Mapping Charge Distribution in Single PbS Core - CdS Arm Nano-Multipod Heterostructures by Off-Axis Electron Holography

Rajesh Chalasani, Alexander Pekin, Alexander Rabkin, Ran E. Abutbul, Oswaldo Diéguez, Yaron Kauffmann, Yuval Golan, Amit Kohn

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

We synthesized PbS core-CdS arm nanomultipod heterostructures (NMHs) that exhibit PbS{111}/CdS{0002} epitaxial relations. The PbS-CdS interface is chemically sharp as determined by aberration corrected transmission electron microscopy (TEM) and compared to density functional theory (DFT) calculations. Ensemble fluorescence measurements show quenching of the optical signal from the CdS arms indicating charge separation due to the heterojunction with PbS. A finite-element three-dimensional (3D) calculation of the Poisson equation shows a type-I heterojunction, which would prevent recombination in the CdS arm after optical excitation. To examine charge redistribution, we used off-axis electron holography (OAEH) in the TEM to map the electrostatic potential across an individual heterojunction. Indeed, a built-in potential of 500 mV is estimated across the junction, though as opposed to the thermal equilibrium calculations significant accumulation of positive charge at the CdS side of the interface is detected. We conclude that the NMH multipod geometry prevents efficient removal of generated charge carriers by the high energy electrons of the TEM. Simulations of generated electron-hole pairs in the insulated CdS arm of the NMH indeed show charge accumulation in agreement with the experimental measurements. Thus, we show that OAEH can be used as a complementary methodology to ensemble measurements by mapping the charge distribution in single NMHs with complex geometries.

Original languageEnglish
Pages (from-to)2778-2787
Number of pages10
JournalNano Letters
Volume17
Issue number5
DOIs
StatePublished - 10 May 2017

Keywords

  • 3D electrostatic simulations
  • PbS core−CdS arm nanomultipod heterostructures
  • built-in potential
  • electrostatic phase mapping
  • focal series exit wave phase reconstruction
  • off-axis electron holography

ASJC Scopus subject areas

  • Bioengineering
  • Chemistry (all)
  • Materials Science (all)
  • Condensed Matter Physics
  • Mechanical Engineering

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