Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
Department Seminar
Host: Akitoshi Shiotari

Thursday, February 23, 2023, 2:00 pm
All are invited to meet around 1:40 pm for a chat with coffee & cookies.
PC Seminar Room, G 2.06, Faradayweg 4
Shigemi Terakawa
MPI of Microstructure Physics, Halle
Structure and Electronic Properties of Ultrathin Indium Films on Si(111)
Ultrathin metal films on atomically flat semiconductor substrates have been of great interest to investigate physical properties of two-dimensional (2D) metals. Indium-adsorbed Si(111) surfaces are one of the most explored metal/semiconductor systems. The double-atomic-layer phase has been extensively studied because of its 2D nearly-free-electron band structure and superconductivity [1-3]. The quasi-1D metallic phase known as the (4×1) phase has also been well investigated because of its metal-insulator transition [4]. However, a single-atomic-layer metal, the thinnest 2D metal, is not yet established. Furthermore, the influence of the metal–semiconductor interface on the properties of the metal layers is poorly understood.

I report the establishment of a single-layer metallic phase of indium on Si(111) and the discovery of a novel indium-magnesium surface alloy on Si(111) with intriguing electronic properties. I succeeded in growing the single-layer phase with high crystallinity [5]. Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES) measurements revealed that the single-layer phase has a uniaxially incommensurate structure and metallic band structure. Moreover, in this system, I discovered the first metal–insulator transition in a single-layer metal film by ARPES and surface conductivity measurements. Next, I succeeded in growing a novel triple-atomic-layer surface alloy by magnesium deposition onto the double-layer phase of indium. ARPES experiments and theoretical calculations revealed that the deposited magnesium is intercalated between the indium layers and silicon substrate to terminate the silicon dangling bonds. As a result, the top two indium layers behave like a freestanding double-layer metal. Through this talk, I will demonstrate the flexibility of the atomic structure of ultrathin indium films dependent on the thickness and interface structure and the accompanied change of the electronic properties.

[1] E. Rotenberg, et al., Phys. Rev. Lett. 91, 246404 (2003).
[2] T. Zhang, et al., Nat. Phys. 6, 104 (2010).
[3] S. Yoshizawa, et al., Nat. Commun. 12, 1462 (2021).
[4] H. W. Yeom, et al., Phys. Rev. Lett. 82, 4898 (1999).
[5] S. Terakawa, et al., J. Phys.: Condens. Matter 30, 365002 (2018).