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Optimization of Ni2+ /Ni3+ ratio in reduced graphene oxide/nickel oxide nanohybrids for platinum free dye sensitized solar cells
No full textA strategy has been explored to design a novel network of reduced graphene oxide (rGO)/nickel oxide (NiO) nanohybrids with optimized Ni2+/Ni3+ ratio for the fabrication of compact, flexible, and large area Pt-free dye sensitized solar cells (DSSCs). The rGO/NiO nanohybrids were synthesized by a hydrothermal method and characterized by field emission scanning electron microscopy, Brunauer-Emmett-Teller analysis, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. These studies demonstrate that the rGO/NiO nanohybrids with Ni2+ rich species show high catalytic activity toward the I/I-3(-) redox reaction. This led to the fabrication of improved DSSCs with power conversion efficiency as high as 3.69% with these nanohybrids as counter electrodes in comparison with DSSC devices containing counter electrodes based on rGO (1.71%) and NiO (0.75%)
Optimized reduction of graphite oxide for highly exfoliated silver nanoparticles anchored graphene sheets for dye sensitized solar cell applications
No full textIn the present work, we have synthesized graphene sheets by optimizing reduction of graphite oxide (GO) by hydrazine hydrate (N2H4 center dot xH(2)O) reducing agent and anchored them with silver nanoparticles (Ag NPs). Morphological and spectroscopic studies confirmed the formation of highly exfoliated graphene sheets separated by Ag NPs with improved C/O ratio. The highly electrocatalytic and exfoliated network of graphene sheets/Ag nanocoatings uniformly adhered to FTO substrate has been utilized as platinum (Pt) free counter electrode (CE) in dye sensitized solar cells (DSSC). Fabricated DSSC with only 2.7 mu m thick TiO2 photoanode exhibited photo conversion efficiency (eta = 3.44%) and short circuit current density (J(sc) = 7.03 mA cm(-2)) comparable to DSSC containing Pt-CE without any loss of open circuit voltage (V-oc = 0.71 V) and fill factor (FF = 0.68)
Investigating unipolar switching in Niobium oxide resistive switches: Correlating quantized conductance and mechanism
Get PDFMemory devices based on resistive switching (RS) have not been fully realised due to lack of understanding of the underlying switching mechanisms. Nature of ion transport responsible for switching and growth of conducting filament in transition metal oxide based RS devices is still in debate. Here, we investigated the mechanism in Niobium oxide based RS devices, which shows unipolar switching with high ON/OFF ratio, good endurance cycles and high retention times. We controlled the boundary conditions between low-conductance insulating and a high-conductance metallic state where conducting filament (CF) can form atomic point contact and exhibit quantized conductance behaviour. Based on the statistics generated from quantized steps data, we demonstrated that the CF is growing atom by atom with the applied voltage sweeps. We also observed stable quantized states, which can be utilized in multistate switchin
Nitrogen doped graphene - Silver nanowire hybrids: An excellent anode material for lithium ion batteries
No full textWe present an in-situ polyol assisted synthesis approach for the preparation of silver nanowires (AgNW) over the nitrogen doped graphene (NG) sheets and has been tested as a viable LIBs anode material for the first time. The use of NG serves as nucleation sites, thereby facilitating the growth of AgNWs. The specific material design of the as-prepared NG-AgNW hybrids involves some advantages, including a continuous AgNW-graphene conducting network. Since AgNWs are electrically conductive, it provides an electrical contact with NG sheets which can effectively help the charge transport process and limit the variations in volume during the lithiation/de-lithiation processes. Apart from this, the insertion of metallic Ag nanowires into a percolated NG network increases the interlayer distance of NG sheets and prevent its restacking. Moreover, the more porous nature of the hybrid structure accommodating the large volume changes of AgNWs. As an anode material for LIBs, the NG-AgNW hybrid displays a remarkable initial discharge capacity of 1215 mAh g(-1) and attains a stable capacity of 724 mAh g(-1) at a current density of 100 mAg(-1) after 50 cycles. The electrode exhibits a stable reversible capacity of 714, 634, 550 and 464 mAh g(-1) at 0.1, 0.2, 0.5, 1 Ag-1 respectively. The reversible capacity (710 mAh g(-1)) at 0.1 Ag-1 is recovered after the cycling at various current densities confirming outstanding rate performance of the material. In addition, the coulombic efficiency, the NG-AgNW anode retains nearly 99% after the second cycle, further indicating its excellent reversibility. The hybrid material exhibits better cycling stability, greater rate capability, capacity retention and superior reversible capacity than that of bare AgNW and NG sheets. Our smart design will pave way for the development of efficient electrode materials for high capacity and long cycle life LIBs
Design optimisation of C ion implantation of alpha-Al2O3 for medical dosimetry
No full textThe present work reports the fabrication and characterization of alpha-Al2O3:C, a highly sensitive low effective atomic number (Z(eff)= 10.7) OSL material for medical dosimetry, through a new approach of doping via implantation. In this study, a Single Crystallinea-Al2O3 (SCALO) and a Sapphire alpha-Al2O3 (SALO) are used and implanted with 100 keV of C+ at various fluences (mol%) from 2.5 x 10(14) ions cm(-2) (similar to 0.04%) to 6.25x 10(15) ions cm(-2) (similar to 1%) and are pre-heated up to 220 degrees C. The structural, optical, morphological and luminescent studies of the Carbon doped a-Al2O3 (alpha-Al2O3:C) are carried out using X-ray diffraction, Ultraviolet-visible spectroscopy (UV-Vis), Photo-luminescence (PL), Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS), Optically Stimulated Luminescence (OSL), and Thermo-Luminescence (TL). The doping of similar to 1 mol% of C+ is found at an optimized doping level due to its high intensity of luminescence. This phenomenon is studied for heavy charged particle (HCP) dosimetry, which might prove effective for cancer treatment. It is found that alpha-ALO:C (both the single crystalline and the sapphire alumina) has the capability to measure large radiation doses (similar to kGy). This is attributed to the generation of stable defects after the incorporation of Carbon that results in a linear response with the dose and in extraordinary efficiency. Thus, this study confirms the development of alpha-Al2O3 by the novel approach of C+ implantation method and the findings result in an efficient medical radiation dosimeter
Enhanced luminescence efficiency of wet chemical route synthesized InP-based quantum dots by a novel method: Probing the humidity sensing properties
No full textIn indium phosphide quantum dots (InP QDs), the presence of surface states due to unbonded indium or phosphorus atoms quenches its photoluminescence (PL) efficiencies. Hence, it is imperative to passivate these surface states to achieve high photoluminescence efficiencies of InP nanocrystals. In this work, a novel postsynthesis nascent H chemical treatment to enhance the quantum yield of single-pot, wet chemical route synthesized InP QD's is reported for the first time. The main advantages of this post-synthesis treatment are: (i) it is easy, inexpensive and reproducible and (ii) it does not involve harsh chemical treatment viz. dipping of InP QDs in HF-based solutions, nor it requires annealing at high temperatures which may be detrimental to the fragile structure of InP. The significant increment in PL intensity upon aforementioned hydrogen treatment is due to the passivation of surface states and structural recrystallization mechanism that promotes radiative recombination of electrons and holes and hence higher lifetime values. An enhancement in PL intensity of as-synthesized InP QDs upon nascent hydrogen treatment is quite remarkable and is even better than that accomplished by InP-ZnS core-shell QDs with similar size-distribution. The hydrophobicity of H-treated InP QD's is found to be more than untreated InP thus implying higher compactness and structural rigidity similar to as achieved by InP-ZnS core-shell QDs. Mechanisms related to nascent hydrogen treatment, photo-oxidation and PL enhancement and its effect on the surface stoichiometry of InP QDs are discussed via structural, morphological, compositional and optical studies corroborated by various complementary techniques viz. SEM, HRTEM, EDAX, NMR, DLS, Zeta Potential, Contact Angle, PL and Transient Absorption respectively. The application of InP films as a humidity sensor has been demonstrated and untreated InP film in particular shows higher sensitivity values upon exposure to humid treatment as compared with H-treated InP and InP-ZnS core-shell QD's respectively
Effect of Ag Ion Implantation on SPR of Cu-C-60 Nanocomposite Thin Film
No full textu-C-60 nanocomposite thin films are synthesized by co-deposition restive heating method on glass, silicon, and TEM grid substrates. Rutherford backscattering spectroscopy (RBS) analysis is used for determining the composition of Cu and thickness of thin film which one found to be similar to 13 at% and similar to 28 nm, respectively. The deposited thin films are irradiated with 100 keV Ag ion at different fluences ranging from 1 x 10(14) to 3 x 10(16) ions/cm(2). Being of low energy, Ag ions got implanted in SiO2 substrate up to a depth of 30-40 nm that results in wide surface plasmon resonance (SPR) band in combination with SPR of Cu nanoparticles. UV-visible absorption spectroscopy demonstrates the SPR peak arises due to copper nanoparticles embedded in fullerene C-60 matrix on irradiation of nanocomposite thin film and its variation under implantation of Ag nanoparticles in SiO2 substrate. Structural modifications due to ion irradiation are analyzed by Raman and transmission electron microscopy (TEM). Raman spectroscopy study reveals the transformation of fullerene C-60 into amorphous carbon (a-C) with increasing fluence. Variation in particle distribution is observed under TEM. The average particle sizes are found to be similar to 4 +/- 0.7 and similar to 6 +/- 0.4 nm for pristine and 100 keV Ag ion-irradiated thin films, respectively. Atomic force microscopy (AFM) confirms the increase in grain size with increase in roughness of nanocomposite thin films under the effect of implantation. X-ray photoelectron spectroscopy (XPS) confirms the presence of Cu and C from their chemical bonding in Cu-C-60 nanocomposite thin films
Enhanced Self-Biased Magnetoelectric Coupling in Laser-Annealed Pb(Zr,Ti)O-3 Thick Film Deposited on Ni Foil
No full textEnhanced and self-biased magnetoelectric (ME) coupling is demonstrated in a laminate heterostructure comprising 4 mu m-thick Pb(Zr,Ti)O-3 (PZT) film deposited on 50 mu m-thick flexible nickel (Ni) foil. A unique fabrication approach, combining room temperature deposition of PZT film by granule spray in vacuum (GSV) process and localized thermal treatment of the film by laser radiation, is utilized. This approach addresses the challenges in integrating ceramic films on metal substrates, which is often limited by the interfacial chemical reactions occurring at high processing temperatures. Laser-induced crystallinity improvement in the PZT thick film led to enhanced dielectric, ferroelectric, and magnetoelectric properties of the PZT/Ni composite. A high self-biased ME response on the order of 3.15 V/cm.Oe was obtained from the laser-annealed PZT/Ni film heterostructure. This value corresponds to a similar to 2000% increment from the ME response (0.16 V/cm.Oe) measured from the as-deposited PZT/Ni sample. This result is also one of the highest reported values among similar ME composite systems. The tunability of self-biased ME coupling in PZT/Ni composite has been found to be related to the demagnetization field in Ni, strain mismatch between PZT and Ni, and flexural moment of the laminate structure. The phase-field model provides quantitative insight into these factors and illustrates their contributions toward the observed self-biased ME response. The results present a viable pathway toward designing and integrating ME components for a new generation of miniaturized tunable electronic devices
Effects of light on ferroelectric polarization and leakage current
No full textWe report the enhancement of polarization in polycrystalline ferroelectric thin films under illumination of light. The (Pb0.6Li0.2Bi0.2) (Zr0.2Ti0.8)O-3 (PLBZT) thin films were fabricated on a Pt/TiO2/SiO2/Si (100) substrate by pulsed-laser deposition (PLD) technique. The illumination of weak monochromatic light having a wavelength comparable to the bandgap of PLBZT showed the development of non-equilibrium charge carriers which enhance switchable polarization and displacement current. A Positive-up Negative-down (PUND) analysis also supports the enhancement of switchable polarization under illumination. The fatigue test indicates nearly 20-30% decrease in polarization after a long time write and read cycles. These results may provide an extra degree of freedom to create electrical WRITE and optical READ logic states
Compositional tuning of ZrNiSn half-Heusler alloys: Thermoelectric characteristics and performance analysis
No full textNanostructuring has rejuvenated great interest in thermoelectric (TE) based power generation by enabling enhanced performance in nano-grained TE materials over their bulk counterparts. In ZrNiSn based half-Heusler (HH), a promising n-type TE materials, we examine the prospects of nanostructuring by synthesizing nano crystalline iso-electronically substituted n-type Zr1-xHfxNiSn HH alloys to achieve a state-of-the-art TE figure-of-merit ZT similar to 1.2 at 873 K, which is similar to 20% higher than its bulk counterparts and corresponds to high conversion efficiency of similar to 9% with output power density similar to 7 Wcm(-2), estimated using cumulative temperature dependence model. Enhanced phonon scattering at nano-scale grain boundaries and crystal defects, arising from nanostructuring and mass defect fluctuation in Hf substituted ZrNiSn alloys resulted in significantly reduced thermal conductivity. It was found that the partial substitution at Zr site with its heavier homologue Hf causes variation in the carrier effective mass and carrier concentration, which at lower Hf concentration results in an enhancement in the power factor