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Applied Nanoscience (v.2, #3)

Preface by P. K. Giri; D. K. Goswami (pp. 177-177).

Antimicrobial chitosan–PVA hydrogel as a nanoreactor and immobilizing matrix for silver nanoparticles by Shekhar Agnihotri; Soumyo Mukherji; Suparna Mukherji (pp. 179-188).

Hydrogels are water-insoluble crosslinked hydrophilic networks capable of retaining a large amount of water. The present work aimed to develop a novel chitosan–PVA-based hydrogel which could behave both as a nanoreactor and an immobilizing matrix for silver nanoparticles (AgNPs) with promising antibacterial applications. The hydrogel containing AgNPs were prepared by repeated freeze–thaw treatment using varying amounts of the crosslinker, followed by in situ reduction with sodium borohydride as a reducing agent. Characterization studies established that the hydrogel provides a controlled and uniform distribution of nanoparticles within the polymeric network without addition of any further stabilizer. The average particle size was found to be 13 nm with size distribution from 8 to 21 nm as per HR-TEM studies. Swelling studies confirmed that higher amount of crosslinker and silver incorporation inside the gel matrices significantly enhanced the porosity and chain entanglement of the polymeric species of the hydrogel, respectively. The AgNP-hydrogel exhibited good antibacterial activity and was found to cause significant reduction in microbial growth (Escherichia coli) in 12 h while such activity was not observed for the hydrogel without AgNPs.

Keywords: Chitosan–PVA hydrogel; Silver nanoparticles; Antibacterial; Swelling study

Effect of target–substrate distance onto the nanostructured rhodium thin films via PLD technique by A. T. T. Mostako; Alika Khare (pp. 189-193).

Rhodium thin films on highly polished stainless steel substrates were fabricated via pulsed laser deposition (PLD) technique. The PLD films of rhodium were observed to be preferentially oriented in Rh(111) plane. The films showed dense columnar structure of nanometric crystallites. The effects of target–substrate distance onto the root mean square roughness, crystal structure, reflectivity and thickness of the PLD rhodium films were investigated.

Keywords: Rhodium; Thin film; Metallic mirror; Pulsed laser deposition

Studies on the de/re-hydrogenation characteristics of nanocrystalline MgH₂ admixed with carbon nanofibres by Rohit R. Shahi; Himanshu Raghubanshi; M. A. Shaz; O. N. Srivastava (pp. 195-201).

In the present investigation, we have synthesized different morphologies of carbon nanofibres (CNFs) to investigate their catalytic effect on the hydrogenation characteristics of 25 h ball-milled MgH₂ (nano MgH₂). The TEM analysis reveals that 25 h of ball-milling leads to the formation of nanocrystalline particles with size ranging between 10 and 20 nm. Different morphologies of CNFs were synthesized by catalytic thermal decomposition of acetylene (C₂H₂) gas over LaNi₅ alloy. Helical carbon nanofibers (HCNFs) were formed at a temperature 650 °C. By increasing the synthesis temperature to 750 °C, planar carbon nanofibres were formed. In order to explore the effectiveness of CNFs towards lowering the decomposition temperature, TPD experiments (at heating rate 5 °C/min) were performed for nano MgH₂ with and without CNFs. It was found that the decomposition temperature is reduced to ~334 and ~300 °C from 367 °C for the PCNF and HCNF catalysed nano MgH₂. It is also found that HCNF admixed nano MgH₂ absorbs ~5.25 wt% within 10 min as compared with pristine nano MgH₂, which absorbs only ~4.2 % within the same time and same condition of temperature and pressure. Thus the HCNF possesses better catalytic activity than PCNF. These different levels of improvement in hydrogenation properties of HCNF catalysed nano MgH₂ is attributed to the morphology of the CNFs.

Keywords: Hydrogen storage materials; MgH₂ ; Carbon nanostructures

Electromagnetic properties of microwave sintered xTiO₂ + (1 − x) CoFe₂O₄ nanocomposites by K. Sadhana; K. Praveena; P. Raju; S. R. Murthy (pp. 203-210).

The nanocomposites of xTiO₂ + (1 − x) CoFe₂O₄ (where 0 ≤ x ≥ 1) were prepared using microwave–hydrothermal method at 165 °C/45 min. The as-synthesized powders were characterized using X-ray diffraction (XRD), transmission electron microscope and Fourier transform infrared spectroscopy. The particle size was found to be ~18, ~22 and 24 nm for TiO₂, CoFe₂O₄, 50 mol% TiO₂ + 50 mol% CoFe₂O₄ composite powder, respectively. The as-prepared powders were densified at 500 °C/30 min using microwave sintering method. The sintered composite samples were characterized using XRD and field emission scanning electron microscopy. The bulk densities of the present composites were increasing with an addition of TiO₂. The saturation magnetization of composites decreased with an increase of TiO₂ content. The grain sizes of all the composite lies between 54 and 78 nm. The addition of TiO₂ to ferrite increased ε′ and ε″ and the resonant frequency of all the sintered samples were found to be >1 GHz. The value of μ″ found to increase with an increase of TiO₂.

Keywords: Microwave sintering; Dielectric properties; Magnetic properties

Synthesis of polymer-supported dendritic palladium nanoparticle catalysts for Suzuki coupling reaction by Eagambaram Murugan; J. Nimita Jebaranjitham; A. Usha (pp. 211-222).

New bead-shaped heterogeneous nanoparticle catalysts viz., amino-terminated poly(amidoamine) (PAMAM) grafted on poly(styrene)-co-Poly(vinylbenzylchloride) (PS-Poly(VBC)) matrices immobilized/stabilized with palladium nanoparticle were prepared by simplified procedure. The first step is the preparation of PS-Poly(VBC) beads by suspension polymerization method. Second, the PAMAM G(0) G(1) and G(2) dendrimers were grafted individually onto the PS-Poly(VBC) matrices via divergent method by repeating two reactions, i.e., Michael addition of methyl acrylate to surface amino groups of aminomethylated PS-Poly(VBC) matrixes followed by amidation of the resulting esters with ethylene diamine. The resulting three types of PAMAM G(0), G(1) and G(2) grafted on PS-Poly(VBC) matrices were complexed individually with PdCl₂ and thus yielded the corresponding new bead-shaped heterogeneous nanoparticle catalyst immobilized with PdNPs. The appearance of surface plasmon resonance band noticed at 547 nm in UV confirms the formation of PdNPs. The SEM result shows that the intensity of white patches due to immobilization of PdNPs increases with generation number and XRD reveals that the crystalline nature was decreased against generation number of the PAMAM. The catalytic efficiency of PS-Poly(VBC)-NH₂-PdNPs-G(0), G(1) and G(2) catalysts were examined by Suzuki coupling reaction performed in mixture of water/ethanol. The observed reaction yield reveals that the activity was proportional to the generation number of PAMAM grafted onto the PS-Poly(VBC) matrices. The percentage of reaction yield (biphenyl) is sustained to ≈70 % even up to five cycles and this in turn confirms the stability of the catalysts. These catalysts can be used to conduct the Suzuki-coupling reaction in continuous mode operation in industrial scale.

Keywords: Heterogeneous nanocatalyst; Palladium nanoparticle; Polystyrene supports; Suzuki-coupling reaction; Poly(amidoamine) dendrimer

Impact of CuO nanoleaves on MWCNTs/GCE nanocomposite film modified electrode for the electrochemical oxidation of folic acid by D. Manoj; D. Ranjith Kumar; J. Santhanalakshmi (pp. 223-230).

The salient features of the present work focus on the synthesis of CuO nanoleaves by alcoholic reduction of Cu(II) chloride in the presence of poly(diallyldimethylammonium chloride) (PDDA) for the application of folic acid oxidation in simulated body fluid environment. PDDA-assisted polyol process allows a conventional impregnation method for the formation of CuO with well-defined leaf-like structure. The structure and morphology of the CuO nanoleaves were characterized by Fourier-transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) analysis. Field emission scanning electron microscope (FESEM) image confirms the formations of CuO with leaf-like morphology and branched side edges. The average size of the resultant CuO nanoleaves was calculated to be 400 nm in length and 150 nm in width. The electrochemical performance of the CuONs/MWCNTs/GCE nanocomposite modified electrode was characterized by cyclic voltammetric (CV) studies. The CuONs/MWCNTs/GCE nanocomposite modified electrode shows good electrochemical activity and it was also found that it possessed prominent electrocatalytic activity toward the oxidation of folic acid with as high a sensitivity as 3.35 μA/μM and a low detection limit (3σ) of 15.2 nM (S/N = 3). Besides, the CuO nanocomposite modified electrode lowers the over potential of folic acid oxidation than the unmodified electrodes.

Keywords: CuO nanoleaves; Multiwalled carbon nanotubes; Folic acid; Electrochemical oxidation; DPV

Efficacy of highly water-dispersed fabricated nano ZnO against clinically isolated bacterial strains by Shouvik Mitra; Prasun Patra; Sourov Chandra; Panchanan Pramanik; Arunava Goswami (pp. 231-238).

Versatile use of zinc oxide nanoparticles (ZNPs) in semiconductors, optical device and solar cells has already been established. Herein we describe synthesis of surface-functionalized ZNP to highly water dispersible constituent and its antibacterial efficiency against clinically isolated bacterial system. ZNP was synthesized by single-step microwave-assisted route using an aqueous buffer solution. Surface of ZNP was functionalized by grafting of phosphonoacetic acid as the coupling agent. Transmission electron microscopy image suggested that functionalized ZNP was smaller in size in comparison with unfunctionalized one. Antibacterial activity against clinically isolated bacterial strains of Escherichia coli, Staphylococcus aureus and Klebseilla sp. was detected with dose dependency. Functionalized ZNP claimed hexagonal crystal structure and exhibited higher dispersibility in aqueous solution which resulted in the production of greater reactive oxygen species and hence destruction of cell membrane leading to its biocidal efficacy. It is worth mentioning that functionalized dispersed fabricated ZNP would be used as potent biocides in medical as well as agricultural sector.

Keywords: Nano ZnO; Surface functionalized; Water dispersed; Antibacterial property

Effect of propylene carbonate as a plasticizer on (PEO)₅₀AgCF₃SO₃:SnO₂ nanocomposite polymer electrolyte by S. Austin Suthanthiraraj; M. Kumara Vadivel (pp. 239-246).

This work deals with the incorporation of propylene carbonate (PC) as a plasticizer in conjunction with poly (ethylene oxide) (PEO), silver triflate (AgCF₃SO₃) and nanocrystalline tin oxide (SnO₂) for obtaining the nanocomposite polymer electrolyte system (PEO)₅₀AgCF₃SO₃:2 wt% SnO₂ + x wt% PC (x = 10, 20, 30 and 40) by solution casting method. The present electrical conductivity data extracted by means of complex impedance spectroscopic analysis in the frequency range 20 Hz–1 MHz and over the temperature domain 298–373 K have demonstrated that the maximum electrical conductivity value of 5.9 × 10⁻⁵ S cm⁻¹ at 298 K would be possessed by the specimen containing 30 wt% PC incorporated into the optimized nanocomposite system (PEO)₅₀AgCF₃SO₃:2 wt% SnO₂. Silver ionic transference number (t _Ag+) data evaluated using AC/DC polarization technique have indicated that the highest t _Ag+ value of 0.52 could be realized in the case of the specimen (PEO)₅₀AgCF₃SO₃:2 wt% SnO₂ + 30 wt% PC, whereas the complexation of the plasticizer within the nanocomposite electrolyte has been deduced from the detailed Fourier transform infrared spectroscopic investigation owing to the fact that such results have revealed the appearance of absorption bands corresponding to free triflate ions (CF₃SO₃ ⁻) and PC. Surface morphological features of pure PEO and (PEO)₅₀AgCF₃SO₃:2 wt% SnO₂ + 30 wt% PC nanocomposite systems were analysed through scanning electron microscope. The feasibility of a reduction in the degree of crystallinity of the plasticized system has been indicated by the X-ray diffraction data and confirmed from differential scanning calorimetric results obtained in terms of quantification of crystallinity and reduction in the glass transition temperature due to the addition of the chosen plasticizer into the nanocomposite polymer electrolyte matrix. Interestingly, the all solid-state cell based on the nanocomposite polymer electrolyte, namely, (PEO)₅₀AgCF₃SO₃:2 wt% SnO₂ + 30 wt% PC and silver anode has exhibited an open circuit voltage of 676 mV and short circuit current of 192 μA at room temperature.

Keywords: Nanocomposites; Polymer electrolyte; Silver triflate; Plasticizer

Structural and magnetic properties of nanocrystalline BaFe₁₂O₁₉ synthesized by microwave-hydrothermal method by K. Sadhana; K. Praveena; S. Matteppanavar; B. Angadi (pp. 247-252).

Nanocrystalline BaFe₁₂O₁₉ powders were prepared by microwave-hydrothermal method at 200 °C/45 min. The as-synthesized powders were characterized by using X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA). The present powders were densified at different temperatures, i.e., 750, 850, 900 and 950 °C for 1 h using microwave sintering method. The phase formation and morphology studies were carried out using XRD and field emission scanning electron microscopy (FE-SEM). The average grain sizes of the sintered samples were found to be in the range of 185–490 nm. The magnetic properties such as saturation magnetization and coercive field of sintered samples were calculated based on magnetization curves. A possible relation between the magnetic hysteresis curves and the microstructure of the sintered samples was investigated.

Keywords: BaFe₁₂O₁₉ ; Microwave-hydrothermal method; Microwave sintering; Magnetic properties

Self-organized growth of bamboo-like carbon nanotube arrays for field emission properties by Balaji Padya; Dipankar Kalita; P. K. Jain; G. Padmanabham; M. Ravi; K. S. Bhat (pp. 253-259).

Well-aligned nitrogen-doped carbon nanotube (N-CNTs) film was fabricated on silicon substrate by thermal chemical vapor deposition process with varying the growth temperature. The effect of growth temperature on morphology, microstructure and crystallinity for the growth of N-CNTs was studied. At all growth temperatures, the bamboo-like morphology of graphene layers with compartments in CNTs were observed in transmission electron microscope micrographs. The doping level and the type of nitrogen-related moieties were determined by X-ray photoelectron spectroscopy analysis. The compartment distance decreases with increase in nitrogen doping level in hexagonal graphite network. The increase in nitrogen doping level in N-CNTs will lead to decrease in crystallinity and in-plane crystallite size. Field emission study of nitrogen-doped carbon nanotubes grown at optimum parameters showed that they are good emitters with a turn-on and threshold field of 0.3 and 1.6 V/μm, respectively. The maximum current density was observed to be 18.8 mA/cm² at the electric field of 2.1 V/μm. It is considered that the enhanced field emission performance of doped nanotube is due to the presence of lone pairs of electrons on nitrogen atom that supplies more electrons to the conduction band.

Keywords: Bamboo-like carbon nanotubes; Field emission; Turn-on field; Threshold field

Magnetoelectric properties of PbZr_0.53Ti_0.47O₃–Ni_0.65Zn_0.35Fe₂O₄ multiferroic nanocomposites by D. K. Pradhan; R. N. P. Chowdhury; T. K. Nath (pp. 261-273).

A different kind of multiferroics with ferroelectric–ferrimagnetic (FE–FM) composites: (1 − x) PbZr_0.53Ti_0.47O₃–x Ni_0.65Zn_0.35Fe₂O₄ with x = 0.10, 0.20 and 0.30, were synthesized by a powder-in-sol precursor hybrid processing route. Structural analysis with X-ray diffraction (XRD) data revealed the presence of both PbZr_0.53Ti_0.47O₃ (PZT) and Ni_0.65Zn_0.35Fe₂O₄ (NZFO) pure phases in the PZT–NZFO composites. Scanning electron micrographs (SEM) clearly disclose distribution of both PZT and NZFO phases throughout the sample. Dielectric and electrical properties of the system have been investigated in a wide range of frequency at different temperatures. Dielectric constant (ε_r) as a function of temperature reveals the paraelectric–FE transition temperature at ~408 °C having maximum value of ε_r at the peak [ε _r ^max = 1,200] with another low temperature anomaly at ~297 °C, very close to the magnetic Curie temperature of the NZFO ferrite (T _c = 300 °C) for the x = 0.1 FE–FM composite. The impedance spectroscopy data of these composites show clearly, contribution of both grain and grain boundary effect in the electrical properties of the composites. Negative temperature coefficient of resistance (NTCR) behavior of the materials indicates their semi-conducting nature. The ac conductivity spectrum is found to obey Johnscher’s power law very well. The temperature-dependent magnetization hysteresis (M–H) loops of the PZT/NZFO composite show excellent non-saturating ferrimagnetic behavior with increase in both coercive field (H _c) and remanent magnetization (M _r) when the NZFO content in the composite is increased. Polarization (P) versus electric field (E) studies at 300 K give conclusive evidence of the presence of spontaneous polarization in all the three composites (x = 0.1, 0.2 and 0.3). However, area of P–E loop, coercive field (E _c) and remanent polarization (P _r) are found to decrease noticeably with the increase of the NZFO content (x) in these composites.

Keywords: Ferroelectrics; Spinel ferrites; Multiferroics; Dielectrics; Impedance spectroscopy

Magnetoelectric and magnetodielectric properties of SBN–CMFO nanocomposites by S. R. Jigajeni; A. N. Tarale; D. J. Salunkhe; S. B. Kulkarni; P. B. Joshi (pp. 275-283).

The paper reports synthesis of nanoparticles of Sr_0.5Ba_0.5Nb₂O₆ (SBN) and Co1.2−xMn xFe_1.8O₄ (CMFO) via ceramic and hydroxide co-precipitation routes, respectively. The nanopowders of SBN–CMFO0.1 (MSBN0.1) and SBN–CMFO0.3 (MSBN0.3) are compacted together to form the desired magnetoelectric/magnetodielectric (ME/MD) composites. The Bi₂O₃ is used as a sintering aid. The Bi₂O₃ at three weight percent is observed to cause agglomeration of SBN and CMFO particles and improve the magnetomechanical coupling. The paper reports synthesis, structural and morphological studies on the MSBN composites. The composites are investigated for their dielectric, ME and MD properties. The results on the magnetocapacitance (MC) are observed interesting and could be correctly understood in terms of the stress-induced variation in the dielectric constant. The MC is observed to remain fairly constant between 10 and 500 kHz and possess a useful magnitude of nearly 4 %.

Keywords: (SrBa)Nb₂O₆ ; (CoMn)_1.2Fe_1.8O₄ ; ME composites; Magnetocapacitance

Effect of ablation time and laser fluence on the optical properties of copper nano colloids prepared by laser ablation technique by H. S. Desarkar; P. Kumbhakar; A. K. Mitra (pp. 285-291).

Copper (Cu) nanoparticles of average sizes (radius in nm) varying between 1.7 and 6 nm have been prepared by 1,064 nm Nd:YAG laser ablation of solid copper target in water medium. The nanostructures of the samples have been characterized using high-resolution transmission electron microscopes (HRTEM). The UV–visible absorption spectra obtained with a UV–visible spectrophotometer show sharp absorptions in the ultraviolet region and visible region due to the interband transition and surface plasmon resonance (SPR) oscillations in Cu nanoparticles, respectively. The increase in the linewidth of the SPR absorption peaks with the reduction in particle sizes are observed due to the intrinsic size effects. The behaviour of the UV–visible spectra associated with the Cu nanoparticles is studied as a function of laser fluence and laser ablation time.

Keywords: Cu nanoparticles; Laser ablation; Surface plasma resonance; Interband transition

Dendrimeric nano-glue material for localized surface plasmon resonance-based fiber-optic sensors by Jitendra Satija; Soumyo Mukherji (pp. 293-297).

In this study, we have investigated dendrimeric architecture as “nano-glue” material for RI-sensitive fiber-optic sensors. Dendrimers are immobilized on fiber-optic probes using a simple method that includes dipping, rinsing and drying of probes at room temperature. Dendrimer binding was confirmed by contact angle measurement and fluorescein isothiocyanate binding studies. These functionalized probes were coated with gold nanoparticles to develop localized surface plasmon resonance-based refractive index sensor. RI sensitivity measurement revealed that the dendrimeric matrix enhanced the RI sensitivity by 1.4-fold compared to two-dimensional amino-silanized sensor matrices. This suggests that dendrimer molecules are better choice as “nano-glue” material for fiber-optic sensors.

Keywords: Dendrimer; Fiber-optic sensor; Gold nanoparticles; Refractive index sensor; Localized surface plasmon resonance

Synthesis and characterization of chitosan–silver nanocomposite by S. Govindan; E. A. K. Nivethaa; R. Saravanan; V. Narayanan; A. Stephen (pp. 299-303).

Chitosan–silver (CS–Ag) nanocomposite materials were synthesized by a simple chemical method. The synthesized CS–Ag nanocomposite contains 20 wt% silver. Silver nanoparticles were synthesized by chemical reduction method as well. The CS–Ag nanocomposite was characterized using Field emission scanning electronic microscope (FESEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The XRD pattern indicated the presence of both silver and chitosan in the nanocomposite. It is observed from the XRD pattern of silver that it is of cubic structure. The spherical morphology of silver nanoparticles was confirmed from the FESEM image. FTIR spectroscopy was used for the structural elucidation. CS–Ag nanocomposite exhibits good antimicrobial and antitumor properties.

Keywords: Nanocomposite; Biocompatible; Chitosan; Silver

Effect of Y-doping on optical properties of multiferroics BiFeO₃ nanoparticles by A. Mukherjee; Sk. M. Hossain; M. Pal; S. Basu (pp. 305-310).

We have synthesized yttrium-doped bismuth ferrite nanoparticles through a modified Pechini technique. X-ray diffractometer, transmission electron microscope (TEM) and ultraviolet–visible spectrophotometer (UV–Vis) probes have been utilized to characterize the nanoparticles. Average particle size estimated from TEM found to be 29 nm for Bi_0.99Y_0.01FeO₃ samples. The band gap of the prepared BFO and BYFO nanoparticles varies from 1.97 to 2.29 eV, that is, within the visible range of the sunlight. This property of these nanoparticles can be utilized in photo catalytic decomposition of organic contaminants, such as Rhodamine-B (RhB) under visible light irradiation. We have explored and observed that RhB degrade up to 8 % while mixed with Bi_0.90Y_0.1FeO₃ for 1 h under 40 W lamp due to photo catalysis together with sensitization.

Keywords: Multiferroics; Y-doped BiFeO₃ nanoparticles; Band gap; Photo catalyst

Investigations on nanocrystalline BST-LSMO magnetodielectric composites by M. M. Sutar; A. N. Tarale; S. R. Jigajeni; S. B. Kulkarni; P. B. Joshi (pp. 311-317).

The paper reports the synthesis of Ba1−xSr xTiO₃ (BST) for x = 0.20, 0.25, and 0.30 via hydroxide co-precipitation route to result into the BST nanoparticles of size nearly 50 nm. The La_0.67Sr_0.33MnO₃ (LSMO) is also synthesized using co-precipitation route to achieve nanocrystaline particles. Further, the magnetodielectric (MD) composites of BST0.20, BST0.25, and BST0.30 are formed by addition of the LSMO at y = 0.1 and 0.2. The parent BST compositions are analysed for its dielectric properties. The composite LSMO-BST (LBST) is investigated for the variation of dielectric constant and impedance spectra as a function of applied magnetic field for the frequency between 500 Hz to 1 MHz. The observations on MD effect show that the dielectric constant possesses contributions due to magnetic field dependant interfacial polarization and variations due to the induced stress.

Keywords: BST; LSMO; Ferroelectric; Magnetodielectric composites; Magneto-capacitance

In silico determination of surface entropy of 1-D copper nanostructures by A. Dutta; M. Bhattacharya; N. Gayathri; G. C. Das; P. Barat (pp. 319-323).

Metallic one-dimensional (1-D) nanostructures are widely studied owing to their important role in developing electronic and electromechanical systems at the nanoscale. In the context of their structures, the large surfaces play a governing role in dictating many of their fundamental characteristics and hence, the surface properties are the most vividly studied issues. In the present work, we employ the harmonic oscillator model to analyze the thermodynamic properties of 1-D copper nanostructures. Our simulations reveal that owing to the large surface to volume ratio, the structural energies of these nanomaterials significantly exceed that of the bulk copper. Nevertheless, the harmonic oscillator approach enables us to directly evaluate the free energy of the system and eventually provides the associated entropy. The calculations are performed for three different crystal orientations and the results clearly indicate that the per atom entropy of thinner nanostructures is larger than their bulk counterpart. This increment in entropy is attributable to the increased degrees of freedom of the surface atoms and has the tendency of stabilizing the surface structure. The harmonic oscillator model works over a reasonable range of temperature and the technique demonstrated here is well extendable to other nanomaterials of interest.

Keywords: 1-D Nanostructure; Atomistic simulation; Harmonic oscillator; Surface entropy

Effect of aggregation on thermal conductivity and viscosity of nanofluids by Gaganpreet; Sunita Srivastava (pp. 325-331).

Nanofluids have drawn large attention because they exhibit anomalous behaviour in their thermo physical properties. There has been an enormous innovation in heat transfer applications of these fluids especially to industrial sectors including transportation, power generation, cooling, thermal therapy for cancer treatment, etc. In the present work, we have studied the anomalous increase in the thermal conductivity and viscosity of nanofluids by taking clustering as one of the causes. It is assumed that the nanoparticles may aggregate on dispersion. Few of these nanoparticles may just touch each other, whereas others may do so along with interfacial layer developed around them (analogous to porous media). The variation in thermal conductivity has been studied with particle concentration, concentration of aggregates and thickness of interfacial layer. The concept of aggregation and equivalent volume fraction has also been used in Kreiger and Dougherty (K-D) model to study the viscosity of nanofluids. The obtained results for thermal conductivity agree well with the available experimental results when the effect of different types of clusters is taken into account. Viscosity increases with the increase in particle aggregate (r _a) and is found to match well for r _a = 3r at low concentration.

Keywords: Thermal conductivity; Viscosity; Aggregation; Nanofluids

Actin-based motility propelled by molecular motors by Sai Pramod Upadyayula; Murali Rangarajan (pp. 333-338).

Actin-based motility of Listeria monocytogenes propelled by filament end-tracking molecular motors has been simulated. Such systems may act as potential nanoscale actuators and shuttles useful in sorting and sensing biomolecules. Filaments are modeled as three-dimensional elastic springs distributed on one end of the capsule and persistently attached to the motile bacterial surface through an end-tracking motor complex. Filament distribution is random, and monomer concentration decreases linearly as a function of position on the bacterial surface. Filament growth rate increases with monomer concentration but decreases with the extent of compression. The growing filaments exert push–pull forces on the bacterial surface. In addition to forces, torques arise due to two factors—distribution of motors on the bacterial surface, and coupling of torsion upon growth due to the right-handed helicity of F-actin—causing the motile object to undergo simultaneous translation and rotation. The trajectory of the bacterium is simulated by performing a force and torque balance on the bacterium. All simulations use a fixed value of torsion. Simulations show strong alignment of the filaments and the long axis of the bacterium along the direction of motion. In the absence of torsion, the bacterial surface essentially moves along the direction of the long axis. When a small amount of the torsion is applied to the bacterial surface, the bacterium is seen to move in right-handed helical trajectories, consistent with experimental observations.

Keywords: Actin-based motility; Molecular motor; Simulation; Listeria

Nanospherical heterolayer in strong electrostatic field by V. A. Harutyunyan (pp. 339-344).

The influence of a strong homogeneous electric field on the states of charge carriers in the structure of quantum dot–quantum well (QDQW) is studied theoretically. It is shown that a strong external field changes radically the character of carrier motion in the structure and leads to an additional field-localization of the particle along the polar angle variable. An explicit form of the wave functions and energy spectrum of single-particle states in the structure in the presence of an external field is obtained. The possibilities of experimental and operational applications of the theoretical results obtained for the study of core/layer/shell structures as well as of hollow spheres are also shown.

Keywords: Nanoheterolayer; Electrostatic field; Localization

Structural stability of nitrogen-doped ultrathin single-walled boron nanotubes: an ab initio study by Sandeep Kumar Jain; Pankaj Srivastava (pp. 345-349).

Ab initio calculations have been performed for determining structural stabilities of nitrogen-doped ultrathin single-walled boron nanotube. We have considered ultrathin boron nanotubes of diameters <0.5 nm, which include mainly three conformations of BNTs viz. zigzag (5,0), armchair (3,3) and chiral (4,2) with diameters 4.60, 4.78 and 4.87 Å, respectively. It has been investigated that α-BNTs are highly stable, while hexagonal BNTs are found to be least stable. In view of increasing structural stability of hexagonal BNTs, substitutional doping of foreign atoms, i.e. nitrogen is chosen. The nitrogen atoms substitute the host atoms at the middle of the tubes. The substitution doping is made with all the three conformations. The structural stabilities of BNTs have been investigated by using density functional theory (DFT). Subsequently, the cohesive energy is calculated, which directly measures the structural stability. The cohesive energy of BNTs has been calculated for different nitrogen concentrations. We found that the structures get energetically more stable with increasing nitrogen concentration. Moreover, it is also revealed that all the three BNTs are almost equally stable for single-atom doping, while the armchair BNT (3,3) is highly stable followed by zigzag (5,0) and chiral (4,2) BNTs for two- and three-atom doping. The structural stability is an important factor for realization of any physical device. Thus, these BNTs can be used for field emission, semiconducting and highly conducting devices at nanoscale.

Keywords: Boron nanotube; Nitrogen-doped nanotube; Structural stability; Cohesive energy; Ultrathin nanotubes; Formation energy

A DFT study for the structural and electronic properties of Zn mSe n nanoclusters by Phool Singh Yadav; Dheeraj Kumar Pandey (pp. 351-357).

An ab initio study has been performed for the stability, structural and electronic properties of 19 small zinc selenide Zn mSe n (m + n = 2–4) nanoclusters. Out of these nanoclusters, one nanocluster is found to be unstable due to its imaginary vibrational frequency. A B3LYP-DFT/6-311G(3df) method is used in the optimization of the geometries of the nanoclusters. We have calculated the zero point energy (ZPE), which is ignored by the other workers. The binding energies (BE), HOMO–LUMO gaps and bond lengths have been obtained for all the optimized nanoclusters. For the same value of ‘m’ and ‘n’, we designate the most stable structure the one, which has maximum final binding energy (FBE) per atom. The adiabatic and vertical ionization potentials (IP) and electron affinities (EA), dipole moments and charge on atoms have been investigated for the most stable nanoclusters. For the same value of ‘m’ and ‘n’, the nanocluster containing maximum number of Se atoms is found to be most stable.

Keywords: DFT study; Semiconductor; Nanoclusters; HOMO–LUMO gap

A density functional study on equilibrium geometries, stabilities and electronic properties of Au₅Li binary clusters by Ajanta Deka; Ramesh Chandra Deka (pp. 359-364).

All electron scalar relativistic calculations have been performed to investigate the electronic structures of isomeric Au₅Li binary clusters at the BLYP/DNP level of theory. The properties of these clusters are compared with the pristine Au₆ clusters. As in case of the pure Au₆ cluster, the minimum energy structure of the bimetallic Au₅Li cluster is triangular with the lithium atom at the mid position. It is found that substitution of a gold atom by a lithium atom in the Au₆ clusters leads to an increase in the binding energy per atom, the HOMO–LUMO gap and the chemical hardness of the structures. Thus, lithium substitution leads to stabilization of the Au₆ clusters. Further, the response of various sites of the minimum-energy triangular Au₅Li and Au₆ clusters towards impending electrophilic and nucleophilic attacks has been determined using DFT-based local reactivity descriptors. It is found that lithium substitution leads to an increase in the number of sites prone to attack by nucleophiles like CO or H₂O.

Keywords: Binary clusters; Lithium substitution; Density functional theory; Relative electrophilicity; Relative nucleophilicity

Spatial correlation in 2D and 3D thin films of conserved binary mixtures in the presence of wetting of substrates by the preferred majority component: interpretation in real scenario by Satya Pal Singh (pp. 365-369).

The spinodal decomposition has got fresh attraction in the past few decades with the advent of new computational problems under very thin geometries. The nanodrops evolve in the phase separation process. The phase separation process itself interplays with the wetting forces and give rise to structures of importance for a wide range of technological applications from spherical nanomagnetic domains to magnetic strips. MC simulation programs for 2D and 3D cases have been written for surface directed phase separation (using metropolis algorithm) to observe the spatial correlation varying with time, which shows a polynomial fitting behavior for 2D case and follow a peculiar trend with time specially, in early stages of evolution indicating a colossal behavior. The two point correlations (Pearson’s linear xy correlation function) if evaluated in 3D case do not show any important oscillatory behavior but instead confirm for the two regimes as phase separation or mixing and the wetting ones. The correct generalization of xy correlation as xyz correlation in 3D case (i.e., product of the three moments) does not seem to be a reliable one because it moves to six to seven decimal places, thus comes out at the cost of loss in confidence limit. Thus, the 3D simulation confirm the two regime behavior indicating that the same colossal behavior of 2D case can exist in real 3D thin film of random binary mixture. Thus, the colossal behavior as obtained for the case of 2D problem is retained, and this may indicate for a quantized or discrete colossal behavior for certain set of composition and interface parameters for definite but small time periods. The corresponding density profiles are also plotted to confirm the distributions of the two components. Such computational studies may help in developing theoretical models for the observed phenomena and to search out for new events at the very bottom of the scale.

Keywords: SDPS; Nanodomains; Spatial correlation; Wetting crossover

Investigations on optical transitions in InAs/InP quantum dash structures by Sanjib Kabi; Abhijit Biswas; Dipankar Biswas; Salil Kumar Biswas (pp. 371-375).

In this paper, we report the dependence of the Gaussian nature of absorption spectra of InAs/InP shallow quantum dot or quantum dash systems on the depth of the dash and also on its relative standard deviation. The dash is considered to be an elongated quantum box with a square base having finite potentials at the boundaries. Our observations reveal that the absorption spectra of the quantum dashes are strongly sensitive to the depth and also on the standard deviation of the dash depth. Predicted results help unveil a better physical insight regarding the optical properties of InAs/InP quantum dash structures. The results are in excellent agreement with reported experimental data of photoluminescence and absorption.

Keywords: Quantum dot; Quantum dash; Gaussian distribution; Absorption

A molecular dynamics simulation study for the mechanical properties of different types of carbon nanotubes by Keka Talukdar; Apurba Krishna Mitra (pp. 377-383).

Carbon nanotubes have caught tremendous attention of the researchers during the last decade due to their excellent mechanical, electrical, optical and thermal properties. The exploitation of these fibers as reinforcing agents in making strong fiber composites has been a primary research topic in the recent investigations on composite materials. Although the theoretical results are rather optimistic, the goal of achieving high strength of the carbon nanotube composites is still not satisfactorily realized. We report here a comparative study of the mechanical properties of single-walled, multi-walled and bundle of single-walled carbon nanotubes. Their mechanical behavior is investigated by molecular dynamics simulation, considering Brenner’s second generation reactive empirical bond order interatomic potential between the carbon atoms making a tube. For a long range interaction, we have defined a weak van der Waals force which acts between different layers of a multi-walled tube or between different tubes of a bundle. Samples of three isolated armchair single-wall carbon nanotubes of different diameters, a multi-wall armchair carbon nanotube and finally a bundle of three armchair single-walled nanotubes of same diameter are taken. Their fracture pattern and buckling behavior are modeled and compared. Significant changes are observed in the mechanical properties of the samples of different types of carbon nanotubes which arise due to the interaction between the shells of a multi-walled tube or the tubes in a bundle.

Keywords: SWCNT; SWCNT bundle; MWCNT; Mechanical properties; MD simulation; Fracture

First-principles study of naphthalene-based single-electron transistor by Sweta Parashar; Pankaj Srivastava; Manisha Pattanaik (pp. 385-388).

We have performed first-principle calculations based on density functional theory (DFT) and non-equilibrium greens functions (NEGF) for calculating the charging energies of molecular system weakly coupled to an environment. We apply this approach to the molecule naphthalene, which is lying flat on gate dielectric between the source and drain electrodes. Our calculated values of charging energy for naphthalene in an isolated case are in good agreement with experimental values. Further, in an electrostatic environment, the result shows renormalization of molecular energy levels and therefore reduces the charging energy of naphthalene. Subsequently, the charge stability diagram of naphthalene based single-electron transistor (SET) has been obtained by calculating the charging energies as a function of an external gate potential. This diagram shows the dependence of SET conductance on the gate voltage and the source-drain bias. Our implementation is intended to predict the charging energies of the naphthalene-based SETs that reveals further scope in realization of the devices at nanoscale.

Keywords: Single-electron transistor; Charging energy; Ionization energy; Electron affinity; Charge stability diagram

First principles calculation on the structure and electronic properties of BNNTs functionalized with isoniazid drug molecule by Nabanita Saikia; Swapan K. Pati; Ramesh C. Deka (pp. 389-400).

One-dimensional nanostructures such as nanowires and nanotubes are stimulating tremendous research interest due to their structural, electronic and magnetic properties. We perform first principles calculation using density functional theory on the structural, and electronics properties of BNNTs adsorbed with isoniazid (INH) drug via noncovalent functionalization using the GGA/PBE functional and DZP basis set implemented in SIESTA program. The band structure, density of states and projected density of states (PDOS) plots suggest that isoniazid prefers to get adsorbed at the hollow site in case of (5,5) BNNT, whereas in (10,0) BNNT it favours the bridge site. The adsorption energy of INH onto (5,5) BNNT is smaller than in (10,0) BNNT which proposes that (10,0) BNNT with a larger radius compared to (5,5) BNNT is more favourable for INH adsorption as the corresponding distortion energy will also be quite lower. Functionalization of (5,5) and (10,0) BNNTs with isoniazid displays the presence of new impurity states (dispersionless bands) within the HOMO–LUMO energy gap of pristine BNNT leading to an increase in reactivity of the INH/BNNT system and lowering of the energy gap of the BNNTs. The PDOS plots show the major contribution towards the dispersionless impurity states is from INH molecule itself rather than from BNNT near the Fermi energy region. To summarize, noncovalent functionalization of BNNTs with isoniazid drug modulates the electronic properties of the pristine BNNT by lowering its energy gap with respect to the Fermi level, as well as demonstrating the preferential site selectivity for adsorption of isoniazid onto the nanotube sidewalls of varying chirality.

Keywords: BNNTs; Isoniazid; DFT; Electronic structure; Wavefunction

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Applied Nanoscience (v.2, #3)

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Applied Nanoscience (v.2, #3)