Okay... I should have been more specific... It's difficult to image
Fresnel technology *for high resolution imaging" using high-energy
x-rays.
The specific paper JD referenced used 18.6-keV x-rays and zone-focused
them to roughly a one-micrometer spot. The earlier paper he referenced
used 3.2 nm x-rays (388 keV) and achieved spatial resolution of about
five nanometers. That's a big difference, and the second paper is
clearly going the wrong direction in terms of imaging resolution.
Since the discussion has been centered on creating images, I was headed
in that direction. If we look at wavelength only, we ought to get
better image resolution with shorter and shorter wavelength. But this
requires we have the ability to make the appropriate "pinhole" or the
appropriate "lens" for the wavelength we are using.
The 5-nm resolution with the 388-keV soft x-rays is actually better than
we can obtain with optical microscopes (0.1 to 0.01 micrometer
resolution). The most recently quoted paper (0.8 micrometer resolution
with 18.6-keV x-rays) is considerably worse than optical resolution.
The same problem occurs for electron microscopy. Higher and higher
electron energy ought to yield better and better resolution in an
electron microscope. However, the best resolution with electron
microscopes comes at about 100 keV and gives resolution of about 0.2 nm.
Going higher than 100 keV with an electron microscope currently yields
poorer resolution because of problems in the lenses.
This is the point I was trying to make with zone plates for x-ray
imaging. Going to higher-energy x-rays (where one might expect better
resolution) does not yield better resolution because of problems
inherrent in zone plate spacings that small and that thick. In the
examples John provided, we see this. The resolution at 18.6-keV was
considerably worse than the resolution at 388-keV, and the 18.6-keV
resolution was worse than optical resolution.
Please note that this doesn't mean the 1-micron resolution at 18.6-keV
is worthless. The 18.6-keV x-rays give some object penetrating
capability to an imaging device designed around it, and it also begins
to open the door for x-ray fluorescence analysis with 1-micron
resolution. Both of these can be extremely useful.
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu