A. E. Blagov

X-ray acoustic resonators for controlling the spatial characteristics of X-radiation

The paper presents the results of studying the acoustic characteristics of special X-ray acousto-optical elements designed for precision control of X-ray beam parameters with time resolution. X-ray measurements revealed a number of specific features of oscillations of X-ray acoustic elements not exhibited in standard electromechanical measurements. The existence of these features is confirmed by numerical calculations computations of the acoustic fields in this type of elements.

Possibilities of Controlling an X-ray Beam with a Crystal Subjected to Long-Wave Ultrasonic Vibrations

X-ray diffraction is experimentally studied in the Laue geometry in a germanium crystal carrying a long-wave ultrasonic wave that creates an alternating lattice deformation along the sample surface. Stroboscopic equipment is used to separate different phases and, correspondingly, different profiles of a spatial deformation distribution from the periodic deformation. A uniform deformation is shown to change the angular position of the X-ray beam, and a nonuniform deformation broadens the angular region of reflection and decreases the peak intensity. Ultrasound can be used to compensate for the static deformation at the place where the single-crystal sample and the resonator are glued together. Apart from the fundamental long-wave harmonic, the crystal contains a parasitic deformation with a shorter wavelength. A simple theoretical model is developed, and it rather accurately describes the experimental results.

Dynamic variation in the lattice parameter of a crystal under ultrasonic treatment in X-ray diffraction experiments

The X-ray diffraction in the Laue geometry is investigated in germanium and silicon single crystals upon excitation of long-wavelength ultrasonic elastic strain waves traveling along the sample surface. The X-ray diffraction beam is bounded by a slit 0.2 mm in size, which is considerably less than the wavelength of the ultrasonic wave. The use of this slit makes it possible to separate crystal regions with a nearly homogeneous strain. As a consequence, the rocking curves stroboscopically measured in a double-crystal dispersionless scheme at different instants of time almost coincide with those for a perfect crystal with a lattice parameter varying in time. The rocking curves measured in a time-integrated mode turn out to be broadened, but their integrated intensities remain unchanged. Possible applications of the developed method are discussed.

In Situ Study of the State of Lysozyme Molecules at the Very Early Stage of the Crystallization Process by Small-Angle X-ray Scattering

The molecular state of hen egg white lysozyme in solution has been studied by small-angle X-ray scattering (SAXS) combined with molecular simulation. The addition of a precipitant is shown to change the state of the protein molecules in solution. The SAXS data were processed using the constructed models of different oligomers. Under the crystallization conditions, lysozyme is shown to be present in solution as monomers (96.0%), dimers (1.9%), and octamers (2.1%), whereas tetramers and hexamers are not found. The modeled structure of the octamer is not consistent with the commonly accepted unit cell containing eight lysozyme molecules. Meanwhile, the modeled octamers are well-fitted to the crystal structure and can serve as building blocks in the course of crystal growth.

Measurement of Rocking Curves of Crystals Using an Acoustically Tunable Monochromator

A new scheme for measuring rocking curves (RCs) based on a previously proposed method for measuring RCs using an X-ray-acoustic analyzer crystal has been developed and implemented. In this scheme, this analyzer crystal is applied as a tunable monochromator, mounted directly after the X-ray source. This new experimental scheme has a number of significant advantages in comparison with the previously proposed scheme. The new scheme is approved and its potential is estimated.

New method for measuring rocking curves in X-ray diffractometry by ultrasonic modulation of the lattice parameter

A method for measuring double-crystal rocking curves with the aid of an X-ray-acoustic analyzer is proposed and implemented. This method makes it possible to perform precise measurements with a high time resolution and without the mechanical rotation of the crystal. The results of testing the method are presented.

In situ study of the growth and degradation processes in tetragonal lysozyme crystals on a silicon substrate by high-resolution X-ray diffractometry

The results of an in situ study of the growth of tetragonal lysozyme crystals by high-resolution X-ray diffractometry are considered. The crystals are grown by the sitting-drop method on crystalline silicon substrates of different types: both on smooth substrates and substrates with artificial surface-relief structures using graphoepitaxy. The crystals are grown in a special hermetically closed crystallization cell, which enables one to obtain images with an optical microscope and perform in situ X-ray diffraction studies in the course of crystal growth. Measurements for lysozyme crystals were carried out in different stages of the crystallization process, including crystal nucleation and growth, developed crystals, the degradation of the crystal structure, and complete destruction.

Control of the crystal lattice strain gradient caused by low-frequency ultrasound

The opportunities of dynamic control of the ultrasound-induced strain gradient in germanium crystal lattice have been studied. Two methods of gradient strain control are offered, which are based on variation in the (i) frequency and (ii) amplitude of ultrasonic vibrations. Both methods have been experimentally implemented.

Measurement of piezoelectric constants of lanthanum-gallium tantalate crystal by X-ray diffraction methods

A method for measuring piezoelectric constants of crystals of intermediate systems by X-ray quasi-multiple-wave diffraction is proposed and implemented. This technique makes it possible to determine the piezoelectric coefficient by measuring variations in the lattice parameter under an external electric field. This method has been approved, its potential is evaluated, and a comparison with high-resolution X-ray diffraction data is performed.

An electromechanical x-ray optical element based on a hysteresis-free monolithic bimorph crystal

A hysteresis-free electrically controlled X-ray optical element based on a monolithic bi-domain bimorphic piezoelectric actuator that is made of lithium niobate crystal was proposed and successfully tested in practice. This element is used for electronically controlled adjustment of the angular position of an X-ray optical monochromator in a range of up to 200″ and is characterized by a high relative linearity (up to 98%), repeatability (the repeatability error is no more than 2%), and low control voltages (up to 100 V). The hysteresis- free behavior of the dependence of the angular position of the element on the control element, which demonstrates the high efficiency of the hysteresis-free monolithic bimorphic piezoactuators as controlled elements of X-ray optics, is shown.