• Volume 29, Issue 6

      November 2006,   pages  547-651

    • Foreword

      S B Krupanidhi D Bahadur Satish Vitta

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    • Synthesis of B–Sb by rapid thermal annealing of B/Sb multilayer films

      S N Das A K Pal

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      Group III–V compound B–Sb films were synthesized from B/Sb/…/B multilayer films deposited by electron gun evaporation onto silicon substrate and subjecting the above multilayer to rapid thermal annealing at 773 K for 3 min. The films were characterized by XRD, TEM, XPS and optical studies. XPS studies indicated the ratio of B : Sb ∼1. XRD and electron diffraction patterns indicated the reflections from (100), (111), (102) and (112) planes of zinc blende BSb. Band gap evaluated from optical studies was ∼ 0.51 eV. Refractive index of the films varied between 1.65 and 2.18 with increasing energy of incident photon and plasma frequency (𝜔p) was estimated to be ∼ 2.378 × 10-14 s-1. The effective mass was computed to be ∼ 0.0845 m𝑒.

    • Surface plasmon effect in nanocrystalline copper/DLC composite films by electrodeposition technique

      S Hussain A K Pal

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      Composite films of nanocrystalline copper embedded in DLC matrix prepared by electrodeposition technique were studied for their optical properties. Particle size and metal volume fractions were tailored by varying the amount of copper containing salt in the electrolyte. Blue-shift of the surface plasmon resonance peak in the absorbance spectra of the films was observed with the reduction in size and volume fraction of metal particles. Mie theory was found to describe the experimental spectra quite well.

    • Optoelectronic and nonlinear optical processes in low dimensional semiconductors

      B P Singh

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      Spatial confinement of quantum excitations on their characteristic wavelength scale in low dimensional materials offers unique possibilities to engineer the electronic structure and thereby control their physical properties by way of simple manipulation of geometrical parameters. This has led to an overwhelming interest in quasi-zero dimensional semiconductors or quantum dots as tunable materials for multitude of exciting applications in optoelectronic and nonlinear optical devices and quantum information processing. Large nonlinear optical response and high luminescence quantum yield expected in these systems is a consequence of huge enhancement of transition probabilities ensuing from quantum confinement. High quantum efficiency of photoluminescence, however, is not usually realized in the case of bare semiconductor nanoparticles owing to the presence of surface states. In this talk, I will focus on the role of quantum confinement and surface states in ascertaining nonlinear optical and optoelectronic properties of II–VI semiconductor quantum dots and their nanocomposites. I will also discuss the influence of nonlinear optical processes on their optoelectronic characteristics.

    • A typical example of a photomagnetic study carried out on a spin-crossover material

      Jean-François Létard Chiara Carbonera Emilie Courcot José Sanchez Costa

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      The light-induced excited spin state trapping (LIESST) is a well known phenomenon in an iron(II) spin-crossover (SCO) material which offers some interesting prospects in data storage. In this work, we present a typical investigation of the photomagnetic properties of a SCO material. At the surface of the sample, the light-induced phenomenon is investigated by using a home-built reflectivity set up and in bulk material by using a quantum design SQUID magnetometer coupled to a light source.

    • High coercivity in nanostructured Co-ferrite thin films

      J H Yin B H Liu J Ding Y C Wang

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      Three methods including sol–gel, rf sputtering and pulsed laser deposition (PLD) have been used for the fabrication of high coercivity Co-ferrite thin films with a nanocrystalline structure. The PLD method is demonstrated to be a possible tool to achieve Co-ferrite films with high coercivity and small grain size at low deposition temperature. High coercivity, over 10 kOe, has been successfully achieved in Co-ferrite films with a thickness of ∼ 100 nm deposited using PLD with a substrate temperature at 550°C. The Co-ferrite films prepared by PLD at over 300°C on different substrates including amorphous glass, quartz and silicon exhibits an obvious (111) textured structure and possesses perpendicular anisotropy. Our study has also shown that the high coercivity is related with a large residual strain, which may induce an additional magnetic anisotropy (stress anisotropy) and at the same time serve as pinning centres, which can restrict the domain wall movement and therefore, increase the coercivity.

    • Towards a versatile platform based on magnetic nanoparticles for in vivo applications

      E Duguet S Vasseur S Mornet G Goglio A Demourgues J Portier F Grasset P Veverka E Pollert

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      Magnetic nanoparticles have attracted wide attention because of their usefulness as contrast agents for magnetic resonance imaging (MRI) or colloidal mediators for cancer magnetic hyperthermia. This paper examines these in vivo applications through an understanding of the problems involved and the current and future possibilities for resolving them. A special emphasis is made on magnetic nanoparticle requirements from a physical viewpoint, the factors affecting their biodistribution and the solutions envisaged for enhancing their half-life in the blood compartment and targeting tumour cells. Then, our synthesis strategies are presented and focused on covalent platforms based on maghemite and dextran and capable to be tailorderivatized by surface molecular chemistry. The opportunity of taking advantage of temperature-dependence of magnetic properties of some complex oxides for controlling the in vivo temperature is also discussed.

    • Energy landscapes for mobile ions in ion conducting solids

      S Adams

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      Structure property function relationships provide valuable guidelines in the systematic development of advanced functional materials with tailored properties. It is demonstrated that an augmented bond valence approach can be effectively used to establish such relationships for solid electrolytes. A bond valence analysis of local structure models for disordered systems or interfaces based on reverse Monte Carlo (RMC) fits or molecular dynamics (MD) simulations yields quantitative predictions of the ion transport characteristics. As demonstrated here for a range of metaphosphate and diborate glasses, the complete description of the energy landscape for mobile ions also provides an effective tool for achieving a more detailed understanding of ion transport in glasses. The investigation of time evolutions can be included, if the bond valence analysis is based on MD trajectories. In principle, this allows quantifying the time and temperature dependence of pathway characteristics, provided that a suitable empirical force-field is available. For the example of LiPO3, the remaining differences between simulated and experimental structures are investigated and a compensation method is discussed.

    • Assembly of Fe3O4 nanoparticles on SiO2 monodisperse spheres

      K C Barick D Bahadur

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      The assembly of superparamagnetic Fe3O4 nanoparticles on submicroscopic SiO2 spheres have been prepared by an in situ reaction using different molar ratios of Fe3+/Fe2+ (50–200%). It has been observed that morphology of the assembly and properties of these hybrid materials composed of SiO2 as core and Fe3O4 nanoparticles as shell depend on the molar ratio of Fe3+/Fe2+.

    • Morphological control and polarization switching in polymer dispersed liquid crystal materials and devices

      K K Raina Pankaj Kumar Praveen Malik

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      Liquid crystals dispersed in polymer systems constitute novel class of optical materials. The precise control of the liquid crystal droplet morphology in the polymer matrix is essentially required to meet the prerequisites of display device. Experiments have been carried out to investigate and identify the material properties and processing conditions required for the precise control of the droplet morphology of the dispersed liquid crystal systems. Polarization switching has been studied. Aligned liquid crystal dispersed systems showed higher polarization over unaligned ones.

    • Analysis of organometallics dispersed polymer composite irradiated with oxygen ions

      N L Singh Anjum Qureshi A K Rakshit D K Avasthi

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      Thin films of polymethyl methacrylate (PMMA) were synthesized. Ferric oxalate was dispersed in PMMA films. These films were irradiated with 80 MeV O6+ ions at a fluence of 1 × 1011 ions/cm2. The radiation induced changes in electrical conductivity, Mössbauer parameter, microhardness and surface roughness were investigated. It is observed that hardness and electrical conductivity of the film increases with the concentration of dispersed ferric oxalate and also with the fluence. It indicates that ion beam irradiation promotes

      1. the metal to polymer bonding and

      2. convert the polymeric structure into hydrogen depleted carbon network.

      Thus irradiation makes the polymer harder and more conductive. Before irradiation, no Mössbauer absorption was observed. The irradiated sample showed Mössbauer absorption, which seems to indicate that there is significant interaction between the metal ion and polymer matrix. Atomic force microscopy shows that the average roughness (𝑅a) of the irradiated film is lower than the unirradiated one.

    • Synthesis of nanocrystalline fluorinated hydroxyapatite by microwave processing and its in vitro dissolution study

      N Rameshbabu T S Sampath Kumar K Prasad Rao

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      Synthetic hydroxyapatite, (Ca10(PO4)6(OH)2, HA), is an important material used for orthopedic and dental implant applications. The biological hydroxyapatite in the human bone and tooth is of nanosize and differs in composition from the stoichiometric HA by the presence of other ions such as carbonate, magnesium, fluoride, etc. Osseointegration is enhanced by using nanocrystalline HA. This stimulates the interest in synthesizing nanocrystalline HA by different routes and among the methods, microwave processing seems to form the fine grain size and uniform characteristic nanocrystalline materials. Fluorinated hydroxyapatite, (FHA, Ca10(PO4)6(OH)2-𝑥F𝑥), possesses higher corrosion resistance in biofluids than pure HA and reduces the risk of dental caries. The present work deals with the synthesis of nanocrystalline FHAs by microwave processing. The crystal size and morphology of the nanopowders were examined by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) methods. The functional groups present in FHA powders were ascertained by Fourier transform infrared spectroscopy (FT–IR) and laser Raman spectroscopy. Since the physiological stability is an important parameter while selecting the material for implantation, the in vitro dissolution studies of FHAs with different fluorine contents were carried out.

    • One-pot size and shape controlled synthesis of DMSO capped iron oxide nanoparticles

      Debanjan Guin Sunkara V Manorama S Radha A K Nigam

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      We report here the capping of iron oxide nanoparticles with dimethyl sulfoxide (DMSO) to make chloroform soluble iron oxide nanoparticles. Size and shape of the capped iron oxide nanoparticles are well controlled by simply varying the reaction parameters. The synthesized nanocrystallites were characterized by thermal analysis (TG–DTA), powder X-ray diffraction (XRD), transmission electron microscopy (TEM) for evaluating phase, structure and morphology. 1H NMR spectra of the synthesized samples confirm DMSO, and the capping of DMSO on the ferrite samples. Shift of the S=O stretching frequency in Fourier transformed infrared (FTIR) spectra indicates that the bonding between DMSO and ferrite is through an oxygen moiety. The magnetic measurements of all the synthesized samples were investigated with a SQUID magnetometer which shows that the magnetic properties are strongly dependent on the size as well as shape of the iron oxide.

    • First order magneto-structural transition in functional magnetic materials: phase-coexistence and metastability

      S B Roy M K Chattopadhyay M A Manekar K J S Sokhey P Chaddah

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      First order magneto-structural transition plays an important role in the functionality of various magnetic materials of current interest like manganese oxide systems showing colossal magnetoresistance, Gd5(Ge, Si)4 alloys showing giant magnetocaloric effects and magnetic shape memory alloys. The key features of this magneto-structural transition are phase-coexistence and metastability. This generality is highlighted with experimental results obtained in a particular class of materials. A generalized framework of disorder influenced first order phase transition is introduced to understand the interesting experimental results which have some bearing on the functionality of the concerned materials.

    • Role of spin polarized tunneling in magnetoresistance and low temperature minimum of polycrystalline La1–𝑥K𝑥MnO3 (𝑥 = 0.05, 0.1, 0.15) prepared by pyrophoric method

      Soma Das T K Dey

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      The low temperature resistivity and magnetoresistance of bulk samples of La1–𝑥K𝑥MnO3 has been investigated between 10 K and 300 K with and without the magnetic field (𝐻 = 0.8 T). All the samples show metal–insulator transitions with Curie temperature (𝑇C) ranging between 260 K and 309 K. At temperature below 60 K, the K-doped manganites exhibit a shallow minimum, which disappears under an applied field of 0.8 T. This field dependent minimum in resistivity, observed in K-doped lanthanum manganites is explained in the light of intergrain tunneling of the charge carriers between anti-ferromagnetically coupled grains of the polycrystalline samples. The field variation of magnetoresistance below 𝑇C follows a phenomenological model which considers spin polarized tunneling at the grain boundaries. The intergranular contribution to the magnetoresistance is separated out from that due to spin polarized tunneling part at the grain boundaries. The temperature dependence of intrinsic contribution to the magnetoresistance follows the prediction of the double exchange model for all values of field at 𝑇 < 𝑇C.

    • Magnetoactive elastomeric composites: Cure, tensile, electrical and magnetic properties

      K Sasikumar G Suresh K A Thomas Reji John V Natarajan T Mukundan R M R Vishnubhatla

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      Magnetically active elastomer materials were prepared by incorporating nickel powder in synthetic elastomeric matrices, polychloroprene and nitrile rubber. Cure characteristics, mechanical, electrical and magnetic properties were experimentally determined for different volume fractions of magnetoactive filler. The cure time decreases sharply for initial filler loading and the decrease is marginal for additional loading of filler. The tensile strength and modulus at 100% strain was found to increase with increase in the volume fraction of nickel due to reinforcement action. The magnetic impedance and a.c. conductivity are found to increase with increase in volume fraction of nickel as well as frequency.

    • Functional finishing in cotton fabrics using zinc oxide nanoparticles

      A Yadav Virendra Prasad A A Kathe Sheela Raj Deepti Yadav C Sundaramoorthy N Vigneshwaran

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      Nanotechnology, according to the National Nanotechnology Initiative (NNI), is defined as utilization of structure with at least one dimension of nanometer size for the construction of materials, devices or systems with novel or significantly improved properties due to their nano-size. The nanostructures are capable of enhancing the physical properties of conventional textiles, in areas such as anti-microbial properties, water repellence, soil-resistance, anti-static, anti-infrared and flame-retardant properties, dyeability, colour fastness and strength of textile materials. In the present work, zinc oxide nanoparticles were prepared by wet chemical method using zinc nitrate and sodium hydroxide as precursors and soluble starch as stabilizing agent. These nanoparticles, which have an average size of 40 nm, were coated on the bleached cotton fabrics (plain weave, 30 s count) using acrylic binder and functional properties of coated fabrics were studied. On an average of 75%, UV blocking was recorded for the cotton fabrics treated with 2% ZnO nanoparticles. Air permeability of the nano-ZnO coated fabrics was significantly higher than the control, hence the increased breathability. In case of nano-ZnO coated fabric, due to its nano-size and uniform distribution, friction was significantly lower than the bulk-ZnO coated fabric as studied by Instron® Automated Materials Testing System. Further studies are under way to evaluate wash fastness, antimicrobial properties, abrasion properties and fabric handle properties.

    • Effect of annealing on magnetic properties and silicide formation at Co/Si interface

      Shivani Agarwal V Ganesan A K Tyagi I P Jain

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      The interaction of Co (30 nm) thin films on Si (100) substrate in UHV using solid state mixing technique has been studied. Cobalt was deposited on silicon substrate using electron beam evaporation at a vacuum of 4 × 10-8 Torr having a deposition rate of about 0.1 Å/s. Reactivity at Co/Si interface is important for the understanding of silicide formation in thin film system. In the present paper, cobalt silicide films were characterized by atomic force microscopy (AFM) and secondary ion mass spectroscopy (SIMS) in terms of the surface and interface morphologies and depth profile, respectively. The roughness of the samples was found to increase up to temperature, 300°C and then decreased with further rise in temperature, which was due to the formation of crystalline CoSi2 phase. The effect of mixing on magnetic properties such as coercivity, remanence etc at interface has been studied using magneto optic Kerr effect (MOKE) techniques at different temperatures. The value of coercivity of pristine sample and 300°C annealed sample was found to be 66 Oe and 40 Oe, respectively, while at high temperature i.e. 748°C, the hysteresis disappears which indicates the formation of CoSi2 compound.

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