S. Shamaila

Magnetic switching of ferromagnetic nanotubes

The magnetic switching of ferromagnetic nanotubes as function of geometrical parameters has been investigated. The modes of magnetization reversal are observed to depend on the geometry of the nanotubes. Time dependent magnetization properties reveal that the nanotubes have strong magnetic viscosity effects. The values of magnetic viscosity coefficient (S) for different applied fields are high near the coercive field.

Gold Nanoparticles: An Efficient Antimicrobial Agent against Enteric Bacterial Human Pathogen

Enteric bacterial human pathogens, i.e., Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Klebsiella pneumoniae, are the major cause of diarrheal infections in children and adults. Their structure badly affects the human immune system. It is important to explore new antibacterial agents instead of antibiotics for treatment. This project is an attempt to explain how gold nanoparticles affect these bacteria. We investigated the important role of the mean particle size, and the inhibition of a bacterium is dose-dependent. Ultra Violet (UV)-visible spectroscopy revealed the size of chemically synthesized gold nanoparticle as 6–40 nm. Atomic force microscopy (AFM) analysis confirmed the size and X-ray diffractometry (XRD) analysis determined the polycrystalline nature of gold nanoparticles. The present findings explained how gold nanoparticles lyse Gram-negative and Gram-positive bacteria.

Electrochemical fabrication and magnetization properties of CoCrPt nanowires and nanotubes

Magnetization properties of CoCrPt alloy nanocylinders (nanowires and nanotubes) fabricated by low cost electrodeposition method have been investigated. Angular dependence of coercivity depicts curling mode of magnetization reversal process for CoCrPt nanowires (NWs) while for nanotubes (NTs) there is a transition from curling to coherent mode as a function of field angle. The effective anisotropy during reversal process is determined from a competition between the magnetostatic interactions, surface effects, and shape anisotropy in NTs while in NWs shape anisotropy is the dominant anisotropy. Furthermore, magnetization and remanence curves describe that the surface effects and dipolar coupling are increased in NTs as compared to the NWs due to their geometry. These results depict that the magnetization properties are influenced by the geometry of nanocylinders, which can become good candidate for ultrahigh density magnetic recording media.

Fabrication and Magnetization Reversal Processes for Co/Cu Multilayer Nanowires

Co/Cu multilayer nanowires fabricated in an array using anodized aluminium oxide (AAO) template has been investigated. Experimental conditions are optimized to fabricate Co/Cu multilayer systems with fixed Cu and variable Co layer thicknesses. Magnetization reversal mode is found to depend on the Co layer thickness. A transition occurs from coherent rotation to a combination of coherent and curling rotation at around t(Co) = 60 nm with increasing t(Co). The reversal modes have been investigated using the magnetic hysteresis loops measured at room temperature for Co/Cu nanowires placed at various angles between the directions of the nanowire axis and external fields using a vibrating sample magnetometer. The magnetic easy axis changes from the direction perpendicular to nanowires to that parallel to the nanowires at around t(Co) = 60 nm, indicating a change in the magnetization reversal mode. The reversal mode for the nanowires with thin disk-shaped Co layers is of a coherent rotation type, while that for long rod-shaped Co layers can be explained by a combination of coherent rotation and a curling mode.

BARIUM TITANATE FILMS FOR ELECTRONIC APPLICATIONS: STRUCTURAL AND DIELECTRIC PROPERTIES

Synthesis of the precursors, using research grade materials and locally available facilities, is optimized in order to obtain a suitable sol for BaTiO3. The optimally synthesized BaTiO3 sol is then spun onto Cu substrates to obtain films of thickness ~0.5 μm. The deposited BaTiO3 films are heated up to a temperature of 300°C. Surface and structural changes, with heating, are observed by optical microscope, scanning electron microscope, atomic force microscope, and X-ray diffraction. The surface cracked in some cases but is generally uniform, as seen with SEM and AFM, in case of optimized conditions. The SEM images reveal large crystallites, which are correlated to the XRD observation of tetragonal perovskite structure of these sol–gel films. The AFM scan, however, shows an rms roughness of 35.6 nm for an area of 3 μm × 3 μm. Tetragonal perovskite BaTiO3 is obtained at a temperature of as low as 300°C. The dielectric constant and loss angle, in the 30 Hz–3 MHz range, are calculated at room temperature and up to 200°C. At high frequencies the dielectric constant (~290) and loss angle (~2 × 10-6) values indicate the usefulness of such films in electronic applications. The leakage current is also measured at room temperature and a conductivity of 2.0 × 10-15 S/cm is obtained.

Ferromagnetic Nanowires and Nanotubes

Nowadays one of the most exciting areas in materials science is the study of nanomaterials due to their potential applications in fields as diverse as optics, electronics, catalysis, magnetism, electrochemistry, information processing and storage, etc. Preparation of inorganic, organic or organic-inorg anic hybrid materials in the nanometer scale can be achieved either by physical or chemical methods. In many cases it requires the use of solids presenting voids or cavities in which the material can be synthesized (Ozin, 1992). This field of nanotechnolog y represents an exciting and rapidly expanding area of research that crosses the borders between physical and engineering sciences. These ideas have driven scientists to develop methods for making nanostructures such as nanowires and nanotubes. Preparation of magnetic materials in the nanometer scale can be achieved by different methods, such as electrochemis try, nano-print techniques, physical deposition combined with micro-fabrication method etc. These techniques have been developed along with a significantly enhanced fundamental understanding (Cao, 2004; Xia et al., 2003; Huczko, 2000; Burda et al., 2005), though the field is involving rapidly with new synthesis methods and new kinds of nanowires or nanotubes. For the growth of nanowires and nanotubes, evaporation condensation growth has been demonstrated for the synthesis of various oxide nanowires and nanotubes. Similarly, dissolution-condensation method has been used for the synthesis of various metallic nanowires from solutions. Various elementary and compound semiconductor nanowires have been synthesized by vapor-liquid- solid (VLS) growth method (Duan & Lieber, 2000). Substrate ledge or step induced growth of nanowires or nanotubes, has also been under investigation (Zach et al., 2000). Among all these methods, the template-based electrodeposition is a very simple, effective, versatile and a low cost technique for the growth of nanowires and nanotubes of various materials. Particularly, the inexpensive formation of periodically ordered structures (e.g., nanotube and nanowire arrays) with a periodicity lower than 100 nm has triggered extensive activities in research. The present, huge progress in nanotechnology is a direct result of the modern trend towards the miniaturization of devices and the development of specific instrumentation that could visualize the nanoworld and allow surface to be studied at nanoscale resolution (Eftekhari, 2008). Practically all the traditional and modern experimental methods for materials growth are used to grow different nanostructured systems and as well as low dimension devices. The differences among the standard techniques of materials growth and the associated growth mechanisms have given place to two well defined strategies for nanostructures fabrication, i.e., nanophysics and nanochemistry (Ozin, 1992) also identified in the current scientific literature as top-down (Lundstrom, 2003) and bottom-up (Yang, 2003),

Antibacterial effects of laser ablated Ni nanoparticles

The interaction of nickel nanoparticles with Escherichia coli (E. coli) bacteria has been studied. The nickel nanoparticles have been fabricated by continuous wave laser ablation of nickel target and their properties are studied using different characterization techniques. The antibacterial activity of nickel nanoparticles was checked against E. coli bacteria. Escherichia coli were cultured in nutrients broth and different concentrations of nickel nanoparticles were added to bacterial culture solution to investigate the interaction of nickel nanoparticles with bacteria and to check toxicity of the nickel nanoparticles against E. coli. The fabricated Ni nanoparticles have exhibited considerable antimicrobial activity against E. coli.

Magnetization Reversal Mechanism for CoFeB Ferromagnetic Nanotube Arrays

CoFeB nanotube arrays are fabricated in anodic aluminum oxide (AAO) membranes and track etched polycarbonate (PCTE) membranes by using an electrochemical method, and their magnetic properties are investigated by vibrating sample magnetometry. The coercivity Hc and remanent squareness SQ of these CoFeB nanotube arrays are derived from hysteresis loops as a function of angle between the field and tube axis. The Hc(θ) curves for CoFeB nanotube arrays in AAO and PCTE membranes show M-type variation, while they change shape from M to mountain-type as the tube length increases. However, the overall easy axis perpendicular to tube axis does not change with tube length. The different angular dependences are attributed to different magnetization reversal mechanisms.