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Basics of X-Ray Powder Diffraction
Training to Become an Independent User of the X-Ray SEF at the Center for Materials Science and Engineering at MIT
Scott A Speakman, Ph.D. speakman@mit.edu (617) 253-6887 http://prism.mit.edu/xray

Required Training to Become an Independent User in the X-Ray SEF

Required Safety Training
• • • • All users must complete the EHS X-ray Safety training Allusers must complete the X-ray Lab Specific Safety Training All users must complete the MIT chemical hygiene training All users must be up to date on their MIT managing hazardous waste training • All users must be registered in CMSE MUMMS
– https://cmse-coral.mit.edu/mumms/home.html

Instrument Specific Training
• These courses cover how to safely operate instruments to collect data • PowderDiffractometers:
– PANalytical X’Pert Pro Multipurpose Powder Diffractometer – Rigaku High-Power Powder Diffractometer – Bruker D8 with GADDS 2-dimensional detector

• Other instruments
– Bruker D8 HRXRD – XRF

Data Analysis Workshops
• Basic XRPD Data Analysis using HighScore Plus
– Primary focus is on phase identification, with some discussion on advanced topics such as lattice parameterand crystallite size calculations

• Profile Fitting and Crystallite Size Determination
– Profile fitting is the most precise way to determine diffraction peak position, intensity, and width for calculating lattice parameters and crystallite size

• Rietveld Refinement
– The Rietveld method is used to refine the crystal structure model of a material. It can be used for quantitative phaseID, lattice parameter and crystallite size calculations, and determine atom positions and occupancies

High Resolution X-Ray Diffraction (HRXRD) Training
• HRXRD is used to analyze epitaxial thin films
– Can determine composition, strain/relaxation, lattice parameters (inplane and out-of-plane), thickness, and defect concentration

• X-Ray Reflectivity (XRR) is used to analyze thin films,including amorphous and non-textured films
– Can determine thickness, roughness, and density

• Introduction Lecture • Instrument training on the Bruker HRXRD • HRXRD Data Analysis Workshop

Introduction to Crystallography and X-Ray Diffraction Theory

Diffraction occurs when light is scattered by a periodic array with long-range order, producing constructive interference at specific angles.• The electrons in an atom coherently scatter light.
– We can regard each atom as a coherent point scatterer – The strength with which an atom scatters light is proportional to the number of electrons around the atom.

• The atoms in a crystal are arranged in a periodic array and thus can diffract light. • The wavelength of X rays are similar to the distance between atoms. • The scattering ofX-rays from atoms produces a diffraction pattern, which contains information about the atomic arrangement within the crystal
• Amorphous materials like glass do not have a periodic array with long-range order, so they do not produce a diffraction pattern

The figure below compares the X-ray diffraction patterns from 3 different forms of SiO2
Counts 4000 2000 0 4000 3000 2000 1000 0 4000 20000 20 30 40 Position [° 2Theta] (Copper (Cu)) 50 Quartz SiO2 Glass

Cristobalite

• • •

These three phases of SiO2 are chemically identical Quartz and cristobalite have two different crystal structures
– – The Si and O atoms are arranged differently, but both have structures with long-range atomic order The difference in their crystal structure is reflected in their different diffractionpatterns

The amorphous glass does not have long-range atomic order and therefore produces only broad scattering peaks

The diffraction pattern is a product of the unique crystal structure of a material
Quartz Cristobalite

• The crystal structure describes the atomic arrangement of a material. • When the atoms are arranged differently, a different diffraction pattern is produced (ie...
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