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Dual photoluminescence and charge transport in an alkoxy biphenyl benzoate ferroelectric liquid crystalline-graphene oxide composite
No full textAn optimized concentration of graphene oxide (GO) has been dispersed in a ferroelectric liquid crystalline (FLC) material namely 4-(octyloxy)-[1,1-biphenyl]-4-yl 4-(heptan-2-yloxy)benzoate, to prepare a FLC-GO composite. Temperature dependent photoluminescence (PL) measurements for the FLC-GO composite were conducted between 30-100 degrees C. We observed a superlinear increase in the PL with increasing temperature. The time resolved luminescence study exhibits a bi-exponential decay time with a shorter life time for the FLC-GO composite and confirms the surface energy transfer from GO to FLC. Charge transport and current-voltage (I-V) characteristics for the FLC-GO composite have been investigated at ambient conditions by using current sensing atomic force microscopy. For the FLC-GO composite, critical diode like nonlinear I-V curves have been obtained in which the charge transport is assigned to the thermally active intermolecular hopping at room temperature. The FLC material yields ionic charge mobilities of 1.45 x 10(-5), 1.26 x 10(-5) and 9.83 x 10(-6) cm(2) V-1 s(-1) in isotropic, chiral nematic (N*) and chiral smectic C (SmC*) phases. The dispersion of GO significantly enhances the ionic mobility in the composite which was observed to be 2.71 x 10(-4), 2.69 x 10(-4) and 2.65 x 10(-4) cm(2) V-1 s(-1) for the aforementioned phase sequence. Physical interactions between GO and FLC molecules were confirmed by FTIR and polarized optical microscopy. In-plane coupling between the orientation of GO and the long molecular axis of the FLC molecules remarkably enhances the band intensity of C?O, ?C-H, COO, C-O and C-H vibrations. The size of multi-domain fan texture in the SmC* phase has been enhanced after the dispersion of GO. The cobweb like networking in the oily streaks texture of the N* phase confirms the interesting molecular architecture via planar anchoring between FLC molecules and GO. This work opens new avenues towards applications in pico-ampere current-regulated electronic devices and opto-electronics
Effect of oxygen pressure on structural and magnetic properties of Nd2NiMnO6 thin films grown on different substrates
No full textDouble perovskites have been studied extensively in the bulk form however very few reports are available on their thin films. Here we are presenting results on first time grew thin films of double perovskite Nd2NiMnO6 (NNMO). We report the comparative structural and magnetic studies of the PLD grown thin films on different substrates i.e. SrTiO3 (STO) and MgO. X-ray diffraction (XRD) profiles show that the film grown on STO is epitaxial whereas it is polycrystalline on MgO substrate. Films on both the substrates were grown at 800 mTorr and 200 mTorr oxygen partial pressure. We observe that the film shows the magnetic behavior similar to the bulk sample. We observe the high-temperature ferromagnetic transition near 192 K along with an additional transition observed in the low temperature region (vicinity of 100 K) in Field cooled (FC) magnetization. Super-exchange interaction between Ni2+-O-Mn4+ is attributed to the ferromagnetic ordering in these samples. Mixed valence states Ni3+ and Mn3+ present in the films leads to antiferromagnetic (AFM) interactions which attributes to the appearance of low temperature magnetic transition. The oxygen pressure applied while growing the thin films was found to affect the magnetic moment of NNMO films significantly
Exploring the Magnetoelectric Coupling at the Composite Interfaces of FE/FM/FE Heterostructures
Get PDFMultiferroic materials have attracted considerable attention as possible candidates for a wide variety of future microelectronic and memory devices, although robust magnetoelectric (ME) coupling between electric and magnetic orders at room temperature still remains difficult to achieve. In order to obtain robust ME coupling at room temperature, we studied the Pb(Fe0.5Nb0.5)O-3/Ni0.65Zn0.35Fe2O4/Pb(Fe0.5Nb0.5)O-3 (PFN/NZFO/PFN) trilayer structure as a representative FE/FM/FE system. We report the ferroelectric, magnetic and ME properties of PFN/NZFO/PFN trilayer nanoscale heterostructure having dimensions 70/20/70 nm, at room temperature. The presence of oly (00l) reflection of PFN and NZFO in the X-ray diffraction (XRD) patterns and electron diffraction patterns in Transmission Electron Microscopy (TEM) confirm the epitaxial growth of multilayer heterostructure. The distribution of the ferroelectric loop area in a wide area has been studied, suggesting that spatial variability of ferroelectric switching behavior is low, and film growth is of high quality. The ferroelectric and magnetic phase transitions of these heterostructures have been found at similar to 575 K and similar to 650 K, respectively which are well above room temperature. These nanostructures exhibit low loss tangent, large saturation polarization (P-s similar to 38 mu C/cm(2)) and magnetization (M-s similar to 48 mu u/cm(3)) with strong ME coupling at room temperature revealing them as potential candidates for nanoscale multifunctional and spintronics device applications
Tunable Mechanical, Electrical, and Thermal Properties of Polymer Nanocomposites through GMA Bridging at Interface
Get PDFPolymer nanocomposites (PNCs) have become an exciting field of current research and have attracted a huge interest among both academia and industry during the last few decades. However, the multifunctional single-nanocomposite film exhibiting the combination of desired structure and properties still remains a big challenge. Herein, we report a novel strategy to address these problems by using versatile polymer glycidyl methacrylate (GMA) as a bridging medium between the filler and the polymer matrix, resulting in high density of interfaces as well as strong interactions, which lead to generation of tunable thermal, mechanical, and electrical properties in the materials. The nanocomposites prepared by GMA bridging exhibit the remarkable combination of thermal (T-d = 342.2 degrees C, T-g = 150.1 degrees C), mechanical (E = 7.6 Gpa and H = 0.45 Gpa) and electrical (sigma = 3.15 x 10(-5) S/cm) properties. Hence, the conjugation approaches related to GMA bridging facilitate a new paradigm for producing multifunctional polymer nanocomposites having a unique combination of multifunctional properties, which can be potentially used in next-generation polymer-based advanced functional devices
Response to comments on "Reduced band gap & charge recombination rate in Se doped alpha-Bi2O3 leads to enhanced photoelectrochemical and photocatalytic performance: Theoretical & experimental insight"
No full textFor better utilization of solar spectrum and complete redox of water for water splitting applications, it is required to have a semiconductor which is photoactive in visible region. In this study, we report theoretical and experimental investigations on morphological and opto-electronic modifications induced in α-Bi2O3 due to Selenium (Se) doping tested for photoelectrochemical (PEC) & photocatalytic properties. Density Functional Theory (DFT) calculations revealed band gap reduction and direct to indirect transitions in Se-doped α-Bi2O3. This reduction in band gap is attributed to hybridization of Se p & Bi s in valence band and Se d & Bi p orbital in conduction band. To support this finding experimentally, we synthesized Se-doped α-Bi2O3 using simple chemical precipitation method and measured its band gap using photoluminescence and UV–Vis spectroscopy. Experimental results also confirmed the reduction in band gap energy and recombination rate of charge carriers as compared to pristine α-Bi2O3 sample. PEC study of Se-doped α-Bi2O3 showed an increased photocurrent density, charge carrier density and lowered impedance, which indicates its efficient solar spectrum utilization and better hydrogen generation efficiency. Photocatalytic measurement also revealed higher rate of dye degradation with Se doped α-Bi2O3
Exploring deep defect state impact on open circuit voltage of conventional and inverted organic solar cells
No full textIn this manuscript, conventional and inverted organic solar cells based on P3HT:PC[60]BM have been explored to understand the effect of deep defect states on the open circuit voltage. The enhancement in the open circuit voltage in the inverted structure compared to the conventional structure has been comprehensively discussed in terms of density of defect states. To comply with the investigation, DC and AC measurements (impedance spectroscopy) at various temperatures have been performed extensively. Enhancement in open circuit voltage at low temperature is observed which is described by the shifting of hole and electron quasi-Fermi levels. The important observation from the defect density of states profile is that the center of Gaussian distribution is shifted to high energy as the temperature is increased which is an indication of the creation of shallow traps in polymers. In the inverted device, the disorder parameter (sigma) is 33 meV, whereas in the conventional device it becomes 75 meV. This implies that the energetic disorder is reduced in an inverted device which helps in the improvement of open circuit voltage
Investigation of dynamic optical behavior of CeO2 thin film using terahertz spectroscopy
No full textDynamic optical behavior of CeO2 thin film has been investigated using Terahertz spectroscopy at room temperature by exciting with different amplitude pulses. The CeO2 thin films have been deposited on Si (100) substrate by RF magnetron sputtering technique. It has been observed that the optical density increases at 0.75 THz on the incident of pulse >= 100 kV/cm indicating that it is possible to induce extremely large amplitude motions in the harmonic potential of the material by direct excitation of CeO2 vibrations with intense THz pulse. This study further shows that it is possible to control the large amplitude motions in the materials using different high power THz pulses, and in turn can control the optical properties, establishing the nonlinear spectroscopy technique for such studies
Longitudinal Characteristics of Martian Electron Density Profiles: MGS Observations
No full textAn analysis of longitudinal characteristics of 5,600 electron density profiles returned from the Mars Global Surveyor's Radio Science experiment is carried out by dividing the entire data set into 33 subsets, keeping solar zenith angle nearly constant. We find that the peak altitude of the photochemical F1 layer (hmF1) exhibits a large degree of longitudinal variability. This variability is not seen in Earth's ionosphere. Since F1 layer is isobaric, this variability in hmF1 represents a large degree of spatial changes in the underlying neutral atmosphere. Though this variability is quite chaotic in most of the subsets, a few subsets provide some evidence for the presence of a well-defined wave. We therefore perform a spectral fit of wave 1-3, as earlier carried out by Bougher et al. (2004, https://doi.org/10.1029/2003JE002154; 2001, https://doi.org/10.1029/2001GL012884), to all 33 subsets. Results indicate that this wave is seen only in 10 of the subsets and is most dominant between 0 to 200 degrees E longitudes. Similar wave is seen in the longitude plots of the peak electron density of F1 layer but with a phase reversal. Further, these 10 subsets are confined mostly between 02 to 04 local solar time, thereby indicating a local time dependence of the wave. We examined the characteristics of electron density profiles located at the crests and troughs and found abnormal upliftment in F1 layer during consecutive occultations (similar to 2 hr). Rapid spatial changes are observed during intervals as short as 2 hr. The ionosphere is lifted up and the peak density decreases when wave 1-3 is present
Electrochemical genosensor based on carboxylated graphene for detection of water-borne pathogen
No full textThis work reports the application of newly synthesized carboxylated graphene nanoflakes (Cx-Gnfs). The Cx-Gnfs were synthesized by wet chemical method in sulfuric acid/nitric acid mixture and was further electrophoretically deposited on indium fin oxide (ITO) coated glass substrates using Mg(2+ )ions which provides an overall charge to the materials for deposition onto the anode. The materials were characterized using SEM, TEM, contact angle, UV-vis spectroscopy, FT-IR, XRD and electrochemically characterized by cyclic voltammetry, chronocoulometry and electrochemical impedance spectroscopy. The sensitive quantitative determination of nucleic acid Escherichia coli O157: H7 (E. coil) has been achieved using Cx-Gnfs and r-GO as the sensing layer using electrochemical impedance spectroscopy. The electrochemical results reveal that the Cx-Gnfs based genosensor exhibits a linear response to complementary DNA (10(-6) M to 10(-17) M) with a detection limit of 1 x 10(-17) M while the rGO based genosensor shows a detection limit of 1 x 10(-15) M. Under optimal conditions, this Cx-Gnfs based genosensor was found to retain about 85% of its initial activity after being used for 6 times
Solution processed hole transport layer towards efficient and cost effective organic solar cells
No full textIn this work, we report Copper Sulfide (CuS) as a solution processed, Inexpensive and effective hole transport layer (HTL) for efficient and low cost organic solar cells. These devices were fabricated using two most studied low band gap donor materials PTB7 and PCDTBT blended with PC71BM as an acceptor material. We have used a simplest device architect such as ITO/CuS/active layer/Al at ambient conditions. The power conversion efficiencies (PCBs) of these devices have been achieved to up to 4.32% and1.76 % for PTB7 and PCDTBT based devices respectively. Finally, we have provided a further example of solution processable CuS as an effective HTL for solution processable organic photovoltaic applications