Enhancement of soft X-ray reflectivity and interface stability in nitridated Pd/Y multilayer mirrors

Abstract

Pd/Y multilayer mirrors operating in the soft X-ray region are characterized by a high theoretical reflectance, reaching 65% at normal incidence in the 8-12 nm wavelength range. However, a severe intermixing of neighboring Pd and Y layers results in an almost total disappearance of the interfaces inside the multilayer structures fabricated by direct current magnetron sputtering and thus a dramatic reflectivity decrease. Based on grazing incidence X-ray reflectometry and X-ray photoelectron spectroscopy, we demonstrate that the stability of the interfaces in Pd/Y multilayer structures can be essentially improved by adding a small amount of nitrogen (4-8%) to the working gas (Ar). High resolution transmission electron microscopy shows that the interlayer width is only 0.9 nm and 0.6 nm for Y(N)-on-Pd(N) and Pd(N)-on-Y(N) interfaces, respectively. A well-defined crystalline texture of YN (200) is observed on the electron diffraction pattern. As a result, the measured reflectance of the Pd(N)/Y(N) multilayer achieves 30% at λ = 9.3 nm. The peak reflectivity value is limited by the remaining interlayers and the formation of the YN compound inside the yttrium layers, resulting in an increased absorption.

Generalized coupled-mode formalism in reciprocal waveguides with gain, loss, anisotropy, or bianisotropy

“…(7). In contrast to the established equivalence of adjointness of the matrix form H of the Maxwell's equations in Xu's work 42 and Lorentz reciprocity, where H is 3D operator, the operatorL is a 2D differential operator. Interestingly, the self-adjointness of the operatorL is also a necessary and sufficient condition to material reciprocity.…”

“…We will refer Eq. (21) as GCMF, in order to be distinct from previous coupled mode equations, typically from Haus and ours 32,42 .…”

“…In the scheme of complex inner product, it turns out that the left eigenstates ψ j can be obtained by performing the Hermitian operation on the right eigenstates φ i , implying the fact that the waveguide Hamiltonian H is Hermitian operator and the integrated power flux flowing along propagation direction, i.e., z-axis, of the waveguide is conserved 32,40,41 . In parallel, the left eigenstates ψ j in a scalar inner product can be obtained by performing the transpose operation and certain operations in field components of the right eigenstates φ i , provided that the waveguide medium is reciprocal and the reaction conservation is fulfilled 41,42 . In the waveguide with gain/losses, the integrated power flux flowing along the waveguide is apparently not conserved, thus the modal coupling model based on the scalar inner product is proposed by Xu et.…”

“…al. 42 to study PT -symmetric waveguides that contain balanced gain and losses. Essentially, the GCMT model 42 is a revision of CMT by Haus 32 by replacing the complex inner product with the scalar inner product, wherein the reciprocity or the reaction conservation still holds.…”

Characterization of Pd/Y multilayers with B4C barrier layers using GIXR and X-ray standing wave enhanced HAXPES

“…The potential applications vary from EUV spectroscopy, plasma diagnosis to synchrotron radiation or free electron laser instruments. A crucial factor is found that may compromise the performance of the mirror: the interdiffusion of Pd and Y. Nitridation of the Pd/Y multilayer by introducing nitrogen during the deposition process can reduce the interdiffusion [2,3]. Yet the nitridated multilayers suffer a reflectance loss.…”