[Maz]

Have you ever felt more then a little dissatisfied with your SEM images?  Black and white just not doing it for you?  Wish you could see height differences at that small of a scale?  Just plain tired of babying that danged machine?  I know that more then once I've dreamed of using a bench top microscope to optically analyze our samples.  Some people have even tried (much to amusement of the rest of us) to jury-rig a set up to make this possible, but so far I've yet to here of any success (Mitch).

However, there is work being done on a method for being able to OPTICALLY analyze samples on the NANOMETER scale.  Yeah, it's not bench top, but it has color, shadows, and did I say color?

And no, I'm not talking about NSOM, the method that is so lousy, inefficient, slow, and delicate that it seriously makes you question your commitment to science. 

For those of you who don't know what NSOM is, I'll do a quick overview.  NSOM (Near Field Scanning Optical Microscopy), is a method of doing sub-diffraction imaging.  Remember that light is actually a self-propagating electromagnetic wave.  Like all waves, light diffracts when shoved through a tiny space (on the order of it's wavelength).  Back in your highschool or lower division physics classes, you probably messed around with single slit diffraction and saw neat patterns like this.

Well, to shine very coherent light "spots" on your samples so that you can see them, you need a very very small aperture.  However when you go to use one that has a diameter close to or less then the wavelength of the light you send through, you see the light diffract.   

So if you are trying to look at a sample and want to resolve details with <1000nm with visible light, your in trouble.  NSOM "gets around" this though, by sticking the NSOM tip very very close to the sample.  As in around 25-50nm away from it.  Why does this work?  When you get the tip that close to the sample, it is acting like a light source because you are inside the first diffraction maximum. 

The setup kind of looks like this:

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Jim Schuck, Molecular Foundry, LBNL

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Now that all seems fine, but inherently you're hitting another problem here.  The tip is so much smaller then your wavelength that it greatly prohibits the photons from getting through.  Of course some will, but now it is a matter of statistics.  The math has been cranked and the transfer efficiency of NSOM is only about 10^-6!!  That means 1 in 1 billion photons sent at the tip gets through!  LOUSY

So now we get to the brighter solution.  heh. 

Or actually, we won't just yet.  This post is starting to get long, and I am starting to get tired.  I think I'll do this in a 3 post manner. 

1.) NSOM and why is bites.  2.) What the heck are Plasmons?  3.) Plasmon-light coupling and Nano-antennas.

Stay tuned...

[Mitch]

How do they make the tips?

[plasmonicfocus]

The tips can be made in a variety of ways, including pulling a heated optical fiber and through wet or dry etching. The highest performing tips are made through chemical etching processes and provide a very steep taper angle. After the tip is made, it is then usually coated with a metal, such as Aluminum, to occlude the light everywhere except over an aperture.

It should be noted that the parent post is a little misleading. Tips do tend to have very poor throughput, and 10^-6 is not an unusual number. But it should be clarified that this represents the amount of light which goes from inside the fiber to the far field in free space outside the fiber. There can actually be quite a bit of energy in the near field near the tip, which does interact with the sample, but does not couple to the far field.