Dr. Michael Rauscher, Senior Director of the ZEISS Microscopy Materials Science Division, speaks to AZoM about field emission scanning electron microscopy - what it is, how it has developed since its invention and what the future holds for the technology.
The year 2015 marks the 50th anniversary of the first commercial scanning electron microscope. How do systems today differ from the early systems of the 1960s?
Of course there’s been a lot of development and performance improvement in many areas since the first microscopes were shipped from Cambridge Instruments, which is now Carl Zeiss Microscopy Ltd.
However, to pick one, I would say that a major milestone was definitely the introduction of thermal field emission sources that enabled a huge leap in obtainable resolution without compromising the systems’ analytical capability. To date, this remains the dominant design for high and ultra-high resolution scanning electron microscopy.
So, for field emission scanning electron microscopy is it fair to say that resolution is still the dominating value driver?
It certainly is a very important factor but other factors are equally important, such as available signal and contrast, the previously mentioned analytical capability but also the flexibility with respect to what type of samples can be imaged.
For example, today we can image samples at high resolutions and using a variety of signals that were considered completely “unimaginable” using electron microscopy only a couple of years back.
Why is this important?
Beyond the pure resolution aspect, researchers are also interested in obtaining all sorts of information about their sample for a complete characterization. A field emission scanning electron microscope generally provides a wealth of signals and contrast mechanisms that help users unlock the secrets of their specimen.
Characterization of the new classes of materials used in modern engineering such as ceramics, oxides, compounds or 2D materials is quite challenging given that they are often susceptible to charging under the electron beam. But this characterization is, of course, important to understand and to tailor their properties.
How is the challenge of characterizing modern materials addressed?
One important enabler is the use of low energies when imaging the sample. This minimizes charging from the very beginning. In order to maintain high resolution and also signal intensity, specially designed optics, such as the Gemini lens that combines probe formation and signal detection in one powerful objective lens, are required.
Very early on, we’ve seen the broad applicative demand for this enabling technology and hence the Gemini design is an integral part of any of our FE-SEMs today and particularly in our new high-resolution Sigma and ultra-high resolution GeminiSEM instrument families.
This means the optical design is key?
As a representative of a company that looks back on a unique legacy in optical innovation for microscopy, I guess the answer needs to be “yes”. However, I would like to add that the intelligent incorporation of detection schemes and the link to analytical techniques, such as EDS, are equally important.
In our newly launched ZEISS GeminiSEM premium instrument family we therefore provide a novel optical design. The Nano-twin lens allows effortless sub-nanometer resolution at low voltage. And the innovative NanoVP concept enables the previously impossible use of in-lens secondary and backscatter detection at pressures of up to 150 Pa providing an unprecedented image quality on charging samples.
At the same time, NanoVP also enables the use of EDS detectors on this kind of sample, providing additional chemical information about specimen composition.
What will be driving innovation in FE-SEM in the future?
This is certainly a tough question. For research I would say that the trend to holistically characterize a sample will continue to drive the market, meaning more diverse and differentiated detection capabilities.
However, I also expect that the link to other microscopy and analysis techniques will become more important in future. Seamlessly connecting data obtained from those individual platforms is then the challenge. But also the fact that users will have less and less time available for any given technique.
As a consequence, ease-of-use and time-to-result aspects need to be considered. In essence, this means that system design in the future has to tackle broader application areas and simultaneously implement throughput oriented workflows.
How does ZEISS address these innovation drivers?
For one thing, we definitely invest heavily in maintaining ZEISS’ leading position in FE- SEM technology with respect to resolution and detection performance. The new ZEISS Sigma and ZEISS GeminiSEM instrument families are clear evidence of this commitment to pushing the boundaries in optical performance. In addition, we are also focusing on further enhancing and extending our correlative microscopy solutions such as Shuttle and Find.
As an example: we have recently pioneered the use of Shuttle and Find to include atomic force microscopy (AFM) - a technique of particular interest to the fascinating field of graphene research.
And while usability and efficiency aspects are uniquely addressed in our FE-SEMs today – see for example the “Four Step Workflow” on the Sigma instrument series – we will definitely extend the capabilities here too. In summary, and if you allow me the historical reference: ZEISS is definitely committed to leading the coming 50 years of SEM innovation too.
About Dr. Michael Rauscher
Since his days as a postgraduate student at Tuebingen University, Germany, Michael has been fascinated by electron and ion optics and, in particular, their application to modern microscopy.
He received his PhD in Applied Physics in 2006 for designing and testing a low voltage focused ion beam system for gentle sample imaging and preparation.
After his studies, he joined Siemens Medical in a project on cancer therapy using carbon ions and subsequently came to ZEISS in 2008 as a product manager for FIB-SEM systems.
Since then, he has held different positions in product management and business development for electron and correlative microscopy.
He is currently senior director of the Materials Science market segment at ZEISS Microscopy and responsible for the microscopy and solutions portfolio from light to electron to X-ray microscopy for this fascinating application field.
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