I want one of those too! But do I need it? by Chris Parmenter
We all know what it is to see a new sports car and want it, or when a neighbour moves to a new house and you wish you could do the same. I’m pretty sure the same is true with microscopes and is especially true with aberration corrected TEMs. When I got into electron microscopy about ten years ago I was clearly told that my TEM suffered from two types of aberration, which would limit the resolution to a few nanometres despite a 200 kV instrument having a theoretical 17 picometer resolution.
“Of course in optical microscopes they have aberration too, but they can make a lens to correct for it. Unfortunately, it isn’t possible to correct an electromagnetic lens and it isn’t possible to make a perfect one either...” That’s what I was told by an EM suite manager back in 2003 and I suppose that for the longest time that was the reality of the everyday user. Fast forward to 2006 at the IMC in Sapporo, where the first presentations were given showing corrected data and at the EMC 2012, my colleague commented that his presentation was the only one ‘not showing corrected data’.
Based on these developments and the clarity if images available, it is not surprising to find oneself asking, “If everyone else has one, why shouldn’t I?” If you’re anything like me, there is often a second, albeit quieter, voice asking, “But do I need it? Would I use it?”
Caption: CeO2 nanoparticle, taken using a 300 kV corrected TEM (Courtesy of Bert Freitag, FEI)
My institution doesn’t currently have a corrected instrument and I know there are researchers around who would love one. After all, why wouldn’t we want the best images? But one must ask, ‘Who would use it? How often? And, what are the implications of having it? As far as I can see an aberration corrected instrument would require the following:
1) Major infrastructural investment to allow the instrument to perform.
2) At least one competent, full time user
3) Serious servicing commitment
4) A string of users to fund the instruments existence.
If these four are not in place, despite it being, on the face of it, a nice idea, it isn’t very practical. To use the car analogy again, a sports car would be nice to get from A to B and turn heads, but isn’t terribly practical or flexible for a family day trip or the school run, which is its main use 95% of the time. Equally, choosing a Humvee for day to day activities with 7mpg seems a bit extreme when a saloon or MPV will do the job with 35-45 mpg.
To counter this somewhat level-headed approach and to show my respect for corrected TEMs, I need to say that if you have the right sample, prepared in the right way (see my last post), and once the instrument is properly set up for your experiment, they are brilliant tools capable of breathtaking images delivering sub-nanometre resolution. One such case is the SALVE (Sub-Angstrom Low Voltage Electron Microscope) project, which is being developed for particular use with carbon materials.
Caption: Images of graphene sheets taken using the SALVE microscope. Reprinted with permission from Andrey Chuvilin, U. A. Kaiser, E. Bichoutskaia, N. A. Besley, A. N. Khlobystov (2010), Direct transformation of graphene to fullerene. Courtesy of Nature Chemistry, 2: 450-453, doi: 10.1038/nchem.644 Copyright 2010 Nature Publishing Group
There are also many other examples where the corrected instruments are being used daily and underpinning applied and fundamental research, many of which are accessible (for example Super STEM) through open access schemes.
Don’t get me wrong I love the idea of crystal clear images (I really do) but in my opinion it isn’t for everyone and isn’t needed most of the time for most user’s samples, especially if their sample prep is not up to scratch. It’s time for us to be realistic and buy according to what our needs are rather than our wants.
What do you think about this post? Do you want a corrected TEM? Have you got one? Let me know your experiences?