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Imaging surface acoustic waves on GaAs by X-ray diffraction techniques

Surface acoustic waves (SAWs) are excited on the GaAs (001) surface by using interdigital transducers, designed for frequencies of up to 900 MHz. The emitted surface phonons with wave-lengths down to 3.5 μm are visualized and characterized by combined x-ray diffraction techniques. By increasing the amplitude of the SAW, high resolution x-ray diffraction profiles show up to 12 phonon-induced satellite reflections besides the GaAs (004) reflection with a width of 9 arcsec each. The diffraction pattern is simulated numerically, applying the kinematical scattering theory to a model crystal of a size adapted to the experimental situation. From fits to measured diffraction profiles at different excitation voltages, the SAW amplitudes were calculated and found to be in the sub-nm range. Using stroboscopic topography, the SAW emission of a focusing transducer geometry is imaged.