[Editors] MIT nanomirrors could enhance telescopes, more

[Elizabeth Thomson]

For Immediate Release
WEDNESDAY, JUNE 11, 2008
Contact: Elizabeth A. Thomson, MIT News Office -- Phone: 617-258-5402  
-- Email: thomson at mit.edu

PHOTOS AVAILABLE

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MIT: nanomirrors could enhance telescopes, more

--Invention could also impact tools for biology, computer chips

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CAMBRIDGE, Mass. - A new way of bending X-ray beams developed by MIT  
researchers could lead to greatly improved space telescopes, as well  
new tools for biology and for the manufacture of semiconductor chips.

X-rays from space provide astronomers with important information  
about the most exotic events and objects in our universe, such as  
dark energy, black holes and neutron stars. But X-rays are  
notoriously difficult to collect and many interesting cosmic sources  
are faint, which makes collecting these high-energy rays difficult  
and time-consuming, even with telescopes on satellites far above our  
X-ray-absorbing atmosphere.

Now a group of researchers from MIT has fabricated a new, highly  
efficient nanoscale Venetian-blind-like device that contains  
thousands of ultrasmooth mirror slats per millimeter for use in  
future improved space-based X-ray telescopes. The so-called Critical- 
Angle Transmission (CAT) gratings feature dense arrays of tens-of- 
nanometer-thin, freely suspended silicon structures that serve as  
efficient mirrors for the reflection and diffraction of nanometer- 
wavelength light-otherwise known as X-rays.

New instrument designs based on these gratings could also lead to  
advances in fields beyond astrophysics, from plasma physics to the  
life and environmental sciences, as well as in extreme ultraviolet  
lithography, a technology of interest to the semiconductor industry.  
The concept behind CAT gratings might also open new avenues for  
devices in neutron optics and for the diffraction of electrons, atoms  
and molecules.

Based on an invention by Ralf Heilmann and Mark Schattenburg of the  
Space Nanotechnology Laboratory (SNL) at the MIT Kavli Institute of  
Astrophysics and Space Research, the daunting fabrication challenges  
were overcome by graduate student Minseung Ahn of the Department of  
Mechanical Engineering at MIT in a yearlong effort, with the help of  
financial support from NASA and a Samsung Fellowship.

Motivated by technology goals for NASA's next-generation X-ray  
telescope, called Constellation-X, the new devices promise to improve  
more than five-fold upon the efficiency of the transmission gratings  
on board NASA's Chandra X-Ray Observatory (launched in 1999), which  
were also built at the Space Nanotechnology Lab. The reason for this  
improvement lies in the fact that in the new design, X-rays are  
reflected very efficiently at very shallow angles-akin to skipping  
stones on water-from the sub-nanometer-smooth sidewalls of the  
silicon slats, through the spaces between the slats. Also, in the  
earlier version the X-rays had to pass through a supporting substrate  
of polyimide, which absorbed many of the rays and reduced the  
grating's efficiency.

The silicon slats-as thin as 35 nanometers, which is comparable to  
the smallest feature sizes still under development in commercial  
computer chip manufacturing-are parallel to each other and separated  
by as little as about 150 nanometers. The slats have to extend many  
micrometers in the remaining two dimensions. “Imagine a thin, 40-foot- 
long, 8-foot-tall mirror, with surface roughness below a tenth of a  
millimeter,” says Heilmann. “Then put tens of thousands of these  
mirrors next to each other, each spaced precisely an inch from the  
next. Now shrink the whole assembly-including the roughness-down by a  
factor of a million, and you have a good CAT grating.”

Recent X-ray test results from a prototype device, obtained with the  
help of Eric Gullikson of Lawrence Berkeley National Laboratory,  
confirmed that it met theoretical expectations. The results of this  
work were published in Optics Express (Vol. 16, No. 12) on June 9.  
They were also presented at the 52nd Intl. Conference on Electron,  
Ion and Photon Beam Technology and Nanofabrication in Portland, Ore.,  
on May 28, and will be presented again at the SPIE Conference on  
Astronomical Telescopes and Instrumentation in Marseille, France, on  
June 23.

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Written by David Chandler, MIT News Office
Story on the web at: http://web.mit.edu/newsoffice/2008/ 
nanomirrors-0609.html