Sugandha Sharma

Synergic effect of graphene and MWCNT fillers on electromagnetic shielding properties of graphene–MWCNT/ABS nanocomposites

Graphene–MWCNT/ABS nanocomposites have been prepared using a solvent-free dry tumble mixing process followed by hot compaction. The combined effect of using two nanofillers (graphene and MWCNTs) on the electrical conductivity and EMI shielding properties of the nanocomposites has been studied. A unique conductive network of MWCNTs and graphene formed due to their different geometrical shapes, besides the high aspect ratios of the MWCNTs. This served to improve the electrical conductivity and the electromagnetic shielding properties. FESEM results for freeze-fractured pellets have confirmed the enhancement in conductivity and shielding of the graphene–MWCNT/ABS nanocomposites and, furthermore, the escape of EM waves through windows/gaps consisting of filler-depleted areas containing ABS. The addition of 1 wt% MWCNTs to a graphene–ABS nanocomposite resulted in a synergistic effect on the EM shielding properties.

Pre-localized MWCNT network for a low percolation threshold in MWCNT/ABS nanocomposites: experiment and theory

Nanocomposites of well-dispersed multi walled carbon nanotubes (MWCNTs) in an acrylonitrile–butadiene–styrene (ABS) matrix were prepared by dry tumble mixing and a subsequent hot compression technique. The preparation method is analysed here to assist in the explanation and understanding of the experimental observations. The vision of the processing method has been confirmed using scanning electron microscopy. As a result of decent dispersion and pre-localization of MWCNTs in the ABS matrix, the electrical conductivity of the nanocomposite as a function of filler content exhibits a distinctive percolation behavior with a percolation threshold of only 0.0005 volume fraction. The high aspect ratio of MWCNTs enables the creation of interconnected networks within the ABS matrix at a very low nanofiller loading, while their high inherent electrical conductivity yields nanocomposites with a high bulk electrical conductivity. To explain the conductivity behaviour, statistical percolation theory and GEM theory are employed. The model parameters elaborated show that both models can adequately describe the behaviour. A comparative analysis of the applicability of percolation theory and GEM theory for expressing the conductivity behavior of the MWCNT/ABS composites with other research works has been performed. Finally, the electrical conductivity of MWCNTs based on the data in this work and elsewhere is evaluated. The universal exponent t is found to be 1.93 for a best-fit value of percolation threshold of 0.000485 vol. fraction of MWCNTs in this work. The D shore hardness results have revealed a random increase in hardness and density with an increasing MWCNT content.

EMI shielding of MWCNT/ABS nanocomposites in contrast to graphite/ABS composites and MWCNT/PS nanocomposites

Acrylonitrile–butadiene–styrene (ABS) nanocomposites filled with multiwall carbon nanotubes (MWCNTs) are prepared through localized conductive patterning, using dry powder tumble mixing succeeded by hot compression technique. Electrical conductivity and complex permittivity together with electromagnetic interference shielding effectiveness (SE) are investigated in 8–12 GHz frequency range. Abrupt increase in dc conductivity by number of orders of magnitude on addition of 5 × 10−4 volume fractions of MWCNTs marked as percolation threshold, has adequately described the conductivity behavior with statistical parameters of percolation and GEM models. The SE of these nanocomposites increases with increase of MWCNTs content. SE ∼ 1 dB at 12 GHz produced with 0.05 wt% MWCNTs grows to ∼40 dB on addition of 5 wt% MWCNTs. SE exhibit marginal dependence or even independence on frequency for most of the compositions with 0–5 wt% MWCNTs. SE reflection (SEref) and absorption (SEabs) both are increasing with the rise of MWCNTs content. However increase in SEabs is faster than SEref in addition to its dominance. Complex dielectric constants in 8–12 GHz frequency range have been calculated by means of S11/S12 parameters using Nicolson Ross Weir algorithm. The variation of the SE as a function of dc conductivity which has rarely been examined in literature, investigated and compared with other polymer composites here.

Structural and optical properties of thermally treated CdO thin films deposited on ITO coated glass substrates for photovoltaic applications

In this study, we have reported effects of post-deposition thermal treatment of cadmium oxide thin films on indium tin oxide coated glass substrates by sol–gel technique using spin coating method. To prepare CdO thin films, a precursor solution based on a derivative from cadmium acetate was gelated and subsequently coated on ITO/glass substrates. Spin coated CdO films were annealed in air at varied temperatures of 300, 400, and 500 °C. The crystallite size, microstrain and dislocation density were estimated from high resolution X-ray diffraction analysis. X-ray diffraction patterns confirmed cubic phase formation in polycrystalline CdO films. Cross-sectional and top surface morphology of the films was studied by field-enhanced scanning electron microscopy. The as-deposited and thermally treated CdO thin films for various annealing temperatures showed an increase in the optical transmittance to 79% from that of 63% of CdO film in the visible and near infrared region. Shrinkage in band gap from 2.6 to 2.4 eV was reported for temperature variation of 300–500 °C. The emission properties of as-deposited and thermally treated CdO thin films were studied by photoluminescence spectrum recorded at 298 K.Graphical Abstract

Growth of ternary CdxZn1−xO thin films in oxygen ambient using pulsed laser deposition

This study reports the growth of cadmium alloyed zinc (CdxZn1-xO) oxide thin films using pulsed laser deposition. The films are deposited on Corning glass substrates at different oxygen pressures of 5, 20, and 40 mTorr. High resolution X-ray diffraction studies reveal mixed phase (hexagonal and cubic) for films deposited at 20 and 40 mTorr, while a cubic phase for film deposited at 5 mTorr pressure. Optical transmittance studies indicate red-shifting of transmission edge as oxygen pressure decreases to 5 mTorr from 20 mTorr, hinting at a possible increase in cadmium content in thin films. Minimum band gap energy is obtained at growth pressure of 5 mTorr. Resistivity measurements have been performed using Hall effect measurement set up at 298 K.

Optimization of polarization compensating interlayers for InGaN/GaN MQW solar cells

Optimization of polarization compensating interlayer (PCI) is performed numerically to improve the photovoltaic properties of InGaN/GaN multiple quantum well solar cell (MQWSC). Simulations are performed to investigate the effect of change in thickness and composition of PCI on the performance of cell. Short circuit current density is increased as we increase the thickness of the PCI. Changing the constitution of PCI not only mitigates the negative effects of polarization-induced electric fields but also reduces the high potential barrier existing at the QW/p-GaN hetero-interface. This claim is validated by the performance shown by the cell containing optimized PCI, as it shows an improved efficiency of 1.54 % under AM1.5G illumination.Optimization of polarization compensating interlayer (PCI) is performed numerically to improve the photovoltaic properties of InGaN/GaN multiple quantum well solar cell (MQWSC). Simulations are performed to investigate the effect of change in thickness and composition of PCI on the performance of cell. Short circuit current density is increased as we increase the thickness of the PCI. Changing the constitution of PCI not only mitigates the negative effects of polarization-induced electric fields but also reduces the high potential barrier existing at the QW/p-GaN hetero-interface. This claim is validated by the performance shown by the cell containing optimized PCI, as it shows an improved efficiency of 1.54 % under AM1.5G illumination.

Effect of Swift Heavy Ion Irradiation on the Structural and Optical Properties of CdO Thin Films

In this study, effects of Ni7+ beam irradiation on structural and optical properties of cadmium oxide thin films deposited on indium tin oxide (ITO) coated glass substrates using sol-gel spin coating technique have been reported. Structural properties of irradiated films (fluence 3 × 1012 ions/cm2) have been studied by glancing angle X-ray diffraction (GAXRD). The films exhibit cubic crystal structure and a high degree of crystallinity. UV-Visible absorption spectra reveal that Ni7+ beam irradiation causes an increase in blueshift of absorption edge for CdO pristine films, leading to enhancement in band gap energy as indicated by Tauc’s plot studies.