the new tem facility at lci, ksu
TRANSCRIPT
The New TEM facility at LCI, KSU
Min Gao
Liquid Crystal Institute
Kent State University
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Questions to be answered
• How does TEM work?
2
• Why thin specimen? How to prepare one?
• What is the TEM at LCI like? Functions available and principles?
• How is the facility running so far? Any exciting results?
• How to use the TEM lab?
Facts about the TEM facility at LCI
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Instruments
Specifications
Applications
What we have at LCI
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• FEI Tecnai F20ST-STEM – Schottky field mission gun – 40 kV-200 kV – 0.24 nm point-to-point resolution – ±70° tilting angle – 0.2 nm spot size
• Attachments
– Low-dose mode & tomography – EDAX energy dispersive x-ray
spectrometer (EDS) – Gatan imaging filter (incl. EELS) – 4k*4K slow scan CCD – Cryo-holder & anti-contaminator
• Assisting equipments – Vitrobot – Plasma cleaner – Vacuum station
How good is this microscope?
Borisevich, 2004
La in γ-Al2O3
Batson et al. Nature 2002
in situ
0.0001
0.001
0.01
0.1
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1800 1840 1880 1920 1960 2000 2040
Reso
luti
on
(A
ng
.-1
)
Year
Electron Microscope
Light Microscope
Corrected EM
Ross
Amici
Abbe
Ruska
Marton
Dietrich
(200keV)
Haider
(200keV)
“It would be very easy to make an analysis of any complicated chemical substance; all one would have to do would be to look at it and see where the atoms are. … I put this out as a challenge: Is there no way to make the electron microscope more powerful?” – Richard P. Feynman, 1959, “There’s Plenty of Room at the Bottom”
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• Second best thing after corrected TEM • It is the best thing considering
• Cost of TEM and maintenance • Easy to use • 85% applications do not need Cs corrector
General description of the TEM facility at LCI
• Things making this facility standing out: the optimum integration of some most advanced TEM techniques, for example: cryoEM
• An application-oriented versatile microscope
• Excellent for materials science/life science/solid state physics/chemistry
• Current setup: nanomaterials/soft-materials requiring simple sample preparation
• A heavily computerized TEM with some bugs-easy to operate
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7
Philips and FEI microscopes
EM420
CM200
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“I've gotta see some atoms, excuse me,“ --Obama
Titan
How much a TEM cost?
• $4-5 per eV
• 200 keV: 1M$ + accessories (easily up to 0.5-1M)
There must be some solid reasons that we need such an expensive machine!
extremely stable high-voltage supplies, extremely stable currents to each electromagnetic coil/lens, continuously-pumped high- or ultra-high-vacuum systems, and a cooling water supply circulation through the lenses and pumps. As they are very sensitive to vibration and external magnetic fields, microscopes designed to achieve high resolutions must be housed in stable buildings (sometimes underground) with special services such as magnetic field cancelling systems.
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How does TEM work?
Importance of thin specimens
Electron-material interaction
Techniques and Information
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50 nm Cu, 25 kV, 5 nm probe, 1000 electrons 50 nm Cu, 200 kV, 1 nm probe, 1000 electrons
Advantage of thin samples
Thin specimen in SEM (Thin specimen in) TEM
Where is my surface? Surface damage 11
What thin samples do you need?
• Represent the material you are studying: sometimes the thicker the better
• Electron transparent: dependent on the accelerating voltage, thickness of the specimen, and atomic number of the specimen.
• Uniformly thin
• Stable under the electron beam
• Conducing and nonmagnetic in the laboratory environment
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Generally speaking: 50-100 nm for conventional TEM; 15 nm for high resolution TEM
How to put the thin samples into the TEM?
• The general form of a TEM specimen is a 3mm thin disk
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Supporting grids
• Put the thin disk into a holder which goes to the TEM sample stage
How to prepare a thin sample?
• Bulk materials: Agate Mortar and Pestle
Wheel Saw Polishing machine
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Dimpler
Ion milling A lot of techniques have been developed to make TEM specimens
• Bulk & thin films:
Focused ion beam: TEM samples
Deposition of Pt protection layer
View from 52°
Start of cutting
Under cut
Au+Pd coating first
Other materials
Nanomaterials:
• Very easy
• Dispersed on supporting carbon film
Biomaterials
• Quite difficult
• Vitrobot
• Ultramicrotomy
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Specimen
Electron-thin specimen interaction
E
E-E
Ef
Characteristic X-rays
EDS
EELS
EFTEM
E
Secondary electrons
Auger electrons
Backscattered Electrons (Rutherford)
Large-angle Incoherent elastically scattered electrons (Rutherford)
Z-contrast
STEM
Light
Cathodoluminescence
e-h pair
EBIC
Inelastically scattered electrons Coherent elastically scattered electrons
Diffraction
Imaging
HRTEM
Other signals from interaction with many nuclei or electrons: Bremsstrahlung x-ray (EDS), Plasma excitation (EELS) …
Incident
electron
beam (E)
Ef Ef Ef
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Reimer, TEM, 1984
Instruments (TEM & STEM)
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O Si Mo
Information from a modern TEM
Gao et al. APL, 72, 2544 (1998)
Gao et al. JAP, 80, 4767 (1996)
Gao & Duan, Mater. Trans. JIM, 39, 883, 1998
Gao et al. PRB, 62, 5413 (2000) Gao et al. Unpublished
Gao et al. Z. Metallkd. 93, 438 (2002)
In situ
EELS/EDS
Si
CBED
Mo/SiOx
Gao et al. PRB, 62, 5413 (2000)
O-K 1s 2p
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Why TEM?
Knowing the limitations of TEM
• Sample preparation (low temperature, low-energy low angle ion milling, FIB-site specific, freeze-fracture, vitreous ethane ice)
• Vacuum environment (environmental EM, in vitro)
• Not so much about properties (in situ, combination) 20
• Artifacts due to 2-D projections (3D TEM)
• Electron beam irradiation and contamination (diffraction imaging, low temperature, low dose, cryoEM)
• Poor Sampling: all TEMs have only examined <1 mm3 of materials! (First use low resolution but better sampling tools)
• Interpretation of images
What have been done in the test running period at LCI?
Service summary
Available techniques
Representative results
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Si_L
C_K O_K
Au+Si+O
Serv
ice
ho
urs
Nu
mb
er
of
sam
ple
s
Week
Weekly service hours and number of samples
Total service hours: 186 Cryo: 83 hrs
Total number of samples: 113 FE
I Cry
o T
rain
ing
Min
in C
hin
a
Cry
o-t
rial
Ho
liday
TEM
Sta
rtu
p
1%6%4%
20%
4%
8%30%
3%4%
20%
Peter Palffy-Muhoray
Quan Li
Oleg Lavrentovich
Tony Jakli
Soumitra Basu
Service hours vs groups
L.C. Chen
Mieteck Jaroniec
Songping Huang
Laurie Broadwater
Teaching
Available TEM techniques
• Imaging (diffraction contract, high resolution, Z-contrast, energy-filtered)
• Diffraction (select-area, convergent beam, large angle CBED, nano-area)
• Spectrometry (EDS, EELS)
• CryoEM
• 3D tomography
• … 24
Imaging (contrast)
• Mass and thickness contrast
• Diffraction contrast
• Phase contrast (e.g., HRTEM)
• Z-contrast
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Imaging (LCI)
TEM bright field image and STEM Z-contrast (dark field) image
Sample from Prof. Peter Palffy-Muhoray’s group
HRTEM
Sample from Prof. Peter Palffy-Muhoray’s group
HRTEM of
quantum dots
Sample from Prof. LC Chien’s group
Diffraction
30 Sample from Dr. Quan Li’s group
An interesting
sample SiOx
C
Au
Sample from Prof. Peter Palffy-Muhoray’s group
EDS spectral imaging
Au
Si
O
Au+Si+O
Si_L
C_K O_K
Sample from Prof. Peter Palffy-Muhoray’s group
Cryo-Vitrobot – Controlled environment: temperature
(4-60°C) and humidity (room cond. – 100%)
– designed for bio and liquid
– A small droplet of liquid is applied to pre-treated carbon film
– Two filter papers are used to blot the liquid and leave a thin layer of liquid (e.g., 100 nm thick, adjustable blot force, time and repetition).
– Shoot the sample into coolant (ethane) and freeze it at very high speed.
First bio-sample
Laurie Broadwater, Chemistry
A thermotropic sample
Sample from Prof. LC Chien’s group
A lyotropic sample
Sample from Prof. Oleg Lavrentovich’s group
• Resolution beyond freeze fracture • Very challenging: <10 e/nm2
Sample from Prof. Jakli’s group
Diffraction in Liquid Crystals Larger area
Sample from Prof. Jakli’s group
3D tomography
• A video taken by Dr. Lee Pullan (FEI) during the cryoEM training
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Plan for the next step
• Self-user Training: – Single operator MG + several self-users – Right now: 1-on-1 based on research needs – Later: a TEM course including lab training if allowed
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• Soon be running regularly
– Rules and operation procedures
– Usage rates (machine use, staff service) and billing
– …
• Web page of the facility
How to use the facility more efficiently • Highly efficient, professional, yet friendly service • The TEM will be aligned by the staff routinely, so you do not
need to be an expert in TEM
• Know your sample as well as possible • If you don’t know TEM so well, have an in-depth discussion
with the staff before scheduling your experiment • Have a student with good experimental skills and a lot of
patience • Analyze your data immediately • Introduce more outside users to keep the rates low • Acknowledge the facility properly • Pay your bill in time • …
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Questions being answered
• How does TEM work?
42
• Why thin specimen? How to prepare one?
• What is the TEM at LCI like? Functions available and principles?
• How is the facility running so far? Any exciting results?
• How to use the TEM lab? [email protected]