Optical piezoelectric transducer for nano-ultrasonics

Abstract

Abstract-Piezoelectric semiconductor strained layers can be treated as piezoelectric transducers to generate nanometer-wavelength and THz-frequency acoustic waves. The mechanism of nano-acoustic wave (NAW) generation in strained piezoelectric layers, induced by femtosecond optical pulses, can be modeled by a macroscopic elastic continuum theory. The optical absorption change of the strained layers modulated by NAW through quantum-confined Franz-Keldysh (QCFK) effects allows optical detection of the propagating NAW. Based on these piezoelectric-based optical principles, we have designed an optical piezoelectric transducer (OPT) to generate NAW. The optically generated NAW is then applied to one-dimensional (1-D) ultrasonic scan for thickness measurement, which is the first step toward multidimensional nano-ultrasonic imaging. By launching a NAW pulse and resolving the returned acoustic echo signal with femtosecond optical pulses, the thickness of the studied layer can be measured with <1 nm resolution. This nano-structured OPT technique will provide the key toward the realization of nano-ultrasonics, which is analogous to the typical ultrasonic techniques but in a nanometer scale.

Highly piezoelectric BaTiO3nanorod bundle arrays using epitaxially grown TiO2nanomaterials

“…Since 2000, piezoelectric nanomaterials have been intensively developed for potential electronic applications such as sensors, actuators, transducers and ultrasonic devices [1][2][3][4]. Lead-based piezoelectric compositions have been widely used in piezoelectric materials such as PbTiO 3, Pb(Zr 0.52 Ti 0.48 )O 3 and 0.67Pb(Mg 1/3 Nb 2/3 )O 3 -0.33PbTiO 3 due to their high electromechanical conversion efficiency compared with leadfree based piezoelectric materials [5][6][7][8][9].…”

“…In addition, (001) oriented TiO 2 infrastructures were prepared to enhance the electrical properties for piezoelectric characteristics. Therefore, the hydrothermal TiO 2 growth reaction was optimized by adjusting the concentrations of Ti(OBu) 4 and HCl in the Ti precursor solution. BaTiO 3 conversion was then conducted using chemically etched TiO 2 nanorod bundles, which were formed into an M-shape to provide a large surface area for effective Ba 2+ ion diffusion into the TiO 2 crystal facet.…”

Acoustic spectroscopy for studies of vitreous silica up to 740 GHz

“…3(b)) to process the traces. 23 Fig. 3(c) shows the filtered signals and the two peaks (corresponding to Echo 1 and Echo 2) can be clearly identified.…”

“…13 The SNR can be improved by post signal processing if the acoustic waves have central frequency with relatively narrow bandwidth. 23 SQW combined with multiple optical pulse engineering provides tunability of acoustic central frequency. 24 However, saturation effects of acoustic generation through piezoelectric coupling would limit the maximum energy of acoustic waves.…”

“…Details of the experimental setup can be found elsewhere. 23 Figure 1(a) shows the schematic diagram of propagating acoustic waves, and Fig. 1(b) shows the optical transmission change of probe as a function of time-delay.…”