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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.