Thursday, December 11, 2008, Condensed Matter Biological Physics Seminar, Dr. Ralf K. Heilman, MIT Kavli Institute for Astrophysics and Space Research, Space Nanotechnology Laboratory, Cambridge MA, "From Nanometers to Gigaparsecs – Critical Angle Transmission Gratings and the WHIM", 4:30 PM, Doherty Hall A310, CMU

Abstract:  The Space Nanotechnology Laboratory (SNL) was established in the early nineties to fabricate the x-ray transmission gratings for the high- and medium energy transmission grating spectrometers for NASA’s Chandra X-ray Observatory that was launched into space in 1999.  We are currently involved in the technology development for the recently announced International X-Ray Observatory (IXO), the designated successor mission for Chandra (launch ~ 2020).  One of IXO’s mission goals is the spectroscopic characterization of the Warm Hot Intergalactic Medium (WHIM) and the Cosmic Web, the largest structure in the universe, in the soft x-ray band.  To help achieve this goal we have developed a new type of blazed x-ray transmission grating that combines the advantages of blazed reflection gratings and phase-shifting transmission gratings, the so-called Critical-Angle Transmission (CAT) grating.  The fabrication of these freestanding, 100-200 nm-period gratings requires advanced lithographic techniques with sub-nm precision – realized via Scanning Beam Interference Lithography – and the anisoptropic etching of nm structures with aspect ratios > 100 and sub-nm roughness.  X-ray tests of CAT grating prototypes show promising agreement with theoretical predictions.

Scanning electron micrograph of a cross section through a 574 nm-period silicon CAT grating before removal of the supporting silicon oxide membrane.