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The effect of elevated temperature on the structural stability and performance of Mo-Si multilayer mirrors is investigated. Mo-Si multilayers deposited by magnetron sputtering are annealed at temperatures ranging from 200 to 800 °C. A detailed and consistent picture of the thermally induced changes in the microstructure is obtained using an array of complementary measurement techniques including small- and large-angle x-ray scattering and high-resolution electron microscopy. The first significant structural changes are observed at 400 °C, characterized by an increase in the width of the amorphous interlayer regions, as well as the nucleation of microcrystallites of silicide in these regions. At higher temperature the Mo layers transform completely into polycrystalline mixtures of Mo5 Si3 and MoSi2 in both the hexagonal and tetragonal phase. The layers of silicide remain intact but exhibit a structural instability, resulting in severely warped layers surrounded by pockets of amorphous Si and voids. By 800 °C the layered structure is completely destroyed and the composition is predominately tetragonal MoSi2 . The performance of the multilayers as normal-incidence x-ray mirrors is measured and correlated with the observed structural modifications. Finally, our results are compared and contrasted with other annealing studies of the Mo-Si system.

Multilayered structures containing thin (1-12 nm) layers ofW or Mo, alternating with C or Si, have been prepared to produce thin cross-sectional specimens, and direct structural information on the atomic scale has been obtained using an ultrahigh resolution electron microscope. Layer thickness and flatness have been analyzed-the average layer thickness varies by up to 0.6 nm from the average value, and the flatness of the layers depends on the quality of the substrate surface. The degree of crystallinity and crystal orientation wit~in the layers has also been examined. This information should enable more accurate theorettcal models to be proposed for the multilayer materials and their x-ray optical properties. The results for the Mo/Si multilayers suggest a model for their growth when prepared by sputtering.

The development of a new time-resolved x-ray spectrometer is reported in which a free-standing x-ray transmission grating is coupled to a soft x-ray streak camera. The instrument measures continuous x-ray spectra with 20-psec temporal resolution and moderate spectral resolution (deltalambda >/= 1 A) over a broad spectral range (0.1-5 keV) with high sensitivity and large information recording capacity. Its capabilities are well suited to investigation of laser-generated plasmas, and they nicely complement the characteristics of other time-resolved spectroscopic techniques presently in use. The transmission grating spectrometer has been used on a variety of laser-plasma experiments. We report the first measurements of the temporal variation of continuous low-energy x-ray spectra from laser-irradiated disk targets.

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