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Liliana Braescu

Universitatea de Vest Timisoara, Timisoara, Romania

Institution web page: http://www.uvt.ro
Personal web page: http://www.info.uvt.ro/~braescu/
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Born: 1967

Interests: PDE, ODE, control theory, stability, domains of attraction, crystal growth, blood coagulation, modeling

Details:
Modern engineering needs of crystals with specified size for use as final products without additional machining. Moreover, the quality of a crystal depends on the distribution of both special added and detrimental impurities. A non-uniform distribution of such impurities along the crystal length and cross-section leads to non-uniform spatial, electrical and optical properties of the crystal. Variations of the concentration of impurities along the crystal length and cross-section are determined by the processes that take place during the crystal manufacturing.

Mathematical models constructed for describing the evolution of the shape of the crystal and/or the distribution of impurities take into account such processes.

The aim of our research is:

-the study of the dependence of the crystal shape on the pulling rate, melt temperature at the meniscus base, pressure in the furnace, vertical temperature gradient in the furnace in the case of EFG method, in view of the choice of the optimal process parameters and to develop a mathematical model based control procedure of the crystal shape.

-a model based evaluation of the impurities of the crystal grown form the melt by various techniques: edge-defined film-fed growth (EFG); Czochralski (Cz); Vertical Bridgman-Stockbarger (VBS); dewetted Bridgman, and find ways to reduce the non-uniformity of the distributions of impurities.

For these complex and rigorous explorations, we use mathematical and numerical tools in order to obtain theoretical and numerical results comparable with experimental data.

Software used:
-COMSOL Multiphysics for coupling different application modes which use partial differential equations: Navier-Stokes, Convection-Diffusion, Moving Mesh, etc.
-MathCAD and Mathematica for simulate the shape of the meniscus, the shape of the crystal and for other numerical data concerning the control, the regions of attractions, etc.
-Table Curve 2D and 3D for fitting the obtained numerical data.

ResearcherID: A-9300-2010

Selected publications:
• L. Braescu, S. Epure, Th. Duffar . Mathematical and numerical analysis of capillarity problems and processes. In Crystal growth processes based on capillarity: Czochralski, floating zone, shaping and crucible techniques, pp. 465-524. John Wiley & Sons Ltd, 2010.

Publications from the ISI database, indexed between 2002-2011, produced in Romania:
• Braescu, L; Balint, AM; Balint, S, Temperature control of filament growth. COMPUTATIONAL MATERIALS SCIENCE, 24 (1-2), pp. 252-256, 2002.
• Braescu, L; Balint, AM; Schlett, Z; Balint, S, The growth of a single crystal filament and of a sheet with pre-established piece-wise constant diameter cross-section and half-thickness, respectively, from the melt in a vacuum by EFG method. JOURNAL OF CRYSTAL GROWTH, 241 (3), pp. 374-378, 2002.
• Braescu, L; Balint, AM; Jadaneantu, I; Balint, S, Modelling of the temperature changes by adequate changes of the pulling rate in the case of sheets and filaments grown from the melt in a vacuum by EFG method. JOURNAL OF CRYSTAL GROWTH, 240 (1-2), pp. 305-312, 2002.
• Braescu, L; Balint, AM; Balint, S, The effect of a periodic movement on the die of the bottom line of the melt/gas meniscus in the case of edge-defined film-fed growth system. JOURNAL OF CRYSTAL GROWTH, 259 (1-2), pp. 121-129, 2003.
• Braescu, L; Balint, AM; Balint, S, Modelling of growth effects of pressure changes in an edge-defined film-fed growth system. JOURNAL OF CRYSTAL GROWTH, 269 (2-4), pp. 617-624, 2004.
• Braescu, L; Balint, AM; Balint, S, The effect of a periodic movement on the die of the bottom line of the melt/gas meniscus in the case of silicon filaments grown from the melt in a vacuum by edge-defined film-fed growth method. SILICON CARBIDE AND RELATED MATERIALS 2003, PTS 1 AND 2. MATERIALS SCIENCE FORUM, 457-460, pp. 127-130, 2004.
• Braescu, L; Balint, AM; Balint, S, Optimization of some growth process parameters of an Nd : YAG cylindrical bar grown in a vacuum by edge-defined film-fed growth method. JOURNAL OF CRYSTAL GROWTH, 268 (1-2), pp. 284-298, 2004.
• Balint, S; Braescu, L; Balint, AM; Szabo, R, Modelling the effects of the pressure changes in the case of the growth of a thin sheet in an edge-defined film-fed growth (EFG) System. JOURNAL OF CRYSTAL GROWTH, 283 (1-2), pp. 15-30, 2005.
• Epure, S; Braescu, L; Balint, S, Modeling the effects of the vertical temperature gradient in the furnace in an edge-defined film-fed growth technique. MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 134 (2-3), pp. 277-281, 2006.
• Braescu, L; Balint, S; Tanasie, L, Numerical studies concerning the dependence of the impurity distribution on the pulling rate and on the radius of the capillary channel in the case of a thin rod grown from the melt by edge-defined film-fed growth (EFG) method. JOURNAL OF CRYSTAL GROWTH, 291 (1), pp. 52-59, 2006.
• Braescu, L; Balint, AM; Szabo, R; Balint, S, Model based optimization of some growth process parameters of a Nd : YVO4 cylindrical bar grown by edge-defined film-fed growth (EFG) method in the presence of the pressure. OPTICAL MATERIALS, 28 (6-7), pp. 631-637, 2006.
• Balint, AM; Braescu, L; Szabo, R; Balint, S, A control procedure for the shape of a Nd : YAG and Nd : YVO4 cylindrical bar grown by edge-defined film-fed growth method under oscillated furnace pressure. OPTICAL MATERIALS, 28 (6-7), pp. 671-675, 2006.
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