X-ray diffraction by surface acoustic waves

Abstract

The possibilities are presented of X-ray diffraction methods for studying the propagation of surface acoustic waves (SAWs) in solids, including diffraction under total external reflection conditions and Bragg diffraction, using acoustically modulated X-ray multilayer mirrors and crystals. SAW propagation was studied using both meridional and sagittal diffraction geometries where the SAW wavevectors and X-ray photons are collinear or perpendicular, respectively. SAW propagation in a crystal leads to sinusoidal modulation of the crystal lattice and the appearance of diffraction satellites on the rocking curve. The intensities and angular positions of these diffraction satellites are determined by the SAW wavelength, amplitude and attenuation. Therefore, diffraction methods allow the analysis of the SAW propagation process and determination of SAW parameters. The influence of X-ray energy on diffraction by acoustically modulated crystals is studied for the first time. It is shown that changes in the X-ray energy can change the angular region where diffraction satellites exist under conditions of total external reflection. By contrast, in the Bragg diffraction region changes in the X-ray photon energy lead to changes in the X-ray penetration depth into the crystal and redistribution of the diffracted intensity among diffraction satellites, but do not change the angular divergence between diffraction satellites on the rocking curve. It is also shown that, in X-ray diffraction on acoustically modulated crystals on a number of successive reflections, a decrease in interplanar spacing leads to an increase in the number of diffraction satellites and a redistribution of diffracted radiation between them.

Status of X-ray Acoustooptics at the Institute of Microelectronics Technology Russian Academy of Sciences

“…In meridional diffraction geometry, the projection of the X-ray wave vector on the crystal surface is collinear with the SAW wave vector. In principle, a scheme of the sagittal diffraction geometry can be realized when the wave vectors of SAW and X-ray radiation are mutually perpendicular [16][17]. The sagittal diffraction geometry is applicable only for small SAW wavelengths, since it is difficult to obtain good angular divergence between diffraction satellites in this scheme.…”

“…The most promising methods for investigation of the SAW propagation process in solids are the methods of scanning electron microscopy [5][6][7][8][9] and X-ray topography and diffraction [10][11][12][13][14][15][16], that enable to visualize the acoustic waves on the crystal surface and to determine the parameters of acoustic wave propagation processes (wavelengths, acoustic wave amplitude, power flow angles, attenuation).…”

Scanning Electron Microscopy Investigation of Surface Acoustic Wave Propagation in a 41° YX-Cut of a LiNbO3 Crystal/Si Layered Structure

“…However, this method does not provide direct information about the process of SAW excitation and propagation in solids. X-ray diffraction [20][21][22][23][24], topography [25][26][27][28][29], and the scanning electron microscopy method [30][31][32] can be used to study the process of acoustic wave propagation in solids. The X-ray diffraction method is based on the process of X-ray diffraction on the crystal lattice modulated by SAW.…”