31 research outputs found
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Study of thin metal films and oxide materials for nanoelectronics applications
Appendix A Pages 132-134 have been removed from this online version of the thesis for publisher copyright reasons. These had contained page images from the cover of Nanotechnology, Vol. 21, Nov 2010 and its corresponding web alertDifferent types of thin metal films and oxide materials are studied
for their potential application in nanoelectronics: gold and copper
films, nickel nanoelectrodes, oxide nanograin superconductors, carboxyl
ferromagnetic microspheres and graphene oxide flakes. The
crystallization and surface morphology of gold and copper films on
SiO2/Si substrates is investigated as a function of annealing temperature.
Annealing arranges the Au crystallites in the [111] direction and
changes the morphology of the surface. Relaxation of the Au layer at
high temperatures is responsible for the initial stages of cluster formation.
These may form at disordered points on the surface and become
islands when the temperature is increased. In the case of Cu/SiO2/Si films, oxides are formed after thermal oxidation at different temperatures
up to 1000 °C. The phase evolution Cu -> Cu + Cu2O -> Cu2O
-> Cu2O + CuO -> CuO is detected. Pure Cu2O films are obtained
at 200 °C, whereas uniform CuO films without structural surface defects
are obtained in the temperature range 300 - 550 °C. A resistivity
phase diagram, which is obtained from the current-voltage response
of the copper oxides, is presented. In the case of thin nickel films,
the necessary reagents, conditions and processes required to obtain
nano and atomic gaps between soft and clean nickel electrodes are described
by using a conventional electrochemical cell. Current-voltage
characteristics are also presented to evaluate possible applications of
the nanogap electrodes in electronic nanodevices.
In addition to the metal surfaces, oxides materials such as the superconductor
LaCaBaCu3O7 (La1113), carboxyl ferromagnetic microparticles
and graphene oxide flakes are studied. La1113 is a high critical temperature superconductor with TC(onset) = 80 K and its
structure is similar to the tetragonal YBCO. This thesis explores the
attachment of La1113 nanograins on Au(111) surfaces through selfassembled
monolayers of HS-C8H16-HS [octane (di)thiol] for their potential
application in nanotransistors. It is found that La1113 particles
(100 nm mean diameter) can be functionalized by octane (di)thiol
without affecting their superconducting critical temperature (TC = 80
K). A design for a superconducting transistor fabricated by immobilized
La1113 nanograins in between two gold electrodes which could
be controlled by an external magnetic field gate is suggested. Furthermore,
the mechanical reorientation of thiolated ferromagnetic microspheres
bridging a pair of gold electrodes under an external magnetic
field is studied. Finally, a
flexible film made of graphene oxide flakes
is prepared and characterized by X ray diffraction. It is achieved by
the chemical oxidation of commercial graphite and the subsequent reaction
with NaOH. It is found that the interlayer distance between
graphene increases upon oxidation due to the formation of chemical
groups and results in the delamination and
flexibility of the flakes.This work was supported by the European Union Program ALBAN (grant number E06D101257PE), the Cambridge Overseas Trust and the Japan Society for the Promotion of Science (grant number P12030
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Carbothermal reduction of mill scales formed on steel billets during continuous casting
AbstractA billet is a bar made from crude steel which surface contains scales which are rich in iron oxides. This study presents the carbothermal reduction of the scales formed in steel billets. The process included the reaction of the iron oxides contents with carbon (in ratio 5:1) and annealing in a tubular furnace under argon atmosphere. The occurred reactions are discussed using thermodynamic calculations and thermal analysis which indicate a three-stage reduction process Fe3O4 ➔ FeO ➔ Fe3C ➔α-Fe with intermediate reactions at the interval temperature 960 and 1300 °C. The X-ray diffraction confirms the reduction to α-Fe with minor presence of unreacted C, magnetite and wustite. Mössbauer spectroscopy analysis was performed at room temperature where a typical sextet corresponding to the dominant α-Fe is shown as well as wustite, magnetite and cementite to a lesser extent. The magnetization measurements confirm the ferromagnetic state corresponding to the α-Fe.</jats:p
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Characterization of steel billet scales generated during the continuous casting process in SIDERPERU steel plant
AbstractTons of waste is produced during iron steel’s industrial production, creating environmental pollution. This work aims to characterize the steel scale formed on the billet surface during the last step of steel production in the SIDERPERU steel plant. Scanning Electron Microscopy (SEM) shows stacked layers one above the other on steel billets scales surface. Energy Dispersive X-ray (EDX) and X-ray Fluorescence (XRF) reveal the high content of Fe and O, with Ca, Si, Mn, and Cr as minority elemental compounds. X-ray Diffraction (XRD) shows FeO, α-Fe2O3 and Fe3O4 as crystallographic phases. Magnetometry reveals Verwey transition and paramagnetic signals that screen the Morin transition. Mössbauer Spectroscopy at room temperature displays magnetic and non-magnetic parts. The non-magnetic part has the hyperfine parameters corresponding to predominant nonstoichiometric wustite. Octahedral (Fe+2/Fe3+) and tetrahedral Fe+3 hyperfine fields of 46.0 and 49.4 T values respectively are associated to nonstoichiometric magnetite and another sextet with a hyperfine field of 52.0 T is related to hematite.</jats:p
Characterization of copper microelectrodes, following a homemade lithography, technique, and gold electroless deposition
We report the fabrication and characterization of copper microelectrodes obtained by a homemade lithography technique and after gold electroless deposition. For the fabrication, planes consisting of arrays of electrodes (black in color) with bow tie shape were designed and printed on a transparent paper (Canson ltd.). Using an embroidery frame with a silk fabric, a photographic emulsion was spread on the silk and simultaneously pressing the Canson paper on it. The system was introduced into a closed box and exposed with a UV light. The designed electrode templates prevented direct exposition of the UV light over copper films and indelible ink was spread over it. After the ink was dried, the copper film is immersed into ferric acid to attack the uncovered copper parts (where there is no ink). In this way, we obtained copper electrodes with initial gap separation of ~142μm and subsequently, they followed electroless deposition of gold to make the copper electrodes to contact. For the characterization, electrical measurements were performed. They present ohmic resistance values in the order of 106 Ω produced by surface scattering of the electrons within the gold microwire and enhanced by oxidation of the copper electrodes
Characterization of copper microelectrodes, following a homemade lithography, technique, and gold electroless deposition
ABSTRACT We report the fabrication and characterization of copper microelectrodes obtained by a homemade lithography technique and after gold electroless deposition. For the fabrication, planes consisting of arrays of electrodes (black in color) with bow tie shape were designed and printed on a transparent paper (Canson ltd.). Using an embroidery frame with a silk fabric, a photographic emulsion was spread on the silk and simultaneously pressing the Canson paper on it. The system was introduced into a closed box and exposed with a UV light. The designed electrode templates prevented direct exposition of the UV light over copper films and indelible ink was spread over it. After the ink was dried, the copper film is immersed into ferric acid to attack the uncovered copper parts (where there is no ink). In this way, we obtained copper electrodes with initial gap separation of ~142μm and subsequently, they followed electroless deposition of gold to make the copper electrodes to contact. For the characterization, electrical measurements were performed. They present ohmic resistance values in the order of 10 6 Ω produced by surface scattering of the electrons within the gold microwire and enhanced by oxidation of the copper electrodes
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Single-phase BiFeO<sub>3</sub> and BiFeO<sub>3</sub>-Fe<sub>2</sub>O<sub>3</sub> nanocomposite photocatalysts for photodegradation of organic dye pollutants.
The application of a novel BiFeO3 (BFO)-Fe2O3 composite (called BFOF) as a photocatalyst for the degradation of methylene blue is reported. To improve the photocatalytic effectiveness of BiFeO3, we synthesized the first BFOF photocatalyst by adjusting the molar ratio of Fe2O3 in BiFeO3 using microwave-assisted co-precipitation. The UV-visible properties of the nanocomposites showed excellent absorption of visible light and reduced electron-hole recombination properties compared to the pure phase BFO. Photocatalytic studies on BFOF10 (90% BFO, 10% Fe2O3), BFOF20 (80% BFO, 20% Fe2O3), and BFOF30 (70% BFO, 30% Fe2O3) have shown that they decompose Methylene Blue (MB) in sunlight better than the pure BFO phase in 70 minutes. The BFOF30 photocatalyst was the most effective at reducing MB when exposed to visible light (94%). Magnetic studies confirm that the most effective catalyst BFOF30 has excellent stability and magnetic recovery properties due to the presence of magnetic phase Fe2O3 in the BFO
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Single-phase BiFeO3 and BiFeO3-Fe2O3 nanocomposite photocatalysts for photodegradation of organic dye pollutants.
Acknowledgements: Pravallika Banoth acknowledges the National Fellowship for Scheduled Tribe Students (NFST) for SRF, funded by the Ministry of Tribal Affairs, Government of India (No. 19012/03/2018-Sch). We acknowledge the facilities provided by the University Grants Commission-Networking Resources (UGC-NRC) of the School of Physics, University of Hyderabad, India. The authors acknowledge funding from the Institute of Eminence project, MHRD, UoH-IoE-RC2-21-017.The application of a novel BiFeO3 (BFO)-Fe2O3 composite (called BFOF) as a photocatalyst for the degradation of methylene blue is reported. To improve the photocatalytic effectiveness of BiFeO3, we synthesized the first BFOF photocatalyst by adjusting the molar ratio of Fe2O3 in BiFeO3 using microwave-assisted co-precipitation. The UV-visible properties of the nanocomposites showed excellent absorption of visible light and reduced electron-hole recombination properties compared to the pure phase BFO. Photocatalytic studies on BFOF10 (90% BFO, 10% Fe2O3), BFOF20 (80% BFO, 20% Fe2O3), and BFOF30 (70% BFO, 30% Fe2O3) have shown that they decompose Methylene Blue (MB) in sunlight better than the pure BFO phase in 70 minutes. The BFOF30 photocatalyst was the most effective at reducing MB when exposed to visible light (94%). Magnetic studies confirm that the most effective catalyst BFOF30 has excellent stability and magnetic recovery properties due to the presence of magnetic phase Fe2O3 in the BFO