Structural, topographical and magnetic evolution of RF-sputtered Fe-Ni alloy based thin films with thermal annealing

Metglas 2826 MB having a nominal composition of Fe40Ni38Mo4B18 is an excellent soft magnetic material and finds application in sensors and memory heads. However, the thin-film forms of Fe40Ni38Mo4B18 are seldom studied, although they are important in micro-electro-mechanical systems/nano-electromechanical systems devices. The stoichiometry of the film plays a vital role in determining the structural and magnetic properties of Fe40Ni38Mo4B18 thin films: retaining the composition in thin films is a challenge. Thin films of 52 nm thickness were fabricated by RF sputtering technique on silicon substrate from a target of nominal composition of Fe40Ni38Mo4B18. The films were annealed at temperatures of 400 °C and 600 °C. The micro-structural studies of films using glancing x-ray diffractometer (GXRD) and transmission electron microscope (TEM) revealed that pristine films are crystalline with (FeNiMo)23B6 phase. Atomic force microscope (AFM) images were subjected to power spectral density analysis to understand the probable surface evolution mechanism during sputtering and annealing. X-ray photoelectron spectroscopy (XPS) was employed to determine the film composition. The sluggish growth of crystallites with annealing is attributed to the presence of molybdenum in the thin film. The observed changes in magnetic properties were correlated with annealing induced structural, compositional and morphological changes

Evolution of structural and magnetic properties of Co–Fe based metallic glass thin films with thermal annealing

Ultra thin films based on CoFe were prepared from a composite target employing thermal evaporation. The microstructure of the films was modified by thermal annealing. The relationship between microstructure and magnetic properties of the films was investigated using techniques like glancing angle X-ray diffraction (GXRD), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). The GXRD and TEM investigations showed an onset of crystallization of CoFe at around 373 K. The magnetic softness of the films improved with thermal annealing but at higher annealing temperature it is found to be deteriorating. Annealing inducedmodification of surface morphology of the alloy thin filmswas probed by atomic force microscopy (AFM). Surface smoothening was observed with thermal annealing and the observed magnetic properties correlate well with surface modifications induced by thermal annealing

Spatial Variability and Contamination of Heavy Metals in the Inter-tidal Systems of a Tropical Environment

Heavy metals in the surface sediments of the two coastal ecosystems of Cochin, southwest India were assessed. The study intends to evaluate the degree of anthropogenic influence on heavy metal concentration in the sediments of the mangrove and adjacent estuarine stations using enrichment factor and geoaccumulation index. The inverse relationship of Cd and Zn with texture in the mangrove sediments suggested the anthropogenic enrichment of these metals in the mangrove systems. In the estuarine sediments, the absence of any significant correlation of the heavy metals with other sedimentary parameters and their strong interdependence revealed the possibility that the input is not through the natural weathering processes. The analysis of enrichment factor indicated a minor enrichment for Pb and Zn in mangrove sediments. While, extremely severe enrichment for Cd, moderate enrichment for Zn and minor enrichment of Pb were observed in estuarine system. The geo accumulation index exhibited very low values for all metals except Zn, indicating the sediments of the mangrove ecosystem are unpolluted to moderately polluted by anthropogenic activities. However, very strongly polluted condition for Cd and a moderately polluted condition for Zn were evident in estuarine sediments

Synthesis and characterization of 3d-transition metals doped ZnO thin films and nanostructures for possible spintronic applications

The objective of the present study is the formation of single phase Zn1−xTMxO thin films by PLD and increase the solubility limit of TM dopants. The TM doped ZnO nanostructures were also grown by hydrothermal method. The structural and morphological variation of ZnO:TM thin films and nanostructures with TM doping concentration is also investigated. The origin and enhancement of ferromagnetism in single phase Zn1−xTMxO thin films and nanostructures using spectroscopic techniques were also studied. The dependence of ablation parameters on the structural and optical properties of ZnO thin films were studied

Tailoring Magnetic Properties of Co-Fe Thin Films by Topographical Modifications Using Thermal Annealing and Swift Heavy Ion Irradiation and Fabrication of Magnetoelectric Multilayers for Device Applications

Magnetism and magnetic materials have been playing a lead role in improving the quality of life. They are increasingly being used in a wide variety of applications ranging from compasses to modern technological devices. Metallic glasses occupy an important position among magnetic materials. They assume importance both from a scientific and an application point of view since they represent an amorphous form of condensed matter with significant deviation from thermodynamic equilibrium. Metallic glasses having good soft magnetic properties are widely used in tape recorder heads, cores of high-power transformers and metallic shields. Superconducting metallic glasses are being used to produce high magnetic fields and magnetic levitation effect. Upon heat treatment, they undergo structural relaxation leading to subtle rearrangements of constituent atoms. This leads to densification of amorphous phase and subsequent nanocrystallisation. The short-range structural relaxation phenomenon gives rise to significant variations in physical, mechanical and magnetic properties. Magnetic amorphous alloys of Co-Fe exhibit excellent soft magnetic properties which make them promising candidates for applications as transformer cores, sensors, and actuators. With the advent of microminiaturization and nanotechnology, thin film forms of these alloys are sought after for soft under layers for perpendicular recording media. The thin film forms of these alloys can also be used for fabrication of magnetic micro electro mechanical systems (magnetic MEMS). In bulk, they are drawn in the form of ribbons, often by melt spinning. The main constituents of these alloys are Co, Fe, Ni, Si, Mo and B. Mo acts as the grain growth inhibitor and Si and B facilitate the amorphous nature in the alloy structure. The ferromagnetic phases such as Co-Fe and Fe-Ni in the alloy composition determine the soft magnetic properties. The grain correlation length, a measure of the grain size, often determines the soft magnetic properties of these alloys. Amorphous alloys could be restructured in to their nanocrystalline counterparts by different techniques. The structure of nanocrystalline material consists of nanosized ferromagnetic crystallites embedded in an amorphous matrix. When the amorphous phase is ferromagnetic, they facilitate exchange coupling between nanocrystallites. This exchange coupling results in the vanishing of magnetocrystalline anisotropy which improves the soft magnetic properties. From a fundamental perspective, exchange correlation length and grain size are the deciding factors that determine the magnetic properties of these nanocrystalline materials. In thin films, surfaces and interfaces predominantly decides the bulk property and hence tailoring the surface roughness and morphology of the film could result in modified magnetic properties. Surface modifications can be achieved by thermal annealing at various temperatures. Ion irradiation is an alternative tool to modify the surface/structural properties. The surface evolution of a thin film under swift heavy ion (SHI) irradiation is an outcome of different competing mechanism. It could be sputtering induced by SHI followed by surface roughening process and the material transport induced smoothening process. The impingement of ions with different fluence on the alloy is bound to produce systematic microstructural changes and this could effectively be used for tailoring magnetic parameters namely coercivity, saturation magnetization, magnetic permeability and remanence of these materials. Swift heavy ion irradiation is a novel and an ingenious tool for surface modification which eventually will lead to changes in the bulk as well as surface magnetic property. SHI has been widely used as a method for the creation of latent tracks in thin films. The bombardment of SHI modifies the surfaces or interfaces or creates defects, which induces strain in the film. These changes will have profound influence on the magnetic anisotropy and the magnetisation of the specimen. Thus inducing structural and morphological changes by thermal annealing and swift heavy ion irradiation, which in turn induce changes in the magnetic properties of these alloys, is one of the motivation of this study. Multiferroic and magneto-electrics is a class of functional materials with wide application potential and are of great interest to material scientists and engineers. Magnetoelectric materials combine both magnetic as well as ferroelectric properties in a single specimen. The dielectric properties of such materials can be controlled by the application of an external magnetic field and the magnetic properties by an electric field. Composites with magnetic and piezo/ferroelectric individual phases are found to have strong magnetoelectric (ME) response at room temperature and hence are preferred to single phasic multiferroic materials. Currently research in this class of materials is towards optimization of the ME coupling by tailoring the piezoelectric and magnetostrictive properties of the two individual components of ME composites. The magnetoelectric coupling constant (MECC) (_ ME) is the parameter that decides the extent of interdependence of magnetic and electric response of the composite structure. Extensive investigates have been carried out in bulk composites possessing on giant ME coupling. These materials are fabricated by either gluing the individual components to each other or mixing the magnetic material to a piezoelectric matrix. The most extensively investigated material combinations are Lead Zirconate Titanate (PZT) or Lead Magnesium Niobate-Lead Titanate (PMNPT) as the piezoelectric, and Terfenol-D as the magnetostrictive phase and the coupling is measured in different configurations like transverse, longitudinal and inplane longitudinal. Fabrication of a lead free multiferroic composite with a strong ME response is the need of the hour from a device application point of view. The multilayer structure is expected to be far superior to bulk composites in terms of ME coupling since the piezoelectric (PE) layer can easily be poled electrically to enhance the piezoelectricity and hence the ME effect. The giant magnetostriction reported in the Co-Fe thin films makes it an ideal candidate for the ferromagnetic component and BaTiO3 which is a well known ferroelectric material with improved piezoelectric properties as the ferroelectric component. The multilayer structure of BaTiO3- CoFe- BaTiO3 is an ideal system to understand the underlying fundamental physics behind the ME coupling mechanism. Giant magnetoelectric coupling coefficient is anticipated for these multilayer structures of BaTiO3-CoFe-BaTiO3. This makes it an ideal candidate for cantilever applications in magnetic MEMS/NEMS devices. SrTiO3 is an incipient ferroelectric material which is paraelectric up to 0K in its pure unstressed form. Recently few studies showed that ferroelectricity can be induced by application of stress or by chemical / isotopic substitution. The search for room temperature magnetoelectric coupling in SrTiO3-CoFe-SrTiO3 multilayer structures is of fundamental interest. Yet another motivation of the present work is to fabricate multilayer structures consisting of CoFe/ BaTiO3 and CoFe/ SrTiO3 for possible giant ME coupling coefficient (MECC) values. These are lead free and hence promising candidates for MEMS applications. The elucidation of mechanism for the giant MECC also will be the part of the objective of this investigation.

Ferrocene-Based Pyridylphosphine Ligands – Coordination Chemistry of Group 10, 11 and 12 Metals

English: The present thesis describes the synthesis of 1,1’-ferrocendiyl-based pyridylphosphine ligands, the exploration of their fundamental coordination chemistry and preliminary experiments with selected complexes aimed at potential applications. One main aspect is the synthesis of the bidentate ferrocene-based pyridylphosphine ligands 1-(Pyrid-2-yl)-1’-diphenylphosphinoferrocene, 1-(Pyrid-3-yl)-1’-diphenylphosphinoferrocene and 1-[(Pyrid-2-yl)methyl]-1’-diphenylphosphinoferrocene. A specific feature of these ligands is the ball-bearing like flexibility of the ferrocenebased backbone. An additional flexibility element is the rotation around the C–C single bonds. Consequently, the donor atoms can realise a wide range of positions with respect to each other and are therefore able to adapt to the coordination requirements of different metal centres. The flexibility of the ligand also plays a role in another key aspect of this work, which concerns the coordination mode, i. e. bridging vs. chelating. In addition to the flexibility, also the position of the donor atoms to each other is important. This is largely affected by the position of the pyridyl nitrogen (pyrid-2-yl vs. pyrid-3-yl) and the methylen group in 1-[(Pyrid-2-yl)methyl]-1’-diphenylphosphinoferrocene. Another interesting point is the combination of a soft phosphorus donor atom with a harder nitrogen donor atom, according to the HSAB principle. This combination generates a unique binding profile, since the pi-acceptor character of the P site is able to stabilise a metal centre in a low oxidation state, while the nitrogen sigma-donor ability can make the metal more susceptible to oxidative addition reactions. A P,N-donor combination can afford hemilabile binding profiles, which would be ideal for catalysis. Beyond 1,2-substituted ferrocene derivatives, which are quite successful in catalytic applications, 1,1’-derivatives are rather underrepresented. While a low-yield synthetic pathway to 1-(Pyrid-2-yl)-1’-diphenylphosphinoferrocene was already described in the literature [I. R. Butler, Organometallics 1992, 11, 74.], it was possible to find a new, improved and simplified synthetic pathway. Both other ligands were unknown prior to this work. Satisfactory results in the synthesis of 1-(Pyrid-3-yl)-1’-diphenylphosphinoferrocene could be achieved by working in analogy to the new synthetic procedure for 1-(Pyrid-2-yl)-1’-diphenylphosphinoferrocene. The synthesis of 1-[(Pyrid-2-yl)methyl]-1’-diphenylphosphinoferrocene has been handled by the group of Prof. Petr Stepnicka from Charles University, Prague, Czech Republic. The synthesis of tridentate ligands with an analogous heterodentate arrangement, was investigated briefly as a sideline of this study. The major part of this thesis deals with the fundamental coordination chemistry towards transition metals of the groups 10, 11 and 12. Due to the well-established catalytic properties of analogous palladium complexes, the coordination chemistry towards palladium (group 10) is of particular interest. The metals zinc and cadmium (group 12) are also of substantial importance because they are redox-inert in their divalent state. This is relevant in view of electrochemical investigations concerning the utilisation of the ligands as molecular redox sensors. Also mercury and the monovalent metals silver and gold (group 11) are included because of their rich coordination chemistry. It is essential to answer questions concerning aspects of the ligands’ coordination mode bearing in mind the HSAB principle.

Many-body theory of laser-induced ultrafast demagnetization and angular momentum transfer in ferromagnetic transition metals

An electronic theory is developed, which describes the ultrafast demagnetization in itinerant ferromagnets following the absorption of a femtosecond laser pulse. The present work intends to elucidate the microscopic physics of this ultrafast phenomenon by identifying its fundamental mechanisms. In particular, it aims to reveal the nature of the involved spin excitations and angular-momentum transfer between spin and lattice, which are still subjects of intensive debate. In the first preliminary part of the thesis the initial stage of the laser-induced demagnetization process is considered. In this stage the electronic system is highly excited by spin-conserving elementary excitations involved in the laser-pulse absorption, while the spin or magnon degrees of freedom remain very weakly excited. The role of electron-hole excitations on the stability of the magnetic order of one- and two-dimensional 3d transition metals (TMs) is investigated by using ab initio density-functional theory. The results show that the local magnetic moments are remarkably stable even at very high levels of local energy density and, therefore, indicate that these moments preserve their identity throughout the entire demagnetization process. In the second main part of the thesis a many-body theory is proposed, which takes into account these local magnetic moments and the local character of the involved spin excitations such as spin fluctuations from the very beginning. In this approach the relevant valence 3d and 4p electrons are described in terms of a multiband model Hamiltonian which includes Coulomb interactions, interatomic hybridizations, spin-orbit interactions, as well as the coupling to the time-dependent laser field on the same footing. An exact numerical time evolution is performed for small ferromagnetic TM clusters. The dynamical simulations show that after ultra-short laser pulse absorption the magnetization of these clusters decreases on a time scale of hundred femtoseconds. In particular, the results reproduce the experimentally observed laser-induced demagnetization in ferromagnets and demonstrate that this effect can be explained in terms of the following purely electronic non-adiabatic mechanism: First, on a time scale of 10–100 fs after laser excitation the spin-orbit coupling yields local angular-momentum transfer between the spins and the electron orbits, while subsequently the orbital angular momentum is very rapidly quenched in the lattice on the time scale of one femtosecond due to interatomic electron hoppings. In combination, these two processes result in a demagnetization within hundred or a few hundred femtoseconds after laser-pulse absorption.

Relaxation and derelaxation of pure and hydrogenated amorphous silicon during thermal annealing experiments

The structural relaxation of pure amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) materials, that occurs during thermal annealing experiments, has been analyzed by Raman spectroscopy and differential scanning calorimetry. Unlike a-Si, the heat evolved from a-Si:H cannot be explained by relaxation of the Si-Si network strain but it reveals a derelaxation of the bond angle strain. Since the state of relaxation after annealing is very similar for pure and hydrogenated materials, our results give strong experimental support to the predicted configurational gap between a-Si and crystalline silicon

Impact of chlorophenols and heavy metals on soil microbiota: their effects on activity and community composition, and resistant strains with potential for bioremetiation

Pollution by toxic compounds is one of the most relevant environmental damages to ecosystems produced by human activity and, therefore, it must be considered in environmental protection and restoration of contaminated sites. According to this purposes, the main goal of this doctoral thesis has been to analyse the impact of several chlorophenols and heavy metals on the microbial communities of two typical Mediterranean soils. The ecological risk concentrations of each pollutant, which have been determined according to respirometric activity and changes in the microbial community composition, and the factors that influence on their effective toxic concentrations (bioavailable pollutants) have been analysed in order to predict their potential impact on different soil ecosystems and provide scientific data for the regulation of the soil protection policies. Moreover, resistant microorganisms with pollutant removal capacities have been isolated from artificially contaminated soil microcosms and tested in axenic cultures, to infer their potential usefulness for bioremediation.

Theoretical studies of systems of biochemical interest containing Fe and Cu transition metals

La presència de la química teòrica i computacional està augmentant en quasi tots els camps de la recerca en química. Els càlculs teòrics poden ajudar a entendre millor l'estructura, les propietats i la reactivitat de compostos metàl·lics d'àrees tan diferents com la química inorgànica, organometàl·lica i bioinorgànica. No obstant això, és imprescindible utilitzar la metodologia adequada per obtenir resultats teòrics fiables. Els estudis d'aquesta tesi es poden dividir en dos grups diferents. El primer grup inclou l'estudi teòric del mecanisme de reacció de diversos sistemes que contenen coure i tenen diferents estructures Cun-O2. Aquests estudies s'han dut a terme amb l'objectiu de profunditzar en la natura dels processos oxidants químics i biològics promoguts per sistemes que contenen coure. En la segona part de la tesi, s'estudia la fiabilitat de diferents tècniques utilitzades per estudiar l'estructura electrònica i la reactivitat de sistemes que contenen coure, ferro i altres metalls de transició.

Influence of dissolved organic matter on the solubility of heavy metals in sewage-sludge-amended soils

Sewage-sludge-amended soils generally contain elevated levels of organic matter and heavy metals compared to control soils. Because organic matter is known to complex with heavy metals, the solubility behavior of the organic matter in such soils may exert a significant influence on the solubility of the metals. Little is known about such a process. Using batch experiments in which the solubility of organic matter in a heavily sludge-amended soil was artificially manipulated, we show that the solubilities of the heavy metals copper (Cu), nickel (Ni), and lead (Pb) show a strong positive relationship to the solubility of organic matter, particularly at high pH. The results suggest that under field conditions, spatiotemporal variations in the solid-solution partitioning of organic matter may have a bearing on the environmental significance (mobility and bioavailability) of these heavy metals.

Availability of heavy metals for uptake by Salix viminalis on a moderately contaminated dredged sediment disposal site

Extractability of Cd. Cr, Cu, Ni, Pb, and Zn in a dredged sediment disposal site was assessed using single extraction Procedures (H2O; 0.01 M CaCl2; 1 M NH4OAc NH4OAc-EDTA. CaCl2-TEA-DTPA). Only Cd and Zn were Found to exceed statutory threshold values for total content. The field was planted with Salix viminalis "Orm" and accumulation of heavy metals in bark, leaves, roots, and wood was evaluated at seven sampling locations along an observed gradient in texture and pollution. Biomass production was high, ranging from 13.2 to 17.8 t ha(1) y(1) dry weight. Metal accumulation in aboveground Plant parts Was low. amounting to the following annually extracted mass or metals per ha: 5034 g Zn, 83 g Cd. W g Cu. 83 g Pb, 12 g Ni and 6 g Cr. The use of accumulating clones and the use of soil amendments might enhance extraction efficiency in future research. (C) 2005 Elsevier Ltd. All rights reserved.

Potential of Brassic rapa, Cannabis sativa, Helianthus annuus and Zea mays for phytoextraction of heavy metals from calcareous dredged sediment derived soils

Remediation of soil pollution is one of the many current environmental challenges. Anthropogenic activity has resulted in the contamination of extended areas of land, the remediation of which is both invasive and expensive by conventional means. Phytoextraction of heavy metals from contaminated soils has the prospect of being a more economic in situ alternative. In addition, phytoextraction targets ecotoxicologically the most relevant soil fraction of these metals, i.e. the bioavailable fraction. Greenhouse experiments were carried out to evaluate the potential of four high biomass crop species in their potential for phytoextraction of heavy metals, with or without with the use of soil amendments (EDTA or EDDS). A calcareous dredged sediment derived surface soil, with high organic matter and clay content and moderate levels of heavy metal pollution, was used in the experiments. No growth depression was observed in EDTA or EDDS treated pots in comparison to untreated controls. Metal accumulation was considered to be low for phytoextraction purposes, despite the use of chelating agents. The low observed shoot concentrations of heavy metals were attributed to the low phytoavailability of heavy metals in this particular soil substrate. The mobilising effects induced by EDTA in the soil were found to be too long-lived for application as a soil amendment in phytoextraction. Although EDDS was found to be more biodegradable, higher effect half lives were observed than reported in literature or observed in previous experiments. These findings caution against the use of any amendment, biodegradable or otherwise, without proper investigation of its effects and the longevity thereof. (C) 2005 Elsevier Ltd. All rights reserved.