Multislice Simulation:
Images and diffraction patterns obtained by
high resolution electron microscopy are not always interpretable
intuitively. Therefore, simulation images are required for
comparison with experimental data. In FACTS two programs suites
are used:
(1)
Cerius molecular modeling and image simulation
software from Molecular Simulations Inc. on a Silicon
Graphics R4000/Elan Unix workstation. Cerius is a
high-end, relatively expensive commercial product.
(2)
JEMS is a simulation package available from
CIME-EPFL Lausanne.
Images and diffraction patterns of a sample with a known
structure may be simulated before experimental work begins to
aid in the recognition of certain thicknesses or zone axes and
to determine appropriate conditions to use for imaging features
of interest. Images can also be simulated to determine whether a
specific instrument will be able to solve a certain problem
http://www.accelrys.com/chemicals/materials/hrtem.html
http://cimewww.epfl.ch/people/Stadelmann/jemsWebSite/jems.html
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Rietveld Analysis:
Powder X-ray diffraction patterns reflect the
a host of materials properties including unit cell parameters,
particle size, atomic positions, stress and strain information,
thermal parameters and so on. In addition, multiphase analysis
is feasible thereby allowing mass balance calculations.
However, this data can only be completely extracted using whole
pattern analysis using an algorithm developed in the 1960’s by
Hugo Rietveld. Several programs for the simulation and
refinement 0f powder X-ray and neutron data are used in FACTS
the two most important being:
(1) TOPAS is a fundamental parameter
version of the Rietveld method developed by Bruker Inc, and
which takes into account diffractometer settings during
refinement.
(2) GSAS The Los Alamos (& Argonne) General Structure
Analysis System is a shareware package that is widely used and
tested.
http://www.bruker.de/
http://www.ncnr.nist.gov/xtal/
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Image Processing:
High resolution TEM images are influenced by
slight misalignment of the electron beam optics or crystal
tilting. Image processing is one tool used to correct for these
effects, and in well aligned images, conduct electron
crystallography. CRISP uses the techniques of
crystallographic image processing to extract information from
electron micrographs. Key features
include
·
General purpose image
processing
- 2 and 3
dimensional structure determination
- focus and
astigmatism correction
- detection and
analysis of dislocations
- rapid forward and
inverse FFT calculation
- combine ED
amplitudes from ELD for accurate structure determination
·
fully automatic or user
steered processing
http://www.calidris-em.com/crisp.htm
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Crystallographic:
The representation of crystal structures in
ways that convey essential information, reveals structural
relationships, and gives clues to underlying properties is an
important final outcome of electron and X-ray analysis. A range
of programs are used in FACTS the most common including:
(1) ATOMS is a program for
drawing all types of atomic structures, including crystals,
polymers and molecules. It can make fully "three-dimensional"
color drawings using the latest system software, or it can make
simple schematic black-and-white drawings for reproduction on a
small scale in publications - or virtually anything between
these extremes.
(2) CaRIne Crystallography is a software which
interactively deals with different geometrical representation of
crystals
real lattices in 3D
surfaces
interfaces, grain boundaries
multi-layers
stereographic projection
reciprocal lattices in 2D and 3D
X-Ray diffraction patterns (XRD)
(3) ICSD Inorganic Crystal Structure Database contains
information on compounds of all inorganic crystal structure
including pure elements, minerals, metals, and intermetallic
compounds (with atomic coordinates, published since 1913). The
data base contains 82 676 entries as of November 2004. It is
updated twice a year, each update comprising about 2000 new
records.
http://www.shapesoftware.com/
http://pro.wanadoo.fr/carine.crystallography/index.html
http://www.fiz-informationsdienste.de/en/DB/icsd/
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Monte Carlo Simulation:
CASINO is a Monte Carlo simulation of electron trajectory
in solid specially designed for low beam interaction in a bulk
and thin foil. This complex single scattering Monte Carlo
program is specifically designed for low energy beam interaction
and can be used to generate many of the recorded signals (X-rays
and backscattered electrons) in a scanning electron microscope.
This program can also be efficiently used for all of the
accelerated voltage found on a field emission scanning electron
microscope(0.1 to 30 KeV).
http://www.gel.usherb.ca/casino/What.html
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