Hitachi SU8230 Cold Field Emission SEM training slides-MCC-3.pdfSEM: Electron Sources Brightness: 10...
Transcript of Hitachi SU8230 Cold Field Emission SEM training slides-MCC-3.pdfSEM: Electron Sources Brightness: 10...
Yale West Campus Mater ials Character ization Core (MCC)
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Hitachi SU8230 Cold Field Emission SEM
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Core Policies
• DO NOT let other people use the facility under your account.
• DO NOT try to fix parts or software issues by yourself!
• DO NOT surf web using instrument computer!
• Follow checklist and SOP! DO NOT explore program!
• Facility usage time at least twice a month, OR receive training
again (two practice sessions within one week).
• No trainings on monthly users
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SEM: Basic Theory
Electron
source
Condensor lens 1
Condensor lens 2
Objective lens
Sample
Objective aperture
Deflection coils
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Tungsten wire LaB6 single crystal Cold Field Emission (CFE)
Brightness: 105 A/cm2sr
Beam size = 50 - 100 kÅ
Operation temperature: 3000 K
Vacuum: 10-5 Torr
Lifetime: 300 hrs
SEM: Electron Sources
Brightness: 10 x
Beam size = 50- 100 kÅ
Operation temperature: 2500 K
Vacuum: 10-7 Torr
Lifetime: 500 - 1000 hrs
Field Assisted
Thermionic Source
- Schottky
Brightness: 500 x
Beam size = 100 - 250 Å
Operation temperature: 2500 K
Vacuum: 10-9 Torr
Lifetime: > 4000 hrs
Brightness: 1000 x
Beam size = 30 - 50 Å
Operation temperature: 300 K
Vacuum: 10-11 Torr
Lifetime: > 10000 hrs
Acc
Voltage
Extraction
Voltage
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p2: Object distance of objective lens
q2: Image distance of objective lens
WD: Working Distance between the bottom of the
objective lens and sample surface
Demagnification Optics
• Demagnification image resolution
• Resolution image intensity
𝑑B = 𝑑G 𝑝1 𝑞1
𝑑p = 𝑑B 𝑝2 𝑊𝐷
Beam size at condenser lens focus plane
dG: Beam size exiting the gun
p1: Object distance of condenser lens
q1: Image distance of condenser lens
Beam size on specimen surface at objective
lens focus plane
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Accelerating voltage (Vacc)
Increasing accelerating voltage
less spherical aberration smaller probe diameter and better resolution
Increase beam penetration obscure surface detail
Increase the probe current at the specimen. A minimum probe current is necessary to obtain an
image with good contrast and a high signal to noise ratio.
Potentially increase charge-up and damage in specimens that are non-conductive and beam
sensitive.
Vacc
Penetration
depth
SEM images of vanadium oxide nanotubes at different acc voltages
Image courtesy http://www.microscopy.ethz.ch/
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Working Distance: the distance between the bottom of the objective lens
and the specimen
Increasing WD
• increased depth of focus
• Increased probe size lower resolution
• increased effects of stray magnetic fields lower resolution
• increased aberrations due to the need for a weaker lens to focus.
Factors Affecting SE Emission: Working Distance (WD)
200 um aperture and 10 mm WD. 200 um aperture and 38 mm WD
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SEM: Electron-Specimen Interactions
Sample
Electron beam
CL X-ray
(1-3 µm) Continuous X-ray
EDX
(1-3 µm)
BSE (~300 nm)
SE (5–50 nm)AE (1-5 nm)
Secondary electrons (SE < 50 eV)
Topographical information
Back-scattered electrons (BSE)
Composition (atomic number) and
topographical information
Characteristic X-ray (EDX) Composition
information (Energy Dispersive X-ray
Spectroscopy)
Auger electrons (AE)
Surface sensitive composition
information
Cathodoluminescence (CL) Electric states
information
Fluorescence
Phosphorescence
Continuous X-ray (Bremsstrahlung) Insulator
charging
Imaging resolution Interaction volume
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Schematic Electron Energy Spectrum
SE forms a large low-energy
peak < 50 eV
Shallow depth of
production topography
information
Small interaction volume
high imaging
resolution, comparable to
e-beam size
Auger Electron (AE)
produces relatively small
peaks on the BSE distribution
Goldstein et al. 1981
50 eV 2000 eV
Kinetic Energy (eV)
Co
un
ts
SE
AE
BSE
Elastic
reflection
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The SEM electromagnetic lenses
can not be machined to perfect
symmetry.
A lack of symmetry an oblong
beam: a disk of minimum
confusion
stronger focusing plane
narrower beam diameter
weaker focusing plane
wider diameter
Lens Aberrations: Astigmatism
Astigmatism correction
Apply current differentially to
stigmator coils circular beam
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SE Detector: Everhart-Thornley (E-T) Detector
E-beam
(0.5–30 kV)
Sample
Faraday Cage
-50 to +200 V
Optical
waveguide
Electron Multiplier
Dynodes
1-2 kV
Output
Photocathode
SE<50 eV
Scintillator
+10kVBSE
E-T detector: low-secondary
electrons are attracted by +200
V on grid and accelerated onto
scintillator by +10 kV bias;
The light produced by
scintillator (phosphor surface)
passes along light pipe to
external photomultiplier (PM)
which converts light to electric
signal.
Back scattered electrons also
detected but less efficiently
because they have higher
energy and are not
significantly deflected by grid
potential.
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Schematic of SU8200: Optics and detection system
• SE detectors:
• SE(L): SE lower detector
• SE(U): SE upper detector
• HA(T): HA-BSE top
detector
• Control/filtering electrode
• Conversion electrode
• Hi-Pass Top Filter
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SE(L) in normal modes (Vacc: 0.5~30 kV)
SE + BSE signal
• SE(L) (secondary electron Lower detector)
• Signal amount is relatively low, but will increase when WD is longer.
• Highly topographical information shadowing effect
• Less sensitive to specimen charge-up
• Signal of the Lower detector is less sensitive to charging artifacts
• Low resolution comparing to upper detector
Sample courtesy of : Nagaoka
University of Technology, Faculty
of Engineering, Dr. Kazunori Sato
Sample: photocatalyst
Vacc: 3 kV
Signal : SE(L)
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SE(U) in normal modes (Vacc: 0.5~30 kV)
• SE(U) (secondary electrons detected with the Upper detector through the objective lens)
• Large signal amount, high detection efficiency
• High resolution at the topmost surface information
• High edge contrast
• Sensitive to specimen charge-up
• BSE not detected.
Sample: photocatalyst
Vacc: 3 kV
Signal : SE(U)
Sample courtesy of : Nagaoka
University of Technology, Faculty
of Engineering, Dr. Kazunori Sato
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LA-BSE in normal modes (Vacc : 0.5~30 kV)
• LA-BSE SE at the control electrode and detected with the Upper detector.
• Amount of SE controlled by variable negative electrode voltage.
• Compositional + Topographic information Mixture of SE and LA-BSE image
• Less sensitive to specimen charging-up
Sample courtesy of : Nagaoka
University of Technology, Faculty
of Engineering, Dr. Kazunori Sato
Sample: photocatalyst
Vacc: 3 kV
Signal : LA-BSE(U)
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HA-BSE in normal modes (Vacc : 0.5~30 kV)
electrode
• HA-BSE (High-Angle Backscattered Electron)
• HA-BSE SE at the conversion electrode and detected with Top detector HA(T).
• Small signal amount
• Rich Compositional information
• Less topographic information
• Less sensitive to specimen charge-up
Mixed particles of
BaCO3/TiO2
Vacc: 1.5 kV
Signal: HA-BSE
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Beam Deceleration (Landing voltage 10 V ~ 2 kV)
• A negative voltage (deceleration voltage, Vrtd up to 3.5 kV) applied to the
specimen, thereby slowing down the primary electron beam to the desired landing
energy.
• Landing voltage (10 V – 2 kV):
Vlnd = Vacc – Vrtd;
Vrtd : Deceleration voltage
• Resolution improved in deceleration mode
Vacc: 500 V
Magnification: 100kx
Al electrolytic capacitor
Vacc: 500 V
Magnification: 100kx
Courtesy of St. Jude Medical, CRMD-U.S.A.
yelectron
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Scanning Transmission Electron Microscope (STEM) Mode
• A STEM image providing internal specimen
information can be obtained simultaneously with
the secondary electron image.
• The optional Bright Field STEM Aperture Unit is
often utilized to generate enhanced contrast
differentiation on materials of similar density.
Specimen: Carbon nanotubes
Vacc: 30 kV Magnification : 250kx
BF-STEM image Internal
information
DF-STEM image surface
information
SE detector
Photon guide
STEM detector
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PhotoDiode (PD) - BSE Detector
SnTe nano-plate
Au contact
SiO2
substrate
I+
I-
V+
V-
V+
V-
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Hitachi SU8000 – Video Summary
https://youtu.be/F9qwfYwwCRMVideo link: