Diffraction Analysis
X-ray diffraction and e-beam diffraction are two key analysis
techniques that help determine the structure of crystal materials like semiconductors. In the nanotechnology world, both diffraction
methods are extremely useful in determining the growth characteristics of a
given synthesis route.
Diffraction is an old concept, originally predicted by Bragg's
Law in 1913, netted the two Braggs (Sir W.H. Bragg and Sir. W.L. Bragg) the
Nobel Prize in 1915. The basic premise
is simple, but the math can get a bit ugly for the uninitiated. Let us consider a single crystal. We know that for a crystal, that the atoms
are arranged in a periodic fashion. In any
regular array of atoms in three dimensions, there will be specific orientations
that appear to have planes of atoms in a dense configuration. In another orientation, there may be large
gaps. While this is a very loose
explanation, the point is that diffraction occurs when an incident x-ray
bounces off a plane of atoms. When
there are many planes, you begin to see patterns of constructive and
destructive interference (like Young's famous slit experiments).
By analyzing the data that you retrieve from such an
experiment you can deduce the physical arrangement of a material. Of course, there's a lot more to this than I'm
discussing. Diffraction is a tricky
subject to do a brief treatment on, so allow me to jump straight to the chase.
In nanotechnology applications, it isn't always possible to
take your sample and mount it into an x-ray diffractor. In this event, you can simply revert to an
e-beam diffraction technique that is available in almost every electron
microscope. This allows the researcher
to do topographical and chemical analysis at the same time. In most cases, an experimenter already knows
what kind of nanomaterial he or she is growing. That makes it easier to determine the structure of the
result. By comparing the values
extracted from the nanomaterial to the bulk values, researchers can figure out how
it's structured.
For instance, let's say you just grew some semiconductor
nanowires. That's fine and dandy, but
there are many questions to be answered.
Are the nanowires a single crystal?
What orientation is the crystal in?
Does the growth technique affect the way the crystal grows? These can all be answered with e-beam
diffraction.
Diffraction is just one tool in a huge toolbox of analysis
techniques available to nanotechnology researchers. Though it's been around since 1913, diffraction is one of the key
techniques that can define the physical structure and organization of a
material.
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