Journal of Nano Research Vol. 24

Abstract: Structural and magnetic properties of ⁵⁷Fe/Ti/Co multilayers (MLs), prepared by Ion beam sputtering on Si substrate have been studied as a function of trilayers (TLs) thickness and modulation periods. X-ray reflectivity (XRR) shows the successful growth of high-quality layered structures along with up to 3^rd order Bragg peaks with distinct Kiessig oscillation. X-ray diffraction (XRD) and Mössbauer studies evidence the formation of different phases mainly at the interfaces. Soft magnetic properties with high saturation values (~800emu/cm³) and high anisotropy field (~20kOe) are observed in the room temperature magnetization curve. The in plane value of coercivities are 18Oe and 60Oe for the 12 and 24 TLs respectively while in the out-of plane direction it increases to nearly 8 and 12 times respectively. The 12 TLs sample shows the presence of two fold anisotropy whereas the 24 TLs sample shows an isotropic behaviour. Low temperature DC magnetization studies evidence the presence of weak antiferromagnetic coupling while the Kelly Henkel plots for these samples show that the dominant exchange interactions between the grains are ferromagnetic.

Abstract: Pure and Aluminium-doped ZnO (Zn_1-xAl_xO) x = 0 to 5 wt% thin films were deposited onto glass substrate by sol-gel spin coating method. The influence of various aluminium concentration in ZnO thin films on the structural, surface, optical and photoconducting properties were investigated. The GIXRD studies confirmed the polycrystalline nature with wurtzite structure of pure and Al doped ZnO films. Films with 1.5 % concentration of aluminium showed maximum absorption and transmission in the UV and visible regions respectively. The FESEM images showed crack free films with increasing grain boundaries upon doping. The average grain size is found to decrease due to aluminium doping. AFM images showed doped films with 1.5 % have better smoothness than other films. The photoconductivity measurements reveal that there is increase in the photocurrent compared to dark current for the Al doped ZnO. The photocurrent reaches its maximum value for ZnO: Al-1.5 % and then decreases upon increase in Al concentration. The photoresponse has slightly degraded upon aluminium doping onto ZnO. Temperature dependent conductivity shows that the thermal activation energy for the film decreases up to 1.5 % aluminium concentration and then increases for other concentrations in the temperature range 308 to 375K.

Abstract: Chitosan is a modified form of Chitin. It is a modified carbohydrate polymer derived by hydrolyzing the aminoacetyl groups of chitin. Chitosan is a biodegradable natural polymer which is, biocompatible, non-toxic. It also shows anti-bacterial properties. This polysaccharide is available in different forms such as nanoparticles, solution, powder, flake, fiber, film, etc. Due to its wide range of physical forms and good reactivity with other compounds, chitosan can produce various blends. Nanoparticles of various natural biopolymers have emerged as potential carrier for drugs in oral controlled drug delivery. Nanostructured drug carriers allow the delivery of not only small-molecule drugs but also of nucleic acids and proteins. Chemical modification of nanoparticles of chitosan is useful for the association of bioactive molecules to polymer and controlling the drug release profile. In recent years focus on chitosan is shifted to its derivatives. This versatile material has broad applications in many different fields. Various physical forms of chitosan and its blends together with other derivatives such as composites and graft copolymers have been developed to overcome limitations of different polymeric materials such as poor mechanical properties and to improve its functionality towards specific applications. Nanoparticles of chitosan and it derivatives are extensively exploited in the field of oral drug delivery. The progress made in converting chitosan and its blends into nanoparticles forms as well as the preparation methods are studied. For preparation of these blends and nanoparticles of chitosan need to be dissolved in for reactions. We also studied its dissolution behavior with different acids. It shows quite interesting results.

Abstract: ZnO nanoparticles were prepared by chemical method using starch as capping agent. Also the polyaniline-zinc oxide (PANI-ZnO) nanocomposites were prepared by in-situ polymerization of aniline monomer with ZnO nanomaterials. The structure and morphology of the ZnO nanoparticles were investigated by X-ray diffraction and scanning electron microscopy. X-ray diffraction revealed the wurtzite structure of ZnO. Average particle size of the ZnO nanoparticles were also calculated from XRD. SEM micrographs showed the spherical shape of ZnO nanoparticles. Band gap energy of ZnO nanoparticles was determined from UV absorbance spectra and confirm quantum confinement. In UV-Vis spectra of PANI salt, two absorption peaks are observed at 320 and 630 nm. These absorption peaks arises due to excitation of the benzene segment including amine structures in polyaniline. A considerable large red shift at 360 nm from 320 nm has been observed for PANI-ZnO nanocomposites. This prominent red shift might occur due to the interaction between the hydroxyl groups of ZnO and the quinoid ring of emeraldine salt. Transport properties of PANI-ZnO nanocomposites were studied in terms of transport parameters such as DC electrical conductivity (σ), charge localization length (α^-1), most probable hopping distance ® and hopping energy (w) using variable range hopping model as described by Ziller to conducting polymers.

Abstract: Ion beam irradiation is a unique non-equilibrium technique for phase formation and material modification. Localized rise in temperature and ultra fast (~10¹² s) dissipations of impinging energy make it an attractive tool for nanostructure synthesize. Dense electronic excitation induced spatial and temporal confinement of high energy in a narrow dimension leads the system to a highly non-equilibrium state and the system then relaxes dynamically inducing nucleation of nanocrystals along the latent track. In the present investigation, amorphous thin films of TiO₂ are irradiated by 100 MeV Ag ion beam. These irradiated thin films are characterized by Atomic Force Microscopy (AFM), Glancing Angle X-ray Diffraction (GAXRD), Transmission Electron Microscopy (TEM) and UV-VIS absorption spectroscopy. AFM and TEM studies indicate formation of circular nanoparticles of size 10±2 nm in a film irradiated at a fluence of 1×10¹² ions.cm^-2_. Nanophase formation is also inferred from the blueshift observed in UV-VIS absorption band edge.

Abstract: Innovations in materials technology in the fields of photovoltaics play an important role in the paradigm shift from fossil fuels to renewable energy sources. The use of solar energy is one of the most important problems in energy utilization. Dye sensitized solar cell (DSSC) technology has been recognized as a competitor to the well developed thin film solar cells. In the present investigation, we have fabricated a device using natural Lawsone (Heena) dye which was used to sensitize zinc oxide (ZnO) films. ZnO seed layer was deposited using chemical bath deposition and slurry was used to deposit ZnO films followed by sintering at 450°C for 30 minutes in air. Performance of nanostructure ZnO photoelectrode using lawsone dye as a function of residence time in the dye solution was studied. For 20 hour dye loading time, we were observed power conversion efficiency around 0.5% which is more as compared to 5 and 14 hours dye loading time.

Abstract: Under tensile deformation, gold nanosheets elongate to form defects via a series of small vacancies leading to structural deformations. Behavior of finite gold nanosheets containing 57 and 73 atoms under load are investigated modeled by many-body Gupta potential. Nanosheets with close packed structure (111) plane of a face-centered-cubic structure are stretched along one of the two symmetry directions of the plane. The accessibility of these structures and their stability under load are found to be the key factors governing the morphological evolution of the gold nanosheets. It is found that major deformation is the formation of vacancies which could be called defects in the sheets and is surprisingly different from the ultimate stretching of a nanocylinder which is via neck formation. Thus this study presents completely new theoretical results for gold nanosheets.

Abstract: We present the structural, surface and electrical properties of La_0.7Ca_0.3MnO₃ (LCMO) thin films of varying film thicknesses from 150 nm to 300 nm on single crystal LaAlO₃ (LAO) (h00) oriented substrate, prepared using Chemical Solution Deposition (CSD) technique. X-ray diffraction study shows that all LCMO films are epitaxial and (h00) oriented. With increasing film thickness all the films displayed excellent transport properties such as a low resistivity, very high metal-insulator transition temperature (T_P). All the LCMO films show T_P above 275 K. The sharp transition causes highest TCR ~6.10 %/K and FCR ~50 %/T at around room temperature in CSD grown LCMO thin films, which has not been reported so far. A strong dependence of the electrical resistivity and TCR on film thickness is attributed to the oxygen optimization and variation in lattice parameter caused by residual compressive strain of the LCMO films.

Abstract: Ag nanoparticles were grown on glass substrate by spin coating of Ag ions (AgNO₃) solution followed by either chemical reduction, in aqueous hydrazine or NaBH₄ solution, or by thermal reduction in H₂ environment. Effects of different reducing agent have been explained. Morphology and absorbance spectra ofAg nanoparticles films, measured by using Scanning Electron Microscopy (SEM) and UV-visible Spectrophotometer techniques, are used to understand effect of reduction process on growth of Ag nanoparticles. To grow uniformly size distributed Ag nanoparticles thermal reduction in H₂ is better than chemical reduction by aqueous either NaBH₄ orhydrazine hydrate solutions.

Abstract: Nanocrystalline Cobalt-doped TiO₂ was prepared by Sol-Gel technique, followed by freeze-drying treatment at-30°C temperature for 12hrs. The obtained Gel was thermally treated at 200,400,600, 800°C. 1%, 2% and 4% Cobalt doped TiO₂ nanopowder has been prepared X-ray Powder Diffraction (XRD), Scanning Electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), was used to study its structural properties. The XRD pattern shows the coexistence of anatase phase and rutile phase. Thermal gravimetric analysis shows Cobalt concentration affects thermal decomposition. UV-Vis Spectroscopy, Photo luminescence (PL), was used to study its Optical properties. Optical Bandgap were calculated with the incorporation of different concentration of cobalt. UV-Visible spectroscopy show variation in band gap for the sample treated at different temperature for same concentration. All Cobalt doped TiO₂ nanostructures shows an appearance of Red shift relative to the bulk TiO₂. The determination of magnetic properties was also carried out by Vibrating Sample Magnetometer.