Oxford instruments are delighted to be presenting 4 of the presentations, in both the SEM and characterisation session and TEM Session 2:
- Combined WDS-EDS,
- Biological applications with EDS
- New Event-Based Direct Detection Camera for Ultra-Fast Cryo-EM
- New Large-Array Direct Detector for Ultra-Fast 4D STEM
Please note that all timings below are Finnish time zone times.
SEM and characterisation
14:00-14:30 Oxford Instruments - Combined WDS-EDS analysis on the SEM
Wavelength Dispersive Spectrometry (WDS) and Energy Dispersive Spectrometry (EDS) utilize the same X-ray signal, generated by bombarding a solid sample with a beam of electrons, to determine elemental composition and distribution. These two microanalytical techniques, which can be employed on electron beam instruments (e.g., scanning electron microscope (SEM)), have different advantages/disadvantages. A higher spectral resolution can be achieved with WDS, and therefore it is possible to resolve X-ray peaks that overlap in the EDS spectrum, resulting in more accurate element identification and quantification. The higher spectral resolution of WDS also brings higher peak to background ratios, and therefore, lower detection limits allowing the accurate quantification of trace elements (>0.1 wt%). A comparative disadvantage of WDS is, unlike EDS, which generates a spectrum for the whole possible range of energies instantaneously, WDS can only measure X-rays of one energy at a time and therefore measurements are typically slower. The count rate achievable with a large area EDS detector is also typically higher, again making analysis via EDS quicker.
On this basis, a highly favourable solution is to combine the two techniques for fast and accurate results, and to do this on a highly flexible instrument for imaging and microanalysis – the SEM. Major – minor elements present in a sample can be measured using EDS, and WDS can be utilized where it is most advantageous – for the accurate quantification of trace elements, or those impacted by peak overlaps. This presentation will demonstrate the advantages of adding a WD spectrometer, with Rowland circle geometry and fully focussing crystals, to an SEM and conducting analysis in combination with EDS. We outline our method and show how using this approach can achieve results that are comparable with those collected on an electron microprobe (EPMA) with multicollection WDS.
14:30-15:00 Oxford Instruments - Bringing EDS to life! Multi-colour electron microscopy on biological samples.
What if we could change the way we analyse biological sample in an electron microscope? What if we could use EDS as a true imaging tool to help us interpret data from our samples?
Multi-colour electron microscopy using energy dispersive x-ray spectrometry (EDS) combines ultrastructural electron data with elemental information about sample composition. The additional ultrastructural differentiation can improve interpretation of features within samples and highlight regions of interest not easily determined using the electron signal alone.
Recent key developments in EDS technology have increased the speed of accurate analysis of light elements in biological samples. A major task remains in selecting the best methods for specimen preparation and determining the influence that choice has on the data we can obtain. This webinar will discuss the workflows involved, from sample prep considerations through to rapid analysis, and highlight how EDS is rapidly becoming a key technology for your biological and biomaterial research questions.
TEM Session 2
15:00-15:30 Direct Electron / Oxford Instruments - Apollo - A New Event-Based Direct Detection Camera for Ultra-Fast Cryo-EM
Over the past 10 years, electron counting with direct detection cameras has become the de facto standard for cryo-EM data acquisition. However, since its initial demonstration in 2009, the technology for electron counting has remained fundamentally unchanged: Electron counting is performed computationally, by thresholding and centroiding blobs on each of a large number of integrating mode frames acquired under a strictly limited TEM beam current. Every new camera generation from each of the three direct detection camera companies has used this brute force counting strategy, featuring only moderate increases in size, speed, and price.
One of the most significant bottlenecks for cryo-EM is the restrictive imaging conditions imposed by electron counting. Maintaining sparse illumination within each frame from the camera is necessary to avoid coincidence loss stemming from the inability to discriminate multiple coincident electrons as separate events. The limited exposure rate imposed by current cameras has two consequences: (1) it places an upper limit on throughput, and (2) it eliminates the microscopist's flexibility to optimize imaging conditions for new methods.
Here, we describe new direct detection technology that-for the first time-performs electron counting in hardware with a 4kx4k sensor, enabling high-quality image acquisition across a wide range of exposure rates with minimal coincidence loss. The resulting camera-called Apollo-delivers the quality of electron counting, while offering the flexibility and ease-of-use of an integrating-mode camera.
15:30-16:00 Oxford Instruments - Celeritas - A New Large-Array Direct Detector for Ultra-Fast 4D STEM
4D STEM is a technique that is becoming increasingly widespread, with a broad range of applications including electric and magnetic field mapping, crystal grain and strain mapping. In contrast to conventional, 2D STEM, where electrons scattered over a large range of angles are collected using a detector that outputs a single intensity value at each probe position, 4D STEM employs a pixelated detector to record a complete scattering pattern at every probe position, yielding an information-rich 4D dataset. One current limitation of 4D STEM is thoughput. Pixelated detector frame rates limit 4D STEM to acquisition speeds that are 1-2 orders of magnitude slower than conventional 2D STEM. Certain 4D STEM applications, particularly crystal grain mapping, may benefit from the use of a detector with a relatively large ~ 1 megapixel array size, and this array size can give the detector the flexibility to perform non-4D STEM applications, such as fast in situ TEM imaging. However, to achieve a megapixel array size, microscopists are limited to a choice between using detectors optimized for low-dose biological TEM imaging, or using detectors that consist of tiled 256 x 256 pixel chips, with areas of missing information between tiles.
Here, we describe Celeritas, a new, ultrafast monolithic active pixel sensor (MAPS) type direct detector specifically designed for 4D STEM. The physical sensor is 1024 × 1024 pixels in size, with 15 µm pixel pitch. At full frame size, the detector readout speed exceeds 2,100 frames per second (fps) Higher speeds are achieved through sub-area readout, with maximum of up to 87,000 fps 256 × 64 pixels, a speed approaching that of conventional 2D STEM. The flexibility of Celeritas allows the user to choose pixel count and speed to suit a variety of different applications and imaging modes.