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One thing they didn’t explain in their research article was their specimen prepping techniques.  It would seem that to create a huge mosiac of thousands of images, each section taken from the specimen block would need to be perfect.  It wouldn’t seem like there would be much room for error in either the preparation or the sectioning.  If you have worked on an ultramicrotome at all, you know how easy it is to completely destroy a block.  Also interesting was that they were using a glass knife on the ultramicrotome instead of a diamond.  While the glass knives can be nearly as sharp, they are definitely not consistent.  A good diamond knife though (upwards of $3,000) will be consistent with every cut, anywhere on the blade, and there is no need to worry about dulling.

All in all, a very cool article that is a good indicator of what the future holds for both neuroscience and microscopy.  With further advances in automation (a la Paul Allen Institute possibly) I imagine that we’ll have whole areas of the brain mapped out by a similar method.

So, why does an electron microscope need a vacuum system you ask?  Well, an electron beam emitted in a chamber with no vacuum present would only travel less than one centimeter.  We need to put the column of the microscope under high vacuum in order to increase the mean free path of electrons.  High vacuum helps to keep the gun area clean as well, and also helps to reduce possible contamination of a specimen.

Vacuum on microscopes is usually measured in Pascals (Pa).  I say usually, because there is no standard and you may see it measured in other formats. 1 Pascal = 7.52×10^-3 torr. 1 torr = 1mm/Hg. 760 torr = atmospheric pressure at sea level (1 atmosphere). Click the link for more information on vacuum.  The TEM and SEM that I use typically work at 10^-4 Pa (TEM) and 10^-3 Pa (SEM). It’s interesting to note that when your column is under high vacuum (10^-4 Pa), there are still about ten billion gas molecules in a cm³ of space.

Vacuum systems on electron microscopes are typically kept running 24/7. This is beneficial to the lenses and seals, as particles won’t have a chance to enter the column. One loose particle, thread, or hair in the column could completely disrupt the vacuum system and may not let it get up to an operational level.

A TEM usually keeps separate areas of the scope under vacuum, and you can shut vacuum off to the separate areas in order to change your sample or retrieve film. This is handy because the column is quite huge on TEMs and it needs to be under higher vacuum than an SEM. If you had to devacuum the whole scope every time you had to change a sample it would probably over an hour to change out your sample. By only having to break the vacuum of the sample holder, you can change out samples in about a minute on a TEM. On the other hand, with the SEM, it takes about three or four minutes between sample changes.

SPMs work in a completely different way when compared to electron microscopes.  SPMs use a very sharp needle – about one atom wide at the tip – to produce an image of a sample.  The needle scans across the sample and the topography is then shown digitally on a monitor.  Because of the sharpness on the needle, these machines are able to image individual atoms.

Amazingly, these machines don’t cost nearly as much as a scanning or transmission electron microscopes.  SEMs and TEMs have large vacuum systems and some heavy duty technology in the form of condensor lenses and detectors which make them very pricey to buy new.  Of course with TEMs and SEMs, one can find these machines for cheap, or free, if you’re willing to pay for shipping, assembly and a service contract.  Service contracts on a TEM can run nearly $20,000/year.  So that free TEM that your local community college is trying to get rid of won’t do much good unless you’re willing to dish out many tens of thousands of dollars each year.

Now, to get back to the title of this post.  Here’s an SPM that costs roughly $90,000.  No room modifications needed, and no service contract.  You may need a vibroisolation table for it, and of course, you’ll need a computer. At this price, the machine is in reach for home use for the more affluent microscopists, or the rich accountant who subscribes to Scientific America and Wired and who just wants cool stuff.

A good idea with a machine like this, and the talent to use it properly would be to contract out to companies that need nanotech research done or to grad students who are doing research and whose universities don’t have an SPM.  It could become a full-time job!  And the overhead is only about $100k.  Ok… don’t all rush out and order one now!

Photo taken from www.fei.com

The resolving power of an SEM is directly related to the accelerating voltage of the electron beam.  The higher the beam, the more that the electrons are penetrating the surface of the specimen. The electrons collected by the Secondary Electron Detector are therefore coming not only from the surface of the specimen, but also deeper within the specimen which will cause the image produced to distort.  This becomes very evident on many SEM’s at about 20,000x or more.  To get good images on many older SEMs above 20,000x requires tricks of the trade, and many times requires the planets to be aligned and the gods to be smiling upon thee.

The FEI Magellen XHR employs the latest research and development and they have been able to deliver a machine in which the accelerating voltage can be taken down below 1kV, I believe even down to 200 volts.  The machine at these extremely low voltages is only forming an image from electrons at the surface of the specimen, thus limiting the distortion that would be produced by higher accelerating voltages.

FEI has a great interactive demo that allows you to see the power of the machine on various samples.  Sooooo cooooool!!!!

Hitachi 2460N Environment SEM. Photo courtesy of UW Oshkosh EM facility.

In upcoming posts, I’m going to discuss my techniques for getting the best images from this machine.

My goal with this blog is to post my better micrographs here, discuss the machinery involved in electron microscopy, discuss prepping techniques, and discuss other various aspects of the science.  I don’t foresee this being a popular website, but if I do come to have some viewers, I will always be happy to post anyone’s electron micrographs.

In college, my major is Psychology – Healthcare Science emphasis, with a minor in Neuroscience and Spanish.