Metrology of Ferroelectric Domain Walls with Scanning Transmission Electron Microscopy

Restricted (Penn State Only)
Author:
Mukherjee, Debangshu
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
April 30, 2018
Committee Members:
  • Nasim Alem, Dissertation Advisor
  • Nasim Alem, Committee Chair
  • Venkatraman Gopalan, Committee Member
  • Roman Engel-Herbert, Committee Member
  • Vincent Henry Crespi, Outside Member
  • James Rondinelli, Special Member
Keywords:
  • scanning transmission electron microscopy
  • domain walls
  • complex oxide
  • metrology
  • ferroelectrics
Abstract:
Aberration corrected Scanning Transmission Electron Microscopy has revolutionized the world of electron optics. This technique has now enabled the atomic level quantification of interfacial structures in complex oxides enabling the picometer precision metrology of polarization. In this work a robust approach for measuring atom positions is first developed, allowing the quantification of atom positions even in BF-STEM images. This technique is used to understand the origin of distortions at the domain wall in lithium niobate. Theory and experiment come together to demonstrate the origin of these displacements are rooted in the increase of polar entropy. In the second part, STEM itself is extended to enable the full diffraction pattern to be analyzed at every scanning position. Combined with picometer precision metrology, a new technique developed - DPC STEM allows the estimation of charge accumulation of interfaces. The combination of STEM imaging and DPC proves for the first time the existence of charged domain walls in polar metals.