Microscopy Techniques
You can do all sorts of fancy chemical vapor deposition and
lithography, but until you take a look at your result with a microscope, you're
running blind.
I can't stress enough how important microscopy is to
nanotechnology. All of our synthesis
efforts would be in vain if we couldn't characterize them. The only reason we know that carbon
nanotubes are actually hollow tubes, is because someone looked at it through an
electron microscope and discovered it.
There are two main kinds of microscopy. The first class of microscopy involves a
stationary sample in line with a high-speed electron gun. Both the scanning electron microscope (SEM)
and transmission electron microscope (TEM) are based on this technique. The second class of microscopy involves a
stationary scanner and a moving sample.
The two microscopes in this class are the atomic force microscope (AFM) and
the scanning tunneling microscope (STM).
Before I get into this, let me just say this: the
differences between the four microscopes are huge. The only two that are slightly similar are the SEM and TEM, but
even then they sill do different things.
Furthermore, each microscope can be used for a variety of measurements
(both qualitative and quantitative).
One interesting aside in the whole matter of microscopy is
that at the nanoscale one must carefully consider how the sample could be
adversely affected by different microscopy techniques.
This isn't such a big problem with a regular light
microscope since photons have no mass.
But when you're firing high-energy electrons at a target sample, damage
is bound to occur. The lesson of the
day is that in most cases, aside from the STM, using microscopy to visually
represent your sample will also do some damage to it.
Another problem is that most microscopes require very
stringent sample preparation. For the
SEM, TEM, and STM, you need to have an ultra thin sample that is also electrically
conductive. There are ways to get
around this, but the fact remains that it could take hours to mount a sample
correctly, not counting the hours that it might take the actually synthesize
the sample.
In an interesting tidbit of trivia, both the SEM and TEM
were the result of institutionalized research, while the STM and subsequent AFM
were solely the work of Binnig and other researchers at IBM between 1981 and
1986.
hide
Home
