J.-M. André

Instrument for research on interfaces and surfaces

We describe an instrument designed for studying the electronic structure of bulk, surface, and deep solid–solid interface. The analysis is made by soft‐x‐ray emission spectroscopy induced by electron bombardment. The target is placed under ultrahigh vacuum and can be prepared and treated in situ. High resolution is achieved both as concerns the photon energy and the electron‐beam energy. Tests have been made in the dispersive mode and in the characteristic isochromat mode. In both cases experimental resolution is in good agreement with the expected one.

Optical constants of amorphous for photons in the range of 60-3000 eV

Optical constants of amorphous have been calculated by the Kramers-Kronig analysis in the continuous spectral region including , O K and Si K absorption edges from the reflection spectra measured using synchrotron radiation. It is the first experiment carried out in such a wide energy region with the same sample. It has been found that for extrapolation of the experimental curve in the high energy region, where the photon energy exceeds the ionization potential of the Si K edge, the relation can be used for energies such that at small grazing angles.

Versatile X‐UV spectrogoniometer with multilayer interference mirrors

A versatile X‐UV spectrogoniometer based on a modular system is described. The heart of the apparatus is a computer‐controlled θ‐2θ goniometer with 1.8 arcs θ angular resolution. This main unit can be connected to with a (+1, −1) double‐crystal premonochromator and a double‐mirror high‐frequency rejector. The dispersive performance of a multilayer interference mirror (MIM) and a lead stearate pseudocrystal are compared at three wavelengths: 13.3 A (Cu‐Lα), 44.8 A (C‐Kα), and 67.7 A (B‐Kα). The MIM appears as a useful dispersing device for a low resolution flat ‘‘one‐crystal’’ spectrometer in this spectral region.

Narrow bandpass multilayer x-ray monochromator

We propose a method to reduce the bandpass of soft x-ray multilayer Bragg reflectors. It consists in etching down to the substrate a multilayer mirror having a large number of bilayers in order to get a lamellar grating with a multilayer bar width representing only 10%–30% of the grating period. The grating is used at the zeroth diffraction order. Once designed, this monochromator was tested with the Lα,β spectra of iron and copper.

Experimental and theoretical studies of orientational dependence of x-ray reflectivity in vicinity of S K-edge in hexagonal CdS crystal

The reflection spectra of a hexagonal CdS crystal in the region of S K-absorption edge were studied both experimentally and theoretically. It was found that the reflection spectrum fine structure as well as the absolute value of reflectivity of the crystal surface cut parallel to the crystal optical axis depends on the surface orientation with respect to the polarization of incoming radiation.

Use of layered synthetic microstructures for the quantitative x-ray analysis of light elements

Measurements of long-wavelength x-rays emitted by light elements can be achieved by using selected layered synthetic microstructures (LSM). For both C Kα and N Kα radiation, W/Si (d = 3.25 nm) LSM was used. Because of the counter efficiency, the C Kα emission has the highest intensity in spite of a calculated reflectivity of the W/Si LSM in favor of the N Kα emission. For B Kα radiation, Mo/Si (d = 5.0 nm), B/Si (d = 4.6 nm) and Ni/C (d = 4.8 nm) LSM were used. Ni/C LSM is the best LSM for the B Kα range because in B/Si LSM the presence of boron gives rise to the anomalous diffusion phenomenon. The intensity, peak-to-background ratio and experimental resolution are better for Ni/C than for Mo/Si LSM. Copyright

X-ray scattering from etched and coated multilayer gratings

Etched and coated multilayer gratings and simple multilayers are investigated by means of x-ray scattering (XRS) and grazing x-ray reflectivity (XRR). Two types of gratings are studied: one lamellar grating coated by a La/B4C stack and two lamellar gratings etched in a Mo/B4C multilayer structure with different cyclic ratios. XRS measurements are presented as reciprocal space mappings or Q-mapping and the origin of the different structures observed in the Q-mapping are discussed in terms of typical coherent and diffuse scattering processes (Bragg spots, grating-Bragg spots, Bragg sheets, grating diffuse sheets, Yoneda wings, etc). From the XRS and XRR measurements, some structural parameters of the mirrors and gratings such as periods and roughness characteristics are estimated.

X-ray spectroscopic application of Cr∕Sc periodic multilayers

The use of Cr∕Sc multilayer interferential mirrors (MIMs) in optical systems such as x-ray microscopes or telescopes have been reported for the water window (between C K- and O K-absorption edges). However, their possibilities in spectroscopic application have never been described in the literature. The purpose of the paper is to report for the first time on the performances of Cr∕Sc MIMs as Bragg dispersive devices for the analysis in wavelength dispersive spectrometry of samples containing N or Sc atoms. The possibility to distinguish the chemical state of the emitting N or Sc atoms is evidenced by using Johan-type and double-crystal spectrometers.

Effective mass of photons in a one-dimensional photonic crystal

Photons propagating within photonic crystals (PCs) can be regarded as quasi-particles having an effective mass. Methods of calculation of this mass from the photonic density of modes are presented for the case of a one-dimensional PC, from both infinite and finite structure. The model is implemented to calculate the influence of the number of unit cells and of absorption for bilayered Bragg structure used as reflectors in the soft-x-ray domain. The physical meaning of the effective photon mass concept is discussed.

B/Si multilayers for soft x-ray and extreme ultraviolet optics

With the development of x-ray sources, high reflectivity and selectivity multilayers for optics are becoming a field of interest for the spectral region of 13–40 nm. In this article, it is shown from theoretical computations that multilayers made of two light materials such as B/Si can be used for these applications. Such multilayers were deposited by electron evaporation. Their physical properties were studied by x-ray reflectometry analyses at two wavelengths: 0.154 and 12.6 nm. The results show that the multilayers are made of dense and pure materials and that the interfacial layer thickness ranges from 0.3 to 0.7 nm.