electron microcopy
DESCRIPTION
Electron Microcopy. 180/198-334 Useful info – many websites. Images here from www.microscopy.ethz.ch/elmi-home.htm. De Brogle wavelength of electrons. 100 KeV electron has 3.7 pm wavelength!. Electron-matter interactions. Electron-matter interactions. EDXS spectrum. Elastic interactions. - PowerPoint PPT PresentationTRANSCRIPT
Electron Microcopy
180/198-334
Useful info – many websites.Images here from
www.microscopy.ethz.ch/elmi-home.htm
De Brogle wavelength of electrons
100 KeV electron has 3.7 pm wavelength!
Electron-matter interactions
Electron-matter interactions
EDXS spectrum
Elastic interactionsNo energy is transferred fromthe electron to the sample.
The electron either passes withoutany interaction (direct beam) oris scattered by the positivepotential inside the electroncloud.
These signals are mainlyexploited in TEM and electrondiffraction.
Inelastic InteractionsEnergy is transferred from theincident electrons to the sample:
secondary electrons, phonons,UV quanta or cathodoluminescenceare produced;
shooting out inner shell electronsleads to the emission of X-raysor Auger electrons.
These signalsare used in analytical electronmicroscopy.
Excellent manuscript: www.microscopy.ethz.ch/downloads/Interactions.pdf
Interaction volumes
Energy dependence
Energy dependence II
Some SEM images
Backscattered electrons
Material contrast
Basic TEM and SEM
Which EM to use?The method that is needed is determined by the question to be solved:
Structure (High-Resolution) Transmission Electron Microscopy Scanning Transmission Electron Microscopy (STEM)
Electron diffraction (ED)Composition Energy-dispersive X-ray spectroscopy (EDXS)
Electron Energy Loss Spectroscopy (EELS)Morphology Scanning Electron Microscopy (SEM)Elemental mapping
Electron Spectroscopic Imaging (ESI)STEM + X-ray spectroscopy / EELSSEM + X-ray spectroscopy
De Brogle wavelength of electrons
100 KeV electron has 3.7 pm wavelength!
Is this the limit?
Scattering and diffraction
• Experiment• Basic structures and how to label them• X-ray diffraction
Experiment
Bragg’s Law
constructive interference destructive interference of waves
Crystal symmetries: finite number!
7 crystal systems: The crystal systems are a grouping of crystal structures according to the axial system used to describe their lattice. Each
crystal system consists of a set of three axes in a particular geometrical arrangement.
Cubic, hexagonal, tetragonal, rhombohedral (also known as trigonal)orthorhombic, monoclinic and triclinic.
14 Bravais lattices: When the crystal systems are combined with the various possible lattice centerings, we arrive at the Bravais lattices. They describe the geometric arrangement of the lattice points, and thereby the translational symmetry of the crystal.
Unit cells of a cubic crystal 3 different Bravais lattices
Directions in a cubic crystal
Miller indices of crystal planes
Examples of low index planes
Important results for cubic systems
Important results for cubic systems