In this Licentiate Thesis, the properties and effects of iron and iron oxide filled carbon nanotube (Fe-CNT) memories are investigated using experimental characterization and quantum physical theoretical models. Memory devices based on the simple assembly of Fe-CNTs between two metallic contacts are presented as a possible application involving the resistive switching phenomena of this material. It is known that the electrical conductivity of these nanotubes changes significantly when the materials are exposed to different atmospheric conditions. In this work, the electrical properties of Fe-CNTs and potential applications as a composite material with a semiconducting polymer matrix are investigated. The current voltage characteristics are directly related to the iron oxide that fills the nanotubes, and the effects are strongly dependent on the applied voltage history. Devices made of Fe-CNTs can thereby be designed fo gas sensors and electric memory technologies. The electrical characterization of the Fe-CNT devices shows that the devices work with an operation ratio (ON/OFF) of 5 μA. The applied operating voltage sequence is -10 V (to write), +8 V (to read ON), +10 V (to erase) and +8 V (to read OFF) monitoring the electrical current. This operation voltage (reading ON/OFF) must be sufficiently higher than the voltage at which the current peak appears; in most cases the peak position is close to 5 V. The memory effect is based on the switching behavior of the material, and this new feature for technological applications such as resistance random access memory (ReRAM). In order to better understand the memory effect in the Fe-CNTs, thesis also presents a study of the surface charge configuration during the operation of the memory devices. Here, Raman scattering analysis is combined with electrical measurements. To identify the material electronic state over a wide range of applied voltage, the Raman spectra are recorded during the device operation and the main Raman active modes of the carbon nanotubes are studied. The applied voltage on the carbon nanotube G-band indicates the presence of Kohn anomalies, which are strongly related to the material’s electronic state. As expected, the same behavior was shown by the other carbon nanotube main modes. The ratio between the D- and G-band intensities (ID/IG) is proposed to be an indicative of the operation’s reproducibility regarding a carbon nanotube memory cell. Moreover, the thermal/electrical characterization indicates the existence of two main hopping charge transports, one between the carbon nanotube walls and the other between the filling and the carbon nanotube. The combination of the hopping processes with the possible iron oxide oxygen migration is suggested as the mechanism for a bipolar resistive switching in this material. Based on these studies, it is found that the iron oxide which fills the carbon nanotube, is a major contribution to the memory effect in the material. Therefore, a theoretical study of hematite (i.e., α-Fe2O3) is performed. Here, the antiferromagnetic (AFM) and ferromagnetic (FM) configurations of α-Fe2O3 are analyzed by means of an atomistic first-principles method within the density functional theory. The interaction potential is described by the local spin density approximation (LSDA) with an on-site Coulomb correction of the Fe d-orbitals according to the LSDA+U method. Several calculations on hematite compounds with high and low concentrations of native defects such as oxygen vacancies, oxygen interstitials, and hydrogen interstitials are studied. The crystalline structure, the atomic-resolved density-of-states (DOS), as well as the magnetic properties of these structures are determined. The theoretical results are compared to earlier published LSDA studies and show that the Coulomb correction within the LSDA+U method improves both the calculated energy gaps and the local magnetic moment. Compared to the regular LSDA calculations, the LSDA+U method yields a slightly smaller unit-cell volume and a 25% increase of the local magnetic for the most stable AFM phase. This is important to consider when investigating the native defects in the compound. The effect is explained by better localization of the energetically lower Fe d-states in the LSDA+U calculations. Interestingly, due to the localization of the d-states the intrinsic α-Fe2O3 is demonstrated to become an AFM insulator when the LSDA+U method is considered. Using the LSDA+U approach, native defects are analyzed. The oxygen vacancies are observed to have a local effect on the DOS due to the electron doping. The oxygen and hydrogen interstitials influence the band-gap energies of the AFM structures. Significant changes are observed in the ground-state energy and also in the magnetization around the defects; this is correlated to Hund’s rules. The presence of the native defects (i.e., vacancies, interstitial oxygen and interstitial hydrogen) in the α-Fe2O3 structures changes the Fe–O and Fe–Fe bonds close to the defects, implying a reduction of the energy gap as well as the local magnetization. The interstitial oxygen strongly stabilizes the AFM phase, also decreases the band-gap energy without forming any defect states in the band-gap region. / <p>QC 20131107</p>

In this study, a magnetic nanomaterial was used for the binding of anionic arsenic species from contaminated groundwater. Iron oxide (Fe3O4) magnetic nanoparticles (NPs) and the surface modified Fe3O4 NPs with 3-aminopropyl-triethoxysilane (3-APTES), Trisodium citrare (TSC) and Chitosan were synthesized with the co-precipitation method. Structural characterizations showed that the four kinds of NPs had different sizes an average particle range size of 15-20 nm was observed with Transmission Electron Microscopy. X-ray diffraction was used to identify the crystalline structure of synthesized Fe3O4 and surface modified NPs. Molecular structure and functional groups present in synthesized magnetic NPs Fe3O4 were identify with infrared analysis. The synthesized Fe3O4 NPs and surface coated NPs were used for determine the binding capacity of Arsenic ions from the synthetic groundwater. The binding of As(III) increased as the dissolved As(III) concentration increased in the solution. From the experiments it was found chitosan-coated NPs are best than other coated and uncoated NPs for arsenite removal from the solution. It was found that if only As(III) ions were present in the water without other anions and cations the binding capacity of the magnetic NPs is very high. The binding capacity of As ions was decreased with presence of other anions and cations in the groundwater because they interfere with arsenic binding sites which presence on the magnetic NPs.

Superparamagnetic -Fe2O3 nanoparticles were synthesized by coprecipitation of ferric and ferrous salts with a base. Resulting nanoparticles were coated with shells, such as poly(N,N- dimethylacrylamide) (PDMAAm), neat and functionalized silica (SiO2 and SiO2-NH2), and polyaniline (PANI). PDMAAm shell was introduced by modification of iron oxide nanoparticle surface with an initiator and N,N-dimethylacrylamide was polymerized producing -Fe2O3&PDMAAm core-shell particles. In case of SiO2-NH2 shell, tetramethyl orthosilicate was used to yield -Fe2O3&SiO2 nanoparticles, which were subsequently modified by (3-aminopropyl)triethoxysilane to prepare γ-Fe2O3&SiO2-NH2 particles. Oxidation of aniline hydrochloride with ammonium persulfate in an aqueous solution of poly(N-vinylpyrrolidone) in the presence of iron oxides produced -Fe2O3&PANI nanoparticles. Finally, the last type of the particles was based on thionin-modified poly(carboxymethyl methacrylate) (PCMMA&Th). The particles were characterized by techniques, such as scanning and transmission electron microscopy (SEM and TEM) and dynamic light scattering (DLS) to determine the particle morphology and hydrodynamic diameter. The presence of the functional groups, chemical composition, and the iron content were investigated by Fourier-transform...

In this thesis the influence of deposition conditions and post-deposition annealing on the structure of ultrathin iron oxide films grown on magnesium oxide (MgO) substrates is studied. The main experimental technique used is synchrotron based x-ray diffraction (XRD) but also x-ray photoelectron spectroscopy (XPS) and low energy electron diffractions (LEED) are used to characterize the samples. Studying the dependency of film structure and thickness the stoichiometry and structure is changing with increasing film thickness. For large film thickness bulk like magnetite (Fe3O4) can be observed. With decreasing thickness the oxide phase is shifting towards a wüstite (FeO) phase. When changing the deposition rate and substrate temperature a strong influence on the Fe3O4 film structure is observed. With both decreasing deposition rates and substrate temperatures the occupancy of the tetrahedral sites is strongly decreasing while the octahedral sites remain almost unaffected. By post-deposition annealing under low oxygen atmosphere it is possible to increase the ordering of the tetrahedral sites. However, this is accompanied by significant diffusion of magnesium into the iron oxide film. During post-deposition annealing of a gamma-Fe2O3 film under high vacuum a reduction of the iron oxide is observed. Increasing the temperature, first, a reduction from gamma-Fe2O3 to Fe3O4 is observed. After further increasing the temperature a reduction from Fe3O4 to FeO is observed.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19189号 / 工博第4066号 / 新制||工||1627(附属図書館) / 32181 / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 北川 進, 教授 濵地 格, 教授 森 泰生 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Steel corrosion is one of the major distress mechanisms that causes the deterioration of reinforced concrete structures around the world. It is an electrochemical reaction between the reinforcing steel and the surrounding concrete that produces a mass loss of the metal. Through the process of corrosion in reinforced concrete, iron ions get oxidized to form corrosion products (CP). Although multiple experiments and studies have been developed to understand the rheological behavior of corrosion products, this topic stays inconclusive. This work aims to characterize corrosion products at micro-scale in order to trace the progress of the formation of rust, to determine its nature and to analyse its rheological behavior in reinforced concrete. An experimental procedure to produce CP in the laboratory is also presented in this research. In addition, material characterization methods have been used to identify the iron oxide phases present in CP, determine their viscosity and rheological behavior and to study how CP flows in a porous media. In order to identify the different stages in the corrosion process, the CP was analysed at 2, 4, 6 and 8 weeks. The experiments identified four phases of iron oxide for each period. Furthermore, it was found that CP behaves as a shear-thinning slurry and as a result, its viscosity decreases with the applied shear rate. In addition, the damage caused by CP on concrete depends on the w/c ratio of the concrete mix and the exposure time to a corroding environment. The rebar mass loss results show that CP is formed in layers around the rebar, and the flow of each CP layer can differ.

No description available.

<p> Aqueous ferrofluid has been prepared via precipitation of iron oxide into a polysaccharide gel matrix followed by degradation of the polymer to form a stable magnetic colloid. Nanocrystalline particles of iron oxide were formed in an alginate network by the alkaline hydrolysis and oxidation of the crosslinking agent, Fe2+, used to bind the linear polysaccharide chains. Methanol was used to inhibit the degradation of alginate by Fe2+ and oxygen during the precipitation and growth of iron oxide particles. In addition, the structural integrity of the gel was maintained in part by interaction between the iron oxide particulate and the alginate matrix. Controlled chemical degradation of the matrix resulted in a aqueous suspension of alginate-stabilized magnetic iron oxide particles. The resulting fluid is orange-brown in color, optically transparent, superparamagnetic and stable between 2.8<pH<10 </p> <p> The magnetic gels were isolated as 2mm beads containing ~2-20 mmole Fe. X-ray and electron diffraction patterns of the composite correspond to maghemite (γ-Fe2O3) and/or magnetite (Fe3O4). At room temperature, the composite material is superparamagnetic with saturation magnetizations in excess of 20 emu g^-1 at 30kOe. TEM photomicrographs of sectioned beads and of the magnetic fluid revealed the presence of spherical nanocrystalline oxide particles with diameters ranging from 3 nm to 6 nm. The iron oxide-alginate colloid has a diameter of 54nm with an average zeta potential of -51.6 mV.</p> / Thesis / Master of Science (MSc)

The capability of precisely controlling the kinetics of therapeutic delivery at the optimal location and rate for a given patient would have great potential to improve health and well-being in a range of current drug therapies (insulin, chemotherapeutics, vaccines, etc.). Indeed, if successfully developed, locally administered injectable drug delivery vehicles capable of remotely-triggered release would be the gold standard for many treatments. Multiple injectable nanocomposites have been investigated for this purpose that are generally comprised of a thermosensitive polymeric material and superparamagnetic iron oxide nanoparticles (SPIONs). SPIONs generate heat when exposed remote alternating magnetic fields (AMFs), and the transfer of this heat to thermosensitive polymers can be used to control the release of therapeutics. Ideally, these systems would be capable of returning to their original state and basal release rate when the external AMF trigger is removed. Several novel injectable nanocomposite materials that explore interactions between SPIONs and thermosensitive polymers to mediate drug release, from the macroscale to the nanoscale, were developed and demonstrated to be capable of remotely-triggered, AMF-mediated enhanced release. The macroscale magnetic nanocomposites have thermosensitive hydrogel and/or microgel components that regulate release based on the heat produced from SPIONs in response to an external AMF. On the millimeter-scale, a microinjection system capable of producing thermosensitive hydrogel beads that could potentially incorporate SPIONs is described. On the nanoscale, nanoparticles with a glass transition temperature and thermosensitive microgels are combined with SPIONs and investigated for their remote, AMF-mediated release characteristics. The engineered macroscale and nanoscale systems are capable of up to ~4:1 and ~7:1 enhancements in release due to an AMF application, respectively, compared to the basal release rate. Collectively, these nanocomposites represent a promising stride towards improved remote-actuation of drug release and a stepping stone for future attempts at precisely controlling the site and kinetics of drug release. / Thesis / Doctor of Philosophy (PhD) / This thesis focuses on the development of nanocomposite materials that can be injected into a specific location in the body and deliver therapeutic drugs by a remote-controlled process. These nanocomposites are composed of magnetic particles and polymers that respond to changes in temperature. The combination of these materials results in nanocomposites that can change their properties in response to specific magnetic fields to switch from releasing drug slowly (or not at all) to releasing drug quickly on demand. The changes are fully reversible and solely depend on whether the external magnetic field is switched on or off. These novel systems offer an alternative to therapies that require frequent injections, such as insulin for diabetes, or therapies that need the drug to be released in very precise locations, such as cancer treatments, and could improve the safety, reduce the risk of side effects, and lower the cost of many medical treatments.

No description available.