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