P. A. Ershov

Terapascal static pressure generation with ultrahigh yield strength nanodiamond

Terapascal static pressure generation is enabled in laboratory due to implementation of nanocrystralline diamond microballs. Studies of materials’ properties at high and ultrahigh pressures lead to discoveries of unique physical and chemical phenomena and a deeper understanding of matter. In high-pressure research, an achievable static pressure limit is imposed by the strength of available strong materials and design of high-pressure devices. Using a high-pressure and high-temperature technique, we synthesized optically transparent microballs of bulk nanocrystalline diamond, which were found to have an exceptional yield strength (~460 GPa at a confining pressure of ~70 GPa) due to the unique microstructure of bulk nanocrystalline diamond. We used the nanodiamond balls in a double-stage diamond anvil cell high-pressure device that allowed us to generate static pressures beyond 1 TPa, as demonstrated by synchrotron x-ray diffraction. Outstanding mechanical properties (strain-dependent elasticity, very high hardness, and unprecedented yield strength) make the nanodiamond balls a unique device for ultrahigh static pressure generation. Structurally isotropic, homogeneous, and made of a low-Z material, they are promising in the field of x-ray optical applications.

Fourier crystal diffractometry based on refractive optics

X-ray refractive lenses are proposed as a Fourier transformer for high-resolution X-ray crystal diffraction. By employing refractive lenses the wave transmitted through the object converts into a spatial intensity distribution at its back focal plane according to the Fourier-transform relations. A theoretical consideration of the Fourier-transform technique is presented. Two types of samples were studied in Bragg reflection geometry: a grating made of strips of a thin SiO2 film on an Si substrate and a grating made by profiling an Si crystal. Fourier patterns recorded at different angles along the rocking curves of the Si 111 Bragg reflection were analysed.

Polymer X-ray refractive nano-lenses fabricated by additive technology

The present work demonstrates the potential applicability of additive manufacturing to X-Ray refractive nano-lenses. A compound refractive lens with a radius of 5 µm was produced by the two-photon polymerization induced lithography. It was successfully tested at the X-ray microfocus laboratory source and a focal spot of 5 μm was measured. An amorphous nature of polymer material combined with the potential of additive technologies may result in a significantly enhanced focusing performance compared to the best examples of modern X-ray compound refractive lenses.

On the problem of the metrology of refractive X-ray optics

A possible metrological approach to investigation of the optical properties, material structure and profile shape of compound refractive lenses (CRL) is proposed. The methods of X-ray radiography and electron microscopy are proposed for characterization of the profile of a refractive lens with a small curvature radius. Investigation of the material for problems of X-ray optics is performed using small-angle scattering and X-ray microscopy.

Highly porous nanoberyllium for X-ray beam speckle suppression

A speckle suppression device containing highly porous nanoberyllium is proposed for manipulating the spatial coherence length and removing undesirable speckle structure during imaging experiments.

Diamond x-ray refractive lenses produced by femto-second laser ablation

Femto-second laser processing of polycrystalline CVD diamond was applied to manufacturing of X-ray planar refractive lenses. Surface morphology and material quality were analyzed with optical and scanning electron microscopy and X-ray radiography. Lenses were tested in a focusing mode at the IIIrd generation synchrotron radiation source (ESRF).

On the formation of X-ray microbeams utilizing a short-focus refractive lens and a laboratory radiation source

The possibility of focusing an X-ray beam from a laboratory radiation source using a short-focus refractive composite lens is shown. The lens consists of 161 spherical biconcave epoxy lenses, each with a curvature radius of 50 μm. A Metal Jet (ExcilliumTM) microfocus X-ray tube, with a focal-spot size of 20 μm and containing a liquid helium anode, is used as a radiation source. The size of the focal spot in the image plane is 2.4 μm, which corresponds to the theoretical estimate. The possibility of using the composite refractive lens to form a parallel polychromatic X-ray beam is demonstrated. The results obtained allow discussion of the possibility of applying short-focus refractive X-ray lenses for X-ray microanalysis using laboratory sources; such microanalysis is currently a prerogative of synchrotron radiation sources only.

Fabrication of 3D x-ray compound refractive lenses by two-photon polymerization lithography (Conference Presentation)

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.

X-ray tomography as a diagnostic method of X-ray refractive optics

This article describes the application of high-resolution X-ray computed tomography to assess the critical parameters of refractive lenses for X-ray optics that determine the quality of compound optical systems. A microfocus Y. Cheetah X-ray system has been used for three-dimensional visualization of the surface and internal structure of refractive lenses made of high-purity aluminum with geometric apertures of 500 and 1500 μm. A Fein Focus X-ray tube with a focal spot size of less than 2 μm provides the resolution necessary for detecting critical-size microstructure defects in the material of the lens.

High-resolution X-ray diffraction based on 1D and 2D refractive lenses

The results of studying a silicon-germanium (Si-Ge) nanoheterostructure using refractive X-ray optics are described. The diffraction patterns near the silicon Bragg-diffraction peak 400 in the focal plane of refractive lenses are recorded and analyzed. The experiments are carried out in two different geometries: using 1D and 2D X-ray compound refractive lenses.