Gigahertz longitudinal acoustic phonons originating from ultrafast ligand field transitions in hematite thin films

• Published in: Chinese physics B Vol. 23; no. 4; pp. 44206 - 1-044206-4
• Main Authors: Xu, Yue, Jin, Zuan-Ming, Zhang, Zheng-Bing, Zhang, Ze-Yu, Lin, Xian, Ma, Guo-Hong, Cheng, Zhen-Xiang
• Format: Journal Article
• Language: English
• Published: 01.04.2014
• Subjects: Acoustics; Decomposition; Excitation; Hematite; Ligands; Phonons; Sound velocity; Thin films
• ISSN: 1674-1056; 1741-4199
• DOI: 10.1088/1674-1056/23/4/044206

The creation and propagation of longitudinal acoustic phonons (LAPs) in high quality hematite thin films ( alpha -Fe sub(2)O sub(3)) epitaxially grown on different substrates (BaTiO sub(3), SrTiO sub(3), and LaAlO sub(3)) are investigated using the femtosecond pump-probe technique. Transient reflection measurements ( Delta R/R) indicate the photo-excited electron dynamics, and the initial decay less than 1 ps and the slow decay of ~500 ps are attributed to the electron-LO phonon coupling and electron-hole nonradiative recombination, respectively. LAPs in alpha -Fe sub(2)O sub(3) film can be created by ultrafast excitation of the ligand field state, such as the ligand field transitions under 800-nm excitation as well as the ligand to metal charge-transfer with 400-nm excitation. The strain modulations of the sound velocity and the out-of-plane elastic properties are demonstrated in alpha -Fe sub(2)O sub(3) film on different substrates.