Interface study of a high-performance W/B₄C X-ray mirror

Abstract

A high‐performance W/B4C multilayer mirror with 80 periods of nominally 1.37 nm was measured by grazing‐incidence small‐angle X ray scattering (GISAXS) in order to analyse the lateral and vertical correlations of the interface roughness within the framework of a scaling concept of multilayer growth. A dynamic growth exponent z = 2.19 (7) was derived, which is close to the value predicted by the Edwards–Wilkinson growth model. The effective number of correlated periods indicates a partial replication of the low interface roughness frequencies. A simulation of the GISAXS pattern based on the Born approximation suggests a zero Hurst fractal parameter H and a logarithmic type of autocorrelation function. The as‐deposited mirror layers are amorphous and exhibit excellent thermal stability up to 1248 K in a 120 s rapid thermal vacuum annealing process. At higher temperatures, the B4C layers decompose and poorly developed crystallites of a boron‐rich W–B hexagonal phase are formed, and yet multilayer collapse is not complete even at 1273 K. Ozone treatment for 3000 s in a reactor with an ozone concentration of 150 mg m−3 results in the formation of an oxidized near‐surface region of a thickness approaching ∼10% of the total multilayer thickness, with a tendency to saturation.

Depth-resolved chemical speciation of a W-B4C multilayer structure

“…Our results are found to be consistent with the investigations reported by Rao et al, [40]. They have shown that W and B 4 C in the W-B 4 C multilayer remain stable up to an annealing temperature of 800 o C. Beyond this temperature (above ∼1000 o C), B 4 C layer starts to decompose into free C or B atoms, which then react with the W atoms to produce more stable chemical phases of the tungsten [41].…”

Stability and normal incidence reflectivity of W/B4C multilayer mirror near the boron K absorption edge

“…After annealing at 800°C, no visible changes were observed as compared to the as-deposited sample. Recently, Siffalovic et al [22] made a similar observation. They performed rapid annealing treatment on a W∕B 4 C multilayer consisting of 80 bilayers with period thickness of 1.37 nm for 120 s. They observed new annealing products after 900°C annealing.…”

Short-Period Multilayer X-ray Mirrors for “Water” and “Carbon Windows” Wavelengths

“…To understand the mixed layer parameters and its behavior under elevated temperature we have given serious consideration to structural and phase transformations of the W/B 4 C multilayer structures under heating (annealing). Siffalovic et al 22 investigated the phase transformations in W/B 4 C structures with the period 1.37 nm at high temperature. The X-ray diffraction analysis showed a series of new peaks appearing under heating to 900 C against a halo of initial amorphous materials.…”