INSTRUMENTS

FEI Titan3 G2 60-300 dual aberration-corrected TEM/STEM

The University of Hawai‘i’s Titan monochromated and dual aberration-corrected (scanning) transmission electron microscope. Credit: John Bradley / LLNL.

Graduate student Jade Comellas learning to use the TEM.

Different TEM holders available at AEMC.

Overview

The Titan (scanning) transmission electron microscope or (S)TEM operates at accelerating voltages between 60 and 300 keV, and electrons are passed through the sample. Dual spherical aberration (Cs) correctors provide a sub-Ångstrom electron probe and sub-Ångstrom imaging of thin specimens, typically only 20-120 nm in thickness.

Specimen petrography / texture / structure can be imaged directly using one of multiple brightfield and darkfield modes — with single-atomic-column resolution, if necessary.

High resolution TEM lattice fringe image of stacking faults in pyroxene. Credit John Bradley.

High angle annular dark field (HAADF) image of an inclusion in ancient chromite. (Rectangle indicates region in EDX maps below.) Image courtesy of Caroline Caplan.

$Nanodiffraction from a osbornite nanocrystal in a comet 81P/Wild 2 calcium aluminum inclusion returned by NASA’s Stardust mission$

Nanodiffraction from a osbornite nanocrystal in a comet 81P/Wild 2 calcium aluminum inclusion returned by NASA’s Stardust mission. Credit: from Chi et al. (2009) Geochim. et Cosmochim. Acta 73, 7150-7161.

Nickel oxidation states in battery materials can be analyzed using electron energy loss spectroscopy (EELS). Credit: John Bradley.

Image of energy-dispersive X-ray spectroscopy (EDX) mapping

Energy-dispersive X-ray spectroscopy (EDX) mapping of the interface region between host chromite and inclusion in an ancient chromite grain. Images courtesy of Caroline Caplan.

The furnace of the Gatan Model 652 double-tilt heating stage.

Crystal structure can be investigated by collecting either selected area or nanobeam electron diffraction patterns.

An optional monochromator can be used to narrow the energy bandwidth of electrons in the incident beam with 0.1-0.2 eV resolution. The monochromated electron beam, in conjunction with the Gatan Tridium energy-filter/electron spectrometer at the base of the microscope, enables electron energy loss spectroscopy (EELS). EELS is used to investigate atomic bonding environments, oxidation states, optical properties, molecular bonding and functional groups in organic materials and, in some samples, detection of liquids and gases.

Compositional mapping and spectroscopy approaching the atomic scale are possible using energy-dispersive X-ray spectroscopy (EDX), and compositional imaging can be obtained using energy-filtered transmission electron microscopy (EFTEM).

In-situ heating experiments are performed using a specialized hot stage sample holder.

Capabilities and characteristics:

Field emission electron gun (FEG) for high brightness and stability
Selectable beam acceleration voltages: 80, 200, 300 kV (Additional acceleration voltages possible.)
Wien filter monochromator and selectable apertures for energy filtered spectroscopy and imaging
high base environmental enclosure for improved noise isolation and Spicer active electromagnetic interference cancellation system
spherical aberration corrector for probe mode (STEM)
spherical aberration corrector for image mode (TEM)
~0.6 Ångstrom spatial resolution in transmission electron microscope (TEM) images
~0.6 Ångstrom spatial resolution in scanning transmission electron microscope (STEM) images
High angle annular dark field detector (HAADF) with variable camera length
Electron diffraction by selected area, micro-diffraction or convergent beam
Energy dispersive x-ray (EDX) spectrometer (EDAX Genesis 4000 solid state Si(Li) detector) for elemental chemistry analysis and mapping.
Elemental chemistry detection limits by EDX down to a few ppm are achievable for long count times on robust samples.
Thickness maps, EFTEM and EELS using an ultra-resolution Gatan Tridiem 866 GIF (Gatan imaging filter)
Energy resolution of 100-150 meV at 200 kV and 150-200 meV at 300 kV are routinely achievable on real samples. (Record-breaking 70 meV resolution recorded on zero loss peak.)
Gatan Model 652 double-tilt heating stage available for in situ heating experiments up to 1000°C on standard 3 mm diameter grids.
NEW! Continuous flow liquid TEM sample holder - The unique design of this TEM holder allows us to observe in real-time, at a subnanometer resolution, the reactionsbetween rocks and liquids enclosed between two electron-transparent windows. The liquid cell TEM sample holder has four important features:
- (i) Continuous flow – Once the sample is prepared, the system seals it within amicrofluidic liquid cell in the holder tip, which is separated from the vacuum of the TEM via a patented sealing mechanism. The sample is then exposed to a continuous flow of liquid running through the environmental cell. The closed-cell guarantees that once they are placed, samples remain within the viewing area. Interchangeable tips and user-replaceable tubing will allow us to perform controlled and cross-contamination-free experiments.
- (ii) Static Cell – It is a sealed-cell liquid holder for static liquid applications.
- (iii) Spectroscopy – The liquid TEM holder includes an energy-dispersive X-ray spectroscopy (EDS) feature for spectroscopic measurement inside the liquid cell. The specialized chips ensure the thinnest possible liquid layer, allowing for electron energy loss spectroscopy (EELS) inside the liquid cell. This in turn allows researchers to perform direct elemental analysis and mapping at high magnifications. The EDS liquid-cell holder’s large viewing angle ensures directaccess from the sample to the EDS detector (even for multiple-detector configurations).
- (iv) Heating – The holder has a heating system that is optimized for moderate temperature requirements. Each chip features its own thin-film heater, which heats the contents of the liquid cell to the boiling point of your solution (maximum 200°C).

The UH Titan (S)TEM was funded by NASA’s Sample Return Laboratory Instrumentation and Data Analysis Program, which is now the Laboratory Analysis of Returned Samples Program.

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