• Volume 42, Issue 1

February 2019

• Nanogels of acetylated ulvan enhance the solubility of hydrophobic drug curcumin

Curcumin (Cur) is a polyphenol showing various bioactivities including anti-tumour activity. However, poor solubility of Cur in aqueous solution is a major barrier to its bioavailability and clinical efficacy. In this study, hydrophobicallymodified ulvan was considered to self-assemble to fabricate nanogels. This is a network of hydrophilic segments with hydrophobic microdomains in the nanopores, which keeps Cur from dispersing into the media and raise Cur solubility in water by 20,000 times. A Cur-loaded acetylated ulvan nanogel was characterized by scanning electron microscopy, transmission electron microscopy and dynamic light scattering. This result confirmed that hydrophobically modified ulvan could be used as a self-organizing assembly nanogel to carry and deliver water-insoluble bioactive compounds.

• Hybrid bilayer gate dielectric-based organic thin film transistors

Organic thin film transistors (OTFTs) are key building blocks for flexible, low cost electronics systems. They provide a viable alternative for silicon-based electronics with added advantages of low cost and flexibility. However, fewissues like high-operating voltage, low-switching speed, high-leakage current and reliability are still a challenge. The overall performance of an OTFT depends on organic semiconductors and gate dielectric interface. In this paper, we review thecurrent status and trends in the choice of dielectric layer for OTFTs. As a starting point, the performance parameters of an OTFT and their dependence on the dielectric layer are briefly discussed. A variety of dielectric materials which includes high-k inorganic, organic, surface coated inorganics and nanocomposites are also presented. The advantages and drawbacksof each of these materials are discussed in detail.We reviewed the latest developments in the dielectric materials especially, self-assembled monolayers (SAMs), hybrid bilayers and nanocomposites. SAM-based OTFTs offer several advantages but shift in the threshold voltage remains a concern. Nanocomposites are a latest addition to the dielectric materials, whichoffer advantages like solution processing and improved dielectric constant but have a rough surface. A hybrid bilayer that incorporates the inorganic dielectric as a base layer and a thin polymer layer over it to improve the surface properties offers several desirable characteristics over the other choices. Hence, we propose that hybrid bilayer gate dielectrics shall play a pivotal role in improving the OTFT performance.

• Effect of pretreatment processes on physicochemical properties of hydroxyapatite synthesized from Puntius conchonius fish scales

The current study emphasizes on the novel idea of synthesizing hydroxyapatite (HAp) from Puntius conchonius fish scales’ bio-waste and study the effect of acid, alkali and acid–alkali pretreatments on its physicochemical properties. Material characterization is carried out to study the physicochemical properties of the synthesized HAp using Fourier transforminfrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDX) and transmission electronmicroscopy (TEM) analysis. FTIRand XRD plots show peaks corresponding to natural bone apatite which confirms the formation of HAp. TG analysis shows a maximum weight loss of 2.28% indicating high thermal stability of HAp beyond 800$^{\circ}$C. SEM micrographs illustrate highly porous morphology with interconnected pores.EDXanalysis of theHApexhibits close proximity of the calcium/phosphorous (Ca/P) ratio to natural bone apatite. TEM micrographs show the formation of polycrystalline HAp particles with size ranging from $38\pm 1.54$ to $219\pm 5.88$ nm. A comparative study on the physicochemical properties of HAp synthesized using three different pretreatment processes is performed. Results reveal that HAp synthesized from acid-treated fish scales show highest yield percentage, better thermal stability and highly porous morphology with a particle size of $38\pm 1.54$ nm. Thus, HAp synthesized from acid-treated fish scales can be a promising candidate for the development of porous bone scaffolds.

• Synthesis, characterization and anticancer activity of selenium nanobiocomposite of L-asparaginase

Selenium is a rare earth nonmetal and an essential micronutrient for animals, and a trace nutrient for humans. It is known to function as a cofactor for reduction of antioxidant enzymes, such as glutathione peroxidase. The selenium nanobiocomposite synthesized using a co-precipitation method with sizes 20–30 nm were confirmed using scanning electron microscopy and they showed maximum absorption between 300 and 400 nm in the ultra-violet spectrum. Fourier transform infrared and H-nuclear magnetic resonance analysis revealed the involvement of various functional groups in the binding of asparaginase to selenium nanoparticles to form the selenium nanobiocomposite. X-ray diffraction analysis confirmed the hexagonal structure of the selenium nanobiocomposite. Methylthiazolyl diphenyl-tetrazolium bromide assay on HT-29, MG-63 and HEPTOcells loaded with the selenium nanobiocomposite revealed a toxicity of 93.62, 94.24 and 87.68%, respectively, for a selenium nanobiocomposite concentration of 1000 $\mu$g ml$^{−1}$. The selenium nanobiocomposite of L-asparaginase opens a new arena in cancer treatment.

• Barrier height modification in Au/Ti/n-GaAs devices with a HfO$_2$ interfacial layer formed by atomic layer deposition

X-ray photoelectron spectroscopy has been carried out to characterize the surface of the hafnia (HfO$_2$) thin films grown on n-GaAs wafer by atomic layer deposition, and the surface morphology of the HfO2 layer on GaAs has beenanalysed using atomic force microscopy. The barrier height (BH) values of 1.03 and 0.93 eV (300 K) for the Au/Ti/HfO$_2$/n-GaAs structures with 3- and 5-nm HfO$_2$ interfacial layers, respectively, have been obtained from the $I –V$ characteristics of the devices, which are higher than the value of 0.77 eV (300 K) for the Au/Ti/n-GaAs diode fabricated by us. Therefore, it can be said that the HfO$_2$ thin layer at the metal/GaAs interface can also be used for BH modification as a gate insulator in GaAs metal-oxide semiconductor (MOS) capacitors and MOS field-effect transistors. The ideality factor values havebeen calculated as 1.028 and 2.72 eV at 400 and 60 K; and as 1.04 and 2.58 eV at 400 and 60 K for the metal–insulating layer–semiconductor (MIS) devices with 3- and 5-nm interfacial layers, respectively. The bias-dependent BH values havebeen calculated for the devices by both Norde’s method and Gaussian distribution (GD) of BHs at each sample temperature. At 320 K, the $\phi_b(V)$ value at 0.70 V for a 3-nm MIS diode is about 1.08 eV from the $\phi_b(V)$ vs. $V$ curve determined by the GD, and about 0.99 eV at 0.58 V for a 5-nm MIS diode. It has been seen that these bias-dependent BH values are in close agreement with those obtained by Norde’s method for the same bias voltage values.

• Silica-coating of nano-Y$_3$Al$_5$O$_{12}$:Ce$^{3+}$ synthesized by self-combustion

Y$_{2.91}$Ce$_{0.09}$Al$_5$O$_{12}$ is obtained by self-combustion, grinding and sol–gel coating. X-ray diffraction, transmission electron microscopy, photoluminescence and absorption measurements were used to identify the structural and optical properties of each step of the process. The process is composed of a combination of chemical and physico-chemical processesincluding combustion and thermal steps, followed by grinding, powder dispersion by acidic passivation, stabilization of particle dispersions with citrate ligands and embedding of yttrium aluminium garnet (YAG) particles into SiO$_2$ shells usinga seeded growth process before drying. The initial state of the obtained powder is composed of 35 nm crystallites, sintered and agglomerated. The grinding step breaks the sintered bridge, while the passivation and citrate adsorption steps separate the particles by electrostatic repulsion before the silica coating. The optical characterizations are performed and compared separately for the powdered samples that represent the initial and final states of our process, and the dispersion sample represents the intermediate state of our process. The optical measurement revealed an important amount of optical defectsat the surface of the particles, compared with micrometric commercial particles. The grinding, nitric acid and citrate steps remove some of these defects. The final state of the sample still possesses lower quantum efficiency than that of a micrometric sample, but the SiO$_2$ coating allows for a perfect separation of the particle, suitable for implementation in small devices.

• The production of graphene–boron nitride nanosheet heterostructures via liquid phase exfoliation assisted by a milling process

Graphene–boron nitride (BN) nanosheet heterostructures have become one of the highly interesting matters in recent times owing to their advantages. In this study, the liquid phase exfoliation method was preferred for production ofgraphene–BN nanosheet heterostructures. However, a pre-milling process was applied to starting materials, instead of the classical liquid phase exfoliation method previously used in the literature. Hexagonal graphite (h-G) and h-BN mixtures were milled for 50 h and the milled powders were subjected to the liquid phase exfoliation process. As a result of the examinations, it was observed that graphene–BN nanosheet heterostructures were successfully synthesized. The widths of the synthesized nanosheets were 300–500 nm and nanosheets were multi-layers. It was seen that a large part of the powder mixture were occurred at high amorphization during the ball milling process. According to X-ray diffraction (XRD) peaks, the amorphization ratio was almost 90%. But, almost all of amorphous structures were removed during acid mixing and the thermal process. But, amorphous structures still existed in samples. In addition, the ball milling process damaged the sheets and defects formed. Despite all these disadvantages, the milling process carried out in this study provided formationof thinner and larger sheets compared with previous similar studies.

• Effect of Nd doping on structural and opto-electronic properties of CdO thin films fabricated by a perfume atomizer spray method

A perfume atomizer-assisted spray pyrolysis method was employed to fabricate undoped and neodymium (Nd)-doped cadmium oxide (CdO) thin films. X-ray diffraction results reveal that all the films are polycrystalline witha cubic structure with a preferential orientation along the (200) direction. Scherrer’s formula was used to calculate the crystallite size of Nd-doped CdO films. Energy dispersive spectroscopy results show that Cd, Nd and O elements are present in Nd-doped CdO thin films. The optical absorption of the doped films is increased along with increasing Nd-doping level. The prepared CdO thin films have a high absorption coefficient in the visible region and the optical band gap is decreased on increasing Nd doping content. The electrical carrier concentration (n) of the deposited films is increased with increasing Nd doping concentration. Photoconductivity studies of a nanostructured Al/Nd–n-CdO/p-Si/Al device showed a non-linear electric characteristics indicating diode-like behaviour. Prepared Nd:CdO films could increase the photo-sensing effect ofthis n-CdO/p-Si heterostructure. These Nd-doped CdO thin films may open a new avenue for photodiode application in near future.

• Liquid hydrogen at the thermodynamic conditions of room temperature and a pressure of 490 GPa

We investigate the effect of nuclear quantum effects in liquid hydrogen at the thermodynamic conditions of room temperature and a pressure of 490 GPa. The calculated pair-correlation function shows that the nuclear quantum effectsare quite significant for the correct description of liquid atomic hydrogen at high pressures.

• C$_{32}$, Si$_{32}$ and B$_{16}$N$_{16}$ as anode electrodes of Li-, Na- and K-ion batteries: theoretical examination

In this study, the potential of C$_{32}$, Si$_{32}$ and B$_{16}$N$_{16}$ nanocages as anode electrodes of Li-,Na- andK-ion batteries via density functional theory was investigated. The effects of halogen-adoption of C$_{32}$, Si$_{32}$ and B$_{16}$N$_{16}$ on potentials of metal-ion batteries were examined. Results showed that B$_{16}$N$_{16}$ as an anode electrode in metal-ion batteries has higher potential than C$_{32}$ and Si$_{32}$. Results illustrated that (i) a K-ion battery has higher cell voltage and higher performance than Li- and Na-ion batteries; (ii) halogen-adoption of nanocages increased the cell voltage of studied metal-ion batteries and (iii) F-adopted metal-ion batteries have higher cell voltage than Cl- and Br-adopted metal-ion batteries. Finally, F–B$_{15}$N$_{16}$ as an anode electrode in K-ion batteries has the highest performance and it can be proposed as novel metal-ion batteries.

• Impact of sulphurization environment on formation of Cu$_2$ZnSn$S_4$ films using electron beam evaporated stacked metallic precursors

The superiority of copper zinc tin sulphide (Cu$_2$ZnSnS$_4$; CZTS) over the existing absorber layer materials is inevitable owing to its cheap, non-toxic and earth abundant constituents with high absorption coefficient value. In thepresent study, CZTS films are prepared by sulphurizing electron beam deposited precursors of glass/Cu/Zn/Sn/Cu and glass/Cu/Sn/Zn/Cu stacking sequences in two different environments i.e., elemental S powder and 5% H$_2$S $+$ N$_2$ gas at different ramping rates. The effect of sulphurization environment and sulphurization ramping rate on the formation of CZTS is investigated using X-ray diffraction and Raman spectroscopy. The morphology and composition of the films are analysed respectively using field emission gun scanning electron microscopy and energy dispersive X-ray spectroscopy. It is observedthat films prepared in elemental S powder at a low ramping rate exhibit better crystallinity with less impurity phases. The presence of ZnS is observed in all the films, while the presence of SnS is observed in films prepared with H$_2$S gas alone, thus concluding that sulphurization in the presence of elemental S powder at a low ramping rate is highly favourable for CZTS film formation. CZTS films with minor ZnS impurity with a bandgap of 1.48 eV is successfully fabricated by usinga glass/Cu/Zn/Sn/Cu precursor stack.

• Controllable preparation of hollow fibrous SrCO$_3$

A simple and economic CO$_2$ bubbling crystallization reactor for preparation of strontium carbonate (SrCO$_3$) was designed. Through monitoring pH and conductivity, hollow SrCO$_3$ fibres without any morphology control agents weresuccessfully obtained. The effects of temperature and CO$_2$ flow rate on the morphology of SrCO$_3$ were analysed. This study presents a new method for carbonate crystal control and growth.

• Sintering behaviour and interfacial toughness of HAp/TCP coatings on HAp/Ti nanocomposite substrates

Spark plasma sintering (SPS) is used in rapid compaction of materials in order to achieve higher compact density and in improving mechanical strength and toughness. However, implants produced by SPS do not have preferred positions for formation of a bone-like apatite layer on their surface due to their high density. Biphasic-calcium phosphate (BCP) ceramics consisting of stable hydroxyapatite (HAp) and soluble tri-calcium phosphate (TCP) are developed to achieve a controllable biodegradation rate and biological stability by adjusting the TCP/HAp ratio. The primary goal of this study is to improve mechanical properties and bioactivity of implants. HAp/20 wt% Ti nanocomposite powders were chosen for bulk, and also HAp/TCP nanocomposite powders were chosen for coatings with weight percentages of 75/25, 50/50 and 25/75, respectively. The samples were sintered for 5 min at a compaction pressure of 30 MPa and at different temperatures of 650 and 750◦C. The phase changes of the coatings are studied by X-ray diffraction. Mechanical properties such as interfacial toughness are investigated. The results show that amount of TCP increases with increasing sintering temperature in HAp/75 wt% TCP coating, however no significant change was observed in amount of TCP in HAp/25 wt% TCP coating. Also,the maximum value of interfacial toughness is equal to 34 MPa mm$^{1/2}$, which was obtained for 75 wt% HAp–25 wt% TCP coating sintered at 750$^{\circ}$C.

• Evans Blue dye removal from contaminated water on calcined and uncalcined Cu-Al-CO$_3$ layered double hydroxide materials prepared by coprecipitation

This work focuses on studying the removal of Evans Blue dye, which is a water pollutant, using Cu-Al-CO$_3$ anionic clay known also as layered double hydroxide (LDH) and its phase calcined at 500$^{\circ}$C (Cu-Al-500). LDH is easy to synthesize by a coprecipitation method at a constant pH; it is non-toxic and non-expensive, constituted of plane sheets containing alternating octahedral stack M(OH)$_6$ formed by divalent (Cu$^{2+}$) and trivalent (Al$^{3+}$) cations and carbonate anions (CO$^{2−}_3$) in the interfoliar space. The X-ray diffraction (XRD) pattern of the formed solids shows that the synthesized phaseis the LDH type, and was confirmed by infrared spectroscopy (FT-IR). Thermogravimetric analysis (TGA) shows that the decarbonation of LDH begins at 500$^{\circ}$C, thus this temperature is chosen for the calcination of this clay. XRD and FT-IR of the calcined phase confirm the obtaining of copper and aluminium oxides. The UV–visible study of the adsorption of Evans Blue is performed by varying different parameters such as the weight of LDH and its calcined phase, the concentration of the dye and the pH of the solution. The obtained isotherms from this kinetic study show that the adsorption of Evans Bluedye is more efficient in the calcined phase compared with the as-synthesized LDH.

• Synthesis and characterization of spin-coated clay/PVDF thin films

This paper reports the fabrication of Cloisite-15A (C-15A)-dispersed polyvinylidene fluoride (PVDF) nanocomposite thin films by spin coating and their characterization for sensor applications. The effects of nanoclay, duration ofultrasonication and spinning speed on the morphology and properties of thin films were studied. The influence of these parameters on the amount of β-phase was analysed using Fourier transform infrared (FTIR) and X-ray diffraction (XRD)techniques. The influence of C-15A on the morphology and surface quality of thin films was analysed by scanning electron microscopy (SEM). Piezoelectric coefficient was measured at 110 Hz and 0.25 N. Contact angle was measured to assess the hydrophobicity of thin films. The β-phase of 82.97% was obtained in the specimens with 5 wt% C-15A, processed at 500 rpm and spun for 35 min. The piezoelectricity of the specimens increased from $−$18 to $−$25 pC N$^{−1}$. Experiments were conducted as per L16 orthogonal array.

• First-principles study of solid solution strengthening in Mg–X (X$=$Al, Er) alloys

To study the solid solution strengthening effect on magnesium (Mg)–X (X$=$Al, Er) alloys, supercell models of Mg, Mg$_{35}$Er and Mg$_{35}$Al are established to perform the first-principles pseudopotential plane wave calculations based on density functional theory. The calculated cohesive energy of Mg$_{35}$Er is lower than that of Mg$_{35}$Al. This indicates thatMg$_{35}$Er has better structural stability than Mg$_{35}$Al. The bulk modulus, Young’s modulus and shear modulus of the solid solutions increases simultaneously when Al and Er are doped into the Mg matrix.Moreover, the solid solution strengthening of Er is much higher than the Al containing alloy. The order of toughness of the three solutions from the highest to the lowestis Mg, Mg$_{35}$Er and Mg$_{35}$Al, while the order of increasing elastic anisotropy is in the reverse order. The number of bonding electrons of Mg$_{35}$Er in the low-energy region of the Fermi level is much higher than that of Mg$_{35}$Al, and the density of states of Mg$_{35}$Er at the Fermi level is higher than that of Mg$_{35}$Al. Compared with Al atoms, Er atoms share more electric charges with Mg atoms, which leads to an increasingly uniform charge distribution around Er atoms.

• Microstructure and mechanical performance of (AlCrNbSiTiV)N films coated by reactive magnetron sputtering

(AlCrNbSiTiV)N films are prepared on cermet cutter tool substrates using direct current reactive magnetron sputtering with a high-entropy alloy target. The use of a grey based Taguchi method to determine the deposition parameters of(AlCrNbSiTiV)N films has been studied by considering multiple performance characteristics. Taguchi quality design concept with an L$_9$ (3$^4$) orthogonal array, signal-to-noise ratio and analysis of variance are used to determine the performance characteristics of the deposition process. The effect of various deposition parameters of (AlCrNbSiTiV)N films on the chemical composition, the microstructure, the morphology, the mechanical performance and cutting performance of the coated cutter in dry machining is determined. The experimental results show a cutter that is coated with (AlCrNbSiTiV)Nexhibits less surface roughness (for workpiece) and flank wear (for cutter), so coated cutter tools have a much longer tool life than the uncoated tools. Transmission electron microscopy patterns confirm that the (AlCrNbSiTiV)N films have a polycrystalline face-centred cubic structure. In the confirmation runs, using grey relational analysis, there are improvements of 3.7% in surface roughness, 69.6% in flank wear and 3.2% in elastic recovery. The Rockwell adhesion test categorizes the coatings as class HF1.

• Dielectric relaxation in a cadmium chloride-doped polymeric blend

The temperature-and frequency-dependent relaxation processes in films of a polymeric blend comprising a polyvinyl alcohol (PVA)/polyvinyl acetate (PVAc) co-polymer blendedwith polyvinyl pyrrolidone (PVP) in equal proportion by weight, and doped with an inorganic metallic salt, cadmium chloride (CdCl$_2$), at 0.0 wt% and 10.2 wt% doping levels (DLs), have been studied using dielectric relaxation spectroscopy (DRS). The frequency response of dielectric parametersfor these samples has been studied with variation in temperature, from 303 up to 373 K, at different fixed frequencies (from 12 Hz up to 200 kHz). Study of Cole–Cole plots reveals a decrease in bulk resistivity of the samples with increase intemperature, which is attributed to thermally induced increase in the mobility of polymer chains. A 10-fold increase in bulk conductivity is observed for doped films with a DL of 10.2 wt%, when compared with the bulk conductivity of the un-doped (0.0 wt% DL) sample. The temperature dependence of dielectric parameters at different frequencies has been studied and the activation energy has been calculated. The relaxation time is found to be of the order of a few milliseconds, which implies that electrical conduction in CdCl$_2$-doped PVA/PVAc–PVP blend films is predominantly due to the migration of ions. Thevariation of AC conductivity with frequency is in agreement with Jonscher’s universal power law. AC conductivity of the sample is found to increase significantly with an increase in temperature of the sample. Frequency-dependent dielectric properties of CdCl$_2$-doped PVA/PVAc–PVP blend films, for various DLs, are also studied at room temperature.

• Ultraviolet B emission from a Gd$^{3+}$-doped BaAl$_2$O$_4$ powder phosphor

A BaAl$_2$O$_4$:Gd$^{3+}$ phosphor was successfully prepared using a combustion technique. An X-ray diffraction pattern was used to characterize the resultant phosphor, and the photoluminescence (PL) of the prepared BaAl$_2$O$_4$:Gd$^{3+}$ was studied. Under a 273-nm excitation, the main emission peak of the phosphor is located at 314 nm, and this is attributedto the ${}^6$P$_{7/2}\to {}^8$S$_{7/2}$ transition of Gd$^{3+}$. Electron paramagnetic resonance (EPR) spectrum appears to be U-shaped, andlines are evident at $g_{\rm eff}\sim 2.14$, 4.56 and 6.75. The PL and EPR analyses indicate the presence of Gd as Gd$^{3+}$ in this sample.

• Haemoglobin/polyindole composites: the novel material for electrochemical supercapacitors

Conducting polymers have recently been employed with metal derivative macromolecules that have led to great improvement in the field of supercapacitor materials. The current work reports on the synthesis of a novel class ofhaemoglobin/polyindole composites (HPCs) through doping of haemoglobin (Hb) into a polyindole (PIN) matrix.HPCs with enhanced electrocapacitive performance were prepared through a cationic surfactant-assisted dilute solution polymerization of indole (IN) in the presence of Hb at various concentrations ranging from 10 to 30% (w/w) and ferric chloride (FeCl$_3$) as an oxidant. The HPCs were characterized through Fourier transform infrared spectra, scanning electron microscopy and simultaneous thermogravimetric analysis. Electrochemical capacitance ($C_s$, F g$^{−1}$) of graphite-based electrodes fabricated from HPCs over stainless steel in the presence of sulphonated polysulphone as a binder has been investigated in KOH solution (1.0 M) with reference to Ag/AgCl at a scan rate (V s$^{−1}$) ranging from 0.001 to 0.2. HPCs with 30% (w/w) of Hb have shown the highest Cs of 294.00 as compared with 112.00 for pure PIN at a scan rate of 0.001 V s$^{−1}$. Successivescans of HPC electrodes show a capacitive decline of $\sim$2% during the first 1000 cycles at a scan rate of 0.1 V s$^{−1}$ in KOH (1.0 M), which indicates the appreciable electrochemical cyclic stability of the HPCs over PIN. Thus, the fabricated HPCs may serve as potential electrode material for development of electrochemical supercapacitors.

Development in lead (Pb)-acid batteries (LABs) is an important area of research. The improvement in this electrochemical device is imperative as it can open several new fronts of technological advancement in different sectorslike automobile, telecommunications, renewable energy, etc. Since the rapid failure of a LAB due to Pb sulphation under partial-state-of-charging, electrode grid corrosion and water loss are some major obstructions in its advancement. The doping of various carbon forms into the negative active material of an electrode has been suggested to be effective at improving the storage capacity and cyclic life of LABs by suppressing irreversible sulphation. This report is an attempt to focus on different theories related to the working mechanism of carbon and to summarize the investigation results observed by various researchers regarding the significant role of nano-carbon additives in LABs. On the basis of that, we tried to compare their performance along with the discussion on the best possible additive.

• Novel sonochemical green approach for synthesis of highly crystalline and thermally stable barium sulphate nanoparticles using Azadirachta indica leaf extract

Nanomaterial synthesized using plant extract is a viable and better alternative to chemical synthesis methods. A simple, nontoxic and inexpensive strategy, which meets the standard of green chemistry, has been introduced for the synthesis of highly crystalline and thermally stable barium sulphate (BaSO$_4$) nanoparticles. This work reports ultrasonic-assisted green synthesis of BaSO$_4$ nanoparticles using Azadirachta indica leaf extract at room temperature. The as-synthesized BaSO$_4$ nanoparticles were subjected to various physiochemical characterization using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission gun-scanning electron microscopy (FEG-SEM), thermogravimetric analysis (TGA) and energy-dispersive X-ray spectroscopy (EDX). XRD explored orthorhombic, highly crystalline and pure BaSO$_4$ (JCPDS: 24-1035) with average crystallite size of 55.6 nm. FEG-SEM study revealed about size (>80 nm) of BaSO$_4$ nanoparticles. Co-precipitation method was also employed to synthesize BaSO$_4$ for comparison between biogenic and chemical methods. The size of BaSO$_4$ nanoparticles obtained using co-precipitation method was very large with rod shape morphology. Novel sonochemical green method is preferable because of its control over particle size as well as morphology. FTIR study confirmed the formation of BaSO$_4$ nanoparticles. High thermal tolerance and stability of BaSO$_4$ nanoparticles was evidenced from single step weight loss in TGA. In addition, strong characteristic signals of barium, sulphur and oxygen in EDX confirmed the purity of ultrasonic-assisted green synthesized BaSO$_4$ nanoparticles. Overall, this one pot, inexpensive and green sonochemical approach is a promising method for the synthesis of BaSO$_4$ nanoparticles, which might be used for various commercial applications.

• Maleic anhydride film deposition through an active screen plasma system

The active screen plasma system has been extensively studied over the past few years, mainly for plasma nitriding purposes. This technique also provides possibilities of treating non-electrical conducting materials, such as polymeric ones, which is unattainable with a conventional DC plasma system. In this work, an active screen plasma setup for maleic anhydride (MA) film deposition on a glass substrate was used. The plasma working gas was a mixture of argon and MA vapour. Films obtained through conventional plasma discharge were compared with the active screen deposition process, in both DC andpulsed-mode plasma. The samples were characterized through Fourier-transform infrared spectroscopy and static contact angle between the film’s surface and droplets of distilled water. Film thickness measurements were performed throughprofilometry. Results showed that MA films obtained through the active screen system are thicker and more efficiently preserve the anhydride groups than those obtained from conventional plasma discharge.

• Synthesis and thermophysical studies of polyanilines

Aniline was polymerized under different experimental conditions such as interfacial polymerization, rapid mixing in hydrochloric acid medium and classical bulk polymerization method using $p$-toluene sulphonic acid. The resultingpolyanilines were characterized by infrared, X-ray diffraction, conductance and scanning electron microscopic analysis. The main emphasis of the paper is to study the thermal response of the synthesized polyanilines by thermogravimetric analysis and differential scanning calorimetry (DSC). The DSC data were utilized further to calculate the specific heat capacities of the synthesized polyanilines as a function of temperature.

• Intercalation of LDH NO$_3$ with short-chain intercalants

Intercalation behaviour of layered-double hydroxide (LDH) with short-chain intercalants (−(CH$_2$)$_n$−, $n$ < 9) is significantly difficult and less reported than with long-chain intercalants. The present study reports an efficientway to intercalate LDH with short-chain intercalants ($n=4$ and 8) and investigates the effect of layer charge on intercalation behaviour of LDHs. Short-chain anionic surfactants were successfully intercalated with synthetic LDHs [Zn$_{1−x}$Al$_x$(OH)$_2$NO$_3 \cdot n$H$_2$O, $x = 0.2−0.33$] by an ion-exchange intercalation technique in a slightly acidic medium(pH $=$ 5.4). The adverse effect of a carbonate anion was avoided by performing the ion-exchange intercalation in slightly acidic medium (pH $=$ 5.4). It was found that basal spacing ($d_{003}$) and experimental organic loading of intercalated LDH (OLDH) increase monotonically with increasing anion-exchange capacity of LDH and intercalant chain length. The evolution of intercalated LDH (O-LDH) structures with increasing intercalant chain length and layered charge has been deciphered by correlating basal spacing of O-LDHs (by X-ray powder diffraction), organic loading data (by thermogravimetric analysis)and molecular conformation of O-LDHs (by Fourier-transform infrared spectroscopy) within the LDH gallery. Successful intercalation of LDH with these short-chain intercalants in slightly acidic medium has not been reported previously.

• Hybrid gate dielectrics: a comparative study between polyvinyl alcohol/SiO$_2$ nanocomposite and pure polyvinyl alcohol thin-film transistors

Polyvinyl alcohol (PVA) thin films as polymer gate dielectrics, with and without SiO$_2$ nanoparticles were fabricated using spin-coating. Surface roughness and hydrophilicity of PVA and PVA/SiO$_2$ thin films were studied bycontact-angle measurements and atomic force microscopy. The dielectric properties were characterized via capacitance and leakage-current measurements on metal–insulator–metal structures. In order to further investigate the application potential of such materials as a replacement for conventional inorganic dielectrics such as SiO$_2$ in organic thin-film transistors, devices were fabricated based on these polymers using $\alpha$, $\omega$-dihexylquaterthiophene as an active layer. Performance of thedeviceswas realized by electrical measurements and Kelvin probe force microscopy. All transistors showed hole and electron mobilities in the low-voltage range. PVA/SiO$_2$ films showed larger capacitance, less hydrophilicity, rougher surfaces and considerable leakage currents compared with those with neat PVA. Although integrating nanoparticles modified surface electronic properties and showed a shift in surface potential as observed in Kelvin probe force measurements, it appears that non-polymeric and neat polymeric dielectric materials could still be a privilege to nanocomposite polymeric dielectrics foroptoelectronic applications.

• Preparation of polyvinylidene fluoride-co-hexafluoropropylene-based polymer gel electrolyte and its performance evaluation for application in EDLCs

Polymer gel electrolyte (PGE) film is prepared by incorporating polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) as polymer, ethylene carbonate (EC)-propylene carbonate (PC) as plasticizers and tetraethylammonium tetrafluoroborate (TEABF$_4$) as salt using solution cast technique. By varying weight percentages of EC-PC-TEABF$_4$ into ahost polymer, different samples of PGE were prepared, and the concentration of EC-PC-TEABF$_4$ was optimized for maximum conductivity, and stability of the prepared film. The maximum ionic conductivity of the order of $4.9 \times 10^{−3}$ S cm$^{−1}$ was determined for 80 wt% of [EC-PC (1:1 v/v)-TEABF$_4$ (1.0 M)]. From the conductivity as a function of temperature,activation energy Ea was calculated and it is about 0.06 eV. Overall, the amorphous structure was confirmed by X-ray diffraction analysis. Dielectric and impedance spectroscopic analysis was also carried out to understand the electrical behaviour of electrolyte using modified Debye’s function. An ionic character of prepared electrolyte was confirmed from DC polarizationmethod. The ionic transference number of 0.91 was calculated from the data while the electrical potential stability window was found to be 3.8 V. The electrical performance of prepared PGE was examined by fabricating electrical double-layer capacitor (EDLC). In a super capacitor, commercially procured activated carbon electrodes were employed. The specific capacitance of EDLC cell is found to be $\sim$60 mF cm$^{−2}$, and equivalent single-electrode capacitance is about 39F g$^{−1}$.

• Effect on dielectric, structural and thermal behaviour of CaCu$_3$Ti$_4$O$_{12}$ in a Nylon 11 matrix

This paper discusses the probability of obtaining high-dielectric permittivity from ceramic–polymer composites by mixing higher dielectric material, CaCu$_3$Ti$_4$O$_{12}$ (CCTO) in a Nylon 11 matrix by the melt-mixing method. The volume percentage of addition of CCTO micro-particles was from 0 to 20 vol%. The dielectric, structural morphology and thermal properties of the composites were analysed using an impedance analyser, a scanning electron microscope, a differential scanning calorimeter and a thermogravimetric analyser, respectively. The permittivity of 50 vol% of the composite is 12, which is increased to that of virgin Nylon 11 of 5.8. Different theoretical models were employed to rationalize the dielectric behaviour of the composite and found to be accurate with that of the experimental data. The thermal behaviour of thecomposites was good after the addition of CCTO micro-particles into it. It provides the means to employ the ceramic–polymer composites at low temperature with less permittivity and loss.

• Biotransformation of ginsenoside using covalently immobilized snailase enzyme onto activated carrageenan gel beads

Ginsenoside transformation has received significant attention from scientists. The main objective of this study is to use immobilized enzymes in ginsenoside transformation. Factors affecting immobilization process were studied; carrageenan beads treated with polyethyleneimine and then activated using glutaraldehyde (GA) were used for snailase enzyme immobilization. The functionalized gel beads were characterized using Fourier transform infrared spectroscopy to verify the modification process. Furthermore, the optimum conditions for biotransformation of ginsenoside were also deliberatedand showed that optimum biotransformation pH is 4.5 and 5–5.5 and temperature 50 and 60$^{\circ}$C for free and immobilized snailase, respectively. Michaelis constants, $K_{\rm m}$ and $V_{\rm max}$, were also studied. The immobilized enzyme retains 96% of its initial activity after being used 10 consecutive times. The results clearly suggested that ginsenoside transformation was performed using immobilized snailase; this process can reduce the transformation cost as the enzyme can be reused many times.

• Enhanced dielectric and piezoelectric properties in microwave sintered (Ba$_{0.997}$Nd$_{0.003}$)TiO$_3$ ceramic when compared to conventional sintered ceramics

Dielectric, conductivity and piezoelectric properties have been studied on (Ba$_{0.997}$Nd$_{0.003}$)TiO$_3$ ceramic samples prepared through microwave sintered (MWS) and conventional sintered (CS) routes and the results are presented in this paper. The room temperature dielectric constant at 10 kHz for CS and MWS samples are 1245 and 5250 respectively. Roomtemperature dielectric constant in MWS sample was almost four times higher than that of the CS sample. The value of $K_t$ is found to be 0.998 and 0.997; whereas the value of $d_{33}$ is 7.72 nm V$^{−1}$ (573 K) and 444.66 nm V$^{−1}$ (573 K) for CS and MWS samples, respectively. In the present study almost 57 times enhancement in piezoelectric charge constant ($d_{33}$) isobserved for the MWS Ba$_{0.997}$Nd$_{0.003}$TiO$_3$ ceramic when compared to the CS ceramic.

• Tunable optical and dielectric properties of polymeric composite materials based on magneso-silicate

Magneso-silicate (MgSi) as an inorganic ion exchange material was synthesized by a precipitation technique. Then, the MgSiwas impregnated into polyacrylamide acrylic acid and its composites (Poly) by condensation polymerization. To study the effect of $\gamma$-radiation, the polyacrylamide acrylic acid and its MgSi samples were synthesized using $\gamma$-irradiatingsystems at 25, 65 and 90 kGy. The variations in the radiation dose and amorphous structure were altered and confirmed by X-ray diffraction (XRD). Moreover, the absorbance and band-gap energy were enhanced by inserting MgSi into the polymeric composites (Poly). Furthermore, variations in temperature with dielectric constant, dielectric loss and conductivity of thesamples at various frequencies from 100, 500, 1000, 2000 to 4000 Hz have been explained.

• Low-level NO gas sensing properties of Zn$_{1−x}$Sn$_x$O nanostructure sensors under UV light irradiation at room temperature

Zn$_{1−x}$Sn$_x$O ($x = 0$, 0.05, 0.10, 0.15, 0.20) nanostructures have been grown through the successive ionic layer adsorption and reaction method. The structural, morphological and compositional properties of the nanostructures have been characterized through X-ray diffraction, scanning electron microscope and energy dispersive X-ray analysis, respectively. The NO gas sensing properties of sensors to 20 ppb have been systematically investigated in the dark and under UV light irradiation. A Zn$_{0.90}$Sn$_{0.10}$O sensor has exhibited the highest response for 20 ppb NO gas compared with other sensors. The sensor response has increased from 1.9 to 43% depending on the UV light irradiation for the Zn$_{0.90}$Sn$_{0.10}$O sensor. Zn$_{0.90}$Sn$_{0.10}$O nanostructure can be used as a suitable gas sensor material for detection of low concentration levels of NO gas.

• Active area cell efficiency (19%) monocrystalline silicon solar cell fabrication using low-cost processing with small footprint laboratory tools

A high efficiency (>18%) industrial large area crystalline silicon wafer solar cell fabrication process generally requires industrial equipment with large footprint, high capital and running costs. Stricter processing window, continuousmonitoring and automated functioning are the reasons for it. However, for any conventional laboratory (lab) it is always difficult to manage these requirements with limited available lab space or insufficient fund and other related resources. In this work, we report a novel way to fabricate high efficiency full area aluminium back surface field monocrystalline silicon wafer solar cells in our lab using low-cost processing with small-footprint fabrication tools for 6 inch pseudo-square industrial wafers. The novelty of our work includes optimization of every fabrication process step, e.g., texturization, emitter diffusion, emitter passivation and anti-reflection coating deposition, edge-isolation, screen printing and co-firing individually. These modifications include tuning of processing tools and processes, utility changes and inclusion of additional process steps.Beaker-based chemical processes, manual diffusion furnace, introduction of low temperature oxidation, low temperature silicon nitride deposition processes, plasma-edge isolation tool, single manual screen printer, single oven drying of metal pastes and co-firing using rapid thermal processing tools were used at our lab. For our cells, actual and active area efficiencies of 18.5 and 19% (measured under AM1.5G 1 Sun condition), respectively, were achieved.

• Novel visible-range luminescence of pristine nanozirconia phosphor using green fabrication techniques

We report unification of pristine nanozirconia phosphor (PNZP), which exhibits orange-red luminescence. PNZP was developed in a lucid manner by the reduction of a zirconyl oxy chloride (ZrOCl$_2$ $·$ ${}^8$H$_2$O) solution with a wet leaf extract of Syzygium cumini (S. cumini) using green fabrication techniques (ultrasonication and microwave irradiation) in the absence of a surfactant and a base, which opens a new avenue for designing novel visible-range luminescence nanophosphors. The ultraviolet–visible spectrum of the aqueous medium containing zirconia nanoparticles showed an absorption peak at around 262 nm. Powder X-ray diffraction study showed that the particles are crystalline in nature, with an average size of $\sim$2.06 nm comprising a tetragonal/monoclinic ZrO$_2$ structure. Photoluminescence spectroscopy study has shown a sharp emission peak at 603 nm and broad emission peaks at 670 and 720 nm at 350 nm excitation. The most useful outcome of this work will be the development of pure nanophosphors using plant extracts which contain different fluorophores, with applications in nanoelectronic devices, catalysis, optoelectronics and piezoelectric devices.

• Synthesis and characterization of porous cytocompatible scaffolds from polyvinyl alcohol–chitosan

In this study, novel porous cytocompatible scaffolds with a 3D nanocomposite structure were synthesized by using nanoclay particles embedded into a biopolymer blend composed of polyvinyl alcohol (PVA) and chitosan (CS).According to the results, the Fourier transform infrared spectrum confirmed the presence of nanoclay, PVA and CS in the scaffold structure. X-ray diffraction outcomes showed the enhancement of crystalline zone in the synthesized 3D scaffolds by increasing the nanoclay content. Scanning electron microscopy (SEM) images revealed the highly porous interconnected microstructure of the scaffolds. Also, the energy-dispersive X-ray spectra verified the presence of nanoclay, PVA and CS in the sample with the highest nanoclay content. According to mechanical properties and porosity of the synthesized 3Dscaffolds, compressive strength (i.e., $3.5 \pm 0.2$ MPa), elastic modulus ($1.42 \pm 0.02$ GPa) and porosity (75–82%) of the sample with the highest nanoclay content was in the range of mechanical properties and porosity of a natural trabecular bone tissue. The swelling of samples in a phosphate-buffered saline solution was less than the swelling in water. In addition, increasing the content of nanoclay decreases the percentage of swelling. Outcomes of cell culture experiments confirmed that the synthesized 3D scaffolds were not toxic and the cell attachment SEM images showed a sufficient attachment of the cell to the interconnected porous structure of the sample. Results suggest that the synthesized 3D scaffold in this study possesses proper microstructure properties and no cytotoxicity to be replaced with natural bone tissues.

• First-principles calculations of opto-electronic properties of IIIAs (III $=$ Al, Ga, In) under influence of spin–orbit interaction effects

In this article, we present first-principles calculations for structural and opto-electric properties of IIIAs (III $=$ Al, Ga, In) in the zinc-blende phase. Our calculations are based on the full potential-linearized augmented planewave method implemented in the WIEN2k code. We employed Perdew–Burke–Ernzerhof generalized gradient and modified Becke–Johnson approximations as exchange–correlation potentials. Our calculated structure parameters are found to be in reasonable agreement with the available literature. It was found that the inclusion of spin–orbit interaction effect shifts the conduction band minima towards the Fermi level and provides band gaps very close to their experimental values. The optical properties such as complex dielectric functions, complex refractive indices, reflectivities, energy loss functions, optical conductivities and absorption coefficients at varied frequencies were investigated in detail. We found that static real part of dielectric functions and refractive index decreases with increase in band gap. Our calculated critical point energies (eV) are consistent with the experimental results.

• Influence of the electrochemical properties of vanadium oxides on specific capacitance by molybdenum doping

Molybdenum (Mo)-doped vanadium dioxide (VO$_2$(B)) nanobelts were successfully synthesized using commercial vanadium pentoxide (V$_2$O$_5$) as the starting material and ammonium molybdate as the dopant by a simple hydrothermal route. Then, Mo-doped VO2(B) nanobelts were transformed to Mo-doped V$_2$O$_5$ nanobelts by calcination at 400$^{\circ}$C under an air atmosphere. The samples were characterized by X-ray powder diffraction,energy-dispersive X-ray spectrometer, elemental mapping, X-ray photoelectron spectroscopy, X-ray fluorescence and transmission electron microscopy techniques. The results showed that Mo-doped VO$_2$(B) and V$_2$O$_5$ solid solution with high purity were obtained. The electrochemical properties of Mo-doped VO$_2$(B) and V$_2$O$_5$ nanobelts as supercapacitor electrodes were measured using cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD). The specific capacitance of VO$_2$(B) nanobelts slightly declines with Mo doping, however, the specific capacitance of V$_2$O$_5$ nanobelts greatly improves with Mo doping. Mo-doped V$_2$O$_5$ nanobelts exhibit the specific capacitance as high as 526 F g$^{−1}$ at the current density of 1 A g$^{−1}$. Both CV and GCD curves show that they have good rate capability and retain 464, 380, 324 and 273 F g$^{−1}$ even at a high-current density of 2, 5, 10 and 20 A g$^{−1}$, respectively. It turns out that Mo-dopedV$_2$O$_5$ nanobelts are ideal materials for supercapacitor electrodes in the present work.

• Effects of deposition parameters on the structure and properties of ZrN, WN and ZrWN films

This paper examines optimal settings for deposition parameters for transition metal nitride (ZrN, WN and ZrWN) thin films that are deposited on tungsten carbide tools and glass substrates using direct current (DC) reactivesputtering with pure Zr and W metal targets and Ar plasma and N$_2$ reactive gases. Experiments using the grey-Taguchi method are conducted to study the effects of deposition parameters (substrate plasma etching time, N$_2$/(N$_2$ $+$ Ar) flow rate, deposition time and substrate temperature) on a film that is deposited on a cutting tool that is used for dry machining and on the films’ mechanical properties. The substrates’ surfaces are etched using oxygen plasma pretreatment. It is clear that the coated film is homogeneous, very compact and exhibits perfect adherence to the substrate. The results of grey relationalanalysis show for the dry turning AISI 304 stainless steel that the surface roughness is approximately $R_{\rm a} = 0.70$ $\mu$m and that the flank wear is approximately 14.02 $\mu$m. The grey relational analysis shows that the period for which the substrate (tungsten carbide tool) is under plasma-etched pretreatment has the most significant effect on both the surface roughnessand flank wear. The coated films are analysed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction and a nano-indenter. The ternary nitride (ZrWN)-coated specimens exhibit better mechanical properties than binary nitride (ZrN and WN) specimens. The optimum ZrWN coating exhibits the greatest hardness ($H$), elastic modulus ($E$) and $H/E$ values.

• Investigation of graphene-reinforced magnesium metal matrix composites processed through a solvent-based powder metallurgy route

In the present investigation, AZ31 alloy is homogeneously reinforced with 0.2, 0.3, 0.4 and 0.5 wt% of reduced graphene oxide (r-GO) nanosheets for the first time through a series of methodologies involving solvent processing, mechanicalalloying, cold pressing and finally sintering under argon atmosphere at 560C. Scanning Electron Microscopy (SEM) assisted with energy-dispersive X-ray analysis revealed that this inventive fabrication route is useful to easily disperse r-GO into the matrix material and thereby attain methodical homogeneity with a uniform particle size. The attained results show that amongst the others, addition of 0.4 wt% r-GO have obviously improved the hardness up to 64.6 HV and also yielded a better inhibition efficiency of 84% on corrosion. Any further increase of r-GO content resulted for significant decrease in the wear rate up to the level of 2.6 mm$^3$ Nm$^{−1}$.

• Large-scale formation of shish-kebab in water-assisted injection-moulded high-density polyethylene with a high-molecular weight

To promote flow-induced orientation and reserve the formation of the shish-kebab structure, a modified injection moulding technology named water-assisted injection moulding (WAIM), was applied to provide twice the shear flow anda rapid cooling rate on high-molecular weight high-density polyethylene (HDPE) melt in a mould cavity. Large-scale distribution of highly oriented shish-kebab was successfully achieved in a WAIM sample with a high-molecular weight. More importantly, the high-orientation degree of lamellae (larger than 0.4) in the thickness direction for a high-molecular weight WAIM sample is >60%, which is much more than a conventional injection-moulded sample (15%). This workprovides a new insight to achieve injection-moulded products with enhanced oriented structures.

• Development of microparticles from wheat glutenins by electrospray and potential application as controlled-release fertilizers

Development of microparticles based on natural polymers has been of interest for researchers due to their applications, such as release systems. Currently, one of the problems presented by agriculture worldwide is the loss offertilizers, i.e., urea, causing environmental pollution and high costs. The aim of this work was to develop microparticles of wheat glutenins by means of electrospray technique, with potential application as a urea controlled-release system in agricultural soils. The microparticles of wheat glutenins were characterized by scanning electron microscopy, Fournier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). In addition, a release kinetic test was performed to evaluate the possible behaviour of wheat-glutenin microparticles in agricultural soils with pH 4, 7 and 10, using buffers as the release medium. TGA indicated that microparticle stability was >100$^{\circ}$C, while FT-IR demonstrated the existence of physical interactions between urea and wheat glutenins. The kinetic tests showed the possible behaviour of the controlled-release fertilizer at pH 4, 7 and 10; rapid release at acidic pH and a decrease in release time at basic pH. With these results, we can conclude that the urea-charged wheat-glutenin microparticles can function as a controlled-release fertilizer in agricultural soils.

• Synthesis, UV-shielding and electromagnetic wave absorbing properties of polyvinylpyrrolidone-TiO$_2$/polyacrylonitrile-SiO$_2$ nanofibre nanocomposites

This paper reports electromagnetic interference (EMI) shielding effectiveness (SE) and UV-shielding performance of polyvinylpyrrolidone (PVP)–TiO$_2$/ polyacrylonitrile (PAN)–SiO$_2$ nanofibre nanocomposites synthesizedvia the single nozzle co-electrospinning method. Herein, three samples with different average diameters were fabricated using 0.3, 0.4 and 0.5 ml h$^{−1}$ flow rates during the electrospinning process.Morphological characterization confirmed that a core–shell structure of nanofibre nanocomposites was formed successfully. The EMI SE of the as-prepared nanofibre nanocomposites was studied using a vector network analyser over the full X-band (8–12 GHz) frequency at room temperature. The experimental results demonstrate excellent microwave absorption properties for all samples. PVP–TiO$_2$/PAN–SiO$_2$ nanofibres with 596.67 nm average diameter show maximum total EMI (110 dB at about 9 GHz) and 98% UV-shielding performance.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 5
October 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019