Avishek Das

Multifunctional BiFeO3/TiO2 nano-heterostructure: Photo-ferroelectricity, rectifying transport, and nonvolatile resistive switching property

Multifunctional BiFeO3 nanostructure anchored TiO2 nanotubes are fabricated by coupling wet chemical and electrochemical routes. BiFeO3/TiO2 nano-heterostructure exhibits white-light-induced ferroelectricity at room temperature. Studies reveal that the photogenerated electrons trapped at the domain/grain boundaries tune the ferroelectric polarization in BiFeO3 nanostructures. The photon controlled saturation and remnant polarization opens up the possibility to design ferroelectric devices based on BiFeO3. The nano-heterostructure also exhibits substantial photovoltaic effect and rectifying characteristics. Photovoltaic property is found to be correlated with the ferroelectric polarization. Furthermore, the nonvolatile resistive switching in BiFeO3/TiO2 nano-heterostructure has been studied, which demonstrates that the observed resistive switching is most likely caused by the electric-field-induced carrier injection/migration and trapping/detrapping process at the hetero-interfaces. Therefore, BiFeO3/TiO2 ...

Investigation of the electrical switching and rectification characteristics of a single standalone n-type ZnO-nanowire/p-Si junction diode

In this work, n-ZnO-nanowire/p-Si junction diodes have been fabricated and characterized both physically as well as electrically. The measurements are performed on a single standalone nanowire diode for the investigation of electrical transport through the nano-junction. The rectification properties of the single n-ZnO nanowire/p-Si diode have been studied for various input waveforms and frequencies. The diodes exhibit very promising rectification as well as switching behavior with no charge storage effect and consequently, a switching time as small as ∼1 ms has been achieved.

Occurrence of equatorial spread F during intense geomagnetic storms

Equatorial spread F (ESF) has been observed in response to the prompt penetration of magnetospheric electric field to equatorial latitudes during intense (minimum Dst ≤ −100 nT; Bz ≤ −10 nT for at least 3 h) magnetic storms using global ion density plots of Defense Meteorological Satellite Program (DMSP) over nearly one solar cycle (1996–2005). Geostationary amplitude scintillation observations from Calcutta at VHF and L band for 1996–2005 and GPS amplitude scintillation measurements during 2004–2005 from the Indian Satellite Based Augmentation System Geostationary and GPS Navigation Outlay (GPS Aided GEO Augmented Navigation) network of stations all over India have been used to corroborate the DMSP observations. Subsequent to the time of southward interplanetary magnetic field Bz crossing −10 nT for an intense storm, it has been observed that within 4 h, ESF is generated at a longitude where the local time is dusk.

Investigating the quasi-oscillatory behavior of electrical parameters with the concentration of D-glucose in aqueous solution

Abstract The impedance, capacitance and conductance of deionized water-glucose polar solution is measured by employing impedance spectroscopy and a quasi-oscillatory nature of variation with glucose content in the solution is observed. Such quasi-oscillatory nature is attributed to the randomly distributed water-water, water-glucose and glucose-glucose dipole interactions at the molecular level in the solution. A relevant analytical model is developed on the basis of such random distribution of the molecular dipoles and the experimental data agree well with those obtained from the theoretical model. The electrical parameters are measured in the frequency range of 100Hz to 4MHz for the volume fractions of glucose with respect to water in the range of 0.1 to 0.5. The impedance, capacitance and conductance are obtained to be in the range of 1.03 kΩ – 112 kΩ, 34.9 pF – 1.66 nF, and 8.95 μS – 52.9 μS respectively for the glucose volume fraction range considered.

Temperature-dependent electrical characteristics of CBD/CBD grown n-ZnO nanowire/p-Si heterojunction diodes

Heterojunction diodes are fabricated using a low-temperature chemical bath deposition of oriented and crystalline ZnO nanowires on a?? ??p-silicon substrate. The electrical transport properties of the heterojunction are investigated at various temperatures by measuring current?voltage (I?V) characteristics in the range of 90?390?K. A thermionic emission (TE) model is used to analyze the transport behavior. The deviation in the experimental value of Richardsons constant for ZnO nanowires is obtained from I?V?T measurement. The temperature dependence of the effective barrier height and ideality factor is attributed to the inhomogeneous barrier height distribution at the n-ZnO NW/p-Si hetero-interface. The TE and barrier inhomogeneity model are simultaneously used to extract the appropriate value of the Richardsons constants in three different temperature regions. Linear fittings for three different temperature regions suggest multiple Gaussian distributions of barrier heights at the junction.

Clustered vacancies in ZnO: chemical aspects and consequences on physical properties

Chemical nature of point defects, their segregation, cluster or complex formation in ZnO is an important area of investigation. In this report, 1.2 MeV Ar ion beam is used to incorporate defects in granular ZnO. Evolution of defective state with irradiation fluence 1 x 10^14 and 1 x 10^16 ions/cm2 has been monitored using XPS, PL and Raman spectroscopic study. XPS study shows presence of oxygen vacancies (VO) in the Ar ion irradiated ZnO. Zn(LMM) Auger spectra clearly identifies transition involving metallic zinc in the irradiated samples. Intense PL emission from IZn related shallow donor bound excitons (DBX) is visible in the 10 K spectra for all samples. Although overall PL is largely reduced with irradiation disorder, DBX intensity is increased for the highest fluence irradiated sample. Raman study indicates damage in both zinc and oxygen sub-lattice by energetic ion beam. Representative Raman modes from defect complexes involving VO, IZn and IO are visible after irradiation with intermediate fluence. Further increase of fluence shows, to some extent, a homogenization of disorder. Huge reduction of resistance is also noted for this sample. Certainly, high irradiation fluence induces a qualitative modification of the conventional (and highly resistive) grain boundary (GB) structure of granular ZnO. Low resistive path, involving IZn related shallow donors, across the GB can be presumed to explain resistance reduction. Open volumes (VZn and VO) agglomerate more and more with increasing irradiation fluence and finally get transformed to voids. Results as a whole have been elucidated with a model which emphasizes possible evolution of new defect microstructure that is distinctively different from the GB related disorder. Based on the model, qualitative explanations of commonly observed radiation hardness, colouration and ferromagnetism in disordered ZnO have been put forward.

Cross talk between photo-pigments and graphene electron cloud - Designing a biodiode

We report emergence of a new electrical material by growing photosynthetic biofilm on a Dirac material, graphene. The material showed new conducting as well as semiconducting properties. Frequency dependent capacitive spectra further indicated presence of electrical isosbestic points(at 0.8 and 9MHz), implying two state dieletric transitions at critical frequencies. A notable reult was a Schottky diode like behavior in the IV curve. Voltage dependent conductance with conductance peaks near the Schottky diode threshold was observed. We obtained facilitated growth of photosynthetic biofilm in presence of graphene. Lastly higher bacterial metabolism was seen in graphene incorporated biofilm. For this zero band gap Dirac material this can only be interpreted as coupling of the electron transport chain of the bacterial biofilm and the graphene electron cloud.

Emerging Electrical Properties of Graphene incorporated Photosynthetic Biofilms

Biofilms have been a breeding ground for creation of novel biomaterials with emergent properties. We report immobilization of hydrophobic graphene by a growing photosynthetic biofilm. We obtained a conductive biomaterial that can form a Schottky diode when grown on a metallic electrode surface. Capacitive spectra on frequency axis were obtained for control biofilm, which showed isosbestic points at 0.9 and 6MHz when RMS voltage was changed. This implies a two state di-electric transition. Immobilization of graphene by biofilm shifts such electrical isosbestic points significantly. The additional implication of the present study is the emergence of voltage dependent conductance with conductance peaks near the Schottky diode threshold. The observed emergent properties may be helpful in biomaterial based design of sensors.We report emergence of a new electrical material by growing photosynthetic biofilm on a Dirac material, graphene. The material showed new conducting as well as semiconducting properties. Frequency dependent capacitive spectra further indicated presence of electrical isosbestic points(at 0.8 and 9MHz), implying two state dieletric transitions at critical frequencies. A notable reult was a Schottky diode like behavior in the IV curve. Voltage dependent conductance with conductance peaks near the Schottky diode threshold was observed. We obtained facilitated growth of photosynthetic biofilm in presence of graphene. Lastly higher bacterial metabolism i was seen in the biofilm in contact with graphene as compared to its normal growth condition. For this zero band gap Dirac material this can only be interpreted as coupling of the electron transport chain of the bacterial biofilm and the graphene electron cloud.

Effect of split application of nitrogen on performance of wheat ( Triticum aestivum L.)

A field experiment was conducted at farmer field of Katihar district during two consecutive years of 2012-13 and 201314 to study the yield of wheat as influenced by split application of nitrogen. The soil is non-calcareous light gray in colour flood plain belongs to the alluvial gangetic plain (Agro climatic zone II). The study was done in Randomized Block Design with four treatments and ten replications with HD 2733 wheat variety to evaluate the observation regarding growth attributes and yield components of individual plant parameters were recorded from randomly selected plants in each plot. The evaluated traits were plant population (m ?2 ), plant height (cm), bearing tillers plant ?1 (no.), non-bearing tillers plant ?1 (no.), spikelets spike ?1 (no.), fertile spikelets spike ?1 (no.) non-fertile spikelets spike ?1 (no.), 1000-seed weight (g), seed yield (t ha ?1 ) and straw yield (t ha ?1 ). Results indicated that the use of three split N applications increased all growth and yield attributes. The best N split strategy corresponded to three N splits: at planting, crown root initiation (CRI), and panicle initiation (PI) stages.