocomposites film, schematic diagram for fabricated Piezoelectric nanogenerator (PENG)

Output voltage of PENG with hand tapping

Fabrication of vertical contact mode Triboelectric Nanogenerator (TENG)

Photoelectrochemical Water Splitting for Hydrogen Generation

Our focus is to develop nanocomposites for efficient photoanodes which can result in enhanced photoelectrochemical water splitting for hydrogen generation under visible light. We have synthesized nanocomposites by combing semiconducing nanostructures with 2D material, CNR, ferroelectric which show higher absorption of visible light, higher separation efficiency of photogenerated electro-hole pairs and with extra functionality for tuning PEC properties.

      Electrical Tuning of Photoelectrochemical Properties of Ferroelectric Nanostructure NaNbO₃ Films

Photoelectrochemical properties of NaNbO₃ nanostructure ferroelectric films are investigated and it is demonstrated that efficiency of photoelectrochemical (PEC) water splitting can be tuned ( from 7% to 23%) by electrical polarization of the NaNbO₃ films.(https://doi.org/10.1063/1.4980100)

      Coupling of Piezoelectric, Semiconducting and Photoexcitation Properties in NaNbO₃ Nanostructures for Controlling Electrical Transport: Realizing an Efficient Piezo-Photoanode and Piezo-Photocatalyst

Demonstrated an efficient coupling between piezoelectric, semiconducting and photoexcitation properties in chemically stable NaNbO₃ semiconductor with an aim to enhance the efficiency of PEC water splitting and photocatalytic activities. It can be used as a potential alternative material for piezophototronic applications.(https://doi.org/10.1016/j.nanoen.2017.05.029)

Plasmonic nanostructures based on TiO₂/Ag/CNT

A visible light active plasmonic photocatalyst, Ag/TiO₂/CNT was synthesized by loading of Ag nanoparticles onto TiO₂/CNT nanocomposite. The ternary Ag/TiO₂/CNT photoanode exhibits a ~4 times higher photocurrent density (0.91 mA/cm²) as compared to the binary TiO₂/CNT photoanode (0.23 mA/cm²). The enhancement in the photocatalytic activity is attributed to the synergistic effect between Ag nanoparticles and MWCNT, which enhance the charge separation efficiency by Schottky barrier formation at Ag/TiO₂ interface and role of MWCNT as an electron reservoir.

     Photosensitization of zinc oxide nanorods with polyaniline

A ~3 fold enhancement in the incident photon-to-electron conversion efficiency is observed for PANI/ZnO nanocomposite ascompared to bare ZnO nanorods. The observed enhancement in the photoelectrochemical activity is attributed to the photosensitization effect of visible light responsive PANI and the formation of type-II heterojunction between ZnO and PANI leading to the efficient separation and faster transfer of photoinduced charge carriers at the interface.(https://doi.org/10.1016/j.ijhydene.2016.08.131)

  Nanostructure Photocatalysts for Efficient Degaradation of Organic Dye

      Enhanced photocatalytic activity and magnetic separation using cadmium sulfide and cobalt ferrite (CdS/CFO) core-shell nanostructures is demonstrated.
Reduced graphene oxide coupled CdS/CoFe₂O₄ ternary nanohybrid with enhanced photocatalytic activity and stability.(DOI: 10.1039/C5RA14889H)

       Polyaniline coupled cadmium Sulfide Nanorods and Nanoflowers: A comparative study for enhanced photocatalytic activity.
(DOI 10.1007/s00396-016-3844-4)

       Enhanced Photosensitization of Zinc Oxide Nanorods using polyaniline for photocatalytic degradation of MB dye.(https://doi.org/10.1016/j.ijhydene.2016.08.131)

Solar Cell

           CZTS nanoparticles for Photovoltaic application.

A core shell structure of dispersible, uniform and small size oleic acid coated CZTS nanoparticles (Size~7nm) was synthesized. A solar cell device based on Al/CZTS/CdS/TiO₂/FTO solar cell was fabricated. J-V characteristics of solar cell device under dark and light condition (100mW/cm²) and the power conversion efficiency of solar cell is obtained to be ~0.65%.(https://doi.org/10.1016/j.apt.2017.06.023)

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