Wednesday Colloquium: Prof. Nasim Alem, Pennsylvania State University  Add To Calendar

  • Date(s): Wednesday, 2/22 3:00 PM to Wednesday, 2/22 4:00 PM
  • Speaker: Prof. Nasim Alem
  • Host: Robert Klie
  • Campus Address: 138 SES (Science and Engineering South)

Title: Defects in Nanostructures: An Ultra-High Resolution Aberration-Corrected Electron Microscopy Study

Abstract: Defects and interfaces can have a profound effect on the macroscale physical, chemical and electronic properties of nanostructures through modifying their local atomic, chemical, and electronic structure.  While defects and interfaces have been a well-studied subject for decades, we know little about their local atomic and chemical structure and their stability and transition dynamics.  The past decade has seen incredible progress in the ability to image the atomic and chemical structure of nanostructures with the development of aberration-corrected transmission electron microscopy. This presentation will focus on our recent efforts on probing the atomic structure and chemistry as well as the local structural distortions at the defect sites and interfaces at the sub-Angstrom resolution in various nanostructures, i.e. 2D crystals and van der Waals heterostructures as well as complex oxides. In this study, ultra-high resolution aberration-corrected electron microscopes is used to investigate the chemical and atomic nature of the interfaces, defects and grain boundaries in atomically thin 2D crystals, such as graphene, hexagonal boron nitride, and the transition metal dichalcogenides, and their heterostructures.  In Addition, this talk will present structural distortions and polarization effects at the interfaces and domain walls in complex oxide systems.  A variety of imaging and spectroscopy techniques, such as phase contrast imaging, scanning transmission electron microscopy (STEM) imaging, electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy (EDS) coupled with first principles calculations, this investigation shows structural distortions at the vacancies, dopants, edges, and grain boundaries due to charge-induced symmetry breaking distortions. This study also explores stability and transition dynamics of defects and grain boundaries in 2D crystals under in situ conditions.