CRYSTAL GROWTH

Author: SALA VERGÉS SANTIAGO.
Year: 2004.
University: AUTÓNOMA DE BARCELONA [www.uab.es].
Place of defense: INSTITUT DE CIÈNCIA DE MATERIALS DE BARCELONA.
Place of preparation: ESCUELA DE POSTGRADO.

Summary: This Doctoral Thesis falls within the field of material processing technologies using fluid tablets (FCs), and specifically within the methods of preparation of finely divided solids with FCs. The methods of crystallization or preparation of solid micro or nanoparticulados with FCs are characterized by the fact that the modulation of variable pressure can abrupt changes in the ability solvatadora environmental solvent, which are transmitted beneficially in a very homogeneous throughout the within the dissolution. The present work shows the process of developing the new method of preparation of materials DELOS finally divided, using FC carbon dioxide as cosolvente in dissolutions expanded with CO2. In the first part of the thesis, demonstrates that the phenomenon of crystallization associated with the new method DELOS cooling is a consequence of suffering a dissolution of the compound to crystallize when it conducts its depressurization until atmospheric pressure. It has been proven that enfriameinto observed is a result of the evaporation of CI2 the dissolution expanded and the associated process of heat exchange that takes place. In this first part of the thesis also shows that it is feasible to apply the method to DELOS materials varied nature with a very significant control of the particle size of the way i Polymorphic obtained. In a second part of the thesis is the use of surfactants in the new developed method is beneficial in reducing the phenomena of aggregation and agglomeration of particles i therefore for the stabilization of these particles obtained by depressurization of dissolutions expanded with CO2 on aqueous solutions with a certain content tensoactivo obtained nanosuspensiones. The last part of the thesis presents studies to molecular-scale solutions in relation to expanded with CO2, which enable highly relevant information in relation to systems utililzados in implementing the method DELOS. In these studies using the infrared spectroscopy technique of high pressure in combination with the approximate semiempírica Linear Solvation Energy Relationships (LSER) and theoretical calculations ab-inito. The results measuring the changes in the field of solvatación of solutes dissolved in solvents expanded with CO2, the nature of interactions soluto-disolvente that tienenlugar in this esfero and effect, at the molecular level, which is the presence of CO2 in the systems under study.

Author: MARTINEZ VAZQUEZ REBECA.
Year: 2004.
University: AUTÓNOMA DE MADRID [www.uam.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: In this doctoral thesis were conducted numerous investigations based on monocrystals YAI3 (B03) 4 (YAB) doped with different rare earth ions such as Nd3 +, Dy3 +, Er3 + and Yb3 +. The monocrystals YAB are interesting because of its non-linear behavior in that regard are widely used in the development of new laser devices. The AB and must be synthesized in the form policristalina before the monocrystals grow, these have been studied temperatures synthesis from oxides of yttria, boron and aluminum to be of 1150Â ° C. In addition they have studied the reaction times of oxides found that the material synthesized may decompose if it keeps the decomposition temperature over 20 hours. He then proceeded to the growth of monocrystals with different concentrations of doping by the method of growth in solution at high temperature, with a solvent-based K2M03010 and B203. The growth was made by spontaneous nucleation in a crucible pt pt sealed with lids to improve the efficiency of the same. We have studied the temperature decomposition of the crystals resulting in a decrease of the same with the increased concentration of dopante. In addition they have 'studied crystalline defects and constant network of different crystals depending on the concentration of dopante. It has studied the external morphology of monocrystals from a theoretical point of view based on the speed of growth of the families of faces (1 01) Y (2-1 O). As for the optical properties of monocrystals have been based on doped with Er: YAB and D: YAB. Have been measured for the first time in monocrystals YAB, the indexes of refraction ordinary and extraordinary, from the visible to near-infrared. With these refractive indices were determined curves Sellmeier for both indexes crystals to hear any wavelength, with a deviation from 5x10-4, has been studied at room temperature polarized absorption of monocrystals YAB and implementing the formalism of Judd-Ofelt we have obtained the three parameters 2 4 AND 6. With these parameters and luminescence spectra from the standard electronic 4F9 / 2 has been calculated half-life of this multiplet radiative electronic (460 s). By half-life measures the fluorescence of state has found a value of 400 s and have calculated the probability of non-radiative-energizing and efficiency of the same quantum state. Finally we have obtained the FTIR spectra of the crystals of D: YAB and Er: YAB, by which have been identified removals due to vibration of the groups borates to higher energies in the case of synthesizing YAB and removals from electronic transitions ions doping.

Author: Zúñiga Pérez Jesús.
Year: 2005.
University: VALENCIA [www.uv.es].
Place of defense: Facultat de Física, Universidad de Valencia.
Place of preparation: Facultat de Física, Universitat de Valencia.

Summary: The thesis deals with the crystal growth and characterization of II-VI oxides in the form of thin layers: ZnO, CdO and Zn1-xCdxO. The three materials have been grown using the technique MOCVD (Metal Organic Chemical Vapor Deposition) using a new configuration of the reactor, in which the metal precursors are introduced by an entry while higher alcohols, which have been used as precursors oxygen others do so for an entry lower. This has resulted in reduced chemical reactions in the gas phase precursors, which always has been a problem in this kind of growth. The study of ZnO has focused on the growth of non-polar orientations, ie directions in which the axis [0001] is contained on the surface of the sample, and are necessary to obtain optoelectronic devices with greater efficiency . The guidelines have not been characterized using polar SFM, analyzing the process of growth (nucleation and formation of the first grains) and through HRXRD, which has identified the mechanisms that limit the structural quality of these guidelines. Finally, the use of a novel technique, Kelvin Probe Microscopy, has revealed the presence of domains load on the surface of samples non-polar faceteadas. The study of CdO has fundamental objective to obtain thin layers with a single crystallographic orientation on sapphire substrates, opening the doors to a technological compatibility between ZnO and CdO. To get thin layers of high quality structural has resorted to the use of sapphire substrates of "r" and "m", as the substrates "in" provoking the emergence of maclas in layers. About Sapphire "r", the optimization of the growth conditions has led to the collection of flat surfaces, while also improving the quality structural equiparándola to that obtained on substrates cubic. Finally, growth on sapphire substrates "m" induces the appearance of nanohilos on the surface of the sample, which has been explained by the nature anisótropo the surface (110) of CdO. Finally, we studied the incorporation of Cd in the network of crystalline ZnO and deformations that this entails. We have managed to introduce up to 8.5% of Cd, which has resulted in a reduction of more than 300 meV of the broadcast fotoluminiscente. The introduction of Cd influences, from a structural point of view, the deformation of the atomic frequencies along the directions [11-20] and [1-100], while the network parameter "c" remains constant .

Author: Ristic Jelena.
Year: 2005.
University: POLITÉCNICA DE MADRID [www.upm.es].
Place of defense: E.T.S.I. de Telecomunicación.
Place of preparation: ETSI Telecomunicacion.

Summary: The group III nitrides are direct band gap semiconductors, covering a broad spectrum of energies of 0.7eV (InN) to 6.2 eV (AlN) making them suitable for applications optoelectrónicas in visible and ultraviolet (UV). So are the major materials for the manufacture of LEDs and lasers in the blue and UV. However layers compact floods epitaxialmente even suffer for his hard doping tipo-py high densities of crystalline defects widespread. Defects substantially degrade the optical properties and electrical equipment and the operation of devices manufactured. The structures nanocolumnares based nitrides presented an alternative for avoiding the disadvantages of compact material, as they have an exceptional quality crystal, introducing absence of widespread defects, and therefore high efficiency optics. The Doctoral thesis focuses on growth by epitaxia beam moléculares (molecular beam epitaxy, MBE) and characterization of structures nanocolumnares of Group III nitrides (GaN, AlGaN and InGaN) as well heterostructures nanocolumnares: nanocolumnas disks quantum (quantum disks , QDisks), diodes homo-and heterounion and nanocavidades columnar including mirrors Bragg, with a view to their application in optoelectronic devices. The techniques of structural characterization and optical (SEM, TEM, PL, CL and Raman spectroscopy) applied provide the information necessary for the optimization of the growth conditions. We undertook a detailed study of the nucleation phase and as a result we propose a model to explain the growth nanocolumnar. Finally, the first LEDs nanocolumnares have been prosecuted and characterized, in a manner demonstrating their potential for the production of optoelectronic devices.