Hybrid AFM-SEM – complementary, not competitive techniques
I have recently been hearing a lot about hybrid AFM-SEMs which are a fairly recent innovation with some commercial entries to market over the past 5 years. So first, let’s discuss them individually.
Although both SEM and AFM are nanoscale microscopic techniques, the communities that engage in them remain rather siloed without much interaction and communication – to the detriment of both communities! The main electron microscopy meeting in the US – M &M – has really struggled to have a strong AFM contingent. AFM symposia and vendors have participated in fits and spurts over the years, but have struggled to have a consistent presence at this dominant microscopy meeting. In fact, my colleague Greg Haugstad and I tried our own hand at it at the 2015 meeting by trying to organize a short course and a symposium at the meeting. The short course was cancelled due to lack of subscribers, but the symposium had good attendance and interest. Still, we felt like outsiders at that meeting. A big AFM symposium usually takes place at the fall MRS. But it remains a setting for AFM enthusiasts; though there are plenty of EM people around at the meeting, they remain at their end of the hallway (or on another floor) at their symposium. Minimal to no interaction.
So maybe a joining of instrumentation can join the communities? We have a lot to learn and gain from each other. On a technical note, I view these techniques as highly complementary. SEM is particularly useful for high throughput screening, high resolution morphology (though no real z data), and chemical information. AFM is complementary in that it provides high resolution properties on the surface including: true topography (with real z), electrical properties, and mechanical properties, though no chemical information. So the marriage of the two techniques could provide you with the ultimate characterization tool! Use the SEM to screen for your area of feature of interest, and then use the AFM to get higher resolution data and surface properties in that area. See the example below of a scratched gold surface measured by low SEM on the left, higher resolution in the middle, and then AFM on the right
[image courtesy of GETec/Nanosurf AFSEM in an FEI Quanta 600 FEG ESEM)
Then you can top it off by using the SEM to get some chemical information as well.
Sounds simple right? Well, the integration of the AFM with SEM turns out to be more complicated to implement. There have been some very good attempts including the BRR microscope from DME/Zeiss (see image below)
a Curlew SPM from Specs (see image below),
Finally, the most recent entry is the afsem from Nanosurf/GETec. Some of the problems with the integrated instrument have included limited SEM vendors, a small subset of AFM modes available for the AFM, and necessary hardware modifications for the SEM that are uncomfortable for users. Still, this is an area of great research and growth, and the options for this capability are rapidly improving so hopefully it will soon become a standard tool in our nanoscale characterization toolkit.
Dalia Yablon, Ph.D.