eCommons

 

FABRICATION, CHARACTERIZATION, AND STRUCTURE TRANSFORMATION OF LEAD CHALCOGENIDE NANOCRYSTAL SUPERLATTICES

Other Titles

Abstract

Access to NC building blocks with precisely controlled size, shape, and composition, and advances in synthetic control over inter-NC coupling have created a fertile opportunity space to design materials particularly interesting for (opto-)electronic applications. The fabrication of epitaxially attached NC superlattices (SLs) on a fluid-fluid interface involves orchestrated translation and orientation of thousands of unconnected NCs. At first glance, this fabrication is rather simple; however, a number of sub-processes and their impact on the SL structure are not yet well understood. Understanding the mechanism and ultimately directing NC SL self-assembly and attachment has important implications on future advances in this emerging field. We fabricated NC SLs containing multiple stages of the SL transformation. We characterized these transient regions with 4D-STEM at single particle level using an electron microscope pixel array detector (EMPAD) and obtained a full description of the NCs crystallographic orientation. We discovered that the hexatic-to-square SL transformation is dominated by translation of pre-aligned NCs correlated along the <11n>AL direction and occurs stochastically within single SL domains. We used the detailed structure characterization obtained from the EMPAD to study the nucleation of NC attachment with molecular dynamics and found that dimer formation is inherent to the attachment mechanism. We present experimental evidence of dimer formation and rationalize the emergence of commonly observed SL defects, such as strain and missing bridges. Our work suggests that these defects are formed due to orientational and translational misalignment in dimers, which have less freedom to rotate and may get trapped in a less favorable (misaligned) states. We investigated the impact of NC size distribution on the local SL order, characterized grain boundaries, and proposed a mechanism for twin boundary formation. Finally, we studied the formation of thermally triggered 1D NC structures. We show that solvent evaporation can be used as a knob to control wire length and to potentially form more complex corrugated assemblies. Our work reveals rich insights into SL structure and transformation and provides a path forward toward the controlled fabrication of ordered SLs.

Journal / Series

Volume & Issue

Description

224 pages

Sponsorship

Date Issued

2020-12

Publisher

Keywords

Disorder; EMPAD; Epixatial attachment; Nanocrystal; Self-assembly; Superlattice

Location

Effective Date

Expiration Date

Sector

Employer

Union

Union Local

NAICS

Number of Workers

Committee Chair

Hanrath, Tobias

Committee Co-Chair

Committee Member

Kourkoutis, Lena F.
Archer, Lynden A.

Degree Discipline

Chemical Engineering

Degree Name

Ph. D., Chemical Engineering

Degree Level

Doctor of Philosophy

Related Version

Related DOI

Related To

Related Part

Based on Related Item

Has Other Format(s)

Part of Related Item

Related To

Related Publication(s)

Link(s) to Related Publication(s)

References

Link(s) to Reference(s)

Previously Published As

Government Document

ISBN

ISMN

ISSN

Other Identifiers

Rights

Rights URI

Types

dissertation or thesis

Accessibility Feature

Accessibility Hazard

Accessibility Summary

Link(s) to Catalog Record