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Title: Study of thin metal films and oxide materials for nanoelectronics applications
Author: De Los Santos Valladares, Luis
ISNI:       0000 0004 2733 9063
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2012
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Different 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.
Supervisor: Barnes, Crispin H. W. Sponsor: European Union Program ALBAN (grant number E06D101257PE) ; Cambridge Overseas Trust ; Japan Society for the Promotion of Science (grant number P12030)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral