MATERIALS CHARACTERIZATION TECHNIQUES: THEORY AND LABORATORY

Specific Foundation / Core

- On the module completion, students will have a complete overview of the possibilities and the application fields of the optical characterization techniques (Raman-, absorption- and luminescence spectroscopy) in terms of their principles, their experimental setups, the methodology and analysis used as well as the obtainable information about the material characterization. Crystalline and amorphous states of matter. Symmetry in direct and inverse space, Crystal directions and planes. Periodicity, symmetry point groups and space. Basic types of crystal structures. Equipment for generation of X-rays (tubes, fixed and rotating anodes, storage rings and synchrotron radiation). Detection of X-rays: scintillation counters, solid state counters, imaging screens. X-ray diffraction of single crystals. Identification of unknown materials using crystalline powder diffractometry. Structure factors and electron density function. Data collection and processing. Preliminary phase identification and improvement of crystalline structures.

- X-ray diffraction: Spectrum of X-rays. X-ray’s Production and application Operation principles of X-Ray Powder Diffractometer Absorbion. X-ray Microscopy. Determination of lattice parameters, strain, grain size, phase composition and preferred orientation. Identification of multiple and single-phase materials. Determination of structural properties, texture and atomic arrangement. polefigures. X-ray topography and tomography. - Laboratory: Principles of X-ray diffraction by the crystalline mater. X-ray single crystal diffractometry. Description and operation of the 4-cycle single crystal diffractometer. Preparation and mounting of the crystal on the instrument. Determination of lattice parameters and space group. Measuring the intensities of reflections and their reduction. Refinement of the structure parameters. Crystallographic packages. Schematic representation of the structure using crystallographic programs. X-ray powder diffractometry. Principles of the X-ray diffraction from crystalline powder. Operating principle of the powder diffractometer. Data collection and data reduction. Refinement of the parameters of the resulting structure by the method Rietveld. Qualitative analysis of the phases. Crystallographic databases of known structures. (PDF: Powder Diffraction File Database). Using PDF. Examples. Crystallographic packages. Identification-recognition and separation of crystalline phases. Indexing - Examples. Crystallite size and crystal cell constant calculation from the diffraction data.-Examples. - Electron microscopy: Interaction of materials with an electron beam. Basic types of microscopes. Transmission electron microscopy. Analysis of images formed by diffracted electrons. Contrast mechanisms (kinematic and dynamical theory). Scanning electron microscopy. Electron channeling patterns. Stoichiometric analysis using x-rays. - Laboratory: Basic principles of Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). TEM specimen preparation techniques. TEM experiment: Determination of crystal defects, selected area electron diffraction analysis, morphology of precipitates and nanoparticles, low-dimensional structures, heterophase and homophase interfaces. - Electrical characterisation: Determination of the electrical conductivity of metals and alloys. Experimental results. Methods for the characterisation of single- and poly-crystalline semiconductors and semiconductor devices. Methods for the determination of resistivity and dielectric strength. Effect of dimensions and inhomogeneities on the electrical properties. - Laboratory: Methodology for the measurement of electrical properties. Van der Pauw method. Hall measurements and determination of electron mobility - classification of materials. Construction of a Gaussmeter apparatus. - Optical Characterisation: Macroscopic theory of materials optical characterization: Complex dielectric function. Optical constants and dispersion relations. Lorentz-, Drude- and Debye-Model. Experimental setups: Operation of conventional single monochromator as well as of far infrared and Raman spectrometers. Processing of: single crystal- powder- and thin film- samples for optical characterization. Recording of: FIR-, Raman-, photoluminescence-, absorption- and reflection- spectra. Analysis of experimental spectra by using macroscopic models: classical oscillator, Kramers-Kroning analysis, interband transitions, free carrier, etc. through commercial and "homemade" fitting programs. Characterization of semiconductors: crystalline and amorphous materials. Lattice dynamic: phonons, phonon modification due to the existence of mechanical stress, lattice disorder, etc. Characterization of semiconductor materials: Free carrier, optical electronic properties - energy gap. Characterization of: impurities, surfaces, interfaces and microstructure of materials. Characterization: of thin films and surface buried single and multiple layers. - Laboratory: Basic principles of the Raman phenomenon. Macroscopic description (modulation of dielectric acceptivity, active scattering cross-sections, Raman tensor, and selection rules). Microscopic treatment (elementary interpretation of the macroscopic treatment through quantum-mechanics, resonance phenomena). Scattering in crystalline and amorphous semiconductors (classical semiconductors, acoustic and optical branches, LO (LA) and TO(TA) oscillations). Evaluation of experimental spectra through fitting and characterisation of materials. Infrared spectroscopies. Specimen preparation (single crystals, powders, thin films of single and multiple layers). Data acquisition of reflection and/or transmission spectra. Analysis of results, study of optical data through Kramers-Kroning software and Lorentz - Drude oscillator fitting software. Oral presentation of the laboratory report. - Laboratory of magnetic materials characterisation: This Lab course consists of three independent experimental sequences covering a wide range of magnetic properties and features widely studied. Students are split in smaller groups and actively participate in experimental procedures and then collect their data and present them after evaluation in scientific reports. 1). Magnetic moment as function of field and temperature. (VSM magnetometry) 2). Recording and quantitative evaluation of Μössbauer spectra in magnetic materials. (Mössbauer spectroscopy) 3). Corellation of structure and magnetism in magnetic nanoparticles. (AC magnetic field heating response) - Computer Applications in Materials Science: Software tools for the analysis and presentation of experimental data. The students simulate experimental results relevant to materials science (mobility, absorption etc) using a combination of software packages including Scientist, Grapher, and Microsoft’s Excel, Word, and Power Point.

x-rays, crystal structure

08-11-2015