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Thermodynamique --- Thermodynamics. --- Adsorption --- Interfacial tension

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Nonlinear optics is a wide research field based on the nonlinear relationship of the electric field component of light and the induced polarization in matter under intense laser illumination. The second order effect second-harmonic generation (SHG) is often used as a surface characterization tool for materials with a center of symmetry. Due to the advantage of probing surfaces and even buried interfaces, specific material properties can be attributed to the material surface instead of the bulk. Moreover, SHG is very sensitive to changes in the surface structure or alignment of molecules thereon. An additional advantage is the non-invasiveness of SHG, which makes the technique applicable to fragile materials. Exploiting these advantages, SHG can be a useful technique in semiconductor industry, since semiconductor devices consist of a sequence of thin layers. Metal-oxide-semiconductor field-effect transistors (MOSFETs) consist of an oxide layer on top of a semiconductor with different contact areas and are the fundamental parts of e.g. computer chips. The interface between these layers determines the power consumption, reliability, operating voltage, leakage current of the resulting device, etc. Optimizing the interfaces between these layers, will result in an optimized transistor performance. SHG can provide valuable insight in interface-specific processes in semiconductor research.In this work, we investigate the surface and interfaces in MOSFETs. We determine the optimal growth conditions with respect to the carrier gas and temperature during atomic layer deposition (ALD) of the oxide layer. During the ALD process, the composition of the bonds at the surface changes, which results in a change in the isotropic contribution of SHG. For thicker oxide layers, it is shown that the SHG response is thickness independent. Moreover, passivation of the interface is important for optimal device properties. Therefore, the influence of the oxidizing agent and number of oxidation steps on a Si capped Ge layer is probed. Since the operation of MOSFET is voltage dependent, electric field-induced second-harmonic generation (EFISH) is performed on Al2O3 and MgO covered Si substrates. The charges contribute to the EFISH signal, hence a change in charge distribution will result in a changing EFISH intensity. We observe the tunneling of holes from the semiconductor layer to the Al2O3 and migration of oxygen vacancies in MgO. Graphene is an upcoming semiconducting material, which is to be incorporated in a new type of transistor. The capability of using SHG as symmetry-sensitive probe and visualization method is tested on graphene and a novel analyzing method based on fast Fourier-transformation is proposed. These findings illustrate the usefulness of SHG and EFISH to probe buried interfaces in semiconducting material and charge separation therein. In this manner, these second-order nonlinear techniques can push the boundaries in semiconductor manufacturing.

544.722 --- Academic collection --- Chemical surface phenomena, interfacial interactions --- Theses

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With the advent of high performance computing, the application areas of the phase-field method, traditionally used to numerically model the phase transformation in metals and alloys, have now spanned into geoscience. A systematic investigation of the two distinct scientific problems in consideration suggest a strong influence of interfacial energy on the natural and induced pattern formation in diffusion-controlled regime.

Oberflächenenergie --- GesteinsadernMultiphase-field model --- Interfacial energy --- Veins --- Multiphasenfeldmodell --- Eutektoider Umwandlungen --- Eutectoid transformations

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In 2005, the hybrid model was published by Prof. H.-D. Alber and Prof. P. Zhu as an alternative to the Allen-Cahn model for the description of phase field transformations. With low interfacial energy, it is more efficient, since the resolution of the diffuse interface is numerically broader for the same solution accuracy and allows coarser meshing. The solutions of both models are associated with energy minimisation and in this work the error terms introduced in the earlier publications are discussed and documented using one and two dimensional numerical simulations. In the last part of this book, phase field problems, initially not coupled with material equations, are combined with linear elasticity and, after simple introductory examples, a growing martensitic inclusion is simulated and compared with literature data. In addition to the confirmed numerical advantage, another phenomenon not previously described in the literature is found: with the hybrid model, in contrast to the examples calculated with the Allen-Cahn model, an inclusion driven mainly by curvature energy does not disappear completely. The opposite problem prevents inclusions from growing from very small initial configurations, but this fact can be remedied by a very finely chosen diffuse interface width and by analysing and adjusting the terms that generate the modelling errors. The last example shows that the hybrid model can be used with numerical advantages despite the above mentioned peculiarities.

Science --- phase field modelling --- elasticity --- interface width --- interfacial energy --- hybrid Allen-Cahn model

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In 2005, the hybrid model was published by Prof. H.-D. Alber and Prof. P. Zhu as an alternative to the Allen-Cahn model for the description of phase field transformations. With low interfacial energy, it is more efficient, since the resolution of the diffuse interface is numerically broader for the same solution accuracy and allows coarser meshing. The solutions of both models are associated with energy minimisation and in this work the error terms introduced in the earlier publications are discussed and documented using one and two dimensional numerical simulations. In the last part of this book, phase field problems, initially not coupled with material equations, are combined with linear elasticity and, after simple introductory examples, a growing martensitic inclusion is simulated and compared with literature data. In addition to the confirmed numerical advantage, another phenomenon not previously described in the literature is found: with the hybrid model, in contrast to the examples calculated with the Allen-Cahn model, an inclusion driven mainly by curvature energy does not disappear completely. The opposite problem prevents inclusions from growing from very small initial configurations, but this fact can be remedied by a very finely chosen diffuse interface width and by analysing and adjusting the terms that generate the modelling errors. The last example shows that the hybrid model can be used with numerical advantages despite the above mentioned peculiarities.

Science / Chemistry --- Science / Physics --- Mathematics --- Science --- phase field modelling --- elasticity --- interface width --- interfacial energy --- hybrid Allen-Cahn model