Hitachi SU8230 Cold Field Emission SEM Yale West Campus Materials - - PowerPoint PPT Presentation

Yale West Campus Materials Characterization Core (MCC) ywcmatsci.yale.edu

Hitachi SU8230 Cold Field Emission SEM

Materials Characterization Core (MCC) ywcmatsci.yale.edu

2/20

Yale West Campus

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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Yale West Campus 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

• bjective lens and sample surface

Demagnification Optics

• Demagnification  image resolution
• Resolution  image intensity

𝑒B = 𝑒G 𝑞1 𝑟1 𝑒p = 𝑒B 𝑞2 𝑋𝐸 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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Yale West Campus 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) Counts

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 +10kV BSE

• 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

• f Engineering, Dr. Kazunori Sato

Sample: photocatalyst Vacc: 3 kV Signal : SE(L)

Materials Characterization Core (MCC) ywcmatsci.yale.edu

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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

• f 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

• f 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.

y electron

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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
• ften 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

Materials Characterization Core (MCC) ywcmatsci.yale.edu

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PhotoDiode (PD) - BSE Detector

SnTe nano-plate Au contact SiO 2 substrate I+ I- V+ V- V+ V-

Materials Characterization Core (MCC) ywcmatsci.yale.edu

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Hitachi SU8000 – Video Summary

https://youtu.be/F9qwfYwwCRM Video link: