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Lightweight, high electrical and thermal conducting carbon-rGO composites foam for superior electromagnetic interference shielding
No full textLightweight and high strength carbon-rGO composite foams were inventively fabricated by simple sacrificial template technique using reduced graphene oxide (rGO) and phenolic resin as a carbon source. The carbon-rGO composite foams were fabricated by two different routes. In one case, rGO was incorporated in phenolic resin and carbon foam developed by several heat treatments. In the other case, graphene oxide (GO) was decorated over carbon foam and converted into rGO decorated carbon foam by heat treatment. The EMI shielding of carbon-rGO composite foams was measured in the X-band frequency range (8.2-12.4 GHz) and mechanisms were systematically studied with respect to the rGO and porous structure. The EMI SE of carbon foams was increased from -23.2 to -50.7 dB by the decoration of 1.0 wt % rGO. The thermal conductivity achieves as high as 1.4 W/(m K) by incorporation of 4.0 wt % rGO in carbon foam. All the results indicated that this effort provided a novel, simple, low-cost concept for fabricating lightweight, high electrical and thermal conducting carbon-rGO composite foam for high-performance EMI shielding applications
Multi-component framework derived SiC composite paper to support efficient thermal transport and high EMI shielding performance
No full textCarbon-based electromagnetic interference (EMI) shielding materials have witnessed a fast evolution in recent years. But challenges of lightweight, flexibility, and good heat dissipation properties required to explore new EMI shielding materials. Herein, a unique SiC-based hybrid composite paper was prepared, as an advanced thermally stable and conductive material for boosting the EMI performance. In this study, a lightweight and flexible network structure of mesocarbon microbeads (MCMB) and multiwall carbon nanotubes (MWCNTs) with polyacrylonitrile (PAN) was developed and SiC was incorporated during the fabrication process or synthesized directly within the matrix structure. EMI shielding effectiveness (SE) of the hybrid composite papers was studied in the X-band frequency region and a maximum EMI SE value of -67 dB was achieved at a frequency of 10.3 GHz. In addition to EMI shielding properties, the hybrid composite paper shows high thermal stability and good thermal conductivity required for proper heat dissipation from the system accompanied by robust mechanical properties. These outcomes make SiC-composite paper attractive material for applications in the lightweight and flexible modern electronic devices with good heat dissipation characteristics
Nanostructured GaN and AlGaN/GaN heterostructure for catalyst-free low-temperature CO sensing
No full textThe use of expensive catalysts (e.g. platinum) and high operation temperature ( > 300 degrees C) has plagued the cost-effectiveness and thereby the commercialization of III-Nitride semiconductors based gas sensing technology. Inadequate research on the development of catalyst-free room-temperature CO sensing using GaN based structures is the critical reason behind the subjugation of this area. Therefore, in the present article, we aimed the development of GaN & AlGaN/GaN heterostructure based gas sensors for catalyst-free low-temperature CO sensing (at 100 ppm). To explore the underlying science behind such mechanism, the morphological, electronic and electrical properties of the devices were thoroughly investigated. The analysis revealed that CO sensing on GaN (and AlGaN/GaN heterostructure) is governed via the chemical nature of ambient-oxidation induced amorphous oxide layer (O-2(-), O2- or OH(- )species), which acts as donor/acceptor state at the surface. Besides, the critical device parameters like Schottky barrier height and electron accumulation associated with series resistance and leakage current (forward/reverse) displayed significant variation with temperature (27-250 degrees C) and perturbed the effective carrier transport/collection and ultimately the device efficiency. The study demonstrates that nanostructured surfaces can open avenues for the development of catalyst-free room temperature operating III-Nitride semiconductor based CO sensors
A high-performance hydrogen sensor based on a reverse-biased MoS2/GaN heterojunction
No full textWe report a MoS2/GaN heterojunction-based gas sensor by depositing MoS2 over a GaN substrate via a highly controllable and scalable sputtering technique coupled with a post sulfurization process in a sulfur-rich environment. The microscopic and spectroscopic measurements expose the presence of highly crystalline and homogenous few atomic layer MoS2 on top of molecular beam epitaxially grown GaN film. Upon hydrogen exposure, the molecular adsorption tuned the barrier height at the MoS2/GaN interface under the reverse biased condition, thus resulting in high sensitivity. Our results reveal that temperature strongly affects the sensitivity of the device and it increases from 21% to 157% for 1% hydrogen with an increase in temperature (25-150 degrees C). For a deeper understanding of carrier dynamics at the heterointerface, we visualized the band alignment across the MoS2/GaN heterojunction having valence band and conduction band offset values of 1.75 and 0.28 eV. The sensing mechanism was demonstrated based on an energy band diagram at the MoS2/GaN interface in the presence and absence of hydrogen exposure. The proposed methodology can be readily applied to other combinations of heterostructures for sensing different gas analytes
AlGaN nanowall network structure grown on sapphire (0001) substrate by laser molecular beam epitaxy
No full textSelf-assembled AlGaN nanowall networks have been grown heteroepitaxially on sapphire (0001) substrate using laser molecular beam epitaxy (LMBE) technique. The effect of growth temperature on the formation of AlGaN nanowall network structure has been studied in the range of 500-700 degrees C. It is found that the growth of AlGaN under strong N-rich flux condition at a high growth temperature of 700 degrees C is conducive for the formation of self-assembled nanowall network. In-situ reflection high energy electron diffraction exhibits the three-dimensional growth of the AlGaN nanowall network structure oriented along c-axis. The nanowall width and pore size are measured to be 10-40 and 30-70 nm, respectively, by using field emission scanning electron microscopy. From room temperature photoluminescence measurement, a strong ultra-violet (UV) emission at about 3.52 eV due to band-to-band transition is obtained for the AlGaN nanowall structure with a high UV-to-yellow luminescence intensity ratio indicating a good optical quality. The grown AlGaN nanowall network is suitable for the applications in field emitters, photo-detectors and other nitride-based optoelectronic devices
An electrochemical biosensor based on novel butylamine capped CZTS nanoparticles immobilized by uricase for uric acid detection
No full textQuaternary chalcopyrite, i.e., Cu(2)ZuSnS(4) (CZTS) nanopartides films have been proposed as a novel matrix system for enzyme-based electrochemical biosensors providing a non-toxic, low-cost alternative for the fabrication of bioelectrodes. The easy tuneability of the band gap of CZTS by varying the cation ratio and size of nanoparticles facilitate to impart desirable electrical properties in the material. Butylamine capped spherical CZTS nanoparticles of size 15-16 nm and band gap 2.65 eV have been synthesized by colloidal hot injection technique. The films of CZTS onto ITO substrates are deposited using dip coating technique, and uricase enzyme have been immobilized onto CZTS films using EDC-NHS binding chemistry. Electrochemical analyses of this bioelectrode revealed that the uricase/CZTS/ITO/glass electrode exhibits good linearity over a wide range of 0-700 M uric acid concentration with a limit of detection (LOD) of 0.066 M. The low value of 0.13 x 10(-4) M of Michaelis-Menten constant (Km) indicate the enhanced affinity of inunobilized enzyme (uricase) towards uric acid. Thus, the present report confirms the promising application of the p-type CZTS thin film matrix for the realization of an electrochemical biosensor
Dielectric/ferroelectric properties of ferroelectric ceramic dispersed poly (vinylidene fluoride) with enhanced beta-phase formation
No full textFree standing and flexible ferroelectric ceramic-polymer composites (PVDF + Phi wt% of BNBT (0.94Na(0)(.)(5)Bi(0)(.)(5)TiO(3)-0.06BaTiO(3))) with 0-3 connectivity were synthesized by solution-casting technique. Composite nature and homogeneous distribution of ceramic filler particles in PVDF were confirmed with x-ray diffraction and scanning electron microscopic analysis. The intensity ratio of beta-phase with respect to alpha-phase i.e., I-20(.2)./I-18.4. (obtained from XRD analysis) and the fraction of electro-active beta phase i.e., F(beta)% (obtained from FTIR analysis) are enhanced with increase in filler concentrations and peaked for 35 wt% of the ceramic filler. An enhancement of the % of crystallinity (calculated from XRD analysis) has been observed with increase in the filler concentrations. The increase of the fraction of beta-phase has been explained on the basis of ion (negatively charged surface ion of the ferroelectric ceramic filler) -dipole (-CH2 dipole of the polymer matrix) interactions, as evidenced from FTIR and UV-VIS absorbance spectra. Relative dielectric permittivity (dielectric constant) and ferroelectric polarization were found to be highest for the composite with 35 we% of ferroelectric ceramic filler. Percolation theory has been successfully employed to explain the observed trend in the dielectric properties with the compositional variation. Significant enhancement in the electro active beta-phase has been correlated with the improved dielectric and ferroelectric properties of the composite
Direct growth of self-aligned single-crystalline GaN nanorod array on flexible Ta foil for photocatalytic solar water-splitting
No full textWe report the direct growth of self-aligned single crystalline GaN nanorod array on flexible Ta metal foil using laser molecular beam epitaxy. Scanning electron microscopy reveals the vertically aligned nano-rods on Ta surface having diameters in the range of 60-80 nm. The nanorods show well-defined hexagonal facets and are quite uniformly distributed across the metal foil. Transmission electron microscopy shows single crystalline nature of the individual rods having c-axis oriented growth with wurtzite structure. Room temperature photoluminescence study exhibits a sharp, intense band-to-band emission without any deep-level bands indicating the excellent optical quality of the GaN nanorod array. X-ray photoemission spectroscopy to elucidate the electronic structure of the nanorods confirms Ga-N bonding and the calculated chemical composition turns out to be slightly Ga rich. Location of valence band maxima also suggests the n-type character of GaN nanorods. The photoelectrochemical water-splitting behaviour of the self-aligned GaN nanorod arrays on Ta foil has been investigated using 1M oxalic acid as the electrolyte with AM 1.5 G simulated solar radiation under 1 Sun (100 mW/cm(2)) conditions. The results demonstrate an effective way of fabricating well-aligned GaN nanorods on flexible metal foils for developing simple, relatively inexpensive, and flexible photo-electrodes for photocatalytic solar water-splitting applications
Directly grown Sr-Co layered double hydroxide (LDH) entangled two dimensional nanosheet film with superior performances
No full textDesigning of electrode with electrochemically rich structure, outstanding mechanical robustness and high electrical conductivity remains a challenge. We report a design of entangled Sr-Co Layered double hydroxides (LDHs) two-dimensional structure for such electrode. The hierarchical electrode with entangled nanosheet exhibit high specific capacitance of 1415 F g(-1) at 5 A g(-1) current density, excellent rate capability, high energy (12.28Whkg(-1)) and power density (567.788 W kg(-1)) and outstanding stability (80% capacity retention over 5000 cycles). The asymmetric device cell of Sr-Co LDH/ACC gives high energy density (27.78 Whkg-1) and power density (499.96Wkg-1) with cyclic performance of 1000 cycles with 95.24% capacitance retention. Further, we provide a detailed analysis of the various electrolyte environment experienced by the electrode and their effect on electrochemical properties. We pick out three different electrolytes; LiOH, NaOH, KOH and show that both selected electrolyte and metal combination for LDHs paves the way for outstanding electrochemical performance
Donor-Acceptor-Donor Copolymers with 3,4-Ethylenedioxythiophene Moiety: Electropolymerization and Effect on Optoelectronic and Electrochromic Properties
No full textThree random copolymers PE-co-M1, PE-co-M2, and PE-co-M3 were obtained by electrochemical polymerization of donor-acceptor-donor monomers M1, M2, and M3 with 3,4-ethylenedioxythiophene moiety, respectively, using a 1:1 molar ratio of the corresponding monomers, to find new properties and a more effective way to control the optoelectronic properties in conjugated system. For comparison purpose, polymers P1, P2, and P3 were prepared from the corresponding monomer units M1-M3, respectively, by electrochemical polymerization. We also present efficient synthesis, characterization, and comparative density functional theory (DFT) calculations of the monomers M1-M3 and polymers P1-P3. Cyclic voltammetry, spectroelectrochemistry, and electrochromic properties of all of the polymers P1-P3 and copolymers PE-co- M1, PE-co-M2, and PE-co-M3 were carried out and a throughout comparison was made. We have shown that electrochemical copolymerization is a powerful strategy to tune the highest occupied molecular orbital energy level, band gap, and color of the copolymer. Thus, this finding clearly indicates that the copolymers show significantly different optoelectronic properties compared to their constituent polymers