Bilayer and trilayer X-ray mirror coatings containing W, Pt, or Ir, in combination with C, C/Co, BC, or BC/Ni: X-ray reflectance, film stress, and temporal stability.

X-ray reflectance and film stress were measured for 12 bilayer and trilayer reflective interference coatings and compared with a single-layer Ir coating. The interference coatings comprise a base layer of W, Pt, or Ir, top layers of either C or , and, in the case of the trilayer coatings, middle layers of either Co or Ni. The coatings were deposited by magnetron sputtering.

Nanometer flat blazed x-ray gratings using ion beam figure correction.

With the development of nanometer accuracy stitching interferometry, ion beam figuring (IBF) of x-ray mirrors can now be achieved with unprecedented performance. However, the process of producing x-ray diffraction gratings on these surfaces may degrade the figure quality due to process errors introduced during the ruling of the grating grooves. To address this challenge, we have investigated the post-production correction of gratings using IBF, where stitching interferometry is used to provide in-process feedback.

Advanced low blaze angle x-ray gratings via nanoimprint replication and plasma etch.

We developed a new method of making ultra-low blaze angle diffraction gratings for x-ray applications. The method is based on reduction of the blaze angle of a master grating by nanoimprint replication followed by a plasma etch. A master blazed grating with a relatively large blaze angle is fabricated by anisotropic wet etching of a Si single crystal substrate.

6000 lines/mm blazed grating for a high-resolution x-ray spectrometer.

We have designed and fabricated a high groove density blazed grating for a Resonant Inelastic X-ray Scattering spectrometer for the new Qerlin beamline at the Advanced Light Source (ALS) synchrotron facility. The gratings were fabricated using a set of nanofabrication techniques including e-beam lithography, nanoimprint, plasma etch, and anisotropic wet etching. Two gratings with groove density of 6000 lines/mm and 3000 lines/mm and optimized for operation in the 1 and 2 negative diffraction order respectively were fabricated and tested.

New method for the determination of photoabsorption from transmittance measurements in the extreme ultraviolet.

We have developed a new method for the determination of photoabsorption at extreme ultraviolet wavelengths longer than 20 nm, where reliable refractive index values are sparse or non-existent. Our method overcomes the obstacle of multiple reflections that occur inside thin films in this spectral range, which up until now has prevented the accurate determination of photoabsorption from transmittance measurements. We have derived a mathematical expression that is independent of internal reflection amplitudes, while taking advantage of the transmittance oscillations stemming from such reflections.

Highly efficient ultra-low blaze angle multilayer grating.

We have developed an advanced process for blaze angle reduction of x-ray gratings for the soft, tender, and EUV spectral ranges. The process is based on planarization of an anisotropically etched Si blazed grating followed by a chemically selective plasma etch. This provides a way to adjust the blaze angle to any lower value with high accuracy.

Reflective binary amplitude grating for soft x-ray shearing and Hartmann wavefront sensing.

We demonstrate a reflective wavefront sensor grating suitable for the characterization of high-quality x-ray beamlines and optical systems with high power densities. Operating at glancing incidence angles, the optical element is deeply etched with a two-level pattern of shearing interferometry gratings and Hartmann wavefront sensor grids. Transverse features block unwanted light, enabling binary amplitude in reflection with high pattern contrast.

Total-Electron-Yield Measurements by Soft X-Ray Irradiation of Insulating Organic Films on Conductive Substrates.

The photocurrent (sample current) of insulating 0.7-μm thick polyethylene terephthalate (PET) films on conductive substrates (C, Au, Cu) was clearly measured through the substrates during soft X-ray irradiation on the PET films. X-ray absorption measurements of the PET/conductive-substrates using the total-electron-yield (TEY) method by measuring sample current easily provide the X-ray absorption spectra (XAS) of PET films, which are independent of the substrates.

Water-Window X-Ray Pulses from a Laser-Plasma Driven Undulator.

Femtosecond (fs) x-ray pulses are a key tool to study the structure and dynamics of matter on its natural length and time scale. To complement radio-frequency accelerator-based large-scale facilities, novel laser-based mechanisms hold promise for compact laboratory-scale x-ray sources. Laser-plasma driven undulator radiation in particular offers high peak-brightness, optically synchronized few-fs pulses reaching into the few-nanometer (nm) regime.

High efficiency Al/Sc-based multilayer coatings in the EUV wavelength range above 40 nanometers.

In this Letter, we have developed new and highly efficient periodic multilayer mirrors Al/Sc, Al/Sc/SiC, and Mo/Al/Sc with optimized reflectance at wavelengths between 40 and 65 nm. We have reached record values in measured peak reflectance: 57.5% at 44.

Lifetime Stability and Microstructure Properties of Cr/B₄C X-ray Reflective Multilayer Coatings.

This paper demonstrates that highly reflective Cr/B₄C multilayer interference coatings with nanometric layer thicknesses, designed to operate in the soft X-ray photon energy range, have stable reflective performance for a period of 3 years after deposition. The microstructure and chemical composition of layers and interfaces within Cr/B₄C multilayers is also examined, with emphasis on the B₄C-on-Cr interface where a significant diffusion layer is formed and on the oxide in the top B₄C layer. Multiple characterization techniques (X-ray reflectivity at different photon energies, X-ray photoelectron spectroscopy, transmission electron microscopy, electron diffraction and X-ray diffraction) are employed and the results reveal a consistent picture of the Cr/B₄C layer structure.

Ultra-low blaze angle gratings for synchrotron and free electron laser applications.

We have developed a method for the manufacture of x-ray diffraction gratings with arbitrarily small blaze angles. These gratings are made by a process in which a high blaze angle grating made by anisotropic etching of Si (111) is subjected to planarization and reactive ion etching. Differential etching of the planarization medium and silicon ensures reduction of the blaze angle.

A carbonaceous two-dimensional lattice with FeN units.

A metal-containing carbonaceous two-dimensional lattice was formed on a graphene plane by sublimation, deposition, and pyrolysis of Fe phthalocyanine (Pc). The formation and growth of the FePc-derived π-conjugated planar system were reflected by its orientation conversion from the perpendicular to horizontal mode and by the N K-edge X-ray absorption near-edge structure.

Large area nanoimprint enables ultra-precise x-ray diffraction gratings.

A process for fabrication of ultra-precise diffraction gratings for high resolution x-ray spectroscopy was developed. A grating pattern with constant or variable line spacing (VLS) is recorded on a quartz plate by use of e-beam lithography with nanometer scale accuracy of the groove placement. The pattern is transferred to a massive grating blank by large area nanoimprint followed by dry or/and wet etching for groove shaping.

Impact of BC co-sputtering on structure and optical performance of Cr/Sc multilayer X-ray mirrors.

The influence of BC incorporation during magnetron sputter deposition of Cr/Sc multilayers intended for soft X-ray reflective optics is investigated. Chemical analysis suggests formation of metal: boride and carbide bonds which stabilize an amorphous layer structure, resulting in smoother interfaces and an increased reflectivity. A near-normal incidence reflectivity of 11.

Amplitude versus phase effects in extreme ultraviolet lithography mask scattering and imaging.

It is now well established that extreme ultraviolet (EUV) mask multilayer roughness leads to wafer-plane line-width roughness (LWR) in the lithography process. Analysis and modeling done to date has assumed, however, that the roughness leading to scatter is primarily a phase effect and that the amplitude can be ignored. Under this assumption, simple scattering measurements can be used to characterize the statistical properties of the mask roughness.

Determining crystal phase purity in c-BP through X-ray absorption spectroscopy.

We employ X-ray absorption near-edge spectroscopy at the boron K-edge and the phosphorus L-edge to study the structural properties of cubic boron phosphide (c-BP) samples. The X-ray absorption spectra are modeled from first-principles within the density functional theory framework using the excited electron core-hole (XCH) approach. A simple structural model of a perfect c-BP crystal accurately reproduces the P L-edge, however it fails to describe the broad and gradual onset of the B K-edge.

Modular soft x-ray spectrometer for applications in energy sciences and quantum materials.

Over the past decade, the advances in grating-based soft X-ray spectrometers have revolutionized the soft X-ray spectroscopies in materials research. However, these novel spectrometers are mostly dedicated designs, which cannot be easily adopted for applications with diverging demands. Here we present a versatile spectrometer design concept based on the Hettrick-Underwood optical scheme that uses modular mechanical components.

Two-color spatial and temporal temperature measurements using a streaked soft x-ray imager.

A dual-channel streaked soft x-ray imager has been designed and used on high energy-density physics experiments at the National Ignition Facility. This streaked imager creates two images of the same x-ray source using two slit apertures and a single shallow angle reflection from a nickel mirror. Thin filters are used to create narrow band pass images at 510 eV and 360 eV.

Refraction effects in soft x-ray multilayer blazed gratings.

A 2500 lines/mm Multilayer Blazed Grating (MBG) optimized for the soft x-ray wavelength range was fabricated and tested. The grating coated with a W/BC multilayer demonstrated a record diffraction efficiency in the 2nd blazed diffraction order in the energy range from 500 to 1200 eV. Detailed investigation of the diffraction properties of the grating demonstrated that the diffraction efficiency of high groove density MBGs is not limited by the normal shadowing effects that limits grazing incidence x-ray grating performance.

A new streaked soft x-ray imager for the National Ignition Facility.

A new streaked soft x-ray imager has been designed for use on high energy-density (HED) physics experiments at the National Ignition Facility based at the Lawrence Livermore National Laboratory. This streaked imager uses a slit aperture, single shallow angle reflection from a nickel mirror, and soft x-ray filtering to, when coupled to one of the NIF's x-ray streak cameras, record a 4× magnification, one-dimensional image of an x-ray source with a spatial resolution of less than 90 μm. The energy band pass produced depends upon the filter material used; for the first qualification shots, vanadium and silver-on-titanium filters were used to gate on photon energy ranges of approximately 300-510 eV and 200-400 eV, respectively.

Performance of a ruthenium beam separator used to separate soft x rays from light generated by a high-order harmonic light source.

We describe the design and fabrication of a ruthenium beam separator used to simultaneously attenuate infrared light and reflect soft x rays. Measurements in the infrared and soft x-ray regions showed the beam separator to have a reflectivity of 50%-85% in the wavelength region from 6 to 10 nm at a grazing incidence angle of 7.5 deg and 4.

Demonstration of the high collection efficiency of a broadband Mo/Si multilayer mirror with a graded multilayer coating on an ellipsoidal substrate.

A graded and broadband Mo/Si multilayer mirror for EUV spectroscopy is demonstrated. This mirror has an average reflectivity profile of 16% in the wavelength region from 15 nm to 17 nm and an effective area of 1100-1500 mm(2). This reflectivity is about 4 times larger than that of a standard Mo/Si multilayer mirror on a 1 in.

Pd/B4C/Y multilayer coatings for extreme ultraviolet applications near 10 nm wavelength.

A new extreme ultraviolet (EUV) multilayer coating has been developed comprising Pd and Y layers with thin B4C barrier layers at each interface, for normal incidence applications near 10 nm wavelength. Periodic, nonperiodic, and dual-stack coatings have been investigated and compared with similar structures comprising either Mo/Y or Pd/B4C bilayers. We find that Pd/B4C/Y multilayers provide higher reflectance than either Mo/Y or Pd/B4C, with much lower film stress than Pd/B4C.