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Ultrafast phonon dynamics of epitaxial atomic layers of Bi on Si(111)

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Title: Ultrafast phonon dynamics of epitaxial atomic layers of Bi on Si(111)
Authors: Ishioka, Kunie Browse this author
Kitajima, Masahiro Browse this author
Misochko, Oleg V. Browse this author
Nagao, Tadaaki Browse this author →KAKEN DB
Issue Date: Mar-2015
Journal Title: Physical Review B
Volume: 91
Issue: 12
Start Page: 125431
Publisher DOI: 10.1103/PhysRevB.91.125431
Abstract: Ultrathin bismuth (Bi) layers on Si(111)-7×7 undergo a structural phase transformation with reducing the number of atomic layers at 3 bilayers (BL). We investigate the phonon dynamics of the Bi films close to the phase transformation by pump-probe reflectivity measurements. Coherent A1g and Eg phonons at 3 and 2 THz are clearly observed for the Bi layers with thicknesses down to 3 BL, confirming their rhombohedral crystalline structure. The A1g frequency exhibits an abrupt redshift and splits into two components at 3 BL, which are attributed to the vertical motions of Bi atoms localized at the surface and subsurface bilayers. The Eg frequency, by contrast, shows a gradual blueshift with reducing the thickness, possibly due to the lateral compressive stress at the Bi/Si interface. Below 3 BL, no coherent phonon signal is detected, in agreement with the phase transformation to the black-phosphoruslike structure. Our observations indicate that the vertical vibrations are significantly softened at 3 BL, but become almost as hard as those in the bulk crystal by adding another bilayer.
Rights: ©2015 American Physical Society
Type: article
URI: http://hdl.handle.net/2115/72128
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 長尾 忠昭

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