Institut des
NanoSciences de Paris
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Soutenance de thèse de Kai Zhang - Lundi 18 octobre 2021 à 10 h

Kai Zhang, doctorant dans l’équipe Physco-chimie et dynamique des surfaces soutient sa thèse le lundi 18 octobre 2021 à 10 h.

Sorbonne Université - 4 place Jussieu - 75005 Paris - Barre 46-56, 2e étage, salle de conférence

Structure and growth of germanene and silicene on Al and Ag surfaces

Abstract

While numerous interesting properties are expected from theoretical calculations for free-standing silicene and germanene, their synthesis remains controversial. This thesis presents an experimental study by scanning tunneling microscopy (STM) and grazing incidence X-ray diffraction (GIXD) of the growth of germanium and silicon on metal surfaces. Three systems have been studied : Ge/Al(111), Ge/Ag(111) and Si/Ag(110). Various ordered reconstructions are observed by STM, depending on the growth temperature. Real-time STM allows me to determine the transitions between these structures. For all cases, STM images acquired during growth show that surface atoms exchange with Si or Ge atoms during deposition. Three ordered structures have been quantitatively analyzed by GIXD. The experimental structure factors obtained have been further compared with the ones simulated from DFT models. For Ge/Al(111), I show that the (3×3) reconstruction corresponds to a two-layer Ge-Al surface alloy, and not to germanene as previously proposed. For Ge/Al(111), I demonstrate the formation of a Ag2Ge surface alloy with a structure similar to the (22 x sqrt(3)) reconstruction of Au(111). However, I demonstrate that further Si deposition on the Si pentamers previously observed on Ag(110) lead to the formation of a dumbbell silicene honeycomb ordered layer.

Jury

  • M. Yann Girard, Lab. MPQ – Université de paris, rapporteur
  • M. Gilles Renaud, CEA, rapporteur
  • Mme. Marie d’Angelo, INSP – Sorbonne Université, examinatrice
  • Mme. Laurence Masson, CINaM – Aix-Marseille Université, examinatrice
  • M. Andrew Mayne, ISMO – CNRS, Examinateur
  • M. Geoffroy Prévot, INSP – Sorbonne Université, Directeur de Thèse
  • M. Romain Bernard, INSP – Sorbonne Université, invité