I suppose the answer depends on resolution and imaging area, but can you provide some ball park measures of imaging times with an SEM?
[Physics] How long does it take to scan a typical scanning electron microscope image
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those answers were all pretty heavy for a physics novice!
I think the answer you are looking for is easier than you might think - you 'see' light through a microscope's lens because your eyes are great photon detectors. without a detector, a light microscope can't create an image.
an electron microscope (there are various types) simply has other types of detectors. depending on what size scale you are looking on the could variously be detecting reflected electrons (the proper term is backscattered), deflected electrons, emitted light from excited electrons, or even variations in various forces. This is the same for light microscopes, you are simply seeing reflected/emitted light.
there are even electron microscopes that rely on quantum tunneling of electrons, and measure the tunneled current, which changes depending on the distance between microscope tip and object.
the point is, all they do is measure interactions of the wave and the object, in the same way your eyes do with a normal light microscope. a computer (or your brain) then models what was detected to resolve an image.
the only other concept you need is that the resolution of any microscope is proportional to the wavelength used. A smaller wavelength can generate better resolution. So the best you can do with a light microscope is violet light, with a wavelength around 400nm. An electron can be seen as a wave as well, and has a far smaller wavelength, in the range of picometres. Marek's suggestion re:wave-particle duality could help here.
I have been trying to put why small wavelengths mean better resolution into simple terms but it is eluding me. Kinda needs diagrams. Maybe someone else can help?
(I presume you mean resolution.)
In an SEM, the limit to resolution is almost always determined by the volume over which the electron beam interacts with the sample. If you shoot a beam into a sample at several keV, electrons will bounce around within a volume of something like a micron in size (depending on the exact voltage, the density and shape of the sample, etc.) We call this the excitation volume. Right where the beam hits, a large number of low energy electrons (secondary electrons) are generated. Since those electrons have an energy of a few tens of eV, they don't come from more than a few nm deep. Of course, secondary electrons are generated from throughout the entire excitation volume, but most of those are trapped within the sample and carried away to ground since the penetration of a low energy electron through a solid is poor. Therefore, your resolution is pretty close to the diameter of the incident beam.
Backscatter electrons by definition are collide elastically, so if your beam is something like 20 keV, then the backscatter electrons will be 20 keV too. This means they can exit the sample from deeper in the excitation volume compared to secondary electrons. Now actually, a backscatter detector sees all the electrons with more than a keV or two of energy. So there are a large number of incident electrons which give up some small amount of energy to electron-sample interactions, and THEN backscatter. In real life, a backscatter detector has a large amount of signal from inelastic electrons which are nevertheless close to the incident beam's energy. These, of course, come from a much larger volume since they are higher energy and less likely to be trapped in the sample even when emitted from a greater depth.
Therefore, practically speaking, backscatter resolution is always worse than secondary resolution. On the other hand, often backscatter sees contrast that secondary cannot see at all.
Theoretically, backscatter could produce the same resolution as secondary: imagine a graphene sheet...
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It's been a decade since I last used an SEM, but back then you would start using a fast scan that was real time i.e. you could move the sample around, change focus, etc and see the effect in real time. However the realtime image is noisy because the numbers of electrons being captured is small. Once you had the picture you wanted you would record them image using a much slower scan to reduce the signal to noise. From memory this took a couple of minutes.