FAQ's for On-demand webinar: Expanding the horizons of materials analysis with (S)TEM and EDX

After switching HT, do we need to redo the alignment of the electron path?

An alignment file needs to be loaded, and, typically, the beam shift and tilt need to be quickly checked. Then, OptiSTEM+ can be used on your specimen to fine-tune the optics to achieve the best resolution. This can be done within 10 minutes of changing the HT.

What's the main difference between the Spectra Ultra (S)TEM and the Spectra 300 (S)TEM?

There are two main differences. The first is that the Spectra Ultra (S)TEM's column maintains constant power between HTs. This means that when you change HT, the stage and optics drift for <5 minutes. On a Spectra 300 (S)TEM, the drift of the stage and the optics can be up to 5 hours becuase the column is only constant power for each HT and not between HTs. Being able to change the HT quickly means that you can use different HTs for different experiments, which results in optimized data for different experiments, e.g., highest resolution STEM at 300 kV and the best EDX signal at 80 kV. The other difference with the Spectra Ultra (S)TEM is that it introduces a new EDX detector, called Ultra-X, that has a massive detection solid angle. The solid angle is 4.45 srad without a holder and 4.04 srad with a holder. This detector is at least two times larger than any other detector on the market, which means that more than two times less dose is required to get the same level of chemical information. Alternatively, mapping with Ultra-X is at least two times faster than with any other EDX detector on the market.

Many thanks to Nestor for the very eduational talk! I wonder what technology XPAD detector uses and what is the difference between that and SDD? Is it a hybrid pixel direct photon countering detector?

XPAD is one of the first prototypes of Ultra-X. Ultra-X was designed by Nestor and engineered by Thermo Fisher Scientific. Ultra-X uses SDD technology.

For the Ultra-X detector, could you please elaborate how you realize >pi sr solid angles? Does anything change around the specimen chamber, e.g., pole piece? Would those changes block some future possibilities, e.g., introduction of cryo-blades/cryo-box like in cryo-EM?

The S-TWIN' pole piece used in combination with Ultra-X has been slightly redesigned with respect to the standard S-TWIN pole piece. This has been done to achieve the very high solid angle of Ultra-X, which is 4.45 srad without a holder and 4.04 srad with a double-tilt analytical holder. This design change of the pole piece still allows for 50 pm spatial resolution at 300 kV and 96 pm at 60 kV and large tilting angles, as is available with the standard S-TWIN lens on a Spectra 300 (S)TEM. A cryo-box is not available on a S-TWIN or an S-TWIN' pole piece. Cryo-blades are not standard on S-TWIN and S-TWIN' pole pieces; however, they could be ordered as a special.

Exciting to see that the detection solid angle is optimized! I wonder…How much room is there to improve on the SDD, or are they operating close to 100% detection efficiency?

Assuming detection efficiency refers to quantum efficiency: The quantum efficiency of modern SDDs is characterized by two effects: low-energy sensitivity is limited by the entrance layers of the chip, and high-energy efficiency is limited by the chip thickness. Ultra-X is built on state-of-the- art SDDs, supplied by one of the well-known SDD suppliers in the business. This results in, for example, the detectability of Be-ka as shown by Nestor and Si-La, a significant improvement compared to Super-X.

Is the Ultra-X symmetric around the alpha tilt axis?

Yes. Ultra-X is symmetric with respect to the alpha tilt axis. This is also true for our Super-X and Dual-X EDX detector solutions. A graph demonstrating this was shown in the presentation.

What pole piece types (what pole piece gap) is the Ultra-X compatable with?

The S-TWIN' pole piece used in combination with Ultra-X has been slightly redesigned with respect to the standard S-TWIN pole piece. This has been done to achieve the very high solid angle of Ultra-X which is 4.45 srad without a holder and 4.04 srad with a double-tilt analytical holder. This design change of the pole piece still allows for 50 pm spatial resolution at 300 kV and 96 pm at 60 kV and large tilting angles, as is available with the standard S-TWIN lens on a Spectra 300 (S)TEM. Ultra-X is only compatible with the S-TWIN' pole piece. The S-TWIN' pole piece has a gap of 5.4 mm, which is the same as the standard S-TWIN pole piece on the Spectra 200 and Spectra 300 (S)TEMs.

Can you share the perspectives that are required for in situ characterization? What are the challenges and expectations?

If by in situ analysis you mean heating/cooling/liquid and gaseous environments, then the key issue is not the XEDS detector, per se, but rather the design of the specimen holder and its penumbra. Argonne has a variety of special holders specifically compatible with these operations. Without question, there will be numerous commercally available ancilliary holders in the not too distant future.

Are there plans to be able to retrofit these detectors on cryo machines like the Krios and Arctica Cryo-TEMs if they proved successful in the biological field?

The Ultra-X detector cannot be retrofltted to a Krios or an Arctica Cryo-TEM; it is available only on a Spectra Ultra (S)TEM. The pole piece used on the Spectra Ultra (S)TEM as been specially designed to maximize the collection efficiency of Ultra-X while not comprimising the spatial resolution or the large tilting angle.

Does the flexibility of HT harm the source lifetime?

The new HT flexibily of the Spectra Ultra (S)TEM has no impact whatsoever on the souce lifetime. The HT can be changed freely to accommodate the specimen you need to investigate or the experiment that you want to do.

For quantification, how do we characterize detector efficiency if we want to calculate the scattering cross-section?

Quantification in STEM EDX is a complicated problem to solve. It critically depends on the specimen thickness, absorption correction, detector geometry, plural scattering, chaneling, etc. This is not unique to Ultra-X, or even EDX, because similar problems are seen in EELS. In EDS quantification, the inoization cross-section is a theoretical value that falls within the K-factors together with the detector efficiency. It is much more accurate to calculate the cross-section instead of measuring it from EDS due to many uncertainties.

How thick are the samples?

This was not measured, but a uniform thickness for measurements taken on all three detector configurations was ensured by collecting all the data from the same region of the specimen.

What was causing heating as a function of HV before that you have removed?

The main lens coils were never designed to maintain constant power between HTs. The Thermo Scientific™ Spectra™ Ultra (S)TEM accommodates a new lens design as well as a constant power scheme for the lens drivers to ensure that the column runs at a constant power regardless of the HT being used. This results in minimal drfit (<5 minutes) after an HT change.

Is the Ultra-X detector different than 4 combined detectors used by ChemiSTEM?

The Ultra-X detector design is fundamentally different than the Super-X design that was introduced with Thermo Scientific ChemiSTEM™ Technology. Ultra-X is multi-segment symmetric racetrack detector design that allows for large detection solid angles (4.45 srad without a holder and 4.04 srad with a doubletilt analytical holder). It is also a well collimated design, which means that spurious peaks (of Fe and Co) are <1%.

Can more information be given about the geometry of the Ultra-X detector?

See answer above

Is the Ultra-X detector segmented like the Super-X and the Dual-X? Are the segments symmetrically arranged and of the same size?

See answer above. Ultra-X has a symmetric design, and the segments are of the same size.

For a Titan Cubed Themis platform, could its Super-X detector be updated to an Ultra-X detector?

Unfortunately, Ultra-X cannot be upgraded to systems in the field. It needs to be combined with a specially designed pole piece (called an S-TWIN' pole piece), which allows for the very large collection solid angle in combination with the highest commercial spatial resolution STEM specifciations. This needs to be done during buildup of a new system in our Eindhoven factory.

Christian, could you please elaborate on why there used to be more spurious signal when using larger detectors and how that is addressed with the new spectrometer?

Generally speaking, it is more difficult to collimate the X-ray signal for large detectors. This was carefully considered in the design of Ultra-X and also in the design of the pole piece that is combined with Ultra-X. The result is an EDX detector that is at least two times larger than any other EDX detector configuration (4.45 srad solid angle without a holder and 4.04 srad with a double-tilt analytical holder), yet it is just as clean as our Super-X EDX detectors, with <1% spurious peaks of Fe and Co.

I am curious to know how is it possible to stabilize HT in 5 minutes??? Are all new Thermo Scientific microscopes able to do this?? 

The main lens coils were never designed to maintain constant power between HTs; they maintained constant power within only one HT. The Spectra Ultra (S)TEM accommodates a new lens design as well as a constant power scheme for the lens drivers to ensure that the column runs at a constant power regardless of the HT being used. This results in minimal drfit (<5 minutes) after an HT change. This new concept has only just been introduced on the Spectra Ultra (S)TEM, so it is not available on the Spectra 200 or Spectra 300 (S)TEMs.

What about amorphous materials much harder?

I am not sure what is meant by this question. If you could elaborate more on the question, then we could investigate.

How strict are requirements for the Spectra Ultra (S)TEM installation in comparison to, e.g., the Talos TEM—floor vibrations, etc., but especially external magnetic field?

The site requirements for a Spectra Ultra (S)TEM are more strict than for a Talos TEM, but they are, generally speaking, very similar to the site requirements of a Spectra 300 (S)TEM. You could contact your local account manager who could follow-up with you on the requirements of the site for a Spectra Ultra (S)TEM.

Is the Ultra-X system a "wet" system? Does it need liquid nitrogen? Is a coldfinger/anti-contamination device included?

Ultra-X is Peltier-cooled, so no liquid nitrogen is required. The Spectra Ultra (S)TEM is still equipped with a cold finger/anticontamination device to absorb any residual moisture around the specimen.

Nestor, can you comment on the probe size used for the perovskites superlattice image and on the fact that the Ba and Ca signals do not go to zero intensity in the other layer?

This was a thicker area of specimen with t/l (t over lambda) of about 1. This means that there was beam broadening of the probe by the time it reached the exit surface. This, as well as a layer of amorphous material formed by the FIB process, contributes to the total signal detected. It is also appropriate to note that channeling effects in specimens of this thickeness are present. Thinner specimens will, of course, mitigate these issues and, for high-resolution studies, will be done in due course. The nominal probe size was in the range of 0.1–0.2 nm and was not critical for the measurements being done.

Can a monochromator be attached to a Spectra Ultra (S)TEM? If yes, what would be the STEM resolution at the best energy resolution with the monochromator switched on?

Yes, a Spectra Ultra (S)TEM can be fitted with an X-FEG/Mono, an X-FEG/UltiMono, or an X-CFEG. Regarding the energy and spatial resolution specifications (with an X-FEG/Mono), this is HT dependent. At 300 kV, the energy resolution specifciation is typically around 0.2 eV (but it is also Gatan filter type dependent), and the STEM spatial resolution with the monochromator on is 60 pm. With the monochromator off, the STEM spatial resolution is 50 pm, and the energy resolution is <1.1 eV. At 60 kV, the energy resolution is (again Gatan filter dependent) <0.2 eV, and the STEM spatial resolution specification is 96 pm.

 

Nestor, beyond fundamental physics, could we do depth-resolved EDS?

If you mean as per the Argonne Scanning Confocal Electron Microscope, not directly. The X-ray detectors are not configured for that operating mode; however, a tomographic study is possible and will facilitate depth distribution studies. We (and many others worldwide) have done such in the past, and we are in the process of doing comparisons using the XPAD here at Argonne.

How does the HV system work?

The main lens coils on the Titan TEM (formerly produced by FEI), Thermo Scientific Themis Z TEM, and Spectra 200 and Spectra 300 (S)TEMs were never designed to maintain constant power between HTs. They only maintained constant power within one HT. The Spectra Ultra (S)TEM accommodates a new lens design as well as a constant power scheme for the lens drivers to ensure that the column runs at a constant power regardless of the HT being used. This results in minimal drift (<5 minutes) after an HT change. This new concept has only just been introduced on the Spectra Ultra (S)TEM, so it is not available on the Spectra 200 or Spectra 300 (S)TEMs.