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Multilayer Optics for the Soft X-Ray and Extreme Ultraviolet
Published online by Cambridge University Press: 29 November 2013
Extract
This article considers a particular class of optic microstructure — multilayers for soft x-ray (SXR, 100 eV[124 Å] to 3,000 eV[4.1 Å] and extreme ultraviolet (EUV, 15 eV[800 Å] to 100 eV[124 Å] optics. Multilayers are manmade vapor-deposited depth-periodic layered micro-stractures of high enough quality to be considered synthetic crystals. Layers of two materials, A and B, having significant differences in their scattering powers for x-rays (electron densities) and of uniform thicknesses ta and tb are combined to form a sample of uniform in-depth period d0 ( = ta + tb). These microstructures are of scientific and technological significance since the high angle of incidence SXR and EUV reflectivities of single film reflectors is ~10−4) and since only a limited number of naturally occurring or synthetic large lattice constant materials efficiently diffraction reflect long wavelength radiation (SXR and EUV).
Multilayer microstructure based SXR and EUV optics are direct analogues to standard quarterwave stacks applied at longer wavelengths with the requirement that absorption must be included. They are also analogous to atomic crystalline lattices in that one multilayer period is equivalent to one lattice plane. Thus, the multilayer structure forms a superlattice that diffraction reflects incident radiation. Multilayer diffraction may be modeled using x-ray scattering theory and obeys the refraction-corrected Bragg's law of crystal lattice diffraction. As will be discussed later, many factors determine the character of the multilayer response to an incident spectrum.
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- Multilayer Materials
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- Copyright © Materials Research Society 1990
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