Structural, optical and magnetic characterisarion of pulsed laser deposited thin films of Zn1-xMxO (M= Mn, Fe, Ni, Cu) transparent magnetic alloys.
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Structural, optical and magnetic characterisarion of pulsed laser deposited thin films of Zn1-xMxO (M= Mn, Fe, Ni, Cu) transparent magnetic alloys.

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Structural, optical and magnetic characterisarion of pulsed laser deposited thin films of Zn1-xMxO (M= Mn, Fe, Ni, Cu) transparent magnetic alloys.

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dc.contributor.advisor Segura García del Río, Alfredo es_ES
dc.contributor.author John Gilliland, Samuel es_ES
dc.contributor.other Universitat de València - FÍSICA APLICADA es_ES
dc.date.accessioned 2010-07-07T15:33:21Z
dc.date.available 2010-07-07T15:33:21Z
dc.date.issued 2009 es_ES
dc.date.submitted 2009-04-02 es_ES
dc.identifier.uri http://www.tesisenred.net/TDX-0311110-121121/ es_ES
dc.identifier.uri http://hdl.handle.net/10550/15798
dc.description.abstract es_ES
dc.format.mimetype application/pdf es_ES
dc.language cat-en-es es_ES
dc.rights eng es_ES
dc.rights Copyright information available at source archive es_ES
dc.subject none es_ES
dc.title Structural, optical and magnetic characterisarion of pulsed laser deposited thin films of Zn1-xMxO (M= Mn, Fe, Ni, Cu) transparent magnetic alloys. es_ES
dc.type info:eu-repo/semantics/doctoralThesis es_ES
dc.description.abstractenglish Zn1-xMxO (M = Mn, Fe, Ni, Cu) films were deposited at optimal conditions over mica and sapphire substrates by laser ablation of polycrystalline targets containing stoichiometric mixtures of chemical compounds. These films were then characterised structurally, electronically, optically and magnetically. The structural characterisation was done by plume emission spectroscopy, XRD, XAS, XRF, electron microscopy and microanalysis to ensure that the expected films had been correctly deposited. Results indicated a constant chemical composition during the growth process and the resulting films grown over sapphire were found to be c-oriented. Maximum dilute cation solubilities were determined at 15%, 2.5%, 0.5% and 1% in the Mn, Fe, Ni and Cu DMSs, respectively. Above these limits, secondary phases were found in diffractograms, supported by a departure of the XAS spectra from wurtzite configuration and certain structures observed in SEM images. Photoelectron spectroscopy measurements were taken to investigate the electronic properties of the films. He-II UPS and Mg K XPS were done to investigate the electronic states of the valence band and core electronic levels respectively. In UPS the effects of p-d repulsion could be directly observed through the energy shift of the O 2p levels, which increased in binding energy in Mn and Fe DMSs but decreased in the case of Zn1-xCuxO, in agreement with predictions. In XPS spectra, analysis of the dilute cation 2p levels and their satellites revealed oxidation states in agreement with the results of the structural characterisation. Optical absorption measurements were taken to investigate the changes in the absorption edge caused by the dilute cation type and concentration at low temperature and high pressure. Results were fitted to a model based on the Elliot-Toyozawa equation to determine the optical properties. Within the solubility limits, the optical bandgap energies of Zn1-xMnxO and Zn1-xFexO films were found to increase by 19 ± 2 meV%Mn -1 and 4 ± 1 meV%Fe -1 respectively, due to the increase in p-d repulsion. However, a decrease was observed in Cu and Ni DMSs, confirming the reversal of the p-d repulsion. In all cases, static disorder increased with dilute cation concentration, shown by the broadening of the continuum width and a broadening and attenuating of the exciton and its resonance with the LO phonon. In Zn1-xMnxO films a pre-edge absorption band was observed and identified as a CTT from Mn 3d levels to the conduction band. Decreasing temperature caused a blue-shift of the absorption edge, the magnitude of which depended on the combined effects of the electron-phonon interaction and static disorder. Applying high pressure in the wurtzite phase also caused a blue-shift of the absorption edge, in agreement with theory for covalently bonded semiconductors. None of the DMSs showed a bandgap energy variation significantly different to pure ZnO. In the rocksalt phase, the pressure coefficient of the direct gap at could be studied, obtaining similar values to pure ZnO in all cases. Transition pressures were explained making reference to chemical pressure effects and metastable rocksalt Zn1-xMnxO films were recovered for Mn concentrations above 19 ± 3 %. Finally a magnetic characterisation was done to determine the magnetisation of the DMS films in function of applied magnetic field and temperature. Results from films grown over mica proved difficult to analyse due to the large substrate magnetic response, so only results from films grown over sapphire are reported. No evidence of ferromagnetism was found in single phase Zn1-xMnxO or Zn1-xFexO. Instead, the films showed paramagnetic behaviour, except in the low temperature limit (<1.8 K), where signs of the onset of antiferromagnetism were observed. __________________________________________________________________________________________________ RESUMEN Se depositaron capas de Zn1-xMxO (M = Mn, Fe, Ni, Cu) en condiciones óptimas sobre sustratos de mica y zafiro por ablación láser de blancos policristalinos compuestos de mezclas estequiométricas de compuestos químicos. Se caracterizaron las capas estructuralmente, electrónicamente, ópticamente y magnéticamente. Se hizo la caracterización estructural mediante espectroscopia de emisión de la pluma, XRD, XAS, XRF, microscopía electrónica y microanálisis para determinar los límites de solubilidad y asegurarse de que se hubieran depositado las capas esperadas. Se tomaron medidas de espectroscopia fotoelectrónica para investigar las propiedades electrónicas de las capas. Se hizo UPS y XPS para investigar los estados electrónicos de la banda de valencia y los estados profundos, respectivamente. El corrimiento de los niveles O 2p mostró un aumento de repulsión p-d en Zn1-xMnxO y Zn1-xFexO y una disminución en Zn1-xCuxO. Se tomaron medidas de absorción óptica para investigar los cambios en el frente de absorción causados por el tipo y la concentración del catión diluido a baja temperatura y alta presión. Se ajustaron los resultados a un modelo basado en la ecuación Elliot- Toyozawa para determinar las propiedades ópticas. La repulsión p-d causó un aumento de la energía del gap de Zn1-xMnxO y Zn1-xFexO en función de la concentración del catión diluido y una disminución en los casos de Zn1-xCuxO y Zn1-xNixO. Se observó una CTT por debajo del gap en Zn1-xMnxO y un aumento de desorden en función de la concentración del catión diluido en todos los DMS. Se explicaron el comportamiento en función de la temperatura haciendo referencia al desorden y la interacción electrón fonón. En función de la presión, los coeficientes del gap se mantuvieron como los de ZnO puro en las fases wurzita y NaCl. Se explicaron las presiones de transición haciendo referencia a la presión química. Finalmente, se hizo una caracterización magnética para determinar la magnetización de las capas DMS de Mn y Fe en función del campo magnético aplicado y la temperatura. Las capas no mostraron ferromagnetismo intrínseco, sino paramagnetismo y señales de antiferromagnetismo en el límite de baja temperatura. es_ES

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