title: Mapping Charge Distribution in Single PbS Core - CdS Arm Nano-Multipod Heterostructures by Off-Axis Electron Holography.
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.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Chalasani
authors.forename: Alexander
authors.initials: A
authors.lastname: Pekin
authors.forename: Alexander
authors.initials: A
authors.lastname: Rabkin
authors.forename: Ran E
authors.initials: RE
authors.lastname: Abutbul
authors.forename: Oswaldo
authors.initials: O
authors.lastname: Diéguez
authors.affiliation: Department of Materials Science and Engineering, Technion - Israel Institute of Technology , Haifa 32000, Israel.
authors.forename: Yaron
authors.initials: Y
authors.lastname: Kauffmann
authors.forename: Yuval
authors.identifier: 0000-0003-1369-0285
authors.initials: Y
authors.lastname: Golan
authors.forename: Amit
authors.initials: A
authors.lastname: Kohn
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