Abstract

In previous work we have identified the Si/B material pair as useful for narrow bandpass optics at wavelengths above the Si L-edge, λ>124 Å.^1,2 Unfortunately, useful boron sputtering targets are not generally available. However, excellent B₄C targets are readily available, and the theoretical reflectivities of Si/B₄C multilayers are only slightly less than for Si/B. In this wavelength region Si is the spacer and B₄C is the absorber-thus breaking the standard rule of thumb, that good spacer/absorber pairs are low/high atomic number. Although the optical constants of B₄C do not have strong contrast with Si, like those of Mo for example, the low absorption allows more interfaces to contribute to the reflection. Theoretical normal-incidence reflectivities calculated for ideal structures start at approximately 65% near the Si L-edge and drop with increasing λ to ~31% at 250 Å, compared to 77% and 37% for Si/Mo. Although the reflectivity is lower for Si/B₄C, having more interfaces contribute results in narrow bandpass mirrors that are more desirable for several applications.

© 1994 Optical Society of America