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The Scanning Transmission Electron Holography Microscope (STEHM) MSC/SMC June 5-8, 2012 Halifax, NS Rodney Herring University of Victoria, Victoria, BC Canada V8W 2Y2 ([email protected]) Scanning Transmission Electron Holography Microscope (STEHM) Infrastructure STEHM – Hitachi HF3300V Fischione Ion Miller (Model 1010) SEM – Hitachi S4800 (+ Bruker EDS) Fischione Plasma Cleaner (Model 1020) FIB – Hitachi HB-2100 Hitachi UV Cleaner (ZoneSEM) Pelco Carbon Coater (Cressington 208C) + 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. The STEHM 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 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 STEHM 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 energyfiltered 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 Formation of Electron Vortex Beams B J McMorran et al. Science 2011;331:192-195 Electron Vortex Beam from Dislocated Hologram Creation of spiral-type wave from a plane wave using hologram with a dislocation. R A Herring Science 2011;331:155-156 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 (highresolution Z-contrast imaging) • HAABFD - high-angle annular bright field imaging (highresolution 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 In Conclusion 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/ Acknowledgements • Canadian Foundation for Innovation • British Columbia Knowledge Development Fund • Hitachi High Technologies Canada • University of Victoria