Ultrasonic attenuation of 700-MHz surface acoustic waves in thin films of superconducting NbN

Abstract

The temperature dependence of the ultrasonic attenuation of 700-MHz surface acoustic waves has been measured for nine films of superconducting NbN varying in thickness from 0.02 to 0.3 pm. The films, sputter deposited on LiNb03 substrates, exhibited attenuation changes in the superconducting state which were very similar in each case. These changes did not, however, follow the predictions of Bardeen, Cooper, and Schrieffer. Instead, they began with a sharp decrease for 1 or 2 dB at the transition temperature followed by a leveling off which remained nearly constant until T & 0.5 T, . It then decreased linearly with temperature until again leveling off below 1.5 K. A tentative explanation is proposed in terms of the Kosterlitz-Thouless vortex-antivortex theory.

Transient grating measurements of film thickness in multilayer metal films

“…Acoustic properties are sensitive to film thickness, film-substrate adhesion, and elastic properties. Acoustic probing of elastic properties has in turn been used to study phase transitions, [1][2][3] surface quality, defects, and interactions with chemical species at a surface. 4 -11 Nondestructive probing through the use of acoustic waves is of particular interest in the microelectronics and coatings industries, and a variety of techniques have evolved including Brillouin scattering, 12 acoustic microscopy, 2,[13][14][15][16][17][18][19][20][21] and techniques which use lasers to generate acoustic waves.…”