X-ray Microscopy
at Stony Brook (3)

1. Why Soft X-ray Microscopy
2. The Scanning Transmission X-ray Microscope
3. X-ray Lenses: Fresnel Zone Plates
4. Example: Biological Applications
5. Example: Environmental Sciences and Cluster Analysis
6. Soft X-ray Diffration and Holography
7. Acknowledgements

X-ray Lenses: Fresnel Zone Plates

Because the refractive index for X-rays differs from 1 by only about 0.1% or less, diffractive lenses are often preferred for X-ray focusing. Fresnel zone plates are circular diffraction gratings with radially decreasing line width. The size of the focal spot and therefore the spatial resolution of the microscope is limited by the width of the finest (outermost) zones.

Schematic of a Fresnel zone plate	Combination of a central stop and an order-sorting aperture (OSA) to isolate the first-order focus

Our group fabricates Fresnel zone plates by electron-beam lithography in a collaboration with Don Tennant at Bell Laboratories.

A trilevel resist process to produce high aspect-ratio structures	Scanning electron micrograph of 40 nm outermost zones

A typical zone plate for soft x-ray scanning microscopy is made of Nickel or Germanium and has a diameter of 160 µm with outermost zones as fine as 30 nm. For good efficiency, zone thicknesses around 200 nm are required.

Former Stony Brook graduate student Aaron Stein using the JEOL JBX-9300FS electron-beam system

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