Recently, the ESRF Optics Group installed a new multilayer deposition facility. This upgrade was motivated by
increasingly demanding requirements for multilayer based x-ray optics on modern 3rd generation synchrotron
beamlines. Improved accuracy, stability, and reproducibility are key issues.
The deposition process is based on non-reactive magnetron sputtering. The machine is equipped with four cathodes
and one ion source for surface treatment. Conducting, insulating, and ferromagnetic materials can be deposited. A
linear substrate motion will enable coatings up to 100 cm long and 15 cm wide.
The talk will describe the basic concept of the machine and will give an overview of the operating conditions. Initial
coating results will complement the presentation.
Periodic multilayers exposed to a non-destructive annealing sequence have shown reversible and irreversible structural
modifications. In-situ x-ray reflectometry experiments at the ESRF bending magnet beam line BM5 demonstrate that
the overall periodic structure remains stable during the annealing process. At the same time, initially present
asymmetric interdiffusion layers have been reduced, in particular, in Ru/B4C.
The controlled thermal treatment of multilayer optics before its installation on synchrotron beam lines can help to
avoid alterations during their use as optical elements. An important issue is the reduction of stress introduced during
the coating process. The evolution of stress in multilayer test coatings deposited on wafers was worked out from
measurements done by optical metrology before and after coating and annealing.
The investigation of the influence of a thermal action on their reflectivity response is a real challenge. We will present
our experimental approach: deposition technique, multilayer choice, isothermal sequence, reflectivity and stress
measurements. We will also discuss compromises made to keep both reflectivity and stress optimized versus thermal
treatment. Future studies will have to deal with the impact of radiation on multilayer optics and its distinction from
Laterally graded W/B4C multilayers were conceived for the focusing of hard X rays at 3rd generation synchrotron sources. They were deposited using a differential sputter coating technique. The multilayer mirror was bent to the correct shape on a dynamical bending device applying automated alignment routines. During experiments on the ESRF beamline ID19 the undulator source was focused vertically to a 41 nm (FWHM) wide line using a photon energy of 24 keV. The measured line width can be attributed to the finite source size, to diffraction effects, and to slope errors of the mirror. The potential impact of beam penetration into the multilayer will be discussed.
Periodic multilayers deposited by Distributed Electron Cyclotron Resonance (DECR) sputtering were studied with synchrotron radiation at the ESRF bending magnet beam line BM5. In situ reflectivity measurements at a photon energy of 20keV have been carried out on these samples during a specific heat treatment. A dedicated furnace has been developed to heat the multilayers under vacuum from room temperature up to 550°C. [Ru/B4C]70 and [W/B4C]40 samples with repetition periods of about 4nm were chosen. Simulations of reflectivity measurements were performed to understand the evolution of layer thicknesses and interface widths. Additional ex-situ reflectivity measurements were done at 8keV before and after the annealing experiments to investigate irreversible effects. We will discuss the heat impact on the layered structure and in which way multilayer optics could be thermally pre-treated before their installation on synchrotron beam lines.
We present the theoretical design, the fabrication, and the performance of double gradient multilayers to be installed on a Kirkpatrick-Baez focusing system for the ESRF bending magnet beam line BM5. The lateral and the depth gradient of the two coatings were chosen in such a way as to obtain a flat reflectivity response of about 25% after two reflections over an energy range from 12keV to 14keV and at an angle of incidence of 0.5deg at the mirror center. Both mirrors were coated with a non-periodic Ru/B4C structure containing 71 individual layers. The overall depth gradient was identical for both multilayers and optimized at the mirror center while the lateral gradient was adapted to the different focal lengths of each of the two KB elements.
To develop narrow-bandpass multilayer monochromators, we have studied small d-spacing WSi2/Si multilayers. We found that WSi2/Si is an excellent multilayer system for achieving both the desired spectral resolution and peak reflectivity. Compared to other traditional multilayer systems such as W/Si, WSi2/Si not only has a lower density and lower absorption, but also is a chemically more stable system, since WSi2 is already a silicide. One thus expects better thermal stability and sharper interfaces for WSi2/Si multilayers. There are two approaches to achieve high-resolution multilayers: either decrease the d spacing or use low absorption materials. By using WSi2/Si, we can utilize both approaches in the same system to achieve good energy resolution and peak reflectivity. Another advantage of this system is that the sputtering rate for Si is much higher than other traditional low-Z materials. Several WSi2/Si multilayers have been fabricated at the Advanced Photon Source (APS) deposition lab using dc magnetron sputtering with constant currents of 0.5 A in Ar at a pressure of 2.3 mTorr. A test sample of [9.65Å-WSi2/10.05Å-Si] × 300 was studied at four institutions: using laboratory x-ray diffractometers with Cu Kα (8.048 keV) wavelength at the APS x-ray lab and at European Synchrotron Radiation Facility (ESRF), and using synchrotron undulator x-rays at 10 keV at MHATT-CAT and at 25 keV at ChemMatCARS-CAT of the APS. The measured first-order reflectivity was 54% with a bandpass of 0.46% at 10 keV and 66% reflectivity with a bandpass of 0.67% at 25 keV of undulator x-rays. Similar results were obtained from Cu Kα x-rays. This result is very attractive for the design of a multilayer monochromator for the ChemMatCARS-CAT to be used in the 20 to 25 keV range. Other small d-spacing multilayers are being studied. Comparison between WSi2/Si and W/Si multilayers will be discussed.
Non periodic Ru/B4C double gradient multilayers were deposited by Distributed Electron Cyclotron Resonance (DECR) sputtering. These coatings will allow focusing with a constant reflectivity of 50% over an energy range from 12 keV to 14 keV. In this case, a lateral gradient is needed to fulfill the Bragg condition along the multilayer length, and a depth gradient is required to obtain the expected energy bandwidth. Our design approach was based on numerical calculations to define each layer thickness independently. During calibration tests, we had to take into account intermixing between Ru and B4C. We will present the importance of layer intermixing of each material (angular shift and bandwidth of first Bragg peak) and how these parameters can be integrated in the design without affecting the required reflectivity profile. We will also discuss compromises made to keep both lateral and depth gradient optimized in view of the technical limitations of our deposition process.