SOLID STATE PHYSICS

Author: CONDE SAÁ JORGE CARLOS.
Year: 2003.
University: VIGO.
Place of defense: ESCUELA TÉCNICA SUPERIOR DE INGENIEROS INDUSTRIALES.
Place of preparation: ESCUELA TÉCNICA SUPERIOR DE INGENIEROS INDUSTRIALES.

Summary: In this Doctoral Thesis presents various tools of analytical and numerical calculations which support experimental research related to thermal processes induced by laser. The theoretical study based on the resolution of the differential equation of heat conduction, with their boundary conditions, has been corroborated with data from experiments in the laboratory. In the first part focuses on the analysis of a material warming induced by applying laser illustrating the growth epitaxial induced by pulsed laser (PLIE). The resolution of the differential equation of heat conduction by analytical and numerical methods has resulted in a comparative study of the temperature distribution in a-Ge and c-Si and, in turn, compare and consider the importance of thermal parameters with the temperature and, finally, we concluded that the numerical finite element method (ANSYS), can best represent processes PLIE due to the incorporation of the dependence of the parameters termofísicos with temperature. This method was successfully applied to obtain SiGe alloys. The central part of the report is dedicated to tackling a more complex processes such as laser ablation, and specifically discusses the phenomena associated with this process, which is widely referenced in the literature such as:-information microstructures. B-deflection boom. It has proposed a theoretical model based on three major assumptions, being particularly relevant Enactment of the surface roughness and allowed to predict these phenomena besides relate to mathematically. The results obtained using finite element numerical simulation is contrasted with experimental data based on laser irradiation on copper and silico. There is an excellent match and, in this way, it confirms the validity of the theoretical model and the soundness of the numerical method.

Author: HERRANZ CASABONA GERVASI.
Year: 2004.
University: BARCELONA.
Place of defense: ICMAB CSIC.
Place of preparation: ICMAB-CSIC.

Author: AGUADO MENENDEZ FERNANDO.
Year: 2004.
University: CANTABRIA.
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: The objective of this work is to study the behavior of compounds with laminar structure with ions Jahn-Teller (JT) Mn3 + and Cu2 + to be subjected to pressure both chemistry (series compounds) as at high hydrostatic pressures up to 45 GPa. In particular, the research work has focused on understanding how they affect the optical properties of these materials and magnetic variations in the structure caused by changes in the composition, size or phase transitions induced by pressure or temperature. Achieving these goals required to characterize the material structure of both long-range and local levels around the ion Jt. This will have experimented with x-ray diffraction and absorption, as well as optical baho pressure spectroscopy that have allowed a complete structural characterization of the composite laminates of chlorides of Cu2 + (series A2CuCl4) and fluorides Mn3 + (AMnF4), as well as the electronic structure. The variation of the optical absorption bands with the pressure along the series AMnF4 has enabled us to obtain the variation in energy JT with the pressure coefficients and coupling electrón-vibración partners at the Eg and T2g. These experiments have been performed in our laboratory and in the Major Facilities neutron (LLB) and synchrotron radiation / LURE and ESRP), both in ambient conditions as low pressure compounds sleccionados for this research. In addition to the experimental work has been necessary to develop models based on the phenomenological theory of crystalline field and the theory of finite groups with the purpose of establishing connections between the electronic and geometrical structures, and thereby have an accurate tool for predicting structures and properties. We have demonstrated that the application of high pressure to compounds of the series A2CuCl4 up to 20 GPa does not allow removing the distortion of JT octaedros CuCl64-. The structure JT has a distinctly molecular energy with a partner 0.3 eV / Cu making it stable compared pressures below 30 GPa. The stability of the distortion JT is favored by the turn of octaedros under pressure / tilting). A similar result was found in the compound of the series AMnF. The pressure reduces all distances liaison Mn-F and JT tetragonal distortion, while the phenomenon of rotation of octaedros preserves distortion in the range of pressures O-20 GPa. The most striking result of this work has been the removal of the JT distortion and high espín-bajo spin transition in the compound CsMnF4, we have achieved by applying a pressure of 37 GPa. Both phenomena occur simultaneously and are associated even remarkable performance piezocroico

Author: PRATS FERRER ALEIX.
Year: 2004.
University: BARCELONA.
Place of defense: FACULTAD DE FÍSICA.
Place of preparation: FACULTAD DE FÍSICA UNIVERSIDAD DE BARCELONA.

Summary: This thesis is based on the study of models related to theories of random surfaces. In theory methods have been used for the numerical simulation model goniheprico of spins in order to study the dynamic behavior in 3 and 2 dimensions. For the model in 2 dimensions, different analytical studies have been done in order to understand both the dynamics and structure of its phases. It looks, on the other hand, the relationship between patterns of complex matrices and hermiticas, drawing an interesting expression for integrals on the unitary group. Finally, the model is generalized war hadronica chirality in order to include the axial anomalia.

Author: HERNANDEZ CAMPO IGNACIO.
Year: 2005.
University: CANTABRIA.
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: The thesis focuses on the pilot study of the properties lumniscentes fluoride with Mn2 + and Cr3 + as optically active units or as components (pure materials) or as impurities. The idea is to establish correlations between structural and optical properties structure in order to know the microscopic mechanism responsible for the phenomena luminescent and the rocesos non-radiative. This has been selected fluoritas of the series Ca1-xSrxF2: Mn2 + and BaF2: Mn2 +, the MnF2 and fluor-elpasolitas A2BMF6: cr3 + (A = K, Rb, IT, B = Na, K, M = Ga, In , Cr). The studies have been performed using spectroscopic techniques depending on the temperature and using high-pressure techniques. The most relevant results are as follows: - The loss of luminescence going from CaF2: Mn2 + SrF2: Mn2 + and BaF2: Mn2 + has been explained by a single expression that contains a non-radiative term, which depends on the stage of structural materials , yn term radiative not only depends on the volume of site sustitucional of Mn2 + and temperature. Based on these results has led fotoluminiscencia in non-luminescent materials through the high pressure. - MnF2 presents a luminescent high efficiency at low temperatures but becomes lumniscente at temperatures greater than 140 K. Efforts have been made to control this loss fotoluminiscencia through two strategies: removing impurities radiative not by reducing the size of particles at the nano-scale and disruption of routes superintercambio through structural changes induced at high pressure. The ground mechanic favors the formation of the phase fotoluminiscente type alpha PbO2 OF MnF2, increasing the temperature deactivation of the luminescence more than 80 K. An important result is that there has been fotolumniscencia in MnF2 at room temperature high pressure. The spectroscopic study of Cr3 + in fluoro-elpasolitas shows that the first absorption band E ~ 10 Dq varies with the distance Local Cr + F of the form R (-3.3) rather than your claculada R (-5). This variation is responsible for the increase in the Stokes shift with increasing pressure and can be explained in terms of the mixture of excited states. The shape and lifetime of fotoluminiscencia of Rb2KCrF6 experiencing great changes with increasing pressure due to the crossing of excited states (ESCO).

Author: JUAN MARIA GARCIA LASTRA.
Year: 2005.
University: CANTABRIA.
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: The thesis is part of the study of computational materials ionic impurificados with transition metals and rare earths. The computational simulation has been carried out by calculation techniques based on the theory of functional density (DFT) and methodologies post-hartree-fock (CASPT2). To study the different systems has been used cluster model. The systems studied share the common feature of the complex, although this may be due to very different reasons: low symmetry centers, impurities Jahn-teller, molecules as impurities or impurities with a high atomic number. There has been considerable emphasis on the effect of electrostatic potential of the rest of the network on the various complexes. The centers studied were as follows:-PAR Fe3 + -O2- in perovskitas cubic - Molecule of REO42- in KCL - Lantanidos trivalent in elpasolitas cubic-MN2 + perovsditas cubic through technical Ksced-ions Jahn-teller Cu2 + and Ni + in perovskitas cubic and layered-ion La2 + BAFCL and SRFCL - Centers Cro69- in ruby, emerald and Alexandrite. It has been determined what is the origin in the difference of color in these three gems.

Author: SARA GARCIA REVILLA.
Year: 2005.
University: CANTABRIA.
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: In this thesis is attempting to discover the microscopic mechanism responsible for the optical properties of a wide variety of rare earth ions (TR) and transition metal (TM). It characterized the phenomenon of upconversion observed in certain compounds impurificados with different combinations TR-TR as Yb3 + -Er3 + and Yb3 + -Tb3 + in KY (WO4) 2, and TR-MT as Yb3 + -Mn2 + and Yb3 + - Ni2 +. This has enabled investigate different processes cooperative excitement, energy transfer and relaxation phenomena of radioactive and non-radiative. On the other hand, explores the origin of the absorption bands and luminscencia of CsCdBr3: Eu2 + and proposes an allocation of the same. It establishes structural correlations around ion optically active measures by optical spectroscopy under high pressure. So, are correlated movements of the excitation and emission bands of Ti3 + Al2O3 with changes in local structure of the complex of Ti3 +-induced pressure. On the other hand, identifies a structural phase transition from the red to a yellow form of Pt (bpy) Cl2 to 17.7 Kbar.

Author: SIERRA ASENSIO CRISTINA.
Year: 2005.
University: COMPLUTENSE DE MADRID.
Place of defense: FACULTAD DE CIENCIAS FÍSICAS.
Place of preparation: FACULTAD DE CIENCIAS FÍSICAS.

Summary: In this paper we present the results obtained upon initiation of synthesis autopropagada high temperature with concentrated solar energy to produce dense coatings of NiAl. The solar installation is used as an element of an expanded Fresnel lens of 889 mm diameter. Obtaining the proper coating has forced evaluate various experimental settings to determine which provides the best bond between the coating and the substrate. Achieving coatings NiAl dense through this kind of reaction has involved the study of the influence on the synthesis, have parameters such as the size of particles of Al, the amount of reactive mass, pressure compaction, how warming, the size of the coating, the power density of the external source and the addition of certain elements in the mix. The study of the experimental parameters has identified several respects. On the one hand, it is noted that small changes in any of these factors can affect the progress of the reaction, and thus the composition of the final product, as well as the macroscopic aspect of this. On the other hand, allowed for the right combination of these parameters for obtaining dense coatings of NiAl in the Fresnel lens used. Como parte de este estudio, se ha evaluado el comportamiento frente al desgaste de recubrimientos de NiAl, así como de otros recubrimientos obtenidos a partir de mezclas de Ni y Al con contenido variable de Ni entre el 45 y el 75 at.

Author: ABRIL TORRALBA OSCAR DE.
Year: 2005.
University: COMPLUTENSE DE MADRID.
Place of defense: FACULTAD DE CIENCIAS FÍSICAS.
Place of preparation: FACULTAD DE CIENCIAS FÍSICAS.

Summary: The doctoral thesis of this work has focused on obtaining magnetic microstructures through various electrochemical techniques and the study of the magnetic properties of structures obtained by these methods. First, in order to obtain magnetic microstructures have been developed in depth two novel techniques for localized electrochemical deposition processes and dissolution of metals. There has been cobalt deposit locally on gold, using the experimental assembly of a scanning electrochemical microscopy (CMEU). This has been used as a microelectrodo cobalt ion source for this metal. One of the most important issues that has had to overcome has been the deprivation of microelectrodo. It has also been made locally dissolve thin films of copper resolution submicrométrica. To locate the dissolution process has been applied ultrashort pulses (tens of nanoseconds) potential to tip of a metal atomic force microscope in electrochemical environment (EC-AFM). The reproducibility of the process has produced a comprehensive study of the latter's dependence on the various parameters which control. For this technique has been developed model, which solved numerically, has allowed reproduce the observed units. In relation to the study of the magnetic properties of microstructures, has studied the effect of how microcintas with weak perpendicular magnetic anisotropy. It has been observed that the jurisdiction of both anisotropies affected quite differently to the hysteresis cycle of the surface and the total volume of the samples. The most important outcome has been seen a great increase in the coercive field on the surface. In order to understand the mechanism that leads to this behavior has developed a model cominio magnetic type "stripe", which has defined a new structure for different regions close to the structure closure Landau-Lifschitz . This model has enabled simulate hysteresis cycle of volume and area of microcintas, by the calculation of the minimum energy structure. It has also enabled simulated images of magnetic domain structure "stripe" Corrugated obtained by magnetic force microscopy (MFM).

Author: RANCHAL SÁNCHEZ ROCÍO.
Year: 2005.
University: COMPLUTENSE DE MADRID.
Place of defense: FACULTAD DE CIENCIAS FÍSICAS.
Place of preparation: FACULTAD DE CIENCIAS FÍSICAS.

Summary: The research work done in this thesis has been directed to study and optimization of two different systems of thin films ferromagnéticas, on the one hand coupled magnetically metal multilayers and other oxides diluted magnetic doped with Co. The first system has been studied multislice permalloy / gadoliio (P / Gd) and the second thin films of La0.5Sr0.5TiO3 doped with Co (Co-LSTO). Both systems show features both from the standpoint of basic physics and from the technology. In intercaras of multilayers of P / Gd exists coupling antifereromagnético as in the multilayers of Fe / Gd or Go / Gd. These multislice the existence of biestabilidad can be used in the development of magnetic sensors. The alloy Ni80Fe20 (Py) are used in many devices due to its low permeability and high coercive field, and it is hoped that the multilayers of P / Gd characteristics very attractive for technological applications. However, as there are few works about this system is its primary characterization in detail (structural, magnetic and electrical). In the study of tricapas P / Gd / Py concluded of the need to optimize the structure due to the diffusion of Ni in Gd that reduces the interaction in the intercara. The existence of temperature compensation (Tcom) in the metal multilayers has been seen as indicative of coupling antiferromagnético in intercara in practically all the papers published so far. The tricapas P / Gd / P, despite its coupling antiferromagnético not submit Tcom due to its high thick and low coupling. This result was explained by a numerical model. After optimizing the system P / Gd, we study the magnetic coupling in these structures. The results show two types of coupling depending on the temperature and thickness of the layer of Py. Between 250 and 140 K, the coupling can be explained by the interaction of the walls of the layer Py with imanación of Gd layer. Below 140 K have shown that there are processes due to the magnetic interaction antiferromagnética Py-Gd. In recent years, research has found a large number of inquiries about the diluted magnetic oxide (ZnO, TiO2, HfO2, ..). These materials are dopa an oxide semiconductor with magnetic impurities to produce a new material that presents semiconductor properties and ferromagnéticas at the same time. In this paper, we have extended the investigations carried out in this area so far, since we started a system of highly correlated electron paramagnetic, LSTO, passing ferromagnetic at room temperature the doparlo with a small amount of Co. In this paper, we have extended the investigations carried out in this area so far, since we started a system of highly correlated electron paramagnetic, LSTO, passing ferromagnetic at room temperature to doparlo with a small amount of Co. First we show that the optimal substrate to obtain thin layers of Co-LSTO low roughness is the STO (001). Not finding signs of aggregates Co. older than 10 nm, we can conclude that the ferromagnetism of Co-LSTO is intrinsic type. This hypothesis is supported pro measures magnetorresistencia tunnel that show a high spin polarization of this material. Finally, we found that the optimal conditions for the growth of Co-LSTO (low pressure oxygen) induce a state of high mobility in the substrate STO.