Browsing by Author "Neeraj Khare"

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A cadmium sulphide-solid electrolyte photoelectrochemical solar cell
(1988) Neeraj Khare
Cadmium sulphide thin film was prepared by a chemical bath deposition technique. This semiconducting film was used to fabricate a photoelectrochemical solar cellwith a solid electrolyte prepared by capturing a ferrous/ ferric cyanide redox couple in an agar-agar gel matrix. The performance of this solid electrolyte photoelectrochemical solar cell has been studied and compared with a liquid electrolyte-CdS photoelectrochemical solar cell containing the same redox couple. © 1988.
A theoretical model of a photoelectrochemical solar cell
(1986) S. Chandra; S.L. Singh; Neeraj Khare
A Schottky barrier theoretical model for explaining the J-V characteristic of a photoelectrochemical solar cell (PESC) has been developed considering the effect of dark current, space-charge recombination, surface states, and detailed charge transfer kinetics at the interface. Both isoenergetic charge transfer and inelastic charge transfers (via surface states) at the interface have been considered and their relative importance are discussed. The theory has been applied to explain the (a) J-V characteristic for n-GaAs/Se2 -, Se2-2 junction and (b) Fermi-level pinning observed in GaAs PESC. The inelastic charge transfer via surfaces states has been shown to play an important role in deciding these characteristics.
Conductance and conduction noise of polycrystalline La0.7Ca0.2Ba0.1MnO3 films on different substrates
(2006) D.P. Singh; Vijay Kumar; G.L. Bhalla; P.K. Siwach; O.N. Srivastava; Neeraj Khare
La0.7Ca0.2Ba0.1MnO3 (LCBMO) films were prepared by ultrasonically assisted spray pyrolysis deposition on LaAlO3 and Al2O3 single crystal substrates. Conductance-voltage (G-V) characteristics and conduction noise of the two films were found to be different. G-V characteristics of LCBMO film on LaAlO3 were linear indicating the spin dependent scattering across the grain boundaries whereas for the film on Al2O3, G-V characteristics at low temperature (T < 210 K) were nonlinear indicating dominant transport mechanism as spin polarized tunnelling. Normalized conduction noise of LCBMO film on LaAlO3 was one order lower to that of film on Al2O3. These differences in conductance-voltage and conduction noise characteristics of the two films are attributed to the presence of more disordered grain boundaries in LCBMO film on Al2O3 as compared to the films on LaAlO3 substrate. © 2006 Elsevier Ltd. All rights reserved.
Effect of temperature on the photoresponse of chlorophyll photoelectrochemical solar cell
(1987) Neeraj Khare
Photoresponses of chlorophyll Photoelectrochemical Solar Cell have been studied at different temperatures. Observed decrease in the photovoltage/ photocurrent has been attributed to the decrease in the population of the excited state of chlorophyll at high temperature. Nature of the variation of the photoresponse has been explained in terms of a theoretical model in which the photoinduced charge transfer responsible for the photovoltage/photocurrent is supposed to take place between the triplet excited state of chlorophyll and oxidised energy levels of the electrolyte. © 1987.
Fabrication and Transport Characteristics of YBCO Step-Edge-Based Josephson Junction on Revived MgO Substrate
(John Wiley and Sons Inc, 2021) Mamta Dahiya; Satyendra Prakash Pal; Neeraj Khare
Herein, the combined impact of ion beam milling and postannealing treatment on the transport properties of deposited YBa2Cu3Ox (YBCO) thin film and fabricated step-edge Josephson junction (JJ) on degraded MgO (100) substrates are investigated, and the obtained results of the YBCO thin film and fabricated step-edge JJ on treated MgO (100) substrate are compared with the YBCO film and step-edge junction on a fresh MgO substrate. Structural study reveals the formation of c-axis-oriented YBCO thin film on revived MgO substrate which is very much comparable with the YBCO film on fresh substrate. Atomic force microscopy (AFM) technique is used to confirm the step heights of the fabricated step-edges on fresh, revived, and degraded MgO substrates. After the treatment, the surface roughness of MgO substrate has reduced from 56 to 1.06 nm which is comparable with the fresh MgO (100) substrate. The acquired values of critical temperatures for as-deposited YBCO thin film on fresh and revived MgO substrates are 89.1 and 88.3 K, respectively, whereas these values are 85.8 and 85.7 K for the fabricated step-edge junction microbridges on these deposited thin films. For both the fabricated step-edge junction on the revived and fresh MgO substrate, the superconductor–normal metal–superconductor-type JJ is confirmed. © 2021 Wiley-VCH GmbH
Hg(Tl)-Ba-Ca-Cu-O high-Tc thin film rf-SQUID operating above 115 K
(Elsevier, 1997) Neeraj Khare; A.K. Gupta; Sangeeta Khare; H.K. Singh; A.K. Saxena; O.N. Srivastava
An rf-SQUID has been fabricated on Hg0.8Tl0.2Ba2Ca2Cu3O 8+δ thin film using natural grain boundary weak links. The film was prepared by the spray pyrolysis technique and had Tc = 123 K. Voltage-flux modulation of the SQUID has been observed up to 117.5 K. The flux noise density, √Sφ of the rf-SQUID is ≈ 2.5 × 10-3Φ0/√Hz at 1 Hz and 77 K. The value of √Sφ remains almost the same when the operating temperature is increased from 77 to 112 K, and its value becomes ≈ 4 × 10-3Φ0/√Hz at 114 K.
Improvement in properties of La0.67Ca0.33MnO3 polycrystalline film due to silver addition
(2001) Neeraj Khare; H.K. Singh; P.K. Siwach; U.P. Mohrail; A.K. Gupta; O.N. Srivastava
A spray pyrolysis technique has been employed to prepare Ag added La0.67Ca0.33MnO3 (Ag-LCMO) polycrystalline film and its properties are compared with those of the La0.67Ca0.33MnO3 (LCMO) film prepared under similar conditions. The addition of silver in LCMO films improves surface morphology and reduces the lattice constant. During the synthesis process, the silver in the Ag-LCMO film melts and segregates at the grain boundaries. The semiconductor-metal transition temperature (Tp) increases by 10 K and normalized voltage noise reduces by more than one order of magnitude. Improvement in surface morphology and better oxygenation of the film due to the presence of silver leads to improvement in the properties of polycrystalline LCMO film.
Ionic noise measurement in polymer electrolytes
(2006) Amreesh Chandra; D.P. Singh; P.K. Singh; Neeraj Khare; S. Chandra
Electrical noise associated with ion transport (termed as "ionic noise") has been measured at different temperatures, using a lock-in amplifier and dynamic signal analyzer for a polymer electrolyte PEO:NH 4I and its CdS dispersed composite. The ionic noise suddenly increases as the polymer passes through its phase transition at T g and T m. The T g-peak in the noise measurement appears more clearly than what it does in DTA/DSC or conductivity measurements. Therefore, we suggest the noise technique as a good probe for studying phase transitions in ion conducting solid electrolytes. Further, the present noise measurements also confirm the known results of DTA/DSC studies that both T g and T m of polymer electrolytes shift on the formation of composites. © Springer-Verlag 2007.
Photoelectrolysis and In Situ Storage of Solar Energy
(1989) S. Chandra; Neeraj Khare
The feasibility of developing a solar energy storage device by coupling a photoelectrolysis cell and a proton conductor H2/O2fuel cell is demonstrated. Thermally grown TiO2film was used as a photoelectrode in the photoelectrolysis cell. Hydrogen uranyl phosphate was used as a proton conductor in the fabrication of the H2/O2fuel cell. © 1989, The Electrochemical Society, Inc. All rights reserved.
Preparation and study of silver added La0.67Ca 0.33MnO3 film
(2004) Neeraj Khare; D.P. Singh; H.K. Singh; A.K. Gupta; P.K. Siwach; O.N. Srivastava
La0.67Ca0.33MnO3 (LCMO) and Ag admixed La0.67Ca0.33MnO3 (Ag-LCMO) polycrystalline films have been prepared on SrTiO3 single crystal (100) substrates by ultrasonic spray pyrolysis technique. These films are characterized using XRD, SEM, and temperature dependence of resistivity (ρ-T) and ac susceptibility (χ-T). The films are having cubic structure with lattice parameters as 3.890 and 3.885Å for LCMO and Ag-LCMO films, respectively. The peek in ρ-T curve (Tp) and the ferromagnetic transition temperature (TC) for the Ag-LCMO film is higher than that of LCMO film. The stability of both the films was tested by repeated measurements of its characteristics over a period of one week after several thermal cycling from room temperature to 77 K. In the LCMO film, the peak in the ρ-T curve (Tp) is found to shift towards lower value and conduction noise of the film increases in the subsequent measurements. In the case of Ag-LCMO the value of Tp, TC and conduction noise of the film did not change even after several measurements. Silver segregating at the grain boundaries in Ag-LCMO polycrystalline film seems to be responsible for improving the characteristics of Ag-LCMO films. © 2003 Elsevier Ltd. All rights reserved.
Reduction in conduction noise of La-Ca-Mn-O polycrystalline films due to Ag addition
(2001) Neeraj Khare; U.P. Moharil; A.K. Gupta; H.K. Singh; O.N. Srivastava
Ag-added La0.67Ca0.33MnO3(Ag-LCMO) polycrystalline films have been prepared on SrTiO3 substrates by the ultrasonic spray pyrolysis technique and their properties are compared with the La0.67Ca0.33MnO3(LCMO) films prepared under similar conditions. Addition of Ag in LCMO films improves their surface morphology and reduces their lattice constant. During the synthesis process, Ag in Ag-LCMO film melts and segregates to grain boundaries. In the Ag-LCMO film, normalized voltage noise reduces by more than one order of magnitude, and peak temperature (Tp) and ferromagnetic transition temperature (Tc) increase by 10 and 20 K, respectively. Improvement in surface morphology and better oxygenation of the film due to the presence of Ag leads to reduction in conduction noise of the LCMO film. © 2001 American Institute of Physics.
Revival of Smooth MgO(100) Surface: Ar Ion-Beam Milling and Postvacuum Annealing in Oxygen Atmosphere
(John Wiley and Sons Inc, 2021) Mamta Dahiya; Satyendra Prakash Pal; Neeraj Khare
A recreation procedure for achieving the smooth and clean surface morphology of the degraded MgO(100) substrates is presented. The surfaces of the degraded MgO(100) substrates are treated with Ar ion-beam milling (IBM) and annealing in O2 atmosphere. After each treatment, the changes in the MgO(100) substrate surface morphology are characterized using X-ray diffraction (XRD), a 3D optical profilometer, atomic force microscopy, and Fourier-transform infrared (FTIR) spectroscopy and compared with a fresh MgO substrate. It is shown that before any treatment, XRD and FTIR spectra show peaks corresponding to hydroxyl and carbonate groups in the degraded samples, whereas after treatment, XRD and FTIR spectra are comparable with the fresh sample. Further, after treatment, the surface roughness Rav value for two used/degraded samples reduces from 129 and 186 nm to 3.96 and 7.91 nm, respectively, after combined Ar IBM and annealing treatment. It is shown that the surface quality of the treated MgO(100) substrate improves in comparison with as it was before any treatment and can be reused for the good quality thin-film deposition. © 2021 Wiley-VCH GmbH
Rf-SQUID effect in Hg(Tl)-Ba-Ca-Cu-O high-Tc thin film up to 121 K
(1998) Neeraj Khare; A.K. Gupta; H.K. Singh; O.N. Srivastava
Hg(Tl)-Ba-Ca-Cu-O high-Tc films have been prepared by the spray pyrolysis technique. The process involves preparation of a precursor film of Ba-Ca-Cu-O followed by annealing in a Hg-TI atmosphere. The resultant film had Tc ≈ 127.5 K and predominantly consisted of 1223 phase. An rf-SQUID has been fabricated using natural grain boundary weak links. The SQUID shows good voltage-flux modulations at 77 K and the peak-to-peak voltage of the modulation remains constant up to 118.5 K. It starts decreasing above 118.5 K and finally disappears at 122 K. The flux noise density of the SQUID at 2 Hz and 77 K is 2 × 10-3Φ0 Hz-1/2. It does not change much up to 117.4 K and shows a peak at 120.5 K.
Study of harmonic generation in Hg(Tl)BaCaCuO thin film
(Elsevier, 1998) Neeraj Khare; A.K. Gupta; S.K. Shrivastava; H.K. Singh; O.N. Srivastava
The generation of higher harmonics in Hg(Tl)BaCaCuO high-Tc thin film is reported, when an ac magnetic field is applied to it. The film has been prepared by the spray pyrolysis technique using two step process and exhibits Tc(R = 0) = 123 K. Application of an ac magnetic field (Hac > Hc1) on the film leads to generation of higher odd harmonics. Further, application of the dc field (Hdc) in addition to the ac field causes generation of even harmonics also. Variations of amplitude of these harmonics as a function of Hac, Hdc and temperature are studied. The variation of second and third harmonic amplitudes with Hdc shows the hysteresis effect. © 1998 Published by Elsevier Science B.V. All rights reserved.
Temperature dependence of conduction noise of MgB2 superconductor
(2008) D.P. Singh; Neeraj Khare; Chandra Shekhar; O.N. Srivastava
Temperature dependent behavior of conduction noise of MgB2 superconductor has been studied. The frequency spectrum of conduction noise shows 1/fα type of behavior, with α = 0.7-0.8. Temperature dependence of conduction noise is found to exhibit two peaks at ∼26 K and ∼38 K respectively. The peak at ∼38 K is attributed to movement of vortices and due to fluctuation in resistance from change of state from superconducting to normal state. The peak in the conduction noise at ∼26 K is ascribed to the movement of vortices due to enhanced thermally activated vortex hopping. The analysis of enhanced conduction noise in the low temperature region indicates the presence large density of fluctuators with activation energies around 0.048 eV. © 2008 Elsevier B.V. All rights reserved.