This paper presents the results of using the laboratory X-ray system to study the diamond X-ray optics: single-crystal diamond plates and diamond X-ray parabolic refractive lenses. The system is equipped with the Excillum MetalJet D2+ 70kV high-brightness X-ray source with a liquid GaIn anode. To analyze the defects of the crystal structure, the X-ray diffraction imaging (topography) technique was applied. Two-dimensional images of the diamond plate were experimentally recorded from (111) crystal plane with 12 μm and 1.5 μm resolution. The images of the X-ray semi-lens were recorded from (400) and (220) crystal planes with 20 μm resolution. These topographs displayed various defects, such as growth striations and dislocations.
We are proposing an X-ray reflecto-interferometry technique using an x-ray microfocus laboratory source for thin-film structure research based on compound refractive lenses. The idea of this technique is to use a very simplified experimental setup where a focused X-ray beam reflected from parallel flat surfaces creates an interference pattern in a wide angular range. Due to this, the interference pattern can be obtained in a single shot without the need to rotate the specimen or the detector. The applicability of this technique has been demonstrated using the MetalJet Excillium microfocus laboratory source, which has GaKα emission line at 9.25 keV. A series of interference patterns for Si3N4 membranes and the experimentally obtained film thickness are in good agreement with the declared characteristics. The main advantages and future possible of the reflecto-interferometry technique are discussed.
The requirement for the high-quality optics for the 4th generation synchrotrons is becoming particularly urgent nowadays. We present a laboratory complex “SynchrotronLike” designed for the X-ray optics tests and development of the X-ray optical techniques before their use on the synchrotron sources. This complex consists of four main parts: 1) microfocus Xray source MetalJet D2+ 70kV, 2) detector module that contains X-ray spectrometer and three X-ray cameras with different resolution and field of view, 3) Micro-Optics Test Bench for X-ray optics tests and development of the X-ray optical techniques, 4) X-ray Single Crystal Diagnostics Endstation for the X-ray diffraction microscopy experiments. This complex was successfully used for the preliminary tests of the X-ray refractive lenses made from polymer, epoxy, and diamond. Moreover, the ultracompact X-ray transfocators, diamond monochromators, and beam-splitters for the 4th generation synchrotron sources were also tested on the “SynchrotronLike”. The unique parameters of our laboratory source, such as high brightness and high beam coherency make it possible to implement versatile experimental synchrotron techniques. Consequently, we managed to get excellent results in the X-ray reflecto-interferometry and X-ray microradian diffraction. The results of the latter technique are presented in this paper.
In the manuscript we report on characterization of single-crystalline (111) plates prepared from type Ib diamonds with nitrogen content of 100-150 ppm and (100) plates prepared from IIa diamond by means of high-resolution rocking curve imaging (RCI). Contrary to a common opinion about intrinsic poor diffraction quality of type Ib diamonds, RCI showed the presence of nearly defect-free areas of several mm2 in the central part of the (111)-oriented diamond plates. In comparison with the (100)-oriented IIa diamond plates prepared by the same HPHT setup the Ib diamonds possess better diffraction quality. The observed broadening of the rocking curves associates with the cutting and polishing processes, causing strains around the edges of the plates and rare defects. An improvement of preparation technique will thus allow to make single-crystalline diamond plates for Laue and Bragg monochromators and beam splitters from type Ib diamond with areas large enough to be used as wavefront-preserving optical elements at 4th generation synchrotron facilities. Contrary to a common opinion about intrinsically poor diffraction quality of type I diamonds, RCI showed the presence of nearly defect-free areas of several mm2 in the central part of the diamond plates. The observed broadening of the rocking curves results from the cutting and polishing processes, causing strains around the edges of the plates and rare defects. An improvement of preparation technique will thus allow to make single-crystalline diamond plates for Laue and Bragg monochromators and beam splitters from type Ib material with areas large enough to be used as optical elements at 4th generation synchrotron facilities.
X-ray reflecto-interferometry technique based on compound refractive lenses using an x-ray laboratory source was proposed to study thin-film structures. The setup for this experiment is very simple: a focused x-ray beam is reflected from parallel flat surfaces, which creates an interference pattern in a wide angular range, therefore the interference pattern can be obtained in a single shot without the need to rotate the sample or the detector. The reflecto-interferograms for Si3N4 membranes were obtained using the MetalJet Excillium micro-focus laboratory source with GaKα emission line at 9.25 keV. The experimentally obtained film thickness is in good agreement with the declared characteristics.
X-ray microscopy is advantageous over conventional optical microscopy because of its high resolution and capability to study the inner structure of materials opaque to visible light. Furthermore, this method does not require metallization and vacuum and therefore it can be used to visualize fragile biological samples that cannot be studied by scanning electron microscopy. Focusing X-ray optics may be roughly divided into three groups based on the physical principle of focusing: reflection, diffraction and refraction. The reflection optics includes curved mirrors, multilayers and capillaries; the diffractive optics includes Fresnel zone plates. Refractive optics comprises X-ray compound refractive lenses (CRLs) that are widely used nowadays because of their compactness and ease of fabrication. Focusing performance of the CRL is determined by the refractive index, absorption, the inner structure of the CRL material and the geometry of the lens. The optimal shape for the lens is parabolic with a small radius of curvature, because the smaller radius of the parabola leads to shorter focal distance and therefore allows to achieve higher resolution. The common choice of the CRL material is beryllium. However the resolution of Be lenses is far below theoretically predicted limits because of the parasitic scattering introduced by the grains in the material. Moreover the existing manufacturing technologies do not allow to achieve radius of curvature less than 50 μm. Polymer materials are also popular for the CRL microfabrication because of their amorphous nature, ease of structuring and low price. Among the advanced lithographic techniques the two-photon polymerization lithography (2PP) holds a special place. It is based on polymer solidification by means of two-photon absorption. Nonlinear character of two-photon absorption leads to the transparency of the out-of focus material, while presence of polymerization threshold reduces resolution far below diffraction limit. Therefore 2PP can be used for fabrication 3D structures of almost arbitrary shape including overhanging and self-intersecting structures.
In this work we introduce the 3D X-ray CRL fabricated by 2PP from the commercially available photoresist ORMOCOMP. Hundred double concave individual lenses formed a CRL with the 60 μm distance between adjacent lenses. Radius of curvature of a single parabolic surface was 3 μm that is comparable to radius of 2D silicon nano-lens made by conventional lithography and much less than achievable radius of 3D Be lens. Physical aperture was 28 μm. The optimal processing parameters (power, incident on the sample, and velocity of the laser beam waist movement) were determined. The fabricated CRL was studied by scanning electron microscopy. It was shown that surface of the lens is smooth and the geometrical parameters do not deviate significantly from that of the model.
Focusing performance of lenses was studied by the knife-edge technique. It was obtained that the focal distance is not larger than 2 cm at the energy of 9.25 keV. The radiation resistance of the CRL was tested at the synchrotron DESY: PETRA-III. The CRL was exposed at the non-focused X-ray radiation with the standard power and the energy of 12 keV for more than 10 hours without visible degradation.
With emergence of focusing X-ray optics many configurations of X-ray microscope have been developed. In this paper we report on a laboratory X-ray microscope based on refractive X-ray optics and microfocus laboratory source. In our experimental setup we use parabolic Compound Refractive X-ray Lens (CRL) made of beryllium and capillary spherical CRL made of epoxy. A copper 2000 mesh grid with 13 μm period and the width of the wire of about 4-5 μm has been clearly resolved with good enough contrast in transmission full-field X-ray microscopy mode. The advantages of the two-lens design have been shown experimentally for both transmission full-field and scanning X-ray microscopes. The discussion of the optimal distances between optical elements in the X-ray microscope is presented.
2D parabolic X-ray compound refractive lens was manufactured by laser micro-machining of a single-crystal diamond.
The lens consists of parabolic half lenses with apertures of 1 mm and parabola apex radii of 200 μm. It has been tested at
the synchrotron undulator source (ID06, ESRF) and at a laboratory setup using MetalJet X-ray tube with a liquid-gallium
jet as the anode. X-ray imaging and focusing modes were used. Unique optical and thermal properties of singlecrystalline
diamond lenses allow them to be applied as focusing, imaging and beam-conditioning elements at high-heat
flux beams of today and future X-ray sources.
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