Post on 05-Jun-2018
transcript
The Scanning Transmission Electron
Holography Microscope (STEHM)
Rodney HerringUniversity of Victoria, Victoria, BC Canada
V8W 2Y2 (rherring@uvic.ca)
MSC/SMCJune 5-8, 2012
Halifax, NS
Scanning Transmission Electron Holography Microscope (STEHM) Infrastructure
Fischione Ion Miller (Model 1010)
STEHM – Hitachi HF3300V
Fischione Plasma Cleaner (Model 1020)
SEM – Hitachi S4800 (+ Bruker EDS) FIB – Hitachi HB-2100
Pelco Carbon Coater (Cressington 208C)
Hitachi UV Cleaner (ZoneSEM)
+ Anatech Metal Coater (Au+Pd)
Scanning Transmission Electron Holography Microscope (STEHM)
Special features of STEHM
• Accelerating voltage • Electron source • Probe forming lenses • Focusing lenses • Projector lenses • Base unit • Housing laboratory
• The STEHM can perform all conventional TEM and STEM imaging and analytical methods but just a lot better.
• Everything that’s good for electron holography is good for high resolution imaging.
Accelerating Voltage (The Top Hat) • Can be used at 300 kV, 200 kV and 60 kV • Multiple voltages enable multiple variables of the
specimen to be determined by electron holography • 300 kV for ultra-high spatial resolution, high-beam
current studies • 200 kV for specimens that damage at 300 kV but not at 200
kV, e.g., silicon. • 60 kV for beam sensitive, biological specimen
• Carbon displaces at ~80 kV • Still able to obtain 1 Å resolution (0.7 Å measured)
The STEHM
The STEHM
The Electron Source (The Brains) • New Cold-FEG Electron Gun Assembly • New materials – very stable in high vacuum. • Electron emitter – tungsten (W) single crystal (~10 nm dia)
• Improved vacuum to 10-13 torr (10-11 Pa) • Just one order less than deep space • Reduced deposition of H on W electron emitting surface
• Electron emission improved by 3x • Previously, Cold-FEG 10x brighter than standard Schottky
FEG • Now 30x brighter than standard Schottky FEG • permanently stable at high electron emission
The Electron Source (The Brains) • Improved electron energy spread • ~ 0.3 eV • Can be reduced by reducing electron extraction voltage • Ultimate performance not yet measured (EELS) • Energy spread decreases (improves) with age of emitter • Necessary for energy-filtered imaging (GIF) and energy-
filtered holography measuring bandgaps and quasiparticle properties
• most coherent electron source of any machine • Required for high resolution imaging and high resolution
holography • Excellent starting point for the electron optics to follow
The STEHM
Probe Forming Lenses (Condenser Lenses)
• Substantially improved over HF3300 performance • Ultra low-noise, quiet electronics • Ultra stable lens currents • Ultra quiet switches between STEM & TEM modes • Smallest probe size not yet determined but will be
much better than 1.0 Å (~ 0.5 Å – 0.7 Å)
The STEHM
Probe Forming Lenses (Condenser Lenses) Special condenser lens apertures
Dislocated hologram aperture • For changing electron beam from plane wave to
electron vortex beams • For manipulating specimen’s electrons, atoms
and nanostructures • Used to filter electron spin polarized electrons
Electron Biprism • One electron biprism above specimen • Forms two beams • For STEM holography and Confocal Electron
Holography
The STEHM
Formation of Electron Vortex Beams
B J McMorran et al. Science 2011;331:192-195
Electron Vortex Beam from Dislocated Hologram
R A Herring Science 2011;331:155-156
Creation of spiral-type wave from a plane wave using hologram with a dislocation.
Herring & Pozzi, Intro to EH (1999).
Electron vortex beams carry orbital angular momentum (OAM) useful for:
• atomic and subatomic scale manipulations stir up currents in superconductors apply magnetic fields at the nanoscale pick and place molecules and atoms make and break electronic bonds (tweezers)
• enable new chemical, crystallographic, optical, electronic, and magnetic information about a sample • enable new technique for magnetic imaging • enable spiral phase microscopy in a TEM • enhance the visibility of edges in samples with low absorption contrast, such as unstained biological specimens, macromolecules, carbon nanotubes, and polymers, without sacrificing spatial resolution. • new capabilities for electron energy loss spectroscopy (EELS) in a TEM • the dark intensity node of the vortex could be used to improve the spatial resolution of the electron microscope
R A Herring Science 2011;331:155-156
The STEHM
Focusing Lenses (The Heart) • First Cs + Cc corrected STEM
• Ultra small, high-current electron probe better than 0.7 Å expected
• Using Secondary Electron detector can see surface atoms and atomic structures of specimen
• For use with HAADF detector for Z-contrast imaging and performing AEM (analytical electron microscopy)
• Necessary for interrogating electron densities between atomic columns of crystals
• For characterization of point defects and small electronic defects, eg., EL2 defect in GaAs.
The STEHM
Focusing Lenses (The Heart) • STEM Cs + Cc corrector
• Contains EXB Wien filter • Only electron microscope with Wien filter • May be possible to produce spin polarized
electron beams having electron spin momentum
• Opens up new research involving: • electron and nuclear spintronics • measurement and characterization of magnetic potentials at atomic scale.
Scanning Transmission Electron Holography Microscope (STEHM)
Focusing Lenses (The Heart) Object lens pole piece
• same as NRC NINT’s HF3300 • +15o rotation using standard holder • tomography holder available with 360o rotation • Ultra-clean vacuum using ZoneTEM • Cs – who cares?
STEHM
Focusing Lenses (The Heart) • First Aplanatic TEM
• First Cs and coma corrected TEM • Cc partially corrected • Coma correction increases high resolution
field-of-view imaging area by 10x • Area increased from ~100 nm to ~one micron
diameter • Ultimate spatial resolution not yet determined • Better than 50 pm measured • Spatial resolution improved using UVic’s $1.2M
STEHM Lab
The STEHM
The Intermediate Lenses (The Legs) • One extra projection lens – higher magnification • Accommodate 3 electron biprisms below specimen
• For new types of beam interference/holography • eg., 3D confocal electron holography, directly
imaging the specimen’s phase information, etc • Magnification between biprisms made equal to one
• Enables lensless, double energy-filtered lattice imaging, etc
• Can split electron wave into four pieces by also using condenser electron biprism above specimen
• Great for quantum mechanic studies involving frustrated electrons and quantum communications
The STEHM
The Intermediate Lenses (The Legs) • Electron holography
• Hologram carrier fringes down to ~4 pm • Fringes can be able to measure electron wave
disturbances due to vibrations less than the wavelength of the electron, i.e., < 2 pm
• May be possible to use for monitoring Earth’s plate tectonics
• ~ 1 million times better than using LASER
The STEHM
The Base (The Feet) • New Base developed for STEHM • Steel composite • More rigid • More vibration dampening • Ultra-stable mechanically • Necessary for high column (~4.5 m) of STEHM
The STEHM Lab
STEHM Lab (The Home) • Five layers of walls protect the STEHM • Aluminum outer wall to remove stray electromagnetic
fields • Steel-clad thermal insulation wall to help maintain room
temperature to + 0.1 oC per hour. • Mu metal shielding to remove stray magnetic fields
including protection around PEELS/GIF • Cooling panels + quiet HVAC with wrap-around sock for
diffuse room air • Isolated foundation directly on top of bed-rock • Sound reducing panels • Over-pressurized room to remove barometric pressure
fluctuations
The STEHM
Special accessories of STEHM • Has almost all analytical and imaging accessories
• SE - Secondary Electron detector for seeing surfaces • EELS – electron energy loss spectrometer for
determining composition (light elements) and molecular state of atoms and molecules
• EDS – x-ray energy dispersive spectrometer for compositions (atomic column x atomic column should be possible)
The STEHM
Special accessories of STEHM (cont’d)
• Imaging energy filter (GIF – Gatan Imaging Filter) for energy-filtered imaging and higher magnification imaging (20x)
• HAADF – high-angle annular dark field imaging (high-resolution Z-contrast imaging)
• HAABFD - high-angle annular bright field imaging (high-resolution STEM imaging)
• Still needed - Cathodoluminescence detector for optoelectronic materials
The STEHM
Specimen holders of STEHM • High-stability single tilt holder for high-resolution
imaging • Double-tilt low background for analytical electron
microscopy • Tomography (360o rotation) for 3-dimensional
imaging • High-stability high-temperature holder (1500 oC) for
molecular dynamic studies • Liquid N2 holder for beam sensitive specimens and
low-temperature studies • Flash freezer for biological fluid specimens (cryoEM)
The STEHM Lab
The Cost • See Excel spread sheet
STEHM Akira Tonomura Fellowship
• In honour of Dr. Akira Tonomura who passed away on May 2, 2012
• Winner of: Emperor Award, Benjamin Franklin Award, Royal Society Award, Honda Award, etc
• To support one scientist and one engineer to use STEHM at UVic for periods of time varying from one month to one year.
• Several fellowships each year are expected to be granted.
• Theoretical to experimental studies involving STEHM • Open to anyone from academia, government, industry
and independents.
Some STEHM Studies
• electron & nuclear spin momentum studies • electron vortex beam specimen manipulation • coherence measurement of quasiparticles • molecular dynamics using TDS electrons • measurement of time using TDS electrons • Stobbs factor – quantitative HREM • 3D strain field measurements using HOLZ and
confocal electron holography • protein crystal structures - nucleation and growth • short range structure of amorphous materials • next generation gene sequencing • monitoring Earth’s tectonic motions • etc., etc., etc.
Summary
The STEHM • One awesome electron microscope
• Enabling awesome science
Don’t use the ABNORMAL infrastructure
Use the STEHM infrastructure for what its worth!
See: Lab Manager - Elaine Humphrey
STEHM infrastructure Trainer – Adam Schuetze http://stehm.uvic.ca/
In Conclusion
Acknowledgements • Canadian Foundation for Innovation
• British Columbia Knowledge Development Fund
• Hitachi High Technologies Canada
• University of Victoria