Terahertz Photoacoustic Generation Using Ultrathin Nickel Nanofilms

Kuan Yu Chou, Chen Ling Wu, Chih Chiang Shen, Jinn Kong Sheu, Chi Kuang Sun

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


Picosecond ultrasonic laser sonar (PULSE), one of the noninvasive technologies with a high thickness sensitivity, is capable of probing multilayer films directly on the production wafers. To reach high spatial resolution in the current PULSE system, generation of terahertz photoacoustic pulses through an ultrathin metal film has been the focus of recent studies. In this study, we propose and demonstrate the high potential of ultrathin nickel (Ni) films for THz photoacoustic generation. After femtosecond laser excitation, the photoacoustic frequency launched by the ultrathin Ni nanofilms could be up to 1.4 THz, corresponding to a record-breaking spatial resolution in the single metallic layer system. We discuss the detailed thickness-dependent mechanism with the two-temperature model, which indicates that the ultrahigh-frequency acoustic signals were generated due to the significant contribution of hot electron pressure in Ni, very different from the case for gold. By looking into the ultrafast hot electron relaxation mechanism, our results provide a guideline to further break the technical limit of the metallic terahertz photoacoustic frequency generation in the near future.

Original languageEnglish
Pages (from-to)3134-3142
Number of pages9
JournalJournal of Physical Chemistry C
Issue number5
Publication statusPublished - 2021 Feb 11

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films


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