Advantages of the Octane SDD Series for the Transmission Electron Microscope (TEM)

The Octane SDD Series for TEM has been developed from the Apollo XLTW series of detectors, in order to offer a new range of instruments consisting of excellent solid angle and maximum sensitivity. This series has a well-established windowless design and an enhanced detector module enclosure. These two features allow the highest possible solid angle to be accomplished in a given microscope configuration.

The support structure of the window can be eliminated by removing the detector window. By removing the window support structure, the solid angle can be enhanced by nearly a factor of two. The customized module enclosure enables the detector to be located nearer to the sample, maximizing the geometrical solid angle. The TEM’s vacuum environment is ideal for using a windowless detector. There is less opportunity to condense water vapor on the cold detector (-25°C), and if required the detector can be rapidly temperature cycled.

Octane SDD Series for TEM

Three detector models are available in the Octane SDD Series for TEM:

  • Octane T Optima: 30 or 60 mm2 active area. Optimized Windowless design for specific TEM columns with solid angles ranging up to 0.5 steradian. It is round in shape.
  • Octane T Plus: 30 mm2 active area. Entry level SDD with super ultra-thin window (SUTW) mountable on all TEMs. The Octane T Plus is round in shape.
  • Octane T Ultra: 100 mm2 active area. Maximum sensitivity SDD available, windowless with solid angle ranging up to 1.1 steradian. The T Ultra detector is oval in shape.

Enhancement in Sensitivity

Figure 1 illustrates a NiO spectrum from the Octane T Ultra. Both the NiL to NiK ratio and the NiL to O K ratios are extremely high. This is because of the windowless feature between the sample and the detector. The sensitivity to N is also significantly improved. A polymer window contains a large concentration of C, which selectively absorbs N. When the window is removed, more N X-rays are allowed to enter the detector.

NiO spectrum from the Octane T Ultra.

Figure 1. NiO spectrum from the Octane T Ultra.

Increase in Peak Intensity

Figure 2 illustrates the spectrum from a SiN 50 nm thick membrane. The spectrum from a SiLi detector is in red, while the windowless Octane spectrum is in green. Both spectra were procured at the same live time and beam current. Sensitivity for higher energy lines such as SiK is also enhanced by the windowless design. The Si intensity is four times more, and the peak intensity of N is 12 times more.

Si3N4 collected on FEI CM200 with ST lens.

Figure 2. Si3N4 collected on FEI CM200 with ST lens.

 

Figure 3 illustrates a sample of mineral glass thin film that is highly characterized by NIST. Using it, quantitative analysis can be checked or the sample can be used to calculate Cliff-Lorimer K-factors. Figure 4 shows the K-factors computed from this spectrum.

A spectrum from a mineral glass thin film characterized by NIST 2063a.

Figure 3. A spectrum from a mineral glass thin film characterized by NIST 2063a.

The Cliff-Lorimer K-factors for the spectrum in Figure 3.

Figure 4. The Cliff-Lorimer K-factors for the spectrum in Figure 3.

TEAM™ EDS Atomic Resolution Drift Correction

The TEAM™ EDS Atomic Resolution Drift Correction was developed especially for the most challenging samples in TEM data collection. The difficulty is to maintain the placement of the beam and sample to gather the right data from samples, which are sensitive to very fine movement. This kind of a drift method needs a quicker correlation process and a better quality reference image.

This process offers both of these capabilities by applying the actual image as the reference image during the time of collection, which reduces the time taken to gather an individual reference image. Additionally, a rapid Fourier transform is used by the correlation procedure instantly in-between collection frames, and makes the essential modifications prior to initiating the next frame. The outcome is maximized image and element signal intensity in the correct locations, which produces maps of high resolution.

A Hitachi HD2700a STEM with aberration correction was used to test a SrTiO3 sample. The conditions included: 200 Kv, 100 pa of beam current and 8000 Kx magnification. Mapping was conducted at a pixel level of 256 x 200 pixels. 150 µsec was the dwell time at each pixel, and the number of frames aquired was 109. The TEAM™ EDS Atomic Resolution Drift was used to correct for drift in the system.

Figure 5 illustrates the STEM image and the SrL and TiK maps. The TiL spots and the SrL bright spots align with the small centered spots and the bright areas of the STEM image, respectively. Applying image processing to the net intensity images and overlaying Ti and Sr offer a distinct image of the atom locations as seen in Figure 6.

The STEM image (top left), SrL map (top right) and TiK map (bottom left) for a sample of SrTiO3.

Figure 5. The STEM image (top left), SrL map (top right) and TiK map (bottom left) for a sample of SrTiO3.

Image showing the atom locations, created by applying image processing to the net intensity images and overlying Sr and Ti. SrL is green and TiL is blue.

Figure 6. Image showing the atom locations, created by applying image processing to the net intensity images and overlying Sr and Ti. SrL is green and TiL is blue.

Applications

Application 1: A Layered Membrane

The DLR Institute of the University of Cologne used the Optima T Plus detector to measure a cross-section of thin film layers on a membrane. These maps as seen in Figure 7 were obtained on a Tecnai F-30 at 200 Kv. The conditions were 3.84 nAmp Screen Current, Condensor 2: 70 µm, 7.68 usec Amp time, 8000 cps, 68000 x microscope magnification. As much as 500 frames were obtained.

The field of view for a layered membrane application. The field of view is 100 nm wide.

Figure 7. The field of view for a layered membrane application. The field of view is 100 nm wide.

Figure 8 illustrates an image of an overlay of the key target elements. (Ga and Pt are from the FIB processing and Cu is from the grid). Figure 9 illustrates a line scan from top to bottom of the area. For easy interpretation, it is rotated 90°.

An overlay of the primary elements of interest. (Cu is from the grid and Ga and Pt are from the FIB processing).

Figure 8. An overlay of the primary elements of interest. (Cu is from the grid and Ga and Pt are from the FIB processing).

A line scan from top to bottom of the area.

Figure 9. A line scan from top to bottom of the area.

Application 2: Clusters of Silicide Particles

Figure 10 shows the STEM image that was achieved using a Tecnai F-20 at 200 Kv. This cluster is made up of silicide particles. While deriving maps, a phase map was developed illustrating the existence of five phases. The blue phase was Ni silicide, the orange phase was Mn silicide, the yellow phase was Si, and the green phase was Co silicide.

The map as seen in Figure 11 was achieved at 128 by 100 pixels. 20,000x was the microscope magnification. A thinner area close to the blue phase edge was measured as seen in Figure 12. It illustrates that the composition is near NiSi. The area’s thickness is not known, creating difficulty for precise analysis. The count rate was more than 20,000 cps, and the total acquisition time was below 5 minutes.

STEM image showing silicide particles that make up a cluster.

Figure 10. STEM image showing silicide particles that make up a cluster.

Phase map showing the presence of five phases in the cluster.

Figure 11. Phase map showing the presence of five phases in the cluster.

A quantification of a thinner area near an edge of the blue phase.

Figure 12. A quantification of a thinner area near an edge of the blue phase.

Application 3: A Line Scan Across a Nanoparticle

Figure 13 illustrates the image, spectrum, and line acquired on a Hitachi HD-2700 dedicated STEM. Pt-Co nanoparticles on graphite are seen as bright particles. The line scan was conducted over a particle of 5 nm diameter. Nestor Zaluzec at Argonne National Laboratory provided the sample.

Image, spectrum and line scan from a nanoparticle.

Figure 13. Image, spectrum and line scan from a nanoparticle.

Conclusion

The Octane SDD Series for TEM offers chemical evaluation at the maximum level possible for single detectors on a column. The Octane detectors accomplish much greater solid angles as opposed to the SiLi detectors that were substituted, and at the same time provide higher sensitivity for light elements. They also eliminate liquid nitrogen.

This information has been sourced, reviewed and adapted from materials provided by EDAX Inc.

For more information on this source, please visit EDAX Inc.

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