Advances in multilayer X-ray optics

Abstract

Abstract We present an overview of advances in multilayer X-ray optics which have been achieved in the past few years. Advances in fabrication, characterization, and theory are described. These mirrors are being used in a variety of synchrotron-related applications such as monochromators and projection lithography, as well as nonsynchrotron applications like astronomy and X-ray laser cavities. Although some of these coatings are produced routinely, much work remains to be done in producing higher quality multilayers with very thin layers (less than ∼ 20 A) and multilayers which are stable at high temperatures. Good multilayers with very thin layers are needed for near normal incidence optics at short wavelengths. Very stable multilayers are needed to withstand the high power loads which can be imposed by synchrotron radiation. New materials and deposition techniques are being applied to these problems. For example, molecular beam epitaxy is being applied to the growth of these multilayers in an effort to produce single-crystal superlattice mirrors. Since the performance of these mirrors is strongly dependent on atomic-scale interface quality, it is necessary to control the fabrication and perform characterization on this length scale. Characterization techniques which have made recent impact include high-resolution TEM, in situ ellipsometry, and energy dispersive X-ray diffraction. Surface analysis techniques such as STM, RHEED, LEED, AES, and XPS are being used to study interface formation and surface structure on a subnanometer scale.