In the x-ray region the reflectivity of a superpolished surface strongly depends on its roughness. This effect may be used to obtain a two-dimensional map of the roughness spatial distribution for flat surface with an average roughness height of the order of one nanometer or less. The method described in the paper cosists in illumination of the sample by a highly collimated x-ray beam, and a line one-dimensional scanning of the sample with simultaneous registration of the specular component of the reflected beam by multielement linear detector. This method may be used to monitor the surface quality of silicon semiconductor wafers, computer hard disks, x-ray and laser mirror substrates etc.
An x-ray multilayer mirror, specially designed to produce resonant absorption at a definite angle of incidence, may be used as an angular dispersive element for refractive x-ray radiography. In this method the signal-to-noise ratio can be significantly enhanced due to suppression of the shot noise produced by the direct beam. Refraction contrast of a copper wire 75 microns in diameter and a human hair was observed using Ni/C multilayer mirror with resonant absorption at CuKa radiation. The multilayer structure consisting of 30 bilayers was designed for CuKa radiation so as to have absorbing resonance of the width of about several arc seconds at a grazing angle of 0.8 degrees. A monochromatic probe x-ray beam with a divergence of approximately 5 arc seconds was obtained from a conventional x-ray tube and a double crystal monochromator set in a strongly dispersive configuration. We have developed theoretical basis for this method, and have experimentally proven that it is possible to create critical components for its practical implementation: a multilayer mirror with resonant absorption, an x-ray imaging photon-counting detector with spatial resolution of about several micrometers, and a probe beam with the divergence of several arc seconds. This result proves the feasibility of x-ray refraction radiography using resonantly absorbing multilayer mirrors manufactured by conventional magnetron sputtering technology.
Multilayer depth-graded structures make possible creating the x-ray mirrors with the reflection angular width of about 0.2 degrees - 0.5 degrees at the wavelength of 1.54 angstrom. Special numerical optimization techniques, such as needle variations, Powell method, and some other were used to calculate the multilayer structures with desired reflection curves. It was found that for CuK radiation and the angular interval 0.5 - 0.9 degrees W-C an W-B4C structures can have the mean reflectivity about 30% with the relative deviation from uniformity better than 0.7%. Such multilayer mirrors were successfully manufactured on quartz substrates with roughness level of about 6 angstrom using magnetron sputtering technology. On this basis the first computer-driven x-ray deflector was designed and tested. For the mirror angular interval of 0.4 degree the output beam deflection interval is equal to 0.8 degree, that is enough for a variety of applications. The laboratory experiments with the deflector included the x-ray raster imaging with the resolution of about 20 micrometers, and automatic beam adjustment and re-aiming. Another possible applications are the x-ray microscopy, compensation for orbital motion of space x-ray telescopes, space x-ray communication.
Design, technology, and applications of x-ray graded multilayer mirrors are discussed in the paper. Various mathematical optimization routines, such as steepest-descent, Powell, conjugated gradients, or needle-variation methods can be used to design depth-graded multilayers. The technology of manufacturing of this type of multilayers is based on the variation of a deposition time, while the spatial distribution of the deposition rate is uniform. Magnetron sputtering technique provides the accuracy of better than 1 angstrom for W/C structures. Laterally graded multilayers with desired spatial period distribution can be manufactured by magnetron sputtering technique using specially shaped slits positioned between the anode and the sample. Laboratory applications of graded mirrors include compact double- mirror conjugated focusing system of a Kirkpatrick-Baez type, programmable x-ray deflector, parabolic collimator with the output beam's angular divergence of 12 arc seconds, and dark- field refraction contrast imaging using multilayer mirrors with resonant absorption.
A new device for rapid non-contact characterization of roughness spatial distribution of flat surfaces is developed. Its operational principle is based on the strong dependence on roughness of the intensity of x-rays reflected from a superpolished surface. This effect may be used to obtain a two-dimensional map of the roughness spatial distribution for flat surfaces with a rms, roughness height of the order of one nanometre. The key components of this device are a precision mechanical one-dimensional scanning stage, a parabolic collimator with vacuum beam path, and a temperature stabilized cooled x-ray linear detector array.
A new device for rapid non-contact characterization of roughness spatial distribution of flat surfaces is developed. Its operational principle is based on the strong dependence on roughness of the intensity of x-rays reflected from a superpolished surface. This effect may be used to obtain a two-dimensional map of the roughness spatial distribution for flat surface with a rms. roughness height of the order of one nanometre. The key components of this device are a precision mechanical one- dimensional scanning stage, a parabolic collimator with vacuum beam path, and a temperature stabilized cooled x-ray linear detector array.
The shape of the angular and spectral reflection curves of depth-graded x-ray multilayer mirrors may be controlled by the proper variation of the layer thicknesses. The determination of the thickness distribution of the layers that gives the best possible approximation to the desired reflection curve profile is a complicated mathematical problem. The present work reports on the application of the needle variations method to the design of graded x-ray multilayer mirrors in both angular and spectral domain.
New technology applications require new types of x-ray mirrors, in particular, mirrors working at different grazing angles. The angular range of standard x-ray mirrors is rather narrow and they cannot provide effective collimating and focusing of x-ray beams. It is shown that the needle optimization technique can be effectively applied to the design of x-ray mirrors with an extended angular range. Experimental results confirm a practical reproducibility of the designs obtained using this procedure.
In the x-ray region, the reflection efficiency of a superpolished surface strongly depends on its roughness. This effect may be used to obtain a 2D map of the roughness spatial distribution for flat surfaces with a rms. roughness height of the order of one nanometer. The basic components of such a device are a precision mechanical 1D scanning stage and a temperature stabilized cooled x-ray linear detector array with quantum efficiency at CuK(alpha ) radiation.