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Transition from n- to p-type conduction concomitant with enhancement of figure-of-merit in Pb doped bismuth telluride: Material to device development
No full textThe majority of industrial, automobile processes, electrical appliances emit waste heat in the low-temperature range (<573 K), hence efficient thermoelectric materials operating in this range are highly needed. Bismuth telluride (Bi2Te3) based alloys are conventional thermoelectric material for the low-temperature application. The pure Bi2Te3 sample synthesized in this work exhibits n-type conduction. We demonstrate that by small doping of Pb at Bi site a transition in electrical transport form n- to p-type is observed. The figure-of-merit (ZT) of n-type Bi2Te3 is similar to 0.47 and optimized Bi1.95Pb0.05Te3 exhibit p-type conduction with enhanced ZT of similar to 0.63 at 386 K. The conversion efficiency of Bi1.95Pb0.05Te3 based single thermoelement with hot pressed Ni/Ag electrical contacts was found to be similar to 4.9% for a temperature difference (Delta T) of 200 K. The efficiency was further enhanced to similar to 12% (at Delta T similar to 494 K) in the segmented thermoelement consisting of Bi1.95Pb0.05Te3 and (AgSbTe2)(0.15)(GeTe)(0.85) (i.e. TAGS-85
Synthesis of MoS2-reduced graphene oxide/Fe3O4 nanocomposite for enhanced electromagnetic interference shielding effectiveness
No full textThis article presents a facile two step hydrothermal process for the synthesis of MoS2-reduced graphene oxide/Fe3O4 (MoS2-rGO/Fe3O4) nanocomposite and its application as an excellent electromagnetic interference shielding material. Characterization tools like; scanning electron microscope, transmission electron microscope, x-ray diffraction, and Raman spectroscopy were used to confirm the formation of nanocomposite and found that spherical Fe3O4 nanoparticles are well dispersed over MoS2-rGO composite with average particle size similar to 25-30 nmwas confirmed by TEM. Structural characterization done by XRD was found inconsistent with the known lattice parameter of MoS2 nanosheet, reduced graphene oxide and Fe3O4 nanoparticles. Electromagnetic shielding effectiveness of MoS2-rGO/Fe3O4 nanocomposite was evaluated and found to be an excellent EMI shielding material in X-band range (8.0-12.0 GHz). MoS2-rGO composite shows poor shielding capacity (SET similar to 3.81 dB) in entire range as compared to MoS2-rGO/Fe3O4 nanocomposite (SET similar to 8.27 dB). It is due to interfacial polarization in the presence of EM field. The result indicates that MoS2-rGO/Fe3O4 nanocomposite provide a new stage for the next generation in high-performance EM wave absorption and EMI shielding effectiveness
Growth and Characterization of Highly Conducting Al-Doped ZnO (AZO) Thin Films for Optoelectronic Applications
No full textA comparative study of undoped ZnO and Al-doped ZnO (AZO) thin films deposited on glass substrate by spray pyrolysis has been carried out at various aqueous molar concentration of zinc acetate. The thin films deposited on glass shows the wurtzite phase of ZnO, confirmed by X-ray diffraction. The optical study shows the high transmittance over 80% in the visible regime. The band gap of AZO thin films shows a blue shift as compared to undoped ZnO, which has been attributed to Burstein-Moss shift. Heat treatment of these samples in vacuum showed the improved conductivity in compared to as-deposited thin films. The electric study shows the minimum resistivity of 8 x 10(-3) Omega-cm and carrier concentration of 6.5 x 10(19) /cm(3) correspond to AZO thin films
Novel facets of multifunctional Ag@Fe3O4 core-shell nanoparticles for multimodal imaging applications
No full textBiocompatible nanoparticles, with magnetic cores and optically active shells, acting as multifunctional materials with a core size of 6 nm encapsulated in silver shells of varying thickness were synthesized through a novel single phase microemulsion method. Incorporation of silver shells onto the magnetite core enhances the intensity of the highest luminescence peak observed for magnetite by a significant luminescence enhancement factor. A blue photoluminescence peak observed in the visible region of spectrum brightens further with the increase in the thickness of silver shell. The magnetic properties of these core-shell nanomaterials show superparamagnetic behavior at room temperature, which is a mandatory criterion for MRI contrast enhancement agents. The hyperthermic response of synthesized magnetite nanoparticles elevates its temperature to 43 degrees C in a sharp span of time, which is above the desired temperature for the therapeutic application of these multifunctional nanomaterials. These excellent optical and magnetic properties, of the material having a size range suitable for cellular uptake, make it a potential candidate for both diagnostic and therapeutic uses in biomedical applications
Detailed Dynamic Mechanical Analysis of Thermomechanically Stable Melt-Processed PEK-MWCNT Nanocomposites
No full textThis article reports the detailed study of dynamic mechanical properties of multiwalled carbon nanotubes/poly(ether ketone) nanocomposites prepared by melt blending. The dynamic mechanical characterisitic parameters such as storage modulus (E'), loss modulus (E") and damping factor (tan delta) were explored in detail to investigate the adhesion factor (A), strength factor (B), efficiency factor (C), and entanglement density (N). Adhesion factor, which is inversely related to the degree of interaction between nanotubes and matrix, decreased with increase in MWCNT loading. Strength factor (B) which is a direct measure of interaction between MWCNTs and PEK increased with increase in MWCNT loading. The effect of nanotubes on moduli of composites is calculated in terms of coefficient of reinforcement (C factor). Lower is the value of coefficient (C) higher will be the effectiveness of reinforcement on moduli of composites. It decreased from value of 1 at 1 wt% MWCNTs loading in PEK to 0.67 at 5 wt% MWCNTs loading which point towards increased effectiveness of MWCNTs at 5 wt% loading for excellent properties. To compliment these findings, entanglement density (N) was also calculated. Furthermore, Cole-Cole analysis was carried out to demonstrate the compatibility of both the components in composite system
Effect of traps on the charge transport in semiconducting polymer PCDTBT
No full textOrganic semiconductors (OSCs) are nowadays called upon as promising candidates for next generation electronics devices. Due to disorder structure of these materials, a high density of traps are present in their energy band gap which affect the performance of these devices. In the present manuscript, we have investigated the role of traps on charge transport in PCDTBT thin film by measuring the temperature dependent J(V) characteristics in hole only device configuration. The obtained results were analyzed by space charge limited (SCL) conduction model. It has been found that the room temperature J(V) characteristics follow Mott-Gurney square law for trap-free SCL conduction. But below 278 K, the current increases according to trap-filling SCL law with traps distributed exponentially in the band gap of semiconductor. Furthermore, after reaching a crossover voltage of V-c similar to 12 V, all the traps filled by injected carriers and the trap-filling SCL current switch to trap-free SCL current. The hole mobility of trap-free SCL current is about one order higher as compared trap-filling SCL current and remains constant with temperature
Enhanced photovoltaic performance of PEDOT:PSS/Si solar cells using hierarchical light trapping scheme
No full textOrganic-inorganic hybrid solar cells have attracted tremendous research attention in recent years owing to their low fabrication cost and potentially high performance. In the present study, hierarchical structures consisting of nanostructures made over micro-textured pyramidal (MPs) silicon surface are used in PEDOT:PSS/Si heterojunction solar cells to achieve a power conversion efficiency (PCE) up to 10.26%. The combined micro-nanostructuring concept provides a superior light trapping ability (compared to only micro-textured Si), mechanical stability (compared to only Si nanowire arrays concept), increased junction area and hence improved photovoltaic (PV) characteristics including short-circuit photocurrent and PCE. Silver assisted electroless wet chemical etching is used to produce nanostructures of different length over the micro-pyramidal Si. The hierarchically structured surfaces have one-fourth reflectance in broad spectral range (300-1100 nm) as compared to micropyramidal Si (similar to 13%) arising from the enhanced light trapping properties of nanostructures owing to multiple interaction of incident light and dimensions equivalent to sub-wavelength structures. Moreover, the hierarchical structures exhibit excellent omnidirectional light trapping ability at wide range of angle of incidence of light and spectral wavelength, which is essential for practical PV applications. This has been demonstrated using solar weighted reflectance corresponding to AM 1.5G solar flux and compared with that of MPs surface. Influence of nanostructuring time on reflectance and PV performance of the solar cell has been investigated. A significant enhancement in PCE up to 0.78% (absolute) and over 8.0% (relative) could be achieved as compared to MPs-Si based hybrid solar cell (control cell) for an optimized hierarchically structured Si surfaces. It is established that an optimal trade-off between reduced reflectance of such surfaces and solar cell performance parameters is essential. Longer nano-structuring despite exhibiting a better light trapping properties results in poor cell efficiency as the nano-structuring also leads to increased surface area and non-conformal coating of the polymer. Hence, increase in photocurrent is also accompanied by a simultaneous deterioration of other cell parameters such as open circuit voltage and fill factor of the device. Nevertheless, a properly designed hierarchical-structured device paves a promising way for developing low-cost and efficient PV applications in the future
Superconducting properties of NbN film, bridge and meanders
Get PDFThe transport properties of superconducting NbN nanostructures in the form of thin film, bridge of width (w) = 50 mu m and three meanders of w = 500, 250 and 100 nm have been investigated by resistance (R) measurements in temperature (T) range = 2 - 300 K and magnetic field (B) range = 0 - 7 Tesla. The nanostructuring was carried out using Focused Ion Beam (FIB) milling. Reduction of sample width results in significant changes in the normal and superconducting state properties. For instance, the observed metallic behavior in the thin film sample is lost and the normal state resistance increases drastically from 2.4 Omega to 418 k Omega for the 100 nm meander. In the superconducting state, the value of critical temperature T-c (upper critical field B-c2 at T = 0 K) reduces gradually with width reduction, it changes from 13.15K(42.8 Tesla) in the case of thin film sample to 5.7K(12.7 Tesla) for the 100 nm meander sample. The superconducting transitions are found to get broader for the bridge sample and the meanders additionally show low-temperature resistive tails. In case of all the samples with reduced width, the transition onsets are found to be rounded at surprisingly high values of T similar to 25K > > T-c. These results are discussed in terms of the possible effects of FIB processing and weak localization in our samples
Modulating the lattice dynamics of n-type Heusler compounds via tuning Ni concentration
No full textReducing the lattice thermal conductivity (kappa(L)) comprises one of the crucial aspects of thermoelectric research. Ternary intermetallic half Heusler compounds have revealed properties promising for thermoelectric applications. Studies have shown that self doping with Ni in Ni based half Heuslers leads to unprecedented lowering in the kappa(L). Although the underlying physical mechanisms have not been explored in detail, with ZrNiSn as a case study, we experimentally investigate the change in kappa(L) with increase in the Ni concentration in Ni based n-type half Heusler alloys. We observe that at excess Ni doping of 3% in the half Heusler lattice, the thermal conductivity reduces by more than 60%. Our density functional theory based analysis on the ongoing phenomena reveals that at ultralow Ni doping, the localized modes of the antisite Ni defect hybridize with the acoustic modes and this plays the most dominant role in scattering of the thermal phonons leading to significant lowering in kappa(L). Our theoretical analysis can be employed for predicting a suitable dopants that may reduce the kappa L prior to the synthesis of the compound in the laboratory
High-yield synthesis and liquid-exfoliation of two-dimensional belt-like hafnium disulphide
No full textProducing environmentally stable monolayers and few-layers of hafnium disulphide (HfS2) with a high yield to reveal its unlocked electronic and optoelectronic applications is still a challenge. HfS2 is a layered two-dimensional material of group-IV transition metal dichalcogenides. For the first time, we demonstrate a simple and cost-effective method to grow layered belt-like nanocrystals of HfS2 with a notably large interlayer spacing followed by their chemical exfoliation. Various microscopic and spectroscopic techniques confirm that these as-grown crystals exfoliate into single or multiple layers in a few minutes using solvent assisted ultrasonification method in N-cyclohexyl-2-pyrrolidone. The exfoliated nanosheets of HfS2 exhibit an indirect bandgap of 1.3 eV with high stability against surface degradation. Furthermore, we demonstrate that these nanosheets hold potential for electronic applications by fabricating a field-effect transistor based on few-layered HfS2, exhibiting a field-effect mobility of 0.95 cm(2)/(V.s) with a high on/off current modulation ratio of 10,000 in ambient conditions. The method is scalable and has a potential significance for both academic and industrial purposes