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Professor Pascal Turban, Rennes, University-CNRS, France

Event Date: 
Monday, November 25, 2019 - 3:30pm to 4:30pm

 

 

Ballistic electron-emission microscopy (BEEM) is an experimental technique measuring the electron current which, injected from the tip of a scanning tunneling microscope (STM) into a thin metallic overlayer, travels through an underlying metal-semiconductor (MS) interface and is finally collected in the semiconductor substrate. Since its discovery, the main applications of BEEM were focused on the study of Schottky-barrier heights and of electron transport across MS interfaces, with a nanometer lateral resolution. Given the current trend in the development of electronic devices at the nanometer scale, these properties make the BEEM technique a powerful tool for the characterization and the control of MS heterostructures. In this talk, I will illustrate some specific potentialities of BEEM for the study of ultrathin metallic films and nanostructures epitaxially grown on III-V semiconductors :

 

  • For simple single-crystalline Schottky contacts, the structural continuity at the epitaxial interface results in the conservation of the electron transverse momentum k// at the MS interface. Due to this transverse momentum conservation rule, BEEM is highly sensitive to the local MS interface electronic structure.
  • For Fe/Au/Fe/GaAs(001) epitaxial spin-valves, the measured hot-electron current is strongly modulated by the application of an external magnetic field. This magnetoresistance amplitude reaches 500% at room-temperature and can be explained by taking into account the previous electronic selection rules at each interface of the heterostructure for both up and down spin channels.
  • Finally, the huge magnetoresistance amplitude achieved in these spin-valves allows the observation of magnetic domains in the Fe electrodes. The performances of BEEM as a magnetic imaging technique with strong contrast and subnanometer lateral resolution are demonstrated on patterned sub-micronic Fe/Au/Fe(001) spin-valves.

 


Pascal Turban obtained a Ph.D degree in Material science in 2001 at the University of Nancy (France) where he developed the molecular beam epitaxy of ferromagnetic metals and oxides for their integration in magnetic tunnel junctions for spin-electronics applications. He then obtained a grant from the Alexander von Humboldt Foundation to join the II. Physikalisches Institut in RWTH Aachen (Rheinisch Westfälische Technische Hochschule, Germany) where he further worked on the correlation between magnetotransport and interface electronic properties. In 2003, he joined the Institute of Physics of Rennes University (IPR, Brittany, France) as an Assistant Professor where he started to develop a Ballistic Electron Emission Microscope under ultrahigh vacuum for the investigation of the local electronic properties of various heterostructures relevant for spin-electronics and molecular electronics applications. He is currently head of the Materials and Nanosciences department at IPR, head of the Nanosciences Nanomaterials and Nanotechnologies Master program in Rennes University, and vice-chair of the condensed-matter division of the French national university council.

 

Event Location: 
McMaster
Location Details: 
JHE 326H