Lamellar Multilayer Grating Research Articles

Cr/C lamellar multilayer grating in conical diffraction mounting for beam splitter used in X-ray free-electron lasers.

A lamellar multilayer grating in a conical diffraction mounting was proposed as a beam splitter for X-ray free-electron lasers. Theoretical calculations demonstrated that the distribution of diffraction efficiency can be adjusted by optimizing the groove depth or d-spacing. A Cr/C multilayer lamellar grating with a line density of approximately 2500 L/mm was fabricated. The performance of the element was measured in the Optics Beamline PM-1 (BESSY-II) at an energy of 1500 eV. A five-order diffraction pattern was recognized, and the diffraction efficiencies of the -/+first-order were approximately 12.6 and 4.4%, respectively. The asymmetric distribution of diffraction efficiency can be caused by the different sidewall angles of the grating groove.

Mo/Si lamellar multilayer gratings with high efficiency and enhanced resolution for the x-ray region of 1000-1700eV.

The d-spacing of the multilayer lamellar grating was theoretically optimized to improve the energy resolution and maintain a high efficiency. Based on the study of the growth behavior of Mo/Si multilayer on the lamellar grating under different sputtering pressures, Ar gas pressure of 1 mTorr was selected, which can fabricate the multilayer with lower roughness and a good replication of the groove shape. An absolute diffraction efficiency of 25.6% and a Cff factor of 1.79 were achieved for the -1st order of the Mo/Si lamellar multilayer grating at an energy of 1700 eV.

Narrowband lamellar multilayer grating with low contrast MoSi2/Si materials for the soft x-ray region

To develop highly efficient narrow-bandwidth multilayer optics for the soft x-ray (SXR) spectroscopy, a low optical contrast MoSi2/Si lamellar multilayer grating (LMG) was proposed and developed. The low contrast LMG allows for a large lamel width which can potentially achieve higher resolution than the conventional LMG and simplify the fabrication. As a first demonstration, a MoSi2/Si multilayer with a d-spacing of 5 nm and 180 bilayers was deposited. The lamellar grating structure with a period of 614 nm, lamel-to-period ratio of 0.38, and lamel height of 670 nm was fabricated in the multilayer with reactive ion etching process. The SXR measurements show a high 0th-order diffraction efficiency of 16%–33% at 876 eV–1648 eV, which reaches around 80% of the unetched multilayer reflectivity. A maximal bandwidth reduction of 2.2 times was obtained compared with the multilayer mirror, indicating an energy resolution of E/ΔE = 108 at 1183 eV. The resolution can be further improved by reducing the multilayer d-spacing and increasing the etching depth.

Study of lamellar multilayer grating near B K-edge and Si L-edge

We present an efficient design of lamellar multilayer grating (LMG) for the extreme ultraviolet/soft X-ray region near both the Si L-edge and B K-edge. The designs of LMGs have been performed by exploring different materials combinations, which are capable of providing high resolution and peak reflectivity. The performance analysis of the designed LMGs is made analytically using the coupled wave theory for single-order regime. That provides an estimation of diffraction efficiency and resolution. The effect of structural imperfections such as tapering of the lamellar profile and interfacial width on the optical properties are also analysed to describe non-ideal LMG structures.

Spectral tailoring of nanoscale EUV and soft x-ray multilayer optics

Extreme ultraviolet and soft X-ray (XUV) multilayer optics have experienced significant development over the past few years, particularly on controlling the spectral characteristics of light for advanced applications like EUV photolithography, space observation, and accelerator- or lab-based XUV experiments. Both planar and three dimensional multilayer structures have been developed to tailor the spectral response in a wide wavelength range. For the planar multilayer optics, different layered schemes are explored. Stacks of periodic multilayers and capping layers are demonstrated to achieve multi-channel reflection or suppression of the reflective properties. Aperiodic multilayer structures enable broadband reflection both in angles and wavelengths, with the possibility of polarization control. The broad wavelength band multilayer is also used to shape attosecond pulses for the study of ultrafast phenomena. Narrowband multilayer monochromators are delivered to bridge the resolution gap between crystals and regular multilayers. High spectral purity multilayers with innovated anti-reflection structures are shown to select spectrally clean XUV radiation from broadband X-ray sources, especially the plasma sources for EUV lithography. Significant progress is also made in the three dimensional multilayer optics, i.e., combining micro- and nanostructures with multilayers, in order to provide new freedom to tune the spectral response. Several kinds of multilayer gratings, including multilayer coated gratings, sliced multilayer gratings, and lamellar multilayer gratings are being pursued for high resolution and high efficiency XUV spectrometers/monochromators, with their advantages and disadvantages, respectively. Multilayer diffraction optics are also developed for spectral purity enhancement. New structures like gratings, zone plates, and pyramids that obtain full suppression of the unwanted radiation and high XUV reflectance are reviewed. Based on the present achievement of the spectral tailoring multilayer optics, the remaining challenges and opportunities for future researches are discussed.

Extended theory of soft x-ray reflection for realistic lamellar multilayer gratings

An extended set of coupled wave equations were derived to describe non-idealized lamellar multilayer grating structures with properties as obtained with state-of-the-art fabrication techniques. These generalized equations can include all relevant effects describing the influence of passivation and contamination layers, non-rectangular lamel profiles and sidewall scalloping. The calculations showed that passivation and contamination plays an important role in that it may significantly reduce peak reflectivity. However, we also derived a condition for layer thicknesses having negligible effects. Slightly positive tapered lamel profiles are shown to further reduce the bandwidth as compared to a rectangular lamel profile, whereas negative tapers significantly increased the bandwidth. The influence of intriguing effects, such as the sidewall scalloping caused by Bosch Deep Reactive Ion Etching, are also modeled. We identified the signature of such scalloping as additional side peaks in the reflectivity spectrum and present parameters with which these can be effectively suppressed.

Single-order operation of lamellar multilayer gratings in the soft x-ray spectral range

We demonstrate single-order operation of Lamellar Multilayer Gratings in the soft x-ray spectral range. The spectral resolution was found to be 3.8 times higher than from an unpatterned multilayer mirror, while there were no significant spectral sideband structures adjacent to the main Bragg peak. The measured spectral bandwidths and peak reflectivities were in good agreement with our theoretical calculations.

Analytic theory of soft x-ray diffraction by lamellar multilayer gratings

An analytic theory describing soft x-ray diffraction by Lamellar Multilayer Gratings (LMG) has been developed. The theory is derived from a coupled waves approach for LMGs operating in the single-order regime, where an incident plane wave can only excite a single diffraction order. The results from calculations based on these very simple analytic expressions are demonstrated to be in excellent agreement with those obtained using the rigorous coupled-waves approach. The conditions for maximum reflectivity and diffraction efficiency are deduced and discussed. A brief investigation into p-polarized radiation diffraction is also performed.

High-resolution, high-reflectivity operation of lamellar multilayer amplitude gratings: identification of the single-order regime

High resolution while maintaining high peak reflectivities can be achieved for Lamellar Multilayer Amplitude Gratings (LMAG) in the soft-x-ray (SXR) region. Using the coupled waves approach (CWA), it is derived that for small lamellar widths only the zeroth diffraction order needs to be considered for LMAG performance calculations, referred to as the single-order regime. In this regime, LMAG performance can be calculated by assuming a conventional multilayer mirror with decreased density, which significantly simplifies the calculations. Novel analytic criteria for the design of LMAGs are derived from the CWA and it is shown, for the first time, that the resolution of an LMAG operating in the single-order regime is not limited by absorption as in conventional multilayer mirrors. It is also shown that the peak reflectivity of an LMAG can then still be as high as that of a conventional multilayer mirror (MM). The performance of LMAGs operating in the single-order regime are thus only limited by technological factors.

Lamellar multilayer amplitude grating as soft-X-ray Bragg monochromator

The design of efficient lamellar multilayer amplitude grating (LMAG) monochromators in terms of bandwidth and peak reflectivity for the soft-X-ray domain, covering the K emission of low atomic-number elements: B to Si, is considered. A Mo / B 4 C LMAG suited for spectrometry in this spectral domain has been designed, fabricated using electron beam lithography together with reactive ion etching and tested with success.

Soft x‐ray multilayer monochromator with improved resolution and low specular background

A new soft-x-ray multilayer monochromator with an improved resolution and a low specular background is presented. The principles of the device, based on the use of a lamellar multilayer amplitude grating (LMAG), are summarized. The techniques of fabrication of the monochromator (multilayer deposition, UV lithography and reactive ion etching) are given. The performance of this new monochromator at photon energies around 1500 eV is demonstrated. Copyright © 2001 John Wiley & Sons, Ltd.

Soft x‐ray multilayer monochromator with improved resolution and low specular background

AbstractA new soft‐x‐ray multilayer monochromator with an improved resolution and a low specular background is presented. The principles of the device, based on the use of a lamellar multilayer amplitude grating (LMAG), are summarized. The techniques of fabrication of the monochromator (multilayer deposition, UV lithography and reactive ion etching) are given. The performance of this new monochromator at photon energies around 1500 eV is demonstrated. Copyright © 2001 John Wiley & Sons, Ltd.

Structural characterization of a lamellar W/Si multilayer grating

A lamellar multilayer grating of the nominal normal and lateral periods 8 and 800 nm, respectively, was obtained by etching a planar amorphous W/Si multilayer up to the substrate. The specular reflectivity, grating truncation rods of nonzero orders, and a reciprocal space map of the scattered intensity close to the total external reflection were measured using the Cu Kα radiation. We demonstrate an extraction of real structural parameters of a fully etched periodic multilayer grating from fitting the measured truncation rods based on the matrix modal eigenvalue approach to the dynamical theory of reflectivity by gratings.

Structural characterization of lamellar multilayer gratings by x-rayreflectivity and scanning electron microscopy

Structural characterization of a fully etched amorphous W/Si multilayer grating with lateral periodicity 800 nm is performed by x-ray reflectivity. Grating truncation rod profiles have been calculated using a matrix modal eigenvalue approach of the dynamical theory of reflectivity by gratings which generalizes the Fresnel transmission and reflection coefficients for lateral diffraction. The interface roughness in rough gratings has been taken into account by a coherent amplitude approach which damps the generalized Fresnel coefficients. Scanning electron microscopy pictures complete the study.

Integral calculation method of the efficiencies of laminar stratified gratings

We present an integral calculation method of the efficiencies of laminar stratified gratings. By stratified grating, we mean a medium whose optical index varies with the depth. The calculation is applied to the Bragg-Fraunhofer optics recently developed for the X-UV optics. The results of the method are compared to modal or differential methods already implemented for lamellar multilayer amplitude gratings.

Numerical studies of multilayer gratings using the method of eigenvectors

The method of eigenvectors has been adapted for numerical studies of lamellar multilayer gratings with a partially etched multilayer stack (phase multilayer gratings). Unlike the existing modal and differential methods, this method can be applied to thick multilayer gratings with a small grating period, and also to the case of grazing incidence of radiation. For the case of soft X-rays, the reciprocity curves have been obtained for different numbers of etched bilayers in a multilayer structure using this method. The numerical calculations based on the proposed method were used to interpret the experimental data on diffraction properties of the Ni/C multilayer grating.

Use of a lamellar multilayer amplitude grating as a narrow bandpass monochromator and energy separator

An experimental study of the diffraction of X rays in the keV region by a lamellar multilayer amplitude grating is described. This optics is obtained by periodic etching of an interferential multilayer mirror down to the substrate. The advantages provided by the etching to the system response and its use as an energy separator are given.

Theoretical and experimental analysis of diffraction by a lamellar amplitude multilayer grating, in conical mountings, for the X-ray domain

In this article, we consider the diffraction of an electromagnetic wave by a lamellar amplitude multilayer grating (LAMG), in conical mountings, when the incident wave vector is not in a plane perpendicular to the grooves. A modal expansion technique based on Bloch's theorem is used with an R-recursive propagation scheme. We compare the zeroth order diffraction efficiency measurements with the theoretical results.

Theoretical and experimental analysis of diffraction by a lamellar amplitude multilayer grating, in conical mountings, for the X-ray domain

Theoretical and experimental analysis of diffraction by a lamellar amplitude multilayer grating, in conical mountings, for the X-ray domain

Method of Eigenvectors for Numerical Studies of Multilayer Gratings

A new approach to numerical studies of lamellar multilayer gratings is developed. It stands out against the existing modal and differential methods by its applicability to thick multilayer gratings with a small grating period, and also to the case of grazing incidence of radiation. The diffraction properties of multilayer gratings are calculated for x rays with the angles of incidence down to zero. Reflection curves are calculated for multilayer gratings with the grating periods down to 5 nm and the number of bilayers up to 1000. The diffraction pictures are developed for all the range of x-ray radiation (soft and hard x rays). It is directly demonstrated that the multilayer grating can be regarded as a two-dimensional crystal. Numerical calculations based on the newly proposed method were used for the interpretation of experimental data on the performance of the Ni/C multilayer grating.