Introduction to the TESCAN MIRA3 LMH Schottky FE-SEM...Microsoft PowerPoint -...
Transcript of Introduction to the TESCAN MIRA3 LMH Schottky FE-SEM...Microsoft PowerPoint -...
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Introduction to the TESCAN MIRA3 LMH Schottky FE-SEM
TESCAN
Global supplier of scientific instrumentsinstruments
Designs and manufactures scanning electron microscopes in Brno, Czech Republic
About 2000 instruments in more than 77 countries
TESCAN USA is based in TESCAN USA is based in Warrendale, PA
Image: Tescan
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Instrumental Capabilities
Secondary electron imaging (Topography contrast)
Backscatter electron imaging(Phase contrast)
Energy-dispersive X-ray spectroscopy (Compositional analysis)
SE are ejected from the k-shell of the specimen atoms by inelastic scattering interactions with beam electrons
Topography Contrast
electrons
SE originate within a few nanometers from the sample surface
Brightness of the SE signal depends on the number of secondary electrons reaching the detectorreaching the detector, providing a topography contrast
Resolution is about 1-2 nm at normal operating conditions
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BSE are back-scattered out of the specimen interaction volume by elastic scattering interactions with specimen
Phase Contrast
atoms
BSE are used to detect contrast between areas with different chemical compositions since elements with high atomic numbers backscatter
l t t lelectrons more strongly than elements with low atomic numbers and, therefore, appear brighter in the image
Compositional Analysis
Analytical technique used for the elemental analysis or chemical characterization of a samplea sample
Interaction of electrons with sample produces characteristic X-rays (elements emit X-rays that have a characteristic energy)
You can do spot analyses to calculate mineral formula;calculate mineral formula; map element abundances; measure element abundances along traverses etc.
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Electron gun and column
Controlunit
Uninterruptible
Dry scroll vacuum pump
Electronics
EDS detector
Sample chamber
EDS
ppower supply
FE-SEM computer
EDS computer
Chamber View
BSE detectorEDS detector
Pole piece
Thin section
Automated stage
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EDS screenFE-SEM screen
Track ballfor advanced
users
Control Panel
Keyboard
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Getting Ready
Samples need to have a conductive surface
Unless you work with metals Unless you work with metals, you need to coat your samples with carbon (or gold)
Prepare your samples prior to scheduled FE-SEM time
Do not touch the surfaces of your coated samples with your bare handsbare hands
If available, store coated samples in a desiccator or desiccator cabinet
Booking Instrument Time
Book instrument time (at the moment use calendar in Katharina Pfaff’s lab)
Book a minimum of one hour instrument time ($35/hr for internal st u e t t e ($35/ o te ausers plus 8.5% overhead)
Leave 30 min time between end of previous session and start of your session
Come ca. 10-15 min before start of your session
Reserved time will be forfeited if you do Reserved time will be forfeited if you do not begin within 10 min of the scheduled start time, but you will still be charged a minimum of one hour instrument time
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Laboratory Rules – All Users
Do not put objects on the instrument as the electron
Image: SF Weekly
instrument as the electron optics is sensitive to vibration
Do not modify the set-up of the instrument in any form (the FE-SEM operates at high voltage)
Sign in log book and provide ISSV number
Sample exchange will be
Start of Session
p gperformed by John DeDecker, Katharina Pfaff (or Thomas Monecke)
We will bring the sample in focus for you at a working distance of 10 mm (SE, BSE and EDS are optimized for this WD)
We will set the operating voltage to 20 kV for you
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Sample Exchange Log Sheet
Date Name User IDHolder Type
Sample Name SE BSE EDS Beam on (time)
Beam off (time)
Total Beam Time
Beam Intensity
Gun Pressure
Column Pressure
Chamber Pressure
Laboratory Rules – Easy Mode Training Level
You are not allowed to vent the h b d h lchamber and change samples
You are not allowed (and do not need) to change z-axis due to the risk of hitting one of the detectors with the sample or the stage
You are not allowed to change b lt f th FE SEMbeam voltage of the FE-SEM
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Use chamber view when you are uncertain where you are on the sample and during significant x- and y-translations
You must switch off the chamber view if you use the EDS system as prolonged use will damage the detector
Graphical User Interface – Easy Mode Training Level
Magnification
Scan Speed
g
WD (Focus)
Brightness/Contrast
Beam Intensity
x- and y-control of stage (not commonly
used because it easier to use control panel)
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Graphical User Interface – Easy Mode Training Level
Change SE/BSE
z-axis control (do not use)
Scan speed
Magnification
Imaging mode
Auto-brightness/contrast
Brightness/contrast
Focus
Astigmatism
Beam Intensity
Wobbling
Picture taking
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Brightness and Contrast
Contrast
Auto
Brightness
Focusing of the Image
Out of focus (SE image) In focus (SE image)
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Choose small object and increase magnification (yellow box)
Adjust focus (WD) until image is in focus
Magnification
Focus (WD)
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Wobbling
Centering of the aperture is conducted by wobbling (i.e., the FE-SEM automatically swings the focus back and forth)
If the aperture is centered, an object should not move in x and y during wobbling but only go in and out of focuswobbling, but only go in and out of focus
C t C t
Wobble
Correct x-position of aperture
Correct y-position of aperture
Sensitivity (1-9 steps)
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Find a small, bright object, increase magnification so that object fills
b t 1/3 1/2 f th ll babout 1/3-1/2 of the yellow box
Adjust x- and y-position of the aperture until object does not move
Remove Astigmatism
Astigmatism is caused by non-circularity in the electron beam, which causes stretching of the image in x- or y-direction
Adjust the x- and y-stigmators, which control the current in the scanning coils of the FE-SEM
Very important for imaging at high resolution
Astigmatism needs to be corrected frequently when working at high magnification as contamination in the column causes astigmatism
If working at low magnification, astigmatism needs to be corrected every time a change in the setting occurs (i.e., beam intensity in easy mode training level)
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Increase magnification of image significantly
Remove Astigmatism
Focus until you cannot improve the focus anymore
Use x- and y-stigmators to remove stretching of the image
Adjust focus as you optimize the x- and y-stigmators
Switching Between SE and BSE
Change SE/BSE
Insert and retract BSE detector only when chamber view is switched on (no real need to do that if BSE detector is in position)
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Improve BSE Images
Initially use auto-brightness and auto-contrast
Make sure you are in focus
Find grain you want to study Find grain you want to study
Decrease brightness and increase contrast at the same time in a way that minerals having lower average atomic number go black while those with higher atomic number go white
Choose a slow scan speed
Need high-quality thin sections and good carbon coat
Use of the EDS System
Blue light means EDS is ready to be used (red light = stand-by mode)
Ch b i t b Chamber view must be switched off when using the EDS
Open Quantax Esprit software on EDS computer and login
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Switch on EDS system
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End of Session
Ask John DeDecker, Katharina Pf ff ( Th M k ) tPfaff (or Thomas Monecke) to vent the sample chamber and return your sample
If you are the last user of the day, ensure that the instrument and the EDS system are turned into stand-by mode
E th t i t i th Ensure that you sign out in the log book
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Laboratory Rules – Easy Mode Training Level
Ask if you are uncertain what to do
This is not a machine to play with you need to think about every– you need to think about every
step before you do it and you have to understand the consequences of every action before you execute it
The instrument is not easy to break in the Easy User Training Level (it is clearly your fault if youLevel (it is clearly your fault if you do)
You are not allowed to give access to other users and you are not allowed to train other users
H f i i !Have fun imaging !