The effects of oxygen partial pressure on the acoustic velocity in zirconia films studied by picosecond ultrasonics

• Published in: Thin solid films 2006-02, Vol.496 (2), p.208-213
• Main Authors: Li, Ta-Ching, Pu, Nen-Wen, Lwo, Ben-Je, Hu, Long-Jang, Kao, Chin-Hsing
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Deposition by sputtering; Exact sciences and technology; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Physics; Picosecond ultrasonics technology; Reactive sputtering; Zirconia
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2005.08.272

We have performed a picosecond ultrasonic study of the effects of oxygen partial pressure on the acoustic velocity in zirconium oxide films made by radio frequency reactive sputtering. To derive more accurate and reliable values of sound velocity, various reflective layers were used to enhance the echo signals of acoustic pulses photoexcited by an ultrafast laser. It is found that the acoustic responses of the samples with a W reflective layer are much stronger than those with a Si or SiO 2 reflective layer. In addition, the W reflective layer generates extra photoacoustic waves, which can be utilized to improve the accuracy of velocity measurement. The thin film velocities we measured were 10∼24% less than the bulk value, and exhibited a strong dependence on the growth conditions and the microstructure of films.