A Foray into Scanning Electron Microscopy

This semester I am enrolled in a very fun seminar called Elementary Scanning Electron Microscopy.  Basically, I am being taught how to use a scanning electron microscope (SEM) and then given free reign to play with it for the rest of the semester.  After a few lectures and labs, the class is given the semester to develop an independent project using the SEM.  In a few months we will all meet again to give a presentation on our results.

For many people the term "scanning electron microscope" means very little.  For others, it may be associated with those characteristic black and white images of teeny tiny little things portrayed in immense detail.  That is pretty much where I was at a few weeks ago, but now, after some lectures and time running the instrument, I have a newfound appreciation for this very cool technology.  As you've probably guessed already, I'm not going to be able to resist giving you at least a brief rundown on how an SEM works.  Cue cartoonish diagram:

Just from looking over this picture you should be able to tell we're dealing with a cool piece of equipment.  I mean the thing at the top is called an "Electron Gun" for crying out loud!  It doesn't get much cooler and more science-y than that.  Let's break this thing down a bit so we can gain a better understanding of what exactly it does.  As you can see, the machine is structured in a vertical column with the electron gun at the top and the specimen at the bottom.  Electrons won't travel through air, so the whole thing is sealed off and the air is sucked out with a pump, leaving a vacuum inside the instrument.  Now the electron gun can fire a beam of electrons down the column, onto the specimen at the bottom.  All those round components inside the column serve to control the size and shape of the beam, as well as determine the number of electrons moving down the column at any given moment.

When the beam of electrons strikes the specimen, it causes a number of things to happen.  Many of the electrons simply bounce back and are aptly called "backscatter electrons."  At the same time, the stimulation of the atoms within the sample by the electron beam produces x-rays and the emission of low-energy "secondary electrons."  While each of these can tell you interesting things about your specimen, we are primarily interested in these secondary electrons for imaging purposes.  They provide detailed information about the topography of the specimen and are used to generate the incredible, close-up images that have made the SEM famous.

One more neat little detail about the SEM is that it works best on specimens that are conductive (i.e. metal).  Many things we are interested in looking at are not at all conductive.  To remedy this, the specimens are coated in a very conductive, malleable metal.  Which one you ask?  Well...gold.  Yes, that's right, if the process weren't cool enough already, it is made all the cooler in that all of the samples we look at are gold coated (even if only a few atoms thick).  Hooray science!

Now, as a reward for making it through all the technical stuff, here are some neat pictures I've taken so far:

This is the tip of a mosquito proboscis.  That's right, that horrible serrated spear is what stabs through your skin so they can drink your blood.  Who knew they were more than just pointy tubes?

Fly face at 37x magnification.  Wait a minute Fly, what's that in your eye?

Let's take a look at 600x magnification. Oh, it looks like dust.  Or pollen?

Still not sure what it is, but here is the presumed pollen at 2600x magnification.